src/expr.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::borrow::Cow;
  12 use std::cmp::min;
  13 use std::iter::repeat;
  14
  15 use config::lists::*;
  16 use syntax::{ast, ptr};
  17 use syntax::codemap::{BytePos, CodeMap, Span};
  18
  19 use chains::rewrite_chain;
  20 use closures;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use comment::{combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
  23               rewrite_comment, rewrite_missing_comment, FindUncommented};
  24 use config::{Config, ControlBraceStyle, IndentStyle};
  25 use lists::{definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting,
  26             struct_lit_shape, struct_lit_tactic, write_list, ListFormatting, ListItem, Separator};
  27 use macros::{rewrite_macro, MacroArg, MacroPosition};
  28 use patterns::{can_be_overflowed_pat, TuplePatField};
  29 use rewrite::{Rewrite, RewriteContext};
  30 use shape::{Indent, Shape};
  31 use spanned::Spanned;
  32 use string::{rewrite_string, StringFormat};
  33 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  34 use utils::{colon_spaces, contains_skip, count_newlines, extra_offset, first_line_width,
  35             inner_attributes, last_line_extendable, last_line_width, mk_sp, outer_attributes,
  36             paren_overhead, ptr_vec_to_ref_vec, semicolon_for_stmt, trimmed_last_line_width,
  37             wrap_str};
  38 use vertical::rewrite_with_alignment;
  39 use visitor::FmtVisitor;
  40
  41 impl Rewrite for ast::Expr {
  42     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  43         format_expr(self, ExprType::SubExpression, context, shape)
  44     }
  45 }
  46
  47 #[derive(Copy, Clone, PartialEq)]
  48 pub enum ExprType {
  49     Statement,
  50     SubExpression,
  51 }
  52
  53 pub fn format_expr(
  54     expr: &ast::Expr,
  55     expr_type: ExprType,
  56     context: &RewriteContext,
  57     shape: Shape,
  58 ) -> Option<String> {
  59     skip_out_of_file_lines_range!(context, expr.span);
  60
  61     if contains_skip(&*expr.attrs) {
  62         return Some(context.snippet(expr.span()).to_owned());
  63     }
  64
  65     let expr_rw = match expr.node {
  66         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  67             &ptr_vec_to_ref_vec(expr_vec),
  68             mk_sp(
  69                 context.snippet_provider.span_after(expr.span, "["),
  70                 expr.span.hi(),
  71             ),
  72             context,
  73             shape,
  74             false,
  75         ),
  76         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  77         ast::ExprKind::Call(ref callee, ref args) => {
  78             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  79             let callee_str = callee.rewrite(context, shape)?;
  80             rewrite_call(context, &callee_str, args, inner_span, shape)
  81         }
  82         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
  83         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
  84             // FIXME: format comments between operands and operator
  85             rewrite_pair(
  86                 &**lhs,
  87                 &**rhs,
  88                 PairParts::new("", &format!(" {} ", context.snippet(op.span)), ""),
  89                 context,
  90                 shape,
  91                 context.config.binop_separator(),
  92             )
  93         }
  94         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
  95         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
  96             context,
  97             path,
  98             fields,
  99             base.as_ref().map(|e| &**e),
 100             expr.span,
 101             shape,
 102         ),
 103         ast::ExprKind::Tup(ref items) => {
 104             rewrite_tuple(context, &ptr_vec_to_ref_vec(items), expr.span, shape)
 105         }
 106         ast::ExprKind::If(..)
 107         | ast::ExprKind::IfLet(..)
 108         | ast::ExprKind::ForLoop(..)
 109         | ast::ExprKind::Loop(..)
 110         | ast::ExprKind::While(..)
 111         | ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 112             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 113         ast::ExprKind::Block(ref block) => {
 114             match expr_type {
 115                 ExprType::Statement => {
 116                     if is_unsafe_block(block) {
 117                         block.rewrite(context, shape)
 118                     } else if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 119                         // Rewrite block without trying to put it in a single line.
 120                         rw
 121                     } else {
 122                         let prefix = block_prefix(context, block, shape)?;
 123                         rewrite_block_with_visitor(context, &prefix, block, shape, true)
 124                     }
 125                 }
 126                 ExprType::SubExpression => block.rewrite(context, shape),
 127             }
 128         }
 129         ast::ExprKind::Match(ref cond, ref arms) => {
 130             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 131         }
 132         ast::ExprKind::Path(ref qself, ref path) => {
 133             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 134         }
 135         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 136             rewrite_assignment(context, lhs, rhs, None, shape)
 137         }
 138         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 139             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 140         }
 141         ast::ExprKind::Continue(ref opt_label) => {
 142             let id_str = match *opt_label {
 143                 Some(label) => format!(" {}", label.ident),
 144                 None => String::new(),
 145             };
 146             Some(format!("continue{}", id_str))
 147         }
 148         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 149             let id_str = match *opt_label {
 150                 Some(label) => format!(" {}", label.ident),
 151                 None => String::new(),
 152             };
 153
 154             if let Some(ref expr) = *opt_expr {
 155                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 156             } else {
 157                 Some(format!("break{}", id_str))
 158             }
 159         }
 160         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 161             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 162         } else {
 163             Some("yield".to_string())
 164         },
 165         ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) => {
 166             closures::rewrite_closure(
 167                 capture,
 168                 movability,
 169                 fn_decl,
 170                 body,
 171                 expr.span,
 172                 context,
 173                 shape,
 174             )
 175         }
 176         ast::ExprKind::Try(..)
 177         | ast::ExprKind::Field(..)
 178         | ast::ExprKind::TupField(..)
 179         | ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 180         ast::ExprKind::Mac(ref mac) => {
 181             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 182                 wrap_str(
 183                     context.snippet(expr.span).to_owned(),
 184                     context.config.max_width(),
 185                     shape,
 186                 )
 187             })
 188         }
 189         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 190         ast::ExprKind::Ret(Some(ref expr)) => {
 191             rewrite_unary_prefix(context, "return ", &**expr, shape)
 192         }
 193         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 194         ast::ExprKind::AddrOf(mutability, ref expr) => {
 195             rewrite_expr_addrof(context, mutability, expr, shape)
 196         }
 197         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 198             &**expr,
 199             &**ty,
 200             PairParts::new("", " as ", ""),
 201             context,
 202             shape,
 203             SeparatorPlace::Front,
 204         ),
 205         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 206             &**expr,
 207             &**ty,
 208             PairParts::new("", ": ", ""),
 209             context,
 210             shape,
 211             SeparatorPlace::Back,
 212         ),
 213         ast::ExprKind::Index(ref expr, ref index) => {
 214             rewrite_index(&**expr, &**index, context, shape)
 215         }
 216         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 217             let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
 218                 ("[ ", " ]")
 219             } else {
 220                 ("[", "]")
 221             };
 222             rewrite_pair(
 223                 &**expr,
 224                 &**repeats,
 225                 PairParts::new(lbr, "; ", rbr),
 226                 context,
 227                 shape,
 228                 SeparatorPlace::Back,
 229             )
 230         }
 231         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 232             let delim = match limits {
 233                 ast::RangeLimits::HalfOpen => "..",
 234                 ast::RangeLimits::Closed => "..=",
 235             };
 236
 237             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 238                 match lhs.node {
 239                     ast::ExprKind::Lit(ref lit) => match lit.node {
 240                         ast::LitKind::FloatUnsuffixed(..) => {
 241                             context.snippet(lit.span).ends_with('.')
 242                         }
 243                         _ => false,
 244                     },
 245                     _ => false,
 246                 }
 247             }
 248
 249             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 250                 (Some(lhs), Some(rhs)) => {
 251                     let sp_delim = if context.config.spaces_around_ranges() {
 252                         format!(" {} ", delim)
 253                     } else if needs_space_before_range(context, lhs) {
 254                         format!(" {}", delim)
 255                     } else {
 256                         delim.to_owned()
 257                     };
 258                     rewrite_pair(
 259                         &*lhs,
 260                         &*rhs,
 261                         PairParts::new("", &sp_delim, ""),
 262                         context,
 263                         shape,
 264                         context.config.binop_separator(),
 265                     )
 266                 }
 267                 (None, Some(rhs)) => {
 268                     let sp_delim = if context.config.spaces_around_ranges() {
 269                         format!("{} ", delim)
 270                     } else {
 271                         delim.to_owned()
 272                     };
 273                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 274                 }
 275                 (Some(lhs), None) => {
 276                     let sp_delim = if context.config.spaces_around_ranges() {
 277                         format!(" {}", delim)
 278                     } else {
 279                         delim.to_owned()
 280                     };
 281                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 282                 }
 283                 (None, None) => Some(delim.to_owned()),
 284             }
 285         }
 286         // We do not format these expressions yet, but they should still
 287         // satisfy our width restrictions.
 288         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => {
 289             Some(context.snippet(expr.span).to_owned())
 290         }
 291         ast::ExprKind::Catch(ref block) => {
 292             if let rw @ Some(_) = rewrite_single_line_block(context, "do catch ", block, shape) {
 293                 rw
 294             } else {
 295                 // 9 = `do catch `
 296                 let budget = shape.width.checked_sub(9).unwrap_or(0);
 297                 Some(format!(
 298                     "{}{}",
 299                     "do catch ",
 300                     block.rewrite(context, Shape::legacy(budget, shape.indent))?
 301                 ))
 302             }
 303         }
 304     };
 305
 306     expr_rw
 307         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 308         .and_then(|expr_str| {
 309             let attrs = outer_attributes(&expr.attrs);
 310             let attrs_str = attrs.rewrite(context, shape)?;
 311             let span = mk_sp(
 312                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 313                 expr.span.lo(),
 314             );
 315             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 316         })
 317 }
 318
 319 #[derive(new, Clone, Copy)]
 320 pub struct PairParts<'a> {
 321     prefix: &'a str,
 322     infix: &'a str,
 323     suffix: &'a str,
 324 }
 325
 326 pub fn rewrite_pair<LHS, RHS>(
 327     lhs: &LHS,
 328     rhs: &RHS,
 329     pp: PairParts,
 330     context: &RewriteContext,
 331     shape: Shape,
 332     separator_place: SeparatorPlace,
 333 ) -> Option<String>
 334 where
 335     LHS: Rewrite,
 336     RHS: Rewrite,
 337 {
 338     let lhs_overhead = match separator_place {
 339         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 340         SeparatorPlace::Front => shape.used_width(),
 341     };
 342     let lhs_shape = Shape {
 343         width: context.budget(lhs_overhead),
 344         ..shape
 345     };
 346     let lhs_result = lhs.rewrite(context, lhs_shape)
 347         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 348
 349     // Try to the both lhs and rhs on the same line.
 350     let rhs_orig_result = shape
 351         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 352         .and_then(|s| s.sub_width(pp.suffix.len()))
 353         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 354     if let Some(ref rhs_result) = rhs_orig_result {
 355         // If the rhs looks like block expression, we allow it to stay on the same line
 356         // with the lhs even if it is multi-lined.
 357         let allow_same_line = rhs_result
 358             .lines()
 359             .next()
 360             .map(|first_line| first_line.ends_with('{'))
 361             .unwrap_or(false);
 362         if !rhs_result.contains('\n') || allow_same_line {
 363             let one_line_width = last_line_width(&lhs_result) + pp.infix.len()
 364                 + first_line_width(rhs_result) + pp.suffix.len();
 365             if one_line_width <= shape.width {
 366                 return Some(format!(
 367                     "{}{}{}{}",
 368                     lhs_result, pp.infix, rhs_result, pp.suffix
 369                 ));
 370             }
 371         }
 372     }
 373
 374     // We have to use multiple lines.
