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
  14 use Indent;
  15 use rewrite::{Rewrite, RewriteContext};
  16 use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic,
  17             DefinitiveListTactic, definitive_tactic};
  18 use string::{StringFormat, rewrite_string};
  19 use utils::{span_after, extra_offset, last_line_width, wrap_str, binary_search};
  20 use visitor::FmtVisitor;
  21 use config::{StructLitStyle, MultilineStyle};
  22 use comment::{FindUncommented, rewrite_comment, contains_comment};
  23 use types::rewrite_path;
  24 use items::{span_lo_for_arg, span_hi_for_arg};
  25 use chains::rewrite_chain;
  26 use macros::rewrite_macro;
  27
  28 use syntax::{ast, ptr};
  29 use syntax::codemap::{CodeMap, Span, BytePos, mk_sp};
  30 use syntax::visit::Visitor;
  31
  32 impl Rewrite for ast::Expr {
  33     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  34         match self.node {
  35             ast::Expr_::ExprVec(ref expr_vec) => {
  36                 rewrite_array(expr_vec.iter().map(|e| &**e),
  37                               self.span,
  38                               context,
  39                               width,
  40                               offset)
  41             }
  42             ast::Expr_::ExprLit(ref l) => {
  43                 match l.node {
  44                     ast::Lit_::LitStr(_, ast::StrStyle::CookedStr) => {
  45                         rewrite_string_lit(context, l.span, width, offset)
  46                     }
  47                     _ => {
  48                         wrap_str(context.snippet(self.span),
  49                                  context.config.max_width,
  50                                  width,
  51                                  offset)
  52                     }
  53                 }
  54             }
  55             ast::Expr_::ExprCall(ref callee, ref args) => {
  56                 let inner_span = mk_sp(callee.span.hi, self.span.hi);
  57                 rewrite_call(context, &**callee, args, inner_span, width, offset)
  58             }
  59             ast::Expr_::ExprParen(ref subexpr) => {
  60                 rewrite_paren(context, subexpr, width, offset)
  61             }
  62             ast::Expr_::ExprBinary(ref op, ref lhs, ref rhs) => {
  63                 rewrite_binary_op(context, op, lhs, rhs, width, offset)
  64             }
  65             ast::Expr_::ExprUnary(ref op, ref subexpr) => {
  66                 rewrite_unary_op(context, op, subexpr, width, offset)
  67             }
  68             ast::Expr_::ExprStruct(ref path, ref fields, ref base) => {
  69                 rewrite_struct_lit(context,
  70                                    path,
  71                                    fields,
  72                                    base.as_ref().map(|e| &**e),
  73                                    self.span,
  74                                    width,
  75                                    offset)
  76             }
  77             ast::Expr_::ExprTup(ref items) => {
  78                 rewrite_tuple_lit(context, items, self.span, width, offset)
  79             }
  80             ast::Expr_::ExprWhile(ref cond, ref block, label) => {
  81                 Loop::new_while(None, cond, block, label).rewrite(context, width, offset)
  82             }
  83             ast::Expr_::ExprWhileLet(ref pat, ref cond, ref block, label) => {
  84                 Loop::new_while(Some(pat), cond, block, label).rewrite(context, width, offset)
  85             }
  86             ast::Expr_::ExprForLoop(ref pat, ref cond, ref block, label) => {
  87                 Loop::new_for(pat, cond, block, label).rewrite(context, width, offset)
  88             }
  89             ast::Expr_::ExprLoop(ref block, label) => {
  90                 Loop::new_loop(block, label).rewrite(context, width, offset)
  91             }
  92             ast::Expr_::ExprBlock(ref block) => {
  93                 block.rewrite(context, width, offset)
  94             }
  95             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
  96                 rewrite_if_else(context,
  97                                 cond,
  98                                 if_block,
  99                                 else_block.as_ref().map(|e| &**e),
 100                                 None,
 101                                 width,
 102                                 offset,
 103                                 true)
 104             }
 105             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 106                 rewrite_if_else(context,
 107                                 cond,
 108                                 if_block,
 109                                 else_block.as_ref().map(|e| &**e),
 110                                 Some(pat),
 111                                 width,
 112                                 offset,
 113                                 true)
 114             }
 115             // We reformat it ourselves because rustc gives us a bad span
 116             // for ranges, see rust#27162
 117             ast::Expr_::ExprRange(ref left, ref right) => {
 118                 rewrite_range(context,
 119                               left.as_ref().map(|e| &**e),
 120                               right.as_ref().map(|e| &**e),
 121                               width,
 122                               offset)
 123             }
 124             ast::Expr_::ExprMatch(ref cond, ref arms, _) => {
 125                 rewrite_match(context, cond, arms, width, offset, self.span)
 126             }
 127             ast::Expr_::ExprPath(ref qself, ref path) => {
 128                 rewrite_path(context, qself.as_ref(), path, width, offset)
 129             }
 130             ast::Expr_::ExprAssign(ref lhs, ref rhs) => {
 131                 rewrite_assignment(context, lhs, rhs, None, width, offset)
 132             }
 133             ast::Expr_::ExprAssignOp(ref op, ref lhs, ref rhs) => {
 134                 rewrite_assignment(context, lhs, rhs, Some(op), width, offset)
 135             }
 136             ast::Expr_::ExprAgain(ref opt_ident) => {
 137                 let id_str = match *opt_ident {
 138                     Some(ident) => format!(" {}", ident.node),
 139                     None => String::new(),
 140                 };
 141                 Some(format!("continue{}", id_str))
 142             }
 143             ast::Expr_::ExprBreak(ref opt_ident) => {
 144                 let id_str = match *opt_ident {
 145                     Some(ident) => format!(" {}", ident.node),
 146                     None => String::new(),
 147                 };
 148                 Some(format!("break{}", id_str))
 149             }
 150             ast::Expr_::ExprClosure(capture, ref fn_decl, ref body) => {
 151                 rewrite_closure(capture,
 152                                 fn_decl,
 153                                 body,
 154                                 self.span,
 155                                 context,
 156                                 width,
 157                                 offset)
 158             }
 159             ast::Expr_::ExprField(..) |
 160             ast::Expr_::ExprTupField(..) |
 161             ast::Expr_::ExprMethodCall(..) => {
 162                 rewrite_chain(self, context, width, offset)
 163             }
 164             ast::Expr_::ExprMac(ref mac) => {
 165                 // Failure to rewrite a marco should not imply failure to
 166                 // rewrite the expression.
