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::Ordering;
  12 use std::borrow::Borrow;
  13 use std::mem::swap;
  14 use std::ops::Deref;
  15 use std::iter::ExactSizeIterator;
  16 use std::fmt::Write;
  17
  18 use {Indent, Spanned};
  19 use codemap::SpanUtils;
  20 use rewrite::{Rewrite, RewriteContext};
  21 use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic,
  22             DefinitiveListTactic, definitive_tactic, ListItem, format_item_list};
  23 use string::{StringFormat, rewrite_string};
  24 use utils::{extra_offset, last_line_width, wrap_str, binary_search, first_line_width,
  25             semicolon_for_stmt, trimmed_last_line_width, left_most_sub_expr, stmt_expr};
  26 use visitor::FmtVisitor;
  27 use config::{Config, StructLitStyle, MultilineStyle, ElseIfBraceStyle, ControlBraceStyle};
  28 use comment::{FindUncommented, rewrite_comment, contains_comment, recover_comment_removed};
  29 use types::rewrite_path;
  30 use items::{span_lo_for_arg, span_hi_for_arg};
  31 use chains::rewrite_chain;
  32 use macros::{rewrite_macro, MacroPosition};
  33
  34 use syntax::{ast, ptr};
  35 use syntax::codemap::{CodeMap, Span, BytePos, mk_sp};
  36 use syntax::parse::classify;
  37
  38 impl Rewrite for ast::Expr {
  39     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  40         format_expr(self, ExprType::SubExpression, context, width, offset)
  41     }
  42 }
  43
  44 #[derive(PartialEq)]
  45 enum ExprType {
  46     Statement,
  47     SubExpression,
  48 }
  49
  50 fn format_expr(expr: &ast::Expr,
  51                expr_type: ExprType,
  52                context: &RewriteContext,
  53                width: usize,
  54                offset: Indent)
  55                -> Option<String> {
  56     let result = match expr.node {
  57         ast::ExprKind::Vec(ref expr_vec) => {
  58             rewrite_array(expr_vec.iter().map(|e| &**e),
  59                           mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi),
  60                           context,
  61                           width,
  62                           offset)
  63         }
  64         ast::ExprKind::Lit(ref l) => {
  65             match l.node {
  66                 ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
  67                     Some(rewrite_string_lit(context, l.span, width, offset))
  68                 }
  69                 _ => {
  70                     wrap_str(context.snippet(expr.span),
  71                              context.config.max_width,
  72                              width,
  73                              offset)
  74                 }
  75             }
  76         }
  77         ast::ExprKind::Call(ref callee, ref args) => {
  78             let inner_span = mk_sp(callee.span.hi, expr.span.hi);
  79             rewrite_call(context, &**callee, args, inner_span, width, offset)
  80         }
  81         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, width, offset),
  82         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
  83             // FIXME: format comments between operands and operator
  84             rewrite_pair(&**lhs,
  85                          &**rhs,
  86                          "",
  87                          &format!(" {} ", context.snippet(op.span)),
  88                          "",
  89                          context,
  90                          width,
  91                          offset)
  92         }
  93         ast::ExprKind::Unary(ref op, ref subexpr) => {
  94             rewrite_unary_op(context, op, subexpr, width, offset)
  95         }
  96         ast::ExprKind::Struct(ref path, ref fields, ref base) => {
  97             rewrite_struct_lit(context,
  98                                path,
  99                                fields,
 100                                base.as_ref().map(|e| &**e),
 101                                expr.span,
 102                                width,
 103                                offset)
 104         }
 105         ast::ExprKind::Tup(ref items) => {
 106             rewrite_tuple(context,
 107                           items.iter().map(|x| &**x),
 108                           expr.span,
 109                           width,
 110                           offset)
 111         }
 112         ast::ExprKind::While(ref cond, ref block, label) => {
 113             Loop::new_while(None, cond, block, label).rewrite(context, width, offset)
 114         }
 115         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => {
 116             Loop::new_while(Some(pat), cond, block, label).rewrite(context, width, offset)
 117         }
 118         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 119             Loop::new_for(pat, cond, block, label).rewrite(context, width, offset)
 120         }
 121         ast::ExprKind::Loop(ref block, label) => {
 122             Loop::new_loop(block, label).rewrite(context, width, offset)
 123         }
 124         ast::ExprKind::Block(ref block) => block.rewrite(context, width, offset),
 125         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => {
 126             rewrite_if_else(context,
 127                             cond,
 128                             expr_type,
 129                             if_block,
 130                             else_block.as_ref().map(|e| &**e),
 131                             expr.span,
 132                             None,
 133                             width,
 134                             offset,
 135                             true)
 136         }
 137         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 138             rewrite_if_else(context,
 139                             cond,
 140                             expr_type,
 141                             if_block,
 142                             else_block.as_ref().map(|e| &**e),
 143                             expr.span,
 144                             Some(pat),
 145                             width,
 146                             offset,
 147                             true)
 148         }
 149         ast::ExprKind::Match(ref cond, ref arms) => {
 150             rewrite_match(context, cond, arms, width, offset, expr.span)
 151         }
 152         ast::ExprKind::Path(ref qself, ref path) => {
 153             rewrite_path(context, true, qself.as_ref(), path, width, offset)
 154         }
 155         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 156             rewrite_assignment(context, lhs, rhs, None, width, offset)
 157         }
 158         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 159             rewrite_assignment(context, lhs, rhs, Some(op), width, offset)
 160         }
 161         ast::ExprKind::Continue(ref opt_ident) => {
 162             let id_str = match *opt_ident {
 163                 Some(ident) => format!(" {}", ident.node),
 164                 None => String::new(),
 165             };
 166             wrap_str(format!("continue{}", id_str),
 167                      context.config.max_width,
 168                      width,
 169                      offset)
 170         }
 171         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 172             let id_str = match *opt_ident {
 173                 Some(ident) => format!(" {}", ident.node),
 174                 None => String::new(),
 175             };
 176
 177             if let Some(ref expr) = *opt_expr {
 178                 rewrite_unary_prefix(context,
 179                                      &format!("break{} ", id_str),
 180                                      &**expr,
 181                                      width,
 182                                      offset)
 183             } else {
 184                 wrap_str(format!("break{}", id_str),
 185                          context.config.max_width,
 186                          width,
 187                          offset)
 188             }
 189         }
 190         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 191             rewrite_closure(capture, fn_decl, body, expr.span, context, width, offset)
 192         }
 193         ast::ExprKind::Try(..) |
 194         ast::ExprKind::Field(..) |
 195         ast::ExprKind::TupField(..) |
 196         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, width, offset),
 197         ast::ExprKind::Mac(ref mac) => {
 198             // Failure to rewrite a marco should not imply failure to
 199             // rewrite the expression.
 200             rewrite_macro(mac, None, context, width, offset, MacroPosition::Expression)
 201                 .or_else(|| {
 202                     wrap_str(context.snippet(expr.span),
 203                              context.config.max_width,
 204                              width,
 205                              offset)
 206                 })
 207         }
 208         ast::ExprKind::Ret(None) => {
 209             wrap_str("return".to_owned(), context.config.max_width, width, offset)
 210         }
 211         ast::ExprKind::Ret(Some(ref expr)) => {
 212             rewrite_unary_prefix(context, "return ", &**expr, width, offset)
 213         }
 214         ast::ExprKind::Box(ref expr) => {
 215             rewrite_unary_prefix(context, "box ", &**expr, width, offset)
 216         }
 217         ast::ExprKind::AddrOf(mutability, ref expr) => {
 218             rewrite_expr_addrof(context, mutability, expr, width, offset)
 219         }
 220         ast::ExprKind::Cast(ref expr, ref ty) => {
 221             rewrite_pair(&**expr, &**ty, "", " as ", "", context, width, offset)
 222         }
 223         ast::ExprKind::Type(ref expr, ref ty) => {
 224             rewrite_pair(&**expr, &**ty, "", ": ", "", context, width, offset)
 225         }
 226         ast::ExprKind::Index(ref expr, ref index) => {
 227             rewrite_index(&**expr, &**index, context, width, offset)
 228         }
 229         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 230             let (lbr, rbr) = if context.config.spaces_within_square_brackets {
 231                 ("[ ", " ]")
 232             } else {
 233                 ("[", "]")
 234             };
 235             rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, width, offset)
 236         }
 237         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 238             let delim = match limits {
 239                 ast::RangeLimits::HalfOpen => "..",
 240                 ast::RangeLimits::Closed => "...",
 241             };
 242
 243             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 244                 (Some(ref lhs), Some(ref rhs)) => {
 245                     let sp_delim = if context.config.spaces_around_ranges {
 246                         format!(" {} ", delim)
 247                     } else {
 248                         delim.into()
 249                     };
 250                     rewrite_pair(&**lhs, &**rhs, "", &sp_delim, "", context, width, offset)
 251                 }
 252                 (None, Some(ref rhs)) => {
 253                     let sp_delim = if context.config.spaces_around_ranges {
 254                         format!("{} ", delim)
 255                     } else {
 256                         delim.into()
 257                     };
 258                     rewrite_unary_prefix(context, &sp_delim, &**rhs, width, offset)
 259                 }
 260                 (Some(ref lhs), None) => {
 261                     let sp_delim = if context.config.spaces_around_ranges {
 262                         format!(" {}", delim)
 263                     } else {
 264                         delim.into()
 265                     };
 266                     rewrite_unary_suffix(context, &sp_delim, &**lhs, width, offset)
 267                 }
 268                 (None, None) => wrap_str(delim.into(), context.config.max_width, width, offset),
 269             }
 270         }
 271         // We do not format these expressions yet, but they should still
 272         // satisfy our width restrictions.
