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;
  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_lit(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, 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.codemap, context.config);
 426         visitor.block_indent = context.block_indent + context.overflow_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         // Push text between last block item and end of block
 475         let snippet = visitor.snippet(mk_sp(visitor.last_pos, self.span.hi));
 476         visitor.buffer.push_str(&snippet);
 477
 478         Some(format!("{}{}", prefix, visitor.buffer))
 479     }
 480 }
 481
 482 // FIXME(#18): implement pattern formatting
 483 impl Rewrite for ast::Pat {
 484     fn rewrite(&self, context: &RewriteContext, _: usize, _: Indent) -> Option<String> {
 485         Some(context.snippet(self.span))
 486     }
 487 }
 488
 489 // Abstraction over for, while and loop expressions
 490 struct Loop<'a> {
 491     cond: Option<&'a ast::Expr>,
 492     block: &'a ast::Block,
 493     label: Option<ast::Ident>,
 494     pat: Option<&'a ast::Pat>,
 495     keyword: &'a str,
 496     matcher: &'a str,
 497     connector: &'a str,
 498 }
 499
 500 impl<'a> Loop<'a> {
 501     fn new_loop(block: &'a ast::Block, label: Option<ast::Ident>) -> Loop<'a> {
 502         Loop {
 503             cond: None,
 504             block: block,
 505             label: label,
 506             pat: None,
 507             keyword: "loop",
 508             matcher: "",
 509             connector: "",
 510         }
 511     }
 512
 513     fn new_while(pat: Option<&'a ast::Pat>,
 514                  cond: &'a ast::Expr,
 515                  block: &'a ast::Block,
 516                  label: Option<ast::Ident>)
 517                  -> Loop<'a> {
 518         Loop {
 519             cond: Some(cond),
 520             block: block,
 521             label: label,
 522             pat: pat,
 523             keyword: "while ",
 524             matcher: match pat {
 525                 Some(..) => "let ",
 526                 None => "",
 527             },
 528             connector: " =",
 529         }
 530     }
 531
 532     fn new_for(pat: &'a ast::Pat,
 533                cond: &'a ast::Expr,
 534                block: &'a ast::Block,
 535                label: Option<ast::Ident>)
 536                -> Loop<'a> {
 537         Loop {
 538             cond: Some(cond),
 539             block: block,
 540             label: label,
 541             pat: Some(pat),
 542             keyword: "for ",
 543             matcher: "",
 544             connector: " in",
 545         }
 546     }
 547 }
 548
 549 impl<'a> Rewrite for Loop<'a> {
 550     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 551         let label_string = rewrite_label(self.label);
 552         // 2 = " {".len()
 553         let inner_width = try_opt!(width.checked_sub(self.keyword.len() + 2 + label_string.len()));
 554         let inner_offset = offset + self.keyword.len() + label_string.len();
 555
 556         let pat_expr_string = match self.cond {
 557             Some(cond) => try_opt!(rewrite_pat_expr(context,
 558                                                     self.pat,
 559                                                     cond,
 560                                                     self.matcher,
 561                                                     self.connector,
 562                                                     inner_width,
 563                                                     inner_offset)),
 564             None => String::new(),
 565         };
 566
 567         // FIXME: this drops any comment between "loop" and the block.
 568         self.block
 569             .rewrite(context, width, offset)
 570             .map(|result| {
 571                 format!("{}{}{} {}",
 572                         label_string,
 573                         self.keyword,
 574                         pat_expr_string,
 575                         result)
 576             })
 577     }
 578 }
 579
 580 fn rewrite_label(label: Option<ast::Ident>) -> String {
 581     match label {
 582         Some(ident) => format!("{}: ", ident),
 583         None => "".to_owned(),
 584     }
 585 }
 586
 587 // Rewrites if-else blocks. If let Some(_) = pat, the expression is
 588 // treated as an if-let-else expression.
 589 fn rewrite_if_else(context: &RewriteContext,
 590                    cond: &ast::Expr,
 591                    if_block: &ast::Block,
 592                    else_block_opt: Option<&ast::Expr>,
 593                    pat: Option<&ast::Pat>,
 594                    width: usize,
 595                    offset: Indent,
 596                    allow_single_line: bool)
 597                    -> Option<String> {
 598     // 3 = "if ", 2 = " {"
 599     let pat_expr_string = try_opt!(rewrite_pat_expr(context,
 600                                                     pat,
 601                                                     cond,
 602                                                     "let ",
 603                                                     " =",
 604                                                     try_opt!(width.checked_sub(3 + 2)),
 605                                                     offset + 3));
 606
 607     // Try to format if-else on single line.