 167                 rewrite_macro(mac, context, width, offset).or_else(|| {
 168                     wrap_str(context.snippet(self.span),
 169                              context.config.max_width,
 170                              width,
 171                              offset)
 172                 })
 173             }
 174             ast::Expr_::ExprRet(None) => {
 175                 wrap_str("return".to_owned(),
 176                          context.config.max_width,
 177                          width,
 178                          offset)
 179             }
 180             ast::Expr_::ExprRet(Some(ref expr)) => {
 181                 rewrite_unary_prefix(context, "return ", expr, width, offset)
 182             }
 183             ast::Expr_::ExprBox(ref expr) => {
 184                 rewrite_unary_prefix(context, "box ", expr, width, offset)
 185             }
 186             ast::Expr_::ExprAddrOf(mutability, ref expr) => {
 187                 rewrite_expr_addrof(context, mutability, &expr, width, offset)
 188             }
 189             // We do not format these expressions yet, but they should still
 190             // satisfy our width restrictions.
 191             ast::Expr_::ExprInPlace(..) |
 192             ast::Expr_::ExprCast(..) |
 193             ast::Expr_::ExprIndex(..) |
 194             ast::Expr_::ExprInlineAsm(..) |
 195             ast::Expr_::ExprRepeat(..) => {
 196                 wrap_str(context.snippet(self.span),
 197                          context.config.max_width,
 198                          width,
 199                          offset)
 200             }
 201         }
 202     }
 203 }
 204
 205 pub fn rewrite_array<'a, I>(expr_iter: I,
 206                             span: Span,
 207                             context: &RewriteContext,
 208                             width: usize,
 209                             offset: Indent)
 210                             -> Option<String>
 211     where I: Iterator<Item = &'a ast::Expr>
 212 {
 213     // 2 for brackets;
 214     let max_item_width = try_opt!(width.checked_sub(2));
 215     let items = itemize_list(context.codemap,
 216                              expr_iter,
 217                              "]",
 218                              |item| item.span.lo,
 219                              |item| item.span.hi,
 220                              // 1 = [
 221                              // FIXME(#133): itemize_list doesn't support
 222                              // rewrite failure. This may not be its
 223                              // responsibility, but that of write_list.
 224                              |item| {
 225                                  item.rewrite(context, max_item_width, offset + 1)
 226                                      .unwrap_or_else(|| context.snippet(item.span))
 227                              },
 228                              span_after(span, "[", context.codemap),
 229                              span.hi)
 230                     .collect::<Vec<_>>();
 231
 232     let tactic = if items.iter().any(|li| li.item.len() > 10 || li.is_multiline()) {
 233         definitive_tactic(&items, ListTactic::HorizontalVertical, max_item_width)
 234     } else {
 235         DefinitiveListTactic::Mixed
 236     };
 237
 238     let fmt = ListFormatting {
 239         tactic: tactic,
 240         separator: ",",
 241         trailing_separator: SeparatorTactic::Never,
 242         indent: offset + 1,
 243         width: max_item_width,
 244         ends_with_newline: false,
 245         config: context.config,
 246     };
 247     let list_str = try_opt!(write_list(&items, &fmt));
 248
 249     Some(format!("[{}]", list_str))
 250 }
 251
 252 // This functions is pretty messy because of the wrapping and unwrapping of
 253 // expressions into and from blocks. See rust issue #27872.
 254 fn rewrite_closure(capture: ast::CaptureClause,
 255                    fn_decl: &ast::FnDecl,
 256                    body: &ast::Block,
 257                    span: Span,
 258                    context: &RewriteContext,
 259                    width: usize,
 260                    offset: Indent)
 261                    -> Option<String> {
 262     let mover = if capture == ast::CaptureClause::CaptureByValue {
 263         "move "
 264     } else {
 265         ""
 266     };
 267     let offset = offset + mover.len();
 268
 269     // 4 = "|| {".len(), which is overconservative when the closure consists of
 270     // a single expression.
 271     let budget = try_opt!(width.checked_sub(4 + mover.len()));
 272     // 1 = |
 273     let argument_offset = offset + 1;
 274     let ret_str = try_opt!(fn_decl.output.rewrite(context, budget, argument_offset));
 275     // 1 = space between arguments and return type.
