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         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 903             let alt_block_sep =
 904                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 905             control_flow
 906                 .rewrite_cond(context, shape, &alt_block_sep)
 907                 .and_then(|rw| Some(rw.0))
 908         }),
 909     }
 910 }
 911
 912 // Abstraction over control flow expressions
 913 #[derive(Debug)]
 914 struct ControlFlow<'a> {
 915     cond: Option<&'a ast::Expr>,
 916     block: &'a ast::Block,
 917     else_block: Option<&'a ast::Expr>,
 918     label: Option<ast::SpannedIdent>,
 919     pat: Option<&'a ast::Pat>,
 920     keyword: &'a str,
 921     matcher: &'a str,
 922     connector: &'a str,
 923     allow_single_line: bool,
 924     // True if this is an `if` expression in an `else if` :-( hacky
 925     nested_if: bool,
 926     span: Span,
 927 }
 928
 929 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 930     match expr.node {
 931         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 932             cond,
 933             None,
 934             if_block,
 935             else_block.as_ref().map(|e| &**e),
 936             expr_type == ExprType::SubExpression,
 937             false,
 938             expr.span,
 939         )),
 940         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 941             Some(ControlFlow::new_if(
 942                 cond,
 943                 Some(pat),
 944                 if_block,
 945                 else_block.as_ref().map(|e| &**e),
 946                 expr_type == ExprType::SubExpression,
 947                 false,
 948                 expr.span,
 949             ))
 950         }
 951         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 952             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 953         }
 954         ast::ExprKind::Loop(ref block, label) => {
 955             Some(ControlFlow::new_loop(block, label, expr.span))
 956         }
 957         ast::ExprKind::While(ref cond, ref block, label) => {
 958             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
 959         }
 960         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 961             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
 962         ),
 963         _ => None,
 964     }
 965 }
 966
 967 impl<'a> ControlFlow<'a> {
 968     fn new_if(
 969         cond: &'a ast::Expr,
 970         pat: Option<&'a ast::Pat>,
 971         block: &'a ast::Block,
 972         else_block: Option<&'a ast::Expr>,
 973         allow_single_line: bool,
 974         nested_if: bool,
 975         span: Span,
 976     ) -> ControlFlow<'a> {
 977         ControlFlow {
 978             cond: Some(cond),
 979             block: block,
 980             else_block: else_block,
 981             label: None,
 982             pat: pat,
 983             keyword: "if",
 984             matcher: match pat {
 985                 Some(..) => "let",
 986                 None => "",
 987             },
 988             connector: " =",
 989             allow_single_line: allow_single_line,
 990             nested_if: nested_if,
 991             span: span,
 992         }
 993     }
 994
 995     fn new_loop(
 996         block: &'a ast::Block,
 997         label: Option<ast::SpannedIdent>,
 998         span: Span,
 999     ) -> ControlFlow<'a> {
1000         ControlFlow {
1001             cond: None,
1002             block: block,
1003             else_block: None,
1004             label: label,
1005             pat: None,
1006             keyword: "loop",
1007             matcher: "",
1008             connector: "",
1009             allow_single_line: false,
1010             nested_if: false,
1011             span: span,
1012         }
1013     }
1014
1015     fn new_while(
1016         pat: Option<&'a ast::Pat>,
1017         cond: &'a ast::Expr,
1018         block: &'a ast::Block,
1019         label: Option<ast::SpannedIdent>,
1020         span: Span,
1021     ) -> ControlFlow<'a> {
1022         ControlFlow {
1023             cond: Some(cond),
1024             block: block,
1025             else_block: None,
1026             label: label,
1027             pat: pat,
1028             keyword: "while",
1029             matcher: match pat {
1030                 Some(..) => "let",
1031                 None => "",
1032             },
1033             connector: " =",
1034             allow_single_line: false,
1035             nested_if: false,
1036             span: span,
1037         }
1038     }
1039
1040     fn new_for(
1041         pat: &'a ast::Pat,
1042         cond: &'a ast::Expr,
1043         block: &'a ast::Block,
1044         label: Option<ast::SpannedIdent>,
1045         span: Span,
1046     ) -> ControlFlow<'a> {
1047         ControlFlow {
1048             cond: Some(cond),
1049             block: block,
1050             else_block: None,
1051             label: label,
1052             pat: Some(pat),
1053             keyword: "for",
1054             matcher: "",
1055             connector: " in",
1056             allow_single_line: false,
1057             nested_if: false,
1058             span: span,
1059         }
1060     }
1061
1062     fn rewrite_single_line(
1063         &self,
1064         pat_expr_str: &str,
1065         context: &RewriteContext,
1066         width: usize,
1067     ) -> Option<String> {
1068         assert!(self.allow_single_line);
1069         let else_block = self.else_block?;
1070         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1071
1072         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1073             if !is_simple_block(self.block, context.codemap)
1074                 || !is_simple_block(else_node, context.codemap)
1075                 || pat_expr_str.contains('\n')
1076             {
1077                 return None;
1078             }
1079
1080             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
1081             let expr = &self.block.stmts[0];
1082             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
1083
1084             let new_width = new_width.checked_sub(if_str.len())?;
1085             let else_expr = &else_node.stmts[0];
1086             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
1087
1088             if if_str.contains('\n') || else_str.contains('\n') {
1089                 return None;
1090             }
1091
1092             let result = format!(
1093                 "{} {} {{ {} }} else {{ {} }}",
1094                 self.keyword,
1095                 pat_expr_str,
1096                 if_str,
1097                 else_str
1098             );
1099
1100             if result.len() <= width {
1101                 return Some(result);
1102             }
1103         }
1104
1105         None
1106     }
1107 }
1108
1109 impl<'a> ControlFlow<'a> {
1110     fn rewrite_cond(
1111         &self,
1112         context: &RewriteContext,
1113         shape: Shape,
1114         alt_block_sep: &str,
1115     ) -> Option<(String, usize)> {
1116         // Do not take the rhs overhead from the upper expressions into account
1117         // when rewriting pattern.
1118         let new_width = context
1119             .config
1120             .max_width()
1121             .checked_sub(shape.used_width())
1122             .unwrap_or(0);
1123         let fresh_shape = Shape {
1124             width: new_width,
1125             ..shape
1126         };
1127         let constr_shape = if self.nested_if {
1128             // We are part of an if-elseif-else chain. Our constraints are tightened.
1129             // 7 = "} else " .len()
1130             fresh_shape.offset_left(7)?
1131         } else {
1132             fresh_shape
1133         };
1134
1135         let label_string = rewrite_label(self.label);
1136         // 1 = space after keyword.
1137         let offset = self.keyword.len() + label_string.len() + 1;
1138
1139         let pat_expr_string = match self.cond {
1140             Some(cond) => {
1141                 let cond_shape = match context.config.control_style() {
1142                     Style::Legacy => constr_shape.shrink_left(offset)?,
1143                     Style::Rfc => constr_shape.offset_left(offset)?,
1144                 };
1145                 rewrite_pat_expr(
1146                     context,
1147                     self.pat,
1148                     cond,
1149                     self.matcher,
1150                     self.connector,
1151                     self.keyword,
1152                     cond_shape,
1153                 )?
1154             }
1155             None => String::new(),
1156         };
1157
1158         let brace_overhead =
1159             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1160                 // 2 = ` {`
1161                 2
1162             } else {
1163                 0
1164             };
1165         let one_line_budget = context
1166             .config
1167             .max_width()
1168             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1169             .unwrap_or(0);
1170         let force_newline_brace = context.config.control_style() == Style::Rfc
1171             && (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget)
1172             && !last_line_extendable(&pat_expr_string);
1173
1174         // Try to format if-else on single line.
