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