 276     let horizontal_budget = budget.checked_sub(ret_str.len() + 1).unwrap_or(0);
 277
 278     let arg_items = itemize_list(context.codemap,
 279                                  fn_decl.inputs.iter(),
 280                                  "|",
 281                                  |arg| span_lo_for_arg(arg),
 282                                  |arg| span_hi_for_arg(arg),
 283                                  |arg| {
 284                                      // FIXME: we should just escalate failure
 285                                      // here, but itemize_list doesn't allow it.
 286                                      arg.rewrite(context, budget, argument_offset)
 287                                         .unwrap_or_else(|| {
 288                                             context.snippet(mk_sp(span_lo_for_arg(arg),
 289                                                                   span_hi_for_arg(arg)))
 290                                         })
 291                                  },
 292                                  span_after(span, "|", context.codemap),
 293                                  body.span.lo);
 294     let item_vec = arg_items.collect::<Vec<_>>();
 295     let tactic = definitive_tactic(&item_vec,
 296                                    ListTactic::HorizontalVertical,
 297                                    horizontal_budget);
 298     let budget = match tactic {
 299         DefinitiveListTactic::Horizontal => horizontal_budget,
 300         _ => budget,
 301     };
 302
 303     let fmt = ListFormatting {
 304         tactic: tactic,
 305         separator: ",",
 306         trailing_separator: SeparatorTactic::Never,
 307         indent: argument_offset,
 308         width: budget,
 309         ends_with_newline: false,
 310         config: context.config,
 311     };
 312     let list_str = try_opt!(write_list(&item_vec, &fmt));
 313     let mut prefix = format!("{}|{}|", mover, list_str);
 314
 315     if !ret_str.is_empty() {
 316         if prefix.contains('\n') {
 317             prefix.push('\n');
 318             prefix.push_str(&argument_offset.to_string(context.config));
 319         } else {
 320             prefix.push(' ');
 321         }
 322         prefix.push_str(&ret_str);
 323     }
 324
 325     // Try to format closure body as a single line expression without braces.
 326     if is_simple_block(body, context.codemap) && !prefix.contains('\n') {
 327         let (spacer, closer) = if ret_str.is_empty() {
 328             (" ", "")
 329         } else {
 330             (" { ", " }")
 331         };
 332         let expr = body.expr.as_ref().unwrap();
 333         // All closure bodies are blocks in the eyes of the AST, but we may not
 334         // want to unwrap them when they only contain a single expression.
 335         let inner_expr = match expr.node {
 336             ast::Expr_::ExprBlock(ref inner) if inner.stmts.is_empty() && inner.expr.is_some() &&
 337                                                 inner.rules ==
 338                                                 ast::BlockCheckMode::DefaultBlock => {
 339                 inner.expr.as_ref().unwrap()
 340             }
 341             _ => expr,
 342         };
 343         let extra_offset = extra_offset(&prefix, offset) + spacer.len();
 344         let budget = try_opt!(width.checked_sub(extra_offset + closer.len()));
 345         let rewrite = inner_expr.rewrite(context, budget, offset + extra_offset);
 346
 347         // Checks if rewrite succeeded and fits on a single line.
 348         let accept_rewrite = rewrite.as_ref().map(|result| !result.contains('\n')).unwrap_or(false);
 349
 350         if accept_rewrite {
 351             return Some(format!("{}{}{}{}", prefix, spacer, rewrite.unwrap(), closer));
 352         }
 353     }
 354
 355     // We couldn't format the closure body as a single line expression; fall
 356     // back to block formatting.
 357     let body_rewrite = body.expr
 358                            .as_ref()
 359                            .and_then(|body_expr| {
 360                                if let ast::Expr_::ExprBlock(ref inner) = body_expr.node {
 361                                    Some(inner.rewrite(&context, 2, Indent::empty()))
 362                                } else {
 363                                    None
 364                                }
 365                            })
 366                            .unwrap_or_else(|| body.rewrite(&context, 2, Indent::empty()));
 367
 368     Some(format!("{} {}", prefix, try_opt!(body_rewrite)))
 369 }
 370
 371 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 372     block_str.map(|block_str| {
 373         if block_str.starts_with("{") && budget >= 2 &&
 374            (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2) {
 375             "{}".to_owned()
 376         } else {
 377             block_str.to_owned()
 378         }
 379     })
 380 }
 381
 382 impl Rewrite for ast::Block {
 383     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 384         let user_str = context.snippet(self.span);
 385         if user_str == "{}" && width >= 2 {
 386             return Some(user_str);
 387         }
 388
 389         let mut visitor = FmtVisitor::from_codemap(context.codemap, context.config);
 390         visitor.block_indent = context.block_indent + context.overflow_indent;
 391
 392         let prefix = match self.rules {
 393             ast::BlockCheckMode::PushUnsafeBlock(..) |
 394             ast::BlockCheckMode::UnsafeBlock(..) => {
 395                 let snippet = context.snippet(self.span);
 396                 let open_pos = try_opt!(snippet.find_uncommented("{"));
 397                 visitor.last_pos = self.span.lo + BytePos(open_pos as u32);
 398
 399                 // Extract comment between unsafe and block start.
