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     ).collect::<Vec<_>>();
 470
 471     if items.is_empty() {
 472         if context.config.spaces_within_square_brackets() {
 473             return Some("[ ]".to_string());
 474         } else {
 475             return Some("[]".to_string());
 476         }
 477     }
 478
 479     let has_long_item = items
 480         .iter()
 481         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 482
 483     let mut tactic = match context.config.array_layout() {
 484         IndentStyle::Block => {
 485             // FIXME wrong shape in one-line case
 486             match shape.width.checked_sub(2 * bracket_size) {
 487                 Some(width) => {
 488                     let tactic =
 489                         ListTactic::LimitedHorizontalVertical(context.config.array_width());
 490                     definitive_tactic(&items, tactic, Separator::Comma, width)
 491                 }
 492                 None => DefinitiveListTactic::Vertical,
 493             }
 494         }
 495         IndentStyle::Visual => if has_long_item || items.iter().any(ListItem::is_multiline) {
 496             definitive_tactic(
 497                 &items,
 498                 ListTactic::LimitedHorizontalVertical(context.config.array_width()),
 499                 Separator::Comma,
 500                 nested_shape.width,
 501             )
 502         } else {
 503             DefinitiveListTactic::Mixed
 504         },
 505     };
 506     let mut ends_with_newline = tactic.ends_with_newline(context.config.array_layout());
 507     if context.config.array_horizontal_layout_threshold() > 0 &&
 508         items.len() > context.config.array_horizontal_layout_threshold()
 509     {
 510         tactic = DefinitiveListTactic::Mixed;
 511         ends_with_newline = false;
 512         if context.config.array_layout() == IndentStyle::Block {
 513             nested_shape = try_opt!(
 514                 shape
 515                     .visual_indent(bracket_size)
 516                     .sub_width(bracket_size * 2)
 517             );
 518         }
 519     }
 520
 521     let fmt = ListFormatting {
 522         tactic: tactic,
 523         separator: ",",
 524         trailing_separator: if trailing_comma {
 525             SeparatorTactic::Always
 526         } else if context.inside_macro || context.config.array_layout() == IndentStyle::Visual {
 527             SeparatorTactic::Never
 528         } else {
 529             SeparatorTactic::Vertical
 530         },
 531         shape: nested_shape,
 532         ends_with_newline: ends_with_newline,
 533         preserve_newline: false,
 534         config: context.config,
 535     };
 536     let list_str = try_opt!(write_list(&items, &fmt));
 537
 538     let result = if context.config.array_layout() == IndentStyle::Visual ||
 539         tactic != DefinitiveListTactic::Vertical
 540     {
 541         if context.config.spaces_within_square_brackets() && list_str.len() > 0 {
 542             format!("[ {} ]", list_str)
 543         } else {
 544             format!("[{}]", list_str)
 545         }
 546     } else {
 547         format!(
 548             "[\n{}{}\n{}]",
 549             nested_shape.indent.to_string(context.config),
 550             list_str,
 551             shape.block().indent.to_string(context.config)
 552         )
 553     };
 554
 555     Some(result)
 556 }
 557
 558 // Return type is (prefix, extra_offset)
 559 fn rewrite_closure_fn_decl(
 560     capture: ast::CaptureBy,
 561     fn_decl: &ast::FnDecl,
 562     body: &ast::Expr,
 563     span: Span,
 564     context: &RewriteContext,
 565     shape: Shape,
 566 ) -> Option<(String, usize)> {
 567     let mover = if capture == ast::CaptureBy::Value {
 568         "move "
 569     } else {
 570         ""
 571     };
 572     // 4 = "|| {".len(), which is overconservative when the closure consists of
 573     // a single expression.
 574     let nested_shape = try_opt!(try_opt!(shape.shrink_left(mover.len())).sub_width(4));
 575
 576     // 1 = |
 577     let argument_offset = nested_shape.indent + 1;
 578     let arg_shape = try_opt!(nested_shape.offset_left(1)).visual_indent(0);
 579     let ret_str = try_opt!(fn_decl.output.rewrite(context, arg_shape));
 580
 581     let arg_items = itemize_list(
 582         context.codemap,
 583         fn_decl.inputs.iter(),
 584         "|",
 585         |arg| span_lo_for_arg(arg),
 586         |arg| span_hi_for_arg(context, arg),
 587         |arg| arg.rewrite(context, arg_shape),
 588         context.codemap.span_after(span, "|"),
 589         body.span.lo,
 590     );
 591     let item_vec = arg_items.collect::<Vec<_>>();
 592     // 1 = space between arguments and return type.
 593     let horizontal_budget = nested_shape
 594         .width
 595         .checked_sub(ret_str.len() + 1)
 596         .unwrap_or(0);
 597     let tactic = definitive_tactic(
 598         &item_vec,
 599         ListTactic::HorizontalVertical,
 600         Separator::Comma,
 601         horizontal_budget,
 602     );
 603     let arg_shape = match tactic {
 604         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 605         _ => arg_shape,
 606     };
 607
 608     let fmt = ListFormatting {
 609         tactic: tactic,
 610         separator: ",",
 611         trailing_separator: SeparatorTactic::Never,
 612         shape: arg_shape,
 613         ends_with_newline: false,
 614         preserve_newline: true,
 615         config: context.config,
 616     };
 617     let list_str = try_opt!(write_list(&item_vec, &fmt));
 618     let mut prefix = format!("{}|{}|", mover, list_str);
 619     // 1 = space between `|...|` and body.
 620     let extra_offset = extra_offset(&prefix, shape) + 1;
 621
 622     if !ret_str.is_empty() {
 623         if prefix.contains('\n') {
 624             prefix.push('\n');
 625             prefix.push_str(&argument_offset.to_string(context.config));
 626         } else {
 627             prefix.push(' ');
 628         }
 629         prefix.push_str(&ret_str);
 630     }
 631
 632     Some((prefix, extra_offset))
 633 }
 634
 635 // This functions is pretty messy because of the rules around closures and blocks:
 636 // FIXME - the below is probably no longer true in full.
 637 //   * if there is a return type, then there must be braces,
 638 //   * given a closure with braces, whether that is parsed to give an inner block
 639 //     or not depends on if there is a return type and if there are statements
 640 //     in that block,
 641 //   * if the first expression in the body ends with a block (i.e., is a
 642 //     statement without needing a semi-colon), then adding or removing braces
 643 //     can change whether it is treated as an expression or statement.
 644 fn rewrite_closure(
 645     capture: ast::CaptureBy,
 646     fn_decl: &ast::FnDecl,
 647     body: &ast::Expr,
 648     span: Span,
 649     context: &RewriteContext,
 650     shape: Shape,
 651 ) -> Option<String> {
 652     let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
 653         capture,
 654         fn_decl,
 655         body,
 656         span,
 657         context,
 658         shape,
 659     ));
 660     // 1 = space between `|...|` and body.
 661     let body_shape = try_opt!(shape.offset_left(extra_offset));
 662
 663     if let ast::ExprKind::Block(ref block) = body.node {
 664         // The body of the closure is an empty block.
 665         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 666             return Some(format!("{} {{}}", prefix));
 667         }
 668
 669         // Figure out if the block is necessary.
 670         let needs_block = block.rules != ast::BlockCheckMode::Default || block.stmts.len() > 1 ||
 671             context.inside_macro ||
 672             block_contains_comment(block, context.codemap) ||
 673             prefix.contains('\n');
 674
 675         let no_return_type = if let ast::FunctionRetTy::Default(_) = fn_decl.output {
 676             true
 677         } else {
 678             false
 679         };
 680         if no_return_type && !needs_block {
 681             // lock.stmts.len() == 1
 682             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 683                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 684                     return Some(rw);
 685                 }
 686             }
 687         }
 688
 689         if !needs_block {
 690             // We need braces, but we might still prefer a one-liner.
 691             let stmt = &block.stmts[0];
 692             // 4 = braces and spaces.
 693             if let Some(body_shape) = body_shape.sub_width(4) {
 694                 // Checks if rewrite succeeded and fits on a single line.
 695                 if let Some(rewrite) = and_one_line(stmt.rewrite(context, body_shape)) {
 696                     return Some(format!("{} {{ {} }}", prefix, rewrite));
 697                 }
 698             }
 699         }
 700
 701         // Either we require a block, or tried without and failed.
 702         rewrite_closure_block(&block, &prefix, context, body_shape)
 703     } else {
 704         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
 705             // The closure originally had a non-block expression, but we can't fit on
 706             // one line, so we'll insert a block.
 707             rewrite_closure_with_block(context, body_shape, &prefix, body)
 708         })
 709     }
 710 }
 711
 712 // Rewrite closure with a single expression wrapping its body with block.
 713 fn rewrite_closure_with_block(
 714     context: &RewriteContext,
 715     shape: Shape,
 716     prefix: &str,
 717     body: &ast::Expr,
 718 ) -> Option<String> {
 719     let block = ast::Block {
 720         stmts: vec![
 721             ast::Stmt {
 722                 id: ast::NodeId::new(0),
 723                 node: ast::StmtKind::Expr(ptr::P(body.clone())),
 724                 span: body.span,
 725             },
 726         ],
 727         id: ast::NodeId::new(0),
 728         rules: ast::BlockCheckMode::Default,
 729         span: body.span,
 730     };
 731     rewrite_closure_block(&block, prefix, context, shape)
 732 }
 733
 734 // Rewrite closure with a single expression without wrapping its body with block.