 375     // Re-evaluate the rhs because we have more space now:
 376     let mut rhs_shape = match context.config.indent_style() {
 377         IndentStyle::Visual => shape
 378             .sub_width(pp.suffix.len() + pp.prefix.len())?
 379             .visual_indent(pp.prefix.len()),
 380         IndentStyle::Block => {
 381             // Try to calculate the initial constraint on the right hand side.
 382             let rhs_overhead = shape.rhs_overhead(context.config);
 383             Shape::indented(shape.indent.block_indent(context.config), context.config)
 384                 .sub_width(rhs_overhead)?
 385         }
 386     };
 387     let infix = match separator_place {
 388         SeparatorPlace::Back => pp.infix.trim_right(),
 389         SeparatorPlace::Front => pp.infix.trim_left(),
 390     };
 391     if separator_place == SeparatorPlace::Front {
 392         rhs_shape = rhs_shape.offset_left(infix.len())?;
 393     }
 394     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 395     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 396     let infix_with_sep = match separator_place {
 397         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 398         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 399     };
 400     Some(format!(
 401         "{}{}{}{}",
 402         lhs_result, infix_with_sep, rhs_result, pp.suffix
 403     ))
 404 }
 405
 406 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 407     exprs: &[&T],
 408     span: Span,
 409     context: &RewriteContext,
 410     shape: Shape,
 411     trailing_comma: bool,
 412 ) -> Option<String> {
 413     let bracket_size = if context.config.spaces_within_parens_and_brackets() {
 414         2 // "[ "
 415     } else {
 416         1 // "["
 417     };
 418
 419     let nested_shape = match context.config.indent_style() {
 420         IndentStyle::Block => shape
 421             .block()
 422             .block_indent(context.config.tab_spaces())
 423             .with_max_width(context.config)
 424             .sub_width(1)?,
 425         IndentStyle::Visual => shape
 426             .visual_indent(bracket_size)
 427             .sub_width(bracket_size * 2)?,
 428     };
 429
 430     let items = itemize_list(
 431         context.snippet_provider,
 432         exprs.iter(),
 433         "]",
 434         ",",
 435         |item| item.span().lo(),
 436         |item| item.span().hi(),
 437         |item| item.rewrite(context, nested_shape),
 438         span.lo(),
 439         span.hi(),
 440         false,
 441     ).collect::<Vec<_>>();
 442
 443     if items.is_empty() {
 444         if context.config.spaces_within_parens_and_brackets() {
 445             return Some("[ ]".to_string());
 446         } else {
 447             return Some("[]".to_string());
 448         }
 449     }
 450
 451     let tactic = array_tactic(context, shape, nested_shape, exprs, &items, bracket_size);
 452     let ends_with_newline = tactic.ends_with_newline(context.config.indent_style());
 453
 454     let fmt = ListFormatting {
 455         tactic,
 456         separator: ",",
 457         trailing_separator: if trailing_comma {
 458             SeparatorTactic::Always
 459         } else if context.inside_macro && !exprs.is_empty() {
 460             let ends_with_bracket = context.snippet(span).ends_with(']');
 461             let bracket_offset = if ends_with_bracket { 1 } else { 0 };
 462             let snippet = context.snippet(mk_sp(span.lo(), span.hi() - BytePos(bracket_offset)));
 463             let last_char_index = snippet.rfind(|c: char| !c.is_whitespace())?;
 464             if &snippet[last_char_index..last_char_index + 1] == "," {
 465                 SeparatorTactic::Always
 466             } else {
 467                 SeparatorTactic::Never
 468             }
 469         } else if context.config.indent_style() == IndentStyle::Visual {
 470             SeparatorTactic::Never
 471         } else {
 472             SeparatorTactic::Vertical
 473         },
 474         separator_place: SeparatorPlace::Back,
 475         shape: nested_shape,
 476         ends_with_newline,
 477         preserve_newline: false,
 478         config: context.config,
 479     };
 480     let list_str = write_list(&items, &fmt)?;
 481
 482     let result = if context.config.indent_style() == IndentStyle::Visual
 483         || tactic == DefinitiveListTactic::Horizontal
 484     {
 485         if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
 486             format!("[ {} ]", list_str)
 487         } else {
 488             format!("[{}]", list_str)
 489         }
 490     } else {
 491         format!(
 492             "[{}{}{}]",
 493             nested_shape.indent.to_string_with_newline(context.config),
 494             list_str,
 495             shape.block().indent.to_string_with_newline(context.config)
 496         )
 497     };
 498
 499     Some(result)
 500 }
 501
 502 fn array_tactic<T: Rewrite + Spanned + ToExpr>(
 503     context: &RewriteContext,
 504     shape: Shape,
 505     nested_shape: Shape,
 506     exprs: &[&T],
 507     items: &[ListItem],
 508     bracket_size: usize,
 509 ) -> DefinitiveListTactic {
 510     let has_long_item = items
 511         .iter()
 512         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 513
 514     match context.config.indent_style() {
 515         IndentStyle::Block => {
 516             let tactic = match shape.width.checked_sub(2 * bracket_size) {
 517                 Some(width) => {
 518                     let tactic = ListTactic::LimitedHorizontalVertical(
 519                         context.config.width_heuristics().array_width,
 520                     );
 521                     definitive_tactic(items, tactic, Separator::Comma, width)
 522                 }
 523                 None => DefinitiveListTactic::Vertical,
 524             };
 525             if tactic == DefinitiveListTactic::Vertical && !has_long_item
 526                 && is_every_args_simple(exprs)
 527             {
 528                 DefinitiveListTactic::Mixed
 529             } else {
 530                 tactic
 531             }
 532         }
 533         IndentStyle::Visual => {
 534             if has_long_item || items.iter().any(ListItem::is_multiline) {
 535                 definitive_tactic(
 536                     items,
 537                     ListTactic::LimitedHorizontalVertical(
 538                         context.config.width_heuristics().array_width,
 539                     ),
 540                     Separator::Comma,
 541                     nested_shape.width,
 542                 )
 543             } else {
 544                 DefinitiveListTactic::Mixed
 545             }
 546         }
 547     }
 548 }
 549
 550 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 551     debug!("nop_block_collapse {:?} {}", block_str, budget);
 552     block_str.map(|block_str| {
 553         if block_str.starts_with('{') && budget >= 2
 554             && (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 555         {
 556             "{}".to_owned()
 557         } else {
 558             block_str.to_owned()
 559         }
 560     })
 561 }
 562
 563 fn rewrite_empty_block(
 564     context: &RewriteContext,
 565     block: &ast::Block,
 566     shape: Shape,
 567 ) -> Option<String> {
 568     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 569     {
 570         return Some("{}".to_owned());
 571     }
 572
 573     // If a block contains only a single-line comment, then leave it on one line.
 574     let user_str = context.snippet(block.span);
 575     let user_str = user_str.trim();
 576     if user_str.starts_with('{') && user_str.ends_with('}') {
 577         let comment_str = user_str[1..user_str.len() - 1].trim();
 578         if block.stmts.is_empty() && !comment_str.contains('\n') && !comment_str.starts_with("//")
 579             && comment_str.len() + 4 <= shape.width
 580         {
 581             return Some(format!("{{ {} }}", comment_str));
 582         }
 583     }
 584
 585     None
 586 }
 587
 588 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 589     Some(match block.rules {
 590         ast::BlockCheckMode::Unsafe(..) => {
 591             let snippet = context.snippet(block.span);
 592             let open_pos = snippet.find_uncommented("{")?;
 593             // Extract comment between unsafe and block start.
 594             let trimmed = &snippet[6..open_pos].trim();
 595
 596             if !trimmed.is_empty() {
 597                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 598                 let budget = shape.width.checked_sub(9)?;
 599                 format!(
 600                     "unsafe {} ",
 601                     rewrite_comment(
 602                         trimmed,
 603                         true,
 604                         Shape::legacy(budget, shape.indent + 7),
 605                         context.config,
 606                     )?
 607                 )
 608             } else {
 609                 "unsafe ".to_owned()
 610             }
 611         }
 612         ast::BlockCheckMode::Default => String::new(),
 613     })
 614 }
 615
 616 fn rewrite_single_line_block(
 617     context: &RewriteContext,
 618     prefix: &str,
 619     block: &ast::Block,
 620     shape: Shape,
 621 ) -> Option<String> {
 622     if is_simple_block(block, context.codemap) {
 623         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 624         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 625         let result = format!("{}{{ {} }}", prefix, expr_str);
 626         if result.len() <= shape.width && !result.contains('\n') {
 627             return Some(result);
 628         }
 629     }
 630     None
 631 }
 632
 633 pub fn rewrite_block_with_visitor(
 634     context: &RewriteContext,
 635     prefix: &str,
 636     block: &ast::Block,
 637     shape: Shape,
 638     has_braces: bool,
 639 ) -> Option<String> {
 640     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 641         return rw;
 642     }
 643
 644     let mut visitor = FmtVisitor::from_context(context);
 645     visitor.block_indent = shape.indent;
 646     visitor.is_if_else_block = context.is_if_else_block;
 647     match block.rules {
 648         ast::BlockCheckMode::Unsafe(..) => {
 649             let snippet = context.snippet(block.span);
 650             let open_pos = snippet.find_uncommented("{")?;
 651             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 652         }
 653         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 654     }
 655
 656     visitor.visit_block(block, None, has_braces);
 657     Some(format!("{}{}", prefix, visitor.buffer))
 658 }
 659
 660 impl Rewrite for ast::Block {
 661     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 662         // shape.width is used only for the single line case: either the empty block `{}`,
 663         // or an unsafe expression `unsafe { e }`.
 664         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 665             return rw;
 666         }
 667
 668         let prefix = block_prefix(context, self, shape)?;
 669
 670         let result = rewrite_block_with_visitor(context, &prefix, self, shape, true);
 671         if let Some(ref result_str) = result {
 672             if result_str.lines().count() <= 3 {
 673                 if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 674                     return rw;
 675                 }
 676             }
 677         }
 678
 679         result
 680     }
 681 }
 682
 683 impl Rewrite for ast::Stmt {
 684     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 685         skip_out_of_file_lines_range!(context, self.span());
 686
 687         let result = match self.node {
 688             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 689             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 690                 let suffix = if semicolon_for_stmt(context, self) {
 691                     ";"
 692                 } else {
 693                     ""
 694                 };
 695
 696                 let shape = shape.sub_width(suffix.len())?;
 697                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 698             }
 699             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 700         };
 701         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 702     }
 703 }
 704
 705 // Rewrite condition if the given expression has one.
