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
  15 use {Indent, Spanned};
  16 use rewrite::{Rewrite, RewriteContext};
  17 use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic,
  18             DefinitiveListTactic, definitive_tactic, ListItem, format_fn_args};
  19 use string::{StringFormat, rewrite_string};
  20 use utils::{span_after, extra_offset, last_line_width, wrap_str, binary_search, first_line_width};
  21 use visitor::FmtVisitor;
  22 use config::{StructLitStyle, MultilineStyle};
  23 use comment::{FindUncommented, rewrite_comment, contains_comment};
  24 use types::rewrite_path;
  25 use items::{span_lo_for_arg, span_hi_for_arg};
  26 use chains::rewrite_chain;
  27 use macros::rewrite_macro;
  28
  29 use syntax::{ast, ptr};
  30 use syntax::codemap::{CodeMap, Span, BytePos, mk_sp};
  31 use syntax::visit::Visitor;
  32
  33 impl Rewrite for ast::Expr {
  34     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  35         match self.node {
  36             ast::Expr_::ExprVec(ref expr_vec) => {
  37                 rewrite_array(expr_vec.iter().map(|e| &**e),
  38                               mk_sp(span_after(self.span, "[", context.codemap), self.span.hi),
  39                               context,
  40                               width,
  41                               offset)
  42             }
  43             ast::Expr_::ExprLit(ref l) => {
  44                 match l.node {
  45                     ast::Lit_::LitStr(_, ast::StrStyle::CookedStr) => {
  46                         rewrite_string_lit(context, l.span, width, offset)
  47                     }
  48                     _ => {
  49                         wrap_str(context.snippet(self.span),
  50                                  context.config.max_width,
  51                                  width,
  52                                  offset)
  53                     }
  54                 }
  55             }
  56             ast::Expr_::ExprCall(ref callee, ref args) => {
  57                 let inner_span = mk_sp(callee.span.hi, self.span.hi);
  58                 rewrite_call(context, &**callee, args, inner_span, width, offset)
  59             }
  60             ast::Expr_::ExprParen(ref subexpr) => {
  61                 rewrite_paren(context, subexpr, width, offset)
  62             }
  63             ast::Expr_::ExprBinary(ref op, ref lhs, ref rhs) => {
  64                 rewrite_binary_op(context, op, lhs, rhs, width, offset)
  65             }
  66             ast::Expr_::ExprUnary(ref op, ref subexpr) => {
  67                 rewrite_unary_op(context, op, subexpr, width, offset)
  68             }
  69             ast::Expr_::ExprStruct(ref path, ref fields, ref base) => {
  70                 rewrite_struct_lit(context,
  71                                    path,
  72                                    fields,
  73                                    base.as_ref().map(|e| &**e),
  74                                    self.span,
  75                                    width,
  76                                    offset)
  77             }
  78             ast::Expr_::ExprTup(ref items) => {
  79                 rewrite_tuple(context, items, self.span, width, offset)
  80             }
  81             ast::Expr_::ExprWhile(ref cond, ref block, label) => {
  82                 Loop::new_while(None, cond, block, label).rewrite(context, width, offset)
  83             }
  84             ast::Expr_::ExprWhileLet(ref pat, ref cond, ref block, label) => {
  85                 Loop::new_while(Some(pat), cond, block, label).rewrite(context, width, offset)
  86             }
  87             ast::Expr_::ExprForLoop(ref pat, ref cond, ref block, label) => {
  88                 Loop::new_for(pat, cond, block, label).rewrite(context, width, offset)
  89             }
  90             ast::Expr_::ExprLoop(ref block, label) => {
  91                 Loop::new_loop(block, label).rewrite(context, width, offset)
  92             }
  93             ast::Expr_::ExprBlock(ref block) => {
  94                 block.rewrite(context, width, offset)
  95             }
  96             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
  97                 rewrite_if_else(context,
  98                                 cond,
  99                                 if_block,
 100                                 else_block.as_ref().map(|e| &**e),
 101                                 None,
 102                                 width,
 103                                 offset,
 104                                 true)
 105             }
 106             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 107                 rewrite_if_else(context,
 108                                 cond,
 109                                 if_block,
 110                                 else_block.as_ref().map(|e| &**e),
 111                                 Some(pat),
 112                                 width,
 113                                 offset,
 114                                 true)
 115             }
 116             ast::Expr_::ExprMatch(ref cond, ref arms) => {
 117                 rewrite_match(context, cond, arms, width, offset, self.span)
 118             }
 119             ast::Expr_::ExprPath(ref qself, ref path) => {
 120                 rewrite_path(context, true, qself.as_ref(), path, width, offset)
 121             }
 122             ast::Expr_::ExprAssign(ref lhs, ref rhs) => {
 123                 rewrite_assignment(context, lhs, rhs, None, width, offset)
 124             }
 125             ast::Expr_::ExprAssignOp(ref op, ref lhs, ref rhs) => {
 126                 rewrite_assignment(context, lhs, rhs, Some(op), width, offset)
 127             }
 128             ast::Expr_::ExprAgain(ref opt_ident) => {
 129                 let id_str = match *opt_ident {
 130                     Some(ident) => format!(" {}", ident.node),
 131                     None => String::new(),
 132                 };
 133                 Some(format!("continue{}", id_str))
 134             }
 135             ast::Expr_::ExprBreak(ref opt_ident) => {
 136                 let id_str = match *opt_ident {
 137                     Some(ident) => format!(" {}", ident.node),
 138                     None => String::new(),
 139                 };
 140                 Some(format!("break{}", id_str))
 141             }
 142             ast::Expr_::ExprClosure(capture, ref fn_decl, ref body) => {
 143                 rewrite_closure(capture, fn_decl, body, self.span, context, width, offset)
 144             }
 145             ast::Expr_::ExprField(..) |
 146             ast::Expr_::ExprTupField(..) |
 147             ast::Expr_::ExprMethodCall(..) => {
 148                 rewrite_chain(self, context, width, offset)
 149             }
 150             ast::Expr_::ExprMac(ref mac) => {
 151                 // Failure to rewrite a marco should not imply failure to
 152                 // rewrite the expression.
 153                 rewrite_macro(mac, context, width, offset).or_else(|| {
 154                     wrap_str(context.snippet(self.span),
 155                              context.config.max_width,
 156                              width,
 157                              offset)
 158                 })
 159             }
 160             ast::Expr_::ExprRet(None) => {
 161                 wrap_str("return".to_owned(), context.config.max_width, width, offset)
 162             }
 163             ast::Expr_::ExprRet(Some(ref expr)) => {
 164                 rewrite_unary_prefix(context, "return ", &**expr, width, offset)
 165             }
 166             ast::Expr_::ExprBox(ref expr) => {
 167                 rewrite_unary_prefix(context, "box ", &**expr, width, offset)
 168             }
 169             ast::Expr_::ExprAddrOf(mutability, ref expr) => {
 170                 rewrite_expr_addrof(context, mutability, expr, width, offset)
 171             }
 172             ast::Expr_::ExprCast(ref expr, ref ty) => {
 173                 rewrite_pair(&**expr, &**ty, "", " as ", "", context, width, offset)
 174             }
 175             ast::Expr_::ExprIndex(ref expr, ref index) => {
 176                 rewrite_pair(&**expr, &**index, "", "[", "]", context, width, offset)
 177             }
 178             ast::Expr_::ExprRepeat(ref expr, ref repeats) => {
 179                 rewrite_pair(&**expr, &**repeats, "[", "; ", "]", context, width, offset)
 180             }
 181             ast::Expr_::ExprRange(Some(ref lhs), Some(ref rhs)) => {
 182                 rewrite_pair(&**lhs, &**rhs, "", "..", "", context, width, offset)
 183             }
 184             ast::Expr_::ExprRange(None, Some(ref rhs)) => {
 185                 rewrite_unary_prefix(context, "..", &**rhs, width, offset)
 186             }
 187             ast::Expr_::ExprRange(Some(ref lhs), None) => {
 188                 Some(format!("{}..",
 189                              try_opt!(lhs.rewrite(context,
 190                                                   try_opt!(width.checked_sub(2)),
 191                                                   offset))))
 192             }
 193             ast::Expr_::ExprRange(None, None) => {
 194                 if width >= 2 {
 195                     Some("..".into())
 196                 } else {
 197                     None
 198                 }
 199             }
 200             // We do not format these expressions yet, but they should still
 201             // satisfy our width restrictions.
