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             inner_attributes, last_line_extendable, last_line_width, left_most_sub_expr, mk_sp,
  35             outer_attributes, paren_overhead, semicolon_for_stmt, stmt_expr,
  36             trimmed_last_line_width, wrap_str};
  37 use vertical::rewrite_with_alignment;
  38 use visitor::FmtVisitor;
  39
  40 impl Rewrite for ast::Expr {
  41     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  42         format_expr(self, ExprType::SubExpression, context, shape)
  43     }
  44 }
  45
  46 #[derive(PartialEq)]
  47 pub enum ExprType {
  48     Statement,
  49     SubExpression,
  50 }
  51
  52 fn combine_attr_and_expr(
  53     context: &RewriteContext,
  54     shape: Shape,
  55     expr: &ast::Expr,
  56     expr_str: &str,
  57 ) -> Option<String> {
  58     let attrs = outer_attributes(&expr.attrs);
  59     let attr_str = try_opt!(attrs.rewrite(context, shape));
  60     let separator = if attr_str.is_empty() {
  61         String::new()
  62     } else {
  63         // Try to recover comments between the attributes and the expression if available.
  64         let missing_snippet = context.snippet(mk_sp(attrs[attrs.len() - 1].span.hi, expr.span.lo));
  65         let comment_opening_pos = missing_snippet.chars().position(|c| c == '/');
  66         let prefer_same_line = if let Some(pos) = comment_opening_pos {
  67             !missing_snippet[..pos].contains('\n')
  68         } else {
  69             !missing_snippet.contains('\n')
  70         };
  71
  72         let trimmed = missing_snippet.trim();
  73         let missing_comment = if trimmed.is_empty() {
  74             String::new()
  75         } else {
  76             try_opt!(rewrite_comment(&trimmed, false, shape, context.config))
  77         };
  78
  79         // 2 = ` ` + ` `
  80         let one_line_width =
  81             attr_str.len() + missing_comment.len() + 2 + first_line_width(expr_str);
  82         let attr_expr_separator = if prefer_same_line && !missing_comment.starts_with("//") &&
  83             one_line_width <= shape.width
  84         {
  85             String::from(" ")
  86         } else {
  87             format!("\n{}", shape.indent.to_string(context.config))
  88         };
  89
  90         if missing_comment.is_empty() {
  91             attr_expr_separator
  92         } else {
  93             // 1 = ` `
  94             let one_line_width =
  95                 last_line_width(&attr_str) + 1 + first_line_width(&missing_comment);
  96             let attr_comment_separator = if prefer_same_line && one_line_width <= shape.width {
  97                 String::from(" ")
  98             } else {
  99                 format!("\n{}", shape.indent.to_string(context.config))
 100             };
 101             attr_comment_separator + &missing_comment + &attr_expr_separator
 102         }
 103     };
 104     Some(format!("{}{}{}", attr_str, separator, expr_str))
 105 }
 106
 107 pub fn format_expr(
 108     expr: &ast::Expr,
 109     expr_type: ExprType,
 110     context: &RewriteContext,
 111     shape: Shape,
 112 ) -> Option<String> {
 113     skip_out_of_file_lines_range!(context, expr.span);
 114
 115     if contains_skip(&*expr.attrs) {
 116         return Some(context.snippet(expr.span()));
 117     }
 118
 119     let expr_rw = match expr.node {
 120         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
 121             expr_vec.iter().map(|e| &**e),
 122             mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi),
 123             context,
 124             shape,
 125             false,
 126         ),
 127         ast::ExprKind::Lit(ref l) => match l.node {
 128             ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
 129                 rewrite_string_lit(context, l.span, shape)
 130             }
 131             _ => wrap_str(
 132                 context.snippet(expr.span),
 133                 context.config.max_width(),
 134                 shape,
 135             ),
 136         },
 137         ast::ExprKind::Call(ref callee, ref args) => {
 138             let inner_span = mk_sp(callee.span.hi, expr.span.hi);
 139             rewrite_call_with_binary_search(
 140                 context,
 141                 &**callee,
 142                 &args.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 143                 inner_span,
 144                 shape,
 145             )
 146         }
 147         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
 148         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
 149             // FIXME: format comments between operands and operator
 150             rewrite_pair(
 151                 &**lhs,
 152                 &**rhs,
 153                 "",
 154                 &format!(" {} ", context.snippet(op.span)),
 155                 "",
 156                 context,
 157                 shape,
 158             )
 159         }
 160         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 161         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 162             context,
 163             path,
 164             fields,
 165             base.as_ref().map(|e| &**e),
 166             expr.span,
 167             shape,
 168         ),
 169         ast::ExprKind::Tup(ref items) => rewrite_tuple(
 170             context,
 171             &items.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 172             expr.span,
 173             shape,
 174         ),
 175         ast::ExprKind::If(..) |
 176         ast::ExprKind::IfLet(..) |
 177         ast::ExprKind::ForLoop(..) |
 178         ast::ExprKind::Loop(..) |
 179         ast::ExprKind::While(..) |
 180         ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 181             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 182         ast::ExprKind::Block(ref block) => {
 183             match expr_type {
 184                 ExprType::Statement => {
 185                     if is_unsafe_block(block) {
 186                         block.rewrite(context, shape)
 187                     } else {
 188                         // Rewrite block without trying to put it in a single line.
 189                         if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 190                             return rw;
 191                         }
 192                         let prefix = try_opt!(block_prefix(context, block, shape));
 193                         rewrite_block_with_visitor(context, &prefix, block, shape)
 194                     }
 195                 }
 196                 ExprType::SubExpression => block.rewrite(context, shape),
 197             }
 198         }
 199         ast::ExprKind::Match(ref cond, ref arms) => {
 200             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 201         }
 202         ast::ExprKind::Path(ref qself, ref path) => {
 203             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 204         }
 205         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 206             rewrite_assignment(context, lhs, rhs, None, shape)
 207         }
 208         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 209             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 210         }
 211         ast::ExprKind::Continue(ref opt_ident) => {
 212             let id_str = match *opt_ident {
 213                 Some(ident) => format!(" {}", ident.node),
 214                 None => String::new(),
 215             };
 216             wrap_str(
 217                 format!("continue{}", id_str),
 218                 context.config.max_width(),
 219                 shape,
 220             )
 221         }
 222         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 223             let id_str = match *opt_ident {
 224                 Some(ident) => format!(" {}", ident.node),
 225                 None => String::new(),
 226             };
 227
 228             if let Some(ref expr) = *opt_expr {
 229                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 230             } else {
 231                 wrap_str(
 232                     format!("break{}", id_str),
 233                     context.config.max_width(),
 234                     shape,
 235                 )
 236             }
 237         }
 238         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 239             rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 240         }
 241         ast::ExprKind::Try(..) |
 242         ast::ExprKind::Field(..) |
 243         ast::ExprKind::TupField(..) |
 244         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 245         ast::ExprKind::Mac(ref mac) => {
 246             // Failure to rewrite a marco should not imply failure to
 247             // rewrite the expression.
 248             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 249                 wrap_str(
 250                     context.snippet(expr.span),
 251                     context.config.max_width(),
 252                     shape,
 253                 )
 254             })
 255         }
 256         ast::ExprKind::Ret(None) => {
 257             wrap_str("return".to_owned(), context.config.max_width(), shape)
 258         }
 259         ast::ExprKind::Ret(Some(ref expr)) => {
 260             rewrite_unary_prefix(context, "return ", &**expr, shape)
 261         }
 262         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 263         ast::ExprKind::AddrOf(mutability, ref expr) => {
 264             rewrite_expr_addrof(context, mutability, expr, shape)
 265         }
 266         ast::ExprKind::Cast(ref expr, ref ty) => {
 267             rewrite_pair(&**expr, &**ty, "", " as ", "", context, shape)
 268         }
 269         ast::ExprKind::Type(ref expr, ref ty) => {
 270             rewrite_pair(&**expr, &**ty, "", ": ", "", context, shape)
 271         }
 272         ast::ExprKind::Index(ref expr, ref index) => {
 273             rewrite_index(&**expr, &**index, context, shape)
 274         }
 275         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 276             let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
 277                 ("[ ", " ]")
 278             } else {
 279                 ("[", "]")
 280             };
 281             rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, shape)
 282         }
 283         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 284             let delim = match limits {
 285                 ast::RangeLimits::HalfOpen => "..",
 286                 ast::RangeLimits::Closed => "...",
 287             };
 288
 289             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 290                 match lhs.node {
 291                     ast::ExprKind::Lit(ref lit) => match lit.node {
 292                         ast::LitKind::FloatUnsuffixed(..) => {
 293                             context.snippet(lit.span).ends_with('.')
 294                         }
 295                         _ => false,
 296                     },
 297                     _ => false,
 298                 }
 299             }
 300
 301             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 302                 (Some(ref lhs), Some(ref rhs)) => {
 303                     let sp_delim = if context.config.spaces_around_ranges() {
 304                         format!(" {} ", delim)
 305                     } else if needs_space_before_range(context, lhs) {
 306                         format!(" {}", delim)
 307                     } else {
 308                         delim.into()
 309                     };
 310                     rewrite_pair(&**lhs, &**rhs, "", &sp_delim, "", context, shape)
 311                 }
 312                 (None, Some(ref rhs)) => {
 313                     let sp_delim = if context.config.spaces_around_ranges() {
 314                         format!("{} ", delim)
 315                     } else {
 316                         delim.into()
 317                     };
 318                     rewrite_unary_prefix(context, &sp_delim, &**rhs, shape)
 319                 }
 320                 (Some(ref lhs), None) => {
 321                     let sp_delim = if context.config.spaces_around_ranges() {
 322                         format!(" {}", delim)
 323                     } else {
 324                         delim.into()
 325                     };
 326                     rewrite_unary_suffix(context, &sp_delim, &**lhs, shape)
 327                 }
 328                 (None, None) => wrap_str(delim.into(), context.config.max_width(), shape),
 329             }
 330         }
 331         // We do not format these expressions yet, but they should still
 332         // satisfy our width restrictions.
 333         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => wrap_str(
 334             context.snippet(expr.span),
 335             context.config.max_width(),
 336             shape,
 337         ),
 338         ast::ExprKind::Catch(ref block) => {
 339             if let rewrite @ Some(_) = rewrite_single_line_block(context, "do catch ", block, shape)
 340             {
 341                 return rewrite;
 342             }
 343             // 9 = `do catch `
 344             let budget = shape.width.checked_sub(9).unwrap_or(0);
 345             Some(format!(
 346                 "{}{}",
 347                 "do catch ",
 348                 try_opt!(block.rewrite(&context, Shape::legacy(budget, shape.indent)))
 349             ))
 350         }
 351     };
 352
 353     expr_rw
 354         .and_then(|expr_str| {
 355             recover_comment_removed(expr_str, expr.span, context, shape)
 356         })
 357         .and_then(|expr_str| {
 358             combine_attr_and_expr(context, shape, expr, &expr_str)
 359         })
 360 }
 361
 362 pub fn rewrite_pair<LHS, RHS>(
 363     lhs: &LHS,
 364     rhs: &RHS,
 365     prefix: &str,
 366     infix: &str,
 367     suffix: &str,
 368     context: &RewriteContext,
 369     shape: Shape,
 370 ) -> Option<String>
 371 where
 372     LHS: Rewrite,
 373     RHS: Rewrite,
 374 {
 375     let sep = if infix.ends_with(' ') { " " } else { "" };
 376     let infix = infix.trim_right();
 377     let lhs_overhead = shape.used_width() + prefix.len() + infix.len();
 378     let lhs_shape = Shape {
 379         width: try_opt!(context.config.max_width().checked_sub(lhs_overhead)),
 380         ..shape
 381     };
 382     let lhs_result = try_opt!(
 383         lhs.rewrite(context, lhs_shape)
 384             .map(|lhs_str| format!("{}{}{}", prefix, lhs_str, infix))
 385     );
 386
 387     // Try to the both lhs and rhs on the same line.