 706 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 707     match expr.node {
 708         ast::ExprKind::Match(ref cond, _) => {
 709             // `match `cond` {`
 710             let cond_shape = match context.config.indent_style() {
 711                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 712                 IndentStyle::Block => shape.offset_left(8)?,
 713             };
 714             cond.rewrite(context, cond_shape)
 715         }
 716         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 717             let alt_block_sep =
 718                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 719             control_flow
 720                 .rewrite_cond(context, shape, &alt_block_sep)
 721                 .and_then(|rw| Some(rw.0))
 722         }),
 723     }
 724 }
 725
 726 // Abstraction over control flow expressions
 727 #[derive(Debug)]
 728 struct ControlFlow<'a> {
 729     cond: Option<&'a ast::Expr>,
 730     block: &'a ast::Block,
 731     else_block: Option<&'a ast::Expr>,
 732     label: Option<ast::Label>,
 733     pat: Option<&'a ast::Pat>,
 734     keyword: &'a str,
 735     matcher: &'a str,
 736     connector: &'a str,
 737     allow_single_line: bool,
 738     // True if this is an `if` expression in an `else if` :-( hacky
 739     nested_if: bool,
 740     span: Span,
 741 }
 742
 743 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 744     match expr.node {
 745         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 746             cond,
 747             None,
 748             if_block,
 749             else_block.as_ref().map(|e| &**e),
 750             expr_type == ExprType::SubExpression,
 751             false,
 752             expr.span,
 753         )),
 754         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 755             Some(ControlFlow::new_if(
 756                 cond,
 757                 Some(pat),
 758                 if_block,
 759                 else_block.as_ref().map(|e| &**e),
 760                 expr_type == ExprType::SubExpression,
 761                 false,
 762                 expr.span,
 763             ))
 764         }
 765         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 766             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 767         }
 768         ast::ExprKind::Loop(ref block, label) => {
 769             Some(ControlFlow::new_loop(block, label, expr.span))
 770         }
 771         ast::ExprKind::While(ref cond, ref block, label) => {
 772             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
 773         }
 774         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 775             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
 776         ),
 777         _ => None,
 778     }
 779 }
 780
 781 impl<'a> ControlFlow<'a> {
 782     fn new_if(
 783         cond: &'a ast::Expr,
 784         pat: Option<&'a ast::Pat>,
 785         block: &'a ast::Block,
 786         else_block: Option<&'a ast::Expr>,
 787         allow_single_line: bool,
 788         nested_if: bool,
 789         span: Span,
 790     ) -> ControlFlow<'a> {
 791         ControlFlow {
 792             cond: Some(cond),
 793             block,
 794             else_block,
 795             label: None,
 796             pat,
 797             keyword: "if",
 798             matcher: match pat {
 799                 Some(..) => "let",
 800                 None => "",
 801             },
 802             connector: " =",
 803             allow_single_line,
 804             nested_if,
 805             span,
 806         }
 807     }
 808
 809     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 810         ControlFlow {
 811             cond: None,
 812             block,
 813             else_block: None,
 814             label,
 815             pat: None,
 816             keyword: "loop",
 817             matcher: "",
 818             connector: "",
 819             allow_single_line: false,
 820             nested_if: false,
 821             span,
 822         }
 823     }
 824
 825     fn new_while(
 826         pat: Option<&'a ast::Pat>,
 827         cond: &'a ast::Expr,
 828         block: &'a ast::Block,
 829         label: Option<ast::Label>,
 830         span: Span,
 831     ) -> ControlFlow<'a> {
 832         ControlFlow {
 833             cond: Some(cond),
 834             block,
 835             else_block: None,
 836             label,
 837             pat,
 838             keyword: "while",
 839             matcher: match pat {
 840                 Some(..) => "let",
 841                 None => "",
 842             },
 843             connector: " =",
 844             allow_single_line: false,
 845             nested_if: false,
 846             span,
 847         }
 848     }
 849
 850     fn new_for(
 851         pat: &'a ast::Pat,
 852         cond: &'a ast::Expr,
 853         block: &'a ast::Block,
 854         label: Option<ast::Label>,
 855         span: Span,
 856     ) -> ControlFlow<'a> {
 857         ControlFlow {
 858             cond: Some(cond),
 859             block,
 860             else_block: None,
 861             label,
 862             pat: Some(pat),
 863             keyword: "for",
 864             matcher: "",
 865             connector: " in",
 866             allow_single_line: false,
 867             nested_if: false,
 868             span,
 869         }
 870     }
 871
 872     fn rewrite_single_line(
 873         &self,
 874         pat_expr_str: &str,
 875         context: &RewriteContext,
 876         width: usize,
 877     ) -> Option<String> {
 878         assert!(self.allow_single_line);
 879         let else_block = self.else_block?;
 880         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 881
 882         if let ast::ExprKind::Block(ref else_node) = else_block.node {
 883             if !is_simple_block(self.block, context.codemap)
 884                 || !is_simple_block(else_node, context.codemap)
 885                 || pat_expr_str.contains('\n')
 886             {
 887                 return None;
 888             }
 889
 890             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 891             let expr = &self.block.stmts[0];
 892             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 893
 894             let new_width = new_width.checked_sub(if_str.len())?;
 895             let else_expr = &else_node.stmts[0];
 896             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 897
 898             if if_str.contains('\n') || else_str.contains('\n') {
 899                 return None;
 900             }
 901
 902             let result = format!(
 903                 "{} {} {{ {} }} else {{ {} }}",
 904                 self.keyword, pat_expr_str, if_str, else_str
 905             );
 906
 907             if result.len() <= width {
 908                 return Some(result);
 909             }
 910         }
 911
 912         None
 913     }
 914 }
 915
 916 impl<'a> ControlFlow<'a> {
 917     fn rewrite_cond(
 918         &self,
 919         context: &RewriteContext,
 920         shape: Shape,
 921         alt_block_sep: &str,
 922     ) -> Option<(String, usize)> {
 923         // Do not take the rhs overhead from the upper expressions into account
 924         // when rewriting pattern.
 925         let new_width = context
 926             .config
 927             .max_width()
 928             .checked_sub(shape.used_width())
 929             .unwrap_or(0);
 930         let fresh_shape = Shape {
 931             width: new_width,
 932             ..shape
 933         };
 934         let constr_shape = if self.nested_if {
 935             // We are part of an if-elseif-else chain. Our constraints are tightened.
 936             // 7 = "} else " .len()
 937             fresh_shape.offset_left(7)?
 938         } else {
 939             fresh_shape
 940         };
 941
 942         let label_string = rewrite_label(self.label);
 943         // 1 = space after keyword.
 944         let offset = self.keyword.len() + label_string.len() + 1;
 945
 946         let pat_expr_string = match self.cond {
 947             Some(cond) => rewrite_pat_expr(
 948                 context,
 949                 self.pat,
 950                 cond,
 951                 self.matcher,
 952                 self.connector,
 953                 self.keyword,
 954                 constr_shape,
 955                 offset,
 956             )?,
 957             None => String::new(),
 958         };
 959
 960         let brace_overhead =
 961             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 962                 // 2 = ` {`
 963                 2
 964             } else {
 965                 0
 966             };
 967         let one_line_budget = context
 968             .config
 969             .max_width()
 970             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
 971             .unwrap_or(0);
 972         let force_newline_brace = (pat_expr_string.contains('\n')
 973             || pat_expr_string.len() > one_line_budget)
 974             && !last_line_extendable(&pat_expr_string);
 975
 976         // Try to format if-else on single line.
 977         if self.allow_single_line
 978             && context
 979                 .config
 980                 .width_heuristics()
 981                 .single_line_if_else_max_width > 0
 982         {
 983             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
 984
 985             if let Some(cond_str) = trial {
 986                 if cond_str.len()
 987                     <= context
 988                         .config
 989                         .width_heuristics()
 990                         .single_line_if_else_max_width
 991                 {
 992                     return Some((cond_str, 0));
 993                 }
 994             }
 995         }
 996
 997         let cond_span = if let Some(cond) = self.cond {
 998             cond.span
 999         } else {
1000             mk_sp(self.block.span.lo(), self.block.span.lo())
1001         };
1002
1003         // `for event in event`
1004         // Do not include label in the span.
1005         let lo = self.label.map_or(self.span.lo(), |label| label.span.hi());
1006         let between_kwd_cond = mk_sp(
1007             context
1008                 .snippet_provider
1009                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1010             self.pat.map_or(cond_span.lo(), |p| {
1011                 if self.matcher.is_empty() {
1012                     p.span.lo()
1013                 } else {
1014                     context
1015                         .snippet_provider
1016                         .span_before(self.span, self.matcher.trim())
1017                 }
1018             }),
1019         );
1020
1021         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1022
1023         let after_cond_comment =
1024             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1025
1026         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1027             ""
1028         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1029             || force_newline_brace
1030         {
1031             alt_block_sep
1032         } else {
1033             " "
1034         };
1035
1036         let used_width = if pat_expr_string.contains('\n') {
1037             last_line_width(&pat_expr_string)
1038         } else {
1039             // 2 = spaces after keyword and condition.
1040             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1041         };
1042
1043         Some((
1044             format!(
1045                 "{}{}{}{}{}",
1046                 label_string,
1047                 self.keyword,
1048                 between_kwd_cond_comment.as_ref().map_or(
1049                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1050                         ""
1051                     } else {
1052                         " "
1053                     },
1054                     |s| &**s,
1055                 ),
1056                 pat_expr_string,
1057                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1058             ),
1059             used_width,
1060         ))
1061     }
1062 }
1063
1064 impl<'a> Rewrite for ControlFlow<'a> {
1065     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1066         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1067
1068         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1069         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1070         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1071         if used_width == 0 {
1072             return Some(cond_str);
1073         }
1074
1075         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1076         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1077         // we should avoid the single line case.
1078         let block_width = if self.else_block.is_some() || self.nested_if {
1079             min(1, block_width)
1080         } else {
1081             block_width
1082         };
1083         let block_shape = Shape {
1084             width: block_width,
1085             ..shape
1086         };
1087         let mut block_context = context.clone();
1088         block_context.is_if_else_block = self.else_block.is_some();
1089         let block_str =
1090             rewrite_block_with_visitor(&block_context, "", self.block, block_shape, true)?;
1091
1092         let mut result = format!("{}{}", cond_str, block_str);
1093
1094         if let Some(else_block) = self.else_block {
1095             let shape = Shape::indented(shape.indent, context.config);
1096             let mut last_in_chain = false;
1097             let rewrite = match else_block.node {
1098                 // If the else expression is another if-else expression, prevent it
1099                 // from being formatted on a single line.
1100                 // Note how we're passing the original shape, as the
1101                 // cost of "else" should not cascade.
1102                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1103                     ControlFlow::new_if(
1104                         cond,
1105                         Some(pat),
1106                         if_block,
1107                         next_else_block.as_ref().map(|e| &**e),
1108                         false,
1109                         true,
1110                         mk_sp(else_block.span.lo(), self.span.hi()),
1111                     ).rewrite(context, shape)
1112                 }
1113                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1114                     ControlFlow::new_if(
1115                         cond,
1116                         None,
1117                         if_block,
1118                         next_else_block.as_ref().map(|e| &**e),
1119                         false,
1120                         true,
1121                         mk_sp(else_block.span.lo(), self.span.hi()),
1122                     ).rewrite(context, shape)
1123                 }
1124                 _ => {
1125                     last_in_chain = true;
1126                     // When rewriting a block, the width is only used for single line
1127                     // blocks, passing 1 lets us avoid that.
1128                     let else_shape = Shape {
1129                         width: min(1, shape.width),
1130                         ..shape
1131                     };
1132                     format_expr(else_block, ExprType::Statement, context, else_shape)
1133                 }
1134             };
1135
1136             let between_kwd_else_block = mk_sp(
1137                 self.block.span.hi(),
1138                 context
1139                     .snippet_provider
1140                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1141             );
1142             let between_kwd_else_block_comment =
1143                 extract_comment(between_kwd_else_block, context, shape);
1144
1145             let after_else = mk_sp(
1146                 context
1147                     .snippet_provider
1148                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1149                 else_block.span.lo(),
1150             );
1151             let after_else_comment = extract_comment(after_else, context, shape);
1152
1153             let between_sep = match context.config.control_brace_style() {
1154                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1155                     &*alt_block_sep
1156                 }
1157                 ControlBraceStyle::AlwaysSameLine => " ",
1158             };
1159             let after_sep = match context.config.control_brace_style() {
1160                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1161                 _ => " ",
1162             };
1163
1164             result.push_str(&format!(
1165                 "{}else{}",
1166                 between_kwd_else_block_comment
1167                     .as_ref()
1168                     .map_or(between_sep, |s| &**s),
1169                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1170             ));
1171             result.push_str(&rewrite?);
1172         }
1173
1174         Some(result)
1175     }
1176 }
1177
1178 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1179     match opt_label {
1180         Some(label) => Cow::from(format!("{}: ", label.ident)),
1181         None => Cow::from(""),
1182     }
1183 }
1184
1185 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1186     match rewrite_missing_comment(span, shape, context) {
1187         Some(ref comment) if !comment.is_empty() => Some(format!(
1188             "{indent}{}{indent}",
1189             comment,
1190             indent = shape.indent.to_string_with_newline(context.config)
1191         )),
1192         _ => None,
1193     }
1194 }
1195
1196 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1197     let snippet = codemap.span_to_snippet(block.span).unwrap();
1198     contains_comment(&snippet)
1199 }
1200
1201 // Checks that a block contains no statements, an expression and no comments.