 202             ast::Expr_::ExprInPlace(..) |
 203             ast::Expr_::ExprInlineAsm(..) => {
 204                 wrap_str(context.snippet(self.span),
 205                          context.config.max_width,
 206                          width,
 207                          offset)
 208             }
 209         }
 210     }
 211 }
 212
 213 pub fn rewrite_pair<LHS, RHS>(lhs: &LHS,
 214                               rhs: &RHS,
 215                               prefix: &str,
 216                               infix: &str,
 217                               suffix: &str,
 218                               context: &RewriteContext,
 219                               width: usize,
 220                               offset: Indent)
 221                               -> Option<String>
 222     where LHS: Rewrite,
 223           RHS: Rewrite
 224 {
 225     let max_width = try_opt!(width.checked_sub(prefix.len() + infix.len() + suffix.len()));
 226
 227     binary_search(1, max_width, |lhs_budget| {
 228         let lhs_offset = offset + prefix.len();
 229         let lhs_str = match lhs.rewrite(context, lhs_budget, lhs_offset) {
 230             Some(result) => result,
 231             None => return Err(Ordering::Greater),
 232         };
 233
 234         let last_line_width = last_line_width(&lhs_str);
 235         let rhs_budget = match max_width.checked_sub(last_line_width) {
 236             Some(b) => b,
 237             None => return Err(Ordering::Less),
 238         };
 239         let rhs_indent = offset + last_line_width + prefix.len() + infix.len();
 240
 241         let rhs_str = match rhs.rewrite(context, rhs_budget, rhs_indent) {
 242             Some(result) => result,
 243             None => return Err(Ordering::Less),
 244         };
 245
 246         Ok(format!("{}{}{}{}{}", prefix, lhs_str, infix, rhs_str, suffix))
 247     })
 248 }
 249
 250 pub fn rewrite_array<'a, I>(expr_iter: I,
 251                             span: Span,
 252                             context: &RewriteContext,
 253                             width: usize,
 254                             offset: Indent)
 255                             -> Option<String>
 256     where I: Iterator<Item = &'a ast::Expr>
 257 {
 258     // 2 for brackets;
 259     let offset = offset + 1;
 260     let inner_context = &RewriteContext { block_indent: offset, ..*context };
 261     let max_item_width = try_opt!(width.checked_sub(2));
 262     let items = itemize_list(context.codemap,
 263                              expr_iter,
 264                              "]",
 265                              |item| item.span.lo,
 266                              |item| item.span.hi,
 267                              // 1 = [
 268                              |item| item.rewrite(&inner_context, max_item_width, offset),
 269                              span.lo,
 270                              span.hi)
 271                     .collect::<Vec<_>>();
 272
 273     let has_long_item = try_opt!(items.iter()
 274                                       .map(|li| li.item.as_ref().map(|s| s.len() > 10))
 275                                       .fold(Some(false),
 276                                             |acc, x| acc.and_then(|y| x.map(|x| x || y))));
 277
 278     let tactic = if has_long_item || items.iter().any(ListItem::is_multiline) {
 279         definitive_tactic(&items, ListTactic::HorizontalVertical, max_item_width)
 280     } else {
 281         DefinitiveListTactic::Mixed
 282     };
 283
 284     let fmt = ListFormatting {
 285         tactic: tactic,
 286         separator: ",",
 287         trailing_separator: SeparatorTactic::Never,
 288         indent: offset,
 289         width: max_item_width,
 290         ends_with_newline: false,
 291         config: context.config,
 292     };
 293     let list_str = try_opt!(write_list(&items, &fmt));
 294
 295     Some(format!("[{}]", list_str))
 296 }
 297
 298 // This functions is pretty messy because of the wrapping and unwrapping of
 299 // expressions into and from blocks. See rust issue #27872.
 300 fn rewrite_closure(capture: ast::CaptureClause,
 301                    fn_decl: &ast::FnDecl,
 302                    body: &ast::Block,
 303                    span: Span,
 304                    context: &RewriteContext,
 305                    width: usize,
 306                    offset: Indent)
 307                    -> Option<String> {
 308     let mover = if capture == ast::CaptureClause::CaptureByValue {
 309         "move "
 310     } else {
 311         ""
 312     };
 313     let offset = offset + mover.len();
 314
 315     // 4 = "|| {".len(), which is overconservative when the closure consists of
 316     // a single expression.
 317     let budget = try_opt!(width.checked_sub(4 + mover.len()));
 318     // 1 = |
 319     let argument_offset = offset + 1;
 320     let ret_str = try_opt!(fn_decl.output.rewrite(context, budget, argument_offset));
 321     // 1 = space between arguments and return type.
 322     let horizontal_budget = budget.checked_sub(ret_str.len() + 1).unwrap_or(0);
 323
 324     let arg_items = itemize_list(context.codemap,
 325                                  fn_decl.inputs.iter(),
 326                                  "|",
 327                                  |arg| span_lo_for_arg(arg),
 328                                  |arg| span_hi_for_arg(arg),
 329                                  |arg| arg.rewrite(context, budget, argument_offset),
 330                                  span_after(span, "|", context.codemap),
 331                                  body.span.lo);
 332     let item_vec = arg_items.collect::<Vec<_>>();
 333     let tactic = definitive_tactic(&item_vec, ListTactic::HorizontalVertical, horizontal_budget);
 334     let budget = match tactic {
 335         DefinitiveListTactic::Horizontal => horizontal_budget,
 336         _ => budget,
 337     };
 338
 339     let fmt = ListFormatting {
 340         tactic: tactic,
 341         separator: ",",
 342         trailing_separator: SeparatorTactic::Never,
 343         indent: argument_offset,
 344         width: budget,
 345         ends_with_newline: false,
 346         config: context.config,
 347     };
 348     let list_str = try_opt!(write_list(&item_vec, &fmt));
 349     let mut prefix = format!("{}|{}|", mover, list_str);
 350
 351     if !ret_str.is_empty() {
 352         if prefix.contains('\n') {
 353             prefix.push('\n');
 354             prefix.push_str(&argument_offset.to_string(context.config));
 355         } else {
 356             prefix.push(' ');
 357         }
 358         prefix.push_str(&ret_str);
 359     }
 360
 361     // Try to format closure body as a single line expression without braces.