 735 fn rewrite_closure_expr(
 736     expr: &ast::Expr,
 737     prefix: &str,
 738     context: &RewriteContext,
 739     shape: Shape,
 740 ) -> Option<String> {
 741     let mut rewrite = expr.rewrite(context, shape);
 742     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 743         rewrite = and_one_line(rewrite);
 744     }
 745     rewrite.map(|rw| format!("{} {}", prefix, rw))
 746 }
 747
 748 // Rewrite closure whose body is block.
 749 fn rewrite_closure_block(
 750     block: &ast::Block,
 751     prefix: &str,
 752     context: &RewriteContext,
 753     shape: Shape,
 754 ) -> Option<String> {
 755     // Start with visual indent, then fall back to block indent if the
 756     // closure is large.
 757     let block_threshold = context.config.closure_block_indent_threshold();
 758     if block_threshold >= 0 {
 759         if let Some(block_str) = block.rewrite(&context, shape) {
 760             if block_str.matches('\n').count() <= block_threshold as usize &&
 761                 !need_block_indent(&block_str, shape)
 762             {
 763                 if let Some(block_str) = block_str.rewrite(context, shape) {
 764                     return Some(format!("{} {}", prefix, block_str));
 765                 }
 766             }
 767         }
 768     }
 769
 770     // The body of the closure is big enough to be block indented, that
 771     // means we must re-format.
 772     let block_shape = shape.block();
 773     let block_str = try_opt!(block.rewrite(&context, block_shape));
 774     Some(format!("{} {}", prefix, block_str))
 775 }
 776
 777 fn and_one_line(x: Option<String>) -> Option<String> {
 778     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 779 }
 780
 781 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 782     debug!("nop_block_collapse {:?} {}", block_str, budget);
 783     block_str.map(|block_str| {
 784         if block_str.starts_with('{') && budget >= 2 &&
 785             (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 786         {
 787             "{}".to_owned()
 788         } else {
 789             block_str.to_owned()
 790         }
 791     })
 792 }
 793
 794 fn rewrite_empty_block(
 795     context: &RewriteContext,
 796     block: &ast::Block,
 797     shape: Shape,
 798 ) -> Option<String> {
 799     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 800     {
 801         return Some("{}".to_owned());
 802     }
 803
 804     // If a block contains only a single-line comment, then leave it on one line.
 805     let user_str = context.snippet(block.span);
 806     let user_str = user_str.trim();
 807     if user_str.starts_with('{') && user_str.ends_with('}') {
 808         let comment_str = user_str[1..user_str.len() - 1].trim();
 809         if block.stmts.is_empty() && !comment_str.contains('\n') &&
 810             !comment_str.starts_with("//") && comment_str.len() + 4 <= shape.width
 811         {
 812             return Some(format!("{{ {} }}", comment_str));
 813         }
 814     }
 815
 816     None
 817 }
 818
 819 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 820     Some(match block.rules {
 821         ast::BlockCheckMode::Unsafe(..) => {
 822             let snippet = context.snippet(block.span);
 823             let open_pos = try_opt!(snippet.find_uncommented("{"));
 824             // Extract comment between unsafe and block start.
 825             let trimmed = &snippet[6..open_pos].trim();
 826
 827             if !trimmed.is_empty() {
 828                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 829                 let budget = try_opt!(shape.width.checked_sub(9));
 830                 format!(
 831                     "unsafe {} ",
 832                     try_opt!(rewrite_comment(
 833                         trimmed,
 834                         true,
 835                         Shape::legacy(budget, shape.indent + 7),
 836                         context.config,
 837                     ))
 838                 )
 839             } else {
 840                 "unsafe ".to_owned()
 841             }
 842         }
 843         ast::BlockCheckMode::Default => String::new(),
 844     })
 845 }
 846
 847 fn rewrite_single_line_block(
 848     context: &RewriteContext,
 849     prefix: &str,
 850     block: &ast::Block,
 851     shape: Shape,
 852 ) -> Option<String> {
 853     if is_simple_block(block, context.codemap) {
 854         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 855         let expr_str = try_opt!(block.stmts[0].rewrite(context, expr_shape));
 856         let result = format!("{}{{ {} }}", prefix, expr_str);
 857         if result.len() <= shape.width && !result.contains('\n') {
 858             return Some(result);
 859         }
 860     }
 861     None
 862 }
 863
 864 fn rewrite_block_with_visitor(
 865     context: &RewriteContext,
 866     prefix: &str,
 867     block: &ast::Block,
 868     shape: Shape,
 869 ) -> Option<String> {
 870     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 871         return rw;
 872     }
 873
 874     let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 875     visitor.block_indent = shape.indent;
 876     visitor.is_if_else_block = context.is_if_else_block;
 877     match block.rules {
 878         ast::BlockCheckMode::Unsafe(..) => {
 879             let snippet = context.snippet(block.span);
 880             let open_pos = try_opt!(snippet.find_uncommented("{"));
 881             visitor.last_pos = block.span.lo + BytePos(open_pos as u32)
 882         }
 883         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo,
 884     }
 885
 886     visitor.visit_block(block, None);
 887     Some(format!("{}{}", prefix, visitor.buffer))
 888 }
 889
 890 impl Rewrite for ast::Block {
 891     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 892         // shape.width is used only for the single line case: either the empty block `{}`,
 893         // or an unsafe expression `unsafe { e }`.
 894         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 895             return rw;
 896         }
 897
 898         let prefix = try_opt!(block_prefix(context, self, shape));
 899         if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 900             return rw;
 901         }
 902
 903         rewrite_block_with_visitor(context, &prefix, self, shape)
 904     }
 905 }
 906
 907 impl Rewrite for ast::Stmt {
 908     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 909         skip_out_of_file_lines_range!(context, self.span());
 910
 911         let result = match self.node {
 912             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 913             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 914                 let suffix = if semicolon_for_stmt(context, self) {
 915                     ";"
 916                 } else {
 917                     ""
 918                 };
 919
 920                 format_expr(
 921                     ex,
 922                     match self.node {
 923                         ast::StmtKind::Expr(_) => ExprType::SubExpression,
 924                         ast::StmtKind::Semi(_) => ExprType::Statement,
 925                         _ => unreachable!(),
 926                     },
 927                     context,
 928                     try_opt!(shape.sub_width(suffix.len())),
 929                 ).map(|s| s + suffix)
 930             }
 931             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 932         };
 933         result.and_then(|res| {
 934             recover_comment_removed(res, self.span(), context, shape)
 935         })
 936     }
 937 }
 938
 939 // Rewrite condition if the given expression has one.