 388     let rhs_orig_result = shape
 389         .offset_left(last_line_width(&lhs_result) + suffix.len() + sep.len())
 390         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 391     if let Some(ref rhs_result) = rhs_orig_result {
 392         // If the rhs looks like block expression, we allow it to stay on the same line
 393         // with the lhs even if it is multi-lined.
 394         let allow_same_line = rhs_result
 395             .lines()
 396             .next()
 397             .map(|first_line| first_line.ends_with('{'))
 398             .unwrap_or(false);
 399         if !rhs_result.contains('\n') || allow_same_line {
 400             return Some(format!("{}{}{}{}", lhs_result, sep, rhs_result, suffix));
 401         }
 402     }
 403
 404     // We have to use multiple lines.
 405     // Re-evaluate the rhs because we have more space now:
 406     let rhs_shape = match context.config.control_style() {
 407         Style::Legacy => {
 408             try_opt!(shape.sub_width(suffix.len() + prefix.len())).visual_indent(prefix.len())
 409         }
 410         Style::Rfc => {
 411             // Try to calculate the initial constraint on the right hand side.
 412             let rhs_overhead = shape.rhs_overhead(context.config);
 413             try_opt!(
 414                 Shape::indented(shape.indent.block_indent(context.config), context.config)
 415                     .sub_width(rhs_overhead)
 416             )
 417         }
 418     };
 419     let rhs_result = try_opt!(rhs.rewrite(context, rhs_shape));
 420     Some(format!(
 421         "{}\n{}{}{}",
 422         lhs_result,
 423         rhs_shape.indent.to_string(context.config),
 424         rhs_result,
 425         suffix
 426     ))
 427 }
 428
 429 pub fn rewrite_array<'a, I>(
 430     expr_iter: I,
 431     span: Span,
 432     context: &RewriteContext,
 433     shape: Shape,
 434     trailing_comma: bool,
 435 ) -> Option<String>
 436 where
 437     I: Iterator<Item = &'a ast::Expr>,
 438 {
 439     let bracket_size = if context.config.spaces_within_square_brackets() {
 440         2 // "[ "
 441     } else {
 442         1 // "["
 443     };
 444
 445     let mut nested_shape = match context.config.array_layout() {
 446         IndentStyle::Block => try_opt!(
 447             shape
 448                 .block()
 449                 .block_indent(context.config.tab_spaces())
 450                 .with_max_width(context.config)
 451                 .sub_width(1)
 452         ),
 453         IndentStyle::Visual => try_opt!(
 454             shape
 455                 .visual_indent(bracket_size)
 456                 .sub_width(bracket_size * 2)
 457         ),
 458     };
 459
 460     let items = itemize_list(
 461         context.codemap,
 462         expr_iter,
 463         "]",
 464         |item| item.span.lo,
 465         |item| item.span.hi,
 466         |item| item.rewrite(context, nested_shape),
 467         span.lo,
 468         span.hi,
 469         false,
 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         false,
 592     );
 593     let item_vec = arg_items.collect::<Vec<_>>();
 594     // 1 = space between arguments and return type.
 595     let horizontal_budget = nested_shape
 596         .width
 597         .checked_sub(ret_str.len() + 1)
 598         .unwrap_or(0);
 599     let tactic = definitive_tactic(
 600         &item_vec,
 601         ListTactic::HorizontalVertical,
 602         Separator::Comma,
 603         horizontal_budget,
 604     );
 605     let arg_shape = match tactic {
 606         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 607         _ => arg_shape,
 608     };
 609
 610     let fmt = ListFormatting {
 611         tactic: tactic,
 612         separator: ",",
 613         trailing_separator: SeparatorTactic::Never,
 614         shape: arg_shape,
 615         ends_with_newline: false,
 616         preserve_newline: true,
 617         config: context.config,
 618     };
 619     let list_str = try_opt!(write_list(&item_vec, &fmt));
 620     let mut prefix = format!("{}|{}|", mover, list_str);
 621     // 1 = space between `|...|` and body.
 622     let extra_offset = extra_offset(&prefix, shape) + 1;
 623
 624     if !ret_str.is_empty() {
 625         if prefix.contains('\n') {
 626             prefix.push('\n');
 627             prefix.push_str(&argument_offset.to_string(context.config));
 628         } else {
 629             prefix.push(' ');
 630         }
 631         prefix.push_str(&ret_str);
 632     }
 633
 634     Some((prefix, extra_offset))
 635 }
 636
 637 // This functions is pretty messy because of the rules around closures and blocks:
 638 // FIXME - the below is probably no longer true in full.
 639 //   * if there is a return type, then there must be braces,
 640 //   * given a closure with braces, whether that is parsed to give an inner block
 641 //     or not depends on if there is a return type and if there are statements
 642 //     in that block,
 643 //   * if the first expression in the body ends with a block (i.e., is a
 644 //     statement without needing a semi-colon), then adding or removing braces
 645 //     can change whether it is treated as an expression or statement.
 646 fn rewrite_closure(
 647     capture: ast::CaptureBy,
 648     fn_decl: &ast::FnDecl,
 649     body: &ast::Expr,
 650     span: Span,
 651     context: &RewriteContext,
 652     shape: Shape,
 653 ) -> Option<String> {
 654     let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
 655         capture,
 656         fn_decl,
 657         body,
 658         span,
 659         context,
 660         shape,
 661     ));
 662     // 1 = space between `|...|` and body.
 663     let body_shape = try_opt!(shape.offset_left(extra_offset));
 664
 665     if let ast::ExprKind::Block(ref block) = body.node {
 666         // The body of the closure is an empty block.
 667         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 668             return Some(format!("{} {{}}", prefix));
 669         }
 670
 671         // Figure out if the block is necessary.
 672         let needs_block = block.rules != ast::BlockCheckMode::Default || block.stmts.len() > 1 ||
 673             context.inside_macro ||
 674             block_contains_comment(block, context.codemap) ||
 675             prefix.contains('\n');
 676
 677         let no_return_type = if let ast::FunctionRetTy::Default(_) = fn_decl.output {
 678             true
 679         } else {
 680             false
 681         };
 682         if no_return_type && !needs_block {
 683             // lock.stmts.len() == 1
 684             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 685                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 686                     return Some(rw);
 687                 }
 688             }
 689         }
 690
 691         if !needs_block {
 692             // We need braces, but we might still prefer a one-liner.
 693             let stmt = &block.stmts[0];
 694             // 4 = braces and spaces.
 695             if let Some(body_shape) = body_shape.sub_width(4) {
 696                 // Checks if rewrite succeeded and fits on a single line.
 697                 if let Some(rewrite) = and_one_line(stmt.rewrite(context, body_shape)) {
 698                     return Some(format!("{} {{ {} }}", prefix, rewrite));
 699                 }
 700             }
 701         }
 702
 703         // Either we require a block, or tried without and failed.
 704         rewrite_closure_block(&block, &prefix, context, body_shape)
 705     } else {
 706         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
 707             // The closure originally had a non-block expression, but we can't fit on
 708             // one line, so we'll insert a block.
 709             rewrite_closure_with_block(context, body_shape, &prefix, body)
 710         })
 711     }
 712 }
 713
 714 // Rewrite closure with a single expression wrapping its body with block.
 715 fn rewrite_closure_with_block(
 716     context: &RewriteContext,
 717     shape: Shape,
 718     prefix: &str,
 719     body: &ast::Expr,
 720 ) -> Option<String> {
 721     let block = ast::Block {
 722         stmts: vec![
 723             ast::Stmt {
 724                 id: ast::NodeId::new(0),
 725                 node: ast::StmtKind::Expr(ptr::P(body.clone())),
 726                 span: body.span,
 727             },
 728         ],
 729         id: ast::NodeId::new(0),
 730         rules: ast::BlockCheckMode::Default,
 731         span: body.span,
 732     };
 733     rewrite_closure_block(&block, prefix, context, shape)
 734 }
 735
 736 // Rewrite closure with a single expression without wrapping its body with block.
 737 fn rewrite_closure_expr(
 738     expr: &ast::Expr,
 739     prefix: &str,
 740     context: &RewriteContext,
 741     shape: Shape,
 742 ) -> Option<String> {
 743     let mut rewrite = expr.rewrite(context, shape);
 744     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 745         rewrite = and_one_line(rewrite);
 746     }
 747     rewrite.map(|rw| format!("{} {}", prefix, rw))
 748 }
 749
 750 // Rewrite closure whose body is block.
 751 fn rewrite_closure_block(
 752     block: &ast::Block,
 753     prefix: &str,
 754     context: &RewriteContext,
 755     shape: Shape,
 756 ) -> Option<String> {
 757     // Start with visual indent, then fall back to block indent if the
 758     // closure is large.
 759     let block_threshold = context.config.closure_block_indent_threshold();
 760     if block_threshold >= 0 {
 761         if let Some(block_str) = block.rewrite(&context, shape) {
 762             if block_str.matches('\n').count() <= block_threshold as usize &&
 763                 !need_block_indent(&block_str, shape)
 764             {
 765                 if let Some(block_str) = block_str.rewrite(context, shape) {
 766                     return Some(format!("{} {}", prefix, block_str));
 767                 }
 768             }
 769         }
 770     }
 771
 772     // The body of the closure is big enough to be block indented, that
 773     // means we must re-format.
 774     let block_shape = shape.block();
 775     let block_str = try_opt!(block.rewrite(&context, block_shape));
 776     Some(format!("{} {}", prefix, block_str))
 777 }
 778
 779 fn and_one_line(x: Option<String>) -> Option<String> {
 780     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 781 }
 782
 783 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 784     debug!("nop_block_collapse {:?} {}", block_str, budget);
 785     block_str.map(|block_str| {
 786         if block_str.starts_with('{') && budget >= 2 &&
 787             (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 788         {
 789             "{}".to_owned()
 790         } else {
 791             block_str.to_owned()
 792         }
 793     })
 794 }
 795
 796 fn rewrite_empty_block(
 797     context: &RewriteContext,
 798     block: &ast::Block,
 799     shape: Shape,
 800 ) -> Option<String> {
 801     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 802     {
 803         return Some("{}".to_owned());
 804     }
 805
 806     // If a block contains only a single-line comment, then leave it on one line.
 807     let user_str = context.snippet(block.span);
 808     let user_str = user_str.trim();
 809     if user_str.starts_with('{') && user_str.ends_with('}') {
 810         let comment_str = user_str[1..user_str.len() - 1].trim();
 811         if block.stmts.is_empty() && !comment_str.contains('\n') &&
 812             !comment_str.starts_with("//") && comment_str.len() + 4 <= shape.width
 813         {
 814             return Some(format!("{{ {} }}", comment_str));
 815         }
 816     }
 817
 818     None
 819 }
 820
 821 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 822     Some(match block.rules {
 823         ast::BlockCheckMode::Unsafe(..) => {
 824             let snippet = context.snippet(block.span);
 825             let open_pos = try_opt!(snippet.find_uncommented("{"));
 826             // Extract comment between unsafe and block start.
