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, Ordering};
  12 use std::fmt::Write;
  13 use std::iter::ExactSizeIterator;
  14
  15 use syntax::{ast, ptr};
  16 use syntax::codemap::{BytePos, CodeMap, Span};
  17 use syntax::parse::classify;
  18
  19 use {Indent, Shape, Spanned};
  20 use chains::rewrite_chain;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use comment::{contains_comment, recover_comment_removed, rewrite_comment, FindUncommented};
  23 use config::{Config, ControlBraceStyle, IndentStyle, MultilineStyle, Style};
  24 use items::{span_hi_for_arg, span_lo_for_arg};
  25 use lists::{definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting,
  26             struct_lit_shape, struct_lit_tactic, write_list, DefinitiveListTactic, ListFormatting,
  27             ListItem, ListTactic, Separator, SeparatorTactic};
  28 use macros::{rewrite_macro, MacroPosition};
  29 use patterns::{can_be_overflowed_pat, TuplePatField};
  30 use rewrite::{Rewrite, RewriteContext};
  31 use string::{rewrite_string, StringFormat};
  32 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  33 use utils::{binary_search, colon_spaces, contains_skip, extra_offset, first_line_width,
  34             last_line_extendable, last_line_width, left_most_sub_expr, mk_sp, paren_overhead,
  35             semicolon_for_stmt, stmt_expr, trimmed_last_line_width, wrap_str};
  36 use vertical::rewrite_with_alignment;
  37 use visitor::FmtVisitor;
  38
  39 impl Rewrite for ast::Expr {
  40     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  41         format_expr(self, ExprType::SubExpression, context, shape)
  42     }
  43 }
  44
  45 #[derive(PartialEq)]
  46 pub enum ExprType {
  47     Statement,
  48     SubExpression,
  49 }
  50
  51 fn combine_attr_and_expr(
  52     context: &RewriteContext,
  53     shape: Shape,
  54     expr: &ast::Expr,
  55     expr_str: &str,
  56 ) -> Option<String> {
  57     let attr_str = try_opt!((&*expr.attrs).rewrite(context, shape));
  58     let separator = if attr_str.is_empty() {
  59         String::new()
  60     } else {
  61         // Try to recover comments between the attributes and the expression if available.
  62         let missing_snippet = context.snippet(mk_sp(
  63             expr.attrs[expr.attrs.len() - 1].span.hi,
  64             expr.span.lo,
  65         ));
  66         let comment_opening_pos = missing_snippet.chars().position(|c| c == '/');
  67         let prefer_same_line = if let Some(pos) = comment_opening_pos {
  68             !missing_snippet[..pos].contains('\n')
  69         } else {
  70             !missing_snippet.contains('\n')
  71         };
  72
  73         let trimmed = missing_snippet.trim();
  74         let missing_comment = if trimmed.is_empty() {
  75             String::new()
  76         } else {
  77             try_opt!(rewrite_comment(&trimmed, false, shape, context.config))
  78         };
  79
  80         // 2 = ` ` + ` `
  81         let one_line_width =
  82             attr_str.len() + missing_comment.len() + 2 + first_line_width(expr_str);
  83         let attr_expr_separator = if prefer_same_line && !missing_comment.starts_with("//") &&
  84             one_line_width <= shape.width
  85         {
  86             String::from(" ")
  87         } else {
  88             format!("\n{}", shape.indent.to_string(context.config))
  89         };
  90
  91         if missing_comment.is_empty() {
  92             attr_expr_separator
  93         } else {
  94             // 1 = ` `
  95             let one_line_width =
  96                 last_line_width(&attr_str) + 1 + first_line_width(&missing_comment);
  97             let attr_comment_separator = if prefer_same_line && one_line_width <= shape.width {
  98                 String::from(" ")
  99             } else {
 100                 format!("\n{}", shape.indent.to_string(context.config))
 101             };
 102             attr_comment_separator + &missing_comment + &attr_expr_separator
 103         }
 104     };
 105     Some(format!("{}{}{}", attr_str, separator, expr_str))
 106 }
 107
 108 pub fn format_expr(
 109     expr: &ast::Expr,
 110     expr_type: ExprType,
 111     context: &RewriteContext,
 112     shape: Shape,
 113 ) -> Option<String> {
 114     skip_out_of_file_lines_range!(context, expr.span);
 115
 116     if contains_skip(&*expr.attrs) {
 117         return Some(context.snippet(expr.span()));
 118     }
 119
 120     let expr_rw = match expr.node {
 121         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
 122             expr_vec.iter().map(|e| &**e),
 123             mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi),
 124             context,
 125             shape,
 126             false,
 127         ),
 128         ast::ExprKind::Lit(ref l) => match l.node {
 129             ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
 130                 rewrite_string_lit(context, l.span, shape)
 131             }
 132             _ => wrap_str(
 133                 context.snippet(expr.span),
 134                 context.config.max_width(),
 135                 shape,
 136             ),
 137         },
 138         ast::ExprKind::Call(ref callee, ref args) => {
 139             let inner_span = mk_sp(callee.span.hi, expr.span.hi);
 140             rewrite_call_with_binary_search(
 141                 context,
 142                 &**callee,
 143                 &args.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 144                 inner_span,
 145                 shape,
 146             )
 147         }
 148         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
 149         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
 150             // FIXME: format comments between operands and operator
 151             rewrite_pair(
 152                 &**lhs,
 153                 &**rhs,
 154                 "",
 155                 &format!(" {} ", context.snippet(op.span)),
 156                 "",
 157                 context,
 158                 shape,
 159             )
 160         }
 161         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 162         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 163             context,
 164             path,
 165             fields,
 166             base.as_ref().map(|e| &**e),
 167             expr.span,
 168             shape,
 169         ),
 170         ast::ExprKind::Tup(ref items) => rewrite_tuple(
 171             context,
 172             &items.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 173             expr.span,
 174             shape,
 175         ),
 176         ast::ExprKind::If(..) |
 177         ast::ExprKind::IfLet(..) |
 178         ast::ExprKind::ForLoop(..) |
 179         ast::ExprKind::Loop(..) |
 180         ast::ExprKind::While(..) |
 181         ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 182             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 183         ast::ExprKind::Block(ref block) => {
 184             match expr_type {
 185                 ExprType::Statement => {
 186                     if is_unsafe_block(block) {
 187                         block.rewrite(context, shape)
 188                     } else {
 189                         // Rewrite block without trying to put it in a single line.
 190                         if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 191                             return rw;
 192                         }
 193                         let prefix = try_opt!(block_prefix(context, block, shape));
 194                         rewrite_block_with_visitor(context, &prefix, block, shape)
 195                     }
 196                 }
 197                 ExprType::SubExpression => block.rewrite(context, shape),
 198             }
 199         }
 200         ast::ExprKind::Match(ref cond, ref arms) => {
 201             rewrite_match(context, cond, arms, shape, expr.span)
 202         }
 203         ast::ExprKind::Path(ref qself, ref path) => {
 204             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 205         }
 206         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 207             rewrite_assignment(context, lhs, rhs, None, shape)
 208         }
 209         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 210             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 211         }
 212         ast::ExprKind::Continue(ref opt_ident) => {
 213             let id_str = match *opt_ident {
 214                 Some(ident) => format!(" {}", ident.node),
 215                 None => String::new(),
 216             };
 217             wrap_str(
 218                 format!("continue{}", id_str),
 219                 context.config.max_width(),
 220                 shape,
 221             )
 222         }
 223         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 224             let id_str = match *opt_ident {
 225                 Some(ident) => format!(" {}", ident.node),
 226                 None => String::new(),
 227             };
 228
 229             if let Some(ref expr) = *opt_expr {
 230                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 231             } else {
 232                 wrap_str(
 233                     format!("break{}", id_str),
 234                     context.config.max_width(),
 235                     shape,
 236                 )
 237             }
 238         }
 239         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 240             rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 241         }
 242         ast::ExprKind::Try(..) |
 243         ast::ExprKind::Field(..) |
 244         ast::ExprKind::TupField(..) |
 245         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 246         ast::ExprKind::Mac(ref mac) => {
 247             // Failure to rewrite a marco should not imply failure to
 248             // rewrite the expression.
 249             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 250                 wrap_str(
 251                     context.snippet(expr.span),
 252                     context.config.max_width(),
 253                     shape,
 254                 )
 255             })
 256         }
 257         ast::ExprKind::Ret(None) => {
 258             wrap_str("return".to_owned(), context.config.max_width(), shape)
 259         }
 260         ast::ExprKind::Ret(Some(ref expr)) => {
 261             rewrite_unary_prefix(context, "return ", &**expr, shape)
 262         }
 263         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 264         ast::ExprKind::AddrOf(mutability, ref expr) => {
 265             rewrite_expr_addrof(context, mutability, expr, shape)
 266         }
 267         ast::ExprKind::Cast(ref expr, ref ty) => {
 268             rewrite_pair(&**expr, &**ty, "", " as ", "", context, shape)
 269         }
 270         ast::ExprKind::Type(ref expr, ref ty) => {
 271             rewrite_pair(&**expr, &**ty, "", ": ", "", context, shape)
 272         }
 273         ast::ExprKind::Index(ref expr, ref index) => {
 274             rewrite_index(&**expr, &**index, context, shape)
 275         }
 276         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 277             let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
 278                 ("[ ", " ]")
 279             } else {
 280                 ("[", "]")
 281             };
 282             rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, shape)
 283         }
 284         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 285             let delim = match limits {
 286                 ast::RangeLimits::HalfOpen => "..",
 287                 ast::RangeLimits::Closed => "...",
 288             };
 289
 290             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 291                 match lhs.node {
 292                     ast::ExprKind::Lit(ref lit) => match lit.node {
 293                         ast::LitKind::FloatUnsuffixed(..) => {
 294                             context.snippet(lit.span).ends_with('.')
 295                         }
 296                         _ => false,
 297                     },
 298                     _ => false,
 299                 }
 300             }
 301
 302             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 303                 (Some(ref lhs), Some(ref rhs)) => {
 304                     let sp_delim = if context.config.spaces_around_ranges() {
 305                         format!(" {} ", delim)
 306                     } else if needs_space_before_range(context, lhs) {
 307                         format!(" {}", delim)
 308                     } else {
 309                         delim.into()
 310                     };
 311                     rewrite_pair(&**lhs, &**rhs, "", &sp_delim, "", context, shape)
 312                 }
 313                 (None, Some(ref rhs)) => {
 314                     let sp_delim = if context.config.spaces_around_ranges() {
 315                         format!("{} ", delim)
 316                     } else {
 317                         delim.into()
 318                     };
 319                     rewrite_unary_prefix(context, &sp_delim, &**rhs, shape)
 320                 }
 321                 (Some(ref lhs), None) => {
 322                     let sp_delim = if context.config.spaces_around_ranges() {
 323                         format!(" {}", delim)
 324                     } else {
 325                         delim.into()
 326                     };
 327                     rewrite_unary_suffix(context, &sp_delim, &**lhs, shape)
 328                 }
 329                 (None, None) => wrap_str(delim.into(), context.config.max_width(), shape),
 330             }
 331         }
 332         // We do not format these expressions yet, but they should still
 333         // satisfy our width restrictions.