 940 fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 941     match expr.node {
 942         ast::ExprKind::Match(ref cond, _) => {
 943             // `match `cond` {`
 944             let cond_shape = match context.config.control_style() {
 945                 Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
 946                 Style::Rfc => try_opt!(shape.offset_left(8)),
 947             };
 948             cond.rewrite(context, cond_shape)
 949         }
 950         ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
 951             stmt_expr(&block.stmts[0]).and_then(|e| rewrite_cond(context, e, shape))
 952         }
 953         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 954             let alt_block_sep =
 955                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 956             control_flow
 957                 .rewrite_cond(context, shape, &alt_block_sep)
 958                 .and_then(|rw| Some(rw.0))
 959         }),
 960     }
 961 }
 962
 963 // Abstraction over control flow expressions
 964 #[derive(Debug)]
 965 struct ControlFlow<'a> {
 966     cond: Option<&'a ast::Expr>,
 967     block: &'a ast::Block,
 968     else_block: Option<&'a ast::Expr>,
 969     label: Option<ast::SpannedIdent>,
 970     pat: Option<&'a ast::Pat>,
 971     keyword: &'a str,
 972     matcher: &'a str,
 973     connector: &'a str,
 974     allow_single_line: bool,
 975     // True if this is an `if` expression in an `else if` :-( hacky
 976     nested_if: bool,
 977     span: Span,
 978 }
 979
 980 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 981     match expr.node {
 982         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 983             cond,
 984             None,
 985             if_block,
 986             else_block.as_ref().map(|e| &**e),
 987             expr_type == ExprType::SubExpression,
 988             false,
 989             expr.span,
 990         )),
 991         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 992             Some(ControlFlow::new_if(
 993                 cond,
 994                 Some(pat),
 995                 if_block,
 996                 else_block.as_ref().map(|e| &**e),
 997                 expr_type == ExprType::SubExpression,
 998                 false,
 999                 expr.span,
1000             ))
1001         }
1002         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
1003             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
1004         }
1005         ast::ExprKind::Loop(ref block, label) => {
1006             Some(ControlFlow::new_loop(block, label, expr.span))
1007         }
1008         ast::ExprKind::While(ref cond, ref block, label) => {
1009             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
1010         }
1011         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
1012             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
1013         ),
1014         _ => None,
1015     }
1016 }
1017
1018 impl<'a> ControlFlow<'a> {
1019     fn new_if(
1020         cond: &'a ast::Expr,
1021         pat: Option<&'a ast::Pat>,
1022         block: &'a ast::Block,
1023         else_block: Option<&'a ast::Expr>,
1024         allow_single_line: bool,
1025         nested_if: bool,
1026         span: Span,
1027     ) -> ControlFlow<'a> {
1028         ControlFlow {
1029             cond: Some(cond),
1030             block: block,
1031             else_block: else_block,
1032             label: None,
1033             pat: pat,
1034             keyword: "if",
1035             matcher: match pat {
1036                 Some(..) => "let",
1037                 None => "",
1038             },
1039             connector: " =",
1040             allow_single_line: allow_single_line,
1041             nested_if: nested_if,
1042             span: span,
1043         }
1044     }
1045
1046     fn new_loop(
1047         block: &'a ast::Block,
1048         label: Option<ast::SpannedIdent>,
1049         span: Span,
1050     ) -> ControlFlow<'a> {
1051         ControlFlow {
1052             cond: None,
1053             block: block,
1054             else_block: None,
1055             label: label,
1056             pat: None,
1057             keyword: "loop",
1058             matcher: "",
1059             connector: "",
1060             allow_single_line: false,
1061             nested_if: false,
1062             span: span,
1063         }
1064     }
1065
1066     fn new_while(
1067         pat: Option<&'a ast::Pat>,
1068         cond: &'a ast::Expr,
1069         block: &'a ast::Block,
1070         label: Option<ast::SpannedIdent>,
1071         span: Span,
1072     ) -> ControlFlow<'a> {
1073         ControlFlow {
1074             cond: Some(cond),
1075             block: block,
1076             else_block: None,
1077             label: label,
1078             pat: pat,
1079             keyword: "while",
1080             matcher: match pat {
1081                 Some(..) => "let",
1082                 None => "",
1083             },
1084             connector: " =",
1085             allow_single_line: false,
1086             nested_if: false,
1087             span: span,
1088         }
1089     }
1090
1091     fn new_for(
1092         pat: &'a ast::Pat,
1093         cond: &'a ast::Expr,
1094         block: &'a ast::Block,
1095         label: Option<ast::SpannedIdent>,
1096         span: Span,
1097     ) -> ControlFlow<'a> {
1098         ControlFlow {
1099             cond: Some(cond),
1100             block: block,
1101             else_block: None,
1102             label: label,
1103             pat: Some(pat),
1104             keyword: "for",
1105             matcher: "",
1106             connector: " in",
1107             allow_single_line: false,
1108             nested_if: false,
1109             span: span,
1110         }
1111     }
1112
1113     fn rewrite_single_line(
1114         &self,
1115         pat_expr_str: &str,
1116         context: &RewriteContext,
1117         width: usize,
1118     ) -> Option<String> {
1119         assert!(self.allow_single_line);
1120         let else_block = try_opt!(self.else_block);
1121         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1122
1123         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1124             if !is_simple_block(self.block, context.codemap) ||
1125                 !is_simple_block(else_node, context.codemap) ||
1126                 pat_expr_str.contains('\n')
1127             {
1128                 return None;
1129             }
1130
1131             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
1132             let expr = &self.block.stmts[0];
1133             let if_str = try_opt!(expr.rewrite(
1134                 context,
1135                 Shape::legacy(new_width, Indent::empty()),
1136             ));
1137
1138             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
1139             let else_expr = &else_node.stmts[0];
1140             let else_str =
1141                 try_opt!(else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1142
1143             if if_str.contains('\n') || else_str.contains('\n') {
1144                 return None;
1145             }
1146
1147             let result = format!(
1148                 "{} {} {{ {} }} else {{ {} }}",
1149                 self.keyword,
1150                 pat_expr_str,
1151                 if_str,
1152                 else_str
1153             );
1154
1155             if result.len() <= width {
1156                 return Some(result);
1157             }
1158         }
1159
1160         None
1161     }
1162 }
1163
1164 impl<'a> ControlFlow<'a> {
1165     fn rewrite_cond(
1166         &self,
1167         context: &RewriteContext,
1168         shape: Shape,
1169         alt_block_sep: &str,
1170     ) -> Option<(String, usize)> {
1171         // Do not take the rhs overhead from the upper expressions into account
1172         // when rewriting pattern.
1173         let new_width = context
1174             .config
1175             .max_width()
1176             .checked_sub(shape.used_width())
1177             .unwrap_or(0);
1178         let fresh_shape = Shape {
1179             width: new_width,
1180             ..shape
1181         };
1182         let constr_shape = if self.nested_if {
1183             // We are part of an if-elseif-else chain. Our constraints are tightened.
1184             // 7 = "} else " .len()
1185             try_opt!(fresh_shape.offset_left(7))
1186         } else {
1187             fresh_shape
1188         };
1189
1190         let label_string = rewrite_label(self.label);
1191         // 1 = space after keyword.
1192         let offset = self.keyword.len() + label_string.len() + 1;
1193
1194         let pat_expr_string = match self.cond {
1195             Some(cond) => {
1196                 let cond_shape = match context.config.control_style() {
1197                     Style::Legacy => try_opt!(constr_shape.shrink_left(offset)),
1198                     Style::Rfc => try_opt!(constr_shape.offset_left(offset)),
1199                 };
1200                 try_opt!(rewrite_pat_expr(
1201                     context,
1202                     self.pat,
1203                     cond,
1204                     self.matcher,
1205                     self.connector,
1206                     self.keyword,
1207                     cond_shape,
1208                 ))
1209             }
1210             None => String::new(),
1211         };
1212
1213         let brace_overhead =
1214             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1215                 // 2 = ` {`
1216                 2
1217             } else {
1218                 0
1219             };
1220         let one_line_budget = context
1221             .config
1222             .max_width()
1223             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1224             .unwrap_or(0);
1225         let force_newline_brace = context.config.control_style() == Style::Rfc &&
1226             (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget) &&
1227             !last_line_extendable(&pat_expr_string);
1228
1229         // Try to format if-else on single line.
1230         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1231             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1232
1233             if let Some(cond_str) = trial {
1234                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1235                     return Some((cond_str, 0));
1236                 }
1237             }
1238         }
1239
1240         let cond_span = if let Some(cond) = self.cond {
1241             cond.span
1242         } else {
1243             mk_sp(self.block.span.lo, self.block.span.lo)
1244         };
1245
1246         // for event in event
1247         let between_kwd_cond = mk_sp(
1248             context.codemap.span_after(self.span, self.keyword.trim()),
1249             self.pat.map_or(
1250                 cond_span.lo,
1251                 |p| if self.matcher.is_empty() {
1252                     p.span.lo
1253                 } else {
1254                     context.codemap.span_before(self.span, self.matcher.trim())
1255                 },
1256             ),
1257         );
1258
1259         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1260
1261         let after_cond_comment =
1262             extract_comment(mk_sp(cond_span.hi, self.block.span.lo), context, shape);
1263
1264         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1265             ""
1266         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine ||
1267             force_newline_brace
1268         {
1269             alt_block_sep
1270         } else {
1271             " "
1272         };
1273
1274         let used_width = if pat_expr_string.contains('\n') {
1275             last_line_width(&pat_expr_string)
1276         } else {
1277             // 2 = spaces after keyword and condition.
1278             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1279         };
1280
1281         Some((
1282             format!(
1283                 "{}{}{}{}{}",
1284                 label_string,
1285                 self.keyword,
1286                 between_kwd_cond_comment.as_ref().map_or(
1287                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1288                         ""
1289                     } else {
1290                         " "
1291                     },
1292                     |s| &**s,
1293                 ),
1294                 pat_expr_string,
1295                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1296             ),
1297             used_width,
1298         ))
1299     }
1300 }
1301
1302 impl<'a> Rewrite for ControlFlow<'a> {
1303     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1304         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1305
1306         let alt_block_sep =
1307             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1308         let (cond_str, used_width) = try_opt!(self.rewrite_cond(context, shape, &alt_block_sep));
1309         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1310         if used_width == 0 {
1311             return Some(cond_str);
1312         }
1313
1314         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1315         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1316         // we should avoid the single line case.
1317         let block_width = if self.else_block.is_some() || self.nested_if {
1318             min(1, block_width)
1319         } else {
1320             block_width
1321         };
1322         let block_shape = Shape {
1323             width: block_width,
1324             ..shape
1325         };
1326         let mut block_context = context.clone();
1327         block_context.is_if_else_block = self.else_block.is_some();
1328         let block_str = try_opt!(rewrite_block_with_visitor(
1329             &block_context,
1330             "",
1331             self.block,
1332             block_shape,
1333         ));
1334
1335         let mut result = format!("{}{}", cond_str, block_str);
1336
1337         if let Some(else_block) = self.else_block {
1338             let shape = Shape::indented(shape.indent, context.config);
1339             let mut last_in_chain = false;
1340             let rewrite = match else_block.node {
1341                 // If the else expression is another if-else expression, prevent it
1342                 // from being formatted on a single line.
1343                 // Note how we're passing the original shape, as the
1344                 // cost of "else" should not cascade.
1345                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1346                     ControlFlow::new_if(
1347                         cond,
1348                         Some(pat),
1349                         if_block,
1350                         next_else_block.as_ref().map(|e| &**e),
1351                         false,
1352                         true,
1353                         mk_sp(else_block.span.lo, self.span.hi),
1354                     ).rewrite(context, shape)
1355                 }
1356                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1357                     ControlFlow::new_if(
1358                         cond,
1359                         None,
1360                         if_block,
1361                         next_else_block.as_ref().map(|e| &**e),
1362                         false,
1363                         true,
1364                         mk_sp(else_block.span.lo, self.span.hi),
1365                     ).rewrite(context, shape)
1366                 }
1367                 _ => {
1368                     last_in_chain = true;
1369                     // When rewriting a block, the width is only used for single line
1370                     // blocks, passing 1 lets us avoid that.