 273         ast::ExprKind::InPlace(..) |
 274         ast::ExprKind::InlineAsm(..) => {
 275             wrap_str(context.snippet(expr.span),
 276                      context.config.max_width,
 277                      width,
 278                      offset)
 279         }
 280     };
 281     result.and_then(|res| recover_comment_removed(res, expr.span, context, width, offset))
 282 }
 283
 284 pub fn rewrite_pair<LHS, RHS>(lhs: &LHS,
 285                               rhs: &RHS,
 286                               prefix: &str,
 287                               infix: &str,
 288                               suffix: &str,
 289                               context: &RewriteContext,
 290                               width: usize,
 291                               offset: Indent)
 292                               -> Option<String>
 293     where LHS: Rewrite,
 294           RHS: Rewrite
 295 {
 296     let lhs_budget = try_opt!(width.checked_sub(prefix.len() + infix.len()));
 297     let rhs_budget = try_opt!(width.checked_sub(suffix.len()));
 298
 299     // Get "full width" rhs and see if it fits on the current line. This
 300     // usually works fairly well since it tends to place operands of
 301     // operations with high precendence close together.
 302     // Note that this is non-conservative, but its just to see if it's even
 303     // worth trying to put everything on one line.
 304     let rhs_result = rhs.rewrite(context, rhs_budget, offset);
 305
 306     if let Some(rhs_result) = rhs_result {
 307         // This is needed in case of line break not caused by a
 308         // shortage of space, but by end-of-line comments, for example.
 309         if !rhs_result.contains('\n') {
 310             let lhs_result = lhs.rewrite(context, lhs_budget, offset);
 311             if let Some(lhs_result) = lhs_result {
 312                 let mut result = format!("{}{}{}", prefix, lhs_result, infix);
 313
 314                 let remaining_width = width.checked_sub(last_line_width(&result)).unwrap_or(0);
 315
 316                 if rhs_result.len() <= remaining_width {
 317                     result.push_str(&rhs_result);
 318                     result.push_str(suffix);
 319                     return Some(result);
 320                 }
 321
 322                 // Try rewriting the rhs into the remaining space.
 323                 let rhs_budget = try_opt!(remaining_width.checked_sub(suffix.len()));
 324                 if let Some(rhs_result) = rhs.rewrite(context, rhs_budget, offset + result.len()) {
 325                     if rhs_result.len() <= remaining_width {
 326                         result.push_str(&rhs_result);
 327                         result.push_str(suffix);
 328                         return Some(result);
 329                     }
 330                 }
 331             }
 332         }
 333     }
 334
 335     // We have to use multiple lines.
 336
 337     // Re-evaluate the rhs because we have more space now:
 338     let infix = infix.trim_right();
 339     let lhs_budget =
 340         try_opt!(context.config.max_width.checked_sub(offset.width() + prefix.len() + infix.len()));
 341     let rhs_budget = try_opt!(rhs_budget.checked_sub(prefix.len()));
 342     let rhs_offset = offset + prefix.len();
 343
 344     let rhs_result = try_opt!(rhs.rewrite(context, rhs_budget, rhs_offset));
 345     let lhs_result = try_opt!(lhs.rewrite(context, lhs_budget, offset));
 346     Some(format!("{}{}{}\n{}{}{}",
 347                  prefix,
 348                  lhs_result,
 349                  infix,
 350                  rhs_offset.to_string(context.config),
 351                  rhs_result,
 352                  suffix))
 353 }
 354
 355 pub fn rewrite_array<'a, I>(expr_iter: I,
 356                             span: Span,
 357                             context: &RewriteContext,
 358                             width: usize,
 359                             offset: Indent)
 360                             -> Option<String>
 361     where I: Iterator<Item = &'a ast::Expr>
 362 {
 363     let bracket_size = if context.config.spaces_within_square_brackets {
 364         2  // "[ "
 365     } else {
 366         1  // "["
 367     };
 368     let offset = offset + bracket_size;
 369     let inner_context = &RewriteContext { block_indent: offset, ..*context };
 370     let max_item_width = try_opt!(width.checked_sub(bracket_size * 2));
 371     let items = itemize_list(context.codemap,
 372                              expr_iter,
 373                              "]",
 374                              |item| item.span.lo,
 375                              |item| item.span.hi,
 376                              |item| item.rewrite(inner_context, max_item_width, offset),
 377                              span.lo,
 378                              span.hi)
 379         .collect::<Vec<_>>();
 380
 381     let has_long_item = try_opt!(items.iter()
 382         .map(|li| li.item.as_ref().map(|s| s.len() > 10))
 383         .fold(Some(false), |acc, x| acc.and_then(|y| x.map(|x| x || y))));
 384
 385     let tactic = if has_long_item || items.iter().any(ListItem::is_multiline) {
 386         definitive_tactic(&items, ListTactic::HorizontalVertical, max_item_width)
 387     } else {
 388         DefinitiveListTactic::Mixed
 389     };
 390
 391     let fmt = ListFormatting {
 392         tactic: tactic,
 393         separator: ",",
 394         trailing_separator: SeparatorTactic::Never,
 395         indent: offset,
 396         width: max_item_width,
 397         ends_with_newline: false,
 398         config: context.config,
 399     };
 400     let list_str = try_opt!(write_list(&items, &fmt));
 401
 402     Some(if context.config.spaces_within_square_brackets && list_str.len() > 0 {
 403         format!("[ {} ]", list_str)
 404     } else {
 405         format!("[{}]", list_str)
 406     })
 407 }
 408
 409 // This functions is pretty messy because of the rules around closures and blocks:
 410 // TODO
 411 //   * if there is a return type, then there must be braces,
 412 //   * given a closure with braces, whether that is parsed to give an inner block
 413 //     or not depends on if there is a return type and if there are statements
 414 //     in that block,
 415 //   * if the first expression in the body ends with a block (i.e., is a
 416 //     statement without needing a semi-colon), then adding or removing braces
 417 //     can change whether it is treated as an expression or statement.
 418 fn rewrite_closure(capture: ast::CaptureBy,
 419                    fn_decl: &ast::FnDecl,
 420                    body: &ast::Expr,
 421                    span: Span,
 422                    context: &RewriteContext,
 423                    width: usize,
 424                    offset: Indent)
 425                    -> Option<String> {
 426     let mover = if capture == ast::CaptureBy::Value {
 427         "move "
 428     } else {
 429         ""
 430     };
 431     let offset = offset + mover.len();
 432
 433     // 4 = "|| {".len(), which is overconservative when the closure consists of
 434     // a single expression.
 435     let budget = try_opt!(width.checked_sub(4 + mover.len()));
 436     // 1 = |
 437     let argument_offset = offset + 1;
 438     let ret_str = try_opt!(fn_decl.output.rewrite(context, budget, argument_offset));
 439
 440     // 1 = space between arguments and return type.
 441     let horizontal_budget = budget.checked_sub(ret_str.len() + 1).unwrap_or(0);
 442
 443     let arg_items = itemize_list(context.codemap,
 444                                  fn_decl.inputs.iter(),
 445                                  "|",
 446                                  |arg| span_lo_for_arg(arg),
 447                                  |arg| span_hi_for_arg(arg),
 448                                  |arg| arg.rewrite(context, budget, argument_offset),
 449                                  context.codemap.span_after(span, "|"),
 450                                  body.span.lo);
 451     let item_vec = arg_items.collect::<Vec<_>>();
 452     let tactic = definitive_tactic(&item_vec, ListTactic::HorizontalVertical, horizontal_budget);
 453     let budget = match tactic {
 454         DefinitiveListTactic::Horizontal => horizontal_budget,
 455         _ => budget,
 456     };
 457
 458     let fmt = ListFormatting {
 459         tactic: tactic,
 460         separator: ",",
 461         trailing_separator: SeparatorTactic::Never,
 462         indent: argument_offset,
 463         width: budget,
 464         ends_with_newline: false,
 465         config: context.config,
 466     };
 467     let list_str = try_opt!(write_list(&item_vec, &fmt));
 468     let mut prefix = format!("{}|{}|", mover, list_str);
 469
 470     if !ret_str.is_empty() {
 471         if prefix.contains('\n') {
 472             prefix.push('\n');
 473             prefix.push_str(&argument_offset.to_string(context.config));
 474         } else {
 475             prefix.push(' ');
 476         }
 477         prefix.push_str(&ret_str);
 478     }
 479
 480     // 1 = space between `|...|` and body.
 481     let extra_offset = extra_offset(&prefix, offset) + 1;
 482     let budget = try_opt!(width.checked_sub(extra_offset));
 483     let total_offset = offset + extra_offset;
 484
 485     if let ast::ExprKind::Block(ref block) = body.node {
 486         // The body of the closure is a block.
 487         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 488             return Some(format!("{} {{}}", prefix));
 489         }
 490
 491         // Figure out if the block is necessary.
