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 }
1241
1242 impl<'a> ArmWrapper<'a> {
1243     pub fn new(arm: &'a ast::Arm, is_last: bool) -> ArmWrapper<'a> {
1244         ArmWrapper { arm, is_last }
1245     }
1246 }
1247
1248 impl<'a> Rewrite for ArmWrapper<'a> {
1249     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1250         rewrite_match_arm(context, self.arm, shape, self.is_last)
1251     }
1252 }
1253
1254 fn rewrite_match(
1255     context: &RewriteContext,
1256     cond: &ast::Expr,
1257     arms: &[ast::Arm],
1258     shape: Shape,
1259     span: Span,
1260     attrs: &[ast::Attribute],
1261 ) -> Option<String> {
1262     // Do not take the rhs overhead from the upper expressions into account
1263     // when rewriting match condition.
1264     let cond_shape = Shape {
1265         width: context.budget(shape.used_width()),
1266         ..shape
1267     };
1268     // 6 = `match `
1269     let cond_shape = match context.config.indent_style() {
1270         IndentStyle::Visual => cond_shape.shrink_left(6)?,
1271         IndentStyle::Block => cond_shape.offset_left(6)?,
1272     };
1273     let cond_str = cond.rewrite(context, cond_shape)?;
1274     let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1275     let block_sep = match context.config.control_brace_style() {
1276         ControlBraceStyle::AlwaysNextLine => alt_block_sep,
1277         _ if last_line_extendable(&cond_str) => " ",
1278         // 2 = ` {`
1279         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => alt_block_sep,
1280         _ => " ",
1281     };
1282
1283     let nested_indent_str = shape
1284         .indent
1285         .block_indent(context.config)
1286         .to_string(context.config);
1287     // Inner attributes.
1288     let inner_attrs = &inner_attributes(attrs);
1289     let inner_attrs_str = if inner_attrs.is_empty() {
1290         String::new()
1291     } else {
1292         inner_attrs
1293             .rewrite(context, shape)
1294             .map(|s| format!("{}{}\n", nested_indent_str, s))?
1295     };
1296
1297     let open_brace_pos = if inner_attrs.is_empty() {
1298         let hi = if arms.is_empty() {
1299             span.hi()
1300         } else {
1301             arms[0].span().lo()
1302         };
1303         context
1304             .snippet_provider
1305             .span_after(mk_sp(cond.span.hi(), hi), "{")
1306     } else {
1307         inner_attrs[inner_attrs.len() - 1].span().hi()
1308     };
1309
1310     if arms.is_empty() {
1311         let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
1312         if snippet.trim().is_empty() {
1313             Some(format!("match {} {{}}", cond_str))
1314         } else {
1315             // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
1316             Some(context.snippet(span).to_owned())
1317         }
1318     } else {
1319         Some(format!(
1320             "match {}{}{{\n{}{}{}\n{}}}",
1321             cond_str,
1322             block_sep,
1323             inner_attrs_str,
1324             nested_indent_str,
1325             rewrite_match_arms(context, arms, shape, span, open_brace_pos)?,
1326             shape.indent.to_string(context.config),
1327         ))
1328     }
1329 }
1330
1331 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
1332     if is_last && config.trailing_comma() == SeparatorTactic::Never {
1333         ""
1334     } else if config.match_block_trailing_comma() {
1335         ","
1336     } else if let ast::ExprKind::Block(ref block) = body.node {
1337         if let ast::BlockCheckMode::Default = block.rules {
1338             ""
1339         } else {
1340             ","
1341         }
1342     } else {
1343         ","
1344     }
1345 }
1346
1347 fn rewrite_match_arms(
1348     context: &RewriteContext,
1349     arms: &[ast::Arm],
1350     shape: Shape,
1351     span: Span,
1352     open_brace_pos: BytePos,
1353 ) -> Option<String> {
1354     let arm_shape = shape
1355         .block_indent(context.config.tab_spaces())
1356         .with_max_width(context.config);
1357
1358     let arm_len = arms.len();
1359     let is_last_iter = repeat(false)
1360         .take(arm_len.checked_sub(1).unwrap_or(0))
1361         .chain(repeat(true));
1362     let items = itemize_list(
1363         context.snippet_provider,
1364         arms.iter()
1365             .zip(is_last_iter)
1366             .map(|(arm, is_last)| ArmWrapper::new(arm, is_last)),
1367         "}",
1368         "|",
1369         |arm| arm.arm.span().lo(),
1370         |arm| arm.arm.span().hi(),
1371         |arm| arm.rewrite(context, arm_shape),
1372         open_brace_pos,
1373         span.hi(),
1374         false,
1375     );
1376     let arms_vec: Vec<_> = items.collect();
1377     let fmt = ListFormatting {
1378         tactic: DefinitiveListTactic::Vertical,
1379         // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
1380         separator: "",
1381         trailing_separator: SeparatorTactic::Never,
1382         separator_place: SeparatorPlace::Back,
1383         shape: arm_shape,
1384         ends_with_newline: true,
1385         preserve_newline: true,
1386         config: context.config,
1387     };
1388
1389     write_list(&arms_vec, &fmt)
1390 }
1391
1392 fn rewrite_match_arm(
1393     context: &RewriteContext,
1394     arm: &ast::Arm,
1395     shape: Shape,
1396     is_last: bool,
1397 ) -> Option<String> {
1398     let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
1399         if contains_skip(&arm.attrs) {
1400             let (_, body) = flatten_arm_body(context, &arm.body);
1401             // `arm.span()` does not include trailing comma, add it manually.
1402             return Some(format!(
1403                 "{}{}",
1404                 context.snippet(arm.span()),
1405                 arm_comma(context.config, body, is_last),
1406             ));
1407         }
1408         let missing_span = mk_sp(
1409             arm.attrs[arm.attrs.len() - 1].span.hi(),
1410             arm.pats[0].span.lo(),
1411         );
1412         (missing_span, arm.attrs.rewrite(context, shape)?)
1413     } else {
1414         (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
1415     };
1416     let pats_str = rewrite_match_pattern(
1417         context,
1418         &arm.pats,
1419         &arm.guard,
1420         arm.beginning_vert.is_some(),
1421         shape,
1422     ).and_then(|pats_str| {
1423         combine_strs_with_missing_comments(
1424             context,
1425             &attrs_str,
1426             &pats_str,
1427             missing_span,
1428             shape,
1429             false,
1430         )
1431     })?;
1432     rewrite_match_body(
1433         context,
1434         &arm.body,
1435         &pats_str,
1436         shape,
1437         arm.guard.is_some(),
1438         is_last,
1439     )
1440 }
1441
1442 /// Returns true if the given pattern is short. A short pattern is defined by the following grammer:
1443 ///
1444 /// [small, ntp]:
1445 ///     - single token
1446 ///     - `&[single-line, ntp]`
1447 ///
1448 /// [small]:
1449 ///     - `[small, ntp]`
1450 ///     - unary tuple constructor `([small, ntp])`
1451 ///     - `&[small]`
1452 fn is_short_pattern(pat: &ast::Pat, pat_str: &str) -> bool {
1453     // We also require that the pattern is reasonably 'small' with its literal width.
