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