1371                     let else_shape = Shape {
1372                         width: min(1, shape.width),
1373                         ..shape
1374                     };
1375                     format_expr(else_block, ExprType::Statement, context, else_shape)
1376                 }
1377             };
1378
1379             let between_kwd_else_block = mk_sp(
1380                 self.block.span.hi,
1381                 context
1382                     .codemap
1383                     .span_before(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1384             );
1385             let between_kwd_else_block_comment =
1386                 extract_comment(between_kwd_else_block, context, shape);
1387
1388             let after_else = mk_sp(
1389                 context
1390                     .codemap
1391                     .span_after(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1392                 else_block.span.lo,
1393             );
1394             let after_else_comment = extract_comment(after_else, context, shape);
1395
1396             let between_sep = match context.config.control_brace_style() {
1397                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1398                     &*alt_block_sep
1399                 }
1400                 ControlBraceStyle::AlwaysSameLine => " ",
1401             };
1402             let after_sep = match context.config.control_brace_style() {
1403                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1404                 _ => " ",
1405             };
1406             try_opt!(
1407                 write!(
1408                     &mut result,
1409                     "{}else{}",
1410                     between_kwd_else_block_comment
1411                         .as_ref()
1412                         .map_or(between_sep, |s| &**s),
1413                     after_else_comment.as_ref().map_or(after_sep, |s| &**s)
1414                 ).ok()
1415             );
1416             result.push_str(&try_opt!(rewrite));
1417         }
1418
1419         Some(result)
1420     }
1421 }
1422
1423 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
1424     match label {
1425         Some(ident) => format!("{}: ", ident.node),
1426         None => "".to_owned(),
1427     }
1428 }
1429
1430 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1431     let comment_str = context.snippet(span);
1432     if contains_comment(&comment_str) {
1433         let comment = try_opt!(rewrite_comment(
1434             comment_str.trim(),
1435             false,
1436             shape,
1437             context.config,
1438         ));
1439         Some(format!(
1440             "\n{indent}{}\n{indent}",
1441             comment,
1442             indent = shape.indent.to_string(context.config)
1443         ))
1444     } else {
1445         None
1446     }
1447 }
1448
1449 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1450     let snippet = codemap.span_to_snippet(block.span).unwrap();
1451     contains_comment(&snippet)
1452 }
1453
1454 // Checks that a block contains no statements, an expression and no comments.
1455 // FIXME: incorrectly returns false when comment is contained completely within
1456 // the expression.
1457 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1458     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
1459         !block_contains_comment(block, codemap))
1460 }
1461
1462 /// Checks whether a block contains at most one statement or expression, and no comments.
1463 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1464     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1465 }
1466
1467 /// Checks whether a block contains no statements, expressions, or comments.
1468 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1469     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1470 }
1471
1472 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1473     match stmt.node {
1474         ast::StmtKind::Expr(..) => true,
1475         _ => false,
1476     }
1477 }
1478
1479 fn is_unsafe_block(block: &ast::Block) -> bool {
1480     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1481         true
1482     } else {
1483         false
1484     }
1485 }
1486
1487 // inter-match-arm-comment-rules:
1488 //  - all comments following a match arm before the start of the next arm
1489 //    are about the second arm
1490 fn rewrite_match_arm_comment(
1491     context: &RewriteContext,
1492     missed_str: &str,
1493     shape: Shape,
1494     arm_indent_str: &str,
1495 ) -> Option<String> {
1496     // The leading "," is not part of the arm-comment
1497     let missed_str = match missed_str.find_uncommented(",") {
1498         Some(n) => &missed_str[n + 1..],
1499         None => &missed_str[..],
1500     };
1501
1502     let mut result = String::new();
1503     // any text not preceeded by a newline is pushed unmodified to the block
1504     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1505     result.push_str(&missed_str[..first_brk]);
1506     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1507
1508     let first = missed_str
1509         .find(|c: char| !c.is_whitespace())
1510         .unwrap_or(missed_str.len());
1511     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1512         // Excessive vertical whitespace before comment should be preserved
1513         // FIXME handle vertical whitespace better
1514         result.push('\n');
1515     }
1516     let missed_str = missed_str[first..].trim();
1517     if !missed_str.is_empty() {
1518         let comment = try_opt!(rewrite_comment(&missed_str, false, shape, context.config));
1519         result.push('\n');
1520         result.push_str(arm_indent_str);
1521         result.push_str(&comment);
1522     }
1523
1524     Some(result)
1525 }
1526
1527 fn rewrite_match(
1528     context: &RewriteContext,
1529     cond: &ast::Expr,
1530     arms: &[ast::Arm],
1531     shape: Shape,
1532     span: Span,
1533     attrs: &[ast::Attribute],
1534 ) -> Option<String> {
1535     if arms.is_empty() {
1536         return None;
1537     }
1538
1539     // Do not take the rhs overhead from the upper expressions into account
1540     // when rewriting match condition.
1541     let new_width = try_opt!(context.config.max_width().checked_sub(shape.used_width()));
1542     let cond_shape = Shape {
1543         width: new_width,
1544         ..shape
1545     };
1546     // 6 = `match `
1547     let cond_shape = match context.config.control_style() {
1548         Style::Legacy => try_opt!(cond_shape.shrink_left(6)),
1549         Style::Rfc => try_opt!(cond_shape.offset_left(6)),
1550     };
1551     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1552     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1553     let block_sep = match context.config.control_brace_style() {
1554         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1555         _ if last_line_extendable(&cond_str) => " ",
1556         // 2 = ` {`
1557         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => &alt_block_sep,
1558         _ => " ",
1559     };
1560
1561     let nested_indent_str = shape
1562         .indent
1563         .block_indent(context.config)
1564         .to_string(context.config);
1565     // Inner attributes.
1566     let inner_attrs = &inner_attributes(attrs);
1567     let inner_attrs_str = if inner_attrs.is_empty() {
1568         String::new()
1569     } else {
1570         try_opt!(
1571             inner_attrs
1572                 .rewrite(context, shape)
1573                 .map(|s| format!("\n{}{}", nested_indent_str, s))
1574         )
1575     };
1576
1577     let open_brace_pos = if inner_attrs.is_empty() {
1578         context
1579             .codemap
1580             .span_after(mk_sp(cond.span.hi, arms[0].span().lo), "{")
1581     } else {
1582         inner_attrs[inner_attrs.len() - 1].span().hi
1583     };
1584
1585     Some(format!(
1586         "match {}{}{{{}{}\n{}}}",
1587         cond_str,
1588         block_sep,
1589         inner_attrs_str,
1590         try_opt!(rewrite_match_arms(
1591             context,
1592             arms,
1593             shape,
1594             span,
1595             open_brace_pos,
1596         )),
1597         shape.indent.to_string(context.config),
1598     ))
1599 }
1600
1601 fn arm_comma(config: &Config, body: &ast::Expr) -> &'static str {
1602     if config.match_block_trailing_comma() {
1603         ","
1604     } else if let ast::ExprKind::Block(ref block) = body.node {
1605         if let ast::BlockCheckMode::Default = block.rules {
1606             ""
1607         } else {
1608             ","
1609         }
1610     } else {
1611         ","
1612     }
1613 }
1614
1615 fn rewrite_match_arms(
1616     context: &RewriteContext,
1617     arms: &[ast::Arm],
1618     shape: Shape,
1619     span: Span,
1620     open_brace_pos: BytePos,
1621 ) -> Option<String> {
1622     let mut result = String::new();
1623
1624     let arm_shape = if context.config.indent_match_arms() {
1625         shape.block_indent(context.config.tab_spaces())
1626     } else {
1627         shape.block_indent(0)
1628     }.with_max_width(context.config);
1629     let arm_indent_str = arm_shape.indent.to_string(context.config);
1630
1631     let arm_num = arms.len();
1632     for (i, arm) in arms.iter().enumerate() {
1633         // Make sure we get the stuff between arms.
1634         let missed_str = if i == 0 {
1635             context.snippet(mk_sp(open_brace_pos, arm.span().lo))
1636         } else {
1637             context.snippet(mk_sp(arms[i - 1].span().hi, arm.span().lo))
1638         };
1639         let comment = try_opt!(rewrite_match_arm_comment(
1640             context,
1641             &missed_str,
1642             arm_shape,
1643             &arm_indent_str,
1644         ));
1645         if !comment.chars().all(|c| c == ' ') {
1646             result.push_str(&comment);
1647         }
1648         result.push('\n');
1649         result.push_str(&arm_indent_str);
1650
1651         let arm_str = rewrite_match_arm(context, arm, arm_shape);
1652         if let Some(ref arm_str) = arm_str {
1653             // Trim the trailing comma if necessary.
1654             if i == arm_num - 1 && context.config.trailing_comma() == SeparatorTactic::Never &&
1655                 arm_str.ends_with(',')
1656             {
1657                 result.push_str(&arm_str[0..arm_str.len() - 1])
1658             } else {
1659                 result.push_str(arm_str)
1660             }
1661         } else {
1662             // We couldn't format the arm, just reproduce the source.