1454     pat_str.len() <= 20 && !pat_str.contains('\n') && is_short_pattern_inner(pat)
1455 }
1456
1457 fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
1458     match pat.node {
1459         ast::PatKind::Wild | ast::PatKind::Lit(_) => true,
1460         ast::PatKind::Ident(_, _, ref pat) => pat.is_none(),
1461         ast::PatKind::Struct(..)
1462         | ast::PatKind::Mac(..)
1463         | ast::PatKind::Slice(..)
1464         | ast::PatKind::Path(..)
1465         | ast::PatKind::Range(..) => false,
1466         ast::PatKind::Tuple(ref subpats, _) => subpats.len() <= 1,
1467         ast::PatKind::TupleStruct(ref path, ref subpats, _) => {
1468             path.segments.len() <= 1 && subpats.len() <= 1
1469         }
1470         ast::PatKind::Box(ref p) | ast::PatKind::Ref(ref p, _) => is_short_pattern_inner(&*p),
1471     }
1472 }
1473
1474 fn rewrite_match_pattern(
1475     context: &RewriteContext,
1476     pats: &[ptr::P<ast::Pat>],
1477     guard: &Option<ptr::P<ast::Expr>>,
1478     has_beginning_vert: bool,
1479     shape: Shape,
1480 ) -> Option<String> {
1481     // Patterns
1482     // 5 = ` => {`
1483     // 2 = `| `
1484     let pat_shape = shape
1485         .sub_width(5)?
1486         .offset_left(if has_beginning_vert { 2 } else { 0 })?;
1487
1488     let pat_strs = pats.iter()
1489         .map(|p| p.rewrite(context, pat_shape))
1490         .collect::<Option<Vec<_>>>()?;
1491
1492     let use_mixed_layout = pats.iter()
1493         .zip(pat_strs.iter())
1494         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1495     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1496     let tactic = if use_mixed_layout {
1497         DefinitiveListTactic::Mixed
1498     } else {
1499         definitive_tactic(
1500             &items,
1501             ListTactic::HorizontalVertical,
1502             Separator::VerticalBar,
1503             pat_shape.width,
1504         )
1505     };
1506     let fmt = ListFormatting {
1507         tactic,
1508         separator: " |",
1509         trailing_separator: SeparatorTactic::Never,
1510         separator_place: context.config.binop_separator(),
1511         shape: pat_shape,
1512         ends_with_newline: false,
1513         preserve_newline: false,
1514         config: context.config,
1515     };
1516     let pats_str = write_list(&items, &fmt)?;
1517     let beginning_vert = if has_beginning_vert { "| " } else { "" };
1518
1519     // Guard
1520     let guard_str = rewrite_guard(context, guard, shape, trimmed_last_line_width(&pats_str))?;
1521
1522     Some(format!("{}{}{}", beginning_vert, pats_str, guard_str))
1523 }
1524
1525 // (extend, body)
1526 // @extend: true if the arm body can be put next to `=>`
1527 // @body: flattened body, if the body is block with a single expression
1528 fn flatten_arm_body<'a>(context: &'a RewriteContext, body: &'a ast::Expr) -> (bool, &'a ast::Expr) {
1529     match body.node {
1530         ast::ExprKind::Block(ref block)
1531             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1532         {
1533             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1534                 (
1535                     !context.config.force_multiline_blocks() && can_extend_match_arm_body(expr),
1536                     &*expr,
1537                 )
1538             } else {
1539                 (false, &*body)
1540             }
1541         }
1542         _ => (
1543             !context.config.force_multiline_blocks() && body.can_be_overflowed(context, 1),
1544             &*body,
1545         ),
1546     }
1547 }
1548
1549 fn rewrite_match_body(
1550     context: &RewriteContext,
1551     body: &ptr::P<ast::Expr>,
1552     pats_str: &str,
1553     shape: Shape,
1554     has_guard: bool,
1555     is_last: bool,
1556 ) -> Option<String> {
1557     let (extend, body) = flatten_arm_body(context, body);
1558     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1559         (true, is_empty_block(block, context.codemap))
1560     } else {
1561         (false, false)
1562     };
1563
1564     let comma = arm_comma(context.config, body, is_last);
1565     let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1566
1567     let combine_orig_body = |body_str: &str| {
1568         let block_sep = match context.config.control_brace_style() {
1569             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1570             _ => " ",
1571         };
1572
1573         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1574     };
1575
1576     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1577     let next_line_indent = if !is_block || is_empty_block {
1578         shape.indent.block_indent(context.config)
1579     } else {
1580         shape.indent
1581     };
1582     let combine_next_line_body = |body_str: &str| {
1583         if is_block {
1584             return Some(format!(
1585                 "{} =>{}{}",
1586                 pats_str,
1587                 next_line_indent.to_string_with_newline(context.config),
1588                 body_str
1589             ));
1590         }
1591
1592         let indent_str = shape.indent.to_string_with_newline(context.config);
1593         let nested_indent_str = next_line_indent.to_string_with_newline(context.config);
1594         let (body_prefix, body_suffix) = if context.config.match_arm_blocks() {
1595             let comma = if context.config.match_block_trailing_comma() {
1596                 ","
1597             } else {
1598                 ""
1599             };
1600             ("{", format!("{}}}{}", indent_str, comma))
1601         } else {
1602             ("", String::from(","))
1603         };
1604
1605         let block_sep = match context.config.control_brace_style() {
1606             ControlBraceStyle::AlwaysNextLine => format!("{}{}", alt_block_sep, body_prefix),
1607             _ if body_prefix.is_empty() => "".to_owned(),
1608             _ if forbid_same_line => format!("{}{}", alt_block_sep, body_prefix),
1609             _ => format!(" {}", body_prefix),
1610         } + &nested_indent_str;
1611
1612         Some(format!(
1613             "{} =>{}{}{}",
1614             pats_str, block_sep, body_str, body_suffix
1615         ))
1616     };
1617
1618     // Let's try and get the arm body on the same line as the condition.
1619     // 4 = ` => `.len()
1620     let orig_body_shape = shape
1621         .offset_left(extra_offset(pats_str, shape) + 4)
1622         .and_then(|shape| shape.sub_width(comma.len()));
1623     let orig_body = if let Some(body_shape) = orig_body_shape {
1624         let rewrite = nop_block_collapse(
1625             format_expr(body, ExprType::Statement, context, body_shape),
1626             body_shape.width,
1627         );
1628
1629         match rewrite {
1630             Some(ref body_str)
1631                 if !forbid_same_line
1632                     && (is_block
1633                         || (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1634             {
1635                 return combine_orig_body(body_str);
1636             }
1637             _ => rewrite,
1638         }
1639     } else {
1640         None
1641     };
1642     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1643
1644     // Try putting body on the next line and see if it looks better.