 362     if is_simple_block(body, context.codemap) && !prefix.contains('\n') {
 363         let (spacer, closer) = if ret_str.is_empty() {
 364             (" ", "")
 365         } else {
 366             (" { ", " }")
 367         };
 368         let expr = body.expr.as_ref().unwrap();
 369         // All closure bodies are blocks in the eyes of the AST, but we may not
 370         // want to unwrap them when they only contain a single expression.
 371         let inner_expr = match expr.node {
 372             ast::Expr_::ExprBlock(ref inner) if inner.stmts.is_empty() && inner.expr.is_some() &&
 373                                                 inner.rules ==
 374                                                 ast::BlockCheckMode::DefaultBlock => {
 375                 inner.expr.as_ref().unwrap()
 376             }
 377             _ => expr,
 378         };
 379         let extra_offset = extra_offset(&prefix, offset) + spacer.len();
 380         let budget = try_opt!(width.checked_sub(extra_offset + closer.len()));
 381         let rewrite = inner_expr.rewrite(context, budget, offset + extra_offset);
 382
 383         // Checks if rewrite succeeded and fits on a single line.
 384         let accept_rewrite = rewrite.as_ref().map(|result| !result.contains('\n')).unwrap_or(false);
 385
 386         if accept_rewrite {
 387             return Some(format!("{}{}{}{}", prefix, spacer, rewrite.unwrap(), closer));
 388         }
 389     }
 390
 391     // We couldn't format the closure body as a single line expression; fall
 392     // back to block formatting.
 393     let body_rewrite = body.expr
 394                            .as_ref()
 395                            .and_then(|body_expr| {
 396                                if let ast::Expr_::ExprBlock(ref inner) = body_expr.node {
 397                                    Some(inner.rewrite(&context, 2, Indent::empty()))
 398                                } else {
 399                                    None
 400                                }
 401                            })
 402                            .unwrap_or_else(|| body.rewrite(&context, 2, Indent::empty()));
 403
 404     Some(format!("{} {}", prefix, try_opt!(body_rewrite)))
 405 }
 406
 407 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 408     block_str.map(|block_str| {
 409         if block_str.starts_with("{") && budget >= 2 &&
 410            (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2) {
 411             "{}".to_owned()
 412         } else {
 413             block_str.to_owned()
 414         }
 415     })
 416 }
 417
 418 impl Rewrite for ast::Block {
 419     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 420         let user_str = context.snippet(self.span);
 421         if user_str == "{}" && width >= 2 {
 422             return Some(user_str);
 423         }
 424
 425         let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config, None);
 426         visitor.block_indent = context.block_indent;
 427
 428         let prefix = match self.rules {
 429             ast::BlockCheckMode::UnsafeBlock(..) => {
 430                 let snippet = context.snippet(self.span);
 431                 let open_pos = try_opt!(snippet.find_uncommented("{"));
 432                 visitor.last_pos = self.span.lo + BytePos(open_pos as u32);
 433
 434                 // Extract comment between unsafe and block start.
 435                 let trimmed = &snippet[6..open_pos].trim();
 436
 437                 let prefix = if !trimmed.is_empty() {
 438                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 439                     let budget = try_opt!(width.checked_sub(9));
 440                     format!("unsafe {} ",
 441                             try_opt!(rewrite_comment(trimmed,
 442                                                      true,
 443                                                      budget,
 444                                                      offset + 7,
 445                                                      context.config)))
 446                 } else {
 447                     "unsafe ".to_owned()
 448                 };
 449
 450                 if is_simple_block(self, context.codemap) && prefix.len() < width {
 451                     let body = self.expr
 452                                    .as_ref()
 453                                    .unwrap()
 454                                    .rewrite(context, width - prefix.len(), offset);
 455                     if let Some(ref expr_str) = body {
 456                         let result = format!("{}{{ {} }}", prefix, expr_str);
 457                         if result.len() <= width && !result.contains('\n') {
 458                             return Some(result);
 459                         }
 460                     }
 461                 }
 462
 463                 prefix
 464             }
 465             ast::BlockCheckMode::DefaultBlock => {
 466                 visitor.last_pos = self.span.lo;
 467
 468                 String::new()
 469             }
 470         };
 471
 472         visitor.visit_block(self);
 473
 474         Some(format!("{}{}", prefix, visitor.buffer))
 475     }
 476 }
 477
 478 // Abstraction over for, while and loop expressions
 479 struct Loop<'a> {
 480     cond: Option<&'a ast::Expr>,
 481     block: &'a ast::Block,
 482     label: Option<ast::Ident>,
 483     pat: Option<&'a ast::Pat>,
 484     keyword: &'a str,
 485     matcher: &'a str,
 486     connector: &'a str,
 487 }
 488
 489 impl<'a> Loop<'a> {
 490     fn new_loop(block: &'a ast::Block, label: Option<ast::Ident>) -> Loop<'a> {
 491         Loop {
 492             cond: None,
 493             block: block,
 494             label: label,
 495             pat: None,
 496             keyword: "loop",
 497             matcher: "",
 498             connector: "",
 499         }
 500     }
 501
 502     fn new_while(pat: Option<&'a ast::Pat>,
 503                  cond: &'a ast::Expr,
 504                  block: &'a ast::Block,
 505                  label: Option<ast::Ident>)
 506                  -> Loop<'a> {
 507         Loop {
 508             cond: Some(cond),
 509             block: block,
 510             label: label,
 511             pat: pat,
 512             keyword: "while ",
 513             matcher: match pat {
 514                 Some(..) => "let ",
 515                 None => "",
 516             },
 517             connector: " =",
 518         }
 519     }
 520
 521     fn new_for(pat: &'a ast::Pat,
 522                cond: &'a ast::Expr,
 523                block: &'a ast::Block,
 524                label: Option<ast::Ident>)
 525                -> Loop<'a> {
 526         Loop {
 527             cond: Some(cond),
 528             block: block,
 529             label: label,
 530             pat: Some(pat),
 531             keyword: "for ",
 532             matcher: "",
 533             connector: " in",
 534         }
 535     }
 536 }
 537
 538 impl<'a> Rewrite for Loop<'a> {
 539     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 540         let label_string = rewrite_label(self.label);
 541         // 2 = " {".len()
 542         let inner_width = try_opt!(width.checked_sub(self.keyword.len() + 2 + label_string.len()));
 543         let inner_offset = offset + self.keyword.len() + label_string.len();
 544
 545         let pat_expr_string = match self.cond {
 546             Some(cond) => try_opt!(rewrite_pat_expr(context,
 547                                                     self.pat,
 548                                                     cond,
 549                                                     self.matcher,
 550                                                     self.connector,
 551                                                     inner_width,
 552                                                     inner_offset)),
 553             None => String::new(),
 554         };
 555
 556         // FIXME: this drops any comment between "loop" and the block.
 557         self.block
 558             .rewrite(context, width, offset)
 559             .map(|result| {
 560                 format!("{}{}{} {}",
 561                         label_string,
 562                         self.keyword,
 563                         pat_expr_string,
 564                         result)
 565             })
 566     }
 567 }
 568
 569 fn rewrite_label(label: Option<ast::Ident>) -> String {
 570     match label {
 571         Some(ident) => format!("{}: ", ident),
 572         None => "".to_owned(),
 573     }
 574 }
 575
 576 // Rewrites if-else blocks. If let Some(_) = pat, the expression is
 577 // treated as an if-let-else expression.