 608     if allow_single_line && context.config.single_line_if_else {
 609         let trial = single_line_if_else(context, &pat_expr_string, if_block, else_block_opt, width);
 610
 611         if trial.is_some() {
 612             return trial;
 613         }
 614     }
 615
 616     let if_block_string = try_opt!(if_block.rewrite(context, width, offset));
 617     let mut result = format!("if {} {}", pat_expr_string, if_block_string);
 618
 619     if let Some(else_block) = else_block_opt {
 620         let rewrite = match else_block.node {
 621             // If the else expression is another if-else expression, prevent it
 622             // from being formatted on a single line.
 623             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 624                 rewrite_if_else(context,
 625                                 cond,
 626                                 if_block,
 627                                 else_block.as_ref().map(|e| &**e),
 628                                 Some(pat),
 629                                 width,
 630                                 offset,
 631                                 false)
 632             }
 633             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
 634                 rewrite_if_else(context,
 635                                 cond,
 636                                 if_block,
 637                                 else_block.as_ref().map(|e| &**e),
 638                                 None,
 639                                 width,
 640                                 offset,
 641                                 false)
 642             }
 643             _ => else_block.rewrite(context, width, offset),
 644         };
 645
 646         result.push_str(" else ");
 647         result.push_str(&&try_opt!(rewrite));
 648     }
 649
 650     Some(result)
 651 }
 652
 653 fn single_line_if_else(context: &RewriteContext,
 654                        pat_expr_str: &str,
 655                        if_node: &ast::Block,
 656                        else_block_opt: Option<&ast::Expr>,
 657                        width: usize)
 658                        -> Option<String> {
 659     let else_block = try_opt!(else_block_opt);
 660     let fixed_cost = "if  {  } else {  }".len();
 661
 662     if let ast::ExprBlock(ref else_node) = else_block.node {
 663         if !is_simple_block(if_node, context.codemap) ||
 664            !is_simple_block(else_node, context.codemap) || pat_expr_str.contains('\n') {
 665             return None;
 666         }
 667
 668         let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 669         let if_expr = if_node.expr.as_ref().unwrap();
 670         let if_str = try_opt!(if_expr.rewrite(context, new_width, Indent::empty()));
 671
 672         let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 673         let else_expr = else_node.expr.as_ref().unwrap();
 674         let else_str = try_opt!(else_expr.rewrite(context, new_width, Indent::empty()));
 675
 676         // FIXME: this check shouldn't be necessary. Rewrites should either fail
 677         // or wrap to a newline when the object does not fit the width.
 678         let fits_line = fixed_cost + pat_expr_str.len() + if_str.len() + else_str.len() <= width;
 679
 680         if fits_line && !if_str.contains('\n') && !else_str.contains('\n') {
 681             return Some(format!("if {} {{ {} }} else {{ {} }}",
 682                                 pat_expr_str,
 683                                 if_str,
 684                                 else_str));
 685         }
 686     }
 687
 688     None
 689 }
 690
 691 // Checks that a block contains no statements, an expression and no comments.
