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::fmt::Write;
  14 use std::iter::{repeat, ExactSizeIterator};
  15
  16 use syntax::{ast, ptr};
  17 use syntax::codemap::{BytePos, CodeMap, Span};
  18 use syntax::parse::classify;
  19
  20 use spanned::Spanned;
  21 use chains::rewrite_chain;
  22 use codemap::{LineRangeUtils, SpanUtils};
  23 use comment::{combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
  24               rewrite_comment, rewrite_missing_comment, FindUncommented};
  25 use config::{Config, ControlBraceStyle, IndentStyle, MultilineStyle, Style};
  26 use items::{span_hi_for_arg, span_lo_for_arg};
  27 use lists::{definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting,
  28             struct_lit_shape, struct_lit_tactic, write_list, DefinitiveListTactic, ListFormatting,
  29             ListItem, ListTactic, Separator, SeparatorPlace, SeparatorTactic};
  30 use macros::{rewrite_macro, MacroArg, MacroPosition};
  31 use patterns::{can_be_overflowed_pat, TuplePatField};
  32 use rewrite::{Rewrite, RewriteContext};
  33 use shape::{Indent, Shape};
  34 use string::{rewrite_string, StringFormat};
  35 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  36 use utils::{colon_spaces, contains_skip, extra_offset, first_line_width, inner_attributes,
  37             last_line_extendable, last_line_width, left_most_sub_expr, mk_sp, outer_attributes,
  38             paren_overhead, ptr_vec_to_ref_vec, semicolon_for_stmt, stmt_expr,
  39             trimmed_last_line_width};
  40 use vertical::rewrite_with_alignment;
  41 use visitor::FmtVisitor;
  42
  43 impl Rewrite for ast::Expr {
  44     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  45         format_expr(self, ExprType::SubExpression, context, shape)
  46     }
  47 }
  48
  49 #[derive(Copy, Clone, PartialEq)]
  50 pub enum ExprType {
  51     Statement,
  52     SubExpression,
  53 }
  54
  55 pub fn format_expr(
  56     expr: &ast::Expr,
  57     expr_type: ExprType,
  58     context: &RewriteContext,
  59     shape: Shape,
  60 ) -> Option<String> {
  61     skip_out_of_file_lines_range!(context, expr.span);
  62
  63     if contains_skip(&*expr.attrs) {
  64         return Some(context.snippet(expr.span()));
  65     }
  66
  67     let expr_rw = match expr.node {
  68         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  69             expr_vec.iter().map(|e| &**e),
  70             mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi()),
  71             context,
  72             shape,
  73             false,
  74         ),
  75         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  76         ast::ExprKind::Call(ref callee, ref args) => {
  77             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  78             let callee_str = try_opt!(callee.rewrite(context, shape));
  79             rewrite_call(context, &callee_str, &args, inner_span, shape)
  80         }
  81         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
  82         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
  83             // FIXME: format comments between operands and operator
  84             rewrite_pair(
  85                 &**lhs,
  86                 &**rhs,
  87                 "",
  88                 &format!(" {} ", context.snippet(op.span)),
  89                 "",
  90                 context,
  91                 shape,
  92                 context.config.binop_separator(),
  93             )
  94         }
  95         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
  96         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
  97             context,
  98             path,
  99             fields,
 100             base.as_ref().map(|e| &**e),
 101             expr.span,
 102             shape,
 103         ),
 104         ast::ExprKind::Tup(ref items) => {
 105             rewrite_tuple(context, &ptr_vec_to_ref_vec(&items), expr.span, shape)
 106         }
 107         ast::ExprKind::If(..) |
 108         ast::ExprKind::IfLet(..) |
 109         ast::ExprKind::ForLoop(..) |
 110         ast::ExprKind::Loop(..) |
 111         ast::ExprKind::While(..) |
 112         ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 113             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 114         ast::ExprKind::Block(ref block) => {
 115             match expr_type {
 116                 ExprType::Statement => {
 117                     if is_unsafe_block(block) {
 118                         block.rewrite(context, shape)
 119                     } else if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 120                         // Rewrite block without trying to put it in a single line.
 121                         rw
 122                     } else {
 123                         let prefix = try_opt!(block_prefix(context, block, shape));
 124                         rewrite_block_with_visitor(context, &prefix, block, shape)
 125                     }
 126                 }
 127                 ExprType::SubExpression => block.rewrite(context, shape),
 128             }
 129         }
 130         ast::ExprKind::Match(ref cond, ref arms) => {
 131             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 132         }
 133         ast::ExprKind::Path(ref qself, ref path) => {
 134             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 135         }
 136         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 137             rewrite_assignment(context, lhs, rhs, None, shape)
 138         }
 139         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 140             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 141         }
 142         ast::ExprKind::Continue(ref opt_ident) => {
 143             let id_str = match *opt_ident {
 144                 Some(ident) => format!(" {}", ident.node),
 145                 None => String::new(),
 146             };
 147             Some(format!("continue{}", id_str))
 148         }
 149         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 150             let id_str = match *opt_ident {
 151                 Some(ident) => format!(" {}", ident.node),
 152                 None => String::new(),
 153             };
 154
 155             if let Some(ref expr) = *opt_expr {
 156                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 157             } else {
 158                 Some(format!("break{}", id_str))
 159             }
 160         }
 161         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 162             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 163         } else {
 164             Some("yield".to_string())
 165         },
 166         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 167             rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 168         }
 169         ast::ExprKind::Try(..) |
 170         ast::ExprKind::Field(..) |
 171         ast::ExprKind::TupField(..) |
 172         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 173         ast::ExprKind::Mac(ref mac) => {
 174             // Failure to rewrite a marco should not imply failure to
 175             // rewrite the expression.
 176             rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 177                 .or_else(|| Some(context.snippet(expr.span)))
 178         }
 179         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 180         ast::ExprKind::Ret(Some(ref expr)) => {
 181             rewrite_unary_prefix(context, "return ", &**expr, shape)
 182         }
 183         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 184         ast::ExprKind::AddrOf(mutability, ref expr) => {
 185             rewrite_expr_addrof(context, mutability, expr, shape)
 186         }
 187         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 188             &**expr,
 189             &**ty,
 190             "",
 191             " as ",
 192             "",
 193             context,
 194             shape,
 195             SeparatorPlace::Front,
 196         ),
 197         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 198             &**expr,
 199             &**ty,
 200             "",
 201             ": ",
 202             "",
 203             context,
 204             shape,
 205             SeparatorPlace::Back,
 206         ),
 207         ast::ExprKind::Index(ref expr, ref index) => {
 208             rewrite_index(&**expr, &**index, context, shape)
 209         }
 210         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 211             let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
 212                 ("[ ", " ]")
 213             } else {
 214                 ("[", "]")
 215             };
 216             rewrite_pair(
 217                 &**expr,
 218                 &**repeats,
 219                 lbr,
 220                 "; ",
 221                 rbr,
 222                 context,
 223                 shape,
 224                 SeparatorPlace::Back,
 225             )
 226         }
 227         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 228             let delim = match limits {
 229                 ast::RangeLimits::HalfOpen => "..",
 230                 ast::RangeLimits::Closed => "..=",
 231             };
 232
 233             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 234                 match lhs.node {
 235                     ast::ExprKind::Lit(ref lit) => match lit.node {
 236                         ast::LitKind::FloatUnsuffixed(..) => {
 237                             context.snippet(lit.span).ends_with('.')
 238                         }
 239                         _ => false,
 240                     },
 241                     _ => false,
 242                 }
 243             }
 244
 245             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 246                 (Some(lhs), Some(rhs)) => {
 247                     let sp_delim = if context.config.spaces_around_ranges() {
 248                         format!(" {} ", delim)
 249                     } else if needs_space_before_range(context, lhs) {
 250                         format!(" {}", delim)
 251                     } else {
 252                         delim.into()
 253                     };
 254                     rewrite_pair(
 255                         &*lhs,
 256                         &*rhs,
 257                         "",
 258                         &sp_delim,
 259                         "",
 260                         context,
 261                         shape,
 262                         SeparatorPlace::Front,
 263                     )
 264                 }
 265                 (None, Some(rhs)) => {
 266                     let sp_delim = if context.config.spaces_around_ranges() {
 267                         format!("{} ", delim)
 268                     } else {
 269                         delim.into()
 270                     };
 271                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 272                 }
 273                 (Some(lhs), None) => {
 274                     let sp_delim = if context.config.spaces_around_ranges() {
 275                         format!(" {}", delim)
 276                     } else {
 277                         delim.into()
 278                     };
 279                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 280                 }
 281                 (None, None) => Some(delim.into()),
 282             }
 283         }
 284         // We do not format these expressions yet, but they should still
 285         // satisfy our width restrictions.
 286         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => {
 287             Some(context.snippet(expr.span))
 288         }
 289         ast::ExprKind::Catch(ref block) => {
 290             if let rw @ Some(_) = rewrite_single_line_block(context, "do catch ", block, shape) {
 291                 rw
 292             } else {
 293                 // 9 = `do catch `
 294                 let budget = shape.width.checked_sub(9).unwrap_or(0);
 295                 Some(format!(
 296                     "{}{}",
 297                     "do catch ",
 298                     try_opt!(block.rewrite(context, Shape::legacy(budget, shape.indent)))
 299                 ))
 300             }
 301         }
 302     };
 303
 304     expr_rw
 305         .and_then(|expr_str| {
 306             recover_comment_removed(expr_str, expr.span, context)
 307         })
 308         .and_then(|expr_str| {
 309             let attrs = outer_attributes(&expr.attrs);
 310             let attrs_str = try_opt!(attrs.rewrite(context, shape));
 311             let span = mk_sp(
 312                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 313                 expr.span.lo(),
 314             );
 315             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 316         })
 317 }
 318
 319 pub fn rewrite_pair<LHS, RHS>(
 320     lhs: &LHS,
 321     rhs: &RHS,
 322     prefix: &str,
 323     infix: &str,
 324     suffix: &str,
 325     context: &RewriteContext,
 326     shape: Shape,
 327     separator_place: SeparatorPlace,
 328 ) -> Option<String>
 329 where
 330     LHS: Rewrite,
 331     RHS: Rewrite,
 332 {
 333     let lhs_overhead = match separator_place {
 334         SeparatorPlace::Back => shape.used_width() + prefix.len() + infix.trim_right().len(),
 335         SeparatorPlace::Front => shape.used_width(),
 336     };
 337     let lhs_shape = Shape {
 338         width: context.budget(lhs_overhead),
 339         ..shape
 340     };
 341     let lhs_result = try_opt!(
 342         lhs.rewrite(context, lhs_shape)
 343             .map(|lhs_str| format!("{}{}", prefix, lhs_str))
 344     );
 345
 346     // Try to the both lhs and rhs on the same line.
 347     let rhs_orig_result = shape
 348         .offset_left(last_line_width(&lhs_result) + infix.len())
 349         .and_then(|s| s.sub_width(suffix.len()))
 350         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 351     if let Some(ref rhs_result) = rhs_orig_result {
 352         // If the rhs looks like block expression, we allow it to stay on the same line
 353         // with the lhs even if it is multi-lined.
 354         let allow_same_line = rhs_result
 355             .lines()
 356             .next()
 357             .map(|first_line| first_line.ends_with('{'))
 358             .unwrap_or(false);
 359         if !rhs_result.contains('\n') || allow_same_line {
 360             let one_line_width = last_line_width(&lhs_result) + infix.len()
 361                 + first_line_width(&rhs_result) + suffix.len();
 362             if one_line_width <= shape.width {
 363                 return Some(format!("{}{}{}{}", lhs_result, infix, rhs_result, suffix));
 364             }
 365         }
 366     }
 367
 368     // We have to use multiple lines.