 578 fn rewrite_if_else(context: &RewriteContext,
 579                    cond: &ast::Expr,
 580                    if_block: &ast::Block,
 581                    else_block_opt: Option<&ast::Expr>,
 582                    pat: Option<&ast::Pat>,
 583                    width: usize,
 584                    offset: Indent,
 585                    allow_single_line: bool)
 586                    -> Option<String> {
 587     // 3 = "if ", 2 = " {"
 588     let pat_expr_string = try_opt!(rewrite_pat_expr(context,
 589                                                     pat,
 590                                                     cond,
 591                                                     "let ",
 592                                                     " =",
 593                                                     try_opt!(width.checked_sub(3 + 2)),
 594                                                     offset + 3));
 595
 596     // Try to format if-else on single line.
 597     if allow_single_line && context.config.single_line_if_else {
 598         let trial = single_line_if_else(context, &pat_expr_string, if_block, else_block_opt, width);
 599
 600         if trial.is_some() {
 601             return trial;
 602         }
 603     }
 604
 605     let if_block_string = try_opt!(if_block.rewrite(context, width, offset));
 606     let mut result = format!("if {} {}", pat_expr_string, if_block_string);
 607
 608     if let Some(else_block) = else_block_opt {
 609         let rewrite = match else_block.node {
 610             // If the else expression is another if-else expression, prevent it
 611             // from being formatted on a single line.
 612             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 613                 rewrite_if_else(context,
 614                                 cond,
 615                                 if_block,
 616                                 else_block.as_ref().map(|e| &**e),
 617                                 Some(pat),
 618                                 width,
 619                                 offset,
 620                                 false)
 621             }
 622             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
 623                 rewrite_if_else(context,
 624                                 cond,
 625                                 if_block,
 626                                 else_block.as_ref().map(|e| &**e),
 627                                 None,
 628                                 width,
 629                                 offset,
 630                                 false)
 631             }
 632             _ => else_block.rewrite(context, width, offset),
 633         };
 634
 635         result.push_str(" else ");
 636         result.push_str(&&try_opt!(rewrite));
 637     }
 638
 639     Some(result)
 640 }
 641
 642 fn single_line_if_else(context: &RewriteContext,
 643                        pat_expr_str: &str,
 644                        if_node: &ast::Block,
 645                        else_block_opt: Option<&ast::Expr>,
 646                        width: usize)
 647                        -> Option<String> {
 648     let else_block = try_opt!(else_block_opt);
 649     let fixed_cost = "if  {  } else {  }".len();
 650
 651     if let ast::ExprBlock(ref else_node) = else_block.node {
 652         if !is_simple_block(if_node, context.codemap) ||
 653            !is_simple_block(else_node, context.codemap) || pat_expr_str.contains('\n') {
 654             return None;
 655         }
 656
 657         let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 658         let if_expr = if_node.expr.as_ref().unwrap();
 659         let if_str = try_opt!(if_expr.rewrite(context, new_width, Indent::empty()));
 660
 661         let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 662         let else_expr = else_node.expr.as_ref().unwrap();
 663         let else_str = try_opt!(else_expr.rewrite(context, new_width, Indent::empty()));
 664
 665         // FIXME: this check shouldn't be necessary. Rewrites should either fail
 666         // or wrap to a newline when the object does not fit the width.
 667         let fits_line = fixed_cost + pat_expr_str.len() + if_str.len() + else_str.len() <= width;
 668
 669         if fits_line && !if_str.contains('\n') && !else_str.contains('\n') {
 670             return Some(format!("if {} {{ {} }} else {{ {} }}",
 671                                 pat_expr_str,
 672                                 if_str,
 673                                 else_str));
 674         }
 675     }
 676
 677     None
 678 }
 679
 680 // Checks that a block contains no statements, an expression and no comments.
 681 fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 682     if !block.stmts.is_empty() || block.expr.is_none() {
 683         return false;
 684     }
 685
 686     let snippet = codemap.span_to_snippet(block.span).unwrap();
 687
 688     !contains_comment(&snippet)
 689 }
 690
 691 // inter-match-arm-comment-rules:
 692 //  - all comments following a match arm before the start of the next arm
 693 //    are about the second arm
 694 fn rewrite_match_arm_comment(context: &RewriteContext,
 695                              missed_str: &str,
 696                              width: usize,
 697                              arm_indent: Indent,
 698                              arm_indent_str: &str)
 699                              -> Option<String> {
 700     // The leading "," is not part of the arm-comment
 701     let missed_str = match missed_str.find_uncommented(",") {
 702         Some(n) => &missed_str[n + 1..],
 703         None => &missed_str[..],
 704     };
 705
 706     let mut result = String::new();
 707     // any text not preceeded by a newline is pushed unmodified to the block
 708     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
 709     result.push_str(&missed_str[..first_brk]);
 710     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
 711
 712     let first = missed_str.find(|c: char| !c.is_whitespace()).unwrap_or(missed_str.len());
 713     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
 714         // Excessive vertical whitespace before comment should be preserved
 715         // TODO handle vertical whitespace better
 716         result.push('\n');
 717     }
 718     let missed_str = missed_str[first..].trim();
 719     if !missed_str.is_empty() {
 720         let comment = try_opt!(rewrite_comment(&missed_str,
 721                                                false,
 722                                                width,
 723                                                arm_indent,
 724                                                context.config));
 725         result.push('\n');
 726         result.push_str(arm_indent_str);
 727         result.push_str(&comment);
 728     }
 729
 730     Some(result)
 731 }
 732
 733 fn rewrite_match(context: &RewriteContext,
 734                  cond: &ast::Expr,
 735                  arms: &[ast::Arm],
 736                  width: usize,
 737                  offset: Indent,
 738                  span: Span)
 739                  -> Option<String> {
 740     if arms.is_empty() {
 741         return None;
 742     }
 743
 744     // `match `cond` {`
 745     let cond_budget = try_opt!(width.checked_sub(8));
 746     let cond_str = try_opt!(cond.rewrite(context, cond_budget, offset + 6));
 747     let mut result = format!("match {} {{", cond_str);
 748
 749     let nested_context = context.nested_context();
 750     let arm_indent = nested_context.block_indent;
 751     let arm_indent_str = arm_indent.to_string(context.config);
 752
 753     let open_brace_pos = span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])),
 754                                     "{",
 755                                     context.codemap);
 756
 757     for (i, arm) in arms.iter().enumerate() {
 758         // Make sure we get the stuff between arms.
 759         let missed_str = if i == 0 {
 760             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
 761         } else {
 762             context.snippet(mk_sp(arm_end_pos(&arms[i - 1]), arm_start_pos(arm)))
 763         };
 764         let comment = try_opt!(rewrite_match_arm_comment(context,
 765                                                          &missed_str,
 766                                                          width,
 767                                                          arm_indent,
 768                                                          &arm_indent_str));
 769         result.push_str(&comment);
 770         result.push('\n');
 771         result.push_str(&arm_indent_str);
 772
 773         let arm_str = arm.rewrite(&nested_context,
 774                                   context.config.max_width - arm_indent.width(),
 775                                   arm_indent);
 776         if let Some(ref arm_str) = arm_str {
 777             result.push_str(arm_str);
 778         } else {
 779             // We couldn't format the arm, just reproduce the source.
 780             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
 781             result.push_str(&snippet);
 782             result.push_str(arm_comma(&arm.body));
 783         }
 784     }
 785     // BytePos(1) = closing match brace.