 692 fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 693     if !block.stmts.is_empty() || block.expr.is_none() {
 694         return false;
 695     }
 696
 697     let snippet = codemap.span_to_snippet(block.span).unwrap();
 698
 699     !contains_comment(&snippet)
 700 }
 701
 702 // inter-match-arm-comment-rules:
 703 //  - all comments following a match arm before the start of the next arm
 704 //    are about the second arm
 705 fn rewrite_match_arm_comment(context: &RewriteContext,
 706                              missed_str: &str,
 707                              width: usize,
 708                              arm_indent: Indent,
 709                              arm_indent_str: &str)
 710                              -> Option<String> {
 711     // The leading "," is not part of the arm-comment
 712     let missed_str = match missed_str.find_uncommented(",") {
 713         Some(n) => &missed_str[n + 1..],
 714         None => &missed_str[..],
 715     };
 716
 717     let mut result = String::new();
 718     // any text not preceeded by a newline is pushed unmodified to the block
 719     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
 720     result.push_str(&missed_str[..first_brk]);
 721     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
 722
 723     let first = missed_str.find(|c: char| !c.is_whitespace()).unwrap_or(missed_str.len());
 724     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
 725         // Excessive vertical whitespace before comment should be preserved
 726         // TODO handle vertical whitespace better
 727         result.push('\n');
 728     }
 729     let missed_str = missed_str[first..].trim();
 730     if !missed_str.is_empty() {
 731         let comment = try_opt!(rewrite_comment(&missed_str,
 732                                                false,
 733                                                width,
 734                                                arm_indent,
 735                                                context.config));
 736         result.push('\n');
 737         result.push_str(arm_indent_str);
 738         result.push_str(&comment);
 739     }
 740
 741     Some(result)
 742 }
 743
 744 fn rewrite_match(context: &RewriteContext,
 745                  cond: &ast::Expr,
 746                  arms: &[ast::Arm],
 747                  width: usize,
 748                  offset: Indent,
 749                  span: Span)
 750                  -> Option<String> {
 751     if arms.is_empty() {
 752         return None;
 753     }
 754
 755     // `match `cond` {`
 756     let cond_budget = try_opt!(width.checked_sub(8));
 757     let cond_str = try_opt!(cond.rewrite(context, cond_budget, offset + 6));
 758     let mut result = format!("match {} {{", cond_str);
 759
 760     let nested_context = context.nested_context();
 761     let arm_indent = nested_context.block_indent + context.overflow_indent;
 762     let arm_indent_str = arm_indent.to_string(context.config);
 763
 764     let open_brace_pos = span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])),
 765                                     "{",
 766                                     context.codemap);
 767
 768     for (i, arm) in arms.iter().enumerate() {
 769         // Make sure we get the stuff between arms.
 770         let missed_str = if i == 0 {
 771             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
 772         } else {
 773             context.snippet(mk_sp(arm_end_pos(&arms[i - 1]), arm_start_pos(arm)))
 774         };
 775         let comment = try_opt!(rewrite_match_arm_comment(context,
 776                                                          &missed_str,
 777                                                          width,
 778                                                          arm_indent,
 779                                                          &arm_indent_str));
 780         result.push_str(&comment);
 781         result.push('\n');
 782         result.push_str(&arm_indent_str);
 783
 784         let arm_str = arm.rewrite(&nested_context,
 785                                   context.config.max_width - arm_indent.width(),
 786                                   arm_indent);
 787         if let Some(ref arm_str) = arm_str {
 788             result.push_str(arm_str);
 789         } else {
 790             // We couldn't format the arm, just reproduce the source.
 791             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
 792             result.push_str(&snippet);
 793         }
 794     }
 795     // BytePos(1) = closing match brace.
 796     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]), span.hi - BytePos(1));
 797     let last_comment = context.snippet(last_span);
 798     let comment = try_opt!(rewrite_match_arm_comment(context,
 799                                                      &last_comment,
 800                                                      width,
 801                                                      arm_indent,
 802                                                      &arm_indent_str));
 803     result.push_str(&comment);
 804     result.push('\n');
 805     result.push_str(&(context.block_indent + context.overflow_indent).to_string(context.config));
 806     result.push('}');
 807     Some(result)
 808 }
 809
 810 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
 811     let &ast::Arm { ref attrs, ref pats, .. } = arm;
 812     if !attrs.is_empty() {
 813         return attrs[0].span.lo;
 814     }
 815
 816     pats[0].span.lo
 817 }
 818
 819 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
 820     arm.body.span.hi
 821 }
 822
 823 // Match arms.
 824 impl Rewrite for ast::Arm {
 825     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 826         let &ast::Arm { ref attrs, ref pats, ref guard, ref body } = self;
 827         let indent_str = offset.to_string(context.config);
 828
 829         // FIXME this is all a bit grotty, would be nice to abstract out the
 830         // treatment of attributes.
 831         let attr_str = if !attrs.is_empty() {
 832             // We only use this visitor for the attributes, should we use it for
 833             // more?
 834             let mut attr_visitor = FmtVisitor::from_codemap(context.codemap, context.config);
 835             attr_visitor.block_indent = context.block_indent;
 836             attr_visitor.last_pos = attrs[0].span.lo;
 837             if attr_visitor.visit_attrs(attrs) {
 838                 // Attributes included a skip instruction.