1645     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1646     let next_line_body = nop_block_collapse(
1647         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1648         next_line_body_shape.width,
1649     );
1650     match (orig_body, next_line_body) {
1651         (Some(ref orig_str), Some(ref next_line_str))
1652             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1653         {
1654             combine_next_line_body(next_line_str)
1655         }
1656         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1657             combine_orig_body(orig_str)
1658         }
1659         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1660             combine_next_line_body(next_line_str)
1661         }
1662         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1663         (None, None) => None,
1664         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1665     }
1666 }
1667
1668 // The `if ...` guard on a match arm.
1669 fn rewrite_guard(
1670     context: &RewriteContext,
1671     guard: &Option<ptr::P<ast::Expr>>,
1672     shape: Shape,
1673     // The amount of space used up on this line for the pattern in
1674     // the arm (excludes offset).
1675     pattern_width: usize,
1676 ) -> Option<String> {
1677     if let Some(ref guard) = *guard {
1678         // First try to fit the guard string on the same line as the pattern.
1679         // 4 = ` if `, 5 = ` => {`
1680         let cond_shape = shape
1681             .offset_left(pattern_width + 4)
1682             .and_then(|s| s.sub_width(5));
1683         if let Some(cond_shape) = cond_shape {
1684             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1685                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1686                     return Some(format!(" if {}", cond_str));
1687                 }
1688             }
1689         }
1690
1691         // Not enough space to put the guard after the pattern, try a newline.
1692         // 3 = `if `, 5 = ` => {`
1693         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1694             .offset_left(3)
1695             .and_then(|s| s.sub_width(5));
1696         if let Some(cond_shape) = cond_shape {
1697             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1698                 return Some(format!(
1699                     "{}if {}",
1700                     cond_shape.indent.to_string_with_newline(context.config),
1701                     cond_str
1702                 ));
1703             }
1704         }
1705
1706         None
1707     } else {
1708         Some(String::new())
1709     }
1710 }
1711
1712 fn rewrite_pat_expr(
1713     context: &RewriteContext,
1714     pat: Option<&ast::Pat>,
1715     expr: &ast::Expr,
1716     matcher: &str,
1717     // Connecting piece between pattern and expression,
1718     // *without* trailing space.
1719     connector: &str,
1720     keyword: &str,
1721     shape: Shape,
1722     offset: usize,
1723 ) -> Option<String> {
1724     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1725     let cond_shape = shape.offset_left(offset)?;
1726     if let Some(pat) = pat {
1727         let matcher = if matcher.is_empty() {
1728             matcher.to_owned()
1729         } else {
1730             format!("{} ", matcher)
1731         };
1732         let pat_shape = cond_shape
1733             .offset_left(matcher.len())?
1734             .sub_width(connector.len())?;
1735         let pat_string = pat.rewrite(context, pat_shape)?;
1736         let result = format!("{}{}{}", matcher, pat_string, connector);
1737         return rewrite_assign_rhs(context, result, expr, cond_shape);
1738     }
1739
1740     let expr_rw = expr.rewrite(context, cond_shape);
1741     // The expression may (partially) fit on the current line.
1742     // We do not allow splitting between `if` and condition.
1743     if keyword == "if" || expr_rw.is_some() {
1744         return expr_rw;
1745     }
1746
1747     // The expression won't fit on the current line, jump to next.
1748     let nested_shape = shape
1749         .block_indent(context.config.tab_spaces())
1750         .with_max_width(context.config);
1751     let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
1752     expr.rewrite(context, nested_shape)
1753         .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
1754 }
1755
1756 fn can_extend_match_arm_body(body: &ast::Expr) -> bool {
1757     match body.node {
1758         // We do not allow `if` to stay on the same line, since we could easily mistake
1759         // `pat => if cond { ... }` and `pat if cond => { ... }`.
1760         ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => false,
1761         ast::ExprKind::ForLoop(..)
1762         | ast::ExprKind::Loop(..)
1763         | ast::ExprKind::While(..)
1764         | ast::ExprKind::WhileLet(..)
1765         | ast::ExprKind::Match(..)
1766         | ast::ExprKind::Block(..)
1767         | ast::ExprKind::Closure(..)
1768         | ast::ExprKind::Array(..)
1769         | ast::ExprKind::Call(..)
1770         | ast::ExprKind::MethodCall(..)
1771         | ast::ExprKind::Mac(..)
1772         | ast::ExprKind::Struct(..)
1773         | ast::ExprKind::Tup(..) => true,
1774         ast::ExprKind::AddrOf(_, ref expr)
1775         | ast::ExprKind::Box(ref expr)
1776         | ast::ExprKind::Try(ref expr)
1777         | ast::ExprKind::Unary(_, ref expr)
1778         | ast::ExprKind::Cast(ref expr, _) => can_extend_match_arm_body(expr),
1779         _ => false,
1780     }
1781 }
1782
1783 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1784     match l.node {
1785         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1786         _ => wrap_str(
1787             context.snippet(l.span).to_owned(),
1788             context.config.max_width(),
1789             shape,
1790         ),
1791     }
1792 }
1793
1794 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1795     let string_lit = context.snippet(span);
1796
1797     if !context.config.format_strings() {
1798         if string_lit
1799             .lines()
1800             .rev()
1801             .skip(1)
1802             .all(|line| line.ends_with('\\'))
1803         {
1804             let new_indent = shape.visual_indent(1).indent;
1805             let indented_string_lit = String::from(
1806                 string_lit
1807                     .lines()
1808                     .map(|line| {
1809                         format!(
1810                             "{}{}",
1811                             new_indent.to_string(context.config),
1812                             line.trim_left()
1813                         )
1814                     })
1815                     .collect::<Vec<_>>()
1816                     .join("\n")
1817                     .trim_left(),
1818             );
1819             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1820         } else {
1821             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1822         }
1823     }
1824
1825     // Remove the quote characters.
1826     let str_lit = &string_lit[1..string_lit.len() - 1];
1827
1828     rewrite_string(
1829         str_lit,
1830         &StringFormat::new(shape.visual_indent(0), context.config),
1831         None,
1832     )
1833 }
1834
1835 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1836 /// format.
1837 ///
1838 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1839 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1840 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1841 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1842     // format! like macros
1843     // From the Rust Standard Library.
1844     ("eprint!", 0),
1845     ("eprintln!", 0),
1846     ("format!", 0),
1847     ("format_args!", 0),
1848     ("print!", 0),
1849     ("println!", 0),
1850     ("panic!", 0),
1851     ("unreachable!", 0),
1852     // From the `log` crate.