 786     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]), span.hi - BytePos(1));
 787     let last_comment = context.snippet(last_span);
 788     let comment = try_opt!(rewrite_match_arm_comment(context,
 789                                                      &last_comment,
 790                                                      width,
 791                                                      arm_indent,
 792                                                      &arm_indent_str));
 793     result.push_str(&comment);
 794     result.push('\n');
 795     result.push_str(&context.block_indent.to_string(context.config));
 796     result.push('}');
 797     Some(result)
 798 }
 799
 800 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
 801     let &ast::Arm { ref attrs, ref pats, .. } = arm;
 802     if !attrs.is_empty() {
 803         return attrs[0].span.lo;
 804     }
 805
 806     pats[0].span.lo
 807 }
 808
 809 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
 810     arm.body.span.hi
 811 }
 812
 813 fn arm_comma(body: &ast::Expr) -> &'static str {
 814     if let ast::ExprBlock(ref block) = body.node {
 815         if let ast::DefaultBlock = block.rules {
 816             ""
 817         } else {
 818             ","
 819         }
 820     } else {
 821         ","
 822     }
 823 }
 824
 825 // Match arms.
 826 impl Rewrite for ast::Arm {
 827     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 828         let &ast::Arm { ref attrs, ref pats, ref guard, ref body } = self;
 829         let indent_str = offset.to_string(context.config);
 830
 831         // FIXME this is all a bit grotty, would be nice to abstract out the
 832         // treatment of attributes.
 833         let attr_str = if !attrs.is_empty() {
 834             // We only use this visitor for the attributes, should we use it for
 835             // more?
 836             let mut attr_visitor = FmtVisitor::from_codemap(context.parse_session,
 837                                                             context.config,
 838                                                             None);
 839             attr_visitor.block_indent = context.block_indent;
 840             attr_visitor.last_pos = attrs[0].span.lo;
 841             if attr_visitor.visit_attrs(attrs) {
 842                 // Attributes included a skip instruction.
 843                 let snippet = context.snippet(mk_sp(attrs[0].span.lo, body.span.hi));
 844                 return Some(snippet);
 845             }
 846             attr_visitor.format_missing(pats[0].span.lo);
 847             attr_visitor.buffer.to_string()
 848         } else {
 849             String::new()
 850         };
 851
 852         // Patterns
 853         // 5 = ` => {`
 854         let pat_budget = try_opt!(width.checked_sub(5));
 855         let pat_strs = try_opt!(pats.iter()
 856                                     .map(|p| p.rewrite(context, pat_budget, offset))
 857                                     .collect::<Option<Vec<_>>>());
 858
 859         let mut total_width = pat_strs.iter().fold(0, |a, p| a + p.len());
 860         // Add ` | `.len().
 861         total_width += (pat_strs.len() - 1) * 3;
 862
 863         let mut vertical = total_width > pat_budget || pat_strs.iter().any(|p| p.contains('\n'));
 864         if !vertical && context.config.take_source_hints {
 865             // If the patterns were previously stacked, keep them stacked.
 866             let pat_span = mk_sp(pats[0].span.lo, pats[pats.len() - 1].span.hi);
 867             let pat_str = context.snippet(pat_span);
 868             vertical = pat_str.contains('\n');
 869         }
 870
 871         let pats_width = if vertical {
 872             pat_strs[pat_strs.len() - 1].len()
 873         } else {
 874             total_width
 875         };
 876
 877         let mut pats_str = String::new();
 878         for p in pat_strs {
 879             if !pats_str.is_empty() {
 880                 if vertical {
 881                     pats_str.push_str(" |\n");
 882                     pats_str.push_str(&indent_str);
 883                 } else {
 884                     pats_str.push_str(" | ");
 885                 }
 886             }
 887             pats_str.push_str(&p);
 888         }
 889
 890         let guard_str = try_opt!(rewrite_guard(context, guard, width, offset, pats_width));
 891
 892         let pats_str = format!("{}{}", pats_str, guard_str);
 893         // Where the next text can start.
 894         let mut line_start = last_line_width(&pats_str);
 895         if !pats_str.contains('\n') {
 896             line_start += offset.width();
 897         }
 898
 899         let comma = arm_comma(body);
 900
 901         // Let's try and get the arm body on the same line as the condition.
 902         // 4 = ` => `.len()
 903         let same_line_body = if context.config.max_width > line_start + comma.len() + 4 {
 904             let budget = context.config.max_width - line_start - comma.len() - 4;
 905             let offset = Indent::new(offset.block_indent, line_start + 4 - offset.block_indent);
 906             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
 907
 908             match rewrite {
 909                 Some(ref body_str) if body_str.len() <= budget || comma.is_empty() =>
 910                     return Some(format!("{}{} => {}{}",
 911                                         attr_str.trim_left(),
 912                                         pats_str,
 913                                         body_str,
 914                                         comma)),
 915                 _ => rewrite,
 916             }
 917         } else {
 918             None
 919         };
 920
 921         if let ast::ExprBlock(_) = body.node {
 922             // We're trying to fit a block in, but it still failed, give up.
 923             return None;
 924         }
 925
 926         let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
 927         let indent = context.block_indent.block_indent(context.config);
 928         let inner_context = &RewriteContext { block_indent: indent, ..*context };
 929         let next_line_body = nop_block_collapse(body.rewrite(inner_context, body_budget, indent),
 930                                                 body_budget);
 931
 932         let body_str = try_opt!(match_arm_heuristic(same_line_body.as_ref().map(|x| &x[..]),
 933                                                     next_line_body.as_ref().map(|x| &x[..])));
 934
 935         let spacer = match same_line_body {
 936             Some(ref body) if body == body_str => " ".to_owned(),
 937             _ => format!("\n{}",
 938                          offset.block_indent(context.config).to_string(context.config)),
 939         };
 940
 941         Some(format!("{}{} =>{}{},",
 942                      attr_str.trim_left(),
 943                      pats_str,
 944                      spacer,
 945                      body_str))
 946     }
 947 }
 948
 949 // Takes two possible rewrites for the match arm body and chooses the "nicest".
 950 fn match_arm_heuristic<'a>(former: Option<&'a str>, latter: Option<&'a str>) -> Option<&'a str> {
 951     match (former, latter) {
 952         (f @ Some(..), None) => f,
 953         (Some(f), Some(l)) if f.chars().filter(|&c| c == '\n').count() <=
 954                               l.chars().filter(|&c| c == '\n').count() => {
 955             Some(f)
 956         }
 957         (_, l) => l,
 958     }
 959 }
 960
 961 // The `if ...` guard on a match arm.
 962 fn rewrite_guard(context: &RewriteContext,
 963                  guard: &Option<ptr::P<ast::Expr>>,
 964                  width: usize,
 965                  offset: Indent,
 966                  // The amount of space used up on this line for the pattern in
 967                  // the arm (excludes offset).
 968                  pattern_width: usize)
 969                  -> Option<String> {
 970     if let &Some(ref guard) = guard {
 971         // First try to fit the guard string on the same line as the pattern.
 972         // 4 = ` if `, 5 = ` => {`
 973         let overhead = pattern_width + 4 + 5;
 974         if overhead < width {
 975             let cond_str = guard.rewrite(context, width - overhead, offset + pattern_width + 4);
 976             if let Some(cond_str) = cond_str {
 977                 return Some(format!(" if {}", cond_str));
 978             }
 979         }
 980
 981         // Not enough space to put the guard after the pattern, try a newline.