1175         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1176             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1177
1178             if let Some(cond_str) = trial {
1179                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1180                     return Some((cond_str, 0));
1181                 }
1182             }
1183         }
1184
1185         let cond_span = if let Some(cond) = self.cond {
1186             cond.span
1187         } else {
1188             mk_sp(self.block.span.lo(), self.block.span.lo())
1189         };
1190
1191         // `for event in event`
1192         // Do not include label in the span.
1193         let lo = self.label.map_or(self.span.lo(), |label| label.span.hi());
1194         let between_kwd_cond = mk_sp(
1195             context
1196                 .codemap
1197                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1198             self.pat
1199                 .map_or(cond_span.lo(), |p| if self.matcher.is_empty() {
1200                     p.span.lo()
1201                 } else {
1202                     context.codemap.span_before(self.span, self.matcher.trim())
1203                 }),
1204         );
1205
1206         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1207
1208         let after_cond_comment =
1209             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1210
1211         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1212             ""
1213         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1214             || force_newline_brace
1215         {
1216             alt_block_sep
1217         } else {
1218             " "
1219         };
1220
1221         let used_width = if pat_expr_string.contains('\n') {
1222             last_line_width(&pat_expr_string)
1223         } else {
1224             // 2 = spaces after keyword and condition.
1225             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1226         };
1227
1228         Some((
1229             format!(
1230                 "{}{}{}{}{}",
1231                 label_string,
1232                 self.keyword,
1233                 between_kwd_cond_comment.as_ref().map_or(
1234                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1235                         ""
1236                     } else {
1237                         " "
1238                     },
1239                     |s| &**s,
1240                 ),
1241                 pat_expr_string,
1242                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1243             ),
1244             used_width,
1245         ))
1246     }
1247 }
1248
1249 impl<'a> Rewrite for ControlFlow<'a> {
1250     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1251         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1252
1253         let alt_block_sep =
1254             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1255         let (cond_str, used_width) = self.rewrite_cond(context, shape, &alt_block_sep)?;
1256         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1257         if used_width == 0 {
1258             return Some(cond_str);
1259         }
1260
1261         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1262         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1263         // we should avoid the single line case.
1264         let block_width = if self.else_block.is_some() || self.nested_if {
1265             min(1, block_width)
1266         } else {
1267             block_width
1268         };
1269         let block_shape = Shape {
1270             width: block_width,
1271             ..shape
1272         };
1273         let mut block_context = context.clone();
1274         block_context.is_if_else_block = self.else_block.is_some();
1275         let block_str = rewrite_block_with_visitor(&block_context, "", self.block, block_shape)?;
1276
1277         let mut result = format!("{}{}", cond_str, block_str);
1278
1279         if let Some(else_block) = self.else_block {
1280             let shape = Shape::indented(shape.indent, context.config);
1281             let mut last_in_chain = false;
1282             let rewrite = match else_block.node {
1283                 // If the else expression is another if-else expression, prevent it
1284                 // from being formatted on a single line.
1285                 // Note how we're passing the original shape, as the
1286                 // cost of "else" should not cascade.
1287                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1288                     ControlFlow::new_if(
1289                         cond,
1290                         Some(pat),
1291                         if_block,
1292                         next_else_block.as_ref().map(|e| &**e),
1293                         false,
1294                         true,
1295                         mk_sp(else_block.span.lo(), self.span.hi()),
1296                     ).rewrite(context, shape)
1297                 }
1298                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1299                     ControlFlow::new_if(
1300                         cond,
1301                         None,
1302                         if_block,
1303                         next_else_block.as_ref().map(|e| &**e),
1304                         false,
1305                         true,
1306                         mk_sp(else_block.span.lo(), self.span.hi()),
1307                     ).rewrite(context, shape)
1308                 }
1309                 _ => {
1310                     last_in_chain = true;
1311                     // When rewriting a block, the width is only used for single line
1312                     // blocks, passing 1 lets us avoid that.
1313                     let else_shape = Shape {
1314                         width: min(1, shape.width),
1315                         ..shape
1316                     };
1317                     format_expr(else_block, ExprType::Statement, context, else_shape)
1318                 }
1319             };
1320
1321             let between_kwd_else_block = mk_sp(
1322                 self.block.span.hi(),
1323                 context
1324                     .codemap
1325                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1326             );
1327             let between_kwd_else_block_comment =
1328                 extract_comment(between_kwd_else_block, context, shape);
1329
1330             let after_else = mk_sp(
1331                 context
1332                     .codemap
1333                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1334                 else_block.span.lo(),
1335             );
1336             let after_else_comment = extract_comment(after_else, context, shape);
1337
1338             let between_sep = match context.config.control_brace_style() {
1339                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1340                     &*alt_block_sep
1341                 }
1342                 ControlBraceStyle::AlwaysSameLine => " ",
1343             };
1344             let after_sep = match context.config.control_brace_style() {
1345                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1346                 _ => " ",
1347             };
1348
1349             result.push_str(&format!(
1350                 "{}else{}",
1351                 between_kwd_else_block_comment
1352                     .as_ref()
1353                     .map_or(between_sep, |s| &**s),
1354                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1355             ));
1356             result.push_str(&rewrite?);
1357         }
1358
1359         Some(result)
1360     }
1361 }
1362
1363 fn rewrite_label(label: Option<ast::SpannedIdent>) -> Cow<'static, str> {
1364     match label {
1365         Some(ident) => Cow::from(format!("{}: ", ident.node)),
1366         None => Cow::from(""),
1367     }
1368 }
1369
1370 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1371     match rewrite_missing_comment(span, shape, context) {
1372         Some(ref comment) if !comment.is_empty() => Some(format!(
1373             "\n{indent}{}\n{indent}",
1374             comment,
1375             indent = shape.indent.to_string(context.config)
1376         )),
1377         _ => None,
1378     }
1379 }
1380
1381 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1382     let snippet = codemap.span_to_snippet(block.span).unwrap();
1383     contains_comment(&snippet)
1384 }
1385
1386 // Checks that a block contains no statements, an expression and no comments.
1387 // FIXME: incorrectly returns false when comment is contained completely within
1388 // the expression.
1389 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1390     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0])
1391         && !block_contains_comment(block, codemap))
1392 }
1393
1394 /// Checks whether a block contains at most one statement or expression, and no comments.
1395 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1396     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1397 }
1398
1399 /// Checks whether a block contains no statements, expressions, or comments.
1400 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1401     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1402 }
1403
1404 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1405     match stmt.node {
1406         ast::StmtKind::Expr(..) => true,
1407         _ => false,
1408     }
1409 }
1410
1411 fn is_unsafe_block(block: &ast::Block) -> bool {
1412     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1413         true
1414     } else {
1415         false
1416     }
1417 }
1418
1419 // A simple wrapper type against ast::Arm. Used inside write_list().
1420 struct ArmWrapper<'a> {
1421     pub arm: &'a ast::Arm,
1422     // True if the arm is the last one in match expression. Used to decide on whether we should add
1423     // trailing comma to the match arm when `config.trailing_comma() == Never`.
1424     pub is_last: bool,
1425 }
1426
1427 impl<'a> ArmWrapper<'a> {
1428     pub fn new(arm: &'a ast::Arm, is_last: bool) -> ArmWrapper<'a> {
1429         ArmWrapper { arm, is_last }
1430     }
1431 }
1432
1433 impl<'a> Rewrite for ArmWrapper<'a> {
1434     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1435         rewrite_match_arm(context, self.arm, shape, self.is_last)
1436     }
1437 }
1438
1439 fn rewrite_match(
1440     context: &RewriteContext,
1441     cond: &ast::Expr,
1442     arms: &[ast::Arm],
1443     shape: Shape,
1444     span: Span,
1445     attrs: &[ast::Attribute],
1446 ) -> Option<String> {
1447     if arms.is_empty() {
1448         return None;
1449     }
1450
1451     // Do not take the rhs overhead from the upper expressions into account
1452     // when rewriting match condition.