1853     ("debug!", 0),
1854     ("error!", 0),
1855     ("info!", 0),
1856     ("warn!", 0),
1857     // write! like macros
1858     ("assert!", 1),
1859     ("debug_assert!", 1),
1860     ("write!", 1),
1861     ("writeln!", 1),
1862     // assert_eq! like macros
1863     ("assert_eq!", 2),
1864     ("assert_ne!", 2),
1865     ("debug_assert_eq!", 2),
1866     ("debug_assert_ne!", 2),
1867 ];
1868
1869 pub fn rewrite_call(
1870     context: &RewriteContext,
1871     callee: &str,
1872     args: &[ptr::P<ast::Expr>],
1873     span: Span,
1874     shape: Shape,
1875 ) -> Option<String> {
1876     let force_trailing_comma = if context.inside_macro {
1877         span_ends_with_comma(context, span)
1878     } else {
1879         false
1880     };
1881     rewrite_call_inner(
1882         context,
1883         callee,
1884         &ptr_vec_to_ref_vec(args),
1885         span,
1886         shape,
1887         context.config.width_heuristics().fn_call_width,
1888         force_trailing_comma,
1889     )
1890 }
1891
1892 pub fn rewrite_call_inner<'a, T>(
1893     context: &RewriteContext,
1894     callee_str: &str,
1895     args: &[&T],
1896     span: Span,
1897     shape: Shape,
1898     args_max_width: usize,
1899     force_trailing_comma: bool,
1900 ) -> Option<String>
1901 where
1902     T: Rewrite + Spanned + ToExpr + 'a,
1903 {
1904     // 2 = `( `, 1 = `(`
1905     let paren_overhead = if context.config.spaces_within_parens_and_brackets() {
1906         2
1907     } else {
1908         1
1909     };
1910     let used_width = extra_offset(callee_str, shape);
1911     let one_line_width = shape
1912         .width
1913         .checked_sub(used_width + 2 * paren_overhead)
1914         .unwrap_or(0);
1915
1916     // 1 = "(" or ")"
1917     let one_line_shape = shape
1918         .offset_left(last_line_width(callee_str) + 1)
1919         .and_then(|shape| shape.sub_width(1))
1920         .unwrap_or(Shape { width: 0, ..shape });
1921     let nested_shape = shape_from_indent_style(
1922         context,
1923         shape,
1924         used_width + 2 * paren_overhead,
1925         used_width + paren_overhead,
1926     )?;
1927
1928     let span_lo = context.snippet_provider.span_after(span, "(");
1929     let args_span = mk_sp(span_lo, span.hi());
1930
1931     let (extendable, list_str) = rewrite_call_args(
1932         context,
1933         args,
1934         args_span,
1935         one_line_shape,
1936         nested_shape,
1937         one_line_width,
1938         args_max_width,
1939         force_trailing_comma,
1940         callee_str,
1941     )?;
1942
1943     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
1944         let mut new_context = context.clone();
1945         new_context.use_block = true;
1946         return rewrite_call_inner(
1947             &new_context,
1948             callee_str,
1949             args,
1950             span,
1951             shape,
1952             args_max_width,
1953             force_trailing_comma,
1954         );
1955     }
1956
1957     let args_shape = Shape {
1958         width: shape
1959             .width
1960             .checked_sub(last_line_width(callee_str))
1961             .unwrap_or(0),
1962         ..shape
1963     };
1964     Some(format!(
1965         "{}{}",
1966         callee_str,
1967         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
1968     ))
1969 }
1970
1971 fn need_block_indent(s: &str, shape: Shape) -> bool {
1972     s.lines().skip(1).any(|s| {
1973         s.find(|c| !char::is_whitespace(c))
1974             .map_or(false, |w| w + 1 < shape.indent.width())
1975     })
1976 }
1977
1978 fn rewrite_call_args<'a, T>(
1979     context: &RewriteContext,
1980     args: &[&T],
1981     span: Span,
1982     one_line_shape: Shape,
1983     nested_shape: Shape,
1984     one_line_width: usize,
1985     args_max_width: usize,
1986     force_trailing_comma: bool,
1987     callee_str: &str,
1988 ) -> Option<(bool, String)>
1989 where
1990     T: Rewrite + Spanned + ToExpr + 'a,
1991 {
1992     let items = itemize_list(
1993         context.snippet_provider,
1994         args.iter(),
1995         ")",
1996         ",",
1997         |item| item.span().lo(),
1998         |item| item.span().hi(),
1999         |item| item.rewrite(context, nested_shape),
2000         span.lo(),
2001         span.hi(),
2002         true,
2003     );
2004     let mut item_vec: Vec<_> = items.collect();
2005
2006     // Try letting the last argument overflow to the next line with block
2007     // indentation. If its first line fits on one line with the other arguments,
2008     // we format the function arguments horizontally.
2009     let tactic = try_overflow_last_arg(
2010         context,
2011         &mut item_vec,
2012         &args[..],
2013         one_line_shape,
2014         nested_shape,
2015         one_line_width,
2016         args_max_width,
2017         callee_str,
2018     );
2019
2020     let fmt = ListFormatting {
2021         tactic,
2022         separator: ",",
2023         trailing_separator: if force_trailing_comma {
2024             SeparatorTactic::Always
2025         } else if context.inside_macro || !context.use_block_indent() {
2026             SeparatorTactic::Never
2027         } else {
2028             context.config.trailing_comma()
2029         },
2030         separator_place: SeparatorPlace::Back,
2031         shape: nested_shape,
2032         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2033         preserve_newline: false,
2034         config: context.config,
2035     };
2036
2037     write_list(&item_vec, &fmt)
2038         .map(|args_str| (tactic == DefinitiveListTactic::Horizontal, args_str))
2039 }
2040
2041 fn try_overflow_last_arg<'a, T>(
2042     context: &RewriteContext,
2043     item_vec: &mut Vec<ListItem>,
2044     args: &[&T],
2045     one_line_shape: Shape,
2046     nested_shape: Shape,
2047     one_line_width: usize,
2048     args_max_width: usize,
2049     callee_str: &str,
2050 ) -> DefinitiveListTactic
2051 where
2052     T: Rewrite + Spanned + ToExpr + 'a,
2053 {
2054     // 1 = "("
2055     let combine_arg_with_callee =
2056         callee_str.len() + 1 <= context.config.tab_spaces() && args.len() == 1;
2057     let overflow_last = combine_arg_with_callee || can_be_overflowed(context, args);
2058
2059     // Replace the last item with its first line to see if it fits with
2060     // first arguments.
2061     let placeholder = if overflow_last {
2062         let mut context = context.clone();
2063         if !combine_arg_with_callee {
2064             if let Some(expr) = args[args.len() - 1].to_expr() {
2065                 if let ast::ExprKind::MethodCall(..) = expr.node {
2066                     context.force_one_line_chain = true;
2067                 }
2068             }
2069         }
2070         last_arg_shape(args, item_vec, one_line_shape, args_max_width).and_then(|arg_shape| {
2071             rewrite_last_arg_with_overflow(&context, args, &mut item_vec[args.len() - 1], arg_shape)
2072         })
2073     } else {
2074         None
2075     };
2076
2077     let mut tactic = definitive_tactic(
2078         &*item_vec,
2079         ListTactic::LimitedHorizontalVertical(args_max_width),
2080         Separator::Comma,
2081         one_line_width,
2082     );
2083
2084     // Replace the stub with the full overflowing last argument if the rewrite
2085     // succeeded and its first line fits with the other arguments.
2086     match (overflow_last, tactic, placeholder) {
2087         (true, DefinitiveListTactic::Horizontal, Some(ref overflowed)) if args.len() == 1 => {
2088             // When we are rewriting a nested function call, we restrict the
2089             // bugdet for the inner function to avoid them being deeply nested.