 369     // Re-evaluate the rhs because we have more space now:
 370     let mut rhs_shape = try_opt!(match context.config.control_style() {
 371         Style::Legacy => shape
 372             .sub_width(suffix.len() + prefix.len())
 373             .map(|s| s.visual_indent(prefix.len())),
 374         Style::Rfc => {
 375             // Try to calculate the initial constraint on the right hand side.
 376             let rhs_overhead = shape.rhs_overhead(context.config);
 377             Shape::indented(shape.indent.block_indent(context.config), context.config)
 378                 .sub_width(rhs_overhead)
 379         }
 380     });
 381     let infix = match separator_place {
 382         SeparatorPlace::Back => infix.trim_right(),
 383         SeparatorPlace::Front => infix.trim_left(),
 384     };
 385     if separator_place == SeparatorPlace::Front {
 386         rhs_shape = try_opt!(rhs_shape.offset_left(infix.len()));
 387     }
 388     let rhs_result = try_opt!(rhs.rewrite(context, rhs_shape));
 389     match separator_place {
 390         SeparatorPlace::Back => Some(format!(
 391             "{}{}\n{}{}{}",
 392             lhs_result,
 393             infix,
 394             rhs_shape.indent.to_string(context.config),
 395             rhs_result,
 396             suffix
 397         )),
 398         SeparatorPlace::Front => Some(format!(
 399             "{}\n{}{}{}{}",
 400             lhs_result,
 401             rhs_shape.indent.to_string(context.config),
 402             infix,
 403             rhs_result,
 404             suffix
 405         )),
 406     }
 407 }
 408
 409 pub fn rewrite_array<'a, I>(
 410     expr_iter: I,
 411     span: Span,
 412     context: &RewriteContext,
 413     shape: Shape,
 414     trailing_comma: bool,
 415 ) -> Option<String>
 416 where
 417     I: Iterator<Item = &'a ast::Expr>,
 418 {
 419     let bracket_size = if context.config.spaces_within_square_brackets() {
 420         2 // "[ "
 421     } else {
 422         1 // "["
 423     };
 424
 425     let nested_shape = match context.config.array_layout() {
 426         IndentStyle::Block => try_opt!(
 427             shape
 428                 .block()
 429                 .block_indent(context.config.tab_spaces())
 430                 .with_max_width(context.config)
 431                 .sub_width(1)
 432         ),
 433         IndentStyle::Visual => try_opt!(
 434             shape
 435                 .visual_indent(bracket_size)
 436                 .sub_width(bracket_size * 2)
 437         ),
 438     };
 439
 440     let items = itemize_list(
 441         context.codemap,
 442         expr_iter,
 443         "]",
 444         |item| item.span.lo(),
 445         |item| item.span.hi(),
 446         |item| item.rewrite(context, nested_shape),
 447         span.lo(),
 448         span.hi(),
 449         false,
 450     ).collect::<Vec<_>>();
 451
 452     if items.is_empty() {
 453         if context.config.spaces_within_square_brackets() {
 454             return Some("[ ]".to_string());
 455         } else {
 456             return Some("[]".to_string());
 457         }
 458     }
 459
 460     let has_long_item = items
 461         .iter()
 462         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 463
 464     let mut tactic = match context.config.array_layout() {
 465         IndentStyle::Block => {
 466             // FIXME wrong shape in one-line case
 467             match shape.width.checked_sub(2 * bracket_size) {
 468                 Some(width) => {
 469                     let tactic =
 470                         ListTactic::LimitedHorizontalVertical(context.config.array_width());
 471                     definitive_tactic(&items, tactic, Separator::Comma, width)
 472                 }
 473                 None => DefinitiveListTactic::Vertical,
 474             }
 475         }
 476         IndentStyle::Visual => if has_long_item || items.iter().any(ListItem::is_multiline) {
 477             definitive_tactic(
 478                 &items,
 479                 ListTactic::LimitedHorizontalVertical(context.config.array_width()),
 480                 Separator::Comma,
 481                 nested_shape.width,
 482             )
 483         } else {
 484             DefinitiveListTactic::Mixed
 485         },
 486     };
 487     let ends_with_newline = tactic.ends_with_newline(context.config.array_layout());
 488     if context.config.array_horizontal_layout_threshold() > 0
 489         && items.len() > context.config.array_horizontal_layout_threshold()
 490     {
 491         tactic = DefinitiveListTactic::Mixed;
 492     }
 493
 494     let fmt = ListFormatting {
 495         tactic: tactic,
 496         separator: ",",
 497         trailing_separator: if trailing_comma {
 498             SeparatorTactic::Always
 499         } else if context.inside_macro || context.config.array_layout() == IndentStyle::Visual {
 500             SeparatorTactic::Never
 501         } else {
 502             SeparatorTactic::Vertical
 503         },
 504         separator_place: SeparatorPlace::Back,
 505         shape: nested_shape,
 506         ends_with_newline: ends_with_newline,
 507         preserve_newline: false,
 508         config: context.config,
 509     };
 510     let list_str = try_opt!(write_list(&items, &fmt));
 511
 512     let result = if context.config.array_layout() == IndentStyle::Visual
 513         || tactic == DefinitiveListTactic::Horizontal
 514     {
 515         if context.config.spaces_within_square_brackets() && !list_str.is_empty() {
 516             format!("[ {} ]", list_str)
 517         } else {
 518             format!("[{}]", list_str)
 519         }
 520     } else {
 521         format!(
 522             "[\n{}{}\n{}]",
 523             nested_shape.indent.to_string(context.config),
 524             list_str,
 525             shape.block().indent.to_string(context.config)
 526         )
 527     };
 528
 529     Some(result)
 530 }
 531
 532 // Return type is (prefix, extra_offset)
 533 fn rewrite_closure_fn_decl(
 534     capture: ast::CaptureBy,
 535     fn_decl: &ast::FnDecl,
 536     body: &ast::Expr,
 537     span: Span,
 538     context: &RewriteContext,
 539     shape: Shape,
 540 ) -> Option<(String, usize)> {
 541     let mover = if capture == ast::CaptureBy::Value {
 542         "move "
 543     } else {
 544         ""
 545     };
 546     // 4 = "|| {".len(), which is overconservative when the closure consists of
 547     // a single expression.
 548     let nested_shape = try_opt!(try_opt!(shape.shrink_left(mover.len())).sub_width(4));
 549
 550     // 1 = |
 551     let argument_offset = nested_shape.indent + 1;
 552     let arg_shape = try_opt!(nested_shape.offset_left(1)).visual_indent(0);
 553     let ret_str = try_opt!(fn_decl.output.rewrite(context, arg_shape));
 554
 555     let arg_items = itemize_list(
 556         context.codemap,
 557         fn_decl.inputs.iter(),
 558         "|",
 559         |arg| span_lo_for_arg(arg),
 560         |arg| span_hi_for_arg(context, arg),
 561         |arg| arg.rewrite(context, arg_shape),
 562         context.codemap.span_after(span, "|"),
 563         body.span.lo(),
 564         false,
 565     );
 566     let item_vec = arg_items.collect::<Vec<_>>();
 567     // 1 = space between arguments and return type.
 568     let horizontal_budget = nested_shape
 569         .width
 570         .checked_sub(ret_str.len() + 1)
 571         .unwrap_or(0);
 572     let tactic = definitive_tactic(
 573         &item_vec,
 574         ListTactic::HorizontalVertical,
 575         Separator::Comma,
 576         horizontal_budget,
 577     );
 578     let arg_shape = match tactic {
 579         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 580         _ => arg_shape,
 581     };
 582
 583     let fmt = ListFormatting {
 584         tactic: tactic,
 585         separator: ",",
 586         trailing_separator: SeparatorTactic::Never,
 587         separator_place: SeparatorPlace::Back,
 588         shape: arg_shape,
 589         ends_with_newline: false,
 590         preserve_newline: true,
 591         config: context.config,
 592     };
 593     let list_str = try_opt!(write_list(&item_vec, &fmt));
 594     let mut prefix = format!("{}|{}|", mover, list_str);
 595     // 1 = space between `|...|` and body.
 596     let extra_offset = extra_offset(&prefix, shape) + 1;
 597
 598     if !ret_str.is_empty() {
 599         if prefix.contains('\n') {
 600             prefix.push('\n');
 601             prefix.push_str(&argument_offset.to_string(context.config));
 602         } else {
 603             prefix.push(' ');
 604         }
 605         prefix.push_str(&ret_str);
 606     }
 607
 608     Some((prefix, extra_offset))
 609 }
 610
 611 // This functions is pretty messy because of the rules around closures and blocks:
 612 // FIXME - the below is probably no longer true in full.
 613 //   * if there is a return type, then there must be braces,
 614 //   * given a closure with braces, whether that is parsed to give an inner block
 615 //     or not depends on if there is a return type and if there are statements
 616 //     in that block,
 617 //   * if the first expression in the body ends with a block (i.e., is a
 618 //     statement without needing a semi-colon), then adding or removing braces
 619 //     can change whether it is treated as an expression or statement.
 620 fn rewrite_closure(
 621     capture: ast::CaptureBy,
 622     fn_decl: &ast::FnDecl,
 623     body: &ast::Expr,
 624     span: Span,
 625     context: &RewriteContext,
 626     shape: Shape,
 627 ) -> Option<String> {
 628     let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
 629         capture,
 630         fn_decl,
 631         body,
 632         span,
 633         context,
 634         shape,
 635     ));
 636     // 1 = space between `|...|` and body.
 637     let body_shape = try_opt!(shape.offset_left(extra_offset));
 638
 639     if let ast::ExprKind::Block(ref block) = body.node {
 640         // The body of the closure is an empty block.
 641         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 642             return Some(format!("{} {{}}", prefix));
 643         }
 644
 645         // Figure out if the block is necessary.
 646         let needs_block = block.rules != ast::BlockCheckMode::Default || block.stmts.len() > 1
 647             || context.inside_macro
 648             || block_contains_comment(block, context.codemap)
 649             || prefix.contains('\n');
 650
 651         let no_return_type = if let ast::FunctionRetTy::Default(_) = fn_decl.output {
 652             true
 653         } else {
 654             false
 655         };
 656         if no_return_type && !needs_block {
 657             // block.stmts.len() == 1
 658             if let Some(expr) = stmt_expr(&block.stmts[0]) {
 659                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 660                     return Some(rw);
 661                 }
 662             }
 663         }
 664
 665         // Either we require a block, or tried without and failed.
 666         rewrite_closure_block(block, &prefix, context, body_shape)
 667     } else {
 668         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
 669             // The closure originally had a non-block expression, but we can't fit on
 670             // one line, so we'll insert a block.
 671             rewrite_closure_with_block(context, body_shape, &prefix, body)
 672         })
 673     }
 674 }
 675
 676 // Rewrite closure with a single expression wrapping its body with block.
 677 fn rewrite_closure_with_block(
 678     context: &RewriteContext,
 679     shape: Shape,
 680     prefix: &str,
 681     body: &ast::Expr,
 682 ) -> Option<String> {
 683     let block = ast::Block {
 684         stmts: vec![
 685             ast::Stmt {
 686                 id: ast::NodeId::new(0),
 687                 node: ast::StmtKind::Expr(ptr::P(body.clone())),
 688                 span: body.span,
 689             },
 690         ],
 691         id: ast::NodeId::new(0),
 692         rules: ast::BlockCheckMode::Default,
 693         span: body.span,
 694     };
 695     rewrite_closure_block(&block, prefix, context, shape)
 696 }
 697
 698 // Rewrite closure with a single expression without wrapping its body with block.