1453     let new_width = context.config.max_width().checked_sub(shape.used_width())?;
1454     let cond_shape = Shape {
1455         width: new_width,
1456         ..shape
1457     };
1458     // 6 = `match `
1459     let cond_shape = match context.config.control_style() {
1460         Style::Legacy => cond_shape.shrink_left(6)?,
1461         Style::Rfc => cond_shape.offset_left(6)?,
1462     };
1463     let cond_str = cond.rewrite(context, cond_shape)?;
1464     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1465     let block_sep = match context.config.control_brace_style() {
1466         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1467         _ if last_line_extendable(&cond_str) => " ",
1468         // 2 = ` {`
1469         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => &alt_block_sep,
1470         _ => " ",
1471     };
1472
1473     let nested_indent_str = shape
1474         .indent
1475         .block_indent(context.config)
1476         .to_string(context.config);
1477     // Inner attributes.
1478     let inner_attrs = &inner_attributes(attrs);
1479     let inner_attrs_str = if inner_attrs.is_empty() {
1480         String::new()
1481     } else {
1482         inner_attrs
1483             .rewrite(context, shape)
1484             .map(|s| format!("{}{}\n", nested_indent_str, s))?
1485     };
1486
1487     let open_brace_pos = if inner_attrs.is_empty() {
1488         context
1489             .codemap
1490             .span_after(mk_sp(cond.span.hi(), arms[0].span().lo()), "{")
1491     } else {
1492         inner_attrs[inner_attrs.len() - 1].span().hi()
1493     };
1494
1495     let arm_indent_str = if context.config.indent_match_arms() {
1496         nested_indent_str
1497     } else {
1498         shape.indent.to_string(context.config)
1499     };
1500
1501     Some(format!(
1502         "match {}{}{{\n{}{}{}\n{}}}",
1503         cond_str,
1504         block_sep,
1505         inner_attrs_str,
1506         arm_indent_str,
1507         rewrite_match_arms(context, arms, shape, span, open_brace_pos,)?,
1508         shape.indent.to_string(context.config),
1509     ))
1510 }
1511
1512 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
1513     if is_last && config.trailing_comma() == SeparatorTactic::Never {
1514         ""
1515     } else if config.match_block_trailing_comma() {
1516         ","
1517     } else if let ast::ExprKind::Block(ref block) = body.node {
1518         if let ast::BlockCheckMode::Default = block.rules {
1519             ""
1520         } else {
1521             ","
1522         }
1523     } else {
1524         ","
1525     }
1526 }
1527
1528 fn rewrite_match_arms(
1529     context: &RewriteContext,
1530     arms: &[ast::Arm],
1531     shape: Shape,
1532     span: Span,
1533     open_brace_pos: BytePos,
1534 ) -> Option<String> {
1535     let arm_shape = if context.config.indent_match_arms() {
1536         shape.block_indent(context.config.tab_spaces())
1537     } else {
1538         shape.block_indent(0)
1539     }.with_max_width(context.config);
1540
1541     let arm_len = arms.len();
1542     let is_last_iter = repeat(false)
1543         .take(arm_len.checked_sub(1).unwrap_or(0))
1544         .chain(repeat(true));
1545     let items = itemize_list(
1546         context.codemap,
1547         arms.iter()
1548             .zip(is_last_iter)
1549             .map(|(arm, is_last)| ArmWrapper::new(arm, is_last)),
1550         "}",
1551         |arm| arm.arm.span().lo(),
1552         |arm| arm.arm.span().hi(),
1553         |arm| arm.rewrite(context, arm_shape),
1554         open_brace_pos,
1555         span.hi(),
1556         false,
1557     );
1558     let arms_vec: Vec<_> = items.collect();
1559     let fmt = ListFormatting {
1560         tactic: DefinitiveListTactic::Vertical,
1561         // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
1562         separator: "",
1563         trailing_separator: SeparatorTactic::Never,
1564         separator_place: SeparatorPlace::Back,
1565         shape: arm_shape,
1566         ends_with_newline: true,
1567         preserve_newline: true,
1568         config: context.config,
1569     };
1570
1571     write_list(&arms_vec, &fmt)
1572 }
1573
1574 fn rewrite_match_arm(
1575     context: &RewriteContext,
1576     arm: &ast::Arm,
1577     shape: Shape,
1578     is_last: bool,
1579 ) -> Option<String> {
1580     let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
1581         if contains_skip(&arm.attrs) {
1582             let (_, body) = flatten_arm_body(context, &arm.body);
1583             // `arm.span()` does not include trailing comma, add it manually.
1584             return Some(format!(
1585                 "{}{}",
1586                 context.snippet(arm.span()),
1587                 arm_comma(context.config, body, is_last),
1588             ));
1589         }
1590         (
1591             mk_sp(
1592                 arm.attrs[arm.attrs.len() - 1].span.hi(),
1593                 arm.pats[0].span.lo(),
1594             ),
1595             arm.attrs.rewrite(context, shape)?,
1596         )
1597     } else {
1598         (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
1599     };
1600     let pats_str =
1601         rewrite_match_pattern(context, &arm.pats, &arm.guard, shape).and_then(|pats_str| {
1602             combine_strs_with_missing_comments(
1603                 context,
1604                 &attrs_str,
1605                 &pats_str,
1606                 missing_span,
1607                 shape,
1608                 false,
1609             )
1610         })?;
1611     rewrite_match_body(
1612         context,
1613         &arm.body,
1614         &pats_str,
1615         shape,
1616         arm.guard.is_some(),
1617         is_last,
1618     )
1619 }
1620
1621 fn rewrite_match_pattern(
1622     context: &RewriteContext,
1623     pats: &[ptr::P<ast::Pat>],
1624     guard: &Option<ptr::P<ast::Expr>>,
1625     shape: Shape,
1626 ) -> Option<String> {
1627     // Patterns
1628     // 5 = ` => {`
1629     let pat_shape = shape.sub_width(5)?;
1630
1631     let pat_strs = pats.iter()
1632         .map(|p| p.rewrite(context, pat_shape))
1633         .collect::<Option<Vec<_>>>()?;
1634
1635     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1636     let tactic = definitive_tactic(
1637         &items,
1638         ListTactic::HorizontalVertical,
1639         Separator::VerticalBar,
1640         pat_shape.width,
1641     );
1642     let fmt = ListFormatting {
1643         tactic: tactic,
1644         separator: " |",
1645         trailing_separator: SeparatorTactic::Never,
1646         separator_place: context.config.match_pattern_separator_break_point(),
1647         shape: pat_shape,
1648         ends_with_newline: false,
1649         preserve_newline: false,
1650         config: context.config,
1651     };
1652     let pats_str = write_list(&items, &fmt)?;
1653
1654     // Guard
1655     let guard_str = rewrite_guard(context, guard, shape, trimmed_last_line_width(&pats_str))?;
1656
1657     Some(format!("{}{}", pats_str, guard_str))
1658 }
1659
1660 // (extend, body)
1661 // @extend: true if the arm body can be put next to `=>`
1662 // @body: flattened body, if the body is block with a single expression
1663 fn flatten_arm_body<'a>(context: &'a RewriteContext, body: &'a ast::Expr) -> (bool, &'a ast::Expr) {
1664     match body.node {
1665         ast::ExprKind::Block(ref block)
1666             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1667         {
1668             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1669                 (
1670                     !context.config.multiline_match_arm_forces_block()
1671                         && expr.can_be_overflowed(context, 1),
1672                     &**expr,
1673                 )
1674             } else {
1675                 (false, &*body)
1676             }
1677         }
1678         _ => (
1679             !context.config.multiline_match_arm_forces_block()
1680                 && body.can_be_overflowed(context, 1),
1681             &*body,
1682         ),
1683     }
1684 }
1685
1686 fn rewrite_match_body(
1687     context: &RewriteContext,
1688     body: &ptr::P<ast::Expr>,
1689     pats_str: &str,
1690     shape: Shape,
1691     has_guard: bool,
1692     is_last: bool,
1693 ) -> Option<String> {
1694     let (extend, body) = flatten_arm_body(context, body);
1695     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1696         (true, is_empty_block(block, context.codemap))
1697     } else {
1698         (false, false)
1699     };
1700     let extend = if context.config.match_arm_forces_newline() {
1701         is_block
1702     } else {
1703         extend
1704     };
1705
1706     let comma = arm_comma(context.config, body, is_last);
1707     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1708     let alt_block_sep = alt_block_sep.as_str();
1709
1710     let combine_orig_body = |body_str: &str| {
1711         let block_sep = match context.config.control_brace_style() {