 400                 let trimmed = &snippet[6..open_pos].trim();
 401
 402                 let prefix = if !trimmed.is_empty() {
 403                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 404                     let budget = try_opt!(width.checked_sub(9));
 405                     format!("unsafe {} ",
 406                             try_opt!(rewrite_comment(trimmed,
 407                                                      true,
 408                                                      budget,
 409                                                      offset + 7,
 410                                                      context.config)))
 411                 } else {
 412                     "unsafe ".to_owned()
 413                 };
 414
 415                 if is_simple_block(self, context.codemap) && prefix.len() < width {
 416                     let body = self.expr
 417                                    .as_ref()
 418                                    .unwrap()
 419                                    .rewrite(context, width - prefix.len(), offset);
 420                     if let Some(ref expr_str) = body {
 421                         let result = format!("{}{{ {} }}", prefix, expr_str);
 422                         if result.len() <= width && !result.contains('\n') {
 423                             return Some(result);
 424                         }
 425                     }
 426                 }
 427
 428                 prefix
 429             }
 430             ast::BlockCheckMode::PopUnsafeBlock(..) |
 431             ast::BlockCheckMode::DefaultBlock => {
 432                 visitor.last_pos = self.span.lo;
 433
 434                 String::new()
 435             }
 436         };
 437
 438         visitor.visit_block(self);
 439
 440         // Push text between last block item and end of block
 441         let snippet = visitor.snippet(mk_sp(visitor.last_pos, self.span.hi));
 442         visitor.buffer.push_str(&snippet);
 443
 444         Some(format!("{}{}", prefix, visitor.buffer))
 445     }
 446 }
 447
 448 // FIXME(#18): implement pattern formatting
 449 impl Rewrite for ast::Pat {
 450     fn rewrite(&self, context: &RewriteContext, _: usize, _: Indent) -> Option<String> {
 451         Some(context.snippet(self.span))
 452     }
 453 }
 454
 455 // Abstraction over for, while and loop expressions
 456 struct Loop<'a> {
 457     cond: Option<&'a ast::Expr>,
 458     block: &'a ast::Block,
 459     label: Option<ast::Ident>,
 460     pat: Option<&'a ast::Pat>,
 461     keyword: &'a str,
 462     matcher: &'a str,
 463     connector: &'a str,
 464 }
 465
 466 impl<'a> Loop<'a> {
 467     fn new_loop(block: &'a ast::Block, label: Option<ast::Ident>) -> Loop<'a> {
 468         Loop {
 469             cond: None,
 470             block: block,
 471             label: label,
 472             pat: None,
 473             keyword: "loop",
 474             matcher: "",
 475             connector: "",
 476         }
 477     }
 478
 479     fn new_while(pat: Option<&'a ast::Pat>,
 480                  cond: &'a ast::Expr,
 481                  block: &'a ast::Block,
 482                  label: Option<ast::Ident>)
 483                  -> Loop<'a> {
 484         Loop {
 485             cond: Some(cond),
 486             block: block,
 487             label: label,
 488             pat: pat,
 489             keyword: "while ",
 490             matcher: match pat {
 491                 Some(..) => "let ",
 492                 None => "",
 493             },
 494             connector: " =",
 495         }
 496     }
 497
 498     fn new_for(pat: &'a ast::Pat,
 499                cond: &'a ast::Expr,
 500                block: &'a ast::Block,
 501                label: Option<ast::Ident>)
 502                -> Loop<'a> {
 503         Loop {
 504             cond: Some(cond),
 505             block: block,
 506             label: label,
 507             pat: Some(pat),
 508             keyword: "for ",
 509             matcher: "",
 510             connector: " in",
 511         }
 512     }
 513 }
 514
 515 impl<'a> Rewrite for Loop<'a> {
 516     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 517         let label_string = rewrite_label(self.label);
 518         // 2 = " {".len()
 519         let inner_width = try_opt!(width.checked_sub(self.keyword.len() + 2 + label_string.len()));
 520         let inner_offset = offset + self.keyword.len() + label_string.len();
 521
 522         let pat_expr_string = match self.cond {
 523             Some(cond) => try_opt!(rewrite_pat_expr(context,
 524                                                     self.pat,
 525                                                     cond,
 526                                                     self.matcher,
 527                                                     self.connector,
 528                                                     inner_width,
 529                                                     inner_offset)),
 530             None => String::new(),
 531         };
 532
 533         // FIXME: this drops any comment between "loop" and the block.
 534         self.block
 535             .rewrite(context, width, offset)
 536             .map(|result| {
 537                 format!("{}{}{} {}",
 538                         label_string,
 539                         self.keyword,
 540                         pat_expr_string,
 541                         result)
 542             })
 543     }
 544 }
 545
 546 fn rewrite_label(label: Option<ast::Ident>) -> String {
 547     match label {
 548         Some(ident) => format!("{}: ", ident),
 549         None => "".to_owned(),
 550     }
 551 }
 552
 553 // FIXME: this doesn't play well with line breaks
 554 fn rewrite_range(context: &RewriteContext,
 555                  left: Option<&ast::Expr>,
 556                  right: Option<&ast::Expr>,
 557                  width: usize,
 558                  offset: Indent)
 559                  -> Option<String> {
 560     let left_string = match left {
 561         Some(expr) => {
 562             // 2 = ..