 699 fn rewrite_closure_expr(
 700     expr: &ast::Expr,
 701     prefix: &str,
 702     context: &RewriteContext,
 703     shape: Shape,
 704 ) -> Option<String> {
 705     let mut rewrite = expr.rewrite(context, shape);
 706     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 707         rewrite = and_one_line(rewrite);
 708     }
 709     rewrite = rewrite.and_then(|rw| {
 710         if context.config.multiline_closure_forces_block() && rw.contains('\n') {
 711             None
 712         } else {
 713             Some(rw)
 714         }
 715     });
 716     rewrite.map(|rw| format!("{} {}", prefix, rw))
 717 }
 718
 719 // Rewrite closure whose body is block.
 720 fn rewrite_closure_block(
 721     block: &ast::Block,
 722     prefix: &str,
 723     context: &RewriteContext,
 724     shape: Shape,
 725 ) -> Option<String> {
 726     // Start with visual indent, then fall back to block indent if the
 727     // closure is large.
 728     let block_threshold = context.config.closure_block_indent_threshold();
 729     if block_threshold >= 0 {
 730         if let Some(block_str) = block.rewrite(context, shape) {
 731             if block_str.matches('\n').count() <= block_threshold as usize
 732                 && !need_block_indent(&block_str, shape)
 733             {
 734                 if let Some(block_str) = block_str.rewrite(context, shape) {
 735                     return Some(format!("{} {}", prefix, block_str));
 736                 }
 737             }
 738         }
 739     }
 740
 741     // The body of the closure is big enough to be block indented, that
 742     // means we must re-format.
 743     let block_shape = shape.block();
 744     let block_str = try_opt!(block.rewrite(context, block_shape));
 745     Some(format!("{} {}", prefix, block_str))
 746 }
 747
 748 fn and_one_line(x: Option<String>) -> Option<String> {
 749     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 750 }
 751
 752 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 753     debug!("nop_block_collapse {:?} {}", block_str, budget);
 754     block_str.map(|block_str| {
 755         if block_str.starts_with('{') && budget >= 2
 756             && (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 757         {
 758             "{}".to_owned()
 759         } else {
 760             block_str.to_owned()
 761         }
 762     })
 763 }
 764
 765 fn rewrite_empty_block(
 766     context: &RewriteContext,
 767     block: &ast::Block,
 768     shape: Shape,
 769 ) -> Option<String> {
 770     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 771     {
 772         return Some("{}".to_owned());
 773     }
 774
 775     // If a block contains only a single-line comment, then leave it on one line.
 776     let user_str = context.snippet(block.span);
 777     let user_str = user_str.trim();
 778     if user_str.starts_with('{') && user_str.ends_with('}') {
 779         let comment_str = user_str[1..user_str.len() - 1].trim();
 780         if block.stmts.is_empty() && !comment_str.contains('\n') && !comment_str.starts_with("//")
 781             && comment_str.len() + 4 <= shape.width
 782         {
 783             return Some(format!("{{ {} }}", comment_str));
 784         }
 785     }
 786
 787     None
 788 }
 789
 790 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 791     Some(match block.rules {
 792         ast::BlockCheckMode::Unsafe(..) => {
 793             let snippet = context.snippet(block.span);
 794             let open_pos = try_opt!(snippet.find_uncommented("{"));
 795             // Extract comment between unsafe and block start.
 796             let trimmed = &snippet[6..open_pos].trim();
 797
 798             if !trimmed.is_empty() {
 799                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 800                 let budget = try_opt!(shape.width.checked_sub(9));
 801                 format!(
 802                     "unsafe {} ",
 803                     try_opt!(rewrite_comment(
 804                         trimmed,
 805                         true,
 806                         Shape::legacy(budget, shape.indent + 7),
 807                         context.config,
 808                     ))
 809                 )
 810             } else {
 811                 "unsafe ".to_owned()
 812             }
 813         }
 814         ast::BlockCheckMode::Default => String::new(),
 815     })
 816 }
 817
 818 fn rewrite_single_line_block(
 819     context: &RewriteContext,
 820     prefix: &str,
 821     block: &ast::Block,
 822     shape: Shape,
 823 ) -> Option<String> {
 824     if is_simple_block(block, context.codemap) {
 825         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 826         let expr_str = try_opt!(block.stmts[0].rewrite(context, expr_shape));
 827         let result = format!("{}{{ {} }}", prefix, expr_str);
 828         if result.len() <= shape.width && !result.contains('\n') {
 829             return Some(result);
 830         }
 831     }
 832     None
 833 }
 834
 835 fn rewrite_block_with_visitor(
 836     context: &RewriteContext,
 837     prefix: &str,
 838     block: &ast::Block,
 839     shape: Shape,
 840 ) -> Option<String> {
 841     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 842         return rw;
 843     }
 844
 845     let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 846     visitor.block_indent = shape.indent;
 847     visitor.is_if_else_block = context.is_if_else_block;
 848     match block.rules {
 849         ast::BlockCheckMode::Unsafe(..) => {
 850             let snippet = context.snippet(block.span);
 851             let open_pos = try_opt!(snippet.find_uncommented("{"));
 852             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 853         }
 854         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 855     }
 856
 857     visitor.visit_block(block, None);
 858     Some(format!("{}{}", prefix, visitor.buffer))
 859 }
 860
 861 impl Rewrite for ast::Block {
 862     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 863         // shape.width is used only for the single line case: either the empty block `{}`,
 864         // or an unsafe expression `unsafe { e }`.
 865         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 866             return rw;
 867         }
 868
 869         let prefix = try_opt!(block_prefix(context, self, shape));
 870
 871         let result = rewrite_block_with_visitor(context, &prefix, self, shape);
 872         if let Some(ref result_str) = result {
 873             if result_str.lines().count() <= 3 {
 874                 if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 875                     return rw;
 876                 }
 877             }
 878         }
 879
 880         result
 881     }
 882 }
 883
 884 impl Rewrite for ast::Stmt {
 885     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 886         skip_out_of_file_lines_range!(context, self.span());
 887
 888         let result = match self.node {
 889             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 890             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 891                 let suffix = if semicolon_for_stmt(context, self) {
 892                     ";"
 893                 } else {
 894                     ""
 895                 };
 896
 897                 let shape = try_opt!(shape.sub_width(suffix.len()));
 898                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 899             }
 900             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 901         };
 902         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 903     }
 904 }
 905
 906 // Rewrite condition if the given expression has one.
 907 fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 908     match expr.node {
 909         ast::ExprKind::Match(ref cond, _) => {
 910             // `match `cond` {`
 911             let cond_shape = match context.config.control_style() {
 912                 Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
 913                 Style::Rfc => try_opt!(shape.offset_left(8)),
 914             };
 915             cond.rewrite(context, cond_shape)
 916         }
 917         ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
 918             stmt_expr(&block.stmts[0]).and_then(|e| rewrite_cond(context, e, shape))
 919         }
 920         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 921             let alt_block_sep =
 922                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 923             control_flow
 924                 .rewrite_cond(context, shape, &alt_block_sep)
 925                 .and_then(|rw| Some(rw.0))
 926         }),
 927     }
 928 }
 929
 930 // Abstraction over control flow expressions
 931 #[derive(Debug)]
 932 struct ControlFlow<'a> {
 933     cond: Option<&'a ast::Expr>,
 934     block: &'a ast::Block,
 935     else_block: Option<&'a ast::Expr>,
 936     label: Option<ast::SpannedIdent>,
 937     pat: Option<&'a ast::Pat>,
 938     keyword: &'a str,
 939     matcher: &'a str,
 940     connector: &'a str,
 941     allow_single_line: bool,
 942     // True if this is an `if` expression in an `else if` :-( hacky
 943     nested_if: bool,
 944     span: Span,
 945 }
 946
 947 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 948     match expr.node {
 949         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 950             cond,
 951             None,
 952             if_block,
 953             else_block.as_ref().map(|e| &**e),
 954             expr_type == ExprType::SubExpression,
 955             false,
 956             expr.span,
 957         )),
 958         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 959             Some(ControlFlow::new_if(
 960                 cond,
 961                 Some(pat),
 962                 if_block,
 963                 else_block.as_ref().map(|e| &**e),
 964                 expr_type == ExprType::SubExpression,
 965                 false,
 966                 expr.span,
 967             ))
 968         }
 969         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 970             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 971         }
 972         ast::ExprKind::Loop(ref block, label) => {
 973             Some(ControlFlow::new_loop(block, label, expr.span))
 974         }
 975         ast::ExprKind::While(ref cond, ref block, label) => {
 976             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
 977         }
 978         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 979             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
 980         ),
 981         _ => None,
 982     }
 983 }
 984
 985 impl<'a> ControlFlow<'a> {
 986     fn new_if(
 987         cond: &'a ast::Expr,
 988         pat: Option<&'a ast::Pat>,
 989         block: &'a ast::Block,
 990         else_block: Option<&'a ast::Expr>,
 991         allow_single_line: bool,
 992         nested_if: bool,
 993         span: Span,
 994     ) -> ControlFlow<'a> {
 995         ControlFlow {
 996             cond: Some(cond),
 997             block: block,
 998             else_block: else_block,
 999             label: None,
1000             pat: pat,
1001             keyword: "if",
1002             matcher: match pat {
1003                 Some(..) => "let",
1004                 None => "",
1005             },
1006             connector: " =",
1007             allow_single_line: allow_single_line,
1008             nested_if: nested_if,
1009             span: span,
1010         }
1011     }
1012
1013     fn new_loop(
1014         block: &'a ast::Block,
1015         label: Option<ast::SpannedIdent>,
1016         span: Span,
1017     ) -> ControlFlow<'a> {
1018         ControlFlow {
1019             cond: None,
1020             block: block,
1021             else_block: None,
1022             label: label,
1023             pat: None,
1024             keyword: "loop",
1025             matcher: "",
1026             connector: "",
1027             allow_single_line: false,
1028             nested_if: false,
1029             span: span,
1030         }
1031     }
1032
1033     fn new_while(
1034         pat: Option<&'a ast::Pat>,
1035         cond: &'a ast::Expr,
1036         block: &'a ast::Block,
1037         label: Option<ast::SpannedIdent>,
1038         span: Span,
1039     ) -> ControlFlow<'a> {
1040         ControlFlow {
1041             cond: Some(cond),
1042             block: block,
1043             else_block: None,
1044             label: label,
1045             pat: pat,
1046             keyword: "while",
1047             matcher: match pat {
1048                 Some(..) => "let",
1049                 None => "",
1050             },
1051             connector: " =",
1052             allow_single_line: false,
1053             nested_if: false,
1054             span: span,
1055         }
1056     }
1057
1058     fn new_for(
1059         pat: &'a ast::Pat,
1060         cond: &'a ast::Expr,
1061         block: &'a ast::Block,
1062         label: Option<ast::SpannedIdent>,
1063         span: Span,
1064     ) -> ControlFlow<'a> {
1065         ControlFlow {
1066             cond: Some(cond),
1067             block: block,
1068             else_block: None,
1069             label: label,
1070             pat: Some(pat),
1071             keyword: "for",
1072             matcher: "",
1073             connector: " in",
1074             allow_single_line: false,
1075             nested_if: false,
1076             span: span,
1077         }
1078     }
1079
1080     fn rewrite_single_line(
1081         &self,
1082         pat_expr_str: &str,
1083         context: &RewriteContext,
1084         width: usize,
1085     ) -> Option<String> {
1086         assert!(self.allow_single_line);
1087         let else_block = try_opt!(self.else_block);
1088         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1089
1090         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1091             if !is_simple_block(self.block, context.codemap)
1092                 || !is_simple_block(else_node, context.codemap)
1093                 || pat_expr_str.contains('\n')
1094             {
1095                 return None;
1096             }
1097
1098             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
1099             let expr = &self.block.stmts[0];
1100             let if_str = try_opt!(expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1101
1102             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
1103             let else_expr = &else_node.stmts[0];
1104             let else_str =
1105                 try_opt!(else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1106
1107             if if_str.contains('\n') || else_str.contains('\n') {
1108                 return None;
1109             }
1110
1111             let result = format!(
1112                 "{} {} {{ {} }} else {{ {} }}",
1113                 self.keyword,
1114                 pat_expr_str,
1115                 if_str,
1116                 else_str
1117             );
1118
1119             if result.len() <= width {
1120                 return Some(result);
1121             }
1122         }
1123
1124         None
1125     }
1126 }
1127
1128 impl<'a> ControlFlow<'a> {
1129     fn rewrite_cond(
1130         &self,
1131         context: &RewriteContext,
1132         shape: Shape,
1133         alt_block_sep: &str,
1134     ) -> Option<(String, usize)> {
1135         // Do not take the rhs overhead from the upper expressions into account
1136         // when rewriting pattern.