 334         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => wrap_str(
 335             context.snippet(expr.span),
 336             context.config.max_width(),
 337             shape,
 338         ),
 339         ast::ExprKind::Catch(ref block) => {
 340             if let rewrite @ Some(_) = rewrite_single_line_block(context, "do catch ", block, shape)
 341             {
 342                 return rewrite;
 343             }
 344             // 9 = `do catch `
 345             let budget = shape.width.checked_sub(9).unwrap_or(0);
 346             Some(format!(
 347                 "{}{}",
 348                 "do catch ",
 349                 try_opt!(block.rewrite(&context, Shape::legacy(budget, shape.indent)))
 350             ))
 351         }
 352     };
 353
 354     expr_rw
 355         .and_then(|expr_str| {
 356             recover_comment_removed(expr_str, expr.span, context, shape)
 357         })
 358         .and_then(|expr_str| {
 359             combine_attr_and_expr(context, shape, expr, &expr_str)
 360         })
 361 }
 362
 363 pub fn rewrite_pair<LHS, RHS>(
 364     lhs: &LHS,
 365     rhs: &RHS,
 366     prefix: &str,
 367     infix: &str,
 368     suffix: &str,
 369     context: &RewriteContext,
 370     shape: Shape,
 371 ) -> Option<String>
 372 where
 373     LHS: Rewrite,
 374     RHS: Rewrite,
 375 {
 376     let sep = if infix.ends_with(' ') { " " } else { "" };
 377     let infix = infix.trim_right();
 378     let lhs_overhead = shape.used_width() + prefix.len() + infix.len();
 379     let lhs_shape = Shape {
 380         width: try_opt!(context.config.max_width().checked_sub(lhs_overhead)),
 381         ..shape
 382     };
 383     let lhs_result = try_opt!(
 384         lhs.rewrite(context, lhs_shape)
 385             .map(|lhs_str| format!("{}{}{}", prefix, lhs_str, infix))
 386     );
 387
 388     // Try to the both lhs and rhs on the same line.
 389     let rhs_orig_result = shape
 390         .offset_left(last_line_width(&lhs_result) + suffix.len() + sep.len())
 391         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 392     if let Some(ref rhs_result) = rhs_orig_result {
 393         // If the rhs looks like block expression, we allow it to stay on the same line
 394         // with the lhs even if it is multi-lined.
 395         let allow_same_line = rhs_result
 396             .lines()
 397             .next()
 398             .map(|first_line| first_line.ends_with('{'))
 399             .unwrap_or(false);
 400         if !rhs_result.contains('\n') || allow_same_line {
 401             return Some(format!("{}{}{}{}", lhs_result, sep, rhs_result, suffix));
 402         }
 403     }
 404
 405     // We have to use multiple lines.
 406     // Re-evaluate the rhs because we have more space now:
 407     let rhs_shape = match context.config.control_style() {
 408         Style::Legacy => {
 409             try_opt!(shape.sub_width(suffix.len() + prefix.len())).visual_indent(prefix.len())
 410         }
 411         Style::Rfc => {
 412             // Try to calculate the initial constraint on the right hand side.
 413             let rhs_overhead = shape.rhs_overhead(context.config);
 414             try_opt!(
 415                 Shape::indented(shape.indent.block_indent(context.config), context.config)
 416                     .sub_width(rhs_overhead)
 417             )
 418         }
 419     };
 420     let rhs_result = try_opt!(rhs.rewrite(context, rhs_shape));
 421     Some(format!(
 422         "{}\n{}{}{}",
 423         lhs_result,
 424         rhs_shape.indent.to_string(context.config),
 425         rhs_result,
 426         suffix
 427     ))
 428 }
 429
 430 pub fn rewrite_array<'a, I>(
 431     expr_iter: I,
 432     span: Span,
 433     context: &RewriteContext,
 434     shape: Shape,
 435     trailing_comma: bool,
 436 ) -> Option<String>
 437 where
 438     I: Iterator<Item = &'a ast::Expr>,
 439 {
 440     let bracket_size = if context.config.spaces_within_square_brackets() {
 441         2 // "[ "
 442     } else {
 443         1 // "["
 444     };
 445
 446     let mut nested_shape = match context.config.array_layout() {
 447         IndentStyle::Block => try_opt!(
 448             shape
 449                 .block()
 450                 .block_indent(context.config.tab_spaces())
 451                 .with_max_width(context.config)
 452                 .sub_width(1)
 453         ),
 454         IndentStyle::Visual => try_opt!(
 455             shape
 456                 .visual_indent(bracket_size)
 457                 .sub_width(bracket_size * 2)
 458         ),
 459     };
 460
 461     let items = itemize_list(
 462         context.codemap,
 463         expr_iter,
 464         "]",
 465         |item| item.span.lo,
 466         |item| item.span.hi,
 467         |item| item.rewrite(context, nested_shape),
 468         span.lo,
 469         span.hi,
 470     ).collect::<Vec<_>>();
 471
 472     if items.is_empty() {
 473         if context.config.spaces_within_square_brackets() {
 474             return Some("[ ]".to_string());
 475         } else {
 476             return Some("[]".to_string());
 477         }
 478     }
 479
 480     let has_long_item = items
 481         .iter()
 482         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 483
 484     let mut tactic = match context.config.array_layout() {
 485         IndentStyle::Block => {
 486             // FIXME wrong shape in one-line case
 487             match shape.width.checked_sub(2 * bracket_size) {
 488                 Some(width) => {
 489                     let tactic =
 490                         ListTactic::LimitedHorizontalVertical(context.config.array_width());
 491                     definitive_tactic(&items, tactic, Separator::Comma, width)
 492                 }
 493                 None => DefinitiveListTactic::Vertical,
 494             }
 495         }
 496         IndentStyle::Visual => if has_long_item || items.iter().any(ListItem::is_multiline) {
 497             definitive_tactic(
 498                 &items,
 499                 ListTactic::LimitedHorizontalVertical(context.config.array_width()),
 500                 Separator::Comma,
 501                 nested_shape.width,
 502             )
 503         } else {
 504             DefinitiveListTactic::Mixed
 505         },
 506     };
 507     let mut ends_with_newline = tactic.ends_with_newline(context.config.array_layout());
 508     if context.config.array_horizontal_layout_threshold() > 0 &&
 509         items.len() > context.config.array_horizontal_layout_threshold()
 510     {
 511         tactic = DefinitiveListTactic::Mixed;
 512         ends_with_newline = false;
 513         if context.config.array_layout() == IndentStyle::Block {
 514             nested_shape = try_opt!(
 515                 shape
 516                     .visual_indent(bracket_size)
 517                     .sub_width(bracket_size * 2)
 518             );
 519         }
 520     }
 521
 522     let fmt = ListFormatting {
 523         tactic: tactic,
 524         separator: ",",
 525         trailing_separator: if trailing_comma {
 526             SeparatorTactic::Always
 527         } else if context.inside_macro || context.config.array_layout() == IndentStyle::Visual {
 528             SeparatorTactic::Never
 529         } else {
 530             SeparatorTactic::Vertical
 531         },
 532         shape: nested_shape,
 533         ends_with_newline: ends_with_newline,
 534         preserve_newline: false,
 535         config: context.config,
 536     };
 537     let list_str = try_opt!(write_list(&items, &fmt));
 538
 539     let result = if context.config.array_layout() == IndentStyle::Visual ||
 540         tactic != DefinitiveListTactic::Vertical
 541     {
 542         if context.config.spaces_within_square_brackets() && list_str.len() > 0 {
 543             format!("[ {} ]", list_str)
 544         } else {
 545             format!("[{}]", list_str)
 546         }
 547     } else {
 548         format!(
 549             "[\n{}{}\n{}]",
 550             nested_shape.indent.to_string(context.config),
 551             list_str,
 552             shape.block().indent.to_string(context.config)
 553         )
 554     };
 555
 556     Some(result)
 557 }
 558
 559 // Return type is (prefix, extra_offset)
 560 fn rewrite_closure_fn_decl(
 561     capture: ast::CaptureBy,
 562     fn_decl: &ast::FnDecl,
 563     body: &ast::Expr,
 564     span: Span,
 565     context: &RewriteContext,
 566     shape: Shape,
 567 ) -> Option<(String, usize)> {
 568     let mover = if capture == ast::CaptureBy::Value {
 569         "move "
 570     } else {
 571         ""
 572     };
 573     // 4 = "|| {".len(), which is overconservative when the closure consists of
 574     // a single expression.
 575     let nested_shape = try_opt!(try_opt!(shape.shrink_left(mover.len())).sub_width(4));
 576
 577     // 1 = |
 578     let argument_offset = nested_shape.indent + 1;
 579     let arg_shape = try_opt!(nested_shape.offset_left(1)).visual_indent(0);
 580     let ret_str = try_opt!(fn_decl.output.rewrite(context, arg_shape));
 581
 582     let arg_items = itemize_list(
 583         context.codemap,
 584         fn_decl.inputs.iter(),
 585         "|",
 586         |arg| span_lo_for_arg(arg),
 587         |arg| span_hi_for_arg(context, arg),
 588         |arg| arg.rewrite(context, arg_shape),
 589         context.codemap.span_after(span, "|"),
 590         body.span.lo,
 591     );
 592     let item_vec = arg_items.collect::<Vec<_>>();
 593     // 1 = space between arguments and return type.
 594     let horizontal_budget = nested_shape
 595         .width
 596         .checked_sub(ret_str.len() + 1)
 597         .unwrap_or(0);
 598     let tactic = definitive_tactic(
 599         &item_vec,
 600         ListTactic::HorizontalVertical,
 601         Separator::Comma,
 602         horizontal_budget,
 603     );
 604     let arg_shape = match tactic {
 605         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 606         _ => arg_shape,
 607     };
 608
 609     let fmt = ListFormatting {
 610         tactic: tactic,
 611         separator: ",",
 612         trailing_separator: SeparatorTactic::Never,
 613         shape: arg_shape,
 614         ends_with_newline: false,
 615         preserve_newline: true,
 616         config: context.config,
 617     };
 618     let list_str = try_opt!(write_list(&item_vec, &fmt));
 619     let mut prefix = format!("{}|{}|", mover, list_str);
 620     // 1 = space between `|...|` and body.
 621     let extra_offset = extra_offset(&prefix, shape) + 1;
 622
 623     if !ret_str.is_empty() {
 624         if prefix.contains('\n') {
 625             prefix.push('\n');
 626             prefix.push_str(&argument_offset.to_string(context.config));
 627         } else {
 628             prefix.push(' ');
 629         }
 630         prefix.push_str(&ret_str);
 631     }
 632
 633     Some((prefix, extra_offset))
 634 }
 635
 636 // This functions is pretty messy because of the rules around closures and blocks:
 637 // FIXME - the below is probably no longer true in full.
 638 //   * if there is a return type, then there must be braces,
 639 //   * given a closure with braces, whether that is parsed to give an inner block
 640 //     or not depends on if there is a return type and if there are statements
 641 //     in that block,
 642 //   * if the first expression in the body ends with a block (i.e., is a
 643 //     statement without needing a semi-colon), then adding or removing braces
 644 //     can change whether it is treated as an expression or statement.