1712             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1713             _ => " ",
1714         };
1715
1716         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1717     };
1718
1719     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1720     let next_line_indent = if is_block {
1721         if is_empty_block {
1722             shape.indent.block_indent(context.config)
1723         } else {
1724             shape.indent
1725         }
1726     } else {
1727         shape.indent.block_indent(context.config)
1728     };
1729     let combine_next_line_body = |body_str: &str| {
1730         if is_block {
1731             return Some(format!(
1732                 "{} =>\n{}{}",
1733                 pats_str,
1734                 next_line_indent.to_string(context.config),
1735                 body_str
1736             ));
1737         }
1738
1739         let indent_str = shape.indent.to_string(context.config);
1740         let nested_indent_str = next_line_indent.to_string(context.config);
1741         let (body_prefix, body_suffix) = if context.config.wrap_match_arms() {
1742             let comma = if context.config.match_block_trailing_comma() {
1743                 ","
1744             } else {
1745                 ""
1746             };
1747             ("{", format!("\n{}}}{}", indent_str, comma))
1748         } else {
1749             ("", String::from(","))
1750         };
1751
1752         let block_sep = match context.config.control_brace_style() {
1753             ControlBraceStyle::AlwaysNextLine => format!("{}{}\n", alt_block_sep, body_prefix),
1754             _ if body_prefix.is_empty() => "\n".to_owned(),
1755             _ if forbid_same_line => format!("{}{}\n", alt_block_sep, body_prefix),
1756             _ => format!(" {}\n", body_prefix),
1757         } + &nested_indent_str;
1758
1759         Some(format!(
1760             "{} =>{}{}{}",
1761             pats_str,
1762             block_sep,
1763             body_str,
1764             body_suffix
1765         ))
1766     };
1767
1768     // Let's try and get the arm body on the same line as the condition.
1769     // 4 = ` => `.len()
1770     let orig_body_shape = shape
1771         .offset_left(extra_offset(pats_str, shape) + 4)
1772         .and_then(|shape| shape.sub_width(comma.len()));
1773     let orig_body = if let Some(body_shape) = orig_body_shape {
1774         let rewrite = nop_block_collapse(
1775             format_expr(body, ExprType::Statement, context, body_shape),
1776             body_shape.width,
1777         );
1778
1779         match rewrite {
1780             Some(ref body_str)
1781                 if !forbid_same_line && !context.config.match_arm_forces_newline()
1782                     && (is_block
1783                         || (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1784             {
1785                 return combine_orig_body(body_str);
1786             }
1787             _ => rewrite,
1788         }
1789     } else {
1790         None
1791     };
1792     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1793
1794     // Try putting body on the next line and see if it looks better.
1795     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1796     let next_line_body = nop_block_collapse(
1797         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1798         next_line_body_shape.width,
1799     );
1800     match (orig_body, next_line_body) {
1801         (Some(ref orig_str), Some(ref next_line_str))
1802             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1803         {
1804             combine_next_line_body(next_line_str)
1805         }
1806         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1807             combine_orig_body(orig_str)
1808         }
1809         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1810             combine_next_line_body(next_line_str)
1811         }
1812         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1813         (None, None) => None,
1814         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1815     }
1816 }
1817
1818 // The `if ...` guard on a match arm.
1819 fn rewrite_guard(
1820     context: &RewriteContext,
1821     guard: &Option<ptr::P<ast::Expr>>,
1822     shape: Shape,
1823     // The amount of space used up on this line for the pattern in
1824     // the arm (excludes offset).
1825     pattern_width: usize,
1826 ) -> Option<String> {
1827     if let Some(ref guard) = *guard {
1828         // First try to fit the guard string on the same line as the pattern.
1829         // 4 = ` if `, 5 = ` => {`
1830         let cond_shape = shape
1831             .offset_left(pattern_width + 4)
1832             .and_then(|s| s.sub_width(5));
1833         if let Some(cond_shape) = cond_shape {
1834             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1835                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1836                     return Some(format!(" if {}", cond_str));
1837                 }
1838             }
1839         }
1840
1841         // Not enough space to put the guard after the pattern, try a newline.
1842         // 3 = `if `, 5 = ` => {`
1843         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1844             .offset_left(3)
1845             .and_then(|s| s.sub_width(5));
1846         if let Some(cond_shape) = cond_shape {
1847             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1848                 return Some(format!(
1849                     "\n{}if {}",
1850                     cond_shape.indent.to_string(context.config),
1851                     cond_str
1852                 ));
1853             }
1854         }
1855
1856         None
1857     } else {
1858         Some(String::new())
1859     }
1860 }
1861
1862 fn rewrite_pat_expr(
1863     context: &RewriteContext,
1864     pat: Option<&ast::Pat>,
1865     expr: &ast::Expr,
1866     matcher: &str,
1867     // Connecting piece between pattern and expression,
1868     // *without* trailing space.
1869     connector: &str,
1870     keyword: &str,
1871     shape: Shape,
1872 ) -> Option<String> {
1873     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1874     if let Some(pat) = pat {
1875         let matcher = if matcher.is_empty() {
1876             matcher.to_owned()
1877         } else {
1878             format!("{} ", matcher)
1879         };
1880         let pat_shape = shape
1881             .offset_left(matcher.len())?
1882             .sub_width(connector.len())?;
1883         let pat_string = pat.rewrite(context, pat_shape)?;
1884         let result = format!("{}{}{}", matcher, pat_string, connector);
1885         return rewrite_assign_rhs(context, result, expr, shape);
1886     }
1887
1888     let expr_rw = expr.rewrite(context, shape);
1889     // The expression may (partially) fit on the current line.
1890     // We do not allow splitting between `if` and condition.
1891     if keyword == "if" || expr_rw.is_some() {
1892         return expr_rw;
1893     }
1894
1895     // The expression won't fit on the current line, jump to next.
1896     let nested_shape = shape
1897         .block_indent(context.config.tab_spaces())
1898         .with_max_width(context.config);
1899     let nested_indent_str = nested_shape.indent.to_string(context.config);
1900     expr.rewrite(context, nested_shape)
1901         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1902 }
1903
1904 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1905     match l.node {
1906         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1907         _ => Some(context.snippet(l.span)),
1908     }
1909 }
1910
1911 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1912     let string_lit = context.snippet(span);
1913
1914     if !context.config.format_strings() && !context.config.force_format_strings() {
1915         if string_lit
1916             .lines()
1917             .rev()
1918             .skip(1)
1919             .all(|line| line.ends_with('\\'))
1920         {
1921             let new_indent = shape.visual_indent(1).indent;
1922             return Some(String::from(
1923                 string_lit
1924                     .lines()
1925                     .map(|line| {
1926                         format!(
1927                             "{}{}",
1928                             new_indent.to_string(context.config),
1929                             line.trim_left()
1930                         )
1931                     })
1932                     .collect::<Vec<_>>()
1933                     .join("\n")
1934                     .trim_left(),
1935             ));
1936         } else {
1937             return Some(string_lit);
1938         }
1939     }
1940
1941     if !context.config.force_format_strings()
1942         && !string_requires_rewrite(context, span, &string_lit, shape)
1943     {
1944         return Some(string_lit);
1945     }
1946
1947     // Remove the quote characters.