 839                 let snippet = context.snippet(mk_sp(attrs[0].span.lo, body.span.hi));
 840                 return Some(snippet);
 841             }
 842             attr_visitor.format_missing(pats[0].span.lo);
 843             attr_visitor.buffer.to_string()
 844         } else {
 845             String::new()
 846         };
 847
 848         // Patterns
 849         // 5 = ` => {`
 850         let pat_budget = try_opt!(width.checked_sub(5));
 851         let pat_strs = try_opt!(pats.iter()
 852                                     .map(|p| {
 853                                         p.rewrite(context,
 854                                                   pat_budget,
 855                                                   offset.block_indent(context.config))
 856                                     })
 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.find('\n').is_some();
 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 = if let ast::ExprBlock(_) = body.node {
 900             ""
 901         } else {
 902             ","
 903         };
 904
 905         // Let's try and get the arm body on the same line as the condition.
 906         // 4 = ` => `.len()
 907         let same_line_body = if context.config.max_width > line_start + comma.len() + 4 {
 908             let budget = context.config.max_width - line_start - comma.len() - 4;
 909             let offset = Indent::new(offset.block_indent, line_start + 4 - offset.block_indent);
 910             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
 911
 912             match rewrite {
 913                 Some(ref body_str) if body_str.len() <= budget || comma.is_empty() =>
 914                     return Some(format!("{}{} => {}{}",
 915                                         attr_str.trim_left(),
 916                                         pats_str,
 917                                         body_str,
 918                                         comma)),
 919                 _ => rewrite,
 920             }
 921         } else {
 922             None
 923         };
 924
 925         if let ast::ExprBlock(_) = body.node {
 926             // We're trying to fit a block in, but it still failed, give up.
 927             return None;
 928         }
 929
 930         let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
 931         let next_line_body = nop_block_collapse(body.rewrite(context,
 932                                                              body_budget,
 933                                                              context.block_indent
 934                                                                     .block_indent(context.config)),
 935                                                 body_budget);
 936
 937         let body_str = try_opt!(match_arm_heuristic(same_line_body.as_ref().map(|x| &x[..]),
 938                                                     next_line_body.as_ref().map(|x| &x[..])));
 939
 940         let spacer = match same_line_body {
 941             Some(ref body) if body == body_str => " ".to_owned(),
 942             _ => format!("\n{}",
 943                          offset.block_indent(context.config).to_string(context.config)),
 944         };
 945
 946         Some(format!("{}{} =>{}{},",
 947                      attr_str.trim_left(),
 948                      pats_str,
 949                      spacer,
 950                      body_str))
 951     }
 952 }
 953
 954 // Takes two possible rewrites for the match arm body and chooses the "nicest".
 955 fn match_arm_heuristic<'a>(former: Option<&'a str>, latter: Option<&'a str>) -> Option<&'a str> {
 956     match (former, latter) {
 957         (f @ Some(..), None) => f,
 958         (Some(f), Some(l)) if f.chars().filter(|&c| c == '\n').count() <=
 959                               l.chars().filter(|&c| c == '\n').count() => {
 960             Some(f)
 961         }
 962         (_, l) => l,
 963     }
 964 }
 965
 966 // The `if ...` guard on a match arm.
 967 fn rewrite_guard(context: &RewriteContext,
 968                  guard: &Option<ptr::P<ast::Expr>>,
 969                  width: usize,
 970                  offset: Indent,
 971                  // The amount of space used up on this line for the pattern in
 972                  // the arm (excludes offset).
 973                  pattern_width: usize)
 974                  -> Option<String> {
 975     if let &Some(ref guard) = guard {
 976         // First try to fit the guard string on the same line as the pattern.
 977         // 4 = ` if `, 5 = ` => {`
 978         let overhead = pattern_width + 4 + 5;
 979         if overhead < width {
 980             let cond_str = guard.rewrite(context, width - overhead, offset + pattern_width + 4);
 981             if let Some(cond_str) = cond_str {
 982                 return Some(format!(" if {}", cond_str));
 983             }
 984         }
 985
 986         // Not enough space to put the guard after the pattern, try a newline.