 492         let needs_block = block.rules != ast::BlockCheckMode::Default || block.stmts.len() > 1 ||
 493                           block_contains_comment(block, context.codemap) ||
 494                           prefix.contains('\n');
 495
 496         if ret_str.is_empty() && !needs_block {
 497             // lock.stmts.len() == 1
 498             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 499                 if let Some(rw) = rewrite_closure_expr(expr,
 500                                                        &prefix,
 501                                                        context,
 502                                                        budget,
 503                                                        total_offset) {
 504                     return Some(rw);
 505                 }
 506             }
 507         }
 508
 509         if !needs_block {
 510             // We need braces, but we might still prefer a one-liner.
 511             let stmt = &block.stmts[0];
 512             // 4 = braces and spaces.
 513             let mut rewrite = stmt.rewrite(context, try_opt!(budget.checked_sub(4)), total_offset);
 514
 515             // Checks if rewrite succeeded and fits on a single line.
 516             rewrite = and_one_line(rewrite);
 517
 518             if let Some(rewrite) = rewrite {
 519                 return Some(format!("{} {{ {} }}", prefix, rewrite));
 520             }
 521         }
 522
 523         // Either we require a block, or tried without and failed.
 524         return rewrite_closure_block(&block, prefix, context, budget);
 525     }
 526
 527     if let Some(rw) = rewrite_closure_expr(body, &prefix, context, budget, total_offset) {
 528         return Some(rw);
 529     }
 530
 531     // The closure originally had a non-block expression, but we can't fit on
 532     // one line, so we'll insert a block.
 533     let block = ast::Block {
 534         stmts: vec![ast::Stmt {
 535                         id: ast::NodeId::new(0),
 536                         node: ast::StmtKind::Expr(ptr::P(body.clone())),
 537                         span: body.span,
 538                     }],
 539         id: ast::NodeId::new(0),
 540         rules: ast::BlockCheckMode::Default,
 541         span: body.span,
 542     };
 543     return rewrite_closure_block(&block, prefix, context, budget);
 544
 545     fn rewrite_closure_expr(expr: &ast::Expr,
 546                             prefix: &str,
 547                             context: &RewriteContext,
 548                             budget: usize,
 549                             offset: Indent)
 550                             -> Option<String> {
 551         let mut rewrite = expr.rewrite(context, budget, offset);
 552         if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 553             rewrite = and_one_line(rewrite);
 554         }
 555         rewrite.map(|rw| format!("{} {}", prefix, rw))
 556     }
 557
 558     fn rewrite_closure_block(block: &ast::Block,
 559                              prefix: String,
 560                              context: &RewriteContext,
 561                              budget: usize)
 562                              -> Option<String> {
 563         // Start with visual indent, then fall back to block indent if the
 564         // closure is large.
 565         let rewrite = try_opt!(block.rewrite(&context, budget, Indent::empty()));
 566
 567         let block_threshold = context.config.closure_block_indent_threshold;
 568         if block_threshold < 0 || rewrite.matches('\n').count() <= block_threshold as usize {
 569             return Some(format!("{} {}", prefix, rewrite));
 570         }
 571
 572         // The body of the closure is big enough to be block indented, that
 573         // means we must re-format.
 574         let mut context = context.clone();
 575         context.block_indent.alignment = 0;
 576         let rewrite = try_opt!(block.rewrite(&context, budget, Indent::empty()));
 577         Some(format!("{} {}", prefix, rewrite))
 578     }
 579 }
 580
 581 fn and_one_line(x: Option<String>) -> Option<String> {
 582     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 583 }
 584
 585 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 586     block_str.map(|block_str| if block_str.starts_with('{') && budget >= 2 &&
 587                                  (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() ==
 588                                   block_str.len() - 2) {
 589         "{}".to_owned()
 590     } else {
 591         block_str.to_owned()
 592     })
 593 }
 594
 595 impl Rewrite for ast::Block {
 596     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 597         // width is used only for the single line case: either the empty block `{}`,
 598         // or an unsafe expression `unsafe { e }`.
 599
 600         let user_str = context.snippet(self.span);
 601         if user_str == "{}" && width >= 2 {
 602             return Some(user_str);
 603         }
 604
 605         let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 606         visitor.block_indent = context.block_indent;
 607
 608         let prefix = match self.rules {
 609             ast::BlockCheckMode::Unsafe(..) => {
 610                 let snippet = context.snippet(self.span);
 611                 let open_pos = try_opt!(snippet.find_uncommented("{"));
 612                 visitor.last_pos = self.span.lo + BytePos(open_pos as u32);
 613
 614                 // Extract comment between unsafe and block start.
 615                 let trimmed = &snippet[6..open_pos].trim();
 616
 617                 let prefix = if !trimmed.is_empty() {
 618                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 619                     let budget = try_opt!(width.checked_sub(9));
 620                     format!("unsafe {} ",
 621                             try_opt!(rewrite_comment(trimmed,
 622                                                      true,
 623                                                      budget,
 624                                                      offset + 7,
 625                                                      context.config)))
 626                 } else {
 627                     "unsafe ".to_owned()
 628                 };
 629
 630                 if is_simple_block(self, context.codemap) && prefix.len() < width {
 631                     let expr_str = self.stmts[0].rewrite(context, width - prefix.len(), offset);
 632                     let expr_str = try_opt!(expr_str);
 633                     let result = format!("{}{{ {} }}", prefix, expr_str);
 634                     if result.len() <= width && !result.contains('\n') {
 635                         return Some(result);
 636                     }
 637                 }
 638
 639                 prefix
 640             }
 641             ast::BlockCheckMode::Default => {
 642                 visitor.last_pos = self.span.lo;
 643
 644                 String::new()
 645             }
 646         };
 647
 648         visitor.visit_block(self);
 649
 650         Some(format!("{}{}", prefix, visitor.buffer))
 651     }
 652 }
 653
 654 impl Rewrite for ast::Stmt {
 655     fn rewrite(&self, context: &RewriteContext, _width: usize, offset: Indent) -> Option<String> {
 656         let result = match self.node {
 657             ast::StmtKind::Local(ref local) => {
 658                 local.rewrite(context, context.config.max_width, offset)
 659             }
 660             ast::StmtKind::Expr(ref ex) |
 661             ast::StmtKind::Semi(ref ex) => {
 662                 let suffix = if semicolon_for_stmt(self) { ";" } else { "" };
 663
 664                 format_expr(ex,
 665                             match self.node {
 666                                 ast::StmtKind::Expr(_) => ExprType::SubExpression,
 667                                 ast::StmtKind::Semi(_) => ExprType::Statement,
 668                                 _ => unreachable!(),
 669                             },
 670                             context,
 671                             context.config.max_width - offset.width() - suffix.len(),
 672                             offset)
 673                     .map(|s| s + suffix)
 674             }
 675             ast::StmtKind::Mac(..) |
 676             ast::StmtKind::Item(..) => None,
 677         };
 678         result.and_then(|res| recover_comment_removed(res, self.span, context, _width, offset))
 679     }
 680 }
 681
 682 // Abstraction over for, while and loop expressions
 683 struct Loop<'a> {
 684     cond: Option<&'a ast::Expr>,
 685     block: &'a ast::Block,
 686     label: Option<ast::SpannedIdent>,
 687     pat: Option<&'a ast::Pat>,
 688     keyword: &'a str,
 689     matcher: &'a str,
 690     connector: &'a str,
 691 }
 692
 693 impl<'a> Loop<'a> {
 694     fn new_loop(block: &'a ast::Block, label: Option<ast::SpannedIdent>) -> Loop<'a> {
 695         Loop {
 696             cond: None,
 697             block: block,
 698             label: label,
 699             pat: None,
 700             keyword: "loop",
 701             matcher: "",
 702             connector: "",
 703         }
 704     }
 705
 706     fn new_while(pat: Option<&'a ast::Pat>,
 707                  cond: &'a ast::Expr,
 708                  block: &'a ast::Block,
 709                  label: Option<ast::SpannedIdent>)
 710                  -> Loop<'a> {
 711         Loop {
 712             cond: Some(cond),
 713             block: block,
 714             label: label,
 715             pat: pat,
 716             keyword: "while ",
 717             matcher: match pat {
 718                 Some(..) => "let ",
 719                 None => "",
 720             },
 721             connector: " =",
 722         }
 723     }
 724
 725     fn new_for(pat: &'a ast::Pat,
 726                cond: &'a ast::Expr,
 727                block: &'a ast::Block,
 728                label: Option<ast::SpannedIdent>)
 729                -> Loop<'a> {
 730         Loop {
 731             cond: Some(cond),
 732             block: block,
 733             label: label,
 734             pat: Some(pat),
 735             keyword: "for ",
 736             matcher: "",
 737             connector: " in",
 738         }
 739     }
 740 }
 741
 742 impl<'a> Rewrite for Loop<'a> {
 743     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 744         let label_string = rewrite_label(self.label);
 745         // 2 = " {".len()
 746         let inner_width = try_opt!(width.checked_sub(self.keyword.len() + 2 + label_string.len()));
 747         let inner_offset = offset + self.keyword.len() + label_string.len();
 748
 749         let pat_expr_string = match self.cond {
 750             Some(cond) => {
 751                 try_opt!(rewrite_pat_expr(context,
 752                                           self.pat,
 753                                           cond,
 754                                           self.matcher,
 755                                           self.connector,
 756                                           inner_width,
 757                                           inner_offset))
 758             }
 759             None => String::new(),
 760         };
 761
 762         let alt_block_sep = String::from("\n") + &context.block_indent.to_string(context.config);
 763         let block_sep = match context.config.control_brace_style {
 764             ControlBraceStyle::AlwaysNextLine => alt_block_sep.as_str(),
 765             ControlBraceStyle::AlwaysSameLine => " ",
 766         };
 767
 768         // This is used only for the empty block case: `{}`
 769         let block_width = try_opt!(width.checked_sub(label_string.len() + self.keyword.len() +
 770                                                      extra_offset(&pat_expr_string, inner_offset) +
 771                                                      1));
 772
 773         // FIXME: this drops any comment between "loop" and the block.