1202 // FIXME: incorrectly returns false when comment is contained completely within
1203 // the expression.
1204 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1205     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0])
1206         && !block_contains_comment(block, codemap))
1207 }
1208
1209 /// Checks whether a block contains at most one statement or expression, and no comments.
1210 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1211     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1212 }
1213
1214 /// Checks whether a block contains no statements, expressions, or comments.
1215 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1216     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1217 }
1218
1219 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1220     match stmt.node {
1221         ast::StmtKind::Expr(..) => true,
1222         _ => false,
1223     }
1224 }
1225
1226 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1227     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1228         true
1229     } else {
1230         false
1231     }
1232 }
1233
1234 /// A simple wrapper type against ast::Arm. Used inside write_list().
1235 struct ArmWrapper<'a> {
1236     pub arm: &'a ast::Arm,
1237     /// True if the arm is the last one in match expression. Used to decide on whether we should add
1238     /// trailing comma to the match arm when `config.trailing_comma() == Never`.
1239     pub is_last: bool,
1240     /// Holds a byte position of `|` at the beginning of the arm pattern, if available.
1241     pub beginning_vert: Option<BytePos>,
1242 }
1243
1244 impl<'a> ArmWrapper<'a> {
1245     pub fn new(
1246         arm: &'a ast::Arm,
1247         is_last: bool,
1248         beginning_vert: Option<BytePos>,
1249     ) -> ArmWrapper<'a> {
1250         ArmWrapper {
1251             arm,
1252             is_last,
1253             beginning_vert,
1254         }
1255     }
1256 }
1257
1258 impl<'a> Spanned for ArmWrapper<'a> {
1259     fn span(&self) -> Span {
1260         if let Some(lo) = self.beginning_vert {
1261             mk_sp(lo, self.arm.span().hi())
1262         } else {
1263             self.arm.span()
1264         }
1265     }
1266 }
1267
1268 impl<'a> Rewrite for ArmWrapper<'a> {
1269     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1270         rewrite_match_arm(context, self.arm, shape, self.is_last, self.beginning_vert)
1271     }
1272 }
1273
1274 fn rewrite_match(
1275     context: &RewriteContext,
1276     cond: &ast::Expr,
1277     arms: &[ast::Arm],
1278     shape: Shape,
1279     span: Span,
1280     attrs: &[ast::Attribute],
1281 ) -> Option<String> {
1282     // Do not take the rhs overhead from the upper expressions into account
1283     // when rewriting match condition.
1284     let cond_shape = Shape {
1285         width: context.budget(shape.used_width()),
1286         ..shape
1287     };
1288     // 6 = `match `
1289     let cond_shape = match context.config.indent_style() {
1290         IndentStyle::Visual => cond_shape.shrink_left(6)?,
1291         IndentStyle::Block => cond_shape.offset_left(6)?,
1292     };
1293     let cond_str = cond.rewrite(context, cond_shape)?;
1294     let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1295     let block_sep = match context.config.control_brace_style() {
1296         ControlBraceStyle::AlwaysNextLine => alt_block_sep,
1297         _ if last_line_extendable(&cond_str) => " ",
1298         // 2 = ` {`
1299         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
1300         _ => " ",
1301     };
1302
1303     let nested_indent_str = shape
1304         .indent
1305         .block_indent(context.config)
1306         .to_string(context.config);
1307     // Inner attributes.
1308     let inner_attrs = &inner_attributes(attrs);
1309     let inner_attrs_str = if inner_attrs.is_empty() {
1310         String::new()
1311     } else {
1312         inner_attrs
1313             .rewrite(context, shape)
1314             .map(|s| format!("{}{}\n", nested_indent_str, s))?
1315     };
1316
1317     let open_brace_pos = if inner_attrs.is_empty() {
1318         let hi = if arms.is_empty() {
1319             span.hi()
1320         } else {
1321             arms[0].span().lo()
1322         };
1323         context
1324             .snippet_provider
1325             .span_after(mk_sp(cond.span.hi(), hi), "{")
1326     } else {
1327         inner_attrs[inner_attrs.len() - 1].span().hi()
1328     };
1329
1330     if arms.is_empty() {
1331         let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
1332         if snippet.trim().is_empty() {
1333             Some(format!("match {} {{}}", cond_str))
1334         } else {
1335             // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
1336             Some(context.snippet(span).to_owned())
1337         }
1338     } else {
1339         Some(format!(
1340             "match {}{}{{\n{}{}{}\n{}}}",
1341             cond_str,
1342             block_sep,
1343             inner_attrs_str,
1344             nested_indent_str,
1345             rewrite_match_arms(context, arms, shape, span, open_brace_pos)?,
1346             shape.indent.to_string(context.config),
1347         ))
1348     }
1349 }
1350
1351 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
1352     if is_last && config.trailing_comma() == SeparatorTactic::Never {
1353         ""
1354     } else if config.match_block_trailing_comma() {
1355         ","
1356     } else if let ast::ExprKind::Block(ref block) = body.node {
1357         if let ast::BlockCheckMode::Default = block.rules {
1358             ""
1359         } else {
1360             ","
1361         }
1362     } else {
1363         ","
1364     }
1365 }
1366
1367 /// Collect a byte position of the beginning `|` for each arm, if available.
1368 fn collect_beginning_verts(
1369     context: &RewriteContext,
1370     arms: &[ast::Arm],
1371     span: Span,
1372 ) -> Vec<Option<BytePos>> {
1373     let mut beginning_verts = Vec::with_capacity(arms.len());
1374     let mut lo = context.snippet_provider.span_after(span, "{");
1375     for arm in arms {
1376         let hi = arm.pats[0].span.lo();
1377         let missing_span = mk_sp(lo, hi);
1378         beginning_verts.push(context.snippet_provider.opt_span_before(missing_span, "|"));
1379         lo = arm.span().hi();
1380     }
1381     beginning_verts
1382 }
1383
1384 fn rewrite_match_arms(
1385     context: &RewriteContext,
1386     arms: &[ast::Arm],
1387     shape: Shape,
1388     span: Span,
1389     open_brace_pos: BytePos,
1390 ) -> Option<String> {
1391     let arm_shape = shape
1392         .block_indent(context.config.tab_spaces())
1393         .with_max_width(context.config);
1394
1395     let arm_len = arms.len();
1396     let is_last_iter = repeat(false)
1397         .take(arm_len.checked_sub(1).unwrap_or(0))
1398         .chain(repeat(true));
1399     let beginning_verts = collect_beginning_verts(context, arms, span);
1400     let items = itemize_list(
1401         context.snippet_provider,
1402         arms.iter()
1403             .zip(is_last_iter)
1404             .zip(beginning_verts.into_iter())
1405             .map(|((arm, is_last), beginning_vert)| ArmWrapper::new(arm, is_last, beginning_vert)),
1406         "}",
1407         "|",
1408         |arm| arm.span().lo(),
1409         |arm| arm.span().hi(),
1410         |arm| arm.rewrite(context, arm_shape),
1411         open_brace_pos,
1412         span.hi(),
1413         false,
1414     );
1415     let arms_vec: Vec<_> = items.collect();
1416     let fmt = ListFormatting {
1417         tactic: DefinitiveListTactic::Vertical,
1418         // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
1419         separator: "",
1420         trailing_separator: SeparatorTactic::Never,
1421         separator_place: SeparatorPlace::Back,
1422         shape: arm_shape,
1423         ends_with_newline: true,
1424         preserve_newline: true,
1425         config: context.config,
1426     };
1427
1428     write_list(&arms_vec, &fmt)
1429 }
1430
1431 fn rewrite_match_arm(
1432     context: &RewriteContext,
1433     arm: &ast::Arm,
1434     shape: Shape,
1435     is_last: bool,
1436     beginning_vert: Option<BytePos>,
1437 ) -> Option<String> {
1438     let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
1439         if contains_skip(&arm.attrs) {
1440             let (_, body) = flatten_arm_body(context, &arm.body);
1441             // `arm.span()` does not include trailing comma, add it manually.
1442             return Some(format!(
1443                 "{}{}",
1444                 context.snippet(arm.span()),
1445                 arm_comma(context.config, body, is_last),
1446             ));
1447         }
1448         let missing_span = mk_sp(
1449             arm.attrs[arm.attrs.len() - 1].span.hi(),
1450             arm.pats[0].span.lo(),
1451         );
1452         (missing_span, arm.attrs.rewrite(context, shape)?)
1453     } else {
1454         (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
1455     };
1456     let pats_str = rewrite_match_pattern(
1457         context,
1458         &arm.pats,
1459         &arm.guard,
1460         beginning_vert.is_some(),
1461         shape,
1462     ).and_then(|pats_str| {
1463         combine_strs_with_missing_comments(
1464             context,
1465             &attrs_str,
1466             &pats_str,
1467             missing_span,
1468             shape,
1469             false,
1470         )
1471     })?;
1472     rewrite_match_body(
1473         context,
1474         &arm.body,
1475         &pats_str,
1476         shape,
1477         arm.guard.is_some(),
1478         is_last,
1479     )
1480 }
1481
1482 /// Returns true if the given pattern is short. A short pattern is defined by the following grammer:
1483 ///
1484 /// [small, ntp]:
1485 ///     - single token
1486 ///     - `&[single-line, ntp]`
1487 ///
1488 /// [small]:
1489 ///     - `[small, ntp]`
1490 ///     - unary tuple constructor `([small, ntp])`
1491 ///     - `&[small]`
1492 fn is_short_pattern(pat: &ast::Pat, pat_str: &str) -> bool {
1493     // We also require that the pattern is reasonably 'small' with its literal width.
1494     pat_str.len() <= 20 && !pat_str.contains('\n') && is_short_pattern_inner(pat)
1495 }
1496
1497 fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
1498     match pat.node {
1499         ast::PatKind::Wild | ast::PatKind::Lit(_) => true,
1500         ast::PatKind::Ident(_, _, ref pat) => pat.is_none(),
1501         ast::PatKind::Struct(..)
1502         | ast::PatKind::Mac(..)
1503         | ast::PatKind::Slice(..)
1504         | ast::PatKind::Path(..)
1505         | ast::PatKind::Range(..) => false,
1506         ast::PatKind::Tuple(ref subpats, _) => subpats.len() <= 1,
1507         ast::PatKind::TupleStruct(ref path, ref subpats, _) => {
1508             path.segments.len() <= 1 && subpats.len() <= 1
1509         }
1510         ast::PatKind::Box(ref p) | ast::PatKind::Ref(ref p, _) => is_short_pattern_inner(&*p),
1511     }
1512 }
1513
1514 fn rewrite_match_pattern(
1515     context: &RewriteContext,
1516     pats: &[ptr::P<ast::Pat>],
1517     guard: &Option<ptr::P<ast::Expr>>,
1518     has_beginning_vert: bool,
1519     shape: Shape,
1520 ) -> Option<String> {
1521     // Patterns
1522     // 5 = ` => {`
1523     // 2 = `| `
1524     let pat_shape = shape
1525         .sub_width(5)?