 987         let overhead = context.config.tab_spaces + 4 + 5;
 988         if overhead < width {
 989             let cond_str = guard.rewrite(context,
 990                                          width - overhead,
 991                                          offset.block_indent(context.config));
 992             if let Some(cond_str) = cond_str {
 993                 return Some(format!("\n{}if {}",
 994                                     offset.block_indent(context.config).to_string(context.config),
 995                                     cond_str));
 996             }
 997         }
 998
 999         None
1000     } else {
1001         Some(String::new())
1002     }
1003 }
1004
1005 fn rewrite_pat_expr(context: &RewriteContext,
1006                     pat: Option<&ast::Pat>,
1007                     expr: &ast::Expr,
1008                     matcher: &str,
1009                     // Connecting piece between pattern and expression,
1010                     // *without* trailing space.
1011                     connector: &str,
1012                     width: usize,
1013                     offset: Indent)
1014                     -> Option<String> {
1015     let pat_offset = offset + matcher.len();
1016     let mut result = match pat {
1017         Some(pat) => {
1018             let pat_budget = try_opt!(width.checked_sub(connector.len() + matcher.len()));
1019             let pat_string = try_opt!(pat.rewrite(context, pat_budget, pat_offset));
1020             format!("{}{}{}", matcher, pat_string, connector)
1021         }
1022         None => String::new(),
1023     };
1024
1025     // Consider only the last line of the pat string.
1026     let extra_offset = extra_offset(&result, offset);
1027
1028     // The expression may (partionally) fit on the current line.
1029     if width > extra_offset + 1 {
1030         let spacer = if pat.is_some() {
1031             " "
1032         } else {
1033             ""
1034         };
1035
1036         let expr_rewrite = expr.rewrite(context,
1037                                         width - extra_offset - spacer.len(),
1038                                         offset + extra_offset + spacer.len());
1039
1040         if let Some(expr_string) = expr_rewrite {
1041             result.push_str(spacer);
1042             result.push_str(&expr_string);
1043             return Some(result);
1044         }
1045     }
1046
1047     // The expression won't fit on the current line, jump to next.
1048     result.push('\n');
1049     result.push_str(&pat_offset.to_string(context.config));
1050
1051     let expr_rewrite = expr.rewrite(context,
1052                                     context.config.max_width - pat_offset.width(),
1053                                     pat_offset);
1054     result.push_str(&&try_opt!(expr_rewrite));
1055
1056     Some(result)
1057 }
1058
1059 fn rewrite_string_lit(context: &RewriteContext,
1060                       span: Span,
1061                       width: usize,
1062                       offset: Indent)
1063                       -> Option<String> {
1064     if !context.config.format_strings {
1065         return Some(context.snippet(span));
1066     }
1067
1068     let fmt = StringFormat {
1069         opener: "\"",
1070         closer: "\"",
1071         line_start: " ",
1072         line_end: "\\",
1073         width: width,
1074         offset: offset,
1075         trim_end: false,
1076         config: context.config,
1077     };
1078
1079     let string_lit = context.snippet(span);
1080     let str_lit = &string_lit[1..string_lit.len() - 1]; // Remove the quote characters.
1081
1082     rewrite_string(str_lit, &fmt)
1083 }
1084
1085 pub fn rewrite_call<R>(context: &RewriteContext,
1086                        callee: &R,
1087                        args: &[ptr::P<ast::Expr>],
1088                        span: Span,
1089                        width: usize,
1090                        offset: Indent)
1091                        -> Option<String>
1092     where R: Rewrite
1093 {
1094     let closure = |callee_max_width| {
1095         rewrite_call_inner(context, callee, callee_max_width, args, span, width, offset)
1096     };
1097
1098     // 2 is for parens
1099     let max_width = try_opt!(width.checked_sub(2));
1100     binary_search(1, max_width, closure)
1101 }
1102
1103 fn rewrite_call_inner<R>(context: &RewriteContext,
1104                          callee: &R,
1105                          max_callee_width: usize,
1106                          args: &[ptr::P<ast::Expr>],
1107                          span: Span,
1108                          width: usize,
1109                          offset: Indent)
1110                          -> Result<String, Ordering>
1111     where R: Rewrite
1112 {
1113     let callee = callee.borrow();
1114     // FIXME using byte lens instead of char lens (and probably all over the
1115     // place too)
1116     let callee_str = match callee.rewrite(context, max_callee_width, offset) {
1117         Some(string) => {
1118             if !string.contains('\n') && string.len() > max_callee_width {
1119                 panic!("{:?} {}", string, max_callee_width);
1120             } else {
1121                 string
1122             }
1123         }
1124         None => return Err(Ordering::Greater),
1125     };
1126
1127     let span_lo = span_after(span, "(", context.codemap);
1128     let span = mk_sp(span_lo, span.hi);
1129
1130     let extra_offset = extra_offset(&callee_str, offset);
1131     // 2 is for parens.