 645 fn rewrite_closure(
 646     capture: ast::CaptureBy,
 647     fn_decl: &ast::FnDecl,
 648     body: &ast::Expr,
 649     span: Span,
 650     context: &RewriteContext,
 651     shape: Shape,
 652 ) -> Option<String> {
 653     let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
 654         capture,
 655         fn_decl,
 656         body,
 657         span,
 658         context,
 659         shape,
 660     ));
 661     // 1 = space between `|...|` and body.
 662     let body_shape = try_opt!(shape.offset_left(extra_offset));
 663
 664     if let ast::ExprKind::Block(ref block) = body.node {
 665         // The body of the closure is an empty block.
 666         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 667             return Some(format!("{} {{}}", prefix));
 668         }
 669
 670         // Figure out if the block is necessary.
 671         let needs_block = block.rules != ast::BlockCheckMode::Default || block.stmts.len() > 1 ||
 672             context.inside_macro ||
 673             block_contains_comment(block, context.codemap) ||
 674             prefix.contains('\n');
 675
 676         let no_return_type = if let ast::FunctionRetTy::Default(_) = fn_decl.output {
 677             true
 678         } else {
 679             false
 680         };
 681         if no_return_type && !needs_block {
 682             // lock.stmts.len() == 1
 683             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 684                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 685                     return Some(rw);
 686                 }
 687             }
 688         }
 689
 690         if !needs_block {
 691             // We need braces, but we might still prefer a one-liner.
 692             let stmt = &block.stmts[0];
 693             // 4 = braces and spaces.
 694             if let Some(body_shape) = body_shape.sub_width(4) {
 695                 // Checks if rewrite succeeded and fits on a single line.
 696                 if let Some(rewrite) = and_one_line(stmt.rewrite(context, body_shape)) {
 697                     return Some(format!("{} {{ {} }}", prefix, rewrite));
 698                 }
 699             }
 700         }
 701
 702         // Either we require a block, or tried without and failed.
 703         rewrite_closure_block(&block, &prefix, context, body_shape)
 704     } else {
 705         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
 706             // The closure originally had a non-block expression, but we can't fit on
 707             // one line, so we'll insert a block.
 708             rewrite_closure_with_block(context, body_shape, &prefix, body)
 709         })
 710     }
 711 }
 712
 713 // Rewrite closure with a single expression wrapping its body with block.
 714 fn rewrite_closure_with_block(
 715     context: &RewriteContext,
 716     shape: Shape,
 717     prefix: &str,
 718     body: &ast::Expr,
 719 ) -> Option<String> {
 720     let block = ast::Block {
 721         stmts: vec![
 722             ast::Stmt {
 723                 id: ast::NodeId::new(0),
 724                 node: ast::StmtKind::Expr(ptr::P(body.clone())),
 725                 span: body.span,
 726             },
 727         ],
 728         id: ast::NodeId::new(0),
 729         rules: ast::BlockCheckMode::Default,
 730         span: body.span,
 731     };
 732     rewrite_closure_block(&block, prefix, context, shape)
 733 }
 734
 735 // Rewrite closure with a single expression without wrapping its body with block.
 736 fn rewrite_closure_expr(
 737     expr: &ast::Expr,
 738     prefix: &str,
 739     context: &RewriteContext,
 740     shape: Shape,
 741 ) -> Option<String> {
 742     let mut rewrite = expr.rewrite(context, shape);
 743     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 744         rewrite = and_one_line(rewrite);
 745     }
 746     rewrite.map(|rw| format!("{} {}", prefix, rw))
 747 }
 748
 749 // Rewrite closure whose body is block.
 750 fn rewrite_closure_block(
 751     block: &ast::Block,
 752     prefix: &str,
 753     context: &RewriteContext,
 754     shape: Shape,
 755 ) -> Option<String> {
 756     // Start with visual indent, then fall back to block indent if the
 757     // closure is large.
 758     let block_threshold = context.config.closure_block_indent_threshold();
 759     if block_threshold >= 0 {
 760         if let Some(block_str) = block.rewrite(&context, shape) {
 761             if block_str.matches('\n').count() <= block_threshold as usize &&
 762                 !need_block_indent(&block_str, shape)
 763             {
 764                 if let Some(block_str) = block_str.rewrite(context, shape) {
 765                     return Some(format!("{} {}", prefix, block_str));
 766                 }
 767             }
 768         }
 769     }
 770
 771     // The body of the closure is big enough to be block indented, that
 772     // means we must re-format.
 773     let block_shape = shape.block();
 774     let block_str = try_opt!(block.rewrite(&context, block_shape));
 775     Some(format!("{} {}", prefix, block_str))
 776 }
 777
 778 fn and_one_line(x: Option<String>) -> Option<String> {
 779     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 780 }
 781
 782 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 783     debug!("nop_block_collapse {:?} {}", block_str, budget);
 784     block_str.map(|block_str| {
 785         if block_str.starts_with('{') && budget >= 2 &&
 786             (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 787         {
 788             "{}".to_owned()
 789         } else {
 790             block_str.to_owned()
 791         }
 792     })
 793 }
 794
 795 fn rewrite_empty_block(
 796     context: &RewriteContext,
 797     block: &ast::Block,
 798     shape: Shape,
 799 ) -> Option<String> {
 800     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 801     {
 802         return Some("{}".to_owned());
 803     }
 804
 805     // If a block contains only a single-line comment, then leave it on one line.
 806     let user_str = context.snippet(block.span);
 807     let user_str = user_str.trim();
 808     if user_str.starts_with('{') && user_str.ends_with('}') {
 809         let comment_str = user_str[1..user_str.len() - 1].trim();
 810         if block.stmts.is_empty() && !comment_str.contains('\n') &&
 811             !comment_str.starts_with("//") && comment_str.len() + 4 <= shape.width
 812         {
 813             return Some(format!("{{ {} }}", comment_str));
 814         }
 815     }
 816
 817     None
 818 }
 819
 820 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 821     Some(match block.rules {
 822         ast::BlockCheckMode::Unsafe(..) => {
 823             let snippet = context.snippet(block.span);
 824             let open_pos = try_opt!(snippet.find_uncommented("{"));
 825             // Extract comment between unsafe and block start.
 826             let trimmed = &snippet[6..open_pos].trim();
 827
 828             if !trimmed.is_empty() {
 829                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 830                 let budget = try_opt!(shape.width.checked_sub(9));
 831                 format!(
 832                     "unsafe {} ",
 833                     try_opt!(rewrite_comment(
 834                         trimmed,
 835                         true,
 836                         Shape::legacy(budget, shape.indent + 7),
 837                         context.config,
 838                     ))
 839                 )
 840             } else {
 841                 "unsafe ".to_owned()
 842             }
 843         }
 844         ast::BlockCheckMode::Default => String::new(),
 845     })
 846 }
 847
 848 fn rewrite_single_line_block(
 849     context: &RewriteContext,
 850     prefix: &str,
 851     block: &ast::Block,
 852     shape: Shape,
 853 ) -> Option<String> {
 854     if is_simple_block(block, context.codemap) {
 855         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 856         let expr_str = try_opt!(block.stmts[0].rewrite(context, expr_shape));
 857         let result = format!("{}{{ {} }}", prefix, expr_str);
 858         if result.len() <= shape.width && !result.contains('\n') {
 859             return Some(result);
 860         }
 861     }
 862     None
 863 }
 864
 865 fn rewrite_block_with_visitor(
 866     context: &RewriteContext,
 867     prefix: &str,
 868     block: &ast::Block,
 869     shape: Shape,
 870 ) -> Option<String> {
 871     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 872         return rw;
 873     }
 874
 875     let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 876     visitor.block_indent = shape.indent;
 877     visitor.is_if_else_block = context.is_if_else_block;
 878     match block.rules {
 879         ast::BlockCheckMode::Unsafe(..) => {
 880             let snippet = context.snippet(block.span);
 881             let open_pos = try_opt!(snippet.find_uncommented("{"));
 882             visitor.last_pos = block.span.lo + BytePos(open_pos as u32)
 883         }
 884         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo,
 885     }
 886
 887     visitor.visit_block(block, None);
 888     Some(format!("{}{}", prefix, visitor.buffer))
 889 }
 890
 891 impl Rewrite for ast::Block {
 892     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 893         // shape.width is used only for the single line case: either the empty block `{}`,
 894         // or an unsafe expression `unsafe { e }`.
 895         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 896             return rw;
 897         }
 898
 899         let prefix = try_opt!(block_prefix(context, self, shape));
 900         if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 901             return rw;
 902         }
 903
 904         rewrite_block_with_visitor(context, &prefix, self, shape)
 905     }
 906 }
 907
 908 impl Rewrite for ast::Stmt {
 909     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 910         skip_out_of_file_lines_range!(context, self.span());
 911
 912         let result = match self.node {
 913             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 914             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 915                 let suffix = if semicolon_for_stmt(context, self) {
 916                     ";"
 917                 } else {
 918                     ""
 919                 };
 920
 921                 format_expr(
 922                     ex,
 923                     match self.node {
 924                         ast::StmtKind::Expr(_) => ExprType::SubExpression,
 925                         ast::StmtKind::Semi(_) => ExprType::Statement,
 926                         _ => unreachable!(),
 927                     },
 928                     context,
 929                     try_opt!(shape.sub_width(suffix.len())),
 930                 ).map(|s| s + suffix)
 931             }
 932             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 933         };
 934         result.and_then(|res| {
 935             recover_comment_removed(res, self.span(), context, shape)
 936         })
 937     }
 938 }
 939
 940 // Rewrite condition if the given expression has one.