2090             // However, when the inner function has a prefix or a suffix
2091             // (e.g. `foo() as u32`), this budget reduction may produce poorly
2092             // formatted code, where a prefix or a suffix being left on its own
2093             // line. Here we explicitlly check those cases.
2094             if count_newlines(overflowed) == 1 {
2095                 let rw = args.last()
2096                     .and_then(|last_arg| last_arg.rewrite(context, nested_shape));
2097                 let no_newline = rw.as_ref().map_or(false, |s| !s.contains('\n'));
2098                 if no_newline {
2099                     item_vec[args.len() - 1].item = rw;
2100                 } else {
2101                     item_vec[args.len() - 1].item = Some(overflowed.to_owned());
2102                 }
2103             } else {
2104                 item_vec[args.len() - 1].item = Some(overflowed.to_owned());
2105             }
2106         }
2107         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2108             item_vec[args.len() - 1].item = placeholder;
2109         }
2110         _ if args.len() >= 1 => {
2111             item_vec[args.len() - 1].item = args.last()
2112                 .and_then(|last_arg| last_arg.rewrite(context, nested_shape));
2113
2114             let default_tactic = || {
2115                 definitive_tactic(
2116                     &*item_vec,
2117                     ListTactic::LimitedHorizontalVertical(args_max_width),
2118                     Separator::Comma,
2119                     one_line_width,
2120                 )
2121             };
2122
2123             // Use horizontal layout for a function with a single argument as long as
2124             // everything fits in a single line.
2125             if args.len() == 1
2126                 && args_max_width != 0 // Vertical layout is forced.
2127                 && !item_vec[0].has_comment()
2128                 && !item_vec[0].inner_as_ref().contains('\n')
2129                 && ::lists::total_item_width(&item_vec[0]) <= one_line_width
2130             {
2131                 tactic = DefinitiveListTactic::Horizontal;
2132             } else {
2133                 tactic = default_tactic();
2134
2135                 if tactic == DefinitiveListTactic::Vertical {
2136                     if let Some((all_simple, num_args_before)) =
2137                         maybe_get_args_offset(callee_str, args)
2138                     {
2139                         let one_line = all_simple
2140                             && definitive_tactic(
2141                                 &item_vec[..num_args_before],
2142                                 ListTactic::HorizontalVertical,
2143                                 Separator::Comma,
2144                                 nested_shape.width,
2145                             ) == DefinitiveListTactic::Horizontal
2146                             && definitive_tactic(
2147                                 &item_vec[num_args_before + 1..],
2148                                 ListTactic::HorizontalVertical,
2149                                 Separator::Comma,
2150                                 nested_shape.width,
2151                             ) == DefinitiveListTactic::Horizontal;
2152
2153                         if one_line {
2154                             tactic = DefinitiveListTactic::SpecialMacro(num_args_before);
2155                         };
2156                     }
2157                 }
2158             }
2159         }
2160         _ => (),
2161     }
2162
2163     tactic
2164 }
2165
2166 fn is_simple_arg(expr: &ast::Expr) -> bool {
2167     match expr.node {
2168         ast::ExprKind::Lit(..) => true,
2169         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
2170         ast::ExprKind::AddrOf(_, ref expr)
2171         | ast::ExprKind::Box(ref expr)
2172         | ast::ExprKind::Cast(ref expr, _)
2173         | ast::ExprKind::Field(ref expr, _)
2174         | ast::ExprKind::Try(ref expr)
2175         | ast::ExprKind::TupField(ref expr, _)
2176         | ast::ExprKind::Unary(_, ref expr) => is_simple_arg(expr),
2177         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
2178             is_simple_arg(lhs) && is_simple_arg(rhs)
2179         }
2180         _ => false,
2181     }
2182 }
2183
2184 fn is_every_args_simple<T: ToExpr>(lists: &[&T]) -> bool {
2185     lists
2186         .iter()
2187         .all(|arg| arg.to_expr().map_or(false, is_simple_arg))
2188 }
2189
2190 /// In case special-case style is required, returns an offset from which we start horizontal layout.
2191 fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
2192     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
2193         .iter()
2194         .find(|&&(s, _)| s == callee_str)
2195     {
2196         let all_simple = args.len() > num_args_before && is_every_args_simple(args);
2197
2198         Some((all_simple, num_args_before))
2199     } else {
2200         None
2201     }
2202 }
2203
2204 /// Returns a shape for the last argument which is going to be overflowed.
2205 fn last_arg_shape<T>(
2206     lists: &[&T],
2207     items: &[ListItem],
2208     shape: Shape,
2209     args_max_width: usize,
2210 ) -> Option<Shape>
2211 where
2212     T: Rewrite + Spanned + ToExpr,
2213 {
2214     let is_nested_call = lists
2215         .iter()
2216         .next()
2217         .and_then(|item| item.to_expr())
2218         .map_or(false, is_nested_call);
2219     if items.len() == 1 && !is_nested_call {
2220         return Some(shape);
2221     }
2222     let offset = items.iter().rev().skip(1).fold(0, |acc, i| {
2223         // 2 = ", "
2224         acc + 2 + i.inner_as_ref().len()
2225     });
2226     Shape {
2227         width: min(args_max_width, shape.width),
2228         ..shape
2229     }.offset_left(offset)
2230 }
2231
2232 fn rewrite_last_arg_with_overflow<'a, T>(
2233     context: &RewriteContext,
2234     args: &[&T],
2235     last_item: &mut ListItem,
2236     shape: Shape,
2237 ) -> Option<String>
2238 where
2239     T: Rewrite + Spanned + ToExpr + 'a,
2240 {
2241     let last_arg = args[args.len() - 1];
2242     let rewrite = if let Some(expr) = last_arg.to_expr() {
2243         match expr.node {
2244             // When overflowing the closure which consists of a single control flow expression,
2245             // force to use block if its condition uses multi line.
2246             ast::ExprKind::Closure(..) => {
2247                 // If the argument consists of multiple closures, we do not overflow
2248                 // the last closure.
2249                 if closures::args_have_many_closure(args) {
2250                     None
2251                 } else {
2252                     closures::rewrite_last_closure(context, expr, shape)
2253                 }
2254             }
2255             _ => expr.rewrite(context, shape),
2256         }
2257     } else {
2258         last_arg.rewrite(context, shape)
2259     };
2260
2261     if let Some(rewrite) = rewrite {
2262         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2263         last_item.item = rewrite_first_line;
2264         Some(rewrite)
2265     } else {
2266         None
2267     }
2268 }
2269
2270 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2271 where
2272     T: Rewrite + Spanned + ToExpr + 'a,
2273 {
2274     args.last()
2275         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2276 }
2277
2278 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2279     match expr.node {
2280         ast::ExprKind::Match(..) => {
2281             (context.use_block_indent() && args_len == 1)
2282                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
2283         }
2284         ast::ExprKind::If(..)
2285         | ast::ExprKind::IfLet(..)
2286         | ast::ExprKind::ForLoop(..)
2287         | ast::ExprKind::Loop(..)