1137         let new_width = context
1138             .config
1139             .max_width()
1140             .checked_sub(shape.used_width())
1141             .unwrap_or(0);
1142         let fresh_shape = Shape {
1143             width: new_width,
1144             ..shape
1145         };
1146         let constr_shape = if self.nested_if {
1147             // We are part of an if-elseif-else chain. Our constraints are tightened.
1148             // 7 = "} else " .len()
1149             try_opt!(fresh_shape.offset_left(7))
1150         } else {
1151             fresh_shape
1152         };
1153
1154         let label_string = rewrite_label(self.label);
1155         // 1 = space after keyword.
1156         let offset = self.keyword.len() + label_string.len() + 1;
1157
1158         let pat_expr_string = match self.cond {
1159             Some(cond) => {
1160                 let cond_shape = match context.config.control_style() {
1161                     Style::Legacy => try_opt!(constr_shape.shrink_left(offset)),
1162                     Style::Rfc => try_opt!(constr_shape.offset_left(offset)),
1163                 };
1164                 try_opt!(rewrite_pat_expr(
1165                     context,
1166                     self.pat,
1167                     cond,
1168                     self.matcher,
1169                     self.connector,
1170                     self.keyword,
1171                     cond_shape,
1172                 ))
1173             }
1174             None => String::new(),
1175         };
1176
1177         let brace_overhead =
1178             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1179                 // 2 = ` {`
1180                 2
1181             } else {
1182                 0
1183             };
1184         let one_line_budget = context
1185             .config
1186             .max_width()
1187             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1188             .unwrap_or(0);
1189         let force_newline_brace = context.config.control_style() == Style::Rfc
1190             && (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget)
1191             && !last_line_extendable(&pat_expr_string);
1192
1193         // Try to format if-else on single line.
1194         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1195             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1196
1197             if let Some(cond_str) = trial {
1198                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1199                     return Some((cond_str, 0));
1200                 }
1201             }
1202         }
1203
1204         let cond_span = if let Some(cond) = self.cond {
1205             cond.span
1206         } else {
1207             mk_sp(self.block.span.lo(), self.block.span.lo())
1208         };
1209
1210         // `for event in event`
1211         // Do not include label in the span.
1212         let lo = self.label.map_or(self.span.lo(), |label| label.span.hi());
1213         let between_kwd_cond = mk_sp(
1214             context
1215                 .codemap
1216                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1217             self.pat
1218                 .map_or(cond_span.lo(), |p| if self.matcher.is_empty() {
1219                     p.span.lo()
1220                 } else {
1221                     context.codemap.span_before(self.span, self.matcher.trim())
1222                 }),
1223         );
1224
1225         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1226
1227         let after_cond_comment =
1228             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1229
1230         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1231             ""
1232         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1233             || force_newline_brace
1234         {
1235             alt_block_sep
1236         } else {
1237             " "
1238         };
1239
1240         let used_width = if pat_expr_string.contains('\n') {
1241             last_line_width(&pat_expr_string)
1242         } else {
1243             // 2 = spaces after keyword and condition.
1244             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1245         };
1246
1247         Some((
1248             format!(
1249                 "{}{}{}{}{}",
1250                 label_string,
1251                 self.keyword,
1252                 between_kwd_cond_comment.as_ref().map_or(
1253                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1254                         ""
1255                     } else {
1256                         " "
1257                     },
1258                     |s| &**s,
1259                 ),
1260                 pat_expr_string,
1261                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1262             ),
1263             used_width,
1264         ))
1265     }
1266 }
1267
1268 impl<'a> Rewrite for ControlFlow<'a> {
1269     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1270         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1271
1272         let alt_block_sep =
1273             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1274         let (cond_str, used_width) = try_opt!(self.rewrite_cond(context, shape, &alt_block_sep));
1275         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1276         if used_width == 0 {
1277             return Some(cond_str);
1278         }
1279
1280         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1281         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1282         // we should avoid the single line case.
1283         let block_width = if self.else_block.is_some() || self.nested_if {
1284             min(1, block_width)
1285         } else {
1286             block_width
1287         };
1288         let block_shape = Shape {
1289             width: block_width,
1290             ..shape
1291         };
1292         let mut block_context = context.clone();
1293         block_context.is_if_else_block = self.else_block.is_some();
1294         let block_str = try_opt!(rewrite_block_with_visitor(
1295             &block_context,
1296             "",
1297             self.block,
1298             block_shape,
1299         ));
1300
1301         let mut result = format!("{}{}", cond_str, block_str);
1302
1303         if let Some(else_block) = self.else_block {
1304             let shape = Shape::indented(shape.indent, context.config);
1305             let mut last_in_chain = false;
1306             let rewrite = match else_block.node {
1307                 // If the else expression is another if-else expression, prevent it
1308                 // from being formatted on a single line.
1309                 // Note how we're passing the original shape, as the
1310                 // cost of "else" should not cascade.
1311                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1312                     ControlFlow::new_if(
1313                         cond,
1314                         Some(pat),
1315                         if_block,
1316                         next_else_block.as_ref().map(|e| &**e),
1317                         false,
1318                         true,
1319                         mk_sp(else_block.span.lo(), self.span.hi()),
1320                     ).rewrite(context, shape)
1321                 }
1322                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1323                     ControlFlow::new_if(
1324                         cond,
1325                         None,
1326                         if_block,
1327                         next_else_block.as_ref().map(|e| &**e),
1328                         false,
1329                         true,
1330                         mk_sp(else_block.span.lo(), self.span.hi()),
1331                     ).rewrite(context, shape)
1332                 }
1333                 _ => {
1334                     last_in_chain = true;
1335                     // When rewriting a block, the width is only used for single line
1336                     // blocks, passing 1 lets us avoid that.
1337                     let else_shape = Shape {
1338                         width: min(1, shape.width),
1339                         ..shape
1340                     };
1341                     format_expr(else_block, ExprType::Statement, context, else_shape)
1342                 }
1343             };
1344
1345             let between_kwd_else_block = mk_sp(
1346                 self.block.span.hi(),
1347                 context
1348                     .codemap
1349                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1350             );
1351             let between_kwd_else_block_comment =
1352                 extract_comment(between_kwd_else_block, context, shape);
1353
1354             let after_else = mk_sp(
1355                 context
1356                     .codemap
1357                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1358                 else_block.span.lo(),
1359             );
1360             let after_else_comment = extract_comment(after_else, context, shape);
1361
1362             let between_sep = match context.config.control_brace_style() {
1363                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1364                     &*alt_block_sep
1365                 }
1366                 ControlBraceStyle::AlwaysSameLine => " ",
1367             };
1368             let after_sep = match context.config.control_brace_style() {
1369                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1370                 _ => " ",
1371             };
1372             try_opt!(
1373                 write!(
1374                     &mut result,
1375                     "{}else{}",
1376                     between_kwd_else_block_comment
1377                         .as_ref()
1378                         .map_or(between_sep, |s| &**s),
1379                     after_else_comment.as_ref().map_or(after_sep, |s| &**s)
1380                 ).ok()
1381             );
1382             result.push_str(&try_opt!(rewrite));
1383         }
1384
1385         Some(result)
1386     }
1387 }
1388
1389 fn rewrite_label(label: Option<ast::SpannedIdent>) -> Cow<'static, str> {
1390     match label {
1391         Some(ident) => Cow::from(format!("{}: ", ident.node)),
1392         None => Cow::from(""),
1393     }
1394 }
1395
1396 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1397     match rewrite_missing_comment(span, shape, context) {
1398         Some(ref comment) if !comment.is_empty() => Some(format!(
1399             "\n{indent}{}\n{indent}",
1400             comment,
1401             indent = shape.indent.to_string(context.config)
1402         )),
1403         _ => None,
1404     }
1405 }
1406
1407 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1408     let snippet = codemap.span_to_snippet(block.span).unwrap();
1409     contains_comment(&snippet)
1410 }
1411
1412 // Checks that a block contains no statements, an expression and no comments.
1413 // FIXME: incorrectly returns false when comment is contained completely within
1414 // the expression.
1415 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1416     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0])
1417         && !block_contains_comment(block, codemap))
1418 }
1419
1420 /// Checks whether a block contains at most one statement or expression, and no comments.
1421 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1422     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1423 }
1424
1425 /// Checks whether a block contains no statements, expressions, or comments.
1426 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1427     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1428 }
1429
1430 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1431     match stmt.node {
1432         ast::StmtKind::Expr(..) => true,
1433         _ => false,
1434     }
1435 }
1436
1437 fn is_unsafe_block(block: &ast::Block) -> bool {
1438     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1439         true
1440     } else {
1441         false
1442     }
1443 }
1444
1445 // A simple wrapper type against ast::Arm. Used inside write_list().
1446 struct ArmWrapper<'a> {
1447     pub arm: &'a ast::Arm,
1448     // True if the arm is the last one in match expression. Used to decide on whether we should add
1449     // trailing comma to the match arm when `config.trailing_comma() == Never`.
1450     pub is_last: bool,
1451 }
1452
1453 impl<'a> ArmWrapper<'a> {
1454     pub fn new(arm: &'a ast::Arm, is_last: bool) -> ArmWrapper<'a> {
1455         ArmWrapper { arm, is_last }
1456     }
1457 }
1458
1459 impl<'a> Rewrite for ArmWrapper<'a> {
1460     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1461         rewrite_match_arm(context, self.arm, shape, self.is_last)
1462     }
1463 }
1464
1465 fn rewrite_match(
1466     context: &RewriteContext,
1467     cond: &ast::Expr,
1468     arms: &[ast::Arm],
1469     shape: Shape,
1470     span: Span,
1471     attrs: &[ast::Attribute],
1472 ) -> Option<String> {
1473     if arms.is_empty() {
1474         return None;
1475     }
1476
1477     // Do not take the rhs overhead from the upper expressions into account
1478     // when rewriting match condition.
1479     let new_width = try_opt!(context.config.max_width().checked_sub(shape.used_width()));
1480     let cond_shape = Shape {
1481         width: new_width,
1482         ..shape
1483     };
1484     // 6 = `match `
1485     let cond_shape = match context.config.control_style() {
1486         Style::Legacy => try_opt!(cond_shape.shrink_left(6)),
1487         Style::Rfc => try_opt!(cond_shape.offset_left(6)),
1488     };
1489     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1490     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1491     let block_sep = match context.config.control_brace_style() {
1492         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1493         _ if last_line_extendable(&cond_str) => " ",
1494         // 2 = ` {`
1495         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => &alt_block_sep,
1496         _ => " ",
1497     };
1498
1499     let nested_indent_str = shape
1500         .indent
1501         .block_indent(context.config)
1502         .to_string(context.config);
1503     // Inner attributes.