 827             let trimmed = &snippet[6..open_pos].trim();
 828
 829             if !trimmed.is_empty() {
 830                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 831                 let budget = try_opt!(shape.width.checked_sub(9));
 832                 format!(
 833                     "unsafe {} ",
 834                     try_opt!(rewrite_comment(
 835                         trimmed,
 836                         true,
 837                         Shape::legacy(budget, shape.indent + 7),
 838                         context.config,
 839                     ))
 840                 )
 841             } else {
 842                 "unsafe ".to_owned()
 843             }
 844         }
 845         ast::BlockCheckMode::Default => String::new(),
 846     })
 847 }
 848
 849 fn rewrite_single_line_block(
 850     context: &RewriteContext,
 851     prefix: &str,
 852     block: &ast::Block,
 853     shape: Shape,
 854 ) -> Option<String> {
 855     if is_simple_block(block, context.codemap) {
 856         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 857         let expr_str = try_opt!(block.stmts[0].rewrite(context, expr_shape));
 858         let result = format!("{}{{ {} }}", prefix, expr_str);
 859         if result.len() <= shape.width && !result.contains('\n') {
 860             return Some(result);
 861         }
 862     }
 863     None
 864 }
 865
 866 fn rewrite_block_with_visitor(
 867     context: &RewriteContext,
 868     prefix: &str,
 869     block: &ast::Block,
 870     shape: Shape,
 871 ) -> Option<String> {
 872     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 873         return rw;
 874     }
 875
 876     let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 877     visitor.block_indent = shape.indent;
 878     visitor.is_if_else_block = context.is_if_else_block;
 879     match block.rules {
 880         ast::BlockCheckMode::Unsafe(..) => {
 881             let snippet = context.snippet(block.span);
 882             let open_pos = try_opt!(snippet.find_uncommented("{"));
 883             visitor.last_pos = block.span.lo + BytePos(open_pos as u32)
 884         }
 885         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo,
 886     }
 887
 888     visitor.visit_block(block, None);
 889     Some(format!("{}{}", prefix, visitor.buffer))
 890 }
 891
 892 impl Rewrite for ast::Block {
 893     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 894         // shape.width is used only for the single line case: either the empty block `{}`,
 895         // or an unsafe expression `unsafe { e }`.
 896         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 897             return rw;
 898         }
 899
 900         let prefix = try_opt!(block_prefix(context, self, shape));
 901         if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 902             return rw;
 903         }
 904
 905         rewrite_block_with_visitor(context, &prefix, self, shape)
 906     }
 907 }
 908
 909 impl Rewrite for ast::Stmt {
 910     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 911         skip_out_of_file_lines_range!(context, self.span());
 912
 913         let result = match self.node {
 914             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 915             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 916                 let suffix = if semicolon_for_stmt(context, self) {
 917                     ";"
 918                 } else {
 919                     ""
 920                 };
 921
 922                 format_expr(
 923                     ex,
 924                     match self.node {
 925                         ast::StmtKind::Expr(_) => ExprType::SubExpression,
 926                         ast::StmtKind::Semi(_) => ExprType::Statement,
 927                         _ => unreachable!(),
 928                     },
 929                     context,
 930                     try_opt!(shape.sub_width(suffix.len())),
 931                 ).map(|s| s + suffix)
 932             }
 933             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 934         };
 935         result.and_then(|res| {
 936             recover_comment_removed(res, self.span(), context, shape)
 937         })
 938     }
 939 }
 940
 941 // Rewrite condition if the given expression has one.
 942 fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 943     match expr.node {
 944         ast::ExprKind::Match(ref cond, _) => {
 945             // `match `cond` {`
 946             let cond_shape = match context.config.control_style() {
 947                 Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
 948                 Style::Rfc => try_opt!(shape.offset_left(8)),
 949             };
 950             cond.rewrite(context, cond_shape)
 951         }
 952         ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
 953             stmt_expr(&block.stmts[0]).and_then(|e| rewrite_cond(context, e, shape))
 954         }
 955         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 956             let alt_block_sep =
 957                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 958             control_flow
 959                 .rewrite_cond(context, shape, &alt_block_sep)
 960                 .and_then(|rw| Some(rw.0))
 961         }),
 962     }
 963 }
 964
 965 // Abstraction over control flow expressions
 966 #[derive(Debug)]
 967 struct ControlFlow<'a> {
 968     cond: Option<&'a ast::Expr>,
 969     block: &'a ast::Block,
 970     else_block: Option<&'a ast::Expr>,
 971     label: Option<ast::SpannedIdent>,
 972     pat: Option<&'a ast::Pat>,
 973     keyword: &'a str,
 974     matcher: &'a str,
 975     connector: &'a str,
 976     allow_single_line: bool,
 977     // True if this is an `if` expression in an `else if` :-( hacky
 978     nested_if: bool,
 979     span: Span,
 980 }
 981
 982 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 983     match expr.node {
 984         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 985             cond,
 986             None,
 987             if_block,
 988             else_block.as_ref().map(|e| &**e),
 989             expr_type == ExprType::SubExpression,
 990             false,
 991             expr.span,
 992         )),
 993         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 994             Some(ControlFlow::new_if(
 995                 cond,
 996                 Some(pat),
 997                 if_block,
 998                 else_block.as_ref().map(|e| &**e),
 999                 expr_type == ExprType::SubExpression,
1000                 false,
1001                 expr.span,
1002             ))
1003         }
1004         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
1005             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
1006         }
1007         ast::ExprKind::Loop(ref block, label) => {
1008             Some(ControlFlow::new_loop(block, label, expr.span))
1009         }
1010         ast::ExprKind::While(ref cond, ref block, label) => {
1011             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
1012         }
1013         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
1014             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
1015         ),
1016         _ => None,
1017     }
1018 }
1019
1020 impl<'a> ControlFlow<'a> {
1021     fn new_if(
1022         cond: &'a ast::Expr,
1023         pat: Option<&'a ast::Pat>,
1024         block: &'a ast::Block,
1025         else_block: Option<&'a ast::Expr>,
1026         allow_single_line: bool,
1027         nested_if: bool,
1028         span: Span,
1029     ) -> ControlFlow<'a> {
1030         ControlFlow {
1031             cond: Some(cond),
1032             block: block,
1033             else_block: else_block,
1034             label: None,
1035             pat: pat,
1036             keyword: "if",
1037             matcher: match pat {
1038                 Some(..) => "let",
1039                 None => "",
1040             },
1041             connector: " =",
1042             allow_single_line: allow_single_line,
1043             nested_if: nested_if,
1044             span: span,
1045         }
1046     }
1047
1048     fn new_loop(
1049         block: &'a ast::Block,
1050         label: Option<ast::SpannedIdent>,
1051         span: Span,
1052     ) -> ControlFlow<'a> {
1053         ControlFlow {
1054             cond: None,
1055             block: block,
1056             else_block: None,
1057             label: label,
1058             pat: None,
1059             keyword: "loop",
1060             matcher: "",
1061             connector: "",
1062             allow_single_line: false,
1063             nested_if: false,
1064             span: span,
1065         }
1066     }
1067
1068     fn new_while(
1069         pat: Option<&'a ast::Pat>,
1070         cond: &'a ast::Expr,
1071         block: &'a ast::Block,
1072         label: Option<ast::SpannedIdent>,
1073         span: Span,
1074     ) -> ControlFlow<'a> {
1075         ControlFlow {
1076             cond: Some(cond),
1077             block: block,
1078             else_block: None,
1079             label: label,
1080             pat: pat,
1081             keyword: "while",
1082             matcher: match pat {
1083                 Some(..) => "let",
1084                 None => "",
1085             },
1086             connector: " =",
1087             allow_single_line: false,
1088             nested_if: false,
1089             span: span,
1090         }
1091     }
1092
1093     fn new_for(
1094         pat: &'a ast::Pat,
1095         cond: &'a ast::Expr,
1096         block: &'a ast::Block,
1097         label: Option<ast::SpannedIdent>,
1098         span: Span,
1099     ) -> ControlFlow<'a> {
1100         ControlFlow {
1101             cond: Some(cond),
1102             block: block,
1103             else_block: None,
1104             label: label,
1105             pat: Some(pat),
1106             keyword: "for",
1107             matcher: "",
1108             connector: " in",
1109             allow_single_line: false,
1110             nested_if: false,
1111             span: span,
1112         }
1113     }
1114
1115     fn rewrite_single_line(
1116         &self,
1117         pat_expr_str: &str,
1118         context: &RewriteContext,
1119         width: usize,
1120     ) -> Option<String> {
1121         assert!(self.allow_single_line);
1122         let else_block = try_opt!(self.else_block);
1123         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1124
1125         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1126             if !is_simple_block(self.block, context.codemap) ||
1127                 !is_simple_block(else_node, context.codemap) ||
1128                 pat_expr_str.contains('\n')
1129             {
1130                 return None;
1131             }
1132
1133             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
1134             let expr = &self.block.stmts[0];
1135             let if_str = try_opt!(expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1136
1137             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
1138             let else_expr = &else_node.stmts[0];
1139             let else_str =
1140                 try_opt!(else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1141
1142             if if_str.contains('\n') || else_str.contains('\n') {
1143                 return None;
1144             }
1145
1146             let result = format!(
1147                 "{} {} {{ {} }} else {{ {} }}",
1148                 self.keyword,
1149                 pat_expr_str,
1150                 if_str,
1151                 else_str
1152             );
1153
1154             if result.len() <= width {
1155                 return Some(result);
1156             }
1157         }
1158
1159         None
1160     }
1161 }
1162
1163 impl<'a> ControlFlow<'a> {
1164     fn rewrite_cond(
1165         &self,
1166         context: &RewriteContext,
1167         shape: Shape,
1168         alt_block_sep: &str,
1169     ) -> Option<(String, usize)> {
1170         // Do not take the rhs overhead from the upper expressions into account
1171         // when rewriting pattern.
1172         let new_width = context
1173             .config
1174             .max_width()
1175             .checked_sub(shape.used_width())
1176             .unwrap_or(0);
1177         let fresh_shape = Shape {
1178             width: new_width,
1179             ..shape
1180         };
1181         let constr_shape = if self.nested_if {
1182             // We are part of an if-elseif-else chain. Our constraints are tightened.
1183             // 7 = "} else " .len()
1184             try_opt!(fresh_shape.offset_left(7))
1185         } else {
1186             fresh_shape
1187         };
1188
1189         let label_string = rewrite_label(self.label);
1190         // 1 = space after keyword.