 941 fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 942     match expr.node {
 943         ast::ExprKind::Match(ref cond, _) => {
 944             // `match `cond` {`
 945             let cond_shape = match context.config.control_style() {
 946                 Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
 947                 Style::Rfc => try_opt!(shape.offset_left(8)),
 948             };
 949             cond.rewrite(context, cond_shape)
 950         }
 951         ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
 952             stmt_expr(&block.stmts[0]).and_then(|e| rewrite_cond(context, e, shape))
 953         }
 954         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 955             let alt_block_sep =
 956                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 957             control_flow
 958                 .rewrite_cond(context, shape, &alt_block_sep)
 959                 .and_then(|rw| Some(rw.0))
 960         }),
 961     }
 962 }
 963
 964 // Abstraction over control flow expressions
 965 #[derive(Debug)]
 966 struct ControlFlow<'a> {
 967     cond: Option<&'a ast::Expr>,
 968     block: &'a ast::Block,
 969     else_block: Option<&'a ast::Expr>,
 970     label: Option<ast::SpannedIdent>,
 971     pat: Option<&'a ast::Pat>,
 972     keyword: &'a str,
 973     matcher: &'a str,
 974     connector: &'a str,
 975     allow_single_line: bool,
 976     // True if this is an `if` expression in an `else if` :-( hacky
 977     nested_if: bool,
 978     span: Span,
 979 }
 980
 981 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 982     match expr.node {
 983         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 984             cond,
 985             None,
 986             if_block,
 987             else_block.as_ref().map(|e| &**e),
 988             expr_type == ExprType::SubExpression,
 989             false,
 990             expr.span,
 991         )),
 992         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 993             Some(ControlFlow::new_if(
 994                 cond,
 995                 Some(pat),
 996                 if_block,
 997                 else_block.as_ref().map(|e| &**e),
 998                 expr_type == ExprType::SubExpression,
 999                 false,
1000                 expr.span,
1001             ))
1002         }
1003         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
1004             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
1005         }
1006         ast::ExprKind::Loop(ref block, label) => {
1007             Some(ControlFlow::new_loop(block, label, expr.span))
1008         }
1009         ast::ExprKind::While(ref cond, ref block, label) => {
1010             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
1011         }
1012         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
1013             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
1014         ),
1015         _ => None,
1016     }
1017 }
1018
1019 impl<'a> ControlFlow<'a> {
1020     fn new_if(
1021         cond: &'a ast::Expr,
1022         pat: Option<&'a ast::Pat>,
1023         block: &'a ast::Block,
1024         else_block: Option<&'a ast::Expr>,
1025         allow_single_line: bool,
1026         nested_if: bool,
1027         span: Span,
1028     ) -> ControlFlow<'a> {
1029         ControlFlow {
1030             cond: Some(cond),
1031             block: block,
1032             else_block: else_block,
1033             label: None,
1034             pat: pat,
1035             keyword: "if",
1036             matcher: match pat {
1037                 Some(..) => "let",
1038                 None => "",
1039             },
1040             connector: " =",
1041             allow_single_line: allow_single_line,
1042             nested_if: nested_if,
1043             span: span,
1044         }
1045     }
1046
1047     fn new_loop(
1048         block: &'a ast::Block,
1049         label: Option<ast::SpannedIdent>,
1050         span: Span,
1051     ) -> ControlFlow<'a> {
1052         ControlFlow {
1053             cond: None,
1054             block: block,
1055             else_block: None,
1056             label: label,
1057             pat: None,
1058             keyword: "loop",
1059             matcher: "",
1060             connector: "",
1061             allow_single_line: false,
1062             nested_if: false,
1063             span: span,
1064         }
1065     }
1066
1067     fn new_while(
1068         pat: Option<&'a ast::Pat>,
1069         cond: &'a ast::Expr,
1070         block: &'a ast::Block,
1071         label: Option<ast::SpannedIdent>,
1072         span: Span,
1073     ) -> ControlFlow<'a> {
1074         ControlFlow {
1075             cond: Some(cond),
1076             block: block,
1077             else_block: None,
1078             label: label,
1079             pat: pat,
1080             keyword: "while",
1081             matcher: match pat {
1082                 Some(..) => "let",
1083                 None => "",
1084             },
1085             connector: " =",
1086             allow_single_line: false,
1087             nested_if: false,
1088             span: span,
1089         }
1090     }
1091
1092     fn new_for(
1093         pat: &'a ast::Pat,
1094         cond: &'a ast::Expr,
1095         block: &'a ast::Block,
1096         label: Option<ast::SpannedIdent>,
1097         span: Span,
1098     ) -> ControlFlow<'a> {
1099         ControlFlow {
1100             cond: Some(cond),
1101             block: block,
1102             else_block: None,
1103             label: label,
1104             pat: Some(pat),
1105             keyword: "for",
1106             matcher: "",
1107             connector: " in",
1108             allow_single_line: false,
1109             nested_if: false,
1110             span: span,
1111         }
1112     }
1113
1114     fn rewrite_single_line(
1115         &self,
1116         pat_expr_str: &str,
1117         context: &RewriteContext,
1118         width: usize,
1119     ) -> Option<String> {
1120         assert!(self.allow_single_line);
1121         let else_block = try_opt!(self.else_block);
1122         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1123
1124         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1125             if !is_simple_block(self.block, context.codemap) ||
1126                 !is_simple_block(else_node, context.codemap) ||
1127                 pat_expr_str.contains('\n')
1128             {
1129                 return None;
1130             }
1131
1132             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
1133             let expr = &self.block.stmts[0];
1134             let if_str = try_opt!(expr.rewrite(
1135                 context,
1136                 Shape::legacy(new_width, Indent::empty()),
1137             ));
1138
1139             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
1140             let else_expr = &else_node.stmts[0];
1141             let else_str =
1142                 try_opt!(else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1143
1144             if if_str.contains('\n') || else_str.contains('\n') {
1145                 return None;
1146             }
1147
1148             let result = format!(
1149                 "{} {} {{ {} }} else {{ {} }}",
1150                 self.keyword,
1151                 pat_expr_str,
1152                 if_str,
1153                 else_str
1154             );
1155
1156             if result.len() <= width {
1157                 return Some(result);
1158             }
1159         }
1160
1161         None
1162     }
1163 }
1164
1165 impl<'a> ControlFlow<'a> {
1166     fn rewrite_cond(
1167         &self,
1168         context: &RewriteContext,
1169         shape: Shape,
1170         alt_block_sep: &str,
1171     ) -> Option<(String, usize)> {
1172         // Do not take the rhs overhead from the upper expressions into account
1173         // when rewriting pattern.
1174         let new_width = context
1175             .config
1176             .max_width()
1177             .checked_sub(shape.used_width())
1178             .unwrap_or(0);
1179         let fresh_shape = Shape {
1180             width: new_width,
1181             ..shape
1182         };
1183         let constr_shape = if self.nested_if {
1184             // We are part of an if-elseif-else chain. Our constraints are tightened.
1185             // 7 = "} else " .len()
1186             try_opt!(fresh_shape.offset_left(7))
1187         } else {
1188             fresh_shape
1189         };
1190
1191         let label_string = rewrite_label(self.label);
1192         // 1 = space after keyword.
1193         let offset = self.keyword.len() + label_string.len() + 1;
1194
1195         let pat_expr_string = match self.cond {
1196             Some(cond) => {
1197                 let cond_shape = match context.config.control_style() {
1198                     Style::Legacy => try_opt!(constr_shape.shrink_left(offset)),
1199                     Style::Rfc => try_opt!(constr_shape.offset_left(offset)),
1200                 };
1201                 try_opt!(rewrite_pat_expr(
1202                     context,
1203                     self.pat,
1204                     cond,
1205                     self.matcher,
1206                     self.connector,
1207                     self.keyword,
1208                     cond_shape,
1209                 ))
1210             }
1211             None => String::new(),
1212         };
1213
1214         let brace_overhead =
1215             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1216                 // 2 = ` {`
1217                 2
1218             } else {
1219                 0
1220             };
1221         let one_line_budget = context
1222             .config
1223             .max_width()
1224             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1225             .unwrap_or(0);
1226         let force_newline_brace = context.config.control_style() == Style::Rfc &&
1227             (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget) &&
1228             !last_line_extendable(&pat_expr_string);
1229
1230         // Try to format if-else on single line.
1231         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1232             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1233
1234             if let Some(cond_str) = trial {
1235                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1236                     return Some((cond_str, 0));
1237                 }
1238             }
1239         }
1240
1241         let cond_span = if let Some(cond) = self.cond {
1242             cond.span
1243         } else {
1244             mk_sp(self.block.span.lo, self.block.span.lo)
1245         };
1246
1247         // for event in event
1248         let between_kwd_cond = mk_sp(
1249             context.codemap.span_after(self.span, self.keyword.trim()),
1250             self.pat.map_or(
1251                 cond_span.lo,
1252                 |p| if self.matcher.is_empty() {
1253                     p.span.lo
1254                 } else {
1255                     context.codemap.span_before(self.span, self.matcher.trim())
1256                 },
1257             ),
1258         );
1259
1260         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1261
1262         let after_cond_comment =
1263             extract_comment(mk_sp(cond_span.hi, self.block.span.lo), context, shape);
1264
1265         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1266             ""
1267         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine ||
1268             force_newline_brace
1269         {
1270             alt_block_sep
1271         } else {
1272             " "
1273         };
1274
1275         let used_width = if pat_expr_string.contains('\n') {
1276             last_line_width(&pat_expr_string)
1277         } else {
1278             // 2 = spaces after keyword and condition.
1279             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1280         };
1281
1282         Some((
1283             format!(
1284                 "{}{}{}{}{}",
1285                 label_string,
1286                 self.keyword,
1287                 between_kwd_cond_comment.as_ref().map_or(
1288                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1289                         ""
1290                     } else {
1291                         " "
1292                     },
1293                     |s| &**s,
1294                 ),
1295                 pat_expr_string,
1296                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1297             ),
1298             used_width,
1299         ))
1300     }
1301 }
1302
1303 impl<'a> Rewrite for ControlFlow<'a> {
1304     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1305         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1306
1307         let alt_block_sep =
1308             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1309         let (cond_str, used_width) = try_opt!(self.rewrite_cond(context, shape, &alt_block_sep));
1310         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1311         if used_width == 0 {
1312             return Some(cond_str);
1313         }
1314
1315         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1316         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1317         // we should avoid the single line case.
1318         let block_width = if self.else_block.is_some() || self.nested_if {
1319             min(1, block_width)
1320         } else {
1321             block_width
1322         };
1323         let block_shape = Shape {
1324             width: block_width,
1325             ..shape
1326         };
1327         let mut block_context = context.clone();
1328         block_context.is_if_else_block = self.else_block.is_some();
1329         let block_str = try_opt!(rewrite_block_with_visitor(
1330             &block_context,
1331             "",
1332             self.block,
1333             block_shape,
1334         ));
1335
1336         let mut result = format!("{}{}", cond_str, block_str);
1337
1338         if let Some(else_block) = self.else_block {
1339             let shape = Shape::indented(shape.indent, context.config);
1340             let mut last_in_chain = false;
1341             let rewrite = match else_block.node {
1342                 // If the else expression is another if-else expression, prevent it
1343                 // from being formatted on a single line.
1344                 // Note how we're passing the original shape, as the
1345                 // cost of "else" should not cascade.
1346                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1347                     ControlFlow::new_if(
1348                         cond,
1349                         Some(pat),
1350                         if_block,
1351                         next_else_block.as_ref().map(|e| &**e),
1352                         false,
1353                         true,
1354                         mk_sp(else_block.span.lo, self.span.hi),
1355                     ).rewrite(context, shape)
1356                 }
1357                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1358                     ControlFlow::new_if(
1359                         cond,
1360                         None,
1361                         if_block,
1362                         next_else_block.as_ref().map(|e| &**e),
1363                         false,
1364                         true,
1365                         mk_sp(else_block.span.lo, self.span.hi),
1366                     ).rewrite(context, shape)
1367                 }
1368                 _ => {
1369                     last_in_chain = true;
1370                     // When rewriting a block, the width is only used for single line
1371                     // blocks, passing 1 lets us avoid that.