1663             let snippet = context.snippet(arm.span());
1664             result.push_str(&snippet);
1665             if context.config.trailing_comma() != SeparatorTactic::Never {
1666                 result.push_str(arm_comma(context.config, &arm.body))
1667             }
1668         }
1669     }
1670     // BytePos(1) = closing match brace.
1671     let last_span = mk_sp(arms[arms.len() - 1].span().hi, span.hi - BytePos(1));
1672     let last_comment = context.snippet(last_span);
1673     let comment = try_opt!(rewrite_match_arm_comment(
1674         context,
1675         &last_comment,
1676         arm_shape,
1677         &arm_indent_str,
1678     ));
1679     result.push_str(&comment);
1680
1681     Some(result)
1682 }
1683
1684 fn rewrite_match_arm(context: &RewriteContext, arm: &ast::Arm, shape: Shape) -> Option<String> {
1685     let attr_str = if !arm.attrs.is_empty() {
1686         if contains_skip(&arm.attrs) {
1687             return None;
1688         }
1689         format!(
1690             "{}\n{}",
1691             try_opt!(arm.attrs.rewrite(context, shape)),
1692             shape.indent.to_string(context.config)
1693         )
1694     } else {
1695         String::new()
1696     };
1697     let pats_str = try_opt!(rewrite_match_pattern(context, &arm.pats, &arm.guard, shape));
1698     let pats_str = attr_str + &pats_str;
1699     rewrite_match_body(context, &arm.body, &pats_str, shape, arm.guard.is_some())
1700 }
1701
1702 fn rewrite_match_pattern(
1703     context: &RewriteContext,
1704     pats: &Vec<ptr::P<ast::Pat>>,
1705     guard: &Option<ptr::P<ast::Expr>>,
1706     shape: Shape,
1707 ) -> Option<String> {
1708     // Patterns
1709     // 5 = ` => {`
1710     let pat_shape = try_opt!(shape.sub_width(5));
1711
1712     let pat_strs = try_opt!(
1713         pats.iter()
1714             .map(|p| p.rewrite(context, pat_shape))
1715             .collect::<Option<Vec<_>>>()
1716     );
1717
1718     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1719     let tactic = definitive_tactic(
1720         &items,
1721         ListTactic::HorizontalVertical,
1722         Separator::VerticalBar,
1723         pat_shape.width,
1724     );
1725     let fmt = ListFormatting {
1726         tactic: tactic,
1727         separator: " |",
1728         trailing_separator: SeparatorTactic::Never,
1729         shape: pat_shape,
1730         ends_with_newline: false,
1731         preserve_newline: false,
1732         config: context.config,
1733     };
1734     let pats_str = try_opt!(write_list(&items, &fmt));
1735
1736     // Guard
1737     let guard_str = try_opt!(rewrite_guard(
1738         context,
1739         guard,
1740         shape,
1741         trimmed_last_line_width(&pats_str),
1742     ));
1743
1744     Some(format!("{}{}", pats_str, guard_str))
1745 }
1746
1747 fn rewrite_match_body(
1748     context: &RewriteContext,
1749     body: &ptr::P<ast::Expr>,
1750     pats_str: &str,
1751     shape: Shape,
1752     has_guard: bool,
1753 ) -> Option<String> {
1754     let (extend, body) = match body.node {
1755         ast::ExprKind::Block(ref block)
1756             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1757         {
1758             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1759                 (expr.can_be_overflowed(context, 1), &**expr)
1760             } else {
1761                 (false, &**body)
1762             }
1763         }
1764         _ => (body.can_be_overflowed(context, 1), &**body),
1765     };
1766
1767     let comma = arm_comma(&context.config, body);
1768     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1769     let alt_block_sep = alt_block_sep.as_str();
1770     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1771         (true, is_empty_block(block, context.codemap))
1772     } else {
1773         (false, false)
1774     };
1775
1776     let combine_orig_body = |body_str: &str| {
1777         let block_sep = match context.config.control_brace_style() {
1778             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1779             _ => " ",
1780         };
1781
1782         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1783     };
1784
1785     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1786     let next_line_indent = if is_block {
1787         shape.indent
1788     } else {
1789         shape.indent.block_indent(context.config)
1790     };
1791     let combine_next_line_body = |body_str: &str| {
1792         if is_block {
1793             return Some(format!(
1794                 "{} =>\n{}{}",
1795                 pats_str,
1796                 next_line_indent.to_string(context.config),
1797                 body_str
1798             ));
1799         }
1800
1801         let indent_str = shape.indent.to_string(context.config);
1802         let nested_indent_str = next_line_indent.to_string(context.config);
1803         let (body_prefix, body_suffix) = if context.config.wrap_match_arms() {
1804             let comma = if context.config.match_block_trailing_comma() {
1805                 ","
1806             } else {
1807                 ""
1808             };
1809             ("{", format!("\n{}}}{}", indent_str, comma))
1810         } else {
1811             ("", String::from(","))
1812         };
1813
1814         let block_sep = match context.config.control_brace_style() {
1815             ControlBraceStyle::AlwaysNextLine => format!("{}{}\n", alt_block_sep, body_prefix),
1816             _ if body_prefix.is_empty() => "\n".to_owned(),
1817             _ if forbid_same_line => format!("{}{}\n", alt_block_sep, body_prefix),
1818             _ => format!(" {}\n", body_prefix),
1819         } + &nested_indent_str;
1820
1821         Some(format!(
1822             "{} =>{}{}{}",
1823             pats_str,
1824             block_sep,
1825             body_str,
1826             body_suffix
1827         ))
1828     };
1829
1830     // Let's try and get the arm body on the same line as the condition.
1831     // 4 = ` => `.len()
1832     let orig_body_shape = shape
1833         .offset_left(extra_offset(&pats_str, shape) + 4)
1834         .and_then(|shape| shape.sub_width(comma.len()));
1835     let orig_body = if let Some(body_shape) = orig_body_shape {
1836         let rewrite = nop_block_collapse(
1837             format_expr(body, ExprType::Statement, context, body_shape),
1838             body_shape.width,
1839         );
1840
1841         match rewrite {
1842             Some(ref body_str)
1843                 if !forbid_same_line &&
1844                     (is_block ||
1845                         (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1846             {
1847                 return combine_orig_body(body_str);
1848             }
1849             _ => rewrite,
1850         }
1851     } else {
1852         None
1853     };
1854     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1855
1856     // Try putting body on the next line and see if it looks better.
1857     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1858     let next_line_body = nop_block_collapse(
1859         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1860         next_line_body_shape.width,
1861     );
1862     match (orig_body, next_line_body) {
1863         (Some(ref orig_str), Some(ref next_line_str))
1864             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1865         {
1866             combine_next_line_body(next_line_str)
1867         }
1868         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1869             combine_orig_body(orig_str)
1870         }
1871         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1872             combine_next_line_body(next_line_str)
1873         }
1874         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1875         (None, None) => None,
1876         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1877     }
1878 }
1879
1880 // The `if ...` guard on a match arm.
1881 fn rewrite_guard(
1882     context: &RewriteContext,
1883     guard: &Option<ptr::P<ast::Expr>>,
1884     shape: Shape,
1885     // The amount of space used up on this line for the pattern in
1886     // the arm (excludes offset).
1887     pattern_width: usize,
1888 ) -> Option<String> {
1889     if let Some(ref guard) = *guard {
1890         // First try to fit the guard string on the same line as the pattern.
1891         // 4 = ` if `, 5 = ` => {`
1892         let cond_shape = shape
1893             .offset_left(pattern_width + 4)
1894             .and_then(|s| s.sub_width(5));
1895         if let Some(cond_shape) = cond_shape {
1896             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1897                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1898                     return Some(format!(" if {}", cond_str));
1899                 }
1900             }
1901         }
1902
1903         // Not enough space to put the guard after the pattern, try a newline.
1904         // 3 = `if `, 5 = ` => {`
1905         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1906             .offset_left(3)
1907             .and_then(|s| s.sub_width(5));
1908         if let Some(cond_shape) = cond_shape {
1909             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1910                 return Some(format!(
1911                     "\n{}if {}",
1912                     cond_shape.indent.to_string(context.config),
1913                     cond_str
1914                 ));
1915             }
1916         }
1917
1918         None
1919     } else {
1920         Some(String::new())
1921     }
1922 }
1923
1924 fn rewrite_pat_expr(
1925     context: &RewriteContext,
1926     pat: Option<&ast::Pat>,
1927     expr: &ast::Expr,
1928     matcher: &str,
1929     // Connecting piece between pattern and expression,
1930     // *without* trailing space.
1931     connector: &str,
1932     keyword: &str,
1933     shape: Shape,
1934 ) -> Option<String> {
1935     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1936     if let Some(pat) = pat {
1937         let matcher = if matcher.is_empty() {
1938             matcher.to_owned()
1939         } else {
1940             format!("{} ", matcher)
1941         };
1942         let pat_shape =
1943             try_opt!(try_opt!(shape.offset_left(matcher.len())).sub_width(connector.len()));
1944         let pat_string = try_opt!(pat.rewrite(context, pat_shape));
1945         let result = format!("{}{}{}", matcher, pat_string, connector);
1946         return rewrite_assign_rhs(context, result, expr, shape);
1947     }
1948
1949     let expr_rw = expr.rewrite(context, shape);
1950     // The expression may (partially) fit on the current line.