1191         let offset = self.keyword.len() + label_string.len() + 1;
1192
1193         let pat_expr_string = match self.cond {
1194             Some(cond) => {
1195                 let cond_shape = match context.config.control_style() {
1196                     Style::Legacy => try_opt!(constr_shape.shrink_left(offset)),
1197                     Style::Rfc => try_opt!(constr_shape.offset_left(offset)),
1198                 };
1199                 try_opt!(rewrite_pat_expr(
1200                     context,
1201                     self.pat,
1202                     cond,
1203                     self.matcher,
1204                     self.connector,
1205                     self.keyword,
1206                     cond_shape,
1207                 ))
1208             }
1209             None => String::new(),
1210         };
1211
1212         let brace_overhead =
1213             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1214                 // 2 = ` {`
1215                 2
1216             } else {
1217                 0
1218             };
1219         let one_line_budget = context
1220             .config
1221             .max_width()
1222             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1223             .unwrap_or(0);
1224         let force_newline_brace = context.config.control_style() == Style::Rfc &&
1225             (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget) &&
1226             !last_line_extendable(&pat_expr_string);
1227
1228         // Try to format if-else on single line.
1229         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1230             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1231
1232             if let Some(cond_str) = trial {
1233                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1234                     return Some((cond_str, 0));
1235                 }
1236             }
1237         }
1238
1239         let cond_span = if let Some(cond) = self.cond {
1240             cond.span
1241         } else {
1242             mk_sp(self.block.span.lo, self.block.span.lo)
1243         };
1244
1245         // for event in event
1246         let between_kwd_cond = mk_sp(
1247             context.codemap.span_after(self.span, self.keyword.trim()),
1248             self.pat
1249                 .map_or(cond_span.lo, |p| if self.matcher.is_empty() {
1250                     p.span.lo
1251                 } else {
1252                     context.codemap.span_before(self.span, self.matcher.trim())
1253                 }),
1254         );
1255
1256         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1257
1258         let after_cond_comment =
1259             extract_comment(mk_sp(cond_span.hi, self.block.span.lo), context, shape);
1260
1261         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1262             ""
1263         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine ||
1264             force_newline_brace
1265         {
1266             alt_block_sep
1267         } else {
1268             " "
1269         };
1270
1271         let used_width = if pat_expr_string.contains('\n') {
1272             last_line_width(&pat_expr_string)
1273         } else {
1274             // 2 = spaces after keyword and condition.
1275             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1276         };
1277
1278         Some((
1279             format!(
1280                 "{}{}{}{}{}",
1281                 label_string,
1282                 self.keyword,
1283                 between_kwd_cond_comment.as_ref().map_or(
1284                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1285                         ""
1286                     } else {
1287                         " "
1288                     },
1289                     |s| &**s,
1290                 ),
1291                 pat_expr_string,
1292                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1293             ),
1294             used_width,
1295         ))
1296     }
1297 }
1298
1299 impl<'a> Rewrite for ControlFlow<'a> {
1300     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1301         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1302
1303         let alt_block_sep =
1304             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1305         let (cond_str, used_width) = try_opt!(self.rewrite_cond(context, shape, &alt_block_sep));
1306         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1307         if used_width == 0 {
1308             return Some(cond_str);
1309         }
1310
1311         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1312         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1313         // we should avoid the single line case.
1314         let block_width = if self.else_block.is_some() || self.nested_if {
1315             min(1, block_width)
1316         } else {
1317             block_width
1318         };
1319         let block_shape = Shape {
1320             width: block_width,
1321             ..shape
1322         };
1323         let mut block_context = context.clone();
1324         block_context.is_if_else_block = self.else_block.is_some();
1325         let block_str = try_opt!(rewrite_block_with_visitor(
1326             &block_context,
1327             "",
1328             self.block,
1329             block_shape,
1330         ));
1331
1332         let mut result = format!("{}{}", cond_str, block_str);
1333
1334         if let Some(else_block) = self.else_block {
1335             let shape = Shape::indented(shape.indent, context.config);
1336             let mut last_in_chain = false;
1337             let rewrite = match else_block.node {
1338                 // If the else expression is another if-else expression, prevent it
1339                 // from being formatted on a single line.
1340                 // Note how we're passing the original shape, as the
1341                 // cost of "else" should not cascade.
1342                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1343                     ControlFlow::new_if(
1344                         cond,
1345                         Some(pat),
1346                         if_block,
1347                         next_else_block.as_ref().map(|e| &**e),
1348                         false,
1349                         true,
1350                         mk_sp(else_block.span.lo, self.span.hi),
1351                     ).rewrite(context, shape)
1352                 }
1353                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1354                     ControlFlow::new_if(
1355                         cond,
1356                         None,
1357                         if_block,
1358                         next_else_block.as_ref().map(|e| &**e),
1359                         false,
1360                         true,
1361                         mk_sp(else_block.span.lo, self.span.hi),
1362                     ).rewrite(context, shape)
1363                 }
1364                 _ => {
1365                     last_in_chain = true;
1366                     // When rewriting a block, the width is only used for single line
1367                     // blocks, passing 1 lets us avoid that.
1368                     let else_shape = Shape {
1369                         width: min(1, shape.width),
1370                         ..shape
1371                     };
1372                     format_expr(else_block, ExprType::Statement, context, else_shape)
1373                 }
1374             };
1375
1376             let between_kwd_else_block = mk_sp(
1377                 self.block.span.hi,
1378                 context
1379                     .codemap
1380                     .span_before(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1381             );
1382             let between_kwd_else_block_comment =
1383                 extract_comment(between_kwd_else_block, context, shape);
1384
1385             let after_else = mk_sp(
1386                 context
1387                     .codemap
1388                     .span_after(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1389                 else_block.span.lo,
1390             );
1391             let after_else_comment = extract_comment(after_else, context, shape);
1392
1393             let between_sep = match context.config.control_brace_style() {
1394                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1395                     &*alt_block_sep
1396                 }
1397                 ControlBraceStyle::AlwaysSameLine => " ",
1398             };
1399             let after_sep = match context.config.control_brace_style() {
1400                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1401                 _ => " ",
1402             };
1403             try_opt!(
1404                 write!(
1405                     &mut result,
1406                     "{}else{}",
1407                     between_kwd_else_block_comment
1408                         .as_ref()
1409                         .map_or(between_sep, |s| &**s),
1410                     after_else_comment.as_ref().map_or(after_sep, |s| &**s)
1411                 ).ok()
1412             );
1413             result.push_str(&try_opt!(rewrite));
1414         }
1415
1416         Some(result)
1417     }
1418 }
1419
1420 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
1421     match label {
1422         Some(ident) => format!("{}: ", ident.node),
1423         None => "".to_owned(),
1424     }
1425 }
1426
1427 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1428     let comment_str = context.snippet(span);
1429     if contains_comment(&comment_str) {
1430         let comment = try_opt!(rewrite_comment(
1431             comment_str.trim(),
1432             false,
1433             shape,
1434             context.config,
1435         ));
1436         Some(format!(
1437             "\n{indent}{}\n{indent}",
1438             comment,
1439             indent = shape.indent.to_string(context.config)
1440         ))
1441     } else {
1442         None
1443     }
1444 }
1445
1446 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1447     let snippet = codemap.span_to_snippet(block.span).unwrap();
1448     contains_comment(&snippet)
1449 }
1450
1451 // Checks that a block contains no statements, an expression and no comments.
1452 // FIXME: incorrectly returns false when comment is contained completely within
1453 // the expression.
1454 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1455     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
1456         !block_contains_comment(block, codemap))
1457 }
1458
1459 /// Checks whether a block contains at most one statement or expression, and no comments.
1460 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1461     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1462 }
1463
1464 /// Checks whether a block contains no statements, expressions, or comments.
1465 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1466     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1467 }
1468
1469 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1470     match stmt.node {
1471         ast::StmtKind::Expr(..) => true,
1472         _ => false,
1473     }
1474 }
1475
1476 fn is_unsafe_block(block: &ast::Block) -> bool {
1477     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1478         true
1479     } else {
1480         false
1481     }
1482 }
1483
1484 // inter-match-arm-comment-rules:
1485 //  - all comments following a match arm before the start of the next arm
1486 //    are about the second arm
1487 fn rewrite_match_arm_comment(
1488     context: &RewriteContext,
1489     missed_str: &str,
1490     shape: Shape,
1491     arm_indent_str: &str,
1492 ) -> Option<String> {
1493     // The leading "," is not part of the arm-comment
1494     let missed_str = match missed_str.find_uncommented(",") {
1495         Some(n) => &missed_str[n + 1..],
1496         None => &missed_str[..],
1497     };
1498
1499     let mut result = String::new();
1500     // any text not preceeded by a newline is pushed unmodified to the block
1501     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1502     result.push_str(&missed_str[..first_brk]);
1503     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1504
1505     let first = missed_str
1506         .find(|c: char| !c.is_whitespace())
1507         .unwrap_or(missed_str.len());
1508     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1509         // Excessive vertical whitespace before comment should be preserved
1510         // FIXME handle vertical whitespace better
1511         result.push('\n');
1512     }
1513     let missed_str = missed_str[first..].trim();
1514     if !missed_str.is_empty() {
1515         let comment = try_opt!(rewrite_comment(&missed_str, false, shape, context.config));
1516         result.push('\n');
1517         result.push_str(arm_indent_str);
1518         result.push_str(&comment);
1519     }
1520
1521     Some(result)
1522 }
1523
1524 fn rewrite_match(
1525     context: &RewriteContext,
1526     cond: &ast::Expr,
1527     arms: &[ast::Arm],
1528     shape: Shape,
1529     span: Span,
1530     attrs: &[ast::Attribute],
1531 ) -> Option<String> {
1532     if arms.is_empty() {
1533         return None;
1534     }
1535
1536     // Do not take the rhs overhead from the upper expressions into account
1537     // when rewriting match condition.
1538     let new_width = try_opt!(context.config.max_width().checked_sub(shape.used_width()));
1539     let cond_shape = Shape {
1540         width: new_width,
1541         ..shape
1542     };
1543     // 6 = `match `
1544     let cond_shape = match context.config.control_style() {
1545         Style::Legacy => try_opt!(cond_shape.shrink_left(6)),
1546         Style::Rfc => try_opt!(cond_shape.offset_left(6)),
1547     };
1548     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1549     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1550     let block_sep = match context.config.control_brace_style() {
1551         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1552         _ if last_line_extendable(&cond_str) => " ",
1553         // 2 = ` {`
1554         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => &alt_block_sep,
1555         _ => " ",
1556     };
1557
1558     let nested_indent_str = shape
1559         .indent
1560         .block_indent(context.config)
1561         .to_string(context.config);
1562     // Inner attributes.
1563     let inner_attrs = &inner_attributes(attrs);
1564     let inner_attrs_str = if inner_attrs.is_empty() {
1565         String::new()
1566     } else {
1567         try_opt!(
1568             inner_attrs
1569                 .rewrite(context, shape)
1570                 .map(|s| format!("\n{}{}", nested_indent_str, s))
1571         )
1572     };
1573
1574     let open_brace_pos = if inner_attrs.is_empty() {
1575         context
1576             .codemap
1577             .span_after(mk_sp(cond.span.hi, arms[0].span().lo), "{")
1578     } else {
1579         inner_attrs[inner_attrs.len() - 1].span().hi
1580     };
1581
1582     Some(format!(
1583         "match {}{}{{{}{}\n{}}}",
1584         cond_str,
1585         block_sep,
1586         inner_attrs_str,
1587         try_opt!(rewrite_match_arms(
1588             context,
1589             arms,
1590             shape,
1591             span,
1592             open_brace_pos,
1593         )),
1594         shape.indent.to_string(context.config),
1595     ))
1596 }
1597
1598 fn arm_comma(config: &Config, body: &ast::Expr) -> &'static str {
1599     if config.match_block_trailing_comma() {
1600         ","
1601     } else if let ast::ExprKind::Block(ref block) = body.node {
1602         if let ast::BlockCheckMode::Default = block.rules {
1603             ""
1604         } else {
1605             ","
1606         }
1607     } else {
1608         ","
1609     }
1610 }
1611
1612 fn rewrite_match_arms(
1613     context: &RewriteContext,
1614     arms: &[ast::Arm],
1615     shape: Shape,
1616     span: Span,
1617     open_brace_pos: BytePos,
1618 ) -> Option<String> {
1619     let mut result = String::new();
1620
1621     let arm_shape = if context.config.indent_match_arms() {
1622         shape.block_indent(context.config.tab_spaces())
1623     } else {
1624         shape.block_indent(0)
1625     }.with_max_width(context.config);
1626     let arm_indent_str = arm_shape.indent.to_string(context.config);
1627
1628     let arm_num = arms.len();
1629     for (i, arm) in arms.iter().enumerate() {
1630         // Make sure we get the stuff between arms.
