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