1951     // We do not allow splitting between `if` and condition.
1952     if keyword == "if" || expr_rw.is_some() {
1953         return expr_rw;
1954     }
1955
1956     // The expression won't fit on the current line, jump to next.
1957     let nested_shape = shape
1958         .block_indent(context.config.tab_spaces())
1959         .with_max_width(context.config);
1960     let nested_indent_str = nested_shape.indent.to_string(context.config);
1961     expr.rewrite(context, nested_shape)
1962         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1963 }
1964
1965 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1966     let string_lit = context.snippet(span);
1967
1968     if !context.config.format_strings() && !context.config.force_format_strings() {
1969         if string_lit
1970             .lines()
1971             .rev()
1972             .skip(1)
1973             .all(|line| line.ends_with('\\'))
1974         {
1975             let new_indent = shape.visual_indent(1).indent;
1976             return Some(String::from(
1977                 string_lit
1978                     .lines()
1979                     .map(|line| {
1980                         new_indent.to_string(context.config) + line.trim_left()
1981                     })
1982                     .collect::<Vec<_>>()
1983                     .join("\n")
1984                     .trim_left(),
1985             ));
1986         } else {
1987             return Some(string_lit);
1988         }
1989     }
1990
1991     if !context.config.force_format_strings() &&
1992         !string_requires_rewrite(context, span, &string_lit, shape)
1993     {
1994         return Some(string_lit);
1995     }
1996
1997     let fmt = StringFormat {
1998         opener: "\"",
1999         closer: "\"",
2000         line_start: " ",
2001         line_end: "\\",
2002         shape: shape,
2003         trim_end: false,
2004         config: context.config,
2005     };
2006
2007     // Remove the quote characters.
2008     let str_lit = &string_lit[1..string_lit.len() - 1];
2009
2010     rewrite_string(str_lit, &fmt)
2011 }
2012
2013 fn string_requires_rewrite(
2014     context: &RewriteContext,
2015     span: Span,
2016     string: &str,
2017     shape: Shape,
2018 ) -> bool {
2019     if context.codemap.lookup_char_pos(span.lo).col.0 != shape.indent.width() {
2020         return true;
2021     }
2022
2023     for (i, line) in string.lines().enumerate() {
2024         if i == 0 {
2025             if line.len() > shape.width {
2026                 return true;
2027             }
2028         } else {
2029             if line.len() > shape.width + shape.indent.width() {
2030                 return true;
2031             }
2032         }
2033     }
2034
2035     false
2036 }
2037
2038 pub fn rewrite_call_with_binary_search<R>(
2039     context: &RewriteContext,
2040     callee: &R,
2041     args: &[&ast::Expr],
2042     span: Span,
2043     shape: Shape,
2044 ) -> Option<String>
2045 where
2046     R: Rewrite,
2047 {
2048     let force_trailing_comma = if context.inside_macro {
2049         span_ends_with_comma(context, span)
2050     } else {
2051         false
2052     };
2053     let closure = |callee_max_width| {
2054         // FIXME using byte lens instead of char lens (and probably all over the
2055         // place too)
2056         let callee_shape = Shape {
2057             width: callee_max_width,
2058             ..shape
2059         };
2060         let callee_str = callee
2061             .rewrite(context, callee_shape)
2062             .ok_or(Ordering::Greater)?;
2063
2064         rewrite_call_inner(
2065             context,
2066             &callee_str,
2067             args,
2068             span,
2069             shape,
2070             context.config.fn_call_width(),
2071             force_trailing_comma,
2072         )
2073     };
2074
2075     binary_search(1, shape.width, closure)
2076 }
2077
2078 pub fn rewrite_call(
2079     context: &RewriteContext,
2080     callee: &str,
2081     args: &[ptr::P<ast::Expr>],
2082     span: Span,
2083     shape: Shape,
2084 ) -> Option<String> {
2085     let force_trailing_comma = if context.inside_macro {
2086         span_ends_with_comma(context, span)
2087     } else {
2088         false
2089     };
2090     rewrite_call_inner(
2091         context,
2092         &callee,
2093         &args.iter().map(|x| &**x).collect::<Vec<_>>(),
2094         span,
2095         shape,
2096         context.config.fn_call_width(),
2097         force_trailing_comma,
2098     ).ok()
2099 }
2100
2101 pub fn rewrite_call_inner<'a, T>(
2102     context: &RewriteContext,
2103     callee_str: &str,
2104     args: &[&T],
2105     span: Span,
2106     shape: Shape,
2107     args_max_width: usize,
2108     force_trailing_comma: bool,
2109 ) -> Result<String, Ordering>
2110 where
2111     T: Rewrite + Spanned + ToExpr + 'a,
2112 {
2113     // 2 = `( `, 1 = `(`
2114     let paren_overhead = if context.config.spaces_within_parens() {
2115         2
2116     } else {
2117         1
2118     };
2119     let used_width = extra_offset(&callee_str, shape);
2120     let one_line_width = shape
2121         .width
2122         .checked_sub(used_width + 2 * paren_overhead)
2123         .ok_or(Ordering::Greater)?;
2124
2125     let nested_shape = shape_from_fn_call_style(
2126         context,
2127         shape,
2128         used_width + 2 * paren_overhead,
2129         used_width + paren_overhead,
2130     ).ok_or(Ordering::Greater)?;
2131
2132     let span_lo = context.codemap.span_after(span, "(");
2133     let args_span = mk_sp(span_lo, span.hi);
2134
2135     let (extendable, list_str) = rewrite_call_args(
2136         context,
2137         args,
2138         args_span,
2139         nested_shape,
2140         one_line_width,
2141         args_max_width,
2142         force_trailing_comma,
2143     ).ok_or(Ordering::Less)?;
2144
2145     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2146         let mut new_context = context.clone();
2147         new_context.use_block = true;
2148         return rewrite_call_inner(
2149             &new_context,
2150             callee_str,
2151             args,
2152             span,
2153             shape,
2154             args_max_width,
2155             force_trailing_comma,
2156         );
2157     }
2158
2159     let args_shape = shape
2160         .sub_width(last_line_width(&callee_str))
2161         .ok_or(Ordering::Less)?;
2162     Ok(format!(
2163         "{}{}",
2164         callee_str,
2165         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2166     ))
2167 }
2168
2169 fn need_block_indent(s: &str, shape: Shape) -> bool {
2170     s.lines().skip(1).any(|s| {
2171         s.find(|c| !char::is_whitespace(c))
2172             .map_or(false, |w| w + 1 < shape.indent.width())
2173     })
2174 }
2175
2176 fn rewrite_call_args<'a, T>(
2177     context: &RewriteContext,
2178     args: &[&T],
2179     span: Span,
2180     shape: Shape,
2181     one_line_width: usize,
2182     args_max_width: usize,
2183     force_trailing_comma: bool,
2184 ) -> Option<(bool, String)>
2185 where
2186     T: Rewrite + Spanned + ToExpr + 'a,
2187 {
2188     let items = itemize_list(
2189         context.codemap,
2190         args.iter(),
2191         ")",
2192         |item| item.span().lo,
2193         |item| item.span().hi,
2194         |item| item.rewrite(context, shape),
2195         span.lo,
2196         span.hi,
2197     );
2198     let mut item_vec: Vec<_> = items.collect();
2199
2200     // Try letting the last argument overflow to the next line with block
2201     // indentation. If its first line fits on one line with the other arguments,
2202     // we format the function arguments horizontally.
2203     let tactic = try_overflow_last_arg(
2204         context,
2205         &mut item_vec,
2206         &args[..],
2207         shape,
2208         one_line_width,
2209         args_max_width,
2210     );
2211
2212     let fmt = ListFormatting {
2213         tactic: tactic,
2214         separator: ",",
2215         trailing_separator: if force_trailing_comma {
2216             SeparatorTactic::Always
2217         } else if context.inside_macro || !context.use_block_indent() {
2218             SeparatorTactic::Never
2219         } else {
2220             context.config.trailing_comma()
2221         },
2222         shape: shape,
2223         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2224         preserve_newline: false,
2225         config: context.config,
2226     };
2227
2228     write_list(&item_vec, &fmt).map(|args_str| {
2229         (tactic != DefinitiveListTactic::Vertical, args_str)
2230     })
2231 }
2232
2233 fn try_overflow_last_arg<'a, T>(
2234     context: &RewriteContext,
2235     item_vec: &mut Vec<ListItem>,
2236     args: &[&T],
2237     shape: Shape,
2238     one_line_width: usize,
2239     args_max_width: usize,
2240 ) -> DefinitiveListTactic
2241 where
2242     T: Rewrite + Spanned + ToExpr + 'a,
2243 {
2244     let overflow_last = can_be_overflowed(&context, args);
2245
2246     // Replace the last item with its first line to see if it fits with
2247     // first arguments.