 774         self.block
 775             .rewrite(context, block_width, offset)
 776             .map(|result| {
 777                 format!("{}{}{}{}{}",
 778                         label_string,
 779                         self.keyword,
 780                         pat_expr_string,
 781                         block_sep,
 782                         result)
 783             })
 784     }
 785 }
 786
 787 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
 788     match label {
 789         Some(ident) => format!("{}: ", ident.node),
 790         None => "".to_owned(),
 791     }
 792 }
 793
 794 fn extract_comment(span: Span,
 795                    context: &RewriteContext,
 796                    offset: Indent,
 797                    width: usize)
 798                    -> Option<String> {
 799     let comment_str = context.snippet(span);
 800     if contains_comment(&comment_str) {
 801         let comment =
 802             try_opt!(rewrite_comment(comment_str.trim(), false, width, offset, context.config));
 803         Some(format!("\n{indent}{}\n{indent}",
 804                      comment,
 805                      indent = offset.to_string(context.config)))
 806     } else {
 807         None
 808     }
 809 }
 810
 811 // Rewrites if-else blocks. If let Some(_) = pat, the expression is
 812 // treated as an if-let-else expression.
 813 fn rewrite_if_else(context: &RewriteContext,
 814                    cond: &ast::Expr,
 815                    expr_type: ExprType,
 816                    if_block: &ast::Block,
 817                    else_block_opt: Option<&ast::Expr>,
 818                    span: Span,
 819                    pat: Option<&ast::Pat>,
 820                    width: usize,
 821                    offset: Indent,
 822                    allow_single_line: bool)
 823                    -> Option<String> {
 824     let (budget, indent) = if !allow_single_line {
 825         // We are part of an if-elseif-else chain. Our constraints are tightened.
 826         // 7 = "} else" .len()
 827         (try_opt!(width.checked_sub(7)), offset + 7)
 828     } else {
 829         (width, offset)
 830     };
 831
 832     // 3 = "if ", 2 = " {"
 833     let pat_penalty = match context.config.else_if_brace_style {
 834         ElseIfBraceStyle::AlwaysNextLine => 3,
 835         _ => 3 + 2,
 836     };
 837     let pat_expr_string = try_opt!(rewrite_pat_expr(context,
 838                                                     pat,
 839                                                     cond,
 840                                                     "let ",
 841                                                     " =",
 842                                                     try_opt!(budget.checked_sub(pat_penalty)),
 843                                                     indent + 3));
 844
 845     // Try to format if-else on single line.
 846     if expr_type == ExprType::SubExpression && allow_single_line &&
 847        context.config.single_line_if_else_max_width > 0 {
 848         let trial = single_line_if_else(context, &pat_expr_string, if_block, else_block_opt, width);
 849
 850         if trial.is_some() &&
 851            trial.as_ref().unwrap().len() <= context.config.single_line_if_else_max_width {
 852             return trial;
 853         }
 854     }
 855
 856     let if_block_string = try_opt!(if_block.rewrite(context, width, offset));
 857
 858     let between_if_cond = mk_sp(context.codemap.span_after(span, "if"),
 859                                 pat.map_or(cond.span.lo,
 860                                            |_| context.codemap.span_before(span, "let")));
 861
 862     let between_if_cond_comment = extract_comment(between_if_cond, context, offset, width);
 863
 864     let after_cond_comment = extract_comment(mk_sp(cond.span.hi, if_block.span.lo),
 865                                              context,
 866                                              offset,
 867                                              width);
 868
 869     let alt_block_sep = String::from("\n") + &context.block_indent.to_string(context.config);
 870     let after_sep = match context.config.else_if_brace_style {
 871         ElseIfBraceStyle::AlwaysNextLine => alt_block_sep.as_str(),
 872         _ => " ",
 873     };
 874     let mut result = format!("if{}{}{}{}",
 875                              between_if_cond_comment.as_ref().map_or(" ", |str| &**str),
 876                              pat_expr_string,
 877                              after_cond_comment.as_ref().map_or(after_sep, |str| &**str),
 878                              if_block_string);
 879
 880     if let Some(else_block) = else_block_opt {
 881         let mut last_in_chain = false;
 882         let rewrite = match else_block.node {
 883             // If the else expression is another if-else expression, prevent it
 884             // from being formatted on a single line.
 885             // Note how we're passing the original width and offset, as the
 886             // cost of "else" should not cascade.
 887             ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
 888                 rewrite_if_else(context,
 889                                 cond,
 890                                 expr_type,
 891                                 if_block,
 892                                 next_else_block.as_ref().map(|e| &**e),
 893                                 mk_sp(else_block.span.lo, span.hi),
 894                                 Some(pat),
 895                                 width,
 896                                 offset,
 897                                 false)
 898             }
 899             ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
 900                 rewrite_if_else(context,
 901                                 cond,
 902                                 expr_type,
 903                                 if_block,
 904                                 next_else_block.as_ref().map(|e| &**e),
 905                                 mk_sp(else_block.span.lo, span.hi),
 906                                 None,
 907                                 width,
 908                                 offset,
 909                                 false)
 910             }
 911             _ => {
 912                 last_in_chain = true;
 913                 else_block.rewrite(context, width, offset)
 914             }
 915         };
 916
 917         let between_if_else_block =
 918             mk_sp(if_block.span.hi,
 919                   context.codemap.span_before(mk_sp(if_block.span.hi, else_block.span.lo), "else"));
 920         let between_if_else_block_comment =
 921             extract_comment(between_if_else_block, context, offset, width);
 922
 923         let after_else = mk_sp(context.codemap
 924                                    .span_after(mk_sp(if_block.span.hi, else_block.span.lo),
 925                                                "else"),
 926                                else_block.span.lo);
 927         let after_else_comment = extract_comment(after_else, context, offset, width);
 928
 929         let between_sep = match context.config.else_if_brace_style {
 930             ElseIfBraceStyle::AlwaysNextLine |
 931             ElseIfBraceStyle::ClosingNextLine => alt_block_sep.as_str(),
 932             ElseIfBraceStyle::AlwaysSameLine => " ",
 933         };
 934         let after_sep = match context.config.else_if_brace_style {
 935             ElseIfBraceStyle::AlwaysNextLine if last_in_chain => alt_block_sep.as_str(),
 936             _ => " ",
 937         };
 938         try_opt!(write!(&mut result,
 939                         "{}else{}",
 940                         between_if_else_block_comment.as_ref()
 941                             .map_or(between_sep, |str| &**str),
 942                         after_else_comment.as_ref().map_or(after_sep, |str| &**str))
 943             .ok());
 944         result.push_str(&try_opt!(rewrite));
 945     }
 946
 947     Some(result)
 948 }
 949
 950 fn single_line_if_else(context: &RewriteContext,
 951                        pat_expr_str: &str,
 952                        if_node: &ast::Block,
 953                        else_block_opt: Option<&ast::Expr>,
 954                        width: usize)
 955                        -> Option<String> {
 956     let else_block = try_opt!(else_block_opt);
 957     let fixed_cost = "if  {  } else {  }".len();
 958
 959     if let ast::ExprKind::Block(ref else_node) = else_block.node {
 960         if !is_simple_block(if_node, context.codemap) ||
 961            !is_simple_block(else_node, context.codemap) || pat_expr_str.contains('\n') {
 962             return None;
 963         }
 964
 965         let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 966         let if_expr = &if_node.stmts[0];
 967         let if_str = try_opt!(if_expr.rewrite(context, new_width, Indent::empty()));
 968
 969         let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 970         let else_expr = &else_node.stmts[0];
 971         let else_str = try_opt!(else_expr.rewrite(context, new_width, Indent::empty()));
 972
 973         // FIXME: this check shouldn't be necessary. Rewrites should either fail
 974         // or wrap to a newline when the object does not fit the width.
 975         let fits_line = fixed_cost + pat_expr_str.len() + if_str.len() + else_str.len() <= width;
 976
 977         if fits_line && !if_str.contains('\n') && !else_str.contains('\n') {
 978             return Some(format!("if {} {{ {} }} else {{ {} }}",
 979                                 pat_expr_str,
 980                                 if_str,
 981                                 else_str));
 982         }
 983     }
 984
 985     None
 986 }
 987
 988 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
 989     let snippet = codemap.span_to_snippet(block.span).unwrap();
 990     contains_comment(&snippet)
 991 }
 992
 993 // Checks that a block contains no statements, an expression and no comments.
 994 // FIXME: incorrectly returns false when comment is contained completely within
 995 // the expression.
 996 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 997     block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
 998     !block_contains_comment(block, codemap)
 999 }
1000
1001 /// Checks whether a block contains at most one statement or expression, and no comments.