 563             let max_width = try_opt!(width.checked_sub(2));
 564             try_opt!(expr.rewrite(context, max_width, offset))
 565         }
 566         None => String::new(),
 567     };
 568
 569     let right_string = match right {
 570         Some(expr) => {
 571             let max_width = try_opt!(width.checked_sub(left_string.len() + 2));
 572             try_opt!(expr.rewrite(context, max_width, offset + 2 + left_string.len()))
 573         }
 574         None => String::new(),
 575     };
 576
 577     Some(format!("{}..{}", left_string, right_string))
 578 }
 579
 580 // Rewrites if-else blocks. If let Some(_) = pat, the expression is
 581 // treated as an if-let-else expression.
 582 fn rewrite_if_else(context: &RewriteContext,
 583                    cond: &ast::Expr,
 584                    if_block: &ast::Block,
 585                    else_block_opt: Option<&ast::Expr>,
 586                    pat: Option<&ast::Pat>,
 587                    width: usize,
 588                    offset: Indent,
 589                    allow_single_line: bool)
 590                    -> Option<String> {
 591     // 3 = "if ", 2 = " {"
 592     let pat_expr_string = try_opt!(rewrite_pat_expr(context,
 593                                                     pat,
 594                                                     cond,
 595                                                     "let ",
 596                                                     " =",
 597                                                     try_opt!(width.checked_sub(3 + 2)),
 598                                                     offset + 3));
 599
 600     // Try to format if-else on single line.
 601     if allow_single_line && context.config.single_line_if_else {
 602         let trial = single_line_if_else(context,
 603                                         &pat_expr_string,
 604                                         if_block,
 605                                         else_block_opt,
 606                                         width);
 607
 608         if trial.is_some() {
 609             return trial;
 610         }
 611     }
 612
 613     let if_block_string = try_opt!(if_block.rewrite(context, width, offset));
 614     let mut result = format!("if {} {}", pat_expr_string, if_block_string);
 615
 616     if let Some(else_block) = else_block_opt {
 617         let rewrite = match else_block.node {
 618             // If the else expression is another if-else expression, prevent it
 619             // from being formatted on a single line.
 620             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 621                 rewrite_if_else(context,
 622                                 cond,
 623                                 if_block,
 624                                 else_block.as_ref().map(|e| &**e),
 625                                 Some(pat),
 626                                 width,
 627                                 offset,
 628                                 false)
 629             }
 630             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
 631                 rewrite_if_else(context,
 632                                 cond,
 633                                 if_block,
 634                                 else_block.as_ref().map(|e| &**e),
 635                                 None,
 636                                 width,
 637                                 offset,
 638                                 false)
 639             }
 640             _ => else_block.rewrite(context, width, offset),
 641         };
 642
 643         result.push_str(" else ");
 644         result.push_str(&&try_opt!(rewrite));
 645     }
 646
 647     Some(result)
 648 }
 649
 650 fn single_line_if_else(context: &RewriteContext,
 651                        pat_expr_str: &str,
 652                        if_node: &ast::Block,
 653                        else_block_opt: Option<&ast::Expr>,
 654                        width: usize)
 655                        -> Option<String> {
 656     let else_block = try_opt!(else_block_opt);
 657     let fixed_cost = "if  {  } else {  }".len();
 658
 659     if let ast::ExprBlock(ref else_node) = else_block.node {
 660         if !is_simple_block(if_node, context.codemap) ||
 661            !is_simple_block(else_node, context.codemap) || pat_expr_str.contains('\n') {
 662             return None;
 663         }
 664
 665         let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 666         let if_expr = if_node.expr.as_ref().unwrap();
 667         let if_str = try_opt!(if_expr.rewrite(context, new_width, Indent::empty()));
 668
 669         let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 670         let else_expr = else_node.expr.as_ref().unwrap();
 671         let else_str = try_opt!(else_expr.rewrite(context, new_width, Indent::empty()));
 672
 673         // FIXME: this check shouldn't be necessary. Rewrites should either fail
 674         // or wrap to a newline when the object does not fit the width.
 675         let fits_line = fixed_cost + pat_expr_str.len() + if_str.len() + else_str.len() <= width;
 676
 677         if fits_line && !if_str.contains('\n') && !else_str.contains('\n') {
 678             return Some(format!("if {} {{ {} }} else {{ {} }}",
 679                                 pat_expr_str,
 680                                 if_str,
 681                                 else_str));
 682         }
 683     }
 684
 685     None
 686 }
 687
 688 // Checks that a block contains no statements, an expression and no comments.