2248     let (orig_last, placeholder) = if overflow_last {
2249         let mut context = context.clone();
2250         if let Some(expr) = args[args.len() - 1].to_expr() {
2251             match expr.node {
2252                 ast::ExprKind::MethodCall(..) => context.force_one_line_chain = true,
2253                 _ => (),
2254             }
2255         }
2256         last_arg_shape(&context, &item_vec, shape, args_max_width)
2257             .map_or((None, None), |arg_shape| {
2258                 rewrite_last_arg_with_overflow(
2259                     &context,
2260                     args,
2261                     &mut item_vec[args.len() - 1],
2262                     arg_shape,
2263                 )
2264             })
2265     } else {
2266         (None, None)
2267     };
2268
2269     let tactic = definitive_tactic(
2270         &*item_vec,
2271         ListTactic::LimitedHorizontalVertical(args_max_width),
2272         Separator::Comma,
2273         one_line_width,
2274     );
2275
2276     // Replace the stub with the full overflowing last argument if the rewrite
2277     // succeeded and its first line fits with the other arguments.
2278     match (overflow_last, tactic, placeholder) {
2279         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2280             item_vec[args.len() - 1].item = placeholder;
2281         }
2282         (true, _, _) => {
2283             item_vec[args.len() - 1].item = orig_last;
2284         }
2285         (false, _, _) => {}
2286     }
2287
2288     tactic
2289 }
2290
2291 fn last_arg_shape(
2292     context: &RewriteContext,
2293     items: &Vec<ListItem>,
2294     shape: Shape,
2295     args_max_width: usize,
2296 ) -> Option<Shape> {
2297     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2298         acc + i.item.as_ref().map_or(0, |s| first_line_width(&s))
2299     });
2300     let max_width = min(args_max_width, shape.width);
2301     let arg_indent = if context.use_block_indent() {
2302         shape.block().indent.block_unindent(context.config)
2303     } else {
2304         shape.block().indent
2305     };
2306     Some(Shape {
2307         width: try_opt!(max_width.checked_sub(overhead)),
2308         indent: arg_indent,
2309         offset: 0,
2310     })
2311 }
2312
2313 // Rewriting closure which is placed at the end of the function call's arg.
2314 // Returns `None` if the reformatted closure 'looks bad'.
2315 fn rewrite_last_closure(
2316     context: &RewriteContext,
2317     expr: &ast::Expr,
2318     shape: Shape,
2319 ) -> Option<String> {
2320     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2321         let body = match body.node {
2322             ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
2323                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2324             }
2325             _ => body,
2326         };
2327         let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
2328             capture,
2329             fn_decl,
2330             body,
2331             expr.span,
2332             context,
2333             shape,
2334         ));
2335         // If the closure goes multi line before its body, do not overflow the closure.
2336         if prefix.contains('\n') {
2337             return None;
2338         }
2339         let body_shape = try_opt!(shape.offset_left(extra_offset));
2340         // When overflowing the closure which consists of a single control flow expression,
2341         // force to use block if its condition uses multi line.
2342         let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
2343             .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
2344             .unwrap_or(false);
2345         if is_multi_lined_cond {
2346             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2347         }
2348
2349         // Seems fine, just format the closure in usual manner.
2350         return expr.rewrite(context, shape);
2351     }
2352     None
2353 }
2354
2355 fn rewrite_last_arg_with_overflow<'a, T>(
2356     context: &RewriteContext,
2357     args: &[&T],
2358     last_item: &mut ListItem,
2359     shape: Shape,
2360 ) -> (Option<String>, Option<String>)
2361 where
2362     T: Rewrite + Spanned + ToExpr + 'a,
2363 {
2364     let last_arg = args[args.len() - 1];
2365     let rewrite = if let Some(expr) = last_arg.to_expr() {
2366         match expr.node {
2367             // When overflowing the closure which consists of a single control flow expression,
2368             // force to use block if its condition uses multi line.
2369             ast::ExprKind::Closure(..) => {
2370                 // If the argument consists of multiple closures, we do not overflow
2371                 // the last closure.
2372                 if args.len() > 1 &&
2373                     args.iter()
2374                         .rev()
2375                         .skip(1)
2376                         .filter_map(|arg| arg.to_expr())
2377                         .any(|expr| match expr.node {
2378                             ast::ExprKind::Closure(..) => true,
2379                             _ => false,
2380                         }) {
2381                     None
2382                 } else {
2383                     rewrite_last_closure(context, expr, shape)
2384                 }
2385             }
2386             _ => expr.rewrite(context, shape),
2387         }
2388     } else {
2389         last_arg.rewrite(context, shape)
2390     };
2391     let orig_last = last_item.item.clone();
2392
2393     if let Some(rewrite) = rewrite {
2394         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2395         last_item.item = rewrite_first_line;
2396         (orig_last, Some(rewrite))
2397     } else {
2398         (orig_last, None)
2399     }
2400 }
2401
2402 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2403 where
2404     T: Rewrite + Spanned + ToExpr + 'a,
2405 {
2406     args.last()
2407         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2408 }
2409
2410 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2411     match expr.node {
2412         ast::ExprKind::Match(..) => {
2413             (context.use_block_indent() && args_len == 1) ||
2414                 (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2415         }
2416         ast::ExprKind::If(..) |
2417         ast::ExprKind::IfLet(..) |
2418         ast::ExprKind::ForLoop(..) |
2419         ast::ExprKind::Loop(..) |
2420         ast::ExprKind::While(..) |
2421         ast::ExprKind::WhileLet(..) => {
2422             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2423         }
2424         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2425             context.use_block_indent() ||
2426                 context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2427         }
2428         ast::ExprKind::Array(..) |
2429         ast::ExprKind::Call(..) |
2430         ast::ExprKind::Mac(..) |
2431         ast::ExprKind::MethodCall(..) |
2432         ast::ExprKind::Struct(..) |
2433         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2434         ast::ExprKind::AddrOf(_, ref expr) |
2435         ast::ExprKind::Box(ref expr) |
2436         ast::ExprKind::Try(ref expr) |
2437         ast::ExprKind::Unary(_, ref expr) |
2438         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2439         _ => false,
2440     }
2441 }
2442
2443 pub fn wrap_args_with_parens(
2444     context: &RewriteContext,
2445     args_str: &str,
2446     is_extendable: bool,
2447     shape: Shape,
2448     nested_shape: Shape,
2449 ) -> String {
2450     if !context.use_block_indent() ||
2451         (context.inside_macro && !args_str.contains('\n') &&
2452             args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2453     {
2454         if context.config.spaces_within_parens() && args_str.len() > 0 {
2455             format!("( {} )", args_str)
2456         } else {
2457             format!("({})", args_str)
2458         }
2459     } else {
2460         format!(
2461             "(\n{}{}\n{})",
2462             nested_shape.indent.to_string(context.config),
2463             args_str,
2464             shape.block().indent.to_string(context.config)
2465         )
2466     }
2467 }
2468
2469 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2470     let snippet = context.snippet(span);
2471     snippet
2472         .trim_right_matches(|c: char| c == ')' || c.is_whitespace())
2473         .ends_with(',')
2474 }
2475
2476 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2477     debug!("rewrite_paren, shape: {:?}", shape);
2478     let total_paren_overhead = paren_overhead(context);
2479     let paren_overhead = total_paren_overhead / 2;
2480     let sub_shape = try_opt!(
2481         shape
2482             .offset_left(paren_overhead)
2483             .and_then(|s| s.sub_width(paren_overhead))
2484     );
2485
2486     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && s.len() > 0 {
2487         format!("( {} )", s)
2488     } else {
2489         format!("({})", s)
2490     };
2491
2492     let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2493     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2494
2495     if subexpr_str.contains('\n') ||
2496         first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2497     {
2498         Some(paren_wrapper(&subexpr_str))
2499     } else {
2500         None
2501     }
2502 }
2503
2504 fn rewrite_index(
2505     expr: &ast::Expr,
2506     index: &ast::Expr,
2507     context: &RewriteContext,
2508     shape: Shape,
2509 ) -> Option<String> {
2510     let expr_str = try_opt!(expr.rewrite(context, shape));
2511
2512     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2513         ("[ ", " ]")
2514     } else {
2515         ("[", "]")
2516     };
2517
2518     let offset = last_line_width(&expr_str) + lbr.len();
2519     let rhs_overhead = shape.rhs_overhead(context.config);
2520     let index_shape = if expr_str.contains('\n') {
2521         Shape::legacy(context.config.max_width(), shape.indent)
2522             .offset_left(offset)
2523             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2524     } else {
2525         shape.visual_indent(offset).sub_width(offset + rbr.len())
2526     };
2527     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2528
2529     // Return if index fits in a single line.
2530     match orig_index_rw {
2531         Some(ref index_str) if !index_str.contains('\n') => {
2532             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2533         }
2534         _ => (),
2535     }
2536
2537     // Try putting index on the next line and see if it fits in a single line.