1948     let str_lit = &string_lit[1..string_lit.len() - 1];
1949
1950     rewrite_string(str_lit, &StringFormat::new(shape, context.config))
1951 }
1952
1953 fn string_requires_rewrite(
1954     context: &RewriteContext,
1955     span: Span,
1956     string: &str,
1957     shape: Shape,
1958 ) -> bool {
1959     if context.codemap.lookup_char_pos(span.lo()).col.0 != shape.indent.width() {
1960         return true;
1961     }
1962
1963     for (i, line) in string.lines().enumerate() {
1964         if i == 0 {
1965             if line.len() > shape.width {
1966                 return true;
1967             }
1968         } else if line.len() > shape.width + shape.indent.width() {
1969             return true;
1970         }
1971     }
1972
1973     false
1974 }
1975
1976 pub fn rewrite_call(
1977     context: &RewriteContext,
1978     callee: &str,
1979     args: &[ptr::P<ast::Expr>],
1980     span: Span,
1981     shape: Shape,
1982 ) -> Option<String> {
1983     let force_trailing_comma = if context.inside_macro {
1984         span_ends_with_comma(context, span)
1985     } else {
1986         false
1987     };
1988     rewrite_call_inner(
1989         context,
1990         callee,
1991         &ptr_vec_to_ref_vec(&args),
1992         span,
1993         shape,
1994         context.config.fn_call_width(),
1995         force_trailing_comma,
1996     )
1997 }
1998
1999 pub fn rewrite_call_inner<'a, T>(
2000     context: &RewriteContext,
2001     callee_str: &str,
2002     args: &[&T],
2003     span: Span,
2004     shape: Shape,
2005     args_max_width: usize,
2006     force_trailing_comma: bool,
2007 ) -> Option<String>
2008 where
2009     T: Rewrite + Spanned + ToExpr + 'a,
2010 {
2011     // 2 = `( `, 1 = `(`
2012     let paren_overhead = if context.config.spaces_within_parens() {
2013         2
2014     } else {
2015         1
2016     };
2017     let used_width = extra_offset(callee_str, shape);
2018     let one_line_width = shape.width.checked_sub(used_width + 2 * paren_overhead)?;
2019
2020     let nested_shape = shape_from_fn_call_style(
2021         context,
2022         shape,
2023         used_width + 2 * paren_overhead,
2024         used_width + paren_overhead,
2025     )?;
2026
2027     let span_lo = context.codemap.span_after(span, "(");
2028     let args_span = mk_sp(span_lo, span.hi());
2029
2030     let (extendable, list_str) = rewrite_call_args(
2031         context,
2032         args,
2033         args_span,
2034         nested_shape,
2035         one_line_width,
2036         args_max_width,
2037         force_trailing_comma,
2038     )?;
2039
2040     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2041         let mut new_context = context.clone();
2042         new_context.use_block = true;
2043         return rewrite_call_inner(
2044             &new_context,
2045             callee_str,
2046             args,
2047             span,
2048             shape,
2049             args_max_width,
2050             force_trailing_comma,
2051         );
2052     }
2053
2054     let args_shape = shape.sub_width(last_line_width(callee_str))?;
2055     Some(format!(
2056         "{}{}",
2057         callee_str,
2058         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2059     ))
2060 }
2061
2062 fn need_block_indent(s: &str, shape: Shape) -> bool {
2063     s.lines().skip(1).any(|s| {
2064         s.find(|c| !char::is_whitespace(c))
2065             .map_or(false, |w| w + 1 < shape.indent.width())
2066     })
2067 }
2068
2069 fn rewrite_call_args<'a, T>(
2070     context: &RewriteContext,
2071     args: &[&T],
2072     span: Span,
2073     shape: Shape,
2074     one_line_width: usize,
2075     args_max_width: usize,
2076     force_trailing_comma: bool,
2077 ) -> Option<(bool, String)>
2078 where
2079     T: Rewrite + Spanned + ToExpr + 'a,
2080 {
2081     let items = itemize_list(
2082         context.codemap,
2083         args.iter(),
2084         ")",
2085         |item| item.span().lo(),
2086         |item| item.span().hi(),
2087         |item| item.rewrite(context, shape),
2088         span.lo(),
2089         span.hi(),
2090         true,
2091     );
2092     let mut item_vec: Vec<_> = items.collect();
2093
2094     // Try letting the last argument overflow to the next line with block
2095     // indentation. If its first line fits on one line with the other arguments,
2096     // we format the function arguments horizontally.
2097     let tactic = try_overflow_last_arg(
2098         context,
2099         &mut item_vec,
2100         &args[..],
2101         shape,
2102         one_line_width,
2103         args_max_width,
2104     );
2105
2106     let fmt = ListFormatting {
2107         tactic: tactic,
2108         separator: ",",
2109         trailing_separator: if force_trailing_comma {
2110             SeparatorTactic::Always
2111         } else if context.inside_macro || !context.use_block_indent() {
2112             SeparatorTactic::Never
2113         } else {
2114             context.config.trailing_comma()
2115         },
2116         separator_place: SeparatorPlace::Back,
2117         shape: shape,
2118         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2119         preserve_newline: false,
2120         config: context.config,
2121     };
2122
2123     write_list(&item_vec, &fmt).map(|args_str| {
2124         (tactic != DefinitiveListTactic::Vertical, args_str)
2125     })
2126 }
2127
2128 fn try_overflow_last_arg<'a, T>(
2129     context: &RewriteContext,
2130     item_vec: &mut Vec<ListItem>,
2131     args: &[&T],
2132     shape: Shape,
2133     one_line_width: usize,
2134     args_max_width: usize,
2135 ) -> DefinitiveListTactic
2136 where
2137     T: Rewrite + Spanned + ToExpr + 'a,
2138 {
2139     let overflow_last = can_be_overflowed(context, args);
2140
2141     // Replace the last item with its first line to see if it fits with
2142     // first arguments.
2143     let placeholder = if overflow_last {
2144         let mut context = context.clone();
2145         if let Some(expr) = args[args.len() - 1].to_expr() {
2146             if let ast::ExprKind::MethodCall(..) = expr.node {
2147                 context.force_one_line_chain = true;
2148             }
2149         }
2150         last_arg_shape(&context, item_vec, shape, args_max_width).and_then(|arg_shape| {
2151             rewrite_last_arg_with_overflow(&context, args, &mut item_vec[args.len() - 1], arg_shape)
2152         })
2153     } else {
2154         None
2155     };
2156
2157     let mut tactic = definitive_tactic(
2158         &*item_vec,
2159         ListTactic::LimitedHorizontalVertical(args_max_width),
2160         Separator::Comma,
2161         one_line_width,
2162     );
2163
2164     // Replace the stub with the full overflowing last argument if the rewrite
2165     // succeeded and its first line fits with the other arguments.
2166     match (overflow_last, tactic, placeholder) {
2167         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2168             item_vec[args.len() - 1].item = placeholder;
2169         }
2170         _ if args.len() >= 1 => {
2171             item_vec[args.len() - 1].item = args.last()
2172                 .and_then(|last_arg| last_arg.rewrite(context, shape));
2173             // Use horizontal layout for a function with a single argument as long as
2174             // everything fits in a single line.
2175             if args.len() == 1
2176                 && args_max_width != 0 // Vertical layout is forced.