1372                     let else_shape = Shape {
1373                         width: min(1, shape.width),
1374                         ..shape
1375                     };
1376                     format_expr(else_block, ExprType::Statement, context, else_shape)
1377                 }
1378             };
1379
1380             let between_kwd_else_block = mk_sp(
1381                 self.block.span.hi,
1382                 context
1383                     .codemap
1384                     .span_before(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1385             );
1386             let between_kwd_else_block_comment =
1387                 extract_comment(between_kwd_else_block, context, shape);
1388
1389             let after_else = mk_sp(
1390                 context
1391                     .codemap
1392                     .span_after(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1393                 else_block.span.lo,
1394             );
1395             let after_else_comment = extract_comment(after_else, context, shape);
1396
1397             let between_sep = match context.config.control_brace_style() {
1398                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1399                     &*alt_block_sep
1400                 }
1401                 ControlBraceStyle::AlwaysSameLine => " ",
1402             };
1403             let after_sep = match context.config.control_brace_style() {
1404                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1405                 _ => " ",
1406             };
1407             try_opt!(
1408                 write!(
1409                     &mut result,
1410                     "{}else{}",
1411                     between_kwd_else_block_comment
1412                         .as_ref()
1413                         .map_or(between_sep, |s| &**s),
1414                     after_else_comment.as_ref().map_or(after_sep, |s| &**s)
1415                 ).ok()
1416             );
1417             result.push_str(&try_opt!(rewrite));
1418         }
1419
1420         Some(result)
1421     }
1422 }
1423
1424 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
1425     match label {
1426         Some(ident) => format!("{}: ", ident.node),
1427         None => "".to_owned(),
1428     }
1429 }
1430
1431 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1432     let comment_str = context.snippet(span);
1433     if contains_comment(&comment_str) {
1434         let comment = try_opt!(rewrite_comment(
1435             comment_str.trim(),
1436             false,
1437             shape,
1438             context.config,
1439         ));
1440         Some(format!(
1441             "\n{indent}{}\n{indent}",
1442             comment,
1443             indent = shape.indent.to_string(context.config)
1444         ))
1445     } else {
1446         None
1447     }
1448 }
1449
1450 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1451     let snippet = codemap.span_to_snippet(block.span).unwrap();
1452     contains_comment(&snippet)
1453 }
1454
1455 // Checks that a block contains no statements, an expression and no comments.
1456 // FIXME: incorrectly returns false when comment is contained completely within
1457 // the expression.
1458 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1459     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
1460         !block_contains_comment(block, codemap))
1461 }
1462
1463 /// Checks whether a block contains at most one statement or expression, and no comments.
1464 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1465     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1466 }
1467
1468 /// Checks whether a block contains no statements, expressions, or comments.
1469 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1470     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1471 }
1472
1473 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1474     match stmt.node {
1475         ast::StmtKind::Expr(..) => true,
1476         _ => false,
1477     }
1478 }
1479
1480 fn is_unsafe_block(block: &ast::Block) -> bool {
1481     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1482         true
1483     } else {
1484         false
1485     }
1486 }
1487
1488 // inter-match-arm-comment-rules:
1489 //  - all comments following a match arm before the start of the next arm
1490 //    are about the second arm
1491 fn rewrite_match_arm_comment(
1492     context: &RewriteContext,
1493     missed_str: &str,
1494     shape: Shape,
1495     arm_indent_str: &str,
1496 ) -> Option<String> {
1497     // The leading "," is not part of the arm-comment
1498     let missed_str = match missed_str.find_uncommented(",") {
1499         Some(n) => &missed_str[n + 1..],
1500         None => &missed_str[..],
1501     };
1502
1503     let mut result = String::new();
1504     // any text not preceeded by a newline is pushed unmodified to the block
1505     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1506     result.push_str(&missed_str[..first_brk]);
1507     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1508
1509     let first = missed_str
1510         .find(|c: char| !c.is_whitespace())
1511         .unwrap_or(missed_str.len());
1512     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1513         // Excessive vertical whitespace before comment should be preserved
1514         // FIXME handle vertical whitespace better
1515         result.push('\n');
1516     }
1517     let missed_str = missed_str[first..].trim();
1518     if !missed_str.is_empty() {
1519         let comment = try_opt!(rewrite_comment(&missed_str, false, shape, context.config));
1520         result.push('\n');
1521         result.push_str(arm_indent_str);
1522         result.push_str(&comment);
1523     }
1524
1525     Some(result)
1526 }
1527
1528 fn rewrite_match(
1529     context: &RewriteContext,
1530     cond: &ast::Expr,
1531     arms: &[ast::Arm],
1532     shape: Shape,
1533     span: Span,
1534 ) -> Option<String> {
1535     if arms.is_empty() {
1536         return None;
1537     }
1538
1539     // Do not take the rhs overhead from the upper expressions into account
1540     // when rewriting match condition.
1541     let new_width = try_opt!(context.config.max_width().checked_sub(shape.used_width()));
1542     let cond_shape = Shape {
1543         width: new_width,
1544         ..shape
1545     };
1546     // 6 = `match `
1547     let cond_shape = match context.config.control_style() {
1548         Style::Legacy => try_opt!(cond_shape.shrink_left(6)),
1549         Style::Rfc => try_opt!(cond_shape.offset_left(6)),
1550     };
1551     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1552     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1553     let block_sep = match context.config.control_brace_style() {
1554         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1555         _ if last_line_extendable(&cond_str) => " ",
1556         // 2 = ` {`
1557         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => &alt_block_sep,
1558         _ => " ",
1559     };
1560
1561     Some(format!(
1562         "match {}{}{{{}\n{}}}",
1563         cond_str,
1564         block_sep,
1565         try_opt!(rewrite_match_arms(context, arms, shape, span, cond.span.hi)),
1566         shape.indent.to_string(context.config),
1567     ))
1568 }
1569
1570 fn arm_comma(config: &Config, body: &ast::Expr) -> &'static str {
1571     if config.match_block_trailing_comma() {
1572         ","
1573     } else if let ast::ExprKind::Block(ref block) = body.node {
1574         if let ast::BlockCheckMode::Default = block.rules {
1575             ""
1576         } else {
1577             ","
1578         }
1579     } else {
1580         ","
1581     }
1582 }
1583
1584 fn rewrite_match_arms(
1585     context: &RewriteContext,
1586     arms: &[ast::Arm],
1587     shape: Shape,
1588     span: Span,
1589     cond_end_pos: BytePos,
1590 ) -> Option<String> {
1591     let mut result = String::new();
1592
1593     let arm_shape = if context.config.indent_match_arms() {
1594         shape.block_indent(context.config.tab_spaces())
1595     } else {
1596         shape.block_indent(0)
1597     }.with_max_width(context.config);
1598     let arm_indent_str = arm_shape.indent.to_string(context.config);
1599
1600     let open_brace_pos = context
1601         .codemap
1602         .span_after(mk_sp(cond_end_pos, arms[0].span().lo), "{");
1603
1604     let arm_num = arms.len();
1605     for (i, arm) in arms.iter().enumerate() {
1606         // Make sure we get the stuff between arms.
1607         let missed_str = if i == 0 {
1608             context.snippet(mk_sp(open_brace_pos, arm.span().lo))
1609         } else {
1610             context.snippet(mk_sp(arms[i - 1].span().hi, arm.span().lo))
1611         };
1612         let comment = try_opt!(rewrite_match_arm_comment(
1613             context,
1614             &missed_str,
1615             arm_shape,
1616             &arm_indent_str,
1617         ));
1618         result.push_str(&comment);
1619         result.push('\n');
1620         result.push_str(&arm_indent_str);
1621
1622         let arm_str = rewrite_match_arm(context, arm, arm_shape);
1623         if let Some(ref arm_str) = arm_str {
1624             // Trim the trailing comma if necessary.
1625             if i == arm_num - 1 && context.config.trailing_comma() == SeparatorTactic::Never &&
1626                 arm_str.ends_with(',')
1627             {
1628                 result.push_str(&arm_str[0..arm_str.len() - 1])
1629             } else {
1630                 result.push_str(arm_str)
1631             }
1632         } else {
1633             // We couldn't format the arm, just reproduce the source.
1634             let snippet = context.snippet(arm.span());
1635             result.push_str(&snippet);
1636             if context.config.trailing_comma() != SeparatorTactic::Never {
1637                 result.push_str(arm_comma(context.config, &arm.body))
1638             }
1639         }
1640     }
1641     // BytePos(1) = closing match brace.
1642     let last_span = mk_sp(arms[arms.len() - 1].span().hi, span.hi - BytePos(1));
1643     let last_comment = context.snippet(last_span);
1644     let comment = try_opt!(rewrite_match_arm_comment(
1645         context,
1646         &last_comment,
1647         arm_shape,
1648         &arm_indent_str,
1649     ));
1650     result.push_str(&comment);
1651
1652     Some(result)
1653 }
1654
1655 fn rewrite_match_arm(context: &RewriteContext, arm: &ast::Arm, shape: Shape) -> Option<String> {
1656     let attr_str = if !arm.attrs.is_empty() {
1657         if contains_skip(&arm.attrs) {
1658             return None;
1659         }
1660         format!(
1661             "{}\n{}",
1662             try_opt!(arm.attrs.rewrite(context, shape)),
1663             shape.indent.to_string(context.config)
1664         )
1665     } else {
1666         String::new()
1667     };
1668     let pats_str = try_opt!(rewrite_match_pattern(context, &arm.pats, &arm.guard, shape));
1669     let pats_str = attr_str + &pats_str;
1670     rewrite_match_body(context, &arm.body, &pats_str, shape, arm.guard.is_some())
1671 }
1672
1673 fn rewrite_match_pattern(
1674     context: &RewriteContext,
1675     pats: &Vec<ptr::P<ast::Pat>>,
1676     guard: &Option<ptr::P<ast::Expr>>,
1677     shape: Shape,
1678 ) -> Option<String> {
1679     // Patterns
1680     // 5 = ` => {`
1681     let pat_shape = try_opt!(shape.sub_width(5));
1682
1683     let pat_strs = try_opt!(
1684         pats.iter()
1685             .map(|p| p.rewrite(context, pat_shape))
1686             .collect::<Option<Vec<_>>>()
1687     );
1688
1689     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1690     let tactic = definitive_tactic(
1691         &items,
1692         ListTactic::HorizontalVertical,
1693         Separator::VerticalBar,
1694         pat_shape.width,
1695     );
1696     let fmt = ListFormatting {
1697         tactic: tactic,
1698         separator: " |",
1699         trailing_separator: SeparatorTactic::Never,
1700         shape: pat_shape,
1701         ends_with_newline: false,
1702         preserve_newline: false,
1703         config: context.config,
1704     };
1705     let pats_str = try_opt!(write_list(&items, &fmt));
1706
1707     // Guard
1708     let guard_str = try_opt!(rewrite_guard(
1709         context,
1710         guard,
1711         shape,
1712         trimmed_last_line_width(&pats_str),
1713     ));
1714
1715     Some(format!("{}{}", pats_str, guard_str))
1716 }
1717
1718 fn rewrite_match_body(
1719     context: &RewriteContext,
1720     body: &ptr::P<ast::Expr>,
1721     pats_str: &str,
1722     shape: Shape,
1723     has_guard: bool,
1724 ) -> Option<String> {
1725     let (extend, body) = match body.node {
1726         ast::ExprKind::Block(ref block)
1727             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1728         {
1729             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1730                 (expr.can_be_overflowed(context, 1), &**expr)
1731             } else {
1732                 (false, &**body)
1733             }
1734         }
1735         _ => (body.can_be_overflowed(context, 1), &**body),
1736     };
1737
1738     let comma = arm_comma(&context.config, body);
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 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1937     let string_lit = context.snippet(span);
1938
1939     if !context.config.format_strings() && !context.config.force_format_strings() {
1940         if string_lit
1941             .lines()
1942             .rev()
1943             .skip(1)
1944             .all(|line| line.ends_with('\\'))
1945         {
1946             let new_indent = shape.visual_indent(1).indent;
1947             return Some(String::from(
1948                 string_lit
1949                     .lines()
1950                     .map(|line| {
1951                         new_indent.to_string(context.config) + line.trim_left()
1952                     })
1953                     .collect::<Vec<_>>()
1954                     .join("\n")
1955                     .trim_left(),
1956             ));
1957         } else {
1958             return Some(string_lit);
1959         }
1960     }
1961
1962     if !context.config.force_format_strings() &&
1963         !string_requires_rewrite(context, span, &string_lit, shape)
1964     {
1965         return Some(string_lit);
1966     }
1967
1968     let fmt = StringFormat {
1969         opener: "\"",
1970         closer: "\"",
1971         line_start: " ",
1972         line_end: "\\",
1973         shape: shape,
1974         trim_end: false,
1975         config: context.config,
1976     };
1977
1978     // Remove the quote characters.