1002 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1003     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1004 }
1005
1006 /// Checks whether a block contains no statements, expressions, or comments.
1007 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1008     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1009 }
1010
1011 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1012     match stmt.node {
1013         ast::StmtKind::Expr(..) => true,
1014         _ => false,
1015     }
1016 }
1017
1018 fn is_unsafe_block(block: &ast::Block) -> bool {
1019     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1020         true
1021     } else {
1022         false
1023     }
1024 }
1025
1026 // inter-match-arm-comment-rules:
1027 //  - all comments following a match arm before the start of the next arm
1028 //    are about the second arm
1029 fn rewrite_match_arm_comment(context: &RewriteContext,
1030                              missed_str: &str,
1031                              width: usize,
1032                              arm_indent: Indent,
1033                              arm_indent_str: &str)
1034                              -> Option<String> {
1035     // The leading "," is not part of the arm-comment
1036     let missed_str = match missed_str.find_uncommented(",") {
1037         Some(n) => &missed_str[n + 1..],
1038         None => &missed_str[..],
1039     };
1040
1041     let mut result = String::new();
1042     // any text not preceeded by a newline is pushed unmodified to the block
1043     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1044     result.push_str(&missed_str[..first_brk]);
1045     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1046
1047     let first = missed_str.find(|c: char| !c.is_whitespace()).unwrap_or(missed_str.len());
1048     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1049         // Excessive vertical whitespace before comment should be preserved
1050         // TODO handle vertical whitespace better
1051         result.push('\n');
1052     }
1053     let missed_str = missed_str[first..].trim();
1054     if !missed_str.is_empty() {
1055         let comment =
1056             try_opt!(rewrite_comment(&missed_str, false, width, arm_indent, context.config));
1057         result.push('\n');
1058         result.push_str(arm_indent_str);
1059         result.push_str(&comment);
1060     }
1061
1062     Some(result)
1063 }
1064
1065 fn rewrite_match(context: &RewriteContext,
1066                  cond: &ast::Expr,
1067                  arms: &[ast::Arm],
1068                  width: usize,
1069                  offset: Indent,
1070                  span: Span)
1071                  -> Option<String> {
1072     if arms.is_empty() {
1073         return None;
1074     }
1075
1076     // `match `cond` {`
1077     let cond_budget = try_opt!(width.checked_sub(8));
1078     let cond_str = try_opt!(cond.rewrite(context, cond_budget, offset + 6));
1079     let alt_block_sep = String::from("\n") + &context.block_indent.to_string(context.config);
1080     let block_sep = match context.config.control_brace_style {
1081         ControlBraceStyle::AlwaysSameLine => " ",
1082         ControlBraceStyle::AlwaysNextLine => alt_block_sep.as_str(),
1083     };
1084     let mut result = format!("match {}{}{{", cond_str, block_sep);
1085
1086     let nested_context = context.nested_context();
1087     let arm_indent = nested_context.block_indent;
1088     let arm_indent_str = arm_indent.to_string(context.config);
1089
1090     let open_brace_pos = context.codemap
1091         .span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])), "{");
1092
1093     for (i, arm) in arms.iter().enumerate() {
1094         // Make sure we get the stuff between arms.
1095         let missed_str = if i == 0 {
1096             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
1097         } else {
1098             context.snippet(mk_sp(arm_end_pos(&arms[i - 1]), arm_start_pos(arm)))
1099         };
1100         let comment = try_opt!(rewrite_match_arm_comment(context,
1101                                                          &missed_str,
1102                                                          width,
1103                                                          arm_indent,
1104                                                          &arm_indent_str));
1105         result.push_str(&comment);
1106         result.push('\n');
1107         result.push_str(&arm_indent_str);
1108
1109         let arm_str = arm.rewrite(&nested_context,
1110                                   context.config.max_width - arm_indent.width(),
1111                                   arm_indent);
1112         if let Some(ref arm_str) = arm_str {
1113             result.push_str(arm_str);
1114         } else {
1115             // We couldn't format the arm, just reproduce the source.
1116             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
1117             result.push_str(&snippet);
1118             result.push_str(arm_comma(context.config, arm, &arm.body));
1119         }
1120     }
1121     // BytePos(1) = closing match brace.
1122     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]), span.hi - BytePos(1));
1123     let last_comment = context.snippet(last_span);
1124     let comment = try_opt!(rewrite_match_arm_comment(context,
1125                                                      &last_comment,
1126                                                      width,
1127                                                      arm_indent,
1128                                                      &arm_indent_str));
1129     result.push_str(&comment);
1130     result.push('\n');
1131     result.push_str(&context.block_indent.to_string(context.config));
1132     result.push('}');
1133     Some(result)
1134 }
1135
1136 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
1137     let &ast::Arm { ref attrs, ref pats, .. } = arm;
1138     if !attrs.is_empty() {
1139         return attrs[0].span.lo;
1140     }
1141
1142     pats[0].span.lo
1143 }
1144
1145 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
1146     arm.body.span.hi
1147 }
1148
1149 fn arm_comma(config: &Config, arm: &ast::Arm, body: &ast::Expr) -> &'static str {
1150     if !config.match_wildcard_trailing_comma {
1151         if arm.pats.len() == 1 && arm.pats[0].node == ast::PatKind::Wild && arm.guard.is_none() {
1152             return "";
1153         }
1154     }
1155
1156     if config.match_block_trailing_comma {
1157         ","
1158     } else if let ast::ExprKind::Block(ref block) = body.node {
1159         if let ast::BlockCheckMode::Default = block.rules {
1160             ""
1161         } else {
1162             ","
1163         }
1164     } else {
1165         ","
1166     }
1167 }
1168
1169 // Match arms.
1170 impl Rewrite for ast::Arm {
1171     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1172         let &ast::Arm { ref attrs, ref pats, ref guard, ref body } = self;
1173
1174         // FIXME this is all a bit grotty, would be nice to abstract out the
1175         // treatment of attributes.
1176         let attr_str = if !attrs.is_empty() {
1177             // We only use this visitor for the attributes, should we use it for
1178             // more?
1179             let mut attr_visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
1180             attr_visitor.block_indent = context.block_indent;
1181             attr_visitor.last_pos = attrs[0].span.lo;
1182             if attr_visitor.visit_attrs(attrs) {
1183                 // Attributes included a skip instruction.
1184                 return None;
1185             }
1186             attr_visitor.format_missing(pats[0].span.lo);
1187             attr_visitor.buffer.to_string()
1188         } else {
1189             String::new()
1190         };
1191
1192         // Patterns
1193         // 5 = ` => {`
1194         let pat_budget = try_opt!(width.checked_sub(5));
1195         let pat_strs = try_opt!(pats.iter()
1196             .map(|p| p.rewrite(context, pat_budget, offset))
1197             .collect::<Option<Vec<_>>>());
1198
1199         let all_simple = pat_strs.iter().all(|p| pat_is_simple(p));
1200         let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1201         let fmt = ListFormatting {
1202             tactic: if all_simple {
1203                 DefinitiveListTactic::Mixed
1204             } else {
1205                 DefinitiveListTactic::Vertical
1206             },
1207             separator: " |",
1208             trailing_separator: SeparatorTactic::Never,
1209             indent: offset,
1210             width: pat_budget,
1211             ends_with_newline: false,
1212             config: context.config,
1213         };
1214         let pats_str = try_opt!(write_list(items, &fmt));
1215
1216         let budget = if pats_str.contains('\n') {
1217             context.config.max_width - offset.width()
1218         } else {
1219             width
1220         };
1221
1222         let guard_str = try_opt!(rewrite_guard(context,
1223                                                guard,
1224                                                budget,
1225                                                offset,
1226                                                trimmed_last_line_width(&pats_str)));
1227
1228         let pats_str = format!("{}{}", pats_str, guard_str);
1229         // Where the next text can start.
1230         let mut line_start = last_line_width(&pats_str);
1231         if !pats_str.contains('\n') {
1232             line_start += offset.width();
1233         }
1234
1235         let body = match body.node {
1236             ast::ExprKind::Block(ref block) if !is_unsafe_block(block) &&
1237                                                is_simple_block(block, context.codemap) &&
1238                                                context.config.wrap_match_arms => {
1239                 if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1240                     expr
1241                 } else {
1242                     &**body
1243                 }
1244             }
1245             _ => &**body,
1246         };
1247
1248         let comma = arm_comma(&context.config, self, body);
1249         let alt_block_sep = String::from("\n") + &context.block_indent.to_string(context.config);
1250
1251         // Let's try and get the arm body on the same line as the condition.
1252         // 4 = ` => `.len()
1253         if context.config.max_width > line_start + comma.len() + 4 {
1254             let budget = context.config.max_width - line_start - comma.len() - 4;
1255             let offset = Indent::new(offset.block_indent, line_start + 4 - offset.block_indent);
1256             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
1257             let is_block = if let ast::ExprKind::Block(..) = body.node {
1258                 true
1259             } else {
1260                 false
1261             };
1262
1263             let block_sep = match context.config.control_brace_style {
1264                 ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep.as_str(),
1265                 _ => " ",
1266             };
1267             match rewrite {
1268                 Some(ref body_str) if !body_str.contains('\n') || !context.config.wrap_match_arms ||
1269                                       is_block => {
1270                     return Some(format!("{}{} =>{}{}{}",
1271                                         attr_str.trim_left(),
1272                                         pats_str,
1273                                         block_sep,
1274                                         body_str,
1275                                         comma));
1276                 }
1277                 _ => {}
1278             }
1279         }
1280
1281         // FIXME: we're doing a second rewrite of the expr; This may not be
1282         // necessary.