2177                 && !item_vec[0].has_comment()
2178                 && !item_vec[0].inner_as_ref().contains('\n')
2179                 && ::lists::total_item_width(&item_vec[0]) <= one_line_width
2180             {
2181                 tactic = DefinitiveListTactic::Horizontal;
2182             } else {
2183                 tactic = definitive_tactic(
2184                     &*item_vec,
2185                     ListTactic::LimitedHorizontalVertical(args_max_width),
2186                     Separator::Comma,
2187                     one_line_width,
2188                 );
2189             }
2190         }
2191         _ => (),
2192     }
2193
2194     tactic
2195 }
2196
2197 fn last_arg_shape(
2198     context: &RewriteContext,
2199     items: &[ListItem],
2200     shape: Shape,
2201     args_max_width: usize,
2202 ) -> Option<Shape> {
2203     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2204         acc + i.item.as_ref().map_or(0, |s| first_line_width(s))
2205     });
2206     let max_width = min(args_max_width, shape.width);
2207     let arg_indent = if context.use_block_indent() {
2208         shape.block().indent.block_unindent(context.config)
2209     } else {
2210         shape.block().indent
2211     };
2212     Some(Shape {
2213         width: max_width.checked_sub(overhead)?,
2214         indent: arg_indent,
2215         offset: 0,
2216     })
2217 }
2218
2219 // Rewriting closure which is placed at the end of the function call's arg.
2220 // Returns `None` if the reformatted closure 'looks bad'.
2221 fn rewrite_last_closure(
2222     context: &RewriteContext,
2223     expr: &ast::Expr,
2224     shape: Shape,
2225 ) -> Option<String> {
2226     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2227         let body = match body.node {
2228             ast::ExprKind::Block(ref block) if is_simple_block(block, context.codemap) => {
2229                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2230             }
2231             _ => body,
2232         };
2233         let (prefix, extra_offset) =
2234             rewrite_closure_fn_decl(capture, fn_decl, body, expr.span, context, shape)?;
2235         // If the closure goes multi line before its body, do not overflow the closure.
2236         if prefix.contains('\n') {
2237             return None;
2238         }
2239         let body_shape = shape.offset_left(extra_offset)?;
2240         // When overflowing the closure which consists of a single control flow expression,
2241         // force to use block if its condition uses multi line.
2242         let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
2243             .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
2244             .unwrap_or(false);
2245         if is_multi_lined_cond {
2246             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2247         }
2248
2249         // Seems fine, just format the closure in usual manner.
2250         return expr.rewrite(context, shape);
2251     }
2252     None
2253 }
2254
2255 fn rewrite_last_arg_with_overflow<'a, T>(
2256     context: &RewriteContext,
2257     args: &[&T],
2258     last_item: &mut ListItem,
2259     shape: Shape,
2260 ) -> Option<String>
2261 where
2262     T: Rewrite + Spanned + ToExpr + 'a,
2263 {
2264     let last_arg = args[args.len() - 1];
2265     let rewrite = if let Some(expr) = last_arg.to_expr() {
2266         match expr.node {
2267             // When overflowing the closure which consists of a single control flow expression,
2268             // force to use block if its condition uses multi line.
2269             ast::ExprKind::Closure(..) => {
2270                 // If the argument consists of multiple closures, we do not overflow
2271                 // the last closure.
2272                 if args.len() > 1
2273                     && args.iter()
2274                         .rev()
2275                         .skip(1)
2276                         .filter_map(|arg| arg.to_expr())
2277                         .any(|expr| match expr.node {
2278                             ast::ExprKind::Closure(..) => true,
2279                             _ => false,
2280                         }) {
2281                     None
2282                 } else {
2283                     rewrite_last_closure(context, expr, shape)
2284                 }
2285             }
2286             _ => expr.rewrite(context, shape),
2287         }
2288     } else {
2289         last_arg.rewrite(context, shape)
2290     };
2291
2292     if let Some(rewrite) = rewrite {
2293         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2294         last_item.item = rewrite_first_line;
2295         Some(rewrite)
2296     } else {
2297         None
2298     }
2299 }
2300
2301 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2302 where
2303     T: Rewrite + Spanned + ToExpr + 'a,
2304 {
2305     args.last()
2306         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2307 }
2308
2309 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2310     match expr.node {
2311         ast::ExprKind::Match(..) => {
2312             (context.use_block_indent() && args_len == 1)
2313                 || (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2314         }
2315         ast::ExprKind::If(..) |
2316         ast::ExprKind::IfLet(..) |
2317         ast::ExprKind::ForLoop(..) |
2318         ast::ExprKind::Loop(..) |
2319         ast::ExprKind::While(..) |
2320         ast::ExprKind::WhileLet(..) => {
2321             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2322         }
2323         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2324             context.use_block_indent()
2325                 || context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2326         }
2327         ast::ExprKind::Array(..) |
2328         ast::ExprKind::Call(..) |
2329         ast::ExprKind::Mac(..) |
2330         ast::ExprKind::MethodCall(..) |
2331         ast::ExprKind::Struct(..) |
2332         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2333         ast::ExprKind::AddrOf(_, ref expr) |
2334         ast::ExprKind::Box(ref expr) |
2335         ast::ExprKind::Try(ref expr) |
2336         ast::ExprKind::Unary(_, ref expr) |
2337         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2338         _ => false,
2339     }
2340 }
2341
2342 pub fn wrap_args_with_parens(
2343     context: &RewriteContext,
2344     args_str: &str,
2345     is_extendable: bool,
2346     shape: Shape,
2347     nested_shape: Shape,
2348 ) -> String {
2349     if !context.use_block_indent()
2350         || (context.inside_macro && !args_str.contains('\n')
2351             && args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2352     {
2353         if context.config.spaces_within_parens() && !args_str.is_empty() {
2354             format!("( {} )", args_str)
2355         } else {
2356             format!("({})", args_str)
2357         }
2358     } else {
2359         format!(
2360             "(\n{}{}\n{})",
2361             nested_shape.indent.to_string(context.config),
2362             args_str,
2363             shape.block().indent.to_string(context.config)
2364         )
2365     }
2366 }
2367
2368 /// Return true if a function call or a method call represented by the given span ends with a
2369 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
2370 /// comma from macro can potentially break the code.
2371 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2372     let mut encountered_closing_paren = false;
2373     for c in context.snippet(span).chars().rev() {
2374         match c {
2375             ',' => return true,
2376             ')' => if encountered_closing_paren {
2377                 return false;
2378             } else {
2379                 encountered_closing_paren = true;
2380             },
2381             _ if c.is_whitespace() => continue,
2382             _ => return false,
2383         }
2384     }
2385     false
2386 }
2387
2388 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2389     debug!("rewrite_paren, shape: {:?}", shape);
2390     let total_paren_overhead = paren_overhead(context);
2391     let paren_overhead = total_paren_overhead / 2;
2392     let sub_shape = shape
2393         .offset_left(paren_overhead)
2394         .and_then(|s| s.sub_width(paren_overhead))?;
2395
2396     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && !s.is_empty() {
2397         format!("( {} )", s)
2398     } else {
2399         format!("({})", s)
2400     };
2401
2402     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
2403     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2404
2405     if subexpr_str.contains('\n')
2406         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2407     {
2408         Some(paren_wrapper(&subexpr_str))
2409     } else {
2410         None
2411     }
2412 }
2413
2414 fn rewrite_index(
2415     expr: &ast::Expr,
2416     index: &ast::Expr,
2417     context: &RewriteContext,
2418     shape: Shape,
2419 ) -> Option<String> {
2420     let expr_str = expr.rewrite(context, shape)?;
2421
2422     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2423         ("[ ", " ]")
2424     } else {
2425         ("[", "]")
2426     };
2427
2428     let offset = last_line_width(&expr_str) + lbr.len();
2429     let rhs_overhead = shape.rhs_overhead(context.config);
2430     let index_shape = if expr_str.contains('\n') {
2431         Shape::legacy(context.config.max_width(), shape.indent)
2432             .offset_left(offset)
2433             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2434     } else {
2435         shape.visual_indent(offset).sub_width(offset + rbr.len())
2436     };
2437     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2438
2439     // Return if index fits in a single line.
2440     match orig_index_rw {
2441         Some(ref index_str) if !index_str.contains('\n') => {
2442             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2443         }
2444         _ => (),
2445     }
2446
2447     // Try putting index on the next line and see if it fits in a single line.