1132     let remaining_width = match width.checked_sub(extra_offset + 2) {
1133         Some(str) => str,
1134         None => return Err(Ordering::Greater),
1135     };
1136     let offset = offset + extra_offset + 1;
1137     let arg_count = args.len();
1138     let block_indent = if arg_count == 1 {
1139         context.block_indent
1140     } else {
1141         offset
1142     };
1143     let inner_context = &RewriteContext { block_indent: block_indent, ..*context };
1144
1145     let items = itemize_list(context.codemap,
1146                              args.iter(),
1147                              ")",
1148                              |item| item.span.lo,
1149                              |item| item.span.hi,
1150                              |item| item.rewrite(&inner_context, remaining_width, offset),
1151                              span.lo,
1152                              span.hi);
1153     let mut item_vec: Vec<_> = items.collect();
1154
1155     // Try letting the last argument overflow to the next line with block
1156     // indentation. If its first line fits on one line with the other arguments,
1157     // we format the function arguments horizontally.
1158     let overflow_last = match args.last().map(|x| &x.node) {
1159         Some(&ast::Expr_::ExprClosure(..)) |
1160         Some(&ast::Expr_::ExprBlock(..)) if arg_count > 1 => true,
1161         _ => false,
1162     } && context.config.chains_overflow_last;
1163
1164     let mut orig_last = None;
1165     let mut placeholder = None;
1166
1167     // Replace the last item with its first line to see if it fits with
1168     // first arguments.
1169     if overflow_last {
1170         let inner_context = &RewriteContext { block_indent: context.block_indent, ..*context };
1171         let rewrite = args.last().unwrap().rewrite(&inner_context, remaining_width, offset);
1172
1173         if let Some(rewrite) = rewrite {
1174             let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
1175             placeholder = Some(rewrite);
1176
1177             swap(&mut item_vec[arg_count - 1].item, &mut orig_last);
1178             item_vec[arg_count - 1].item = rewrite_first_line;
1179         }
1180     }
1181
1182     let tactic = definitive_tactic(&item_vec,
1183                                    ListTactic::LimitedHorizontalVertical(context.config
1184                                                                                 .fn_call_width),
1185                                    remaining_width);
1186
1187     // Replace the stub with the full overflowing last argument if the rewrite
1188     // succeeded and its first line fits with the other arguments.
1189     match (overflow_last, tactic, placeholder) {
1190         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
1191             item_vec[arg_count - 1].item = placeholder;
1192         }
1193         (true, _, _) => {
1194             item_vec[arg_count - 1].item = orig_last;
1195         }
1196         (false, _, _) => {}
1197     }
1198
1199     let fmt = ListFormatting {
1200         tactic: tactic,
1201         separator: ",",
1202         trailing_separator: SeparatorTactic::Never,
1203         indent: offset,
1204         width: width,
1205         ends_with_newline: false,
1206         config: context.config,
1207     };
1208
1209     // format_fn_args(items, remaining_width, offset, context.config)
1210
1211     let list_str = match write_list(&item_vec, &fmt) {
1212         Some(str) => str,
1213         None => return Err(Ordering::Less),
1214     };
1215
1216     Ok(format!("{}({})", callee_str, list_str))
1217 }
1218
1219 fn rewrite_paren(context: &RewriteContext,
1220                  subexpr: &ast::Expr,
1221                  width: usize,
1222                  offset: Indent)
1223                  -> Option<String> {
1224     debug!("rewrite_paren, width: {}, offset: {:?}", width, offset);
1225     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1226     // paren on the same line as the subexpr.