1631         let missed_str = if i == 0 {
1632             context.snippet(mk_sp(open_brace_pos, arm.span().lo))
1633         } else {
1634             context.snippet(mk_sp(arms[i - 1].span().hi, arm.span().lo))
1635         };
1636         let comment = try_opt!(rewrite_match_arm_comment(
1637             context,
1638             &missed_str,
1639             arm_shape,
1640             &arm_indent_str,
1641         ));
1642         if !comment.chars().all(|c| c == ' ') {
1643             result.push_str(&comment);
1644         }
1645         result.push('\n');
1646         result.push_str(&arm_indent_str);
1647
1648         let arm_str = rewrite_match_arm(context, arm, arm_shape);
1649         if let Some(ref arm_str) = arm_str {
1650             // Trim the trailing comma if necessary.
1651             if i == arm_num - 1 && context.config.trailing_comma() == SeparatorTactic::Never &&
1652                 arm_str.ends_with(',')
1653             {
1654                 result.push_str(&arm_str[0..arm_str.len() - 1])
1655             } else {
1656                 result.push_str(arm_str)
1657             }
1658         } else {
1659             // We couldn't format the arm, just reproduce the source.
1660             let snippet = context.snippet(arm.span());
1661             result.push_str(&snippet);
1662             if context.config.trailing_comma() != SeparatorTactic::Never {
1663                 result.push_str(arm_comma(context.config, &arm.body))
1664             }
1665         }
1666     }
1667     // BytePos(1) = closing match brace.
1668     let last_span = mk_sp(arms[arms.len() - 1].span().hi, span.hi - BytePos(1));
1669     let last_comment = context.snippet(last_span);
1670     let comment = try_opt!(rewrite_match_arm_comment(
1671         context,
1672         &last_comment,
1673         arm_shape,
1674         &arm_indent_str,
1675     ));
1676     result.push_str(&comment);
1677
1678     Some(result)
1679 }
1680
1681 fn rewrite_match_arm(context: &RewriteContext, arm: &ast::Arm, shape: Shape) -> Option<String> {
1682     let attr_str = if !arm.attrs.is_empty() {
1683         if contains_skip(&arm.attrs) {
1684             return None;
1685         }
1686         format!(
1687             "{}\n{}",
1688             try_opt!(arm.attrs.rewrite(context, shape)),
1689             shape.indent.to_string(context.config)
1690         )
1691     } else {
1692         String::new()
1693     };
1694     let pats_str = try_opt!(rewrite_match_pattern(context, &arm.pats, &arm.guard, shape));
1695     let pats_str = attr_str + &pats_str;
1696     rewrite_match_body(context, &arm.body, &pats_str, shape, arm.guard.is_some())
1697 }
1698
1699 fn rewrite_match_pattern(
1700     context: &RewriteContext,
1701     pats: &Vec<ptr::P<ast::Pat>>,
1702     guard: &Option<ptr::P<ast::Expr>>,
1703     shape: Shape,
1704 ) -> Option<String> {
1705     // Patterns
1706     // 5 = ` => {`
1707     let pat_shape = try_opt!(shape.sub_width(5));
1708
1709     let pat_strs = try_opt!(
1710         pats.iter()
1711             .map(|p| p.rewrite(context, pat_shape))
1712             .collect::<Option<Vec<_>>>()
1713     );
1714
1715     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1716     let tactic = definitive_tactic(
1717         &items,
1718         ListTactic::HorizontalVertical,
1719         Separator::VerticalBar,
1720         pat_shape.width,
1721     );
1722     let fmt = ListFormatting {
1723         tactic: tactic,
1724         separator: " |",
1725         trailing_separator: SeparatorTactic::Never,
1726         shape: pat_shape,
1727         ends_with_newline: false,
1728         preserve_newline: false,
1729         config: context.config,
1730     };
1731     let pats_str = try_opt!(write_list(&items, &fmt));
1732
1733     // Guard
1734     let guard_str = try_opt!(rewrite_guard(
1735         context,
1736         guard,
1737         shape,
1738         trimmed_last_line_width(&pats_str),
1739     ));
1740
1741     Some(format!("{}{}", pats_str, guard_str))
1742 }
1743
1744 fn rewrite_match_body(
1745     context: &RewriteContext,
1746     body: &ptr::P<ast::Expr>,
1747     pats_str: &str,
1748     shape: Shape,
1749     has_guard: bool,
1750 ) -> Option<String> {
1751     let (extend, body) = match body.node {
1752         ast::ExprKind::Block(ref block)
1753             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1754         {
1755             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1756                 (expr.can_be_overflowed(context, 1), &**expr)
1757             } else {
1758                 (false, &**body)
1759             }
1760         }
1761         _ => (body.can_be_overflowed(context, 1), &**body),
1762     };
1763
1764     let comma = arm_comma(&context.config, body);
1765     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1766     let alt_block_sep = alt_block_sep.as_str();
1767     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1768         (true, is_empty_block(block, context.codemap))
1769     } else {
1770         (false, false)
1771     };
1772
1773     let combine_orig_body = |body_str: &str| {
1774         let block_sep = match context.config.control_brace_style() {
1775             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1776             _ => " ",
1777         };
1778
1779         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1780     };
1781
1782     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1783     let next_line_indent = if is_block {
1784         shape.indent
1785     } else {
1786         shape.indent.block_indent(context.config)
1787     };
1788     let combine_next_line_body = |body_str: &str| {
1789         if is_block {
1790             return Some(format!(
1791                 "{} =>\n{}{}",
1792                 pats_str,
1793                 next_line_indent.to_string(context.config),
1794                 body_str
1795             ));
1796         }
1797
1798         let indent_str = shape.indent.to_string(context.config);
1799         let nested_indent_str = next_line_indent.to_string(context.config);
1800         let (body_prefix, body_suffix) = if context.config.wrap_match_arms() {
1801             let comma = if context.config.match_block_trailing_comma() {
1802                 ","
1803             } else {
1804                 ""
1805             };
1806             ("{", format!("\n{}}}{}", indent_str, comma))
1807         } else {
1808             ("", String::from(","))
1809         };
1810
1811         let block_sep = match context.config.control_brace_style() {
1812             ControlBraceStyle::AlwaysNextLine => format!("{}{}\n", alt_block_sep, body_prefix),
1813             _ if body_prefix.is_empty() => "\n".to_owned(),
1814             _ if forbid_same_line => format!("{}{}\n", alt_block_sep, body_prefix),
1815             _ => format!(" {}\n", body_prefix),
1816         } + &nested_indent_str;
1817
1818         Some(format!(
1819             "{} =>{}{}{}",
1820             pats_str,
1821             block_sep,
1822             body_str,
1823             body_suffix
1824         ))
1825     };
1826
1827     // Let's try and get the arm body on the same line as the condition.
1828     // 4 = ` => `.len()
1829     let orig_body_shape = shape
1830         .offset_left(extra_offset(&pats_str, shape) + 4)
1831         .and_then(|shape| shape.sub_width(comma.len()));
1832     let orig_body = if let Some(body_shape) = orig_body_shape {
1833         let rewrite = nop_block_collapse(
1834             format_expr(body, ExprType::Statement, context, body_shape),
1835             body_shape.width,
1836         );
1837
1838         match rewrite {
1839             Some(ref body_str)
1840                 if !forbid_same_line &&
1841                     (is_block ||
1842                         (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1843             {
1844                 return combine_orig_body(body_str);
1845             }
1846             _ => rewrite,
1847         }
1848     } else {
1849         None
1850     };
1851     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1852
1853     // Try putting body on the next line and see if it looks better.
1854     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1855     let next_line_body = nop_block_collapse(
1856         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1857         next_line_body_shape.width,
1858     );
1859     match (orig_body, next_line_body) {
1860         (Some(ref orig_str), Some(ref next_line_str))
1861             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1862         {
1863             combine_next_line_body(next_line_str)
1864         }
1865         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1866             combine_orig_body(orig_str)
1867         }
1868         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1869             combine_next_line_body(next_line_str)
1870         }
1871         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1872         (None, None) => None,
1873         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1874     }
1875 }
1876
1877 // The `if ...` guard on a match arm.
1878 fn rewrite_guard(
1879     context: &RewriteContext,
1880     guard: &Option<ptr::P<ast::Expr>>,
1881     shape: Shape,
1882     // The amount of space used up on this line for the pattern in
1883     // the arm (excludes offset).
1884     pattern_width: usize,
1885 ) -> Option<String> {
1886     if let Some(ref guard) = *guard {
1887         // First try to fit the guard string on the same line as the pattern.
1888         // 4 = ` if `, 5 = ` => {`
1889         let cond_shape = shape
1890             .offset_left(pattern_width + 4)
1891             .and_then(|s| s.sub_width(5));
1892         if let Some(cond_shape) = cond_shape {
1893             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1894                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1895                     return Some(format!(" if {}", cond_str));
1896                 }
1897             }
1898         }
1899
1900         // Not enough space to put the guard after the pattern, try a newline.
1901         // 3 = `if `, 5 = ` => {`
1902         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1903             .offset_left(3)
1904             .and_then(|s| s.sub_width(5));
1905         if let Some(cond_shape) = cond_shape {
1906             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1907                 return Some(format!(
1908                     "\n{}if {}",
1909                     cond_shape.indent.to_string(context.config),
1910                     cond_str
1911                 ));
1912             }
1913         }
1914
1915         None
1916     } else {
1917         Some(String::new())
1918     }
1919 }
1920
1921 fn rewrite_pat_expr(
1922     context: &RewriteContext,
1923     pat: Option<&ast::Pat>,
1924     expr: &ast::Expr,
1925     matcher: &str,
1926     // Connecting piece between pattern and expression,
1927     // *without* trailing space.
1928     connector: &str,
1929     keyword: &str,
1930     shape: Shape,
1931 ) -> Option<String> {
1932     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1933     if let Some(pat) = pat {
1934         let matcher = if matcher.is_empty() {
1935             matcher.to_owned()
1936         } else {
1937             format!("{} ", matcher)
1938         };
1939         let pat_shape =
1940             try_opt!(try_opt!(shape.offset_left(matcher.len())).sub_width(connector.len()));
1941         let pat_string = try_opt!(pat.rewrite(context, pat_shape));
1942         let result = format!("{}{}{}", matcher, pat_string, connector);
1943         return rewrite_assign_rhs(context, result, expr, shape);
1944     }
1945
1946     let expr_rw = expr.rewrite(context, shape);
1947     // The expression may (partially) fit on the current line.