2448     let indent = shape.indent.block_indent(context.config);
2449     let index_shape = Shape::indented(indent, context.config).offset_left(lbr.len())?;
2450     let index_shape = index_shape.sub_width(rbr.len() + rhs_overhead)?;
2451     let new_index_rw = index.rewrite(context, index_shape);
2452     match (orig_index_rw, new_index_rw) {
2453         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2454             "{}\n{}{}{}{}",
2455             expr_str,
2456             indent.to_string(context.config),
2457             lbr,
2458             new_index_str,
2459             rbr
2460         )),
2461         (None, Some(ref new_index_str)) => Some(format!(
2462             "{}\n{}{}{}{}",
2463             expr_str,
2464             indent.to_string(context.config),
2465             lbr,
2466             new_index_str,
2467             rbr
2468         )),
2469         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2470         _ => None,
2471     }
2472 }
2473
2474 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2475     if base.is_some() {
2476         return false;
2477     }
2478
2479     fields.iter().all(|field| !field.is_shorthand)
2480 }
2481
2482 fn rewrite_struct_lit<'a>(
2483     context: &RewriteContext,
2484     path: &ast::Path,
2485     fields: &'a [ast::Field],
2486     base: Option<&'a ast::Expr>,
2487     span: Span,
2488     shape: Shape,
2489 ) -> Option<String> {
2490     debug!("rewrite_struct_lit: shape {:?}", shape);
2491
2492     enum StructLitField<'a> {
2493         Regular(&'a ast::Field),
2494         Base(&'a ast::Expr),
2495     }
2496
2497     // 2 = " {".len()
2498     let path_shape = shape.sub_width(2)?;
2499     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
2500
2501     if fields.is_empty() && base.is_none() {
2502         return Some(format!("{} {{}}", path_str));
2503     }
2504
2505     // Foo { a: Foo } - indent is +3, width is -5.
2506     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
2507
2508     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2509     let body_lo = context.codemap.span_after(span, "{");
2510     let fields_str = if struct_lit_can_be_aligned(fields, &base)
2511         && context.config.struct_field_align_threshold() > 0
2512     {
2513         rewrite_with_alignment(
2514             fields,
2515             context,
2516             shape,
2517             mk_sp(body_lo, span.hi()),
2518             one_line_width,
2519         )?
2520     } else {
2521         let field_iter = fields
2522             .into_iter()
2523             .map(StructLitField::Regular)
2524             .chain(base.into_iter().map(StructLitField::Base));
2525
2526         let span_lo = |item: &StructLitField| match *item {
2527             StructLitField::Regular(field) => field.span().lo(),
2528             StructLitField::Base(expr) => {
2529                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
2530                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
2531                 let pos = snippet.find_uncommented("..").unwrap();
2532                 last_field_hi + BytePos(pos as u32)
2533             }
2534         };
2535         let span_hi = |item: &StructLitField| match *item {
2536             StructLitField::Regular(field) => field.span().hi(),
2537             StructLitField::Base(expr) => expr.span.hi(),
2538         };
2539         let rewrite = |item: &StructLitField| match *item {
2540             StructLitField::Regular(field) => {
2541                 // The 1 taken from the v_budget is for the comma.
2542                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
2543             }
2544             StructLitField::Base(expr) => {
2545                 // 2 = ..
2546                 expr.rewrite(context, v_shape.offset_left(2)?)
2547                     .map(|s| format!("..{}", s))
2548             }
2549         };
2550
2551         let items = itemize_list(
2552             context.codemap,
2553             field_iter,
2554             "}",
2555             span_lo,
2556             span_hi,
2557             rewrite,
2558             body_lo,
2559             span.hi(),
2560             false,
2561         );
2562         let item_vec = items.collect::<Vec<_>>();
2563
2564         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2565         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2566         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2567
2568         write_list(&item_vec, &fmt)?
2569     };
2570
2571     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2572     Some(format!("{} {{{}}}", path_str, fields_str))
2573
2574     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2575     // of space, we should fall back to BlockIndent.
2576 }
2577
2578 pub fn wrap_struct_field(
2579     context: &RewriteContext,
2580     fields_str: &str,
2581     shape: Shape,
2582     nested_shape: Shape,
2583     one_line_width: usize,
2584 ) -> String {
2585     if context.config.struct_lit_style() == IndentStyle::Block
2586         && (fields_str.contains('\n')
2587             || context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti
2588             || fields_str.len() > one_line_width)
2589     {
2590         format!(
2591             "\n{}{}\n{}",
2592             nested_shape.indent.to_string(context.config),
2593             fields_str,
2594             shape.indent.to_string(context.config)
2595         )
2596     } else {
2597         // One liner or visual indent.
2598         format!(" {} ", fields_str)
2599     }
2600 }
2601
2602 pub fn struct_lit_field_separator(config: &Config) -> &str {
2603     colon_spaces(
2604         config.space_before_struct_lit_field_colon(),
2605         config.space_after_struct_lit_field_colon(),
2606     )
2607 }
2608
2609 pub fn rewrite_field(
2610     context: &RewriteContext,
2611     field: &ast::Field,
2612     shape: Shape,
2613     prefix_max_width: usize,
2614 ) -> Option<String> {
2615     if contains_skip(&field.attrs) {
2616         return Some(context.snippet(field.span()));
2617     }
2618     let name = &field.ident.node.to_string();
2619     if field.is_shorthand {
2620         Some(name.to_string())
2621     } else {
2622         let mut separator = String::from(struct_lit_field_separator(context.config));
2623         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2624             separator.push(' ');
2625         }
2626         let overhead = name.len() + separator.len();
2627         let expr_shape = shape.offset_left(overhead)?;
2628         let expr = field.expr.rewrite(context, expr_shape);
2629
2630         let mut attrs_str = field.attrs.rewrite(context, shape)?;
2631         if !attrs_str.is_empty() {
2632             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2633         };
2634
2635         match expr {
2636             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2637             None => {
2638                 let expr_offset = shape.indent.block_indent(context.config);
2639                 let expr = field
2640                     .expr
2641                     .rewrite(context, Shape::indented(expr_offset, context.config));
2642                 expr.map(|s| {
2643                     format!(
2644                         "{}{}:\n{}{}",
2645                         attrs_str,
2646                         name,
2647                         expr_offset.to_string(context.config),
2648                         s
2649                     )
2650                 })
2651             }
2652         }
2653     }
2654 }
2655
2656 fn shape_from_fn_call_style(
2657     context: &RewriteContext,
2658     shape: Shape,
2659     overhead: usize,
2660     offset: usize,
2661 ) -> Option<Shape> {
2662     if context.use_block_indent() {
2663         // 1 = ","
2664         shape
2665             .block()
2666             .block_indent(context.config.tab_spaces())
2667             .with_max_width(context.config)
2668             .sub_width(1)
2669     } else {
2670         shape.visual_indent(offset).sub_width(overhead)
2671     }
2672 }
2673
2674 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2675     context: &RewriteContext,
2676     items: &[&T],
2677     span: Span,
2678     shape: Shape,
2679 ) -> Option<String>
2680 where
2681     T: Rewrite + Spanned + ToExpr + 'a,
2682 {
2683     let mut items = items.iter();
2684     // In case of length 1, need a trailing comma
2685     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2686     if items.len() == 1 {
2687         // 3 = "(" + ",)"
2688         let nested_shape = shape.sub_width(3)?.visual_indent(1);
2689         return items.next().unwrap().rewrite(context, nested_shape).map(
2690             |s| if context.config.spaces_within_parens() {
2691                 format!("( {}, )", s)
2692             } else {
2693                 format!("({},)", s)
2694             },
2695         );
2696     }
2697
2698     let list_lo = context.codemap.span_after(span, "(");
2699     let nested_shape = shape.sub_width(2)?.visual_indent(1);
2700     let items = itemize_list(
2701         context.codemap,
2702         items,
2703         ")",
2704         |item| item.span().lo(),
2705         |item| item.span().hi(),
2706         |item| item.rewrite(context, nested_shape),
2707         list_lo,
2708         span.hi() - BytePos(1),
2709         false,
2710     );
2711     let item_vec: Vec<_> = items.collect();
2712     let tactic = definitive_tactic(
2713         &item_vec,
2714         ListTactic::HorizontalVertical,
2715         Separator::Comma,
2716         nested_shape.width,
2717     );
2718     let fmt = ListFormatting {
2719         tactic: tactic,
2720         separator: ",",
2721         trailing_separator: SeparatorTactic::Never,
2722         separator_place: SeparatorPlace::Back,
2723         shape: shape,
2724         ends_with_newline: false,
2725         preserve_newline: false,
2726         config: context.config,
2727     };
2728     let list_str = write_list(&item_vec, &fmt)?;
2729
2730     if context.config.spaces_within_parens() && !list_str.is_empty() {
2731         Some(format!("( {} )", list_str))
2732     } else {
2733         Some(format!("({})", list_str))
2734     }
2735 }
2736
2737 pub fn rewrite_tuple<'a, T>(
2738     context: &RewriteContext,
2739     items: &[&T],
2740     span: Span,
2741     shape: Shape,
2742 ) -> Option<String>
2743 where
2744     T: Rewrite + Spanned + ToExpr + 'a,
2745 {
2746     debug!("rewrite_tuple {:?}", shape);
2747     if context.use_block_indent() {
2748         // We use the same rule as function calls for rewriting tuples.