 982         let overhead = context.config.tab_spaces + 4 + 5;
 983         if overhead < width {
 984             let cond_str = guard.rewrite(context,
 985                                          width - overhead,
 986                                          offset.block_indent(context.config));
 987             if let Some(cond_str) = cond_str {
 988                 return Some(format!("\n{}if {}",
 989                                     offset.block_indent(context.config).to_string(context.config),
 990                                     cond_str));
 991             }
 992         }
 993
 994         None
 995     } else {
 996         Some(String::new())
 997     }
 998 }
 999
1000 fn rewrite_pat_expr(context: &RewriteContext,
1001                     pat: Option<&ast::Pat>,
1002                     expr: &ast::Expr,
1003                     matcher: &str,
1004                     // Connecting piece between pattern and expression,
1005                     // *without* trailing space.
1006                     connector: &str,
1007                     width: usize,
1008                     offset: Indent)
1009                     -> Option<String> {
1010     let pat_offset = offset + matcher.len();
1011     let mut result = match pat {
1012         Some(pat) => {
1013             let pat_budget = try_opt!(width.checked_sub(connector.len() + matcher.len()));
1014             let pat_string = try_opt!(pat.rewrite(context, pat_budget, pat_offset));
1015             format!("{}{}{}", matcher, pat_string, connector)
1016         }
1017         None => String::new(),
1018     };
1019
1020     // Consider only the last line of the pat string.
1021     let extra_offset = extra_offset(&result, offset);
1022
1023     // The expression may (partionally) fit on the current line.
1024     if width > extra_offset + 1 {
1025         let spacer = if pat.is_some() {
1026             " "
1027         } else {
1028             ""
1029         };
1030
1031         let expr_rewrite = expr.rewrite(context,
1032                                         width - extra_offset - spacer.len(),
1033                                         offset + extra_offset + spacer.len());
1034
1035         if let Some(expr_string) = expr_rewrite {
1036             result.push_str(spacer);
1037             result.push_str(&expr_string);
1038             return Some(result);
1039         }
1040     }
1041
1042     // The expression won't fit on the current line, jump to next.
1043     result.push('\n');
1044     result.push_str(&pat_offset.to_string(context.config));
1045
1046     let expr_rewrite = expr.rewrite(context,
1047                                     context.config.max_width - pat_offset.width(),
1048                                     pat_offset);
1049     result.push_str(&&try_opt!(expr_rewrite));
1050
1051     Some(result)
1052 }
1053
1054 fn rewrite_string_lit(context: &RewriteContext,
1055                       span: Span,
1056                       width: usize,
1057                       offset: Indent)
1058                       -> Option<String> {
1059     if !context.config.format_strings {
1060         return Some(context.snippet(span));
1061     }
1062
1063     let fmt = StringFormat {
1064         opener: "\"",
1065         closer: "\"",
1066         line_start: " ",
1067         line_end: "\\",
1068         width: width,
1069         offset: offset,
1070         trim_end: false,
1071         config: context.config,
1072     };
1073
1074     let string_lit = context.snippet(span);
1075     let str_lit = &string_lit[1..string_lit.len() - 1]; // Remove the quote characters.
1076
1077     rewrite_string(str_lit, &fmt)
1078 }
1079
1080 pub fn rewrite_call<R>(context: &RewriteContext,
1081                        callee: &R,
1082                        args: &[ptr::P<ast::Expr>],
1083                        span: Span,
1084                        width: usize,
1085                        offset: Indent)
1086                        -> Option<String>
1087     where R: Rewrite
1088 {
1089     let closure = |callee_max_width| {
1090         rewrite_call_inner(context, callee, callee_max_width, args, span, width, offset)
1091     };
1092
1093     // 2 is for parens
1094     let max_width = try_opt!(width.checked_sub(2));
1095     binary_search(1, max_width, closure)
1096 }
1097
1098 fn rewrite_call_inner<R>(context: &RewriteContext,
1099                          callee: &R,
1100                          max_callee_width: usize,
1101                          args: &[ptr::P<ast::Expr>],
1102                          span: Span,
1103                          width: usize,
1104                          offset: Indent)
1105                          -> Result<String, Ordering>
1106     where R: Rewrite
1107 {
1108     let callee = callee.borrow();
1109     // FIXME using byte lens instead of char lens (and probably all over the
1110     // place too)
1111     let callee_str = match callee.rewrite(context, max_callee_width, offset) {
1112         Some(string) => {
1113             if !string.contains('\n') && string.len() > max_callee_width {
1114                 panic!("{:?} {}", string, max_callee_width);
1115             } else {
1116                 string
1117             }
1118         }
1119         None => return Err(Ordering::Greater),
1120     };
1121
1122     let span_lo = span_after(span, "(", context.codemap);
1123     let span = mk_sp(span_lo, span.hi);
1124
1125     let extra_offset = extra_offset(&callee_str, offset);
1126     // 2 is for parens.
1127     let remaining_width = match width.checked_sub(extra_offset + 2) {
1128         Some(str) => str,
1129         None => return Err(Ordering::Greater),
1130     };
1131     let offset = offset + extra_offset + 1;
1132     let arg_count = args.len();
1133     let block_indent = if arg_count == 1 {
1134         context.block_indent
1135     } else {
1136         offset
1137     };
1138     let inner_context = &RewriteContext { block_indent: block_indent, ..*context };
1139
1140     let items = itemize_list(context.codemap,
1141                              args.iter(),
1142                              ")",
1143                              |item| item.span.lo,
1144                              |item| item.span.hi,
1145                              |item| item.rewrite(&inner_context, remaining_width, offset),
1146                              span.lo,
1147                              span.hi);
1148     let mut item_vec: Vec<_> = items.collect();
1149
1150     // Try letting the last argument overflow to the next line with block
1151     // indentation. If its first line fits on one line with the other arguments,
1152     // we format the function arguments horizontally.
1153     let overflow_last = match args.last().map(|x| &x.node) {
1154         Some(&ast::Expr_::ExprClosure(..)) |
1155         Some(&ast::Expr_::ExprBlock(..)) if arg_count > 1 => true,
1156         _ => false,
1157     } && context.config.chains_overflow_last;
1158
1159     let mut orig_last = None;
1160     let mut placeholder = None;
1161
1162     // Replace the last item with its first line to see if it fits with
1163     // first arguments.
1164     if overflow_last {
1165         let inner_context = &RewriteContext { block_indent: context.block_indent, ..*context };
1166         let rewrite = args.last().unwrap().rewrite(&inner_context, remaining_width, offset);
1167
1168         if let Some(rewrite) = rewrite {
1169             let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
1170             placeholder = Some(rewrite);
1171
1172             swap(&mut item_vec[arg_count - 1].item, &mut orig_last);
1173             item_vec[arg_count - 1].item = rewrite_first_line;
1174         }
1175     }
1176
1177     let tactic = definitive_tactic(&item_vec,
1178                                    ListTactic::LimitedHorizontalVertical(context.config
1179                                                                                 .fn_call_width),
1180                                    remaining_width);
1181
1182     // Replace the stub with the full overflowing last argument if the rewrite
1183     // succeeded and its first line fits with the other arguments.