2538     let indent = shape.indent.block_indent(context.config);
2539     let index_shape = try_opt!(Shape::indented(indent, context.config).offset_left(lbr.len()));
2540     let index_shape = try_opt!(index_shape.sub_width(rbr.len() + rhs_overhead));
2541     let new_index_rw = index.rewrite(context, index_shape);
2542     match (orig_index_rw, new_index_rw) {
2543         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2544             "{}\n{}{}{}{}",
2545             expr_str,
2546             indent.to_string(&context.config),
2547             lbr,
2548             new_index_str,
2549             rbr
2550         )),
2551         (None, Some(ref new_index_str)) => Some(format!(
2552             "{}\n{}{}{}{}",
2553             expr_str,
2554             indent.to_string(&context.config),
2555             lbr,
2556             new_index_str,
2557             rbr
2558         )),
2559         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2560         _ => None,
2561     }
2562 }
2563
2564 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2565     if base.is_some() {
2566         return false;
2567     }
2568
2569     fields.iter().all(|field| !field.is_shorthand)
2570 }
2571
2572 fn rewrite_struct_lit<'a>(
2573     context: &RewriteContext,
2574     path: &ast::Path,
2575     fields: &'a [ast::Field],
2576     base: Option<&'a ast::Expr>,
2577     span: Span,
2578     shape: Shape,
2579 ) -> Option<String> {
2580     debug!("rewrite_struct_lit: shape {:?}", shape);
2581
2582     enum StructLitField<'a> {
2583         Regular(&'a ast::Field),
2584         Base(&'a ast::Expr),
2585     }
2586
2587     // 2 = " {".len()
2588     let path_shape = try_opt!(shape.sub_width(2));
2589     let path_str = try_opt!(rewrite_path(
2590         context,
2591         PathContext::Expr,
2592         None,
2593         path,
2594         path_shape,
2595     ));
2596
2597     if fields.len() == 0 && base.is_none() {
2598         return Some(format!("{} {{}}", path_str));
2599     }
2600
2601     // Foo { a: Foo } - indent is +3, width is -5.
2602     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
2603
2604     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2605     let body_lo = context.codemap.span_after(span, "{");
2606     let fields_str = if struct_lit_can_be_aligned(fields, &base) &&
2607         context.config.struct_field_align_threshold() > 0
2608     {
2609         try_opt!(rewrite_with_alignment(
2610             fields,
2611             context,
2612             shape,
2613             mk_sp(body_lo, span.hi),
2614             one_line_width,
2615         ))
2616     } else {
2617         let field_iter = fields
2618             .into_iter()
2619             .map(StructLitField::Regular)
2620             .chain(base.into_iter().map(StructLitField::Base));
2621
2622         let span_lo = |item: &StructLitField| match *item {
2623             StructLitField::Regular(field) => field.span().lo,
2624             StructLitField::Base(expr) => {
2625                 let last_field_hi = fields.last().map_or(span.lo, |field| field.span.hi);
2626                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo));
2627                 let pos = snippet.find_uncommented("..").unwrap();
2628                 last_field_hi + BytePos(pos as u32)
2629             }
2630         };
2631         let span_hi = |item: &StructLitField| match *item {
2632             StructLitField::Regular(field) => field.span().hi,
2633             StructLitField::Base(expr) => expr.span.hi,
2634         };
2635         let rewrite = |item: &StructLitField| match *item {
2636             StructLitField::Regular(field) => {
2637                 // The 1 taken from the v_budget is for the comma.
2638                 rewrite_field(context, field, try_opt!(v_shape.sub_width(1)), 0)
2639             }
2640             StructLitField::Base(expr) => {
2641                 // 2 = ..
2642                 expr.rewrite(context, try_opt!(v_shape.offset_left(2)))
2643                     .map(|s| format!("..{}", s))
2644             }
2645         };
2646
2647         let items = itemize_list(
2648             context.codemap,
2649             field_iter,
2650             "}",
2651             span_lo,
2652             span_hi,
2653             rewrite,
2654             body_lo,
2655             span.hi,
2656         );
2657         let item_vec = items.collect::<Vec<_>>();
2658
2659         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2660         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2661         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2662
2663         try_opt!(write_list(&item_vec, &fmt))
2664     };
2665
2666     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2667     Some(format!("{} {{{}}}", path_str, fields_str))
2668
2669     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2670     // of space, we should fall back to BlockIndent.
2671 }
2672
2673 pub fn wrap_struct_field(
2674     context: &RewriteContext,
2675     fields_str: &str,
2676     shape: Shape,
2677     nested_shape: Shape,
2678     one_line_width: usize,
2679 ) -> String {
2680     if context.config.struct_lit_style() == IndentStyle::Block &&
2681         (fields_str.contains('\n') ||
2682             context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti ||
2683             fields_str.len() > one_line_width)
2684     {
2685         format!(
2686             "\n{}{}\n{}",
2687             nested_shape.indent.to_string(context.config),
2688             fields_str,
2689             shape.indent.to_string(context.config)
2690         )
2691     } else {
2692         // One liner or visual indent.
2693         format!(" {} ", fields_str)
2694     }
2695 }
2696
2697 pub fn struct_lit_field_separator(config: &Config) -> &str {
2698     colon_spaces(
2699         config.space_before_struct_lit_field_colon(),
2700         config.space_after_struct_lit_field_colon(),
2701     )
2702 }
2703
2704 pub fn rewrite_field(
2705     context: &RewriteContext,
2706     field: &ast::Field,
2707     shape: Shape,
2708     prefix_max_width: usize,
2709 ) -> Option<String> {
2710     if contains_skip(&field.attrs) {
2711         return wrap_str(
2712             context.snippet(field.span()),
2713             context.config.max_width(),
2714             shape,
2715         );
2716     }
2717     let name = &field.ident.node.to_string();
2718     if field.is_shorthand {
2719         Some(name.to_string())
2720     } else {
2721         let mut separator = String::from(struct_lit_field_separator(context.config));
2722         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2723             separator.push(' ');
2724         }
2725         let overhead = name.len() + separator.len();
2726         let expr_shape = try_opt!(shape.offset_left(overhead));
2727         let expr = field.expr.rewrite(context, expr_shape);
2728
2729         let mut attrs_str = try_opt!(field.attrs.rewrite(context, shape));
2730         if !attrs_str.is_empty() {
2731             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2732         };
2733
2734         match expr {
2735             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2736             None => {
2737                 let expr_offset = shape.indent.block_indent(context.config);
2738                 let expr = field
2739                     .expr
2740                     .rewrite(context, Shape::indented(expr_offset, context.config));
2741                 expr.map(|s| {
2742                     format!(
2743                         "{}{}:\n{}{}",
2744                         attrs_str,
2745                         name,
2746                         expr_offset.to_string(&context.config),
2747                         s
2748                     )
2749                 })
2750             }
2751         }
2752     }
2753 }
2754
2755 fn shape_from_fn_call_style(
2756     context: &RewriteContext,
2757     shape: Shape,
2758     overhead: usize,
2759     offset: usize,
2760 ) -> Option<Shape> {
2761     if context.use_block_indent() {
2762         // 1 = ","
2763         shape
2764             .block()
2765             .block_indent(context.config.tab_spaces())
2766             .with_max_width(context.config)
2767             .sub_width(1)
2768     } else {
2769         shape.visual_indent(offset).sub_width(overhead)
2770     }
2771 }
2772
2773 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2774     context: &RewriteContext,
2775     items: &[&T],
2776     span: Span,
2777     shape: Shape,
2778 ) -> Option<String>
2779 where
2780     T: Rewrite + Spanned + ToExpr + 'a,
2781 {
2782     let mut items = items.iter();
2783     // In case of length 1, need a trailing comma
2784     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2785     if items.len() == 1 {
2786         // 3 = "(" + ",)"
2787         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
2788         return items.next().unwrap().rewrite(context, nested_shape).map(
2789             |s| if context.config.spaces_within_parens() {
2790                 format!("( {}, )", s)
2791             } else {
2792                 format!("({},)", s)
2793             },
2794         );
2795     }
2796
2797     let list_lo = context.codemap.span_after(span, "(");
2798     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
2799     let items = itemize_list(
2800         context.codemap,
2801         items,
2802         ")",
2803         |item| item.span().lo,
2804         |item| item.span().hi,
2805         |item| item.rewrite(context, nested_shape),
2806         list_lo,
2807         span.hi - BytePos(1),
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
2989     fn count_line_breaks(src: &str) -> usize {
2990         src.chars().filter(|&x| x == '\n').count()
2991     }
2992
2993     !next_line_rhs.contains('\n') ||
2994         count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2995 }
2996
2997 fn rewrite_expr_addrof(
2998     context: &RewriteContext,
2999     mutability: ast::Mutability,
3000     expr: &ast::Expr,
3001     shape: Shape,
3002 ) -> Option<String> {
3003     let operator_str = match mutability {
3004         ast::Mutability::Immutable => "&",
3005         ast::Mutability::Mutable => "&mut ",
3006     };
3007     rewrite_unary_prefix(context, operator_str, expr, shape)
3008 }
3009
3010 pub trait ToExpr {
3011     fn to_expr(&self) -> Option<&ast::Expr>;
3012     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
3013 }
3014
3015 impl ToExpr for ast::Expr {
3016     fn to_expr(&self) -> Option<&ast::Expr> {
3017         Some(self)
3018     }
3019
3020     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3021         can_be_overflowed_expr(context, self, len)
3022     }
3023 }
3024
3025 impl ToExpr for ast::Ty {
3026     fn to_expr(&self) -> Option<&ast::Expr> {
3027         None
3028     }
3029
3030     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3031         can_be_overflowed_type(context, self, len)
3032     }
3033 }
3034
3035 impl<'a> ToExpr for TuplePatField<'a> {
3036     fn to_expr(&self) -> Option<&ast::Expr> {
3037         None
3038     }
3039
3040     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3041         can_be_overflowed_pat(context, self, len)
3042     }
3043 }
3044
3045 impl<'a> ToExpr for ast::StructField {
3046     fn to_expr(&self) -> Option<&ast::Expr> {
3047         None
3048     }
3049
3050     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
3051         false
3052     }
3053 }