1979     let str_lit = &string_lit[1..string_lit.len() - 1];
1980
1981     rewrite_string(str_lit, &fmt)
1982 }
1983
1984 fn string_requires_rewrite(
1985     context: &RewriteContext,
1986     span: Span,
1987     string: &str,
1988     shape: Shape,
1989 ) -> bool {
1990     if context.codemap.lookup_char_pos(span.lo).col.0 != shape.indent.width() {
1991         return true;
1992     }
1993
1994     for (i, line) in string.lines().enumerate() {
1995         if i == 0 {
1996             if line.len() > shape.width {
1997                 return true;
1998             }
1999         } else {
2000             if line.len() > shape.width + shape.indent.width() {
2001                 return true;
2002             }
2003         }
2004     }
2005
2006     false
2007 }
2008
2009 pub fn rewrite_call_with_binary_search<R>(
2010     context: &RewriteContext,
2011     callee: &R,
2012     args: &[&ast::Expr],
2013     span: Span,
2014     shape: Shape,
2015 ) -> Option<String>
2016 where
2017     R: Rewrite,
2018 {
2019     let force_trailing_comma = if context.inside_macro {
2020         span_ends_with_comma(context, span)
2021     } else {
2022         false
2023     };
2024     let closure = |callee_max_width| {
2025         // FIXME using byte lens instead of char lens (and probably all over the
2026         // place too)
2027         let callee_shape = Shape {
2028             width: callee_max_width,
2029             ..shape
2030         };
2031         let callee_str = callee
2032             .rewrite(context, callee_shape)
2033             .ok_or(Ordering::Greater)?;
2034
2035         rewrite_call_inner(
2036             context,
2037             &callee_str,
2038             args,
2039             span,
2040             shape,
2041             context.config.fn_call_width(),
2042             force_trailing_comma,
2043         )
2044     };
2045
2046     binary_search(1, shape.width, closure)
2047 }
2048
2049 pub fn rewrite_call(
2050     context: &RewriteContext,
2051     callee: &str,
2052     args: &[ptr::P<ast::Expr>],
2053     span: Span,
2054     shape: Shape,
2055 ) -> Option<String> {
2056     let force_trailing_comma = if context.inside_macro {
2057         span_ends_with_comma(context, span)
2058     } else {
2059         false
2060     };
2061     rewrite_call_inner(
2062         context,
2063         &callee,
2064         &args.iter().map(|x| &**x).collect::<Vec<_>>(),
2065         span,
2066         shape,
2067         context.config.fn_call_width(),
2068         force_trailing_comma,
2069     ).ok()
2070 }
2071
2072 pub fn rewrite_call_inner<'a, T>(
2073     context: &RewriteContext,
2074     callee_str: &str,
2075     args: &[&T],
2076     span: Span,
2077     shape: Shape,
2078     args_max_width: usize,
2079     force_trailing_comma: bool,
2080 ) -> Result<String, Ordering>
2081 where
2082     T: Rewrite + Spanned + ToExpr + 'a,
2083 {
2084     // 2 = `( `, 1 = `(`
2085     let paren_overhead = if context.config.spaces_within_parens() {
2086         2
2087     } else {
2088         1
2089     };
2090     let used_width = extra_offset(&callee_str, shape);
2091     let one_line_width = shape
2092         .width
2093         .checked_sub(used_width + 2 * paren_overhead)
2094         .ok_or(Ordering::Greater)?;
2095
2096     let nested_shape = shape_from_fn_call_style(
2097         context,
2098         shape,
2099         used_width + 2 * paren_overhead,
2100         used_width + paren_overhead,
2101     ).ok_or(Ordering::Greater)?;
2102
2103     let span_lo = context.codemap.span_after(span, "(");
2104     let args_span = mk_sp(span_lo, span.hi);
2105
2106     let (extendable, list_str) = rewrite_call_args(
2107         context,
2108         args,
2109         args_span,
2110         nested_shape,
2111         one_line_width,
2112         args_max_width,
2113         force_trailing_comma,
2114     ).ok_or(Ordering::Less)?;
2115
2116     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2117         let mut new_context = context.clone();
2118         new_context.use_block = true;
2119         return rewrite_call_inner(
2120             &new_context,
2121             callee_str,
2122             args,
2123             span,
2124             shape,
2125             args_max_width,
2126             force_trailing_comma,
2127         );
2128     }
2129
2130     let args_shape = shape
2131         .sub_width(last_line_width(&callee_str))
2132         .ok_or(Ordering::Less)?;
2133     Ok(format!(
2134         "{}{}",
2135         callee_str,
2136         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2137     ))
2138 }
2139
2140 fn need_block_indent(s: &str, shape: Shape) -> bool {
2141     s.lines().skip(1).any(|s| {
2142         s.find(|c| !char::is_whitespace(c))
2143             .map_or(false, |w| w + 1 < shape.indent.width())
2144     })
2145 }
2146
2147 fn rewrite_call_args<'a, T>(
2148     context: &RewriteContext,
2149     args: &[&T],
2150     span: Span,
2151     shape: Shape,
2152     one_line_width: usize,
2153     args_max_width: usize,
2154     force_trailing_comma: bool,
2155 ) -> Option<(bool, String)>
2156 where
2157     T: Rewrite + Spanned + ToExpr + 'a,
2158 {
2159     let items = itemize_list(
2160         context.codemap,
2161         args.iter(),
2162         ")",
2163         |item| item.span().lo,
2164         |item| item.span().hi,
2165         |item| item.rewrite(context, shape),
2166         span.lo,
2167         span.hi,
2168     );
2169     let mut item_vec: Vec<_> = items.collect();
2170
2171     // Try letting the last argument overflow to the next line with block
2172     // indentation. If its first line fits on one line with the other arguments,
2173     // we format the function arguments horizontally.
2174     let tactic = try_overflow_last_arg(
2175         context,
2176         &mut item_vec,
2177         &args[..],
2178         shape,
2179         one_line_width,
2180         args_max_width,
2181     );
2182
2183     let fmt = ListFormatting {
2184         tactic: tactic,
2185         separator: ",",
2186         trailing_separator: if force_trailing_comma {
2187             SeparatorTactic::Always
2188         } else if context.inside_macro || !context.use_block_indent() {
2189             SeparatorTactic::Never
2190         } else {
2191             context.config.trailing_comma()
2192         },
2193         shape: shape,
2194         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2195         preserve_newline: false,
2196         config: context.config,
2197     };
2198
2199     write_list(&item_vec, &fmt).map(|args_str| {
2200         (tactic != DefinitiveListTactic::Vertical, args_str)
2201     })
2202 }
2203
2204 fn try_overflow_last_arg<'a, T>(
2205     context: &RewriteContext,
2206     item_vec: &mut Vec<ListItem>,
2207     args: &[&T],
2208     shape: Shape,
2209     one_line_width: usize,
2210     args_max_width: usize,
2211 ) -> DefinitiveListTactic
2212 where
2213     T: Rewrite + Spanned + ToExpr + 'a,
2214 {
2215     let overflow_last = can_be_overflowed(&context, args);
2216
2217     // Replace the last item with its first line to see if it fits with
2218     // first arguments.
2219     let (orig_last, placeholder) = if overflow_last {
2220         let mut context = context.clone();
2221         if let Some(expr) = args[args.len() - 1].to_expr() {
2222             match expr.node {
2223                 ast::ExprKind::MethodCall(..) => context.force_one_line_chain = true,
2224                 _ => (),
2225             }
2226         }
2227         last_arg_shape(&context, &item_vec, shape, args_max_width)
2228             .map_or((None, None), |arg_shape| {
2229                 rewrite_last_arg_with_overflow(
2230                     &context,
2231                     args,
2232                     &mut item_vec[args.len() - 1],
2233                     arg_shape,
2234                 )
2235             })
2236     } else {
2237         (None, None)
2238     };
2239
2240     let tactic = definitive_tactic(
2241         &*item_vec,
2242         ListTactic::LimitedHorizontalVertical(args_max_width),
2243         Separator::Comma,
2244         one_line_width,
2245     );
2246
2247     // Replace the stub with the full overflowing last argument if the rewrite
2248     // succeeded and its first line fits with the other arguments.
2249     match (overflow_last, tactic, placeholder) {
2250         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2251             item_vec[args.len() - 1].item = placeholder;
2252         }
2253         (true, _, _) => {
2254             item_vec[args.len() - 1].item = orig_last;
2255         }
2256         (false, _, _) => {}
2257     }
2258
2259     tactic
2260 }
2261
2262 fn last_arg_shape(
2263     context: &RewriteContext,
2264     items: &Vec<ListItem>,
2265     shape: Shape,
2266     args_max_width: usize,
2267 ) -> Option<Shape> {
2268     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2269         acc + i.item.as_ref().map_or(0, |s| first_line_width(&s))
2270     });
2271     let max_width = min(args_max_width, shape.width);
2272     let arg_indent = if context.use_block_indent() {
2273         shape.block().indent.block_unindent(context.config)
2274     } else {
2275         shape.block().indent
2276     };
2277     Some(Shape {
2278         width: try_opt!(max_width.checked_sub(overhead)),
2279         indent: arg_indent,
2280         offset: 0,
2281     })
2282 }
2283
2284 // Rewriting closure which is placed at the end of the function call's arg.
2285 // Returns `None` if the reformatted closure 'looks bad'.
2286 fn rewrite_last_closure(
2287     context: &RewriteContext,
2288     expr: &ast::Expr,
2289     shape: Shape,
2290 ) -> Option<String> {
2291     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2292         let body = match body.node {
2293             ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
2294                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2295             }
2296             _ => body,
2297         };
2298         let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
2299             capture,
2300             fn_decl,
2301             body,
2302             expr.span,
2303             context,
2304             shape,
2305         ));
2306         // If the closure goes multi line before its body, do not overflow the closure.