1184     match (overflow_last, tactic, placeholder) {
1185         (true,
1186          DefinitiveListTactic::Horizontal,
1187          placeholder @ Some(..)) => {
1188             item_vec[arg_count - 1].item = placeholder;
1189         }
1190         (true, _, _) => {
1191             item_vec[arg_count - 1].item = orig_last;
1192         }
1193         (false, _, _) => {}
1194     }
1195
1196     let fmt = ListFormatting {
1197         tactic: tactic,
1198         separator: ",",
1199         trailing_separator: SeparatorTactic::Never,
1200         indent: offset,
1201         width: width,
1202         ends_with_newline: false,
1203         config: context.config,
1204     };
1205
1206     let list_str = match write_list(&item_vec, &fmt) {
1207         Some(str) => str,
1208         None => return Err(Ordering::Less),
1209     };
1210
1211     Ok(format!("{}({})", callee_str, list_str))
1212 }
1213
1214 fn rewrite_paren(context: &RewriteContext,
1215                  subexpr: &ast::Expr,
1216                  width: usize,
1217                  offset: Indent)
1218                  -> Option<String> {
1219     debug!("rewrite_paren, width: {}, offset: {:?}", width, offset);
1220     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1221     // paren on the same line as the subexpr.
1222     let subexpr_str = subexpr.rewrite(context, try_opt!(width.checked_sub(2)), offset + 1);
1223     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1224     subexpr_str.map(|s| format!("({})", s))
1225 }
1226
1227 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1228                           path: &ast::Path,
1229                           fields: &'a [ast::Field],
1230                           base: Option<&'a ast::Expr>,
1231                           span: Span,
1232                           width: usize,
1233                           offset: Indent)
1234                           -> Option<String> {
1235     debug!("rewrite_struct_lit: width {}, offset {:?}", width, offset);
1236     assert!(!fields.is_empty() || base.is_some());
1237
1238     enum StructLitField<'a> {
1239         Regular(&'a ast::Field),
1240         Base(&'a ast::Expr),
1241     }
1242
1243     // 2 = " {".len()
1244     let path_budget = try_opt!(width.checked_sub(2));
1245     let path_str = try_opt!(rewrite_path(context, true, None, path, path_budget, offset));
1246
1247     // Foo { a: Foo } - indent is +3, width is -5.
1248     let h_budget = width.checked_sub(path_str.len() + 5).unwrap_or(0);
1249     let (indent, v_budget) = match context.config.struct_lit_style {
1250         StructLitStyle::Visual => {
1251             (offset + path_str.len() + 3, h_budget)
1252         }
1253         StructLitStyle::Block => {
1254             // If we are all on one line, then we'll ignore the indent, and we
1255             // have a smaller budget.
1256             let indent = context.block_indent.block_indent(context.config);
1257             let v_budget = context.config.max_width.checked_sub(indent.width()).unwrap_or(0);
1258             (indent, v_budget)
1259         }
1260     };
1261
1262     let field_iter = fields.into_iter()
1263                            .map(StructLitField::Regular)
1264                            .chain(base.into_iter().map(StructLitField::Base));
1265
1266     let inner_context = &RewriteContext { block_indent: indent, ..*context };
1267
1268     let items = itemize_list(context.codemap,
1269                              field_iter,
1270                              "}",
1271                              |item| {
1272                                  match *item {
1273                                      StructLitField::Regular(ref field) => field.span.lo,
1274                                      StructLitField::Base(ref expr) => {
1275                                          let last_field_hi = fields.last().map_or(span.lo,
1276                                                                                   |field| {
1277                                                                                       field.span.hi
1278                                                                                   });
1279                                          let snippet = context.snippet(mk_sp(last_field_hi,
1280                                                                              expr.span.lo));
1281                                          let pos = snippet.find_uncommented("..").unwrap();
1282                                          last_field_hi + BytePos(pos as u32)
1283                                      }
1284                                  }
1285                              },
1286                              |item| {
1287                                  match *item {
1288                                      StructLitField::Regular(ref field) => field.span.hi,
1289                                      StructLitField::Base(ref expr) => expr.span.hi,
1290                                  }
1291                              },
1292                              |item| {
1293                                  match *item {
1294                                      StructLitField::Regular(ref field) => {
1295                                          rewrite_field(inner_context, &field, v_budget, indent)
1296                                      }
1297                                      StructLitField::Base(ref expr) => {
1298                                          // 2 = ..
1299                                          expr.rewrite(inner_context,
1300                                                       try_opt!(v_budget.checked_sub(2)),
1301                                                       indent + 2)
1302                                              .map(|s| format!("..{}", s))
1303                                      }
1304                                  }
1305                              },
1306                              span_after(span, "{", context.codemap),
1307                              span.hi);
1308     let item_vec = items.collect::<Vec<_>>();
1309
1310     let tactic = {
1311         let mut prelim_tactic = match (context.config.struct_lit_style, fields.len()) {
1312             (StructLitStyle::Visual, 1) => ListTactic::HorizontalVertical,
1313             _ => context.config.struct_lit_multiline_style.to_list_tactic(),
1314         };
1315
1316         if prelim_tactic == ListTactic::HorizontalVertical && fields.len() > 1 {
1317             prelim_tactic = ListTactic::LimitedHorizontalVertical(context.config.struct_lit_width);
1318         }
1319
1320         definitive_tactic(&item_vec, prelim_tactic, h_budget)
1321     };
1322
1323     let budget = match tactic {
1324         DefinitiveListTactic::Horizontal => h_budget,
1325         _ => v_budget,
1326     };
1327
1328     let fmt = ListFormatting {
1329         tactic: tactic,
1330         separator: ",",
1331         trailing_separator: if base.is_some() {
1332             SeparatorTactic::Never
1333         } else {
1334             context.config.struct_lit_trailing_comma
1335         },
1336         indent: indent,
1337         width: budget,
1338         ends_with_newline: false,
1339         config: context.config,
1340     };
1341     let fields_str = try_opt!(write_list(&item_vec, &fmt));
1342
1343     let format_on_newline = || {
1344         let inner_indent = context.block_indent
1345                                   .block_indent(context.config)
1346                                   .to_string(context.config);
1347         let outer_indent = context.block_indent.to_string(context.config);
1348         Some(format!("{} {{\n{}{}\n{}}}",
1349                      path_str,
1350                      inner_indent,
1351                      fields_str,
1352                      outer_indent))
1353     };
1354
1355     match (context.config.struct_lit_style,
1356            context.config.struct_lit_multiline_style) {
1357         (StructLitStyle::Block, _) if fields_str.contains('\n') || fields_str.len() > h_budget =>
1358             format_on_newline(),
1359         (StructLitStyle::Block, MultilineStyle::ForceMulti) => format_on_newline(),
1360         _ => Some(format!("{} {{ {} }}", path_str, fields_str)),
1361     }
1362
1363     // FIXME if context.config.struct_lit_style == Visual, but we run out
1364     // of space, we should fall back to BlockIndent.