1504     let inner_attrs = &inner_attributes(attrs);
1505     let inner_attrs_str = if inner_attrs.is_empty() {
1506         String::new()
1507     } else {
1508         try_opt!(
1509             inner_attrs
1510                 .rewrite(context, shape)
1511                 .map(|s| format!("{}{}\n", nested_indent_str, s))
1512         )
1513     };
1514
1515     let open_brace_pos = if inner_attrs.is_empty() {
1516         context
1517             .codemap
1518             .span_after(mk_sp(cond.span.hi(), arms[0].span().lo()), "{")
1519     } else {
1520         inner_attrs[inner_attrs.len() - 1].span().hi()
1521     };
1522
1523     let arm_indent_str = if context.config.indent_match_arms() {
1524         nested_indent_str
1525     } else {
1526         shape.indent.to_string(context.config)
1527     };
1528
1529     Some(format!(
1530         "match {}{}{{\n{}{}{}\n{}}}",
1531         cond_str,
1532         block_sep,
1533         inner_attrs_str,
1534         arm_indent_str,
1535         try_opt!(rewrite_match_arms(
1536             context,
1537             arms,
1538             shape,
1539             span,
1540             open_brace_pos,
1541         )),
1542         shape.indent.to_string(context.config),
1543     ))
1544 }
1545
1546 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
1547     if is_last && config.trailing_comma() == SeparatorTactic::Never {
1548         ""
1549     } else if config.match_block_trailing_comma() {
1550         ","
1551     } else if let ast::ExprKind::Block(ref block) = body.node {
1552         if let ast::BlockCheckMode::Default = block.rules {
1553             ""
1554         } else {
1555             ","
1556         }
1557     } else {
1558         ","
1559     }
1560 }
1561
1562 fn rewrite_match_arms(
1563     context: &RewriteContext,
1564     arms: &[ast::Arm],
1565     shape: Shape,
1566     span: Span,
1567     open_brace_pos: BytePos,
1568 ) -> Option<String> {
1569     let arm_shape = if context.config.indent_match_arms() {
1570         shape.block_indent(context.config.tab_spaces())
1571     } else {
1572         shape.block_indent(0)
1573     }.with_max_width(context.config);
1574
1575     let arm_len = arms.len();
1576     let is_last_iter = repeat(false)
1577         .take(arm_len.checked_sub(1).unwrap_or(0))
1578         .chain(repeat(true));
1579     let items = itemize_list(
1580         context.codemap,
1581         arms.iter()
1582             .zip(is_last_iter)
1583             .map(|(arm, is_last)| ArmWrapper::new(arm, is_last)),
1584         "}",
1585         |arm| arm.arm.span().lo(),
1586         |arm| arm.arm.span().hi(),
1587         |arm| arm.rewrite(context, arm_shape),
1588         open_brace_pos,
1589         span.hi(),
1590         false,
1591     );
1592     let arms_vec: Vec<_> = items.collect();
1593     let fmt = ListFormatting {
1594         tactic: DefinitiveListTactic::Vertical,
1595         // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
1596         separator: "",
1597         trailing_separator: SeparatorTactic::Never,
1598         separator_place: SeparatorPlace::Back,
1599         shape: arm_shape,
1600         ends_with_newline: true,
1601         preserve_newline: true,
1602         config: context.config,
1603     };
1604
1605     write_list(&arms_vec, &fmt)
1606 }
1607
1608 fn rewrite_match_arm(
1609     context: &RewriteContext,
1610     arm: &ast::Arm,
1611     shape: Shape,
1612     is_last: bool,
1613 ) -> Option<String> {
1614     let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
1615         if contains_skip(&arm.attrs) {
1616             let (_, body) = flatten_arm_body(context, &arm.body);
1617             // `arm.span()` does not include trailing comma, add it manually.
1618             return Some(format!(
1619                 "{}{}",
1620                 context.snippet(arm.span()),
1621                 arm_comma(context.config, body, is_last),
1622             ));
1623         }
1624         (
1625             mk_sp(
1626                 arm.attrs[arm.attrs.len() - 1].span.hi(),
1627                 arm.pats[0].span.lo(),
1628             ),
1629             try_opt!(arm.attrs.rewrite(context, shape)),
1630         )
1631     } else {
1632         (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
1633     };
1634     let pats_str = try_opt!(
1635         rewrite_match_pattern(context, &arm.pats, &arm.guard, shape).and_then(|pats_str| {
1636             combine_strs_with_missing_comments(
1637                 context,
1638                 &attrs_str,
1639                 &pats_str,
1640                 missing_span,
1641                 shape,
1642                 false,
1643             )
1644         })
1645     );
1646     rewrite_match_body(
1647         context,
1648         &arm.body,
1649         &pats_str,
1650         shape,
1651         arm.guard.is_some(),
1652         is_last,
1653     )
1654 }
1655
1656 fn rewrite_match_pattern(
1657     context: &RewriteContext,
1658     pats: &[ptr::P<ast::Pat>],
1659     guard: &Option<ptr::P<ast::Expr>>,
1660     shape: Shape,
1661 ) -> Option<String> {
1662     // Patterns
1663     // 5 = ` => {`
1664     let pat_shape = try_opt!(shape.sub_width(5));
1665
1666     let pat_strs = try_opt!(
1667         pats.iter()
1668             .map(|p| p.rewrite(context, pat_shape))
1669             .collect::<Option<Vec<_>>>()
1670     );
1671
1672     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1673     let tactic = definitive_tactic(
1674         &items,
1675         ListTactic::HorizontalVertical,
1676         Separator::VerticalBar,
1677         pat_shape.width,
1678     );
1679     let fmt = ListFormatting {
1680         tactic: tactic,
1681         separator: " |",
1682         trailing_separator: SeparatorTactic::Never,
1683         separator_place: context.config.match_pattern_separator_break_point(),
1684         shape: pat_shape,
1685         ends_with_newline: false,
1686         preserve_newline: false,
1687         config: context.config,
1688     };
1689     let pats_str = try_opt!(write_list(&items, &fmt));
1690
1691     // Guard
1692     let guard_str = try_opt!(rewrite_guard(
1693         context,
1694         guard,
1695         shape,
1696         trimmed_last_line_width(&pats_str),
1697     ));
1698
1699     Some(format!("{}{}", pats_str, guard_str))
1700 }
1701
1702 // (extend, body)
1703 // @extend: true if the arm body can be put next to `=>`
1704 // @body: flattened body, if the body is block with a single expression
1705 fn flatten_arm_body<'a>(context: &'a RewriteContext, body: &'a ast::Expr) -> (bool, &'a ast::Expr) {
1706     match body.node {
1707         ast::ExprKind::Block(ref block)
1708             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1709         {
1710             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1711                 (
1712                     !context.config.multiline_match_arm_forces_block()
1713                         && expr.can_be_overflowed(context, 1),
1714                     &**expr,
1715                 )
1716             } else {
1717                 (false, &*body)
1718             }
1719         }
1720         _ => (
1721             !context.config.multiline_match_arm_forces_block()
1722                 && body.can_be_overflowed(context, 1),
1723             &*body,
1724         ),
1725     }
1726 }
1727
1728 fn rewrite_match_body(
1729     context: &RewriteContext,
1730     body: &ptr::P<ast::Expr>,
1731     pats_str: &str,
1732     shape: Shape,
1733     has_guard: bool,
1734     is_last: bool,
1735 ) -> Option<String> {
1736     let (extend, body) = flatten_arm_body(context, body);
1737
1738     let comma = arm_comma(context.config, body, is_last);
1739     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1740     let alt_block_sep = alt_block_sep.as_str();
1741     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1742         (true, is_empty_block(block, context.codemap))
1743     } else {
1744         (false, false)
1745     };
1746
1747     let combine_orig_body = |body_str: &str| {
1748         let block_sep = match context.config.control_brace_style() {
1749             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1750             _ => " ",
1751         };
1752
1753         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1754     };
1755
1756     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1757     let next_line_indent = if is_block {
1758         shape.indent
1759     } else {
1760         shape.indent.block_indent(context.config)
1761     };
1762     let combine_next_line_body = |body_str: &str| {
1763         if is_block {
1764             return Some(format!(
1765                 "{} =>\n{}{}",
1766                 pats_str,
1767                 next_line_indent.to_string(context.config),
1768                 body_str
1769             ));
1770         }
1771
1772         let indent_str = shape.indent.to_string(context.config);
1773         let nested_indent_str = next_line_indent.to_string(context.config);
1774         let (body_prefix, body_suffix) = if context.config.wrap_match_arms() {
1775             let comma = if context.config.match_block_trailing_comma() {
1776                 ","
1777             } else {
1778                 ""
1779             };
1780             ("{", format!("\n{}}}{}", indent_str, comma))
1781         } else {
1782             ("", String::from(","))
1783         };
1784
1785         let block_sep = match context.config.control_brace_style() {
1786             ControlBraceStyle::AlwaysNextLine => format!("{}{}\n", alt_block_sep, body_prefix),
1787             _ if body_prefix.is_empty() => "\n".to_owned(),
1788             _ if forbid_same_line => format!("{}{}\n", alt_block_sep, body_prefix),
1789             _ => format!(" {}\n", body_prefix),
1790         } + &nested_indent_str;
1791
1792         Some(format!(
1793             "{} =>{}{}{}",
1794             pats_str,
1795             block_sep,
1796             body_str,
1797             body_suffix
1798         ))
1799     };
1800
1801     // Let's try and get the arm body on the same line as the condition.
1802     // 4 = ` => `.len()
1803     let orig_body_shape = shape
1804         .offset_left(extra_offset(pats_str, shape) + 4)
1805         .and_then(|shape| shape.sub_width(comma.len()));
1806     let orig_body = if let Some(body_shape) = orig_body_shape {
1807         let rewrite = nop_block_collapse(
1808             format_expr(body, ExprType::Statement, context, body_shape),
1809             body_shape.width,
1810         );
1811
1812         match rewrite {
1813             Some(ref body_str)
1814                 if !forbid_same_line
1815                     && (is_block
1816                         || (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1817             {
1818                 return combine_orig_body(body_str);
1819             }
1820             _ => rewrite,
1821         }
1822     } else {
1823         None
1824     };
1825     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1826
1827     // Try putting body on the next line and see if it looks better.
1828     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1829     let next_line_body = nop_block_collapse(
1830         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1831         next_line_body_shape.width,
1832     );
1833     match (orig_body, next_line_body) {
1834         (Some(ref orig_str), Some(ref next_line_str))
1835             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1836         {
1837             combine_next_line_body(next_line_str)
1838         }
1839         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1840             combine_orig_body(orig_str)
1841         }
1842         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1843             combine_next_line_body(next_line_str)
1844         }
1845         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1846         (None, None) => None,
1847         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1848     }
1849 }
1850
1851 // The `if ...` guard on a match arm.
1852 fn rewrite_guard(
1853     context: &RewriteContext,
1854     guard: &Option<ptr::P<ast::Expr>>,
1855     shape: Shape,
1856     // The amount of space used up on this line for the pattern in
1857     // the arm (excludes offset).
1858     pattern_width: usize,
1859 ) -> Option<String> {
1860     if let Some(ref guard) = *guard {
1861         // First try to fit the guard string on the same line as the pattern.