1283         let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
1284         let indent = context.block_indent.block_indent(context.config);
1285         let inner_context = &RewriteContext { block_indent: indent, ..*context };
1286         let next_line_body =
1287             try_opt!(nop_block_collapse(body.rewrite(inner_context, body_budget, indent),
1288                                         body_budget));
1289         let indent_str = offset.block_indent(context.config).to_string(context.config);
1290         let (body_prefix, body_suffix) = if context.config.wrap_match_arms {
1291             if context.config.match_block_trailing_comma {
1292                 ("{", "},")
1293             } else {
1294                 ("{", "}")
1295             }
1296         } else {
1297             ("", "")
1298         };
1299
1300         let block_sep = match context.config.control_brace_style {
1301             ControlBraceStyle::AlwaysNextLine => alt_block_sep + body_prefix + "\n",
1302             ControlBraceStyle::AlwaysSameLine => String::from(" ") + body_prefix + "\n",
1303         };
1304         Some(format!("{}{} =>{}{}{}\n{}{}",
1305                      attr_str.trim_left(),
1306                      pats_str,
1307                      block_sep,
1308                      indent_str,
1309                      next_line_body,
1310                      offset.to_string(context.config),
1311                      body_suffix))
1312     }
1313 }
1314
1315 // A pattern is simple if it is very short or it is short-ish and just a path.
1316 // E.g. `Foo::Bar` is simple, but `Foo(..)` is not.
1317 fn pat_is_simple(pat_str: &str) -> bool {
1318     pat_str.len() <= 16 ||
1319     (pat_str.len() <= 24 && pat_str.chars().all(|c| c.is_alphabetic() || c == ':'))
1320 }
1321
1322 // The `if ...` guard on a match arm.
1323 fn rewrite_guard(context: &RewriteContext,
1324                  guard: &Option<ptr::P<ast::Expr>>,
1325                  width: usize,
1326                  offset: Indent,
1327                  // The amount of space used up on this line for the pattern in
1328                  // the arm (excludes offset).
1329                  pattern_width: usize)
1330                  -> Option<String> {
1331     if let Some(ref guard) = *guard {
1332         // First try to fit the guard string on the same line as the pattern.
1333         // 4 = ` if `, 5 = ` => {`
1334         let overhead = pattern_width + 4 + 5;
1335         if overhead < width {
1336             let cond_str = guard.rewrite(context, width - overhead, offset + pattern_width + 4);
1337             if let Some(cond_str) = cond_str {
1338                 return Some(format!(" if {}", cond_str));
1339             }
1340         }
1341
1342         // Not enough space to put the guard after the pattern, try a newline.
1343         let overhead = offset.block_indent(context.config).width() + 4 + 5;
1344         if overhead < width {
1345             let cond_str = guard.rewrite(context,
1346                                          width - overhead,
1347                                          // 3 == `if `
1348                                          offset.block_indent(context.config) + 3);
1349             if let Some(cond_str) = cond_str {
1350                 return Some(format!("\n{}if {}",
1351                                     offset.block_indent(context.config).to_string(context.config),
1352                                     cond_str));
1353             }
1354         }
1355
1356         None
1357     } else {
1358         Some(String::new())
1359     }
1360 }
1361
1362 fn rewrite_pat_expr(context: &RewriteContext,
1363                     pat: Option<&ast::Pat>,
1364                     expr: &ast::Expr,
1365                     matcher: &str,
1366                     // Connecting piece between pattern and expression,
1367                     // *without* trailing space.
1368                     connector: &str,
1369                     width: usize,
1370                     offset: Indent)
1371                     -> Option<String> {
1372     let pat_offset = offset + matcher.len();
1373     let mut result = match pat {
1374         Some(pat) => {
1375             let pat_budget = try_opt!(width.checked_sub(connector.len() + matcher.len()));
1376             let pat_string = try_opt!(pat.rewrite(context, pat_budget, pat_offset));
1377             format!("{}{}{}", matcher, pat_string, connector)
1378         }
1379         None => String::new(),
1380     };
1381
1382     // Consider only the last line of the pat string.
1383     let extra_offset = extra_offset(&result, offset);
1384
1385     // The expression may (partionally) fit on the current line.
1386     if width > extra_offset + 1 {
1387         let spacer = if pat.is_some() { " " } else { "" };
1388
1389         let expr_rewrite = expr.rewrite(context,
1390                                         try_opt!(width.checked_sub(extra_offset + spacer.len())),
1391                                         offset + extra_offset + spacer.len());
1392
1393         if let Some(expr_string) = expr_rewrite {
1394             let pat_simple =
1395                 pat.and_then(|p| p.rewrite(context, context.config.max_width, Indent::empty()))
1396                     .map(|s| pat_is_simple(&s));
1397
1398             if pat.is_none() || pat_simple.unwrap_or(false) || !expr_string.contains('\n') {
1399                 result.push_str(spacer);
1400                 result.push_str(&expr_string);
1401                 return Some(result);
1402             }
1403         }
1404     }
1405
1406     let nested = context.nested_context();
1407
1408     // The expression won't fit on the current line, jump to next.
1409     result.push('\n');
1410     result.push_str(&nested.block_indent.to_string(context.config));
1411
1412     let expr_rewrite =
1413         expr.rewrite(&nested,
1414                      try_opt!(context.config.max_width.checked_sub(nested.block_indent.width())),
1415                      nested.block_indent);
1416     result.push_str(&try_opt!(expr_rewrite));
1417
1418     Some(result)
1419 }
1420
1421 fn rewrite_string_lit(context: &RewriteContext,
1422                       span: Span,
1423                       width: usize,
1424                       offset: Indent)
1425                       -> String {
1426     let string_lit = context.snippet(span);
1427
1428     if !context.config.format_strings && !context.config.force_format_strings {
1429         return string_lit;
1430     }
1431
1432     if !context.config.force_format_strings &&
1433        !string_requires_rewrite(context, span, &string_lit, width, offset) {
1434         return string_lit;
1435     }
1436
1437     let fmt = StringFormat {
1438         opener: "\"",
1439         closer: "\"",
1440         line_start: " ",
1441         line_end: "\\",
1442         width: width,
1443         offset: offset,
1444         trim_end: false,
1445         config: context.config,
1446     };
1447
1448     // Remove the quote characters.
1449     let str_lit = &string_lit[1..string_lit.len() - 1];
1450
1451     rewrite_string(str_lit, &fmt).unwrap_or_else(|| string_lit.to_owned())
1452 }
1453
1454 fn string_requires_rewrite(context: &RewriteContext,
1455                            span: Span,
1456                            string: &str,
1457                            width: usize,
1458                            offset: Indent)
1459                            -> bool {
1460     if context.codemap.lookup_char_pos(span.lo).col.0 != offset.width() {
1461         return true;
1462     }
1463
1464     for (i, line) in string.lines().enumerate() {
1465         if i == 0 {
1466             if line.len() > width {
1467                 return true;
1468             }
1469         } else {
1470             if line.len() > width + offset.width() {
1471                 return true;
1472             }
1473         }
1474     }
1475
1476     false
1477 }
1478
1479 pub fn rewrite_call<R>(context: &RewriteContext,
1480                        callee: &R,
1481                        args: &[ptr::P<ast::Expr>],
1482                        span: Span,
1483                        width: usize,
1484                        offset: Indent)
1485                        -> Option<String>
1486     where R: Rewrite
1487 {
1488     let closure = |callee_max_width| {
1489         rewrite_call_inner(context, callee, callee_max_width, args, span, width, offset)
1490     };
1491
1492     // 2 is for parens
1493     let max_width = try_opt!(width.checked_sub(2));
1494     binary_search(1, max_width, closure)
1495 }
1496
1497 fn rewrite_call_inner<R>(context: &RewriteContext,
1498                          callee: &R,
1499                          max_callee_width: usize,
1500                          args: &[ptr::P<ast::Expr>],
1501                          span: Span,
1502                          width: usize,
1503                          offset: Indent)
1504                          -> Result<String, Ordering>
1505     where R: Rewrite
1506 {
1507     let callee = callee.borrow();
1508     // FIXME using byte lens instead of char lens (and probably all over the
1509     // place too)
1510     let callee_str = match callee.rewrite(context, max_callee_width, offset) {
1511         Some(string) => {
1512             if !string.contains('\n') && string.len() > max_callee_width {
1513                 panic!("{:?} {}", string, max_callee_width);
1514             } else {
1515                 string
1516             }
1517         }
1518         None => return Err(Ordering::Greater),
1519     };
1520
1521     let span_lo = context.codemap.span_after(span, "(");
1522     let span = mk_sp(span_lo, span.hi);
1523
1524     let extra_offset = extra_offset(&callee_str, offset);
1525     // 2 is for parens.