2307         if prefix.contains('\n') {
2308             return None;
2309         }
2310         let body_shape = try_opt!(shape.offset_left(extra_offset));
2311         // When overflowing the closure which consists of a single control flow expression,
2312         // force to use block if its condition uses multi line.
2313         let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
2314             .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
2315             .unwrap_or(false);
2316         if is_multi_lined_cond {
2317             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2318         }
2319
2320         // Seems fine, just format the closure in usual manner.
2321         return expr.rewrite(context, shape);
2322     }
2323     None
2324 }
2325
2326 fn rewrite_last_arg_with_overflow<'a, T>(
2327     context: &RewriteContext,
2328     args: &[&T],
2329     last_item: &mut ListItem,
2330     shape: Shape,
2331 ) -> (Option<String>, Option<String>)
2332 where
2333     T: Rewrite + Spanned + ToExpr + 'a,
2334 {
2335     let last_arg = args[args.len() - 1];
2336     let rewrite = if let Some(expr) = last_arg.to_expr() {
2337         match expr.node {
2338             // When overflowing the closure which consists of a single control flow expression,
2339             // force to use block if its condition uses multi line.
2340             ast::ExprKind::Closure(..) => {
2341                 // If the argument consists of multiple closures, we do not overflow
2342                 // the last closure.
2343                 if args.len() > 1 &&
2344                     args.iter()
2345                         .rev()
2346                         .skip(1)
2347                         .filter_map(|arg| arg.to_expr())
2348                         .any(|expr| match expr.node {
2349                             ast::ExprKind::Closure(..) => true,
2350                             _ => false,
2351                         }) {
2352                     None
2353                 } else {
2354                     rewrite_last_closure(context, expr, shape)
2355                 }
2356             }
2357             _ => expr.rewrite(context, shape),
2358         }
2359     } else {
2360         last_arg.rewrite(context, shape)
2361     };
2362     let orig_last = last_item.item.clone();
2363
2364     if let Some(rewrite) = rewrite {
2365         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2366         last_item.item = rewrite_first_line;
2367         (orig_last, Some(rewrite))
2368     } else {
2369         (orig_last, None)
2370     }
2371 }
2372
2373 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2374 where
2375     T: Rewrite + Spanned + ToExpr + 'a,
2376 {
2377     args.last()
2378         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2379 }
2380
2381 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2382     match expr.node {
2383         ast::ExprKind::Match(..) => {
2384             (context.use_block_indent() && args_len == 1) ||
2385                 (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2386         }
2387         ast::ExprKind::If(..) |
2388         ast::ExprKind::IfLet(..) |
2389         ast::ExprKind::ForLoop(..) |
2390         ast::ExprKind::Loop(..) |
2391         ast::ExprKind::While(..) |
2392         ast::ExprKind::WhileLet(..) => {
2393             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2394         }
2395         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2396             context.use_block_indent() ||
2397                 context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2398         }
2399         ast::ExprKind::Array(..) |
2400         ast::ExprKind::Call(..) |
2401         ast::ExprKind::Mac(..) |
2402         ast::ExprKind::MethodCall(..) |
2403         ast::ExprKind::Struct(..) |
2404         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2405         ast::ExprKind::AddrOf(_, ref expr) |
2406         ast::ExprKind::Box(ref expr) |
2407         ast::ExprKind::Try(ref expr) |
2408         ast::ExprKind::Unary(_, ref expr) |
2409         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2410         _ => false,
2411     }
2412 }
2413
2414 pub fn wrap_args_with_parens(
2415     context: &RewriteContext,
2416     args_str: &str,
2417     is_extendable: bool,
2418     shape: Shape,
2419     nested_shape: Shape,
2420 ) -> String {
2421     if !context.use_block_indent() ||
2422         (context.inside_macro && !args_str.contains('\n') &&
2423             args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2424     {
2425         if context.config.spaces_within_parens() && args_str.len() > 0 {
2426             format!("( {} )", args_str)
2427         } else {
2428             format!("({})", args_str)
2429         }
2430     } else {
2431         format!(
2432             "(\n{}{}\n{})",
2433             nested_shape.indent.to_string(context.config),
2434             args_str,
2435             shape.block().indent.to_string(context.config)
2436         )
2437     }
2438 }
2439
2440 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2441     let snippet = context.snippet(span);
2442     snippet
2443         .trim_right_matches(|c: char| c == ')' || c.is_whitespace())
2444         .ends_with(',')
2445 }
2446
2447 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2448     debug!("rewrite_paren, shape: {:?}", shape);
2449     let total_paren_overhead = paren_overhead(context);
2450     let paren_overhead = total_paren_overhead / 2;
2451     let sub_shape = try_opt!(
2452         shape
2453             .offset_left(paren_overhead)
2454             .and_then(|s| s.sub_width(paren_overhead))
2455     );
2456
2457     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && s.len() > 0 {
2458         format!("( {} )", s)
2459     } else {
2460         format!("({})", s)
2461     };
2462
2463     let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2464     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2465
2466     if subexpr_str.contains('\n') ||
2467         first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2468     {
2469         Some(paren_wrapper(&subexpr_str))
2470     } else {
2471         None
2472     }
2473 }
2474
2475 fn rewrite_index(
2476     expr: &ast::Expr,
2477     index: &ast::Expr,
2478     context: &RewriteContext,
2479     shape: Shape,
2480 ) -> Option<String> {
2481     let expr_str = try_opt!(expr.rewrite(context, shape));
2482
2483     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2484         ("[ ", " ]")
2485     } else {
2486         ("[", "]")
2487     };
2488
2489     let offset = last_line_width(&expr_str) + lbr.len();
2490     let rhs_overhead = shape.rhs_overhead(context.config);
2491     let index_shape = if expr_str.contains('\n') {
2492         Shape::legacy(context.config.max_width(), shape.indent)
2493             .offset_left(offset)
2494             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2495     } else {
2496         shape.visual_indent(offset).sub_width(offset + rbr.len())
2497     };
2498     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2499
2500     // Return if index fits in a single line.
2501     match orig_index_rw {
2502         Some(ref index_str) if !index_str.contains('\n') => {
2503             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2504         }
2505         _ => (),
2506     }
2507
2508     // Try putting index on the next line and see if it fits in a single line.
2509     let indent = shape.indent.block_indent(context.config);
2510     let index_shape = try_opt!(Shape::indented(indent, context.config).offset_left(lbr.len()));
2511     let index_shape = try_opt!(index_shape.sub_width(rbr.len() + rhs_overhead));
2512     let new_index_rw = index.rewrite(context, index_shape);
2513     match (orig_index_rw, new_index_rw) {
2514         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2515             "{}\n{}{}{}{}",
2516             expr_str,
2517             indent.to_string(&context.config),
2518             lbr,
2519             new_index_str,
2520             rbr
2521         )),
2522         (None, Some(ref new_index_str)) => Some(format!(
2523             "{}\n{}{}{}{}",
2524             expr_str,
2525             indent.to_string(&context.config),
2526             lbr,
2527             new_index_str,
2528             rbr
2529         )),
2530         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2531         _ => None,
2532     }
2533 }
2534
2535 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2536     if base.is_some() {
2537         return false;
2538     }
2539
2540     fields.iter().all(|field| !field.is_shorthand)
2541 }
2542
2543 fn rewrite_struct_lit<'a>(
2544     context: &RewriteContext,
2545     path: &ast::Path,
2546     fields: &'a [ast::Field],
2547     base: Option<&'a ast::Expr>,
2548     span: Span,
2549     shape: Shape,
2550 ) -> Option<String> {
2551     debug!("rewrite_struct_lit: shape {:?}", shape);
2552
2553     enum StructLitField<'a> {
2554         Regular(&'a ast::Field),
2555         Base(&'a ast::Expr),
2556     }
2557
2558     // 2 = " {".len()
2559     let path_shape = try_opt!(shape.sub_width(2));
2560     let path_str = try_opt!(rewrite_path(
2561         context,
2562         PathContext::Expr,
2563         None,
2564         path,
2565         path_shape,
2566     ));
2567
2568     if fields.len() == 0 && base.is_none() {
2569         return Some(format!("{} {{}}", path_str));
2570     }
2571
2572     // Foo { a: Foo } - indent is +3, width is -5.
2573     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
2574
2575     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2576     let body_lo = context.codemap.span_after(span, "{");
2577     let fields_str = if struct_lit_can_be_aligned(fields, &base) &&
2578         context.config.struct_field_align_threshold() > 0
2579     {
2580         try_opt!(rewrite_with_alignment(
2581             fields,
2582             context,
2583             shape,
2584             mk_sp(body_lo, span.hi),
2585             one_line_width,
2586         ))
2587     } else {
2588         let field_iter = fields
2589             .into_iter()
2590             .map(StructLitField::Regular)
2591             .chain(base.into_iter().map(StructLitField::Base));
2592
2593         let span_lo = |item: &StructLitField| match *item {
2594             StructLitField::Regular(field) => field.span().lo,
2595             StructLitField::Base(expr) => {
2596                 let last_field_hi = fields.last().map_or(span.lo, |field| field.span.hi);
2597                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo));
2598                 let pos = snippet.find_uncommented("..").unwrap();
2599                 last_field_hi + BytePos(pos as u32)
2600             }
2601         };
2602         let span_hi = |item: &StructLitField| match *item {
2603             StructLitField::Regular(field) => field.span().hi,
2604             StructLitField::Base(expr) => expr.span.hi,
2605         };
2606         let rewrite = |item: &StructLitField| match *item {
2607             StructLitField::Regular(field) => {
2608                 // The 1 taken from the v_budget is for the comma.
2609                 rewrite_field(context, field, try_opt!(v_shape.sub_width(1)), 0)
2610             }
2611             StructLitField::Base(expr) => {
2612                 // 2 = ..
2613                 expr.rewrite(context, try_opt!(v_shape.offset_left(2)))
2614                     .map(|s| format!("..{}", s))
2615             }
2616         };
2617
2618         let items = itemize_list(
2619             context.codemap,
2620             field_iter,
2621             "}",
2622             span_lo,
2623             span_hi,
2624             rewrite,
2625             body_lo,
2626             span.hi,
2627         );
2628         let item_vec = items.collect::<Vec<_>>();
2629
2630         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2631         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2632         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2633
2634         try_opt!(write_list(&item_vec, &fmt))
2635     };
2636
2637     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2638     Some(format!("{} {{{}}}", path_str, fields_str))
2639
2640     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2641     // of space, we should fall back to BlockIndent.
2642 }
2643
2644 pub fn wrap_struct_field(
2645     context: &RewriteContext,
2646     fields_str: &str,
2647     shape: Shape,
2648     nested_shape: Shape,
2649     one_line_width: usize,
2650 ) -> String {
2651     if context.config.struct_lit_style() == IndentStyle::Block &&
2652         (fields_str.contains('\n') ||
2653             context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti ||
2654             fields_str.len() > one_line_width)
2655     {
2656         format!(
2657             "\n{}{}\n{}",
2658             nested_shape.indent.to_string(context.config),
2659             fields_str,
2660             shape.indent.to_string(context.config)
2661         )
2662     } else {
2663         // One liner or visual indent.