1862         // 4 = ` if `, 5 = ` => {`
1863         let cond_shape = shape
1864             .offset_left(pattern_width + 4)
1865             .and_then(|s| s.sub_width(5));
1866         if let Some(cond_shape) = cond_shape {
1867             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1868                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1869                     return Some(format!(" if {}", cond_str));
1870                 }
1871             }
1872         }
1873
1874         // Not enough space to put the guard after the pattern, try a newline.
1875         // 3 = `if `, 5 = ` => {`
1876         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1877             .offset_left(3)
1878             .and_then(|s| s.sub_width(5));
1879         if let Some(cond_shape) = cond_shape {
1880             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1881                 return Some(format!(
1882                     "\n{}if {}",
1883                     cond_shape.indent.to_string(context.config),
1884                     cond_str
1885                 ));
1886             }
1887         }
1888
1889         None
1890     } else {
1891         Some(String::new())
1892     }
1893 }
1894
1895 fn rewrite_pat_expr(
1896     context: &RewriteContext,
1897     pat: Option<&ast::Pat>,
1898     expr: &ast::Expr,
1899     matcher: &str,
1900     // Connecting piece between pattern and expression,
1901     // *without* trailing space.
1902     connector: &str,
1903     keyword: &str,
1904     shape: Shape,
1905 ) -> Option<String> {
1906     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1907     if let Some(pat) = pat {
1908         let matcher = if matcher.is_empty() {
1909             matcher.to_owned()
1910         } else {
1911             format!("{} ", matcher)
1912         };
1913         let pat_shape =
1914             try_opt!(try_opt!(shape.offset_left(matcher.len())).sub_width(connector.len()));
1915         let pat_string = try_opt!(pat.rewrite(context, pat_shape));
1916         let result = format!("{}{}{}", matcher, pat_string, connector);
1917         return rewrite_assign_rhs(context, result, expr, shape);
1918     }
1919
1920     let expr_rw = expr.rewrite(context, shape);
1921     // The expression may (partially) fit on the current line.
1922     // We do not allow splitting between `if` and condition.
1923     if keyword == "if" || expr_rw.is_some() {
1924         return expr_rw;
1925     }
1926
1927     // The expression won't fit on the current line, jump to next.
1928     let nested_shape = shape
1929         .block_indent(context.config.tab_spaces())
1930         .with_max_width(context.config);
1931     let nested_indent_str = nested_shape.indent.to_string(context.config);
1932     expr.rewrite(context, nested_shape)
1933         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1934 }
1935
1936 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1937     match l.node {
1938         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1939         _ => Some(context.snippet(l.span)),
1940     }
1941 }
1942
1943 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1944     let string_lit = context.snippet(span);
1945
1946     if !context.config.format_strings() && !context.config.force_format_strings() {
1947         if string_lit
1948             .lines()
1949             .rev()
1950             .skip(1)
1951             .all(|line| line.ends_with('\\'))
1952         {
1953             let new_indent = shape.visual_indent(1).indent;
1954             return Some(String::from(
1955                 string_lit
1956                     .lines()
1957                     .map(|line| {
1958                         format!(
1959                             "{}{}",
1960                             new_indent.to_string(context.config),
1961                             line.trim_left()
1962                         )
1963                     })
1964                     .collect::<Vec<_>>()
1965                     .join("\n")
1966                     .trim_left(),
1967             ));
1968         } else {
1969             return Some(string_lit);
1970         }
1971     }
1972
1973     if !context.config.force_format_strings()
1974         && !string_requires_rewrite(context, span, &string_lit, shape)
1975     {
1976         return Some(string_lit);
1977     }
1978
1979     // Remove the quote characters.
1980     let str_lit = &string_lit[1..string_lit.len() - 1];
1981
1982     rewrite_string(str_lit, &StringFormat::new(shape, context.config))
1983 }
1984
1985 fn string_requires_rewrite(
1986     context: &RewriteContext,
1987     span: Span,
1988     string: &str,
1989     shape: Shape,
1990 ) -> bool {
1991     if context.codemap.lookup_char_pos(span.lo()).col.0 != shape.indent.width() {
1992         return true;
1993     }
1994
1995     for (i, line) in string.lines().enumerate() {
1996         if i == 0 {
1997             if line.len() > shape.width {
1998                 return true;
1999             }
2000         } else if line.len() > shape.width + shape.indent.width() {
2001             return true;
2002         }
2003     }
2004
2005     false
2006 }
2007
2008 pub fn rewrite_call(
2009     context: &RewriteContext,
2010     callee: &str,
2011     args: &[ptr::P<ast::Expr>],
2012     span: Span,
2013     shape: Shape,
2014 ) -> Option<String> {
2015     let force_trailing_comma = if context.inside_macro {
2016         span_ends_with_comma(context, span)
2017     } else {
2018         false
2019     };
2020     rewrite_call_inner(
2021         context,
2022         callee,
2023         &ptr_vec_to_ref_vec(&args),
2024         span,
2025         shape,
2026         context.config.fn_call_width(),
2027         force_trailing_comma,
2028     )
2029 }
2030
2031 pub fn rewrite_call_inner<'a, T>(
2032     context: &RewriteContext,
2033     callee_str: &str,
2034     args: &[&T],
2035     span: Span,
2036     shape: Shape,
2037     args_max_width: usize,
2038     force_trailing_comma: bool,
2039 ) -> Option<String>
2040 where
2041     T: Rewrite + Spanned + ToExpr + 'a,
2042 {
2043     // 2 = `( `, 1 = `(`
2044     let paren_overhead = if context.config.spaces_within_parens() {
2045         2
2046     } else {
2047         1
2048     };
2049     let used_width = extra_offset(callee_str, shape);
2050     let one_line_width = try_opt!(shape.width.checked_sub(used_width + 2 * paren_overhead));
2051
2052     let nested_shape = try_opt!(shape_from_fn_call_style(
2053         context,
2054         shape,
2055         used_width + 2 * paren_overhead,
2056         used_width + paren_overhead,
2057     ));
2058
2059     let span_lo = context.codemap.span_after(span, "(");
2060     let args_span = mk_sp(span_lo, span.hi());
2061
2062     let (extendable, list_str) = try_opt!(rewrite_call_args(
2063         context,
2064         args,
2065         args_span,
2066         nested_shape,
2067         one_line_width,
2068         args_max_width,
2069         force_trailing_comma,
2070     ));
2071
2072     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2073         let mut new_context = context.clone();
2074         new_context.use_block = true;
2075         return rewrite_call_inner(
2076             &new_context,
2077             callee_str,
2078             args,
2079             span,
2080             shape,
2081             args_max_width,
2082             force_trailing_comma,
2083         );
2084     }
2085
2086     let args_shape = try_opt!(shape.sub_width(last_line_width(callee_str)));
2087     Some(format!(
2088         "{}{}",
2089         callee_str,
2090         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2091     ))
2092 }
2093
2094 fn need_block_indent(s: &str, shape: Shape) -> bool {
2095     s.lines().skip(1).any(|s| {
2096         s.find(|c| !char::is_whitespace(c))
2097             .map_or(false, |w| w + 1 < shape.indent.width())
2098     })
2099 }
2100
2101 fn rewrite_call_args<'a, T>(
2102     context: &RewriteContext,
2103     args: &[&T],
2104     span: Span,
2105     shape: Shape,
2106     one_line_width: usize,
2107     args_max_width: usize,
2108     force_trailing_comma: bool,
2109 ) -> Option<(bool, String)>
2110 where
2111     T: Rewrite + Spanned + ToExpr + 'a,
2112 {
2113     let items = itemize_list(
2114         context.codemap,
2115         args.iter(),
2116         ")",
2117         |item| item.span().lo(),
2118         |item| item.span().hi(),
2119         |item| item.rewrite(context, shape),
2120         span.lo(),
2121         span.hi(),
2122         true,
2123     );
2124     let mut item_vec: Vec<_> = items.collect();
2125
2126     // Try letting the last argument overflow to the next line with block
2127     // indentation. If its first line fits on one line with the other arguments,
2128     // we format the function arguments horizontally.
2129     let tactic = try_overflow_last_arg(
2130         context,
2131         &mut item_vec,
2132         &args[..],
2133         shape,
2134         one_line_width,
2135         args_max_width,
2136     );
2137
2138     let fmt = ListFormatting {
2139         tactic: tactic,
2140         separator: ",",
2141         trailing_separator: if force_trailing_comma {
2142             SeparatorTactic::Always
2143         } else if context.inside_macro || !context.use_block_indent() {
2144             SeparatorTactic::Never
2145         } else {
2146             context.config.trailing_comma()
2147         },
2148         separator_place: SeparatorPlace::Back,
2149         shape: shape,
2150         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2151         preserve_newline: false,
2152         config: context.config,
2153     };
2154
2155     write_list(&item_vec, &fmt).map(|args_str| {
2156         (tactic != DefinitiveListTactic::Vertical, args_str)
2157     })
2158 }
2159
2160 fn try_overflow_last_arg<'a, T>(
2161     context: &RewriteContext,
2162     item_vec: &mut Vec<ListItem>,
2163     args: &[&T],
2164     shape: Shape,
2165     one_line_width: usize,
2166     args_max_width: usize,
2167 ) -> DefinitiveListTactic
2168 where
2169     T: Rewrite + Spanned + ToExpr + 'a,
2170 {
2171     let overflow_last = can_be_overflowed(context, args);
2172
2173     // Replace the last item with its first line to see if it fits with
2174     // first arguments.
2175     let placeholder = if overflow_last {
2176         let mut context = context.clone();
2177         if let Some(expr) = args[args.len() - 1].to_expr() {
2178             if let ast::ExprKind::MethodCall(..) = expr.node {
2179                 context.force_one_line_chain = true;
2180             }
2181         }
2182         last_arg_shape(&context, item_vec, shape, args_max_width).and_then(|arg_shape| {
2183             rewrite_last_arg_with_overflow(&context, args, &mut item_vec[args.len() - 1], arg_shape)
2184         })
2185     } else {
2186         None
2187     };
2188
2189     let mut tactic = definitive_tactic(
2190         &*item_vec,
2191         ListTactic::LimitedHorizontalVertical(args_max_width),
2192         Separator::Comma,
2193         one_line_width,
2194     );
2195
2196     // Replace the stub with the full overflowing last argument if the rewrite
2197     // succeeded and its first line fits with the other arguments.
2198     match (overflow_last, tactic, placeholder) {
2199         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2200             item_vec[args.len() - 1].item = placeholder;
2201         }
2202         _ if args.len() >= 1 => {
2203             item_vec[args.len() - 1].item = args.last()
2204                 .and_then(|last_arg| last_arg.rewrite(context, shape));
2205             // Use horizontal layout for a function with a single argument as long as
2206             // everything fits in a single line.
2207             if args.len() == 1
2208                 && args_max_width != 0 // Vertical layout is forced.
2209                 && !item_vec[0].has_comment()
2210                 && !item_vec[0].inner_as_ref().contains('\n')
2211                 && ::lists::total_item_width(&item_vec[0]) <= one_line_width
2212             {
2213                 tactic = DefinitiveListTactic::Horizontal;
2214             } else {
2215                 tactic = definitive_tactic(
2216                     &*item_vec,
2217                     ListTactic::LimitedHorizontalVertical(args_max_width),
2218                     Separator::Comma,
2219                     one_line_width,
2220                 );
2221             }
2222         }
2223         _ => (),
2224     }
2225
2226     tactic
2227 }
2228
2229 fn last_arg_shape(
2230     context: &RewriteContext,
2231     items: &[ListItem],
2232     shape: Shape,
2233     args_max_width: usize,
2234 ) -> Option<Shape> {
2235     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2236         acc + i.item.as_ref().map_or(0, |s| first_line_width(s))
2237     });
2238     let max_width = min(args_max_width, shape.width);
2239     let arg_indent = if context.use_block_indent() {
2240         shape.block().indent.block_unindent(context.config)
2241     } else {
2242         shape.block().indent
2243     };
2244     Some(Shape {
2245         width: try_opt!(max_width.checked_sub(overhead)),
2246         indent: arg_indent,
2247         offset: 0,
2248     })
2249 }
2250
2251 // Rewriting closure which is placed at the end of the function call's arg.