1227     let subexpr_str = subexpr.rewrite(context, try_opt!(width.checked_sub(2)), offset + 1);
1228     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1229     subexpr_str.map(|s| format!("({})", s))
1230 }
1231
1232 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1233                           path: &ast::Path,
1234                           fields: &'a [ast::Field],
1235                           base: Option<&'a ast::Expr>,
1236                           span: Span,
1237                           width: usize,
1238                           offset: Indent)
1239                           -> Option<String> {
1240     debug!("rewrite_struct_lit: width {}, offset {:?}", width, offset);
1241     assert!(!fields.is_empty() || base.is_some());
1242
1243     enum StructLitField<'a> {
1244         Regular(&'a ast::Field),
1245         Base(&'a ast::Expr),
1246     }
1247
1248     // 2 = " {".len()
1249     let path_budget = try_opt!(width.checked_sub(2));
1250     let path_str = try_opt!(path.rewrite(context, path_budget, offset));
1251
1252     // Foo { a: Foo } - indent is +3, width is -5.
1253     let h_budget = width.checked_sub(path_str.len() + 5).unwrap_or(0);
1254     let (indent, v_budget) = match context.config.struct_lit_style {
1255         StructLitStyle::Visual => {
1256             (offset + path_str.len() + 3, h_budget)
1257         }
1258         StructLitStyle::Block => {
1259             // If we are all on one line, then we'll ignore the indent, and we
1260             // have a smaller budget.
1261             let indent = context.block_indent.block_indent(context.config);
1262             let v_budget = context.config.max_width.checked_sub(indent.width()).unwrap_or(0);
1263             (indent, v_budget)
1264         }
1265     };
1266
1267     let field_iter = fields.into_iter()
1268                            .map(StructLitField::Regular)
1269                            .chain(base.into_iter().map(StructLitField::Base));
1270
1271     let inner_context = &RewriteContext { block_indent: indent, ..*context };
1272
1273     let items = itemize_list(context.codemap,
1274                              field_iter,
1275                              "}",
1276                              |item| {
1277                                  match *item {
1278                                      StructLitField::Regular(ref field) => field.span.lo,
1279                                      StructLitField::Base(ref expr) => {
1280                                          let last_field_hi = fields.last().map_or(span.lo,
1281                                                                                   |field| {
1282                                                                                       field.span.hi
1283                                                                                   });
1284                                          let snippet = context.snippet(mk_sp(last_field_hi,
1285                                                                              expr.span.lo));
1286                                          let pos = snippet.find_uncommented("..").unwrap();
1287                                          last_field_hi + BytePos(pos as u32)
1288                                      }
1289                                  }
1290                              },
1291                              |item| {
1292                                  match *item {
1293                                      StructLitField::Regular(ref field) => field.span.hi,
1294                                      StructLitField::Base(ref expr) => expr.span.hi,
1295                                  }
1296                              },
1297                              |item| {
1298                                  match *item {
1299                                      StructLitField::Regular(ref field) => {
1300                                          rewrite_field(inner_context, &field, v_budget, indent)
1301                                      }
1302                                      StructLitField::Base(ref expr) => {
1303                                          // 2 = ..
1304                                          expr.rewrite(inner_context,
1305                                                       try_opt!(v_budget.checked_sub(2)),
1306                                                       indent + 2)
1307                                              .map(|s| format!("..{}", s))
1308                                      }
1309                                  }
1310                              },
1311                              span_after(span, "{", context.codemap),
1312                              span.hi);
1313     let item_vec = items.collect::<Vec<_>>();
1314
1315     let tactic = {
1316         let mut prelim_tactic = match (context.config.struct_lit_style, fields.len()) {
1317             (StructLitStyle::Visual, 1) => ListTactic::HorizontalVertical,
1318             _ => context.config.struct_lit_multiline_style.to_list_tactic(),
1319         };
1320
1321         if prelim_tactic == ListTactic::HorizontalVertical && fields.len() > 1 {
1322             prelim_tactic = ListTactic::LimitedHorizontalVertical(context.config.struct_lit_width);