1526     let remaining_width = match width.checked_sub(extra_offset + 2) {
1527         Some(str) => str,
1528         None => return Err(Ordering::Greater),
1529     };
1530     let offset = offset + extra_offset + 1;
1531     let arg_count = args.len();
1532     let block_indent = if arg_count == 1 {
1533         context.block_indent
1534     } else {
1535         offset
1536     };
1537     let inner_context = &RewriteContext { block_indent: block_indent, ..*context };
1538
1539     let items = itemize_list(context.codemap,
1540                              args.iter(),
1541                              ")",
1542                              |item| item.span.lo,
1543                              |item| item.span.hi,
1544                              |item| item.rewrite(inner_context, remaining_width, offset),
1545                              span.lo,
1546                              span.hi);
1547     let mut item_vec: Vec<_> = items.collect();
1548
1549     // Try letting the last argument overflow to the next line with block
1550     // indentation. If its first line fits on one line with the other arguments,
1551     // we format the function arguments horizontally.
1552     let overflow_last = match args.last().map(|x| &x.node) {
1553         Some(&ast::ExprKind::Closure(..)) |
1554         Some(&ast::ExprKind::Block(..)) if arg_count > 1 => true,
1555         _ => false,
1556     } && context.config.chains_overflow_last;
1557
1558     let mut orig_last = None;
1559     let mut placeholder = None;
1560
1561     // Replace the last item with its first line to see if it fits with
1562     // first arguments.
1563     if overflow_last {
1564         let inner_context = &RewriteContext { block_indent: context.block_indent, ..*context };
1565         let rewrite = args.last().unwrap().rewrite(inner_context, remaining_width, offset);
1566
1567         if let Some(rewrite) = rewrite {
1568             let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
1569             placeholder = Some(rewrite);
1570
1571             swap(&mut item_vec[arg_count - 1].item, &mut orig_last);
1572             item_vec[arg_count - 1].item = rewrite_first_line;
1573         }
1574     }
1575
1576     let tactic = definitive_tactic(&item_vec,
1577                                    ListTactic::LimitedHorizontalVertical(context.config
1578                                        .fn_call_width),
1579                                    remaining_width);
1580
1581     // Replace the stub with the full overflowing last argument if the rewrite
1582     // succeeded and its first line fits with the other arguments.
1583     match (overflow_last, tactic, placeholder) {
1584         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
1585             item_vec[arg_count - 1].item = placeholder;
1586         }
1587         (true, _, _) => {
1588             item_vec[arg_count - 1].item = orig_last;
1589         }
1590         (false, _, _) => {}
1591     }
1592
1593     let fmt = ListFormatting {
1594         tactic: tactic,
1595         separator: ",",
1596         trailing_separator: SeparatorTactic::Never,
1597         indent: offset,
1598         width: width,
1599         ends_with_newline: false,
1600         config: context.config,
1601     };
1602
1603     let list_str = match write_list(&item_vec, &fmt) {
1604         Some(str) => str,
1605         None => return Err(Ordering::Less),
1606     };
1607
1608     Ok(if context.config.spaces_within_parens && list_str.len() > 0 {
1609         format!("{}( {} )", callee_str, list_str)
1610     } else {
1611         format!("{}({})", callee_str, list_str)
1612     })
1613 }
1614
1615 fn rewrite_paren(context: &RewriteContext,
1616                  subexpr: &ast::Expr,
1617                  width: usize,
1618                  offset: Indent)
1619                  -> Option<String> {
1620     debug!("rewrite_paren, width: {}, offset: {:?}", width, offset);
1621     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1622     // paren on the same line as the subexpr.
1623     let subexpr_str = subexpr.rewrite(context, try_opt!(width.checked_sub(2)), offset + 1);
1624     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1625
1626     subexpr_str.map(|s| if context.config.spaces_within_parens && s.len() > 0 {
1627         format!("( {} )", s)
1628     } else {
1629         format!("({})", s)
1630     })
1631 }
1632
1633 fn rewrite_index(expr: &ast::Expr,
1634                  index: &ast::Expr,
1635                  context: &RewriteContext,
1636                  width: usize,
1637                  offset: Indent)
1638                  -> Option<String> {
1639     let expr_str = try_opt!(expr.rewrite(context, width, offset));
1640
1641     let (lbr, rbr) = if context.config.spaces_within_square_brackets {
1642         ("[ ", " ]")
1643     } else {
1644         ("[", "]")
1645     };
1646
1647     let budget = width.checked_sub(expr_str.len() + lbr.len() + rbr.len()).unwrap_or(0);
1648     let index_str = index.rewrite(context, budget, offset);
1649     if let Some(index_str) = index_str {
1650         return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
1651     }
1652
1653     let indent = offset.block_indent(&context.config);
1654     let indent = indent.to_string(&context.config);
1655     // FIXME this is not right, since we don't take into account that width
1656     // might be reduced from max_width by something on the right.
1657     let budget =
1658         try_opt!(context.config.max_width.checked_sub(indent.len() + lbr.len() + rbr.len()));
1659     let index_str = try_opt!(index.rewrite(context, budget, offset));
1660     Some(format!("{}\n{}{}{}{}", expr_str, indent, lbr, index_str, rbr))
1661 }
1662
1663 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1664                           path: &ast::Path,
1665                           fields: &'a [ast::Field],
1666                           base: Option<&'a ast::Expr>,
1667                           span: Span,
1668                           width: usize,
1669                           offset: Indent)
1670                           -> Option<String> {
1671     debug!("rewrite_struct_lit: width {}, offset {:?}", width, offset);
1672
1673     enum StructLitField<'a> {
1674         Regular(&'a ast::Field),
1675         Base(&'a ast::Expr),
1676     }
1677
1678     // 2 = " {".len()
1679     let path_budget = try_opt!(width.checked_sub(2));
1680     let path_str = try_opt!(rewrite_path(context, true, None, path, path_budget, offset));
1681
1682     // Foo { a: Foo } - indent is +3, width is -5.
1683     let h_budget = width.checked_sub(path_str.len() + 5).unwrap_or(0);
1684     // The 1 taken from the v_budget is for the comma.
1685     let (indent, v_budget) = match context.config.struct_lit_style {
1686         StructLitStyle::Visual => (offset + path_str.len() + 3, h_budget),
1687         StructLitStyle::Block => {
1688             // If we are all on one line, then we'll ignore the indent, and we
1689             // have a smaller budget.
1690             let indent = context.block_indent.block_indent(context.config);
1691             let v_budget = context.config.max_width.checked_sub(indent.width()).unwrap_or(0);
1692             (indent, v_budget)
1693         }
1694     };
1695
1696     let field_iter = fields.into_iter()
1697         .map(StructLitField::Regular)
1698         .chain(base.into_iter().map(StructLitField::Base));
1699
1700     let inner_context = &RewriteContext { block_indent: indent, ..*context };
1701
1702     let items = itemize_list(context.codemap,
1703                              field_iter,
1704                              "}",
1705                              |item| match *item {
1706                                  StructLitField::Regular(field) => field.span.lo,
1707                                  StructLitField::Base(expr) => {
1708                                      let last_field_hi = fields.last()
1709                                          .map_or(span.lo, |field| field.span.hi);
1710                                      let snippet =
1711                                          context.snippet(mk_sp(last_field_hi, expr.span.lo));
1712                                      let pos = snippet.find_uncommented("..").unwrap();
1713                                      last_field_hi + BytePos(pos as u32)
1714                                  }
1715                              },
1716                              |item| match *item {
1717                                  StructLitField::Regular(field) => field.span.hi,
1718                                  StructLitField::Base(expr) => expr.span.hi,
1719                              },
1720                              |item| {
1721         match *item {
1722             StructLitField::Regular(field) => {
1723                 rewrite_field(inner_context,
1724                               field,
1725                               v_budget.checked_sub(1).unwrap_or(0),
1726                               indent)
1727             }
1728             StructLitField::Base(expr) => {
1729                 // 2 = ..
1730                 expr.rewrite(inner_context, try_opt!(v_budget.checked_sub(2)), indent + 2)
1731                     .map(|s| format!("..{}", s))
1732             }
1733         }
1734     },
1735                              context.codemap.span_after(span, "{"),
1736                              span.hi);
1737     let item_vec = items.collect::<Vec<_>>();
1738
1739     let tactic = {
1740         let mut prelim_tactic = match (context.config.struct_lit_style, fields.len()) {
1741             (StructLitStyle::Visual, 1) => ListTactic::HorizontalVertical,
1742             _ => context.config.struct_lit_multiline_style.to_list_tactic(),
1743         };
1744
1745         if prelim_tactic == ListTactic::HorizontalVertical && fields.len() > 1 {
1746             prelim_tactic = ListTactic::LimitedHorizontalVertical(context.config.struct_lit_width);
1747         }
1748
1749         definitive_tactic(&item_vec, prelim_tactic, h_budget)
1750     };
1751
1752     let budget = match tactic {
1753         DefinitiveListTactic::Horizontal => h_budget,
1754         _ => v_budget,
1755     };
1756
1757     let ends_with_newline = context.config.struct_lit_style != StructLitStyle::Visual &&
1758                             tactic == DefinitiveListTactic::Vertical;
1759
1760     let fmt = ListFormatting {
1761         tactic: tactic,
1762         separator: ",",
1763         trailing_separator: if base.is_some() {
1764             SeparatorTactic::Never
1765         } else {
1766             context.config.struct_lit_trailing_comma
1767         },
1768         indent: indent,
1769         width: budget,
1770         ends_with_newline: ends_with_newline,
1771         config: context.config,
1772     };
1773     let fields_str = try_opt!(write_list(&item_vec, &fmt));
1774
1775     if fields_str.is_empty() {
1776         return Some(format!("{} {{}}", path_str));
1777     }
1778
1779     let format_on_newline = || {
1780         let inner_indent = context.block_indent
1781             .block_indent(context.config)
1782             .to_string(context.config);
1783         let outer_indent = context.block_indent.to_string(context.config);
1784         Some(format!("{} {{\n{}{}\n{}}}",
1785                      path_str,
1786                      inner_indent,
1787                      fields_str,
1788                      outer_indent))
1789     };
1790
1791     match (context.config.struct_lit_style, context.config.struct_lit_multiline_style) {
1792         (StructLitStyle::Block, _) if fields_str.contains('\n') || fields_str.len() > h_budget => {
1793             format_on_newline()
1794         }
1795         (StructLitStyle::Block, MultilineStyle::ForceMulti) => format_on_newline(),
1796         _ => Some(format!("{} {{ {} }}", path_str, fields_str)),
1797     }
1798
1799     // FIXME if context.config.struct_lit_style == Visual, but we run out
1800     // of space, we should fall back to BlockIndent.