 689 fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 690     if !block.stmts.is_empty() || block.expr.is_none() {
 691         return false;
 692     }
 693
 694     let snippet = codemap.span_to_snippet(block.span).unwrap();
 695
 696     !contains_comment(&snippet)
 697 }
 698
 699 // inter-match-arm-comment-rules:
 700 //  - all comments following a match arm before the start of the next arm
 701 //    are about the second arm
 702 fn rewrite_match_arm_comment(context: &RewriteContext,
 703                              missed_str: &str,
 704                              width: usize,
 705                              arm_indent: Indent,
 706                              arm_indent_str: &str)
 707                              -> Option<String> {
 708     // The leading "," is not part of the arm-comment
 709     let missed_str = match missed_str.find_uncommented(",") {
 710         Some(n) => &missed_str[n+1..],
 711         None => &missed_str[..],
 712     };
 713
 714     let mut result = String::new();
 715     // any text not preceeded by a newline is pushed unmodified to the block
 716     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
 717     result.push_str(&missed_str[..first_brk]);
 718     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
 719
 720     let first = missed_str.find(|c: char| !c.is_whitespace()).unwrap_or(missed_str.len());
 721     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
 722         // Excessive vertical whitespace before comment should be preserved
 723         // TODO handle vertical whitespace better
 724         result.push('\n');
 725     }
 726     let missed_str = missed_str[first..].trim();
 727     if !missed_str.is_empty() {
 728         let comment = try_opt!(rewrite_comment(&missed_str,
 729                                                false,
 730                                                width,
 731                                                arm_indent,
 732                                                context.config));
 733         result.push('\n');
 734         result.push_str(arm_indent_str);
 735         result.push_str(&comment);
 736     }
 737
 738     Some(result)
 739 }
 740
 741 fn rewrite_match(context: &RewriteContext,
 742                  cond: &ast::Expr,
 743                  arms: &[ast::Arm],
 744                  width: usize,
 745                  offset: Indent,
 746                  span: Span)
 747                  -> Option<String> {
 748     if arms.is_empty() {
 749         return None;
 750     }
 751
 752     // `match `cond` {`
 753     let cond_budget = try_opt!(width.checked_sub(8));
 754     let cond_str = try_opt!(cond.rewrite(context, cond_budget, offset + 6));
 755     let mut result = format!("match {} {{", cond_str);
 756
 757     let nested_context = context.nested_context();
 758     let arm_indent = nested_context.block_indent + context.overflow_indent;
 759     let arm_indent_str = arm_indent.to_string(context.config);
 760
 761     let open_brace_pos = span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])),
 762                                     "{",
 763                                     context.codemap);
 764
 765     for (i, arm) in arms.iter().enumerate() {
 766         // Make sure we get the stuff between arms.
 767         let missed_str = if i == 0 {
 768             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
 769         } else {
 770             context.snippet(mk_sp(arm_end_pos(&arms[i-1]), arm_start_pos(arm)))
 771         };
 772         let comment = try_opt!(rewrite_match_arm_comment(context,
 773                                                          &missed_str,
 774                                                          width,
 775                                                          arm_indent,
 776                                                          &arm_indent_str));
 777         result.push_str(&comment);
 778         result.push('\n');
 779         result.push_str(&arm_indent_str);
 780
 781         let arm_str = arm.rewrite(&nested_context,
 782                                   context.config.max_width - arm_indent.width(),
 783                                   arm_indent);
 784         if let Some(ref arm_str) = arm_str {
 785             result.push_str(arm_str);
 786         } else {
 787             // We couldn't format the arm, just reproduce the source.
 788             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
 789             result.push_str(&snippet);
 790         }
 791     }
 792     // BytePos(1) = closing match brace.
 793     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]),
 794                           span.hi - BytePos(1));
 795     let last_comment = context.snippet(last_span);
 796     let comment = try_opt!(rewrite_match_arm_comment(context,
 797                                                      &last_comment,
 798                                                      width,
 799                                                      arm_indent,
 800                                                      &arm_indent_str));
 801     result.push_str(&comment);
 802     result.push('\n');
 803     result.push_str(&(context.block_indent + context.overflow_indent).to_string(context.config));
 804     result.push('}');
 805     Some(result)
 806 }
 807
 808 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
 809     let &ast::Arm { ref attrs, ref pats, .. } = arm;
 810     if !attrs.is_empty() {
 811         return attrs[0].span.lo
 812     }
 813
 814     pats[0].span.lo
 815 }
 816
 817 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
 818     arm.body.span.hi
 819 }
 820
 821 // Match arms.
 822 impl Rewrite for ast::Arm {
 823     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 824         let &ast::Arm { ref attrs, ref pats, ref guard, ref body } = self;
 825         let indent_str = offset.to_string(context.config);
 826
 827         // FIXME this is all a bit grotty, would be nice to abstract out the
 828         // treatment of attributes.
 829         let attr_str = if !attrs.is_empty() {
 830             // We only use this visitor for the attributes, should we use it for
 831             // more?
 832             let mut attr_visitor = FmtVisitor::from_codemap(context.codemap, context.config);
 833             attr_visitor.block_indent = context.block_indent;
 834             attr_visitor.last_pos = attrs[0].span.lo;
 835             if attr_visitor.visit_attrs(attrs) {
 836                 // Attributes included a skip instruction.
 837                 let snippet = context.snippet(mk_sp(attrs[0].span.lo, body.span.hi));
 838                 return Some(snippet);
 839             }
 840             attr_visitor.format_missing(pats[0].span.lo);
 841             attr_visitor.buffer.to_string()
 842         } else {
 843             String::new()
 844         };
 845
 846         // Patterns
 847         // 5 = ` => {`
 848         let pat_budget = try_opt!(width.checked_sub(5));
 849         let pat_strs = try_opt!(pats.iter()
 850                                     .map(|p| {
 851                                         p.rewrite(context,
 852                                                   pat_budget,
 853                                                   offset.block_indent(context.config))
 854                                     })
 855                                     .collect::<Option<Vec<_>>>());
 856
 857         let mut total_width = pat_strs.iter().fold(0, |a, p| a + p.len());
 858         // Add ` | `.len().
 859         total_width += (pat_strs.len() - 1) * 3;
 860
 861         let mut vertical = total_width > pat_budget || pat_strs.iter().any(|p| p.contains('\n'));
 862         if !vertical && context.config.take_source_hints {
 863             // If the patterns were previously stacked, keep them stacked.