2252 // Returns `None` if the reformatted closure 'looks bad'.
2253 fn rewrite_last_closure(
2254     context: &RewriteContext,
2255     expr: &ast::Expr,
2256     shape: Shape,
2257 ) -> Option<String> {
2258     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2259         let body = match body.node {
2260             ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
2261                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2262             }
2263             _ => body,
2264         };
2265         let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
2266             capture,
2267             fn_decl,
2268             body,
2269             expr.span,
2270             context,
2271             shape,
2272         ));
2273         // If the closure goes multi line before its body, do not overflow the closure.
2274         if prefix.contains('\n') {
2275             return None;
2276         }
2277         let body_shape = try_opt!(shape.offset_left(extra_offset));
2278         // When overflowing the closure which consists of a single control flow expression,
2279         // force to use block if its condition uses multi line.
2280         let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
2281             .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
2282             .unwrap_or(false);
2283         if is_multi_lined_cond {
2284             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2285         }
2286
2287         // Seems fine, just format the closure in usual manner.
2288         return expr.rewrite(context, shape);
2289     }
2290     None
2291 }
2292
2293 fn rewrite_last_arg_with_overflow<'a, T>(
2294     context: &RewriteContext,
2295     args: &[&T],
2296     last_item: &mut ListItem,
2297     shape: Shape,
2298 ) -> Option<String>
2299 where
2300     T: Rewrite + Spanned + ToExpr + 'a,
2301 {
2302     let last_arg = args[args.len() - 1];
2303     let rewrite = if let Some(expr) = last_arg.to_expr() {
2304         match expr.node {
2305             // When overflowing the closure which consists of a single control flow expression,
2306             // force to use block if its condition uses multi line.
2307             ast::ExprKind::Closure(..) => {
2308                 // If the argument consists of multiple closures, we do not overflow
2309                 // the last closure.
2310                 if args.len() > 1
2311                     && args.iter()
2312                         .rev()
2313                         .skip(1)
2314                         .filter_map(|arg| arg.to_expr())
2315                         .any(|expr| match expr.node {
2316                             ast::ExprKind::Closure(..) => true,
2317                             _ => false,
2318                         }) {
2319                     None
2320                 } else {
2321                     rewrite_last_closure(context, expr, shape)
2322                 }
2323             }
2324             _ => expr.rewrite(context, shape),
2325         }
2326     } else {
2327         last_arg.rewrite(context, shape)
2328     };
2329
2330     if let Some(rewrite) = rewrite {
2331         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2332         last_item.item = rewrite_first_line;
2333         Some(rewrite)
2334     } else {
2335         None
2336     }
2337 }
2338
2339 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2340 where
2341     T: Rewrite + Spanned + ToExpr + 'a,
2342 {
2343     args.last()
2344         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2345 }
2346
2347 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2348     match expr.node {
2349         ast::ExprKind::Match(..) => {
2350             (context.use_block_indent() && args_len == 1)
2351                 || (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2352         }
2353         ast::ExprKind::If(..) |
2354         ast::ExprKind::IfLet(..) |
2355         ast::ExprKind::ForLoop(..) |
2356         ast::ExprKind::Loop(..) |
2357         ast::ExprKind::While(..) |
2358         ast::ExprKind::WhileLet(..) => {
2359             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2360         }
2361         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2362             context.use_block_indent()
2363                 || context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2364         }
2365         ast::ExprKind::Array(..) |
2366         ast::ExprKind::Call(..) |
2367         ast::ExprKind::Mac(..) |
2368         ast::ExprKind::MethodCall(..) |
2369         ast::ExprKind::Struct(..) |
2370         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2371         ast::ExprKind::AddrOf(_, ref expr) |
2372         ast::ExprKind::Box(ref expr) |
2373         ast::ExprKind::Try(ref expr) |
2374         ast::ExprKind::Unary(_, ref expr) |
2375         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2376         _ => false,
2377     }
2378 }
2379
2380 pub fn wrap_args_with_parens(
2381     context: &RewriteContext,
2382     args_str: &str,
2383     is_extendable: bool,
2384     shape: Shape,
2385     nested_shape: Shape,
2386 ) -> String {
2387     if !context.use_block_indent()
2388         || (context.inside_macro && !args_str.contains('\n')
2389             && args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2390     {
2391         if context.config.spaces_within_parens() && !args_str.is_empty() {
2392             format!("( {} )", args_str)
2393         } else {
2394             format!("({})", args_str)
2395         }
2396     } else {
2397         format!(
2398             "(\n{}{}\n{})",
2399             nested_shape.indent.to_string(context.config),
2400             args_str,
2401             shape.block().indent.to_string(context.config)
2402         )
2403     }
2404 }
2405
2406 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2407     let snippet = context.snippet(span);
2408     snippet
2409         .trim_right_matches(|c: char| c == ')' || c.is_whitespace())
2410         .ends_with(',')
2411 }
2412
2413 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2414     debug!("rewrite_paren, shape: {:?}", shape);
2415     let total_paren_overhead = paren_overhead(context);
2416     let paren_overhead = total_paren_overhead / 2;
2417     let sub_shape = try_opt!(
2418         shape
2419             .offset_left(paren_overhead)
2420             .and_then(|s| s.sub_width(paren_overhead))
2421     );
2422
2423     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && !s.is_empty() {
2424         format!("( {} )", s)
2425     } else {
2426         format!("({})", s)
2427     };
2428
2429     let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2430     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2431
2432     if subexpr_str.contains('\n')
2433         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2434     {
2435         Some(paren_wrapper(&subexpr_str))
2436     } else {
2437         None
2438     }
2439 }
2440
2441 fn rewrite_index(
2442     expr: &ast::Expr,
2443     index: &ast::Expr,
2444     context: &RewriteContext,
2445     shape: Shape,
2446 ) -> Option<String> {
2447     let expr_str = try_opt!(expr.rewrite(context, shape));
2448
2449     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2450         ("[ ", " ]")
2451     } else {
2452         ("[", "]")
2453     };
2454
2455     let offset = last_line_width(&expr_str) + lbr.len();
2456     let rhs_overhead = shape.rhs_overhead(context.config);
2457     let index_shape = if expr_str.contains('\n') {
2458         Shape::legacy(context.config.max_width(), shape.indent)
2459             .offset_left(offset)
2460             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2461     } else {
2462         shape.visual_indent(offset).sub_width(offset + rbr.len())
2463     };
2464     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2465
2466     // Return if index fits in a single line.
2467     match orig_index_rw {
2468         Some(ref index_str) if !index_str.contains('\n') => {
2469             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2470         }
2471         _ => (),
2472     }
2473
2474     // Try putting index on the next line and see if it fits in a single line.
2475     let indent = shape.indent.block_indent(context.config);
2476     let index_shape = try_opt!(Shape::indented(indent, context.config).offset_left(lbr.len()));
2477     let index_shape = try_opt!(index_shape.sub_width(rbr.len() + rhs_overhead));
2478     let new_index_rw = index.rewrite(context, index_shape);
2479     match (orig_index_rw, new_index_rw) {
2480         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2481             "{}\n{}{}{}{}",
2482             expr_str,
2483             indent.to_string(context.config),
2484             lbr,
2485             new_index_str,
2486             rbr
2487         )),
2488         (None, Some(ref new_index_str)) => Some(format!(
2489             "{}\n{}{}{}{}",
2490             expr_str,
2491             indent.to_string(context.config),
2492             lbr,
2493             new_index_str,
2494             rbr
2495         )),
2496         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2497         _ => None,
2498     }
2499 }
2500
2501 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2502     if base.is_some() {
2503         return false;
2504     }
2505
2506     fields.iter().all(|field| !field.is_shorthand)
2507 }
2508
2509 fn rewrite_struct_lit<'a>(
2510     context: &RewriteContext,
2511     path: &ast::Path,
2512     fields: &'a [ast::Field],
2513     base: Option<&'a ast::Expr>,
2514     span: Span,
2515     shape: Shape,
2516 ) -> Option<String> {
2517     debug!("rewrite_struct_lit: shape {:?}", shape);
2518
2519     enum StructLitField<'a> {
2520         Regular(&'a ast::Field),
2521         Base(&'a ast::Expr),
2522     }
2523
2524     // 2 = " {".len()
2525     let path_shape = try_opt!(shape.sub_width(2));
2526     let path_str = try_opt!(rewrite_path(
2527         context,
2528         PathContext::Expr,
2529         None,
2530         path,
2531         path_shape,
2532     ));
2533
2534     if fields.is_empty() && base.is_none() {
2535         return Some(format!("{} {{}}", path_str));
2536     }
2537
2538     // Foo { a: Foo } - indent is +3, width is -5.
2539     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
2540
2541     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2542     let body_lo = context.codemap.span_after(span, "{");
2543     let fields_str = if struct_lit_can_be_aligned(fields, &base)
2544         && context.config.struct_field_align_threshold() > 0
2545     {
2546         try_opt!(rewrite_with_alignment(
2547             fields,
2548             context,
2549             shape,
2550             mk_sp(body_lo, span.hi()),
2551             one_line_width,
2552         ))
2553     } else {
2554         let field_iter = fields
2555             .into_iter()
2556             .map(StructLitField::Regular)
2557             .chain(base.into_iter().map(StructLitField::Base));
2558
2559         let span_lo = |item: &StructLitField| match *item {
2560             StructLitField::Regular(field) => field.span().lo(),
2561             StructLitField::Base(expr) => {
2562                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
2563                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
2564                 let pos = snippet.find_uncommented("..").unwrap();
2565                 last_field_hi + BytePos(pos as u32)
2566             }
2567         };
2568         let span_hi = |item: &StructLitField| match *item {
2569             StructLitField::Regular(field) => field.span().hi(),
2570             StructLitField::Base(expr) => expr.span.hi(),
2571         };
2572         let rewrite = |item: &StructLitField| match *item {
2573             StructLitField::Regular(field) => {
2574                 // The 1 taken from the v_budget is for the comma.
2575                 rewrite_field(context, field, try_opt!(v_shape.sub_width(1)), 0)
2576             }
2577             StructLitField::Base(expr) => {
2578                 // 2 = ..
2579                 expr.rewrite(context, try_opt!(v_shape.offset_left(2)))
2580                     .map(|s| format!("..{}", s))
2581             }
2582         };
2583
2584         let items = itemize_list(
2585             context.codemap,
2586             field_iter,
2587             "}",
2588             span_lo,
2589             span_hi,
2590             rewrite,
2591             body_lo,
2592             span.hi(),
2593             false,
2594         );
2595         let item_vec = items.collect::<Vec<_>>();
2596
2597         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2598         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2599         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2600
2601         try_opt!(write_list(&item_vec, &fmt))
2602     };
2603
2604     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2605     Some(format!("{} {{{}}}", path_str, fields_str))
2606
2607     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2608     // of space, we should fall back to BlockIndent.
2609 }
2610
2611 pub fn wrap_struct_field(
2612     context: &RewriteContext,
2613     fields_str: &str,
2614     shape: Shape,
2615     nested_shape: Shape,
2616     one_line_width: usize,
2617 ) -> String {
2618     if context.config.struct_lit_style() == IndentStyle::Block
2619         && (fields_str.contains('\n')
2620             || context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti
2621             || fields_str.len() > one_line_width)
2622     {
2623         format!(
2624             "\n{}{}\n{}",
2625             nested_shape.indent.to_string(context.config),
2626             fields_str,
2627             shape.indent.to_string(context.config)
2628         )
2629     } else {
2630         // One liner or visual indent.