1801 }
1802
1803 pub fn type_annotation_separator(config: &Config) -> &str {
1804     match (config.space_before_type_annotation, config.space_after_type_annotation_colon) {
1805         (true, true) => " : ",
1806         (true, false) => " :",
1807         (false, true) => ": ",
1808         (false, false) => ":",
1809     }
1810 }
1811
1812 fn rewrite_field(context: &RewriteContext,
1813                  field: &ast::Field,
1814                  width: usize,
1815                  offset: Indent)
1816                  -> Option<String> {
1817     let name = &field.ident.node.to_string();
1818     let separator = type_annotation_separator(context.config);
1819     let overhead = name.len() + separator.len();
1820     let expr = field.expr.rewrite(context,
1821                                   try_opt!(width.checked_sub(overhead)),
1822                                   offset + overhead);
1823
1824     match expr {
1825         Some(e) => Some(format!("{}{}{}", name, separator, e)),
1826         None => {
1827             let expr_offset = offset.block_indent(context.config);
1828             let expr = field.expr.rewrite(context,
1829                                           try_opt!(context.config
1830                                               .max_width
1831                                               .checked_sub(expr_offset.width())),
1832                                           expr_offset);
1833             expr.map(|s| format!("{}:\n{}{}", name, expr_offset.to_string(&context.config), s))
1834         }
1835     }
1836 }
1837
1838 pub fn rewrite_tuple<'a, I>(context: &RewriteContext,
1839                             mut items: I,
1840                             span: Span,
1841                             width: usize,
1842                             offset: Indent)
1843                             -> Option<String>
1844     where I: ExactSizeIterator,
1845           <I as Iterator>::Item: Deref,
1846           <I::Item as Deref>::Target: Rewrite + Spanned + 'a
1847 {
1848     let indent = offset + 1;
1849     let aligned = RewriteContext { block_indent: indent, ..context.clone() };
1850
1851     // In case of length 1, need a trailing comma
1852     if items.len() == 1 {
1853         // 3 = "(" + ",)"
1854         let budget = try_opt!(width.checked_sub(3));
1855         return items.next()
1856             .unwrap()
1857             .rewrite(&aligned, budget, indent)
1858             .map(|s| if context.config.spaces_within_parens {
1859                 format!("( {}, )", s)
1860             } else {
1861                 format!("({},)", s)
1862             });
1863     }
1864
1865     let list_lo = context.codemap.span_after(span, "(");
1866     let budget = try_opt!(width.checked_sub(2));
1867     let items = itemize_list(context.codemap,
1868                              items,
1869                              ")",
1870                              |item| item.span().lo,
1871                              |item| item.span().hi,
1872                              |item| item.rewrite(&aligned, budget, indent),
1873                              list_lo,
1874                              span.hi - BytePos(1));
1875     let list_str = try_opt!(format_item_list(items, budget, indent, context.config));
1876
1877     if context.config.spaces_within_parens && list_str.len() > 0 {
1878         Some(format!("( {} )", list_str))
1879     } else {
1880         Some(format!("({})", list_str))
1881     }
1882 }
1883
1884 pub fn rewrite_unary_prefix<R: Rewrite>(context: &RewriteContext,
1885                                         prefix: &str,
1886                                         rewrite: &R,
1887                                         width: usize,
1888                                         offset: Indent)
1889                                         -> Option<String> {
1890     rewrite.rewrite(context,
1891                  try_opt!(width.checked_sub(prefix.len())),
1892                  offset + prefix.len())
1893         .map(|r| format!("{}{}", prefix, r))
1894 }
1895
1896 // FIXME: this is probably not correct for multi-line Rewrites. we should
1897 // subtract suffix.len() from the last line budget, not the first!
1898 pub fn rewrite_unary_suffix<R: Rewrite>(context: &RewriteContext,
1899                                         suffix: &str,
1900                                         rewrite: &R,
1901                                         width: usize,
1902                                         offset: Indent)
1903                                         -> Option<String> {
1904     rewrite.rewrite(context, try_opt!(width.checked_sub(suffix.len())), offset)
1905         .map(|mut r| {
1906             r.push_str(suffix);
1907             r
1908         })
1909 }
1910
1911 fn rewrite_unary_op(context: &RewriteContext,
1912                     op: &ast::UnOp,
1913                     expr: &ast::Expr,
1914                     width: usize,
1915                     offset: Indent)
1916                     -> Option<String> {
1917     // For some reason, an UnOp is not spanned like BinOp!
1918     let operator_str = match *op {
1919         ast::UnOp::Deref => "*",
1920         ast::UnOp::Not => "!",
1921         ast::UnOp::Neg => "-",
1922     };
1923     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1924 }
1925
1926 fn rewrite_assignment(context: &RewriteContext,
1927                       lhs: &ast::Expr,
1928                       rhs: &ast::Expr,
1929                       op: Option<&ast::BinOp>,
1930                       width: usize,
1931                       offset: Indent)
1932                       -> Option<String> {
1933     let operator_str = match op {
1934         Some(op) => context.snippet(op.span),
1935         None => "=".to_owned(),
1936     };
1937
1938     // 1 = space between lhs and operator.
1939     let max_width = try_opt!(width.checked_sub(operator_str.len() + 1));
1940     let lhs_str = format!("{} {}",
1941                           try_opt!(lhs.rewrite(context, max_width, offset)),
1942                           operator_str);
1943
1944     rewrite_assign_rhs(context, lhs_str, rhs, width, offset)
1945 }
1946
1947 // The left hand side must contain everything up to, and including, the
1948 // assignment operator.
1949 pub fn rewrite_assign_rhs<S: Into<String>>(context: &RewriteContext,
1950                                            lhs: S,
1951                                            ex: &ast::Expr,
1952                                            width: usize,
1953                                            offset: Indent)
1954                                            -> Option<String> {
1955     let mut result = lhs.into();
1956     let last_line_width = last_line_width(&result) -
1957                           if result.contains('\n') {
1958         offset.width()
1959     } else {
1960         0
1961     };
1962     // 1 = space between operator and rhs.
1963     let max_width = try_opt!(width.checked_sub(last_line_width + 1));
1964     let rhs = ex.rewrite(context, max_width, offset + last_line_width + 1);
1965
1966     fn count_line_breaks(src: &str) -> usize {
1967         src.chars().filter(|&x| x == '\n').count()
1968     }
1969
1970     match rhs {
1971         Some(ref new_str) if count_line_breaks(new_str) < 2 => {
1972             result.push(' ');
1973             result.push_str(new_str);
1974         }
1975         _ => {
1976             // Expression did not fit on the same line as the identifier or is
1977             // at least three lines big. Try splitting the line and see
1978             // if that works better.
1979             let new_offset = offset.block_indent(context.config);
1980             let max_width = try_opt!((width + offset.width()).checked_sub(new_offset.width()));
1981             let inner_context = context.nested_context();
1982             let new_rhs = ex.rewrite(&inner_context, max_width, new_offset);
1983
1984             // FIXME: DRY!
1985             match (rhs, new_rhs) {
1986                 (Some(ref orig_rhs), Some(ref replacement_rhs))
1987                     if count_line_breaks(orig_rhs) >
1988                        count_line_breaks(replacement_rhs) + 1 => {
1989                     result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1990                     result.push_str(replacement_rhs);
1991                 }
1992                 (None, Some(ref final_rhs)) => {
1993                     result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1994                     result.push_str(final_rhs);
1995                 }
1996                 (None, None) => return None,
1997                 (Some(ref orig_rhs), _) => {
1998                     result.push(' ');
1999                     result.push_str(orig_rhs);
2000                 }
2001             }
2002         }
2003     }
2004
2005     Some(result)
2006 }
2007
2008 fn rewrite_expr_addrof(context: &RewriteContext,
2009                        mutability: ast::Mutability,
2010                        expr: &ast::Expr,
2011                        width: usize,
2012                        offset: Indent)
2013                        -> Option<String> {
2014     let operator_str = match mutability {
2015         ast::Mutability::Immutable => "&",
2016         ast::Mutability::Mutable => "&mut ",
2017     };
2018     rewrite_unary_prefix(context, operator_str, expr, width, offset)
2019 }