1365 }
1366
1367 fn rewrite_field(context: &RewriteContext,
1368                  field: &ast::Field,
1369                  width: usize,
1370                  offset: Indent)
1371                  -> Option<String> {
1372     let name = &field.ident.node.to_string();
1373     let overhead = name.len() + 2;
1374     let expr = field.expr.rewrite(context,
1375                                   try_opt!(width.checked_sub(overhead)),
1376                                   offset + overhead);
1377     expr.map(|s| format!("{}: {}", name, s))
1378 }
1379
1380 pub fn rewrite_tuple<'a, R>(context: &RewriteContext,
1381                             items: &'a [ptr::P<R>],
1382                             span: Span,
1383                             width: usize,
1384                             offset: Indent)
1385                             -> Option<String>
1386     where R: Rewrite + Spanned + 'a
1387 {
1388     debug!("rewrite_tuple_lit: width: {}, offset: {:?}", width, offset);
1389     let indent = offset + 1;
1390     // In case of length 1, need a trailing comma
1391     if items.len() == 1 {
1392         // 3 = "(" + ",)"
1393         let budget = try_opt!(width.checked_sub(3));
1394         return items[0].rewrite(context, budget, indent).map(|s| format!("({},)", s));
1395     }
1396
1397     let items = itemize_list(context.codemap,
1398                              items.iter(),
1399                              ")",
1400                              |item| item.span().lo,
1401                              |item| item.span().hi,
1402                              |item| {
1403                                  let inner_width = try_opt!(context.config
1404                                                                    .max_width
1405                                                                    .checked_sub(indent.width() +
1406                                                                                 1));
1407                                  item.rewrite(context, inner_width, indent)
1408                              },
1409                              span.lo + BytePos(1), // Remove parens
1410                              span.hi - BytePos(1));
1411     let budget = try_opt!(width.checked_sub(2));
1412     let list_str = try_opt!(format_fn_args(items, budget, indent, context.config));
1413
1414     Some(format!("({})", list_str))
1415 }
1416
1417 fn rewrite_binary_op(context: &RewriteContext,
1418                      op: &ast::BinOp,
1419                      lhs: &ast::Expr,
1420                      rhs: &ast::Expr,
1421                      width: usize,
1422                      offset: Indent)
1423                      -> Option<String> {
1424     // FIXME: format comments between operands and operator
1425
1426     let operator_str = context.snippet(op.span);
1427
1428     // Get "full width" rhs and see if it fits on the current line. This
1429     // usually works fairly well since it tends to place operands of
1430     // operations with high precendence close together.
1431     let rhs_result = try_opt!(rhs.rewrite(context, width, offset));
1432
1433     // Second condition is needed in case of line break not caused by a
1434     // shortage of space, but by end-of-line comments, for example.
1435     // Note that this is non-conservative, but its just to see if it's even
1436     // worth trying to put everything on one line.
1437     if rhs_result.len() + 2 + operator_str.len() < width && !rhs_result.contains('\n') {
1438         // 1 = space between lhs expr and operator
1439         if let Some(mut result) = lhs.rewrite(context, width - 1 - operator_str.len(), offset) {
1440             result.push(' ');
1441             result.push_str(&operator_str);
1442             result.push(' ');
1443
1444             let remaining_width = width.checked_sub(last_line_width(&result)).unwrap_or(0);
1445
1446             if rhs_result.len() <= remaining_width {
1447                 result.push_str(&rhs_result);
1448                 return Some(result);
1449             }
1450
1451             if let Some(rhs_result) = rhs.rewrite(context, remaining_width, offset + result.len()) {
1452                 if rhs_result.len() <= remaining_width {
1453                     result.push_str(&rhs_result);
1454                     return Some(result);
1455                 }
1456             }
1457         }
1458     }
1459
1460     // We have to use multiple lines.
1461
1462     // Re-evaluate the lhs because we have more space now:
1463     let budget = try_opt!(context.config
1464                                  .max_width
1465                                  .checked_sub(offset.width() + 1 + operator_str.len()));
1466     Some(format!("{} {}\n{}{}",
1467                  try_opt!(lhs.rewrite(context, budget, offset)),
1468                  operator_str,
1469                  offset.to_string(context.config),
1470                  rhs_result))
1471 }
1472
1473 pub fn rewrite_unary_prefix<R: Rewrite>(context: &RewriteContext,
1474                                         prefix: &str,
1475                                         rewrite: &R,
1476                                         width: usize,
1477                                         offset: Indent)
1478                                         -> Option<String> {
1479     rewrite.rewrite(context,
1480                     try_opt!(width.checked_sub(prefix.len())),
1481                     offset + prefix.len())
1482            .map(|r| format!("{}{}", prefix, r))
1483 }
1484
1485 fn rewrite_unary_op(context: &RewriteContext,
1486                     op: &ast::UnOp,
1487                     expr: &ast::Expr,
1488                     width: usize,
1489                     offset: Indent)
1490                     -> Option<String> {
1491     // For some reason, an UnOp is not spanned like BinOp!
1492     let operator_str = match *op {
1493         ast::UnOp::UnDeref => "*",
1494         ast::UnOp::UnNot => "!",
1495         ast::UnOp::UnNeg => "-",
1496     };
1497     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1498 }
1499
1500 fn rewrite_assignment(context: &RewriteContext,
1501                       lhs: &ast::Expr,
1502                       rhs: &ast::Expr,
1503                       op: Option<&ast::BinOp>,
1504                       width: usize,
1505                       offset: Indent)
1506                       -> Option<String> {
1507     let operator_str = match op {
1508         Some(op) => context.snippet(op.span),
1509         None => "=".to_owned(),
1510     };
1511
1512     // 1 = space between lhs and operator.
1513     let max_width = try_opt!(width.checked_sub(operator_str.len() + 1));
1514     let lhs_str = format!("{} {}",
1515                           try_opt!(lhs.rewrite(context, max_width, offset)),
1516                           operator_str);
1517
1518     rewrite_assign_rhs(&context, lhs_str, rhs, width, offset)
1519 }
1520
1521 // The left hand side must contain everything up to, and including, the
1522 // assignment operator.
1523 pub fn rewrite_assign_rhs<S: Into<String>>(context: &RewriteContext,
1524                                            lhs: S,
1525                                            ex: &ast::Expr,
1526                                            width: usize,
1527                                            offset: Indent)
1528                                            -> Option<String> {
1529     let mut result = lhs.into();
1530     let last_line_width = last_line_width(&result) -
1531                           if result.contains('\n') {
1532         offset.width()
1533     } else {
1534         0
1535     };
1536     // 1 = space between operator and rhs.
1537     let max_width = try_opt!(width.checked_sub(last_line_width + 1));
1538     let rhs = ex.rewrite(&context, max_width, offset + last_line_width + 1);
1539
1540     match rhs {
1541         Some(new_str) => {
1542             result.push(' ');
1543             result.push_str(&new_str)
1544         }
1545         None => {
1546             // Expression did not fit on the same line as the identifier. Retry
1547             // on the next line.
1548             let new_offset = offset.block_indent(context.config);
1549             result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1550
1551             // FIXME: we probably should related max_width to width instead of
1552             // config.max_width where is the 1 coming from anyway?
1553             let max_width = try_opt!(context.config.max_width.checked_sub(new_offset.width() + 1));
1554             let inner_context = context.nested_context();
1555             let rhs = ex.rewrite(&inner_context, max_width, new_offset);
1556
1557             result.push_str(&&try_opt!(rhs));
1558         }
1559     }
1560
1561     Some(result)
1562 }
1563
1564 fn rewrite_expr_addrof(context: &RewriteContext,
1565                        mutability: ast::Mutability,
1566                        expr: &ast::Expr,
1567                        width: usize,
1568                        offset: Indent)
1569                        -> Option<String> {
1570     let operator_str = match mutability {
1571         ast::Mutability::MutImmutable => "&",
1572         ast::Mutability::MutMutable => "&mut ",
1573     };
1574     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1575 }