1323         }
1324
1325         definitive_tactic(&item_vec, prelim_tactic, h_budget)
1326     };
1327
1328     let budget = match tactic {
1329         DefinitiveListTactic::Horizontal => h_budget,
1330         _ => v_budget,
1331     };
1332
1333     let fmt = ListFormatting {
1334         tactic: tactic,
1335         separator: ",",
1336         trailing_separator: if base.is_some() {
1337             SeparatorTactic::Never
1338         } else {
1339             context.config.struct_lit_trailing_comma
1340         },
1341         indent: indent,
1342         width: budget,
1343         ends_with_newline: false,
1344         config: context.config,
1345     };
1346     let fields_str = try_opt!(write_list(&item_vec, &fmt));
1347
1348     let format_on_newline = || {
1349         let inner_indent = context.block_indent
1350                                   .block_indent(context.config)
1351                                   .to_string(context.config);
1352         let outer_indent = context.block_indent.to_string(context.config);
1353         Some(format!("{} {{\n{}{}\n{}}}",
1354                      path_str,
1355                      inner_indent,
1356                      fields_str,
1357                      outer_indent))
1358     };
1359
1360     match (context.config.struct_lit_style,
1361            context.config.struct_lit_multiline_style) {
1362         (StructLitStyle::Block, _) if fields_str.contains('\n') || fields_str.len() > h_budget =>
1363             format_on_newline(),
1364         (StructLitStyle::Block, MultilineStyle::ForceMulti) => format_on_newline(),
1365         _ => Some(format!("{} {{ {} }}", path_str, fields_str)),
1366     }
1367
1368     // FIXME if context.config.struct_lit_style == Visual, but we run out
1369     // of space, we should fall back to BlockIndent.
1370 }
1371
1372 fn rewrite_field(context: &RewriteContext,
1373                  field: &ast::Field,
1374                  width: usize,
1375                  offset: Indent)
1376                  -> Option<String> {
1377     let name = &field.ident.node.to_string();
1378     let overhead = name.len() + 2;
1379     let expr = field.expr.rewrite(context,
1380                                   try_opt!(width.checked_sub(overhead)),
1381                                   offset + overhead);
1382     expr.map(|s| format!("{}: {}", name, s))
1383 }
1384
1385 fn rewrite_tuple_lit(context: &RewriteContext,
1386                      items: &[ptr::P<ast::Expr>],
1387                      span: Span,
1388                      width: usize,
1389                      offset: Indent)
1390                      -> Option<String> {
1391     debug!("rewrite_tuple_lit: width: {}, offset: {:?}", width, offset);
1392     let indent = offset + 1;
1393     // In case of length 1, need a trailing comma
1394     if items.len() == 1 {
1395         // 3 = "(" + ",)"
1396         let budget = try_opt!(width.checked_sub(3));
1397         return items[0].rewrite(context, budget, indent).map(|s| format!("({},)", s));
1398     }
1399
1400     let items = itemize_list(context.codemap,
1401                              items.iter(),
1402                              ")",
1403                              |item| item.span.lo,
1404                              |item| item.span.hi,
1405                              |item| {
1406                                  let inner_width = context.config.max_width - indent.width() - 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
1531     // 1 = space between operator and rhs.
1532     let max_width = try_opt!(width.checked_sub(result.len() + 1));
1533     let rhs = ex.rewrite(&context, max_width, offset + result.len() + 1);
1534
1535     match rhs {
1536         Some(new_str) => {
1537             result.push(' ');
1538             result.push_str(&new_str)
1539         }
1540         None => {
1541             // Expression did not fit on the same line as the identifier. Retry
1542             // on the next line.
1543             let new_offset = offset.block_indent(context.config);
1544             result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1545
1546             // FIXME: we probably should related max_width to width instead of config.max_width
1547             // where is the 1 coming from anyway?
1548             let max_width = try_opt!(context.config.max_width.checked_sub(new_offset.width() + 1));
1549             let rhs_indent = Indent::new(context.config.tab_spaces, 0);
1550             let overflow_context = context.overflow_context(rhs_indent);
1551             let rhs = ex.rewrite(&overflow_context, max_width, new_offset);
1552
1553             result.push_str(&&try_opt!(rhs));
1554         }
1555     }
1556
1557     Some(result)
1558 }
1559
1560 fn rewrite_expr_addrof(context: &RewriteContext,
1561                        mutability: ast::Mutability,
1562                        expr: &ast::Expr,
1563                        width: usize,
1564                        offset: Indent)
1565                        -> Option<String> {
1566     let operator_str = match mutability {
1567         ast::Mutability::MutImmutable => "&",
1568         ast::Mutability::MutMutable => "&mut ",
1569     };
1570     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1571 }