2288         | ast::ExprKind::While(..)
2289         | ast::ExprKind::WhileLet(..) => {
2290             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2291         }
2292         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2293             context.use_block_indent()
2294                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
2295         }
2296         ast::ExprKind::Array(..)
2297         | ast::ExprKind::Call(..)
2298         | ast::ExprKind::Mac(..)
2299         | ast::ExprKind::MethodCall(..)
2300         | ast::ExprKind::Struct(..)
2301         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2302         ast::ExprKind::AddrOf(_, ref expr)
2303         | ast::ExprKind::Box(ref expr)
2304         | ast::ExprKind::Try(ref expr)
2305         | ast::ExprKind::Unary(_, ref expr)
2306         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2307         _ => false,
2308     }
2309 }
2310
2311 fn is_nested_call(expr: &ast::Expr) -> bool {
2312     match expr.node {
2313         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
2314         ast::ExprKind::AddrOf(_, ref expr)
2315         | ast::ExprKind::Box(ref expr)
2316         | ast::ExprKind::Try(ref expr)
2317         | ast::ExprKind::Unary(_, ref expr)
2318         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
2319         _ => false,
2320     }
2321 }
2322
2323 pub fn wrap_args_with_parens(
2324     context: &RewriteContext,
2325     args_str: &str,
2326     is_extendable: bool,
2327     shape: Shape,
2328     nested_shape: Shape,
2329 ) -> String {
2330     let paren_overhead = paren_overhead(context);
2331     let fits_one_line = args_str.len() + paren_overhead <= shape.width;
2332     let extend_width = if args_str.is_empty() {
2333         paren_overhead
2334     } else {
2335         paren_overhead / 2
2336     };
2337     if !context.use_block_indent()
2338         || (context.inside_macro && !args_str.contains('\n') && fits_one_line)
2339         || (is_extendable && extend_width <= shape.width)
2340     {
2341         let mut result = String::with_capacity(args_str.len() + 4);
2342         if context.config.spaces_within_parens_and_brackets() && !args_str.is_empty() {
2343             result.push_str("( ");
2344             result.push_str(args_str);
2345             result.push_str(" )");
2346         } else {
2347             result.push_str("(");
2348             result.push_str(args_str);
2349             result.push_str(")");
2350         }
2351         result
2352     } else {
2353         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
2354         let indent_str = shape.block().indent.to_string_with_newline(context.config);
2355         let mut result =
2356             String::with_capacity(args_str.len() + 2 + indent_str.len() + nested_indent_str.len());
2357         result.push_str("(");
2358         if !args_str.is_empty() {
2359             result.push_str(&nested_indent_str);
2360             result.push_str(args_str);
2361         }
2362         result.push_str(&indent_str);
2363         result.push_str(")");
2364         result
2365     }
2366 }
2367
2368 /// Return true if a function call or a method call represented by the given span ends with a
2369 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
2370 /// comma from macro can potentially break the code.
2371 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2372     let mut encountered_closing_paren = false;
2373     for c in context.snippet(span).chars().rev() {
2374         match c {
2375             ',' => return true,
2376             ')' => if encountered_closing_paren {
2377                 return false;
2378             } else {
2379                 encountered_closing_paren = true;
2380             },
2381             _ if c.is_whitespace() => continue,
2382             _ => return false,
2383         }
2384     }
2385     false
2386 }
2387
2388 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2389     debug!("rewrite_paren, shape: {:?}", shape);
2390     let total_paren_overhead = paren_overhead(context);
2391     let paren_overhead = total_paren_overhead / 2;
2392     let sub_shape = shape
2393         .offset_left(paren_overhead)
2394         .and_then(|s| s.sub_width(paren_overhead))?;
2395
2396     let paren_wrapper = |s: &str| {
2397         if context.config.spaces_within_parens_and_brackets() && !s.is_empty() {
2398             format!("( {} )", s)
2399         } else {
2400             format!("({})", s)
2401         }
2402     };
2403
2404     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
2405     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2406
2407     if subexpr_str.contains('\n')
2408         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2409     {
2410         Some(paren_wrapper(&subexpr_str))
2411     } else {
2412         None
2413     }
2414 }
2415
2416 fn rewrite_index(
2417     expr: &ast::Expr,
2418     index: &ast::Expr,
2419     context: &RewriteContext,
2420     shape: Shape,
2421 ) -> Option<String> {
2422     let expr_str = expr.rewrite(context, shape)?;
2423
2424     let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
2425         ("[ ", " ]")
2426     } else {
2427         ("[", "]")
2428     };
2429
2430     let offset = last_line_width(&expr_str) + lbr.len();
2431     let rhs_overhead = shape.rhs_overhead(context.config);
2432     let index_shape = if expr_str.contains('\n') {
2433         Shape::legacy(context.config.max_width(), shape.indent)
2434             .offset_left(offset)
2435             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2436     } else {
2437         shape.visual_indent(offset).sub_width(offset + rbr.len())
2438     };
2439     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2440
2441     // Return if index fits in a single line.
2442     match orig_index_rw {
2443         Some(ref index_str) if !index_str.contains('\n') => {
2444             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2445         }
2446         _ => (),
2447     }
2448
2449     // Try putting index on the next line and see if it fits in a single line.
2450     let indent = shape.indent.block_indent(context.config);
2451     let index_shape = Shape::indented(indent, context.config).offset_left(lbr.len())?;
2452     let index_shape = index_shape.sub_width(rbr.len() + rhs_overhead)?;
2453     let new_index_rw = index.rewrite(context, index_shape);
2454     match (orig_index_rw, new_index_rw) {
2455         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2456             "{}{}{}{}{}",
2457             expr_str,
2458             indent.to_string_with_newline(context.config),
2459             lbr,
2460             new_index_str,
2461             rbr
2462         )),
2463         (None, Some(ref new_index_str)) => Some(format!(
2464             "{}{}{}{}{}",
2465             expr_str,
2466             indent.to_string_with_newline(context.config),
2467             lbr,
2468             new_index_str,
2469             rbr
2470         )),
2471         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2472         _ => None,
2473     }
2474 }
2475
2476 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2477     if base.is_some() {
2478         return false;
2479     }
2480
2481     fields.iter().all(|field| !field.is_shorthand)
2482 }
2483
2484 fn rewrite_struct_lit<'a>(
2485     context: &RewriteContext,
2486     path: &ast::Path,
2487     fields: &'a [ast::Field],
2488     base: Option<&'a ast::Expr>,
2489     span: Span,
2490     shape: Shape,
2491 ) -> Option<String> {
2492     debug!("rewrite_struct_lit: shape {:?}", shape);
2493
2494     enum StructLitField<'a> {
2495         Regular(&'a ast::Field),
2496         Base(&'a ast::Expr),
2497     }
2498
2499     // 2 = " {".len()
2500     let path_shape = shape.sub_width(2)?;
2501     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
2502
2503     if fields.is_empty() && base.is_none() {
2504         return Some(format!("{} {{}}", path_str));
2505     }
2506
2507     // Foo { a: Foo } - indent is +3, width is -5.
