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