2631         format!(" {} ", fields_str)
2632     }
2633 }
2634
2635 pub fn struct_lit_field_separator(config: &Config) -> &str {
2636     colon_spaces(
2637         config.space_before_struct_lit_field_colon(),
2638         config.space_after_struct_lit_field_colon(),
2639     )
2640 }
2641
2642 pub fn rewrite_field(
2643     context: &RewriteContext,
2644     field: &ast::Field,
2645     shape: Shape,
2646     prefix_max_width: usize,
2647 ) -> Option<String> {
2648     if contains_skip(&field.attrs) {
2649         return Some(context.snippet(field.span()));
2650     }
2651     let name = &field.ident.node.to_string();
2652     if field.is_shorthand {
2653         Some(name.to_string())
2654     } else {
2655         let mut separator = String::from(struct_lit_field_separator(context.config));
2656         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2657             separator.push(' ');
2658         }
2659         let overhead = name.len() + separator.len();
2660         let expr_shape = try_opt!(shape.offset_left(overhead));
2661         let expr = field.expr.rewrite(context, expr_shape);
2662
2663         let mut attrs_str = try_opt!(field.attrs.rewrite(context, shape));
2664         if !attrs_str.is_empty() {
2665             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2666         };
2667
2668         match expr {
2669             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2670             None => {
2671                 let expr_offset = shape.indent.block_indent(context.config);
2672                 let expr = field
2673                     .expr
2674                     .rewrite(context, Shape::indented(expr_offset, context.config));
2675                 expr.map(|s| {
2676                     format!(
2677                         "{}{}:\n{}{}",
2678                         attrs_str,
2679                         name,
2680                         expr_offset.to_string(context.config),
2681                         s
2682                     )
2683                 })
2684             }
2685         }
2686     }
2687 }
2688
2689 fn shape_from_fn_call_style(
2690     context: &RewriteContext,
2691     shape: Shape,
2692     overhead: usize,
2693     offset: usize,
2694 ) -> Option<Shape> {
2695     if context.use_block_indent() {
2696         // 1 = ","
2697         shape
2698             .block()
2699             .block_indent(context.config.tab_spaces())
2700             .with_max_width(context.config)
2701             .sub_width(1)
2702     } else {
2703         shape.visual_indent(offset).sub_width(overhead)
2704     }
2705 }
2706
2707 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2708     context: &RewriteContext,
2709     items: &[&T],
2710     span: Span,
2711     shape: Shape,
2712 ) -> Option<String>
2713 where
2714     T: Rewrite + Spanned + ToExpr + 'a,
2715 {
2716     let mut items = items.iter();
2717     // In case of length 1, need a trailing comma
2718     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2719     if items.len() == 1 {
2720         // 3 = "(" + ",)"
2721         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
2722         return items.next().unwrap().rewrite(context, nested_shape).map(
2723             |s| if context.config.spaces_within_parens() {
2724                 format!("( {}, )", s)
2725             } else {
2726                 format!("({},)", s)
2727             },
2728         );
2729     }
2730
2731     let list_lo = context.codemap.span_after(span, "(");
2732     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
2733     let items = itemize_list(
2734         context.codemap,
2735         items,
2736         ")",
2737         |item| item.span().lo(),
2738         |item| item.span().hi(),
2739         |item| item.rewrite(context, nested_shape),
2740         list_lo,
2741         span.hi() - BytePos(1),
2742         false,
2743     );
2744     let item_vec: Vec<_> = items.collect();
2745     let tactic = definitive_tactic(
2746         &item_vec,
2747         ListTactic::HorizontalVertical,
2748         Separator::Comma,
2749         nested_shape.width,
2750     );
2751     let fmt = ListFormatting {
2752         tactic: tactic,
2753         separator: ",",
2754         trailing_separator: SeparatorTactic::Never,
2755         separator_place: SeparatorPlace::Back,
2756         shape: shape,
2757         ends_with_newline: false,
2758         preserve_newline: false,
2759         config: context.config,
2760     };
2761     let list_str = try_opt!(write_list(&item_vec, &fmt));
2762
2763     if context.config.spaces_within_parens() && !list_str.is_empty() {
2764         Some(format!("( {} )", list_str))
2765     } else {
2766         Some(format!("({})", list_str))
2767     }
2768 }
2769
2770 pub fn rewrite_tuple<'a, T>(
2771     context: &RewriteContext,
2772     items: &[&T],
2773     span: Span,
2774     shape: Shape,
2775 ) -> Option<String>
2776 where
2777     T: Rewrite + Spanned + ToExpr + 'a,
2778 {
2779     debug!("rewrite_tuple {:?}", shape);
2780     if context.use_block_indent() {
2781         // We use the same rule as function calls for rewriting tuples.
2782         let force_trailing_comma = if context.inside_macro {
2783             span_ends_with_comma(context, span)
2784         } else {
2785             items.len() == 1
2786         };
2787         rewrite_call_inner(
2788             context,
2789             &String::new(),
2790             items,
2791             span,
2792             shape,
2793             context.config.fn_call_width(),
2794             force_trailing_comma,
2795         )
2796     } else {
2797         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2798     }
2799 }
2800
2801 pub fn rewrite_unary_prefix<R: Rewrite>(
2802     context: &RewriteContext,
2803     prefix: &str,
2804     rewrite: &R,
2805     shape: Shape,
2806 ) -> Option<String> {
2807     rewrite
2808         .rewrite(context, try_opt!(shape.offset_left(prefix.len())))
2809         .map(|r| format!("{}{}", prefix, r))
2810 }
2811
2812 // FIXME: this is probably not correct for multi-line Rewrites. we should
2813 // subtract suffix.len() from the last line budget, not the first!
2814 pub fn rewrite_unary_suffix<R: Rewrite>(
2815     context: &RewriteContext,
2816     suffix: &str,
2817     rewrite: &R,
2818     shape: Shape,
2819 ) -> Option<String> {
2820     rewrite
2821         .rewrite(context, try_opt!(shape.sub_width(suffix.len())))
2822         .map(|mut r| {
2823             r.push_str(suffix);
2824             r
2825         })
2826 }
2827
2828 fn rewrite_unary_op(
2829     context: &RewriteContext,
2830     op: &ast::UnOp,
2831     expr: &ast::Expr,
2832     shape: Shape,
2833 ) -> Option<String> {
2834     // For some reason, an UnOp is not spanned like BinOp!
2835     let operator_str = match *op {
2836         ast::UnOp::Deref => "*",
2837         ast::UnOp::Not => "!",
2838         ast::UnOp::Neg => "-",
2839     };
2840     rewrite_unary_prefix(context, operator_str, expr, shape)
2841 }
2842
2843 fn rewrite_assignment(
2844     context: &RewriteContext,
2845     lhs: &ast::Expr,
2846     rhs: &ast::Expr,
2847     op: Option<&ast::BinOp>,
2848     shape: Shape,
2849 ) -> Option<String> {
2850     let operator_str = match op {
2851         Some(op) => context.snippet(op.span),
2852         None => "=".to_owned(),
2853     };
2854
2855     // 1 = space between lhs and operator.
2856     let lhs_shape = try_opt!(shape.sub_width(operator_str.len() + 1));
2857     let lhs_str = format!(
2858         "{} {}",
2859         try_opt!(lhs.rewrite(context, lhs_shape)),
2860         operator_str
2861     );
2862
2863     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2864 }
2865
2866 // The left hand side must contain everything up to, and including, the
2867 // assignment operator.
2868 pub fn rewrite_assign_rhs<S: Into<String>>(
2869     context: &RewriteContext,
2870     lhs: S,
2871     ex: &ast::Expr,
2872     shape: Shape,
2873 ) -> Option<String> {
2874     let lhs = lhs.into();
2875     let last_line_width = last_line_width(&lhs) - if lhs.contains('\n') {
2876         shape.indent.width()
2877     } else {
2878         0
2879     };
2880     // 1 = space between operator and rhs.
2881     let orig_shape = try_opt!(shape.offset_left(last_line_width + 1));
2882     let rhs = try_opt!(choose_rhs(
2883         context,
2884         ex,
2885         orig_shape,
2886         ex.rewrite(context, orig_shape)
2887     ));
2888     Some(lhs + &rhs)
2889 }
2890
2891 fn choose_rhs(
2892     context: &RewriteContext,
2893     expr: &ast::Expr,
2894     shape: Shape,
2895     orig_rhs: Option<String>,
2896 ) -> Option<String> {
2897     match orig_rhs {
2898         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2899             Some(format!(" {}", new_str))
2900         }
2901         _ => {
2902             // Expression did not fit on the same line as the identifier.
2903             // Try splitting the line and see if that works better.
2904             let new_shape = try_opt!(
2905                 Shape::indented(
2906                     shape.block().indent.block_indent(context.config),
2907                     context.config,
2908                 ).sub_width(shape.rhs_overhead(context.config))
2909             );
2910             let new_rhs = expr.rewrite(context, new_shape);
2911             let new_indent_str = &new_shape.indent.to_string(context.config);
2912
2913             match (orig_rhs, new_rhs) {
2914                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2915                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2916                 }
2917                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2918                 (None, None) => None,
2919                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2920             }
2921         }
2922     }
2923 }
2924
2925 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2926     fn count_line_breaks(src: &str) -> usize {
2927         src.chars().filter(|&x| x == '\n').count()
2928     }
2929
2930     !next_line_rhs.contains('\n')
2931         || count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2932 }
2933
2934 fn rewrite_expr_addrof(
2935     context: &RewriteContext,
2936     mutability: ast::Mutability,
2937     expr: &ast::Expr,
2938     shape: Shape,
2939 ) -> Option<String> {
2940     let operator_str = match mutability {
2941         ast::Mutability::Immutable => "&",
2942         ast::Mutability::Mutable => "&mut ",
2943     };
2944     rewrite_unary_prefix(context, operator_str, expr, shape)
2945 }
2946
2947 pub trait ToExpr {
2948     fn to_expr(&self) -> Option<&ast::Expr>;
2949     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2950 }
2951
2952 impl ToExpr for ast::Expr {
2953     fn to_expr(&self) -> Option<&ast::Expr> {
2954         Some(self)
2955     }
2956
2957     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2958         can_be_overflowed_expr(context, self, len)
2959     }
2960 }
2961
2962 impl ToExpr for ast::Ty {
2963     fn to_expr(&self) -> Option<&ast::Expr> {
2964         None
2965     }
2966
2967     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2968         can_be_overflowed_type(context, self, len)
2969     }
2970 }
2971
2972 impl<'a> ToExpr for TuplePatField<'a> {
2973     fn to_expr(&self) -> Option<&ast::Expr> {
2974         None
2975     }
2976
2977     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2978         can_be_overflowed_pat(context, self, len)
2979     }
2980 }
2981
2982 impl<'a> ToExpr for ast::StructField {
2983     fn to_expr(&self) -> Option<&ast::Expr> {
2984         None
2985     }
2986
2987     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2988         false
2989     }
2990 }
2991
2992 impl<'a> ToExpr for MacroArg {
2993     fn to_expr(&self) -> Option<&ast::Expr> {
2994         match *self {
2995             MacroArg::Expr(ref expr) => Some(expr),
2996             _ => None,
2997         }
2998     }
2999
3000     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3001         match *self {
3002             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
3003             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
3004             MacroArg::Pat(..) => false,
3005         }
3006     }
3007 }