2749         let force_trailing_comma = if context.inside_macro {
2750             span_ends_with_comma(context, span)
2751         } else {
2752             items.len() == 1
2753         };
2754         rewrite_call_inner(
2755             context,
2756             &String::new(),
2757             items,
2758             span,
2759             shape,
2760             context.config.fn_call_width(),
2761             force_trailing_comma,
2762         )
2763     } else {
2764         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2765     }
2766 }
2767
2768 pub fn rewrite_unary_prefix<R: Rewrite>(
2769     context: &RewriteContext,
2770     prefix: &str,
2771     rewrite: &R,
2772     shape: Shape,
2773 ) -> Option<String> {
2774     rewrite
2775         .rewrite(context, shape.offset_left(prefix.len())?)
2776         .map(|r| format!("{}{}", prefix, r))
2777 }
2778
2779 // FIXME: this is probably not correct for multi-line Rewrites. we should
2780 // subtract suffix.len() from the last line budget, not the first!
2781 pub fn rewrite_unary_suffix<R: Rewrite>(
2782     context: &RewriteContext,
2783     suffix: &str,
2784     rewrite: &R,
2785     shape: Shape,
2786 ) -> Option<String> {
2787     rewrite
2788         .rewrite(context, shape.sub_width(suffix.len())?)
2789         .map(|mut r| {
2790             r.push_str(suffix);
2791             r
2792         })
2793 }
2794
2795 fn rewrite_unary_op(
2796     context: &RewriteContext,
2797     op: &ast::UnOp,
2798     expr: &ast::Expr,
2799     shape: Shape,
2800 ) -> Option<String> {
2801     // For some reason, an UnOp is not spanned like BinOp!
2802     let operator_str = match *op {
2803         ast::UnOp::Deref => "*",
2804         ast::UnOp::Not => "!",
2805         ast::UnOp::Neg => "-",
2806     };
2807     rewrite_unary_prefix(context, operator_str, expr, shape)
2808 }
2809
2810 fn rewrite_assignment(
2811     context: &RewriteContext,
2812     lhs: &ast::Expr,
2813     rhs: &ast::Expr,
2814     op: Option<&ast::BinOp>,
2815     shape: Shape,
2816 ) -> Option<String> {
2817     let operator_str = match op {
2818         Some(op) => context.snippet(op.span),
2819         None => "=".to_owned(),
2820     };
2821
2822     // 1 = space between lhs and operator.
2823     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2824     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2825
2826     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2827 }
2828
2829 // The left hand side must contain everything up to, and including, the
2830 // assignment operator.
2831 pub fn rewrite_assign_rhs<S: Into<String>>(
2832     context: &RewriteContext,
2833     lhs: S,
2834     ex: &ast::Expr,
2835     shape: Shape,
2836 ) -> Option<String> {
2837     let lhs = lhs.into();
2838     let last_line_width = last_line_width(&lhs) - if lhs.contains('\n') {
2839         shape.indent.width()
2840     } else {
2841         0
2842     };
2843     // 1 = space between operator and rhs.
2844     let orig_shape = shape.offset_left(last_line_width + 1)?;
2845     let rhs = choose_rhs(context, ex, orig_shape, ex.rewrite(context, orig_shape))?;
2846     Some(lhs + &rhs)
2847 }
2848
2849 fn choose_rhs(
2850     context: &RewriteContext,
2851     expr: &ast::Expr,
2852     shape: Shape,
2853     orig_rhs: Option<String>,
2854 ) -> Option<String> {
2855     match orig_rhs {
2856         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2857             Some(format!(" {}", new_str))
2858         }
2859         _ => {
2860             // Expression did not fit on the same line as the identifier.
2861             // Try splitting the line and see if that works better.
2862             let new_shape = Shape::indented(
2863                 shape.block().indent.block_indent(context.config),
2864                 context.config,
2865             ).sub_width(shape.rhs_overhead(context.config))?;
2866             let new_rhs = expr.rewrite(context, new_shape);
2867             let new_indent_str = &new_shape.indent.to_string(context.config);
2868
2869             match (orig_rhs, new_rhs) {
2870                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2871                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2872                 }
2873                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2874                 (None, None) => None,
2875                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2876             }
2877         }
2878     }
2879 }
2880
2881 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2882     fn count_line_breaks(src: &str) -> usize {
2883         src.chars().filter(|&x| x == '\n').count()
2884     }
2885
2886     !next_line_rhs.contains('\n')
2887         || count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2888 }
2889
2890 fn rewrite_expr_addrof(
2891     context: &RewriteContext,
2892     mutability: ast::Mutability,
2893     expr: &ast::Expr,
2894     shape: Shape,
2895 ) -> Option<String> {
2896     let operator_str = match mutability {
2897         ast::Mutability::Immutable => "&",
2898         ast::Mutability::Mutable => "&mut ",
2899     };
2900     rewrite_unary_prefix(context, operator_str, expr, shape)
2901 }
2902
2903 pub trait ToExpr {
2904     fn to_expr(&self) -> Option<&ast::Expr>;
2905     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2906 }
2907
2908 impl ToExpr for ast::Expr {
2909     fn to_expr(&self) -> Option<&ast::Expr> {
2910         Some(self)
2911     }
2912
2913     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2914         can_be_overflowed_expr(context, self, len)
2915     }
2916 }
2917
2918 impl ToExpr for ast::Ty {
2919     fn to_expr(&self) -> Option<&ast::Expr> {
2920         None
2921     }
2922
2923     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2924         can_be_overflowed_type(context, self, len)
2925     }
2926 }
2927
2928 impl<'a> ToExpr for TuplePatField<'a> {
2929     fn to_expr(&self) -> Option<&ast::Expr> {
2930         None
2931     }
2932
2933     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2934         can_be_overflowed_pat(context, self, len)
2935     }
2936 }
2937
2938 impl<'a> ToExpr for ast::StructField {
2939     fn to_expr(&self) -> Option<&ast::Expr> {
2940         None
2941     }
2942
2943     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2944         false
2945     }
2946 }
2947
2948 impl<'a> ToExpr for MacroArg {
2949     fn to_expr(&self) -> Option<&ast::Expr> {
2950         match *self {
2951             MacroArg::Expr(ref expr) => Some(expr),
2952             _ => None,
2953         }
2954     }
2955
2956     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2957         match *self {
2958             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2959             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2960             MacroArg::Pat(..) => false,
2961         }
2962     }
2963 }