1948     // We do not allow splitting between `if` and condition.
1949     if keyword == "if" || expr_rw.is_some() {
1950         return expr_rw;
1951     }
1952
1953     // The expression won't fit on the current line, jump to next.
1954     let nested_shape = shape
1955         .block_indent(context.config.tab_spaces())
1956         .with_max_width(context.config);
1957     let nested_indent_str = nested_shape.indent.to_string(context.config);
1958     expr.rewrite(context, nested_shape)
1959         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1960 }
1961
1962 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1963     let string_lit = context.snippet(span);
1964
1965     if !context.config.format_strings() && !context.config.force_format_strings() {
1966         if string_lit
1967             .lines()
1968             .rev()
1969             .skip(1)
1970             .all(|line| line.ends_with('\\'))
1971         {
1972             let new_indent = shape.visual_indent(1).indent;
1973             return Some(String::from(
1974                 string_lit
1975                     .lines()
1976                     .map(|line| {
1977                         new_indent.to_string(context.config) + line.trim_left()
1978                     })
1979                     .collect::<Vec<_>>()
1980                     .join("\n")
1981                     .trim_left(),
1982             ));
1983         } else {
1984             return Some(string_lit);
1985         }
1986     }
1987
1988     if !context.config.force_format_strings() &&
1989         !string_requires_rewrite(context, span, &string_lit, shape)
1990     {
1991         return Some(string_lit);
1992     }
1993
1994     let fmt = StringFormat {
1995         opener: "\"",
1996         closer: "\"",
1997         line_start: " ",
1998         line_end: "\\",
1999         shape: shape,
2000         trim_end: false,
2001         config: context.config,
2002     };
2003
2004     // Remove the quote characters.
2005     let str_lit = &string_lit[1..string_lit.len() - 1];
2006
2007     rewrite_string(str_lit, &fmt)
2008 }
2009
2010 fn string_requires_rewrite(
2011     context: &RewriteContext,
2012     span: Span,
2013     string: &str,
2014     shape: Shape,
2015 ) -> bool {
2016     if context.codemap.lookup_char_pos(span.lo).col.0 != shape.indent.width() {
2017         return true;
2018     }
2019
2020     for (i, line) in string.lines().enumerate() {
2021         if i == 0 {
2022             if line.len() > shape.width {
2023                 return true;
2024             }
2025         } else {
2026             if line.len() > shape.width + shape.indent.width() {
2027                 return true;
2028             }
2029         }
2030     }
2031
2032     false
2033 }
2034
2035 pub fn rewrite_call_with_binary_search<R>(
2036     context: &RewriteContext,
2037     callee: &R,
2038     args: &[&ast::Expr],
2039     span: Span,
2040     shape: Shape,
2041 ) -> Option<String>
2042 where
2043     R: Rewrite,
2044 {
2045     let force_trailing_comma = if context.inside_macro {
2046         span_ends_with_comma(context, span)
2047     } else {
2048         false
2049     };
2050     let closure = |callee_max_width| {
2051         // FIXME using byte lens instead of char lens (and probably all over the
2052         // place too)
2053         let callee_shape = Shape {
2054             width: callee_max_width,
2055             ..shape
2056         };
2057         let callee_str = callee
2058             .rewrite(context, callee_shape)
2059             .ok_or(Ordering::Greater)?;
2060
2061         rewrite_call_inner(
2062             context,
2063             &callee_str,
2064             args,
2065             span,
2066             shape,
2067             context.config.fn_call_width(),
2068             force_trailing_comma,
2069         )
2070     };
2071
2072     binary_search(1, shape.width, closure)
2073 }
2074
2075 pub fn rewrite_call(
2076     context: &RewriteContext,
2077     callee: &str,
2078     args: &[ptr::P<ast::Expr>],
2079     span: Span,
2080     shape: Shape,
2081 ) -> Option<String> {
2082     let force_trailing_comma = if context.inside_macro {
2083         span_ends_with_comma(context, span)
2084     } else {
2085         false
2086     };
2087     rewrite_call_inner(
2088         context,
2089         &callee,
2090         &args.iter().map(|x| &**x).collect::<Vec<_>>(),
2091         span,
2092         shape,
2093         context.config.fn_call_width(),
2094         force_trailing_comma,
2095     ).ok()
2096 }
2097
2098 pub fn rewrite_call_inner<'a, T>(
2099     context: &RewriteContext,
2100     callee_str: &str,
2101     args: &[&T],
2102     span: Span,
2103     shape: Shape,
2104     args_max_width: usize,
2105     force_trailing_comma: bool,
2106 ) -> Result<String, Ordering>
2107 where
2108     T: Rewrite + Spanned + ToExpr + 'a,
2109 {
2110     // 2 = `( `, 1 = `(`
2111     let paren_overhead = if context.config.spaces_within_parens() {
2112         2
2113     } else {
2114         1
2115     };
2116     let used_width = extra_offset(&callee_str, shape);
2117     let one_line_width = shape
2118         .width
2119         .checked_sub(used_width + 2 * paren_overhead)
2120         .ok_or(Ordering::Greater)?;
2121
2122     let nested_shape = shape_from_fn_call_style(
2123         context,
2124         shape,
2125         used_width + 2 * paren_overhead,
2126         used_width + paren_overhead,
2127     ).ok_or(Ordering::Greater)?;
2128
2129     let span_lo = context.codemap.span_after(span, "(");
2130     let args_span = mk_sp(span_lo, span.hi);
2131
2132     let (extendable, list_str) = rewrite_call_args(
2133         context,
2134         args,
2135         args_span,
2136         nested_shape,
2137         one_line_width,
2138         args_max_width,
2139         force_trailing_comma,
2140     ).ok_or(Ordering::Less)?;
2141
2142     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2143         let mut new_context = context.clone();
2144         new_context.use_block = true;
2145         return rewrite_call_inner(
2146             &new_context,
2147             callee_str,
2148             args,
2149             span,
2150             shape,
2151             args_max_width,
2152             force_trailing_comma,
2153         );
2154     }
2155
2156     let args_shape = shape
2157         .sub_width(last_line_width(&callee_str))
2158         .ok_or(Ordering::Less)?;
2159     Ok(format!(
2160         "{}{}",
2161         callee_str,
2162         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2163     ))
2164 }
2165
2166 fn need_block_indent(s: &str, shape: Shape) -> bool {
2167     s.lines().skip(1).any(|s| {
2168         s.find(|c| !char::is_whitespace(c))
2169             .map_or(false, |w| w + 1 < shape.indent.width())
2170     })
2171 }
2172
2173 fn rewrite_call_args<'a, T>(
2174     context: &RewriteContext,
2175     args: &[&T],
2176     span: Span,
2177     shape: Shape,
2178     one_line_width: usize,
2179     args_max_width: usize,
2180     force_trailing_comma: bool,
2181 ) -> Option<(bool, String)>
2182 where
2183     T: Rewrite + Spanned + ToExpr + 'a,
2184 {
2185     let items = itemize_list(
2186         context.codemap,
2187         args.iter(),
2188         ")",
2189         |item| item.span().lo,
2190         |item| item.span().hi,
2191         |item| item.rewrite(context, shape),
2192         span.lo,
2193         span.hi,
2194         true,
2195     );
2196     let mut item_vec: Vec<_> = items.collect();
2197
2198     // Try letting the last argument overflow to the next line with block
2199     // indentation. If its first line fits on one line with the other arguments,
2200     // we format the function arguments horizontally.
2201     let tactic = try_overflow_last_arg(
2202         context,
2203         &mut item_vec,
2204         &args[..],
2205         shape,
2206         one_line_width,
2207         args_max_width,
2208     );
2209
2210     let fmt = ListFormatting {
2211         tactic: tactic,
2212         separator: ",",
2213         trailing_separator: if force_trailing_comma {
2214             SeparatorTactic::Always
2215         } else if context.inside_macro || !context.use_block_indent() {
2216             SeparatorTactic::Never
2217         } else {
2218             context.config.trailing_comma()
2219         },
2220         shape: shape,
2221         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2222         preserve_newline: false,
2223         config: context.config,
2224     };
2225
2226     write_list(&item_vec, &fmt).map(|args_str| {
2227         (tactic != DefinitiveListTactic::Vertical, args_str)
2228     })
2229 }
2230
2231 fn try_overflow_last_arg<'a, T>(
2232     context: &RewriteContext,
2233     item_vec: &mut Vec<ListItem>,
2234     args: &[&T],
2235     shape: Shape,
2236     one_line_width: usize,
2237     args_max_width: usize,
2238 ) -> DefinitiveListTactic
2239 where
2240     T: Rewrite + Spanned + ToExpr + 'a,
2241 {
2242     let overflow_last = can_be_overflowed(&context, args);
2243
2244     // Replace the last item with its first line to see if it fits with
2245     // first arguments.
2246     let placeholder = if overflow_last {
2247         let mut context = context.clone();
2248         if let Some(expr) = args[args.len() - 1].to_expr() {
2249             match expr.node {
2250                 ast::ExprKind::MethodCall(..) => context.force_one_line_chain = true,
2251                 _ => (),
2252             }
2253         }
2254         last_arg_shape(&context, &item_vec, shape, args_max_width).and_then(|arg_shape| {
2255             rewrite_last_arg_with_overflow(&context, args, &mut item_vec[args.len() - 1], arg_shape)
2256         })
2257     } else {
2258         None
2259     };
2260
2261     let mut tactic = definitive_tactic(
2262         &*item_vec,
2263         ListTactic::LimitedHorizontalVertical(args_max_width),
2264         Separator::Comma,
2265         one_line_width,
2266     );
2267
2268     // Replace the stub with the full overflowing last argument if the rewrite
2269     // succeeded and its first line fits with the other arguments.
2270     match (overflow_last, tactic, placeholder) {
2271         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2272             item_vec[args.len() - 1].item = placeholder;
2273         }
2274         _ if args.len() >= 1 => {
2275             item_vec[args.len() - 1].item = args.last()
2276                 .and_then(|last_arg| last_arg.rewrite(context, shape));
2277             tactic = definitive_tactic(
2278                 &*item_vec,
2279                 ListTactic::LimitedHorizontalVertical(args_max_width),
2280                 Separator::Comma,
2281                 one_line_width,
2282             );
2283         }
2284         _ => (),
2285     }
2286
2287     tactic
2288 }
2289
2290 fn last_arg_shape(
2291     context: &RewriteContext,
2292     items: &Vec<ListItem>,
2293     shape: Shape,
2294     args_max_width: usize,
2295 ) -> Option<Shape> {
2296     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2297         acc + i.item.as_ref().map_or(0, |s| first_line_width(&s))
2298     });
2299     let max_width = min(args_max_width, shape.width);
2300     let arg_indent = if context.use_block_indent() {
2301         shape.block().indent.block_unindent(context.config)
2302     } else {
2303         shape.block().indent
2304     };
2305     Some(Shape {
2306         width: try_opt!(max_width.checked_sub(overhead)),
2307         indent: arg_indent,
2308         offset: 0,
2309     })
2310 }
2311
2312 // Rewriting closure which is placed at the end of the function call's arg.