2664         format!(" {} ", fields_str)
2665     }
2666 }
2667
2668 pub fn struct_lit_field_separator(config: &Config) -> &str {
2669     colon_spaces(
2670         config.space_before_struct_lit_field_colon(),
2671         config.space_after_struct_lit_field_colon(),
2672     )
2673 }
2674
2675 pub fn rewrite_field(
2676     context: &RewriteContext,
2677     field: &ast::Field,
2678     shape: Shape,
2679     prefix_max_width: usize,
2680 ) -> Option<String> {
2681     if contains_skip(&field.attrs) {
2682         return wrap_str(
2683             context.snippet(field.span()),
2684             context.config.max_width(),
2685             shape,
2686         );
2687     }
2688     let name = &field.ident.node.to_string();
2689     if field.is_shorthand {
2690         Some(name.to_string())
2691     } else {
2692         let mut separator = String::from(struct_lit_field_separator(context.config));
2693         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2694             separator.push(' ');
2695         }
2696         let overhead = name.len() + separator.len();
2697         let expr_shape = try_opt!(shape.offset_left(overhead));
2698         let expr = field.expr.rewrite(context, expr_shape);
2699
2700         let mut attrs_str = try_opt!(field.attrs.rewrite(context, shape));
2701         if !attrs_str.is_empty() {
2702             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2703         };
2704
2705         match expr {
2706             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2707             None => {
2708                 let expr_offset = shape.indent.block_indent(context.config);
2709                 let expr = field
2710                     .expr
2711                     .rewrite(context, Shape::indented(expr_offset, context.config));
2712                 expr.map(|s| {
2713                     format!(
2714                         "{}{}:\n{}{}",
2715                         attrs_str,
2716                         name,
2717                         expr_offset.to_string(&context.config),
2718                         s
2719                     )
2720                 })
2721             }
2722         }
2723     }
2724 }
2725
2726 fn shape_from_fn_call_style(
2727     context: &RewriteContext,
2728     shape: Shape,
2729     overhead: usize,
2730     offset: usize,
2731 ) -> Option<Shape> {
2732     if context.use_block_indent() {
2733         // 1 = ","
2734         shape
2735             .block()
2736             .block_indent(context.config.tab_spaces())
2737             .with_max_width(context.config)
2738             .sub_width(1)
2739     } else {
2740         shape.visual_indent(offset).sub_width(overhead)
2741     }
2742 }
2743
2744 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2745     context: &RewriteContext,
2746     items: &[&T],
2747     span: Span,
2748     shape: Shape,
2749 ) -> Option<String>
2750 where
2751     T: Rewrite + Spanned + ToExpr + 'a,
2752 {
2753     let mut items = items.iter();
2754     // In case of length 1, need a trailing comma
2755     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2756     if items.len() == 1 {
2757         // 3 = "(" + ",)"
2758         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
2759         return items.next().unwrap().rewrite(context, nested_shape).map(
2760             |s| if context.config.spaces_within_parens() {
2761                 format!("( {}, )", s)
2762             } else {
2763                 format!("({},)", s)
2764             },
2765         );
2766     }
2767
2768     let list_lo = context.codemap.span_after(span, "(");
2769     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
2770     let items = itemize_list(
2771         context.codemap,
2772         items,
2773         ")",
2774         |item| item.span().lo,
2775         |item| item.span().hi,
2776         |item| item.rewrite(context, nested_shape),
2777         list_lo,
2778         span.hi - BytePos(1),
2779     );
2780     let item_vec: Vec<_> = items.collect();
2781     let tactic = definitive_tactic(
2782         &item_vec,
2783         ListTactic::HorizontalVertical,
2784         Separator::Comma,
2785         nested_shape.width,
2786     );
2787     let fmt = ListFormatting {
2788         tactic: tactic,
2789         separator: ",",
2790         trailing_separator: SeparatorTactic::Never,
2791         shape: shape,
2792         ends_with_newline: false,
2793         preserve_newline: false,
2794         config: context.config,
2795     };
2796     let list_str = try_opt!(write_list(&item_vec, &fmt));
2797
2798     if context.config.spaces_within_parens() && list_str.len() > 0 {
2799         Some(format!("( {} )", list_str))
2800     } else {
2801         Some(format!("({})", list_str))
2802     }
2803 }
2804
2805 pub fn rewrite_tuple<'a, T>(
2806     context: &RewriteContext,
2807     items: &[&T],
2808     span: Span,
2809     shape: Shape,
2810 ) -> Option<String>
2811 where
2812     T: Rewrite + Spanned + ToExpr + 'a,
2813 {
2814     debug!("rewrite_tuple {:?}", shape);
2815     if context.use_block_indent() {
2816         // We use the same rule as funcation call for rewriting tuple.
2817         let force_trailing_comma = if context.inside_macro {
2818             span_ends_with_comma(context, span)
2819         } else {
2820             items.len() == 1
2821         };
2822         rewrite_call_inner(
2823             context,
2824             &String::new(),
2825             items,
2826             span,
2827             shape,
2828             context.config.fn_call_width(),
2829             force_trailing_comma,
2830         ).ok()
2831     } else {
2832         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2833     }
2834 }
2835
2836 pub fn rewrite_unary_prefix<R: Rewrite>(
2837     context: &RewriteContext,
2838     prefix: &str,
2839     rewrite: &R,
2840     shape: Shape,
2841 ) -> Option<String> {
2842     rewrite
2843         .rewrite(context, try_opt!(shape.offset_left(prefix.len())))
2844         .map(|r| format!("{}{}", prefix, r))
2845 }
2846
2847 // FIXME: this is probably not correct for multi-line Rewrites. we should
2848 // subtract suffix.len() from the last line budget, not the first!
2849 pub fn rewrite_unary_suffix<R: Rewrite>(
2850     context: &RewriteContext,
2851     suffix: &str,
2852     rewrite: &R,
2853     shape: Shape,
2854 ) -> Option<String> {
2855     rewrite
2856         .rewrite(context, try_opt!(shape.sub_width(suffix.len())))
2857         .map(|mut r| {
2858             r.push_str(suffix);
2859             r
2860         })
2861 }
2862
2863 fn rewrite_unary_op(
2864     context: &RewriteContext,
2865     op: &ast::UnOp,
2866     expr: &ast::Expr,
2867     shape: Shape,
2868 ) -> Option<String> {
2869     // For some reason, an UnOp is not spanned like BinOp!
2870     let operator_str = match *op {
2871         ast::UnOp::Deref => "*",
2872         ast::UnOp::Not => "!",
2873         ast::UnOp::Neg => "-",
2874     };
2875     rewrite_unary_prefix(context, operator_str, expr, shape)
2876 }
2877
2878 fn rewrite_assignment(
2879     context: &RewriteContext,
2880     lhs: &ast::Expr,
2881     rhs: &ast::Expr,
2882     op: Option<&ast::BinOp>,
2883     shape: Shape,
2884 ) -> Option<String> {
2885     let operator_str = match op {
2886         Some(op) => context.snippet(op.span),
2887         None => "=".to_owned(),
2888     };
2889
2890     // 1 = space between lhs and operator.
2891     let lhs_shape = try_opt!(shape.sub_width(operator_str.len() + 1));
2892     let lhs_str = format!(
2893         "{} {}",
2894         try_opt!(lhs.rewrite(context, lhs_shape)),
2895         operator_str
2896     );
2897
2898     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2899 }
2900
2901 // The left hand side must contain everything up to, and including, the
2902 // assignment operator.
2903 pub fn rewrite_assign_rhs<S: Into<String>>(
2904     context: &RewriteContext,
2905     lhs: S,
2906     ex: &ast::Expr,
2907     shape: Shape,
2908 ) -> Option<String> {
2909     let lhs = lhs.into();
2910     let last_line_width = last_line_width(&lhs) - if lhs.contains('\n') {
2911         shape.indent.width()
2912     } else {
2913         0
2914     };
2915     // 1 = space between operator and rhs.
2916     let orig_shape = try_opt!(shape.offset_left(last_line_width + 1));
2917     let rhs = try_opt!(choose_rhs(
2918         context,
2919         ex,
2920         shape,
2921         ex.rewrite(context, orig_shape)
2922     ));
2923     Some(lhs + &rhs)
2924 }
2925
2926 fn choose_rhs(
2927     context: &RewriteContext,
2928     expr: &ast::Expr,
2929     shape: Shape,
2930     orig_rhs: Option<String>,
2931 ) -> Option<String> {
2932     match orig_rhs {
2933         Some(ref new_str) if !new_str.contains('\n') => Some(format!(" {}", new_str)),
2934         _ => {
2935             // Expression did not fit on the same line as the identifier.
2936             // Try splitting the line and see if that works better.
2937             let new_shape = try_opt!(
2938                 Shape::indented(
2939                     shape.block().indent.block_indent(context.config),
2940                     context.config,
2941                 ).sub_width(shape.rhs_overhead(context.config))
2942             );
2943             let new_rhs = expr.rewrite(context, new_shape);
2944             let new_indent_str = &new_shape.indent.to_string(context.config);
2945
2946             match (orig_rhs, new_rhs) {
2947                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2948                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2949                 }
2950                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2951                 (None, None) => None,
2952                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2953             }
2954         }
2955     }
2956 }
2957
2958 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2959
2960     fn count_line_breaks(src: &str) -> usize {
2961         src.chars().filter(|&x| x == '\n').count()
2962     }
2963
2964     !next_line_rhs.contains('\n') ||
2965         count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2966 }
2967
2968 fn rewrite_expr_addrof(
2969     context: &RewriteContext,
2970     mutability: ast::Mutability,
2971     expr: &ast::Expr,
2972     shape: Shape,
2973 ) -> Option<String> {
2974     let operator_str = match mutability {
2975         ast::Mutability::Immutable => "&",
2976         ast::Mutability::Mutable => "&mut ",
2977     };
2978     rewrite_unary_prefix(context, operator_str, expr, shape)
2979 }
2980
2981 pub trait ToExpr {
2982     fn to_expr(&self) -> Option<&ast::Expr>;
2983     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2984 }
2985
2986 impl ToExpr for ast::Expr {
2987     fn to_expr(&self) -> Option<&ast::Expr> {
2988         Some(self)
2989     }
2990
2991     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2992         can_be_overflowed_expr(context, self, len)
2993     }
2994 }
2995
2996 impl ToExpr for ast::Ty {
2997     fn to_expr(&self) -> Option<&ast::Expr> {
2998         None
2999     }
3000
3001     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3002         can_be_overflowed_type(context, self, len)
3003     }
3004 }
3005
3006 impl<'a> ToExpr for TuplePatField<'a> {
3007     fn to_expr(&self) -> Option<&ast::Expr> {
3008         None
3009     }
3010
3011     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3012         can_be_overflowed_pat(context, self, len)
3013     }
3014 }
3015
3016 impl<'a> ToExpr for ast::StructField {
3017     fn to_expr(&self) -> Option<&ast::Expr> {
3018         None
3019     }
3020
3021     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
3022         false
3023     }
3024 }