1526         .offset_left(if has_beginning_vert { 2 } else { 0 })?;
1527
1528     let pat_strs = pats.iter()
1529         .map(|p| p.rewrite(context, pat_shape))
1530         .collect::<Option<Vec<_>>>()?;
1531
1532     let use_mixed_layout = pats.iter()
1533         .zip(pat_strs.iter())
1534         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1535     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1536     let tactic = if use_mixed_layout {
1537         DefinitiveListTactic::Mixed
1538     } else {
1539         definitive_tactic(
1540             &items,
1541             ListTactic::HorizontalVertical,
1542             Separator::VerticalBar,
1543             pat_shape.width,
1544         )
1545     };
1546     let fmt = ListFormatting {
1547         tactic,
1548         separator: " |",
1549         trailing_separator: SeparatorTactic::Never,
1550         separator_place: context.config.binop_separator(),
1551         shape: pat_shape,
1552         ends_with_newline: false,
1553         preserve_newline: false,
1554         config: context.config,
1555     };
1556     let pats_str = write_list(&items, &fmt)?;
1557     let beginning_vert = if has_beginning_vert { "| " } else { "" };
1558
1559     // Guard
1560     let guard_str = rewrite_guard(context, guard, shape, trimmed_last_line_width(&pats_str))?;
1561
1562     Some(format!("{}{}{}", beginning_vert, pats_str, guard_str))
1563 }
1564
1565 // (extend, body)
1566 // @extend: true if the arm body can be put next to `=>`
1567 // @body: flattened body, if the body is block with a single expression
1568 fn flatten_arm_body<'a>(context: &'a RewriteContext, body: &'a ast::Expr) -> (bool, &'a ast::Expr) {
1569     match body.node {
1570         ast::ExprKind::Block(ref block)
1571             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1572         {
1573             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1574                 (
1575                     !context.config.force_multiline_blocks() && can_extend_match_arm_body(expr),
1576                     &*expr,
1577                 )
1578             } else {
1579                 (false, &*body)
1580             }
1581         }
1582         _ => (
1583             !context.config.force_multiline_blocks() && body.can_be_overflowed(context, 1),
1584             &*body,
1585         ),
1586     }
1587 }
1588
1589 fn rewrite_match_body(
1590     context: &RewriteContext,
1591     body: &ptr::P<ast::Expr>,
1592     pats_str: &str,
1593     shape: Shape,
1594     has_guard: bool,
1595     is_last: bool,
1596 ) -> Option<String> {
1597     let (extend, body) = flatten_arm_body(context, body);
1598     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1599         (true, is_empty_block(block, context.codemap))
1600     } else {
1601         (false, false)
1602     };
1603
1604     let comma = arm_comma(context.config, body, is_last);
1605     let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1606
1607     let combine_orig_body = |body_str: &str| {
1608         let block_sep = match context.config.control_brace_style() {
1609             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1610             _ => " ",
1611         };
1612
1613         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1614     };
1615
1616     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1617     let next_line_indent = if !is_block || is_empty_block {
1618         shape.indent.block_indent(context.config)
1619     } else {
1620         shape.indent
1621     };
1622     let combine_next_line_body = |body_str: &str| {
1623         if is_block {
1624             return Some(format!(
1625                 "{} =>{}{}",
1626                 pats_str,
1627                 next_line_indent.to_string_with_newline(context.config),
1628                 body_str
1629             ));
1630         }
1631
1632         let indent_str = shape.indent.to_string_with_newline(context.config);
1633         let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
1634         let (body_prefix, body_suffix) = if context.config.match_arm_blocks() {
1635             let comma = if context.config.match_block_trailing_comma() {
1636                 ","
1637             } else {
1638                 ""
1639             };
1640             ("{", format!("{}}}{}", indent_str, comma))
1641         } else {
1642             ("", String::from(","))
1643         };
1644
1645         let block_sep = match context.config.control_brace_style() {
1646             ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
1647             _ if body_prefix.is_empty() => "".to_owned(),
1648             _ if forbid_same_line => format!("{}{}", alt_block_sep, body_prefix),
1649             _ => format!(" {}", body_prefix),
1650         } + &nested_indent_str;
1651
1652         Some(format!(
1653             "{} =>{}{}{}",
1654             pats_str, block_sep, body_str, body_suffix
1655         ))
1656     };
1657
1658     // Let's try and get the arm body on the same line as the condition.
1659     // 4 = ` => `.len()
1660     let orig_body_shape = shape
1661         .offset_left(extra_offset(pats_str, shape) + 4)
1662         .and_then(|shape| shape.sub_width(comma.len()));
1663     let orig_body = if let Some(body_shape) = orig_body_shape {
1664         let rewrite = nop_block_collapse(
1665             format_expr(body, ExprType::Statement, context, body_shape),
1666             body_shape.width,
1667         );
1668
1669         match rewrite {
1670             Some(ref body_str)
1671                 if !forbid_same_line
1672                     && (is_block
1673                         || (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1674             {
1675                 return combine_orig_body(body_str);
1676             }
1677             _ => rewrite,
1678         }
1679     } else {
1680         None
1681     };
1682     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1683
1684     // Try putting body on the next line and see if it looks better.
1685     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1686     let next_line_body = nop_block_collapse(
1687         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1688         next_line_body_shape.width,
1689     );
1690     match (orig_body, next_line_body) {
1691         (Some(ref orig_str), Some(ref next_line_str))
1692             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1693         {
1694             combine_next_line_body(next_line_str)
1695         }
1696         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1697             combine_orig_body(orig_str)
1698         }
1699         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1700             combine_next_line_body(next_line_str)
1701         }
1702         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1703         (None, None) => None,
1704         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1705     }
1706 }
1707
1708 // The `if ...` guard on a match arm.
1709 fn rewrite_guard(
1710     context: &RewriteContext,
1711     guard: &Option<ptr::P<ast::Expr>>,
1712     shape: Shape,
1713     // The amount of space used up on this line for the pattern in
1714     // the arm (excludes offset).
1715     pattern_width: usize,
1716 ) -> Option<String> {
1717     if let Some(ref guard) = *guard {
1718         // First try to fit the guard string on the same line as the pattern.
1719         // 4 = ` if `, 5 = ` => {`
1720         let cond_shape = shape
1721             .offset_left(pattern_width + 4)
1722             .and_then(|s| s.sub_width(5));
1723         if let Some(cond_shape) = cond_shape {
1724             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1725                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1726                     return Some(format!(" if {}", cond_str));
1727                 }
1728             }
1729         }
1730
1731         // Not enough space to put the guard after the pattern, try a newline.
1732         // 3 = `if `, 5 = ` => {`
1733         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1734             .offset_left(3)
1735             .and_then(|s| s.sub_width(5));
1736         if let Some(cond_shape) = cond_shape {
1737             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1738                 return Some(format!(
1739                     "{}if {}",
1740                     cond_shape.indent.to_string_with_newline(context.config),
1741                     cond_str
1742                 ));
1743             }
1744         }
1745
1746         None
1747     } else {
1748         Some(String::new())
1749     }
1750 }
1751
1752 fn rewrite_pat_expr(
1753     context: &RewriteContext,
1754     pat: Option<&ast::Pat>,
1755     expr: &ast::Expr,
1756     matcher: &str,
1757     // Connecting piece between pattern and expression,
1758     // *without* trailing space.
1759     connector: &str,
1760     keyword: &str,
1761     shape: Shape,
1762     offset: usize,
1763 ) -> Option<String> {
1764     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1765     let cond_shape = shape.offset_left(offset)?;
1766     if let Some(pat) = pat {
1767         let matcher = if matcher.is_empty() {
1768             matcher.to_owned()
1769         } else {
1770             format!("{} ", matcher)
1771         };
1772         let pat_shape = cond_shape
1773             .offset_left(matcher.len())?
1774             .sub_width(connector.len())?;
1775         let pat_string = pat.rewrite(context, pat_shape)?;
1776         let result = format!("{}{}{}", matcher, pat_string, connector);
1777         return rewrite_assign_rhs(context, result, expr, cond_shape);
1778     }
1779
1780     let expr_rw = expr.rewrite(context, cond_shape);
1781     // The expression may (partially) fit on the current line.
1782     // We do not allow splitting between `if` and condition.
1783     if keyword == "if" || expr_rw.is_some() {
1784         return expr_rw;
1785     }
1786
1787     // The expression won't fit on the current line, jump to next.
1788     let nested_shape = shape
1789         .block_indent(context.config.tab_spaces())
1790         .with_max_width(context.config);
1791     let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
1792     expr.rewrite(context, nested_shape)
1793         .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
1794 }
1795
1796 fn can_extend_match_arm_body(body: &ast::Expr) -> bool {
1797     match body.node {
1798         // We do not allow `if` to stay on the same line, since we could easily mistake
1799         // `pat => if cond { ... }` and `pat if cond => { ... }`.
1800         ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => false,
1801         ast::ExprKind::ForLoop(..)
1802         | ast::ExprKind::Loop(..)
1803         | ast::ExprKind::While(..)
1804         | ast::ExprKind::WhileLet(..)
1805         | ast::ExprKind::Match(..)
1806         | ast::ExprKind::Block(..)
1807         | ast::ExprKind::Closure(..)
1808         | ast::ExprKind::Array(..)
1809         | ast::ExprKind::Call(..)
1810         | ast::ExprKind::MethodCall(..)
1811         | ast::ExprKind::Mac(..)
1812         | ast::ExprKind::Struct(..)
1813         | ast::ExprKind::Tup(..) => true,
1814         ast::ExprKind::AddrOf(_, ref expr)
1815         | ast::ExprKind::Box(ref expr)
1816         | ast::ExprKind::Try(ref expr)
1817         | ast::ExprKind::Unary(_, ref expr)
1818         | ast::ExprKind::Cast(ref expr, _) => can_extend_match_arm_body(expr),
1819         _ => false,
1820     }
1821 }
1822
1823 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1824     match l.node {
1825         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1826         _ => wrap_str(
1827             context.snippet(l.span).to_owned(),
1828             context.config.max_width(),
1829             shape,
1830         ),
1831     }
1832 }
1833
1834 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1835     let string_lit = context.snippet(span);
1836
1837     if !context.config.format_strings() {
1838         if string_lit
1839             .lines()
1840             .rev()
1841             .skip(1)
1842             .all(|line| line.ends_with('\\'))
1843         {
1844             let new_indent = shape.visual_indent(1).indent;
1845             let indented_string_lit = String::from(
1846                 string_lit
1847                     .lines()
1848                     .map(|line| {
1849                         format!(
1850                             "{}{}",
1851                             new_indent.to_string(context.config),
1852                             line.trim_left()
1853                         )
1854                     })
1855                     .collect::<Vec<_>>()
1856                     .join("\n")
1857                     .trim_left(),
1858             );
1859             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1860         } else {
1861             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1862         }
1863     }
1864
1865     // Remove the quote characters.
1866     let str_lit = &string_lit[1..string_lit.len() - 1];
1867
1868     rewrite_string(
1869         str_lit,
1870         &StringFormat::new(shape.visual_indent(0), context.config),
1871         None,
1872     )
1873 }
1874
1875 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1876 /// format.
1877 ///
1878 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1879 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1880 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1881 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1882     // format! like macros
1883     // From the Rust Standard Library.
1884     ("eprint!", 0),
1885     ("eprintln!", 0),
1886     ("format!", 0),
1887     ("format_args!", 0),
1888     ("print!", 0),
1889     ("println!", 0),
1890     ("panic!", 0),
1891     ("unreachable!", 0),
1892     // From the `log` crate.