2313 // Returns `None` if the reformatted closure 'looks bad'.
2314 fn rewrite_last_closure(
2315     context: &RewriteContext,
2316     expr: &ast::Expr,
2317     shape: Shape,
2318 ) -> Option<String> {
2319     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2320         let body = match body.node {
2321             ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
2322                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2323             }
2324             _ => body,
2325         };
2326         let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
2327             capture,
2328             fn_decl,
2329             body,
2330             expr.span,
2331             context,
2332             shape,
2333         ));
2334         // If the closure goes multi line before its body, do not overflow the closure.
2335         if prefix.contains('\n') {
2336             return None;
2337         }
2338         let body_shape = try_opt!(shape.offset_left(extra_offset));
2339         // When overflowing the closure which consists of a single control flow expression,
2340         // force to use block if its condition uses multi line.
2341         let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
2342             .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
2343             .unwrap_or(false);
2344         if is_multi_lined_cond {
2345             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2346         }
2347
2348         // Seems fine, just format the closure in usual manner.
2349         return expr.rewrite(context, shape);
2350     }
2351     None
2352 }
2353
2354 fn rewrite_last_arg_with_overflow<'a, T>(
2355     context: &RewriteContext,
2356     args: &[&T],
2357     last_item: &mut ListItem,
2358     shape: Shape,
2359 ) -> Option<String>
2360 where
2361     T: Rewrite + Spanned + ToExpr + 'a,
2362 {
2363     let last_arg = args[args.len() - 1];
2364     let rewrite = if let Some(expr) = last_arg.to_expr() {
2365         match expr.node {
2366             // When overflowing the closure which consists of a single control flow expression,
2367             // force to use block if its condition uses multi line.
2368             ast::ExprKind::Closure(..) => {
2369                 // If the argument consists of multiple closures, we do not overflow
2370                 // the last closure.
2371                 if args.len() > 1 &&
2372                     args.iter()
2373                         .rev()
2374                         .skip(1)
2375                         .filter_map(|arg| arg.to_expr())
2376                         .any(|expr| match expr.node {
2377                             ast::ExprKind::Closure(..) => true,
2378                             _ => false,
2379                         }) {
2380                     None
2381                 } else {
2382                     rewrite_last_closure(context, expr, shape)
2383                 }
2384             }
2385             _ => expr.rewrite(context, shape),
2386         }
2387     } else {
2388         last_arg.rewrite(context, shape)
2389     };
2390
2391     if let Some(rewrite) = rewrite {
2392         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2393         last_item.item = rewrite_first_line;
2394         Some(rewrite)
2395     } else {
2396         None
2397     }
2398 }
2399
2400 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2401 where
2402     T: Rewrite + Spanned + ToExpr + 'a,
2403 {
2404     args.last()
2405         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2406 }
2407
2408 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2409     match expr.node {
2410         ast::ExprKind::Match(..) => {
2411             (context.use_block_indent() && args_len == 1) ||
2412                 (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2413         }
2414         ast::ExprKind::If(..) |
2415         ast::ExprKind::IfLet(..) |
2416         ast::ExprKind::ForLoop(..) |
2417         ast::ExprKind::Loop(..) |
2418         ast::ExprKind::While(..) |
2419         ast::ExprKind::WhileLet(..) => {
2420             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2421         }
2422         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2423             context.use_block_indent() ||
2424                 context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2425         }
2426         ast::ExprKind::Array(..) |
2427         ast::ExprKind::Call(..) |
2428         ast::ExprKind::Mac(..) |
2429         ast::ExprKind::MethodCall(..) |
2430         ast::ExprKind::Struct(..) |
2431         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2432         ast::ExprKind::AddrOf(_, ref expr) |
2433         ast::ExprKind::Box(ref expr) |
2434         ast::ExprKind::Try(ref expr) |
2435         ast::ExprKind::Unary(_, ref expr) |
2436         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2437         _ => false,
2438     }
2439 }
2440
2441 pub fn wrap_args_with_parens(
2442     context: &RewriteContext,
2443     args_str: &str,
2444     is_extendable: bool,
2445     shape: Shape,
2446     nested_shape: Shape,
2447 ) -> String {
2448     if !context.use_block_indent() ||
2449         (context.inside_macro && !args_str.contains('\n') &&
2450             args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2451     {
2452         if context.config.spaces_within_parens() && args_str.len() > 0 {
2453             format!("( {} )", args_str)
2454         } else {
2455             format!("({})", args_str)
2456         }
2457     } else {
2458         format!(
2459             "(\n{}{}\n{})",
2460             nested_shape.indent.to_string(context.config),
2461             args_str,
2462             shape.block().indent.to_string(context.config)
2463         )
2464     }
2465 }
2466
2467 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2468     let snippet = context.snippet(span);
2469     snippet
2470         .trim_right_matches(|c: char| c == ')' || c.is_whitespace())
2471         .ends_with(',')
2472 }
2473
2474 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2475     debug!("rewrite_paren, shape: {:?}", shape);
2476     let total_paren_overhead = paren_overhead(context);
2477     let paren_overhead = total_paren_overhead / 2;
2478     let sub_shape = try_opt!(
2479         shape
2480             .offset_left(paren_overhead)
2481             .and_then(|s| s.sub_width(paren_overhead))
2482     );
2483
2484     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && s.len() > 0 {
2485         format!("( {} )", s)
2486     } else {
2487         format!("({})", s)
2488     };
2489
2490     let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2491     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2492
2493     if subexpr_str.contains('\n') ||
2494         first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2495     {
2496         Some(paren_wrapper(&subexpr_str))
2497     } else {
2498         None
2499     }
2500 }
2501
2502 fn rewrite_index(
2503     expr: &ast::Expr,
2504     index: &ast::Expr,
2505     context: &RewriteContext,
2506     shape: Shape,
2507 ) -> Option<String> {
2508     let expr_str = try_opt!(expr.rewrite(context, shape));
2509
2510     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2511         ("[ ", " ]")
2512     } else {
2513         ("[", "]")
2514     };
2515
2516     let offset = last_line_width(&expr_str) + lbr.len();
2517     let rhs_overhead = shape.rhs_overhead(context.config);
2518     let index_shape = if expr_str.contains('\n') {
2519         Shape::legacy(context.config.max_width(), shape.indent)
2520             .offset_left(offset)
2521             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2522     } else {
2523         shape.visual_indent(offset).sub_width(offset + rbr.len())
2524     };
2525     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2526
2527     // Return if index fits in a single line.
2528     match orig_index_rw {
2529         Some(ref index_str) if !index_str.contains('\n') => {
2530             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2531         }
2532         _ => (),
2533     }
2534
2535     // Try putting index on the next line and see if it fits in a single line.
2536     let indent = shape.indent.block_indent(context.config);
2537     let index_shape = try_opt!(Shape::indented(indent, context.config).offset_left(lbr.len()));
2538     let index_shape = try_opt!(index_shape.sub_width(rbr.len() + rhs_overhead));
2539     let new_index_rw = index.rewrite(context, index_shape);
2540     match (orig_index_rw, new_index_rw) {
2541         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2542             "{}\n{}{}{}{}",
2543             expr_str,
2544             indent.to_string(&context.config),
2545             lbr,
2546             new_index_str,
2547             rbr
2548         )),
2549         (None, Some(ref new_index_str)) => Some(format!(
2550             "{}\n{}{}{}{}",
2551             expr_str,
2552             indent.to_string(&context.config),
2553             lbr,
2554             new_index_str,
2555             rbr
2556         )),
2557         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2558         _ => None,
2559     }
2560 }
2561
2562 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2563     if base.is_some() {
2564         return false;
2565     }
2566
2567     fields.iter().all(|field| !field.is_shorthand)
2568 }
2569
2570 fn rewrite_struct_lit<'a>(
2571     context: &RewriteContext,
2572     path: &ast::Path,
2573     fields: &'a [ast::Field],
2574     base: Option<&'a ast::Expr>,
2575     span: Span,
2576     shape: Shape,
2577 ) -> Option<String> {
2578     debug!("rewrite_struct_lit: shape {:?}", shape);
2579
2580     enum StructLitField<'a> {
2581         Regular(&'a ast::Field),
2582         Base(&'a ast::Expr),
2583     }
2584
2585     // 2 = " {".len()
2586     let path_shape = try_opt!(shape.sub_width(2));
2587     let path_str = try_opt!(rewrite_path(
2588         context,
2589         PathContext::Expr,
2590         None,
2591         path,
2592         path_shape,
2593     ));
2594
2595     if fields.len() == 0 && base.is_none() {
2596         return Some(format!("{} {{}}", path_str));
2597     }
2598
2599     // Foo { a: Foo } - indent is +3, width is -5.
2600     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
2601
2602     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2603     let body_lo = context.codemap.span_after(span, "{");
2604     let fields_str = if struct_lit_can_be_aligned(fields, &base) &&
2605         context.config.struct_field_align_threshold() > 0
2606     {
2607         try_opt!(rewrite_with_alignment(
2608             fields,
2609             context,
2610             shape,
2611             mk_sp(body_lo, span.hi),
2612             one_line_width,
2613         ))
2614     } else {
2615         let field_iter = fields
2616             .into_iter()
2617             .map(StructLitField::Regular)
2618             .chain(base.into_iter().map(StructLitField::Base));
2619
2620         let span_lo = |item: &StructLitField| match *item {
2621             StructLitField::Regular(field) => field.span().lo,
2622             StructLitField::Base(expr) => {
2623                 let last_field_hi = fields.last().map_or(span.lo, |field| field.span.hi);
2624                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo));
2625                 let pos = snippet.find_uncommented("..").unwrap();
2626                 last_field_hi + BytePos(pos as u32)
2627             }
2628         };
2629         let span_hi = |item: &StructLitField| match *item {
2630             StructLitField::Regular(field) => field.span().hi,
2631             StructLitField::Base(expr) => expr.span.hi,
2632         };
2633         let rewrite = |item: &StructLitField| match *item {
2634             StructLitField::Regular(field) => {
2635                 // The 1 taken from the v_budget is for the comma.
2636                 rewrite_field(context, field, try_opt!(v_shape.sub_width(1)), 0)
2637             }
2638             StructLitField::Base(expr) => {
2639                 // 2 = ..
2640                 expr.rewrite(context, try_opt!(v_shape.offset_left(2)))
2641                     .map(|s| format!("..{}", s))
2642             }
2643         };
2644
2645         let items = itemize_list(
2646             context.codemap,
2647             field_iter,
2648             "}",
2649             span_lo,
2650             span_hi,
2651             rewrite,
2652             body_lo,
2653             span.hi,
2654             false,
2655         );
2656         let item_vec = items.collect::<Vec<_>>();
2657
2658         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2659         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2660         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2661
2662         try_opt!(write_list(&item_vec, &fmt))
2663     };
2664
2665     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2666     Some(format!("{} {{{}}}", path_str, fields_str))
2667
2668     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2669     // of space, we should fall back to BlockIndent.
2670 }
2671
2672 pub fn wrap_struct_field(
2673     context: &RewriteContext,
2674     fields_str: &str,
2675     shape: Shape,
2676     nested_shape: Shape,
2677     one_line_width: usize,
2678 ) -> String {
2679     if context.config.struct_lit_style() == IndentStyle::Block &&
2680         (fields_str.contains('\n') ||
2681             context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti ||
2682             fields_str.len() > one_line_width)
2683     {
2684         format!(
2685             "\n{}{}\n{}",
2686             nested_shape.indent.to_string(context.config),
2687             fields_str,
2688             shape.indent.to_string(context.config)
2689         )
2690     } else {
2691         // One liner or visual indent.