2508     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
2509
2510     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2511     let body_lo = context.snippet_provider.span_after(span, "{");
2512     let fields_str = if struct_lit_can_be_aligned(fields, &base)
2513         && context.config.struct_field_align_threshold() > 0
2514     {
2515         rewrite_with_alignment(
2516             fields,
2517             context,
2518             shape,
2519             mk_sp(body_lo, span.hi()),
2520             one_line_width,
2521         )?
2522     } else {
2523         let field_iter = fields
2524             .into_iter()
2525             .map(StructLitField::Regular)
2526             .chain(base.into_iter().map(StructLitField::Base));
2527
2528         let span_lo = |item: &StructLitField| match *item {
2529             StructLitField::Regular(field) => field.span().lo(),
2530             StructLitField::Base(expr) => {
2531                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
2532                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
2533                 let pos = snippet.find_uncommented("..").unwrap();
2534                 last_field_hi + BytePos(pos as u32)
2535             }
2536         };
2537         let span_hi = |item: &StructLitField| match *item {
2538             StructLitField::Regular(field) => field.span().hi(),
2539             StructLitField::Base(expr) => expr.span.hi(),
2540         };
2541         let rewrite = |item: &StructLitField| match *item {
2542             StructLitField::Regular(field) => {
2543                 // The 1 taken from the v_budget is for the comma.
2544                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
2545             }
2546             StructLitField::Base(expr) => {
2547                 // 2 = ..
2548                 expr.rewrite(context, v_shape.offset_left(2)?)
2549                     .map(|s| format!("..{}", s))
2550             }
2551         };
2552
2553         let items = itemize_list(
2554             context.snippet_provider,
2555             field_iter,
2556             "}",
2557             ",",
2558             span_lo,
2559             span_hi,
2560             rewrite,
2561             body_lo,
2562             span.hi(),
2563             false,
2564         );
2565         let item_vec = items.collect::<Vec<_>>();
2566
2567         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2568         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2569         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2570
2571         write_list(&item_vec, &fmt)?
2572     };
2573
2574     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2575     Some(format!("{} {{{}}}", path_str, fields_str))
2576
2577     // FIXME if context.config.indent_style() == Visual, but we run out
2578     // of space, we should fall back to BlockIndent.
2579 }
2580
2581 pub fn wrap_struct_field(
2582     context: &RewriteContext,
2583     fields_str: &str,
2584     shape: Shape,
2585     nested_shape: Shape,
2586     one_line_width: usize,
2587 ) -> String {
2588     if context.config.indent_style() == IndentStyle::Block
2589         && (fields_str.contains('\n') || !context.config.struct_lit_single_line()
2590             || fields_str.len() > one_line_width)
2591     {
2592         format!(
2593             "{}{}{}",
2594             nested_shape.indent.to_string_with_newline(context.config),
2595             fields_str,
2596             shape.indent.to_string_with_newline(context.config)
2597         )
2598     } else {
2599         // One liner or visual indent.
2600         format!(" {} ", fields_str)
2601     }
2602 }
2603
2604 pub fn struct_lit_field_separator(config: &Config) -> &str {
2605     colon_spaces(config.space_before_colon(), config.space_after_colon())
2606 }
2607
2608 pub fn rewrite_field(
2609     context: &RewriteContext,
2610     field: &ast::Field,
2611     shape: Shape,
2612     prefix_max_width: usize,
2613 ) -> Option<String> {
2614     if contains_skip(&field.attrs) {
2615         return Some(context.snippet(field.span()).to_owned());
2616     }
2617     let mut attrs_str = field.attrs.rewrite(context, shape)?;
2618     if !attrs_str.is_empty() {
2619         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
2620     };
2621     let name = field.ident.node.to_string();
2622     if field.is_shorthand {
2623         Some(attrs_str + &name)
2624     } else {
2625         let mut separator = String::from(struct_lit_field_separator(context.config));
2626         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2627             separator.push(' ');
2628         }
2629         let overhead = name.len() + separator.len();
2630         let expr_shape = shape.offset_left(overhead)?;
2631         let expr = field.expr.rewrite(context, expr_shape);
2632
2633         match expr {
2634             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
2635                 Some(attrs_str + &name)
2636             }
2637             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2638             None => {
2639                 let expr_offset = shape.indent.block_indent(context.config);
2640                 let expr = field
2641                     .expr
2642                     .rewrite(context, Shape::indented(expr_offset, context.config));
2643                 expr.map(|s| {
2644                     format!(
2645                         "{}{}:\n{}{}",
2646                         attrs_str,
2647                         name,
2648                         expr_offset.to_string(context.config),
2649                         s
2650                     )
2651                 })
2652             }
2653         }
2654     }
2655 }
2656
2657 fn shape_from_indent_style(
2658     context: &RewriteContext,
2659     shape: Shape,
2660     overhead: usize,
2661     offset: usize,
2662 ) -> Option<Shape> {
2663     if context.use_block_indent() {
2664         // 1 = ","
2665         shape
2666             .block()
2667             .block_indent(context.config.tab_spaces())
2668             .with_max_width(context.config)
2669             .sub_width(1)
2670     } else {
2671         shape.visual_indent(offset).sub_width(overhead)
2672     }
2673 }
2674
2675 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2676     context: &RewriteContext,
2677     items: &[&T],
2678     span: Span,
2679     shape: Shape,
2680 ) -> Option<String>
2681 where
2682     T: Rewrite + Spanned + ToExpr + 'a,
2683 {
2684     let mut items = items.iter();
2685     // In case of length 1, need a trailing comma
2686     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2687     if items.len() == 1 {
2688         // 3 = "(" + ",)"
2689         let nested_shape = shape.sub_width(3)?.visual_indent(1);
2690         return items
2691             .next()
2692             .unwrap()
2693             .rewrite(context, nested_shape)
2694             .map(|s| {
2695                 if context.config.spaces_within_parens_and_brackets() {
2696                     format!("( {}, )", s)
2697                 } else {
2698                     format!("({},)", s)
2699                 }
2700             });
2701     }
2702
2703     let list_lo = context.snippet_provider.span_after(span, "(");
2704     let nested_shape = shape.sub_width(2)?.visual_indent(1);
2705     let items = itemize_list(
2706         context.snippet_provider,
2707         items,
2708         ")",
2709         ",",
2710         |item| item.span().lo(),
2711         |item| item.span().hi(),
2712         |item| item.rewrite(context, nested_shape),
2713         list_lo,
2714         span.hi() - BytePos(1),
2715         false,
2716     );
2717     let item_vec: Vec<_> = items.collect();
2718     let tactic = definitive_tactic(
2719         &item_vec,
2720         ListTactic::HorizontalVertical,
2721         Separator::Comma,
2722         nested_shape.width,
2723     );
2724     let fmt = ListFormatting {
2725         tactic,
2726         separator: ",",
2727         trailing_separator: SeparatorTactic::Never,
2728         separator_place: SeparatorPlace::Back,
2729         shape,
2730         ends_with_newline: false,
2731         preserve_newline: false,
2732         config: context.config,
2733     };
2734     let list_str = write_list(&item_vec, &fmt)?;
2735
2736     if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
2737         Some(format!("( {} )", list_str))
2738     } else {
2739         Some(format!("({})", list_str))
2740     }
2741 }
2742
2743 pub fn rewrite_tuple<'a, T>(
2744     context: &RewriteContext,
2745     items: &[&T],
2746     span: Span,
2747     shape: Shape,
2748 ) -> Option<String>
2749 where
2750     T: Rewrite + Spanned + ToExpr + 'a,
2751 {
2752     debug!("rewrite_tuple {:?}", shape);
2753     if context.use_block_indent() {
2754         // We use the same rule as function calls for rewriting tuples.