 864             let pat_span = mk_sp(pats[0].span.lo, pats[pats.len() - 1].span.hi);
 865             let pat_str = context.snippet(pat_span);
 866             vertical = pat_str.find('\n').is_some();
 867         }
 868
 869         let pats_width = if vertical {
 870             pat_strs[pat_strs.len() - 1].len()
 871         } else {
 872             total_width
 873         };
 874
 875         let mut pats_str = String::new();
 876         for p in pat_strs {
 877             if !pats_str.is_empty() {
 878                 if vertical {
 879                     pats_str.push_str(" |\n");
 880                     pats_str.push_str(&indent_str);
 881                 } else {
 882                     pats_str.push_str(" | ");
 883                 }
 884             }
 885             pats_str.push_str(&p);
 886         }
 887
 888         let guard_str = try_opt!(rewrite_guard(context, guard, width, offset, pats_width));
 889
 890         let pats_str = format!("{}{}", pats_str, guard_str);
 891         // Where the next text can start.
 892         let mut line_start = last_line_width(&pats_str);
 893         if !pats_str.contains('\n') {
 894             line_start += offset.width();
 895         }
 896
 897         let comma = if let ast::ExprBlock(_) = body.node {
 898             ""
 899         } else {
 900             ","
 901         };
 902
 903         // Let's try and get the arm body on the same line as the condition.
 904         // 4 = ` => `.len()
 905         let same_line_body = if context.config.max_width > line_start + comma.len() + 4 {
 906             let budget = context.config.max_width - line_start - comma.len() - 4;
 907             let offset = Indent::new(offset.block_indent,
 908                                      line_start + 4 - offset.block_indent);
 909             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
 910
 911             match rewrite {
 912                 Some(ref body_str) if body_str.len() <= budget || comma.is_empty() =>
 913                     return Some(format!("{}{} => {}{}",
 914                                         attr_str.trim_left(),
 915                                         pats_str,
 916                                         body_str,
 917                                         comma)),
 918                 _ => rewrite,
 919             }
 920         } else {
 921             None
 922         };
 923
 924         if let ast::ExprBlock(_) = body.node {
 925             // We're trying to fit a block in, but it still failed, give up.
 926             return None;
 927         }
 928
 929         let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
 930         let next_line_body = nop_block_collapse(body.rewrite(context,
 931                                                              body_budget,
 932                                                              context.block_indent
 933                                                                     .block_indent(context.config)),
 934                                                 body_budget);
 935
 936         let body_str = try_opt!(match_arm_heuristic(same_line_body.as_ref().map(|x| &x[..]),
 937                                                     next_line_body.as_ref().map(|x| &x[..])));
 938
 939         let spacer = match same_line_body {
 940             Some(ref body) if body == body_str => " ".to_owned(),
 941             _ => format!("\n{}",
 942                          offset.block_indent(context.config).to_string(context.config)),
 943         };
 944
 945         Some(format!("{}{} =>{}{},",
 946                      attr_str.trim_left(),
 947                      pats_str,
 948                      spacer,
 949                      body_str))
 950     }
 951 }
 952
 953 // Takes two possible rewrites for the match arm body and chooses the "nicest".
 954 fn match_arm_heuristic<'a>(former: Option<&'a str>, latter: Option<&'a str>) -> Option<&'a str> {
 955     match (former, latter) {
 956         (f @ Some(..), None) => f,
 957         (Some(f), Some(l)) if f.chars().filter(|&c| c == '\n').count() <=
 958                               l.chars().filter(|&c| c == '\n').count() => {
 959             Some(f)
 960         }
 961         (_, l) => l,
 962     }
 963 }
 964
 965 // The `if ...` guard on a match arm.
 966 fn rewrite_guard(context: &RewriteContext,
 967                  guard: &Option<ptr::P<ast::Expr>>,
 968                  width: usize,
 969                  offset: Indent,
 970                  // The amount of space used up on this line for the pattern in
 971                  // the arm (excludes offset).
 972                  pattern_width: usize)
 973                  -> Option<String> {
 974     if let &Some(ref guard) = guard {
 975         // First try to fit the guard string on the same line as the pattern.
 976         // 4 = ` if `, 5 = ` => {`
 977         let overhead = pattern_width + 4 + 5;
 978         if overhead < width {
 979             let cond_str = guard.rewrite(context, width - overhead, offset + pattern_width + 4);
 980             if let Some(cond_str) = cond_str {
 981                 return Some(format!(" if {}", cond_str));
 982             }
 983         }
 984
 985         // Not enough space to put the guard after the pattern, try a newline.
 986         let overhead = context.config.tab_spaces + 4 + 5;
 987         if overhead < width {
 988             let cond_str = guard.rewrite(context,
 989                                          width - overhead,
 990                                          offset.block_indent(context.config));
 991             if let Some(cond_str) = cond_str {
 992                 return Some(format!("\n{}if {}",
 993                                     offset.block_indent(context.config).to_string(context.config),
 994                                     cond_str));
 995             }
 996         }
 997
 998         None
 999     } else {
1000         Some(String::new())
1001     }
1002 }
1003
1004 fn rewrite_pat_expr(context: &RewriteContext,
1005                     pat: Option<&ast::Pat>,
1006                     expr: &ast::Expr,
1007                     matcher: &str,
1008                     // Connecting piece between pattern and expression,
1009                     // *without* trailing space.