2692         format!(" {} ", fields_str)
2693     }
2694 }
2695
2696 pub fn struct_lit_field_separator(config: &Config) -> &str {
2697     colon_spaces(
2698         config.space_before_struct_lit_field_colon(),
2699         config.space_after_struct_lit_field_colon(),
2700     )
2701 }
2702
2703 pub fn rewrite_field(
2704     context: &RewriteContext,
2705     field: &ast::Field,
2706     shape: Shape,
2707     prefix_max_width: usize,
2708 ) -> Option<String> {
2709     if contains_skip(&field.attrs) {
2710         return wrap_str(
2711             context.snippet(field.span()),
2712             context.config.max_width(),
2713             shape,
2714         );
2715     }
2716     let name = &field.ident.node.to_string();
2717     if field.is_shorthand {
2718         Some(name.to_string())
2719     } else {
2720         let mut separator = String::from(struct_lit_field_separator(context.config));
2721         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2722             separator.push(' ');
2723         }
2724         let overhead = name.len() + separator.len();
2725         let expr_shape = try_opt!(shape.offset_left(overhead));
2726         let expr = field.expr.rewrite(context, expr_shape);
2727
2728         let mut attrs_str = try_opt!(field.attrs.rewrite(context, shape));
2729         if !attrs_str.is_empty() {
2730             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2731         };
2732
2733         match expr {
2734             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2735             None => {
2736                 let expr_offset = shape.indent.block_indent(context.config);
2737                 let expr = field
2738                     .expr
2739                     .rewrite(context, Shape::indented(expr_offset, context.config));
2740                 expr.map(|s| {
2741                     format!(
2742                         "{}{}:\n{}{}",
2743                         attrs_str,
2744                         name,
2745                         expr_offset.to_string(&context.config),
2746                         s
2747                     )
2748                 })
2749             }
2750         }
2751     }
2752 }
2753
2754 fn shape_from_fn_call_style(
2755     context: &RewriteContext,
2756     shape: Shape,
2757     overhead: usize,
2758     offset: usize,
2759 ) -> Option<Shape> {
2760     if context.use_block_indent() {
2761         // 1 = ","
2762         shape
2763             .block()
2764             .block_indent(context.config.tab_spaces())
2765             .with_max_width(context.config)
2766             .sub_width(1)
2767     } else {
2768         shape.visual_indent(offset).sub_width(overhead)
2769     }
2770 }
2771
2772 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2773     context: &RewriteContext,
2774     items: &[&T],
2775     span: Span,
2776     shape: Shape,
2777 ) -> Option<String>
2778 where
2779     T: Rewrite + Spanned + ToExpr + 'a,
2780 {
2781     let mut items = items.iter();
2782     // In case of length 1, need a trailing comma
2783     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2784     if items.len() == 1 {
2785         // 3 = "(" + ",)"
2786         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
2787         return items.next().unwrap().rewrite(context, nested_shape).map(
2788             |s| if context.config.spaces_within_parens() {
2789                 format!("( {}, )", s)
2790             } else {
2791                 format!("({},)", s)
2792             },
2793         );
2794     }
2795
2796     let list_lo = context.codemap.span_after(span, "(");
2797     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
2798     let items = itemize_list(
2799         context.codemap,
2800         items,
2801         ")",
2802         |item| item.span().lo,
2803         |item| item.span().hi,
2804         |item| item.rewrite(context, nested_shape),
2805         list_lo,
2806         span.hi - BytePos(1),
2807         false,
2808     );
2809     let item_vec: Vec<_> = items.collect();
2810     let tactic = definitive_tactic(
2811         &item_vec,
2812         ListTactic::HorizontalVertical,
2813         Separator::Comma,
2814         nested_shape.width,
2815     );
2816     let fmt = ListFormatting {
2817         tactic: tactic,
2818         separator: ",",
2819         trailing_separator: SeparatorTactic::Never,
2820         shape: shape,
2821         ends_with_newline: false,
2822         preserve_newline: false,
2823         config: context.config,
2824     };
2825     let list_str = try_opt!(write_list(&item_vec, &fmt));
2826
2827     if context.config.spaces_within_parens() && list_str.len() > 0 {
2828         Some(format!("( {} )", list_str))
2829     } else {
2830         Some(format!("({})", list_str))
2831     }
2832 }
2833
2834 pub fn rewrite_tuple<'a, T>(
2835     context: &RewriteContext,
2836     items: &[&T],
2837     span: Span,
2838     shape: Shape,
2839 ) -> Option<String>
2840 where
2841     T: Rewrite + Spanned + ToExpr + 'a,
2842 {
2843     debug!("rewrite_tuple {:?}", shape);
2844     if context.use_block_indent() {
2845         // We use the same rule as funcation call for rewriting tuple.
2846         let force_trailing_comma = if context.inside_macro {
2847             span_ends_with_comma(context, span)
2848         } else {
2849             items.len() == 1
2850         };
2851         rewrite_call_inner(
2852             context,
2853             &String::new(),
2854             items,
2855             span,
2856             shape,
2857             context.config.fn_call_width(),
2858             force_trailing_comma,
2859         ).ok()
2860     } else {
2861         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2862     }
2863 }
2864
2865 pub fn rewrite_unary_prefix<R: Rewrite>(
2866     context: &RewriteContext,
2867     prefix: &str,
2868     rewrite: &R,
2869     shape: Shape,
2870 ) -> Option<String> {
2871     rewrite
2872         .rewrite(context, try_opt!(shape.offset_left(prefix.len())))
2873         .map(|r| format!("{}{}", prefix, r))
2874 }
2875
2876 // FIXME: this is probably not correct for multi-line Rewrites. we should
2877 // subtract suffix.len() from the last line budget, not the first!
2878 pub fn rewrite_unary_suffix<R: Rewrite>(
2879     context: &RewriteContext,
2880     suffix: &str,
2881     rewrite: &R,
2882     shape: Shape,
2883 ) -> Option<String> {
2884     rewrite
2885         .rewrite(context, try_opt!(shape.sub_width(suffix.len())))
2886         .map(|mut r| {
2887             r.push_str(suffix);
2888             r
2889         })
2890 }
2891
2892 fn rewrite_unary_op(
2893     context: &RewriteContext,
2894     op: &ast::UnOp,
2895     expr: &ast::Expr,
2896     shape: Shape,
2897 ) -> Option<String> {
2898     // For some reason, an UnOp is not spanned like BinOp!
2899     let operator_str = match *op {
2900         ast::UnOp::Deref => "*",
2901         ast::UnOp::Not => "!",
2902         ast::UnOp::Neg => "-",
2903     };
2904     rewrite_unary_prefix(context, operator_str, expr, shape)
2905 }
2906
2907 fn rewrite_assignment(
2908     context: &RewriteContext,
2909     lhs: &ast::Expr,
2910     rhs: &ast::Expr,
2911     op: Option<&ast::BinOp>,
2912     shape: Shape,
2913 ) -> Option<String> {
2914     let operator_str = match op {
2915         Some(op) => context.snippet(op.span),
2916         None => "=".to_owned(),
2917     };
2918
2919     // 1 = space between lhs and operator.
2920     let lhs_shape = try_opt!(shape.sub_width(operator_str.len() + 1));
2921     let lhs_str = format!(
2922         "{} {}",
2923         try_opt!(lhs.rewrite(context, lhs_shape)),
2924         operator_str
2925     );
2926
2927     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2928 }
2929
2930 // The left hand side must contain everything up to, and including, the
2931 // assignment operator.
2932 pub fn rewrite_assign_rhs<S: Into<String>>(
2933     context: &RewriteContext,
2934     lhs: S,
2935     ex: &ast::Expr,
2936     shape: Shape,
2937 ) -> Option<String> {
2938     let lhs = lhs.into();
2939     let last_line_width = last_line_width(&lhs) - if lhs.contains('\n') {
2940         shape.indent.width()
2941     } else {
2942         0
2943     };
2944     // 1 = space between operator and rhs.
2945     let orig_shape = try_opt!(shape.offset_left(last_line_width + 1));
2946     let rhs = try_opt!(choose_rhs(
2947         context,
2948         ex,
2949         shape,
2950         ex.rewrite(context, orig_shape)
2951     ));
2952     Some(lhs + &rhs)
2953 }
2954
2955 fn choose_rhs(
2956     context: &RewriteContext,
2957     expr: &ast::Expr,
2958     shape: Shape,
2959     orig_rhs: Option<String>,
2960 ) -> Option<String> {
2961     match orig_rhs {
2962         Some(ref new_str) if !new_str.contains('\n') => Some(format!(" {}", new_str)),
2963         _ => {
2964             // Expression did not fit on the same line as the identifier.
2965             // Try splitting the line and see if that works better.
2966             let new_shape = try_opt!(
2967                 Shape::indented(
2968                     shape.block().indent.block_indent(context.config),
2969                     context.config,
2970                 ).sub_width(shape.rhs_overhead(context.config))
2971             );
2972             let new_rhs = expr.rewrite(context, new_shape);
2973             let new_indent_str = &new_shape.indent.to_string(context.config);
2974
2975             match (orig_rhs, new_rhs) {
2976                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2977                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2978                 }
2979                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2980                 (None, None) => None,
2981                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2982             }
2983         }
2984     }
2985 }
2986
2987 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2988     fn count_line_breaks(src: &str) -> usize {
2989         src.chars().filter(|&x| x == '\n').count()
2990     }
2991
2992     !next_line_rhs.contains('\n') ||
2993         count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2994 }
2995
2996 fn rewrite_expr_addrof(
2997     context: &RewriteContext,
2998     mutability: ast::Mutability,
2999     expr: &ast::Expr,
3000     shape: Shape,
3001 ) -> Option<String> {
3002     let operator_str = match mutability {
3003         ast::Mutability::Immutable => "&",
3004         ast::Mutability::Mutable => "&mut ",
3005     };
3006     rewrite_unary_prefix(context, operator_str, expr, shape)
3007 }
3008
3009 pub trait ToExpr {
3010     fn to_expr(&self) -> Option<&ast::Expr>;
3011     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
3012 }
3013
3014 impl ToExpr for ast::Expr {
3015     fn to_expr(&self) -> Option<&ast::Expr> {
3016         Some(self)
3017     }
3018
3019     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3020         can_be_overflowed_expr(context, self, len)
3021     }
3022 }
3023
3024 impl ToExpr for ast::Ty {
3025     fn to_expr(&self) -> Option<&ast::Expr> {
3026         None
3027     }
3028
3029     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3030         can_be_overflowed_type(context, self, len)
3031     }
3032 }
3033
3034 impl<'a> ToExpr for TuplePatField<'a> {
3035     fn to_expr(&self) -> Option<&ast::Expr> {
3036         None
3037     }
3038
3039     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3040         can_be_overflowed_pat(context, self, len)
3041     }
3042 }
3043
3044 impl<'a> ToExpr for ast::StructField {
3045     fn to_expr(&self) -> Option<&ast::Expr> {
3046         None
3047     }
3048
3049     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
3050         false
3051     }
3052 }