1893     ("debug!", 0),
1894     ("error!", 0),
1895     ("info!", 0),
1896     ("warn!", 0),
1897     // write! like macros
1898     ("assert!", 1),
1899     ("debug_assert!", 1),
1900     ("write!", 1),
1901     ("writeln!", 1),
1902     // assert_eq! like macros
1903     ("assert_eq!", 2),
1904     ("assert_ne!", 2),
1905     ("debug_assert_eq!", 2),
1906     ("debug_assert_ne!", 2),
1907 ];
1908
1909 pub fn rewrite_call(
1910     context: &RewriteContext,
1911     callee: &str,
1912     args: &[ptr::P<ast::Expr>],
1913     span: Span,
1914     shape: Shape,
1915 ) -> Option<String> {
1916     let force_trailing_comma = if context.inside_macro {
1917         span_ends_with_comma(context, span)
1918     } else {
1919         false
1920     };
1921     rewrite_call_inner(
1922         context,
1923         callee,
1924         &ptr_vec_to_ref_vec(args),
1925         span,
1926         shape,
1927         context.config.width_heuristics().fn_call_width,
1928         force_trailing_comma,
1929     )
1930 }
1931
1932 pub fn rewrite_call_inner<'a, T>(
1933     context: &RewriteContext,
1934     callee_str: &str,
1935     args: &[&T],
1936     span: Span,
1937     shape: Shape,
1938     args_max_width: usize,
1939     force_trailing_comma: bool,
1940 ) -> Option<String>
1941 where
1942     T: Rewrite + Spanned + ToExpr + 'a,
1943 {
1944     // 2 = `( `, 1 = `(`
1945     let paren_overhead = if context.config.spaces_within_parens_and_brackets() {
1946         2
1947     } else {
1948         1
1949     };
1950     let used_width = extra_offset(callee_str, shape);
1951     let one_line_width = shape
1952         .width
1953         .checked_sub(used_width + 2 * paren_overhead)
1954         .unwrap_or(0);
1955
1956     // 1 = "(" or ")"
1957     let one_line_shape = shape
1958         .offset_left(last_line_width(callee_str) + 1)
1959         .and_then(|shape| shape.sub_width(1))
1960         .unwrap_or(Shape { width: 0, ..shape });
1961     let nested_shape = shape_from_indent_style(
1962         context,
1963         shape,
1964         used_width + 2 * paren_overhead,
1965         used_width + paren_overhead,
1966     )?;
1967
1968     let span_lo = context.snippet_provider.span_after(span, "(");
1969     let args_span = mk_sp(span_lo, span.hi());
1970
1971     let (extendable, list_str) = rewrite_call_args(
1972         context,
1973         args,
1974         args_span,
1975         one_line_shape,
1976         nested_shape,
1977         one_line_width,
1978         args_max_width,
1979         force_trailing_comma,
1980         callee_str,
1981     )?;
1982
1983     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
1984         let mut new_context = context.clone();
1985         new_context.use_block = true;
1986         return rewrite_call_inner(
1987             &new_context,
1988             callee_str,
1989             args,
1990             span,
1991             shape,
1992             args_max_width,
1993             force_trailing_comma,
1994         );
1995     }
1996
1997     let args_shape = Shape {
1998         width: shape
1999             .width
2000             .checked_sub(last_line_width(callee_str))
2001             .unwrap_or(0),
2002         ..shape
2003     };
2004     Some(format!(
2005         "{}{}",
2006         callee_str,
2007         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2008     ))
2009 }
2010
2011 fn need_block_indent(s: &str, shape: Shape) -> bool {
2012     s.lines().skip(1).any(|s| {
2013         s.find(|c| !char::is_whitespace(c))
2014             .map_or(false, |w| w + 1 < shape.indent.width())
2015     })
2016 }
2017
2018 fn rewrite_call_args<'a, T>(
2019     context: &RewriteContext,
2020     args: &[&T],
2021     span: Span,
2022     one_line_shape: Shape,
2023     nested_shape: Shape,
2024     one_line_width: usize,
2025     args_max_width: usize,
2026     force_trailing_comma: bool,
2027     callee_str: &str,
2028 ) -> Option<(bool, String)>
2029 where
2030     T: Rewrite + Spanned + ToExpr + 'a,
2031 {
2032     let items = itemize_list(
2033         context.snippet_provider,
2034         args.iter(),
2035         ")",
2036         ",",
2037         |item| item.span().lo(),
2038         |item| item.span().hi(),
2039         |item| item.rewrite(context, nested_shape),
2040         span.lo(),
2041         span.hi(),
2042         true,
2043     );
2044     let mut item_vec: Vec<_> = items.collect();
2045
2046     // Try letting the last argument overflow to the next line with block
2047     // indentation. If its first line fits on one line with the other arguments,
2048     // we format the function arguments horizontally.
2049     let tactic = try_overflow_last_arg(
2050         context,
2051         &mut item_vec,
2052         &args[..],
2053         one_line_shape,
2054         nested_shape,
2055         one_line_width,
2056         args_max_width,
2057         callee_str,
2058     );
2059
2060     let fmt = ListFormatting {
2061         tactic,
2062         separator: ",",
2063         trailing_separator: if force_trailing_comma {
2064             SeparatorTactic::Always
2065         } else if context.inside_macro || !context.use_block_indent() {
2066             SeparatorTactic::Never
2067         } else {
2068             context.config.trailing_comma()
2069         },
2070         separator_place: SeparatorPlace::Back,
2071         shape: nested_shape,
2072         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2073         preserve_newline: false,
2074         config: context.config,
2075     };
2076
2077     write_list(&item_vec, &fmt)
2078         .map(|args_str| (tactic == DefinitiveListTactic::Horizontal, args_str))
2079 }
2080
2081 fn try_overflow_last_arg<'a, T>(
2082     context: &RewriteContext,
2083     item_vec: &mut Vec<ListItem>,
2084     args: &[&T],
2085     one_line_shape: Shape,
2086     nested_shape: Shape,
2087     one_line_width: usize,
2088     args_max_width: usize,
2089     callee_str: &str,
2090 ) -> DefinitiveListTactic
2091 where
2092     T: Rewrite + Spanned + ToExpr + 'a,
2093 {
2094     // 1 = "("
2095     let combine_arg_with_callee =
2096         callee_str.len() + 1 <= context.config.tab_spaces() && args.len() == 1;
2097     let overflow_last = combine_arg_with_callee || can_be_overflowed(context, args);
2098
2099     // Replace the last item with its first line to see if it fits with
2100     // first arguments.
2101     let placeholder = if overflow_last {
2102         let mut context = context.clone();
2103         if !combine_arg_with_callee {
2104             if let Some(expr) = args[args.len() - 1].to_expr() {
2105                 if let ast::ExprKind::MethodCall(..) = expr.node {
2106                     context.force_one_line_chain = true;
2107                 }
2108             }
2109         }
2110         last_arg_shape(args, item_vec, one_line_shape, args_max_width).and_then(|arg_shape| {
2111             rewrite_last_arg_with_overflow(&context, args, &mut item_vec[args.len() - 1], arg_shape)
2112         })
2113     } else {
2114         None
2115     };
2116
2117     let mut tactic = definitive_tactic(
2118         &*item_vec,
2119         ListTactic::LimitedHorizontalVertical(args_max_width),
2120         Separator::Comma,
2121         one_line_width,
2122     );
2123
2124     // Replace the stub with the full overflowing last argument if the rewrite
2125     // succeeded and its first line fits with the other arguments.
2126     match (overflow_last, tactic, placeholder) {
2127         (true, DefinitiveListTactic::Horizontal, Some(ref overflowed)) if args.len() == 1 => {
2128             // When we are rewriting a nested function call, we restrict the
2129             // bugdet for the inner function to avoid them being deeply nested.
2130             // However, when the inner function has a prefix or a suffix
2131             // (e.g. `foo() as u32`), this budget reduction may produce poorly
2132             // formatted code, where a prefix or a suffix being left on its own
2133             // line. Here we explicitlly check those cases.
2134             if count_newlines(overflowed) == 1 {
2135                 let rw = args.last()
2136                     .and_then(|last_arg| last_arg.rewrite(context, nested_shape));
2137                 let no_newline = rw.as_ref().map_or(false, |s| !s.contains('\n'));
2138                 if no_newline {
2139                     item_vec[args.len() - 1].item = rw;
2140                 } else {
2141                     item_vec[args.len() - 1].item = Some(overflowed.to_owned());
2142                 }
2143             } else {
2144                 item_vec[args.len() - 1].item = Some(overflowed.to_owned());
2145             }
2146         }
2147         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2148             item_vec[args.len() - 1].item = placeholder;
2149         }
2150         _ if args.len() >= 1 => {
2151             item_vec[args.len() - 1].item = args.last()
2152                 .and_then(|last_arg| last_arg.rewrite(context, nested_shape));
2153
2154             let default_tactic = || {
2155                 definitive_tactic(
2156                     &*item_vec,
2157                     ListTactic::LimitedHorizontalVertical(args_max_width),
2158                     Separator::Comma,
2159                     one_line_width,
2160                 )
2161             };
2162
2163             // Use horizontal layout for a function with a single argument as long as
2164             // everything fits in a single line.
2165             if args.len() == 1
2166                 && args_max_width != 0 // Vertical layout is forced.
2167                 && !item_vec[0].has_comment()
2168                 && !item_vec[0].inner_as_ref().contains('\n')
2169                 && ::lists::total_item_width(&item_vec[0]) <= one_line_width
2170             {
2171                 tactic = DefinitiveListTactic::Horizontal;
2172             } else {
2173                 tactic = default_tactic();
2174
2175                 if tactic == DefinitiveListTactic::Vertical {
2176                     if let Some((all_simple, num_args_before)) =
2177                         maybe_get_args_offset(callee_str, args)
2178                     {
2179                         let one_line = all_simple
2180                             && definitive_tactic(
2181                                 &item_vec[..num_args_before],
2182                                 ListTactic::HorizontalVertical,
2183                                 Separator::Comma,
2184                                 nested_shape.width,
2185                             ) == DefinitiveListTactic::Horizontal
2186                             && definitive_tactic(
2187                                 &item_vec[num_args_before + 1..],
2188                                 ListTactic::HorizontalVertical,
2189                                 Separator::Comma,
2190                                 nested_shape.width,
2191                             ) == DefinitiveListTactic::Horizontal;
2192
2193                         if one_line {
2194                             tactic = DefinitiveListTactic::SpecialMacro(num_args_before);
2195                         };
2196                     }
2197                 }
2198             }
2199         }
2200         _ => (),
2201     }
2202
2203     tactic
2204 }
2205
2206 fn is_simple_arg(expr: &ast::Expr) -> bool {
2207     match expr.node {
2208         ast::ExprKind::Lit(..) => true,
2209         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
2210         ast::ExprKind::AddrOf(_, ref expr)
2211         | ast::ExprKind::Box(ref expr)
2212         | ast::ExprKind::Cast(ref expr, _)
2213         | ast::ExprKind::Field(ref expr, _)
2214         | ast::ExprKind::Try(ref expr)
2215         | ast::ExprKind::TupField(ref expr, _)
2216         | ast::ExprKind::Unary(_, ref expr) => is_simple_arg(expr),
2217         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
2218             is_simple_arg(lhs) && is_simple_arg(rhs)
2219         }
2220         _ => false,
2221     }
2222 }
2223
2224 fn is_every_args_simple<T: ToExpr>(lists: &[&T]) -> bool {
2225     lists
2226         .iter()
2227         .all(|arg| arg.to_expr().map_or(false, is_simple_arg))
2228 }
2229
2230 /// In case special-case style is required, returns an offset from which we start horizontal layout.
2231 fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
2232     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
2233         .iter()
2234         .find(|&&(s, _)| s == callee_str)
2235     {
2236         let all_simple = args.len() > num_args_before && is_every_args_simple(args);
2237
2238         Some((all_simple, num_args_before))
2239     } else {
2240         None
2241     }
2242 }
2243
2244 /// Returns a shape for the last argument which is going to be overflowed.