2755         let force_trailing_comma = if context.inside_macro {
2756             span_ends_with_comma(context, span)
2757         } else {
2758             items.len() == 1
2759         };
2760         rewrite_call_inner(
2761             context,
2762             &String::new(),
2763             items,
2764             span,
2765             shape,
2766             context.config.width_heuristics().fn_call_width,
2767             force_trailing_comma,
2768         )
2769     } else {
2770         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2771     }
2772 }
2773
2774 pub fn rewrite_unary_prefix<R: Rewrite>(
2775     context: &RewriteContext,
2776     prefix: &str,
2777     rewrite: &R,
2778     shape: Shape,
2779 ) -> Option<String> {
2780     rewrite
2781         .rewrite(context, shape.offset_left(prefix.len())?)
2782         .map(|r| format!("{}{}", prefix, r))
2783 }
2784
2785 // FIXME: this is probably not correct for multi-line Rewrites. we should
2786 // subtract suffix.len() from the last line budget, not the first!
2787 pub fn rewrite_unary_suffix<R: Rewrite>(
2788     context: &RewriteContext,
2789     suffix: &str,
2790     rewrite: &R,
2791     shape: Shape,
2792 ) -> Option<String> {
2793     rewrite
2794         .rewrite(context, shape.sub_width(suffix.len())?)
2795         .map(|mut r| {
2796             r.push_str(suffix);
2797             r
2798         })
2799 }
2800
2801 fn rewrite_unary_op(
2802     context: &RewriteContext,
2803     op: &ast::UnOp,
2804     expr: &ast::Expr,
2805     shape: Shape,
2806 ) -> Option<String> {
2807     // For some reason, an UnOp is not spanned like BinOp!
2808     let operator_str = match *op {
2809         ast::UnOp::Deref => "*",
2810         ast::UnOp::Not => "!",
2811         ast::UnOp::Neg => "-",
2812     };
2813     rewrite_unary_prefix(context, operator_str, expr, shape)
2814 }
2815
2816 fn rewrite_assignment(
2817     context: &RewriteContext,
2818     lhs: &ast::Expr,
2819     rhs: &ast::Expr,
2820     op: Option<&ast::BinOp>,
2821     shape: Shape,
2822 ) -> Option<String> {
2823     let operator_str = match op {
2824         Some(op) => context.snippet(op.span),
2825         None => "=",
2826     };
2827
2828     // 1 = space between lhs and operator.
2829     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2830     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2831
2832     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2833 }
2834
2835 // The left hand side must contain everything up to, and including, the
2836 // assignment operator.
2837 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2838     context: &RewriteContext,
2839     lhs: S,
2840     ex: &R,
2841     shape: Shape,
2842 ) -> Option<String> {
2843     let lhs = lhs.into();
2844     let last_line_width = last_line_width(&lhs)
2845         .checked_sub(if lhs.contains('\n') {
2846             shape.indent.width()
2847         } else {
2848             0
2849         })
2850         .unwrap_or(0);
2851     // 1 = space between operator and rhs.
2852     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2853         width: 0,
2854         offset: shape.offset + last_line_width + 1,
2855         ..shape
2856     });
2857     let rhs = choose_rhs(context, ex, orig_shape, ex.rewrite(context, orig_shape))?;
2858     Some(lhs + &rhs)
2859 }
2860
2861 pub fn choose_rhs<R: Rewrite>(
2862     context: &RewriteContext,
2863     expr: &R,
2864     shape: Shape,
2865     orig_rhs: Option<String>,
2866 ) -> Option<String> {
2867     match orig_rhs {
2868         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2869             Some(format!(" {}", new_str))
2870         }
2871         _ => {
2872             // Expression did not fit on the same line as the identifier.
2873             // Try splitting the line and see if that works better.
2874             let new_shape =
2875                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2876                     .sub_width(shape.rhs_overhead(context.config))?;
2877             let new_rhs = expr.rewrite(context, new_shape);
2878             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2879
2880             match (orig_rhs, new_rhs) {
2881                 (Some(ref orig_rhs), Some(ref new_rhs))
2882                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2883                         .is_none() =>
2884                 {
2885                     Some(format!(" {}", orig_rhs))
2886                 }
2887                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2888                     Some(format!("{}{}", new_indent_str, new_rhs))
2889                 }
2890                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2891                 (None, None) => None,
2892                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2893             }
2894         }
2895     }
2896 }
2897
2898 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2899     !next_line_rhs.contains('\n') || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2900 }
2901
2902 fn rewrite_expr_addrof(
2903     context: &RewriteContext,
2904     mutability: ast::Mutability,
2905     expr: &ast::Expr,
2906     shape: Shape,
2907 ) -> Option<String> {
2908     let operator_str = match mutability {
2909         ast::Mutability::Immutable => "&",
2910         ast::Mutability::Mutable => "&mut ",
2911     };
2912     rewrite_unary_prefix(context, operator_str, expr, shape)
2913 }
2914
2915 pub trait ToExpr {
2916     fn to_expr(&self) -> Option<&ast::Expr>;
2917     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2918 }
2919
2920 impl ToExpr for ast::Expr {
2921     fn to_expr(&self) -> Option<&ast::Expr> {
2922         Some(self)
2923     }
2924
2925     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2926         can_be_overflowed_expr(context, self, len)
2927     }
2928 }
2929
2930 impl ToExpr for ast::Ty {
2931     fn to_expr(&self) -> Option<&ast::Expr> {
2932         None
2933     }
2934
2935     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2936         can_be_overflowed_type(context, self, len)
2937     }
2938 }
2939
2940 impl<'a> ToExpr for TuplePatField<'a> {
2941     fn to_expr(&self) -> Option<&ast::Expr> {
2942         None
2943     }
2944
2945     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2946         can_be_overflowed_pat(context, self, len)
2947     }
2948 }
2949
2950 impl<'a> ToExpr for ast::StructField {
2951     fn to_expr(&self) -> Option<&ast::Expr> {
2952         None
2953     }
2954
2955     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2956         false
2957     }
2958 }
2959
2960 impl<'a> ToExpr for MacroArg {
2961     fn to_expr(&self) -> Option<&ast::Expr> {
2962         match *self {
2963             MacroArg::Expr(ref expr) => Some(expr),
2964             _ => None,
2965         }
2966     }
2967
2968     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2969         match *self {
2970             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2971             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2972             MacroArg::Pat(..) => false,
2973         }
2974     }
2975 }