2245 fn last_arg_shape<T>(
2246     lists: &[&T],
2247     items: &[ListItem],
2248     shape: Shape,
2249     args_max_width: usize,
2250 ) -> Option<Shape>
2251 where
2252     T: Rewrite + Spanned + ToExpr,
2253 {
2254     let is_nested_call = lists
2255         .iter()
2256         .next()
2257         .and_then(|item| item.to_expr())
2258         .map_or(false, is_nested_call);
2259     if items.len() == 1 && !is_nested_call {
2260         return Some(shape);
2261     }
2262     let offset = items.iter().rev().skip(1).fold(0, |acc, i| {
2263         // 2 = ", "
2264         acc + 2 + i.inner_as_ref().len()
2265     });
2266     Shape {
2267         width: min(args_max_width, shape.width),
2268         ..shape
2269     }.offset_left(offset)
2270 }
2271
2272 fn rewrite_last_arg_with_overflow<'a, T>(
2273     context: &RewriteContext,
2274     args: &[&T],
2275     last_item: &mut ListItem,
2276     shape: Shape,
2277 ) -> Option<String>
2278 where
2279     T: Rewrite + Spanned + ToExpr + 'a,
2280 {
2281     let last_arg = args[args.len() - 1];
2282     let rewrite = if let Some(expr) = last_arg.to_expr() {
2283         match expr.node {
2284             // When overflowing the closure which consists of a single control flow expression,
2285             // force to use block if its condition uses multi line.
2286             ast::ExprKind::Closure(..) => {
2287                 // If the argument consists of multiple closures, we do not overflow
2288                 // the last closure.
2289                 if closures::args_have_many_closure(args) {
2290                     None
2291                 } else {
2292                     closures::rewrite_last_closure(context, expr, shape)
2293                 }
2294             }
2295             _ => expr.rewrite(context, shape),
2296         }
2297     } else {
2298         last_arg.rewrite(context, shape)
2299     };
2300
2301     if let Some(rewrite) = rewrite {
2302         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2303         last_item.item = rewrite_first_line;
2304         Some(rewrite)
2305     } else {
2306         None
2307     }
2308 }
2309
2310 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2311 where
2312     T: Rewrite + Spanned + ToExpr + 'a,
2313 {
2314     args.last()
2315         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2316 }
2317
2318 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2319     match expr.node {
2320         ast::ExprKind::Match(..) => {
2321             (context.use_block_indent() && args_len == 1)
2322                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
2323         }
2324         ast::ExprKind::If(..)
2325         | ast::ExprKind::IfLet(..)
2326         | ast::ExprKind::ForLoop(..)
2327         | ast::ExprKind::Loop(..)
2328         | ast::ExprKind::While(..)
2329         | ast::ExprKind::WhileLet(..) => {
2330             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2331         }
2332         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2333             context.use_block_indent()
2334                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
2335         }
2336         ast::ExprKind::Array(..)
2337         | ast::ExprKind::Call(..)
2338         | ast::ExprKind::Mac(..)
2339         | ast::ExprKind::MethodCall(..)
2340         | ast::ExprKind::Struct(..)
2341         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2342         ast::ExprKind::AddrOf(_, ref expr)
2343         | ast::ExprKind::Box(ref expr)
2344         | ast::ExprKind::Try(ref expr)
2345         | ast::ExprKind::Unary(_, ref expr)
2346         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2347         _ => false,
2348     }
2349 }
2350
2351 fn is_nested_call(expr: &ast::Expr) -> bool {
2352     match expr.node {
2353         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
2354         ast::ExprKind::AddrOf(_, ref expr)
2355         | ast::ExprKind::Box(ref expr)
2356         | ast::ExprKind::Try(ref expr)
2357         | ast::ExprKind::Unary(_, ref expr)
2358         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
2359         _ => false,
2360     }
2361 }
2362
2363 pub fn wrap_args_with_parens(
2364     context: &RewriteContext,
2365     args_str: &str,
2366     is_extendable: bool,
2367     shape: Shape,
2368     nested_shape: Shape,
2369 ) -> String {
2370     let paren_overhead = paren_overhead(context);
2371     let fits_one_line = args_str.len() + paren_overhead <= shape.width;
2372     let extend_width = if args_str.is_empty() {
2373         paren_overhead
2374     } else {
2375         paren_overhead / 2
2376     };
2377     if !context.use_block_indent()
2378         || (context.inside_macro && !args_str.contains('\n') && fits_one_line)
2379         || (is_extendable && extend_width <= shape.width)
2380     {
2381         let mut result = String::with_capacity(args_str.len() + 4);
2382         if context.config.spaces_within_parens_and_brackets() && !args_str.is_empty() {
2383             result.push_str("( ");
2384             result.push_str(args_str);
2385             result.push_str(" )");
2386         } else {
2387             result.push_str("(");
2388             result.push_str(args_str);
2389             result.push_str(")");
2390         }
2391         result
2392     } else {
2393         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
2394         let indent_str = shape.block().indent.to_string_with_newline(context.config);
2395         let mut result =
2396             String::with_capacity(args_str.len() + 2 + indent_str.len() + nested_indent_str.len());
2397         result.push_str("(");
2398         if !args_str.is_empty() {
2399             result.push_str(&nested_indent_str);
2400             result.push_str(args_str);
2401         }
2402         result.push_str(&indent_str);
2403         result.push_str(")");
2404         result
2405     }
2406 }
2407
2408 /// Return true if a function call or a method call represented by the given span ends with a
2409 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
2410 /// comma from macro can potentially break the code.
2411 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2412     let mut encountered_closing_paren = false;
2413     for c in context.snippet(span).chars().rev() {
2414         match c {
2415             ',' => return true,
2416             ')' => if encountered_closing_paren {
2417                 return false;
2418             } else {
2419                 encountered_closing_paren = true;
2420             },
2421             _ if c.is_whitespace() => continue,
2422             _ => return false,
2423         }
2424     }
2425     false
2426 }
2427
2428 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2429     debug!("rewrite_paren, shape: {:?}", shape);
2430     let total_paren_overhead = paren_overhead(context);
2431     let paren_overhead = total_paren_overhead / 2;
2432     let sub_shape = shape
2433         .offset_left(paren_overhead)
2434         .and_then(|s| s.sub_width(paren_overhead))?;
2435
2436     let paren_wrapper = |s: &str| {
2437         if context.config.spaces_within_parens_and_brackets() && !s.is_empty() {
2438             format!("( {} )", s)
2439         } else {
2440             format!("({})", s)
2441         }
2442     };
2443
2444     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
2445     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2446
2447     if subexpr_str.contains('\n')
2448         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2449     {
2450         Some(paren_wrapper(&subexpr_str))
2451     } else {
2452         None
2453     }
2454 }
2455
2456 fn rewrite_index(
2457     expr: &ast::Expr,
2458     index: &ast::Expr,
2459     context: &RewriteContext,
2460     shape: Shape,
2461 ) -> Option<String> {
2462     let expr_str = expr.rewrite(context, shape)?;
2463
2464     let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
2465         ("[ ", " ]")
2466     } else {
2467         ("[", "]")
2468     };
2469
2470     let offset = last_line_width(&expr_str) + lbr.len();
2471     let rhs_overhead = shape.rhs_overhead(context.config);
2472     let index_shape = if expr_str.contains('\n') {
2473         Shape::legacy(context.config.max_width(), shape.indent)
2474             .offset_left(offset)
2475             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2476     } else {
2477         shape.visual_indent(offset).sub_width(offset + rbr.len())
2478     };
2479     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2480
2481     // Return if index fits in a single line.
2482     match orig_index_rw {
2483         Some(ref index_str) if !index_str.contains('\n') => {
2484             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2485         }
2486         _ => (),
2487     }
2488
2489     // Try putting index on the next line and see if it fits in a single line.
2490     let indent = shape.indent.block_indent(context.config);
2491     let index_shape = Shape::indented(indent, context.config).offset_left(lbr.len())?;
2492     let index_shape = index_shape.sub_width(rbr.len() + rhs_overhead)?;
2493     let new_index_rw = index.rewrite(context, index_shape);
2494     match (orig_index_rw, new_index_rw) {
2495         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2496             "{}{}{}{}{}",
2497             expr_str,
2498             indent.to_string_with_newline(context.config),
2499             lbr,
2500             new_index_str,
2501             rbr
2502         )),
2503         (None, Some(ref new_index_str)) => Some(format!(
2504             "{}{}{}{}{}",
2505             expr_str,
2506             indent.to_string_with_newline(context.config),
2507             lbr,
2508             new_index_str,
2509             rbr
2510         )),
2511         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2512         _ => None,
2513     }
2514 }
2515
2516 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2517     if base.is_some() {
2518         return false;
2519     }
2520
2521     fields.iter().all(|field| !field.is_shorthand)
2522 }
2523
2524 fn rewrite_struct_lit<'a>(
2525     context: &RewriteContext,
2526     path: &ast::Path,
2527     fields: &'a [ast::Field],
2528     base: Option<&'a ast::Expr>,
2529     span: Span,
2530     shape: Shape,
2531 ) -> Option<String> {
2532     debug!("rewrite_struct_lit: shape {:?}", shape);
2533
2534     enum StructLitField<'a> {
2535         Regular(&'a ast::Field),
2536         Base(&'a ast::Expr),
2537     }
2538
2539     // 2 = " {".len()
2540     let path_shape = shape.sub_width(2)?;
2541     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
2542
2543     if fields.is_empty() && base.is_none() {
2544         return Some(format!("{} {{}}", path_str));
2545     }
2546
2547     // Foo { a: Foo } - indent is +3, width is -5.
2548     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
2549
2550     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2551     let body_lo = context.snippet_provider.span_after(span, "{");
2552     let fields_str = if struct_lit_can_be_aligned(fields, &base)
2553         && context.config.struct_field_align_threshold() > 0
2554     {
2555         rewrite_with_alignment(
2556             fields,
2557             context,
2558             shape,
2559             mk_sp(body_lo, span.hi()),
2560             one_line_width,
2561         )?
2562     } else {
2563         let field_iter = fields
2564             .into_iter()
2565             .map(StructLitField::Regular)
2566             .chain(base.into_iter().map(StructLitField::Base));
2567
2568         let span_lo = |item: &StructLitField| match *item {
2569             StructLitField::Regular(field) => field.span().lo(),
2570             StructLitField::Base(expr) => {
2571                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
2572                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
2573                 let pos = snippet.find_uncommented("..").unwrap();
2574                 last_field_hi + BytePos(pos as u32)
2575             }
2576         };
2577         let span_hi = |item: &StructLitField| match *item {
2578             StructLitField::Regular(field) => field.span().hi(),
2579             StructLitField::Base(expr) => expr.span.hi(),
2580         };
2581         let rewrite = |item: &StructLitField| match *item {
2582             StructLitField::Regular(field) => {
2583                 // The 1 taken from the v_budget is for the comma.
2584                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
2585             }
2586             StructLitField::Base(expr) => {
2587                 // 2 = ..
2588                 expr.rewrite(context, v_shape.offset_left(2)?)
2589                     .map(|s| format!("..{}", s))
2590             }
2591         };
2592
2593         let items = itemize_list(
2594             context.snippet_provider,
2595             field_iter,
2596             "}",
2597             ",",
2598             span_lo,
2599             span_hi,
2600             rewrite,
2601             body_lo,
2602             span.hi(),
2603             false,
2604         );
2605         let item_vec = items.collect::<Vec<_>>();
2606
2607         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2608         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2609         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2610
2611         write_list(&item_vec, &fmt)?
2612     };
2613
2614     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2615     Some(format!("{} {{{}}}", path_str, fields_str))
2616
2617     // FIXME if context.config.indent_style() == Visual, but we run out
2618     // of space, we should fall back to BlockIndent.
2619 }
2620
2621 pub fn wrap_struct_field(
2622     context: &RewriteContext,
2623     fields_str: &str,
2624     shape: Shape,
2625     nested_shape: Shape,
2626     one_line_width: usize,
2627 ) -> String {
2628     if context.config.indent_style() == IndentStyle::Block
2629         && (fields_str.contains('\n') || !context.config.struct_lit_single_line()
2630             || fields_str.len() > one_line_width)
2631     {
2632         format!(
2633             "{}{}{}",
2634             nested_shape.indent.to_string_with_newline(context.config),
2635             fields_str,
2636             shape.indent.to_string_with_newline(context.config)
2637         )
2638     } else {
2639         // One liner or visual indent.
2640         format!(" {} ", fields_str)
2641     }
2642 }
2643
2644 pub fn struct_lit_field_separator(config: &Config) -> &str {
2645     colon_spaces(config.space_before_colon(), config.space_after_colon())
2646 }
2647
2648 pub fn rewrite_field(
2649     context: &RewriteContext,
2650     field: &ast::Field,
2651     shape: Shape,
2652     prefix_max_width: usize,
2653 ) -> Option<String> {
2654     if contains_skip(&field.attrs) {
2655         return Some(context.snippet(field.span()).to_owned());
2656     }
2657     let mut attrs_str = field.attrs.rewrite(context, shape)?;
2658     if !attrs_str.is_empty() {
2659         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
2660     };
2661     let name = field.ident.node.to_string();
2662     if field.is_shorthand {
2663         Some(attrs_str + &name)
2664     } else {
2665         let mut separator = String::from(struct_lit_field_separator(context.config));
2666         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2667             separator.push(' ');
2668         }
2669         let overhead = name.len() + separator.len();
2670         let expr_shape = shape.offset_left(overhead)?;
2671         let expr = field.expr.rewrite(context, expr_shape);
2672
2673         match expr {
2674             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
2675                 Some(attrs_str + &name)
2676             }
2677             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2678             None => {
2679                 let expr_offset = shape.indent.block_indent(context.config);
2680                 let expr = field
2681                     .expr
2682                     .rewrite(context, Shape::indented(expr_offset, context.config));
2683                 expr.map(|s| {
2684                     format!(
2685                         "{}{}:\n{}{}",
2686                         attrs_str,
2687                         name,
2688                         expr_offset.to_string(context.config),
2689                         s
2690                     )
2691                 })
2692             }
2693         }
2694     }
2695 }
2696
2697 fn shape_from_indent_style(
2698     context: &RewriteContext,
2699     shape: Shape,
2700     overhead: usize,
2701     offset: usize,
2702 ) -> Option<Shape> {
2703     if context.use_block_indent() {
2704         // 1 = ","
2705         shape
2706             .block()
2707             .block_indent(context.config.tab_spaces())
2708             .with_max_width(context.config)
2709             .sub_width(1)
2710     } else {
2711         shape.visual_indent(offset).sub_width(overhead)
2712     }
2713 }
2714
2715 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2716     context: &RewriteContext,
2717     items: &[&T],
2718     span: Span,
2719     shape: Shape,
2720 ) -> Option<String>
2721 where
2722     T: Rewrite + Spanned + ToExpr + 'a,
2723 {
2724     let mut items = items.iter();
2725     // In case of length 1, need a trailing comma
2726     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2727     if items.len() == 1 {
2728         // 3 = "(" + ",)"
2729         let nested_shape = shape.sub_width(3)?.visual_indent(1);
2730         return items
2731             .next()
2732             .unwrap()
2733             .rewrite(context, nested_shape)
2734             .map(|s| {
2735                 if context.config.spaces_within_parens_and_brackets() {
2736                     format!("( {}, )", s)
2737                 } else {
2738                     format!("({},)", s)
2739                 }
2740             });
2741     }
2742
2743     let list_lo = context.snippet_provider.span_after(span, "(");
2744     let nested_shape = shape.sub_width(2)?.visual_indent(1);
2745     let items = itemize_list(
2746         context.snippet_provider,
2747         items,
2748         ")",
2749         ",",
2750         |item| item.span().lo(),
2751         |item| item.span().hi(),
2752         |item| item.rewrite(context, nested_shape),
2753         list_lo,
2754         span.hi() - BytePos(1),
2755         false,
2756     );
2757     let item_vec: Vec<_> = items.collect();
2758     let tactic = definitive_tactic(
2759         &item_vec,
2760         ListTactic::HorizontalVertical,
2761         Separator::Comma,
2762         nested_shape.width,
2763     );
2764     let fmt = ListFormatting {
2765         tactic,
2766         separator: ",",
2767         trailing_separator: SeparatorTactic::Never,
2768         separator_place: SeparatorPlace::Back,
2769         shape,
2770         ends_with_newline: false,
2771         preserve_newline: false,
2772         config: context.config,
2773     };
2774     let list_str = write_list(&item_vec, &fmt)?;
2775
2776     if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
2777         Some(format!("( {} )", list_str))
2778     } else {
2779         Some(format!("({})", list_str))
2780     }
2781 }
2782
2783 pub fn rewrite_tuple<'a, T>(
2784     context: &RewriteContext,
2785     items: &[&T],
2786     span: Span,
2787     shape: Shape,
2788 ) -> Option<String>
2789 where
2790     T: Rewrite + Spanned + ToExpr + 'a,
2791 {
2792     debug!("rewrite_tuple {:?}", shape);
2793     if context.use_block_indent() {
2794         // We use the same rule as function calls for rewriting tuples.
2795         let force_trailing_comma = if context.inside_macro {
2796             span_ends_with_comma(context, span)
2797         } else {
2798             items.len() == 1
2799         };
2800         rewrite_call_inner(
2801             context,
2802             &String::new(),
2803             items,
2804             span,
2805             shape,
2806             context.config.width_heuristics().fn_call_width,
2807             force_trailing_comma,
2808         )
2809     } else {
2810         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2811     }
2812 }
2813
2814 pub fn rewrite_unary_prefix<R: Rewrite>(
2815     context: &RewriteContext,
2816     prefix: &str,
2817     rewrite: &R,
2818     shape: Shape,
2819 ) -> Option<String> {
2820     rewrite
2821         .rewrite(context, shape.offset_left(prefix.len())?)
2822         .map(|r| format!("{}{}", prefix, r))
2823 }
2824
2825 // FIXME: this is probably not correct for multi-line Rewrites. we should
2826 // subtract suffix.len() from the last line budget, not the first!
2827 pub fn rewrite_unary_suffix<R: Rewrite>(
2828     context: &RewriteContext,
2829     suffix: &str,
2830     rewrite: &R,
2831     shape: Shape,
2832 ) -> Option<String> {
2833     rewrite
2834         .rewrite(context, shape.sub_width(suffix.len())?)
2835         .map(|mut r| {
2836             r.push_str(suffix);
2837             r
2838         })
2839 }
2840
2841 fn rewrite_unary_op(
2842     context: &RewriteContext,
2843     op: &ast::UnOp,
2844     expr: &ast::Expr,
2845     shape: Shape,
2846 ) -> Option<String> {
2847     // For some reason, an UnOp is not spanned like BinOp!
2848     let operator_str = match *op {
2849         ast::UnOp::Deref => "*",
2850         ast::UnOp::Not => "!",
2851         ast::UnOp::Neg => "-",
2852     };
2853     rewrite_unary_prefix(context, operator_str, expr, shape)
2854 }
2855
2856 fn rewrite_assignment(
2857     context: &RewriteContext,
2858     lhs: &ast::Expr,
2859     rhs: &ast::Expr,
2860     op: Option<&ast::BinOp>,
2861     shape: Shape,
2862 ) -> Option<String> {
2863     let operator_str = match op {
2864         Some(op) => context.snippet(op.span),
2865         None => "=",
2866     };
2867
2868     // 1 = space between lhs and operator.
2869     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2870     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2871
2872     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2873 }
2874
2875 // The left hand side must contain everything up to, and including, the
2876 // assignment operator.
2877 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2878     context: &RewriteContext,
2879     lhs: S,
2880     ex: &R,
2881     shape: Shape,
2882 ) -> Option<String> {
2883     let lhs = lhs.into();
2884     let last_line_width = last_line_width(&lhs)
2885         .checked_sub(if lhs.contains('\n') {
2886             shape.indent.width()
2887         } else {
2888             0
2889         })
2890         .unwrap_or(0);
2891     // 1 = space between operator and rhs.
2892     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2893         width: 0,
2894         offset: shape.offset + last_line_width + 1,
2895         ..shape
2896     });
2897     let rhs = choose_rhs(context, ex, orig_shape, ex.rewrite(context, orig_shape))?;
2898     Some(lhs + &rhs)
2899 }
2900
2901 pub fn choose_rhs<R: Rewrite>(
2902     context: &RewriteContext,
2903     expr: &R,
2904     shape: Shape,
2905     orig_rhs: Option<String>,
2906 ) -> Option<String> {
2907     match orig_rhs {
2908         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2909             Some(format!(" {}", new_str))
2910         }
2911         _ => {
2912             // Expression did not fit on the same line as the identifier.
2913             // Try splitting the line and see if that works better.
2914             let new_shape =
2915                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2916                     .sub_width(shape.rhs_overhead(context.config))?;
2917             let new_rhs = expr.rewrite(context, new_shape);
2918             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2919
2920             match (orig_rhs, new_rhs) {
2921                 (Some(ref orig_rhs), Some(ref new_rhs))
2922                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2923                         .is_none() =>
2924                 {
2925                     Some(format!(" {}", orig_rhs))
2926                 }
2927                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2928                     Some(format!("{}{}", new_indent_str, new_rhs))
2929                 }
2930                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2931                 (None, None) => None,
2932                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2933             }
2934         }
2935     }
2936 }
2937
2938 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2939     !next_line_rhs.contains('\n') || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2940 }
2941
2942 fn rewrite_expr_addrof(
2943     context: &RewriteContext,
2944     mutability: ast::Mutability,
2945     expr: &ast::Expr,
2946     shape: Shape,
2947 ) -> Option<String> {
2948     let operator_str = match mutability {
2949         ast::Mutability::Immutable => "&",
2950         ast::Mutability::Mutable => "&mut ",
2951     };
2952     rewrite_unary_prefix(context, operator_str, expr, shape)
2953 }
2954
2955 pub trait ToExpr {
2956     fn to_expr(&self) -> Option<&ast::Expr>;
2957     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2958 }
2959
2960 impl ToExpr for ast::Expr {
2961     fn to_expr(&self) -> Option<&ast::Expr> {
2962         Some(self)
2963     }
2964
2965     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2966         can_be_overflowed_expr(context, self, len)
2967     }
2968 }
2969
2970 impl ToExpr for ast::Ty {
2971     fn to_expr(&self) -> Option<&ast::Expr> {
2972         None
2973     }
2974
2975     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2976         can_be_overflowed_type(context, self, len)
2977     }
2978 }
2979
2980 impl<'a> ToExpr for TuplePatField<'a> {
2981     fn to_expr(&self) -> Option<&ast::Expr> {
2982         None
2983     }
2984
2985     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2986         can_be_overflowed_pat(context, self, len)
2987     }
2988 }
2989
2990 impl<'a> ToExpr for ast::StructField {
2991     fn to_expr(&self) -> Option<&ast::Expr> {
2992         None
2993     }
2994
2995     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2996         false
2997     }
2998 }
2999
3000 impl<'a> ToExpr for MacroArg {
3001     fn to_expr(&self) -> Option<&ast::Expr> {
3002         match *self {
3003             MacroArg::Expr(ref expr) => Some(expr),
3004             _ => None,
3005         }
3006     }
3007
3008     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3009         match *self {
3010             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
3011             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
3012             MacroArg::Pat(..) => false,
3013         }
3014     }
3015 }