1010                     connector: &str,
1011                     width: usize,
1012                     offset: Indent)
1013                     -> Option<String> {
1014     let pat_offset = offset + matcher.len();
1015     let mut result = match pat {
1016         Some(pat) => {
1017             let pat_budget = try_opt!(width.checked_sub(connector.len() + matcher.len()));
1018             let pat_string = try_opt!(pat.rewrite(context, pat_budget, pat_offset));
1019             format!("{}{}{}", matcher, pat_string, connector)
1020         }
1021         None => String::new(),
1022     };
1023
1024     // Consider only the last line of the pat string.
1025     let extra_offset = extra_offset(&result, offset);
1026
1027     // The expression may (partionally) fit on the current line.
1028     if width > extra_offset + 1 {
1029         let spacer = if pat.is_some() {
1030             " "
1031         } else {
1032             ""
1033         };
1034
1035         let expr_rewrite = expr.rewrite(context,
1036                                         width - extra_offset - spacer.len(),
1037                                         offset + extra_offset + spacer.len());
1038
1039         if let Some(expr_string) = expr_rewrite {
1040             result.push_str(spacer);
1041             result.push_str(&expr_string);
1042             return Some(result);
1043         }
1044     }
1045
1046     // The expression won't fit on the current line, jump to next.
1047     result.push('\n');
1048     result.push_str(&pat_offset.to_string(context.config));
1049
1050     let expr_rewrite = expr.rewrite(context,
1051                                     context.config.max_width - pat_offset.width(),
1052                                     pat_offset);
1053     result.push_str(&&try_opt!(expr_rewrite));
1054
1055     Some(result)
1056 }
1057
1058 fn rewrite_string_lit(context: &RewriteContext,
1059                       span: Span,
1060                       width: usize,
1061                       offset: Indent)
1062                       -> Option<String> {
1063     if !context.config.format_strings {
1064         return Some(context.snippet(span));
1065     }
1066
1067     let fmt = StringFormat {
1068         opener: "\"",
1069         closer: "\"",
1070         line_start: " ",
1071         line_end: "\\",
1072         width: width,
1073         offset: offset,
1074         trim_end: false,
1075         config: context.config,
1076     };
1077
1078     let string_lit = context.snippet(span);
1079     let str_lit = &string_lit[1..string_lit.len() - 1]; // Remove the quote characters.
1080
1081     rewrite_string(str_lit, &fmt)
1082 }
1083
1084 pub fn rewrite_call<R>(context: &RewriteContext,
1085                        callee: &R,
1086                        args: &[ptr::P<ast::Expr>],
1087                        span: Span,
1088                        width: usize,
1089                        offset: Indent)
1090                        -> Option<String>
1091     where R: Rewrite
1092 {
1093     let closure = |callee_max_width| {
1094         rewrite_call_inner(context,
1095                            callee,
1096                            callee_max_width,
1097                            args,
1098                            span,
1099                            width,
1100                            offset)
1101     };
1102
1103     // 2 is for parens
1104     let max_width = try_opt!(width.checked_sub(2));
1105     binary_search(1, max_width, closure)
1106 }
1107
1108 fn rewrite_call_inner<R>(context: &RewriteContext,
1109                          callee: &R,
1110                          max_callee_width: usize,
1111                          args: &[ptr::P<ast::Expr>],
1112                          span: Span,
1113                          width: usize,
1114                          offset: Indent)
1115                          -> Result<String, Ordering>
1116     where R: Rewrite
1117 {
1118     let callee = callee.borrow();
1119     // FIXME using byte lens instead of char lens (and probably all over the
1120     // place too)
1121     let callee_str = match callee.rewrite(context, max_callee_width, offset) {
1122         Some(string) => {
1123             if !string.contains('\n') && string.len() > max_callee_width {
1124                 panic!("{:?} {}", string, max_callee_width);
1125             } else {
1126                 string
1127             }
1128         }
1129         None => return Err(Ordering::Greater),
1130     };
1131
1132     let span_lo = span_after(span, "(", context.codemap);
1133     let span = mk_sp(span_lo, span.hi);
1134
1135     let extra_offset = extra_offset(&callee_str, offset);
1136     // 2 is for parens.
1137     let remaining_width = match width.checked_sub(extra_offset + 2) {
1138         Some(str) => str,
1139         None => return Err(Ordering::Greater),
1140     };
1141     let offset = offset + extra_offset + 1;
1142     let block_indent = if args.len() == 1 {
1143         context.block_indent
1144     } else {
1145         offset
1146     };
1147     let inner_context = &RewriteContext { block_indent: block_indent, ..*context };
1148
1149     let items = itemize_list(context.codemap,
1150                              args.iter(),
1151                              ")",
1152                              |item| item.span.lo,
1153                              |item| item.span.hi,
1154                              // Take old span when rewrite fails.
1155                              |item| {
1156                                  item.rewrite(&inner_context, remaining_width, offset)
1157                                      .unwrap_or(context.snippet(item.span))
1158                              },
1159                              span.lo,
1160                              span.hi);
1161
1162     let list_str = match ::lists::format_fn_args(items, remaining_width, offset, context.config) {
1163         Some(str) => str,
1164         None => return Err(Ordering::Less),
1165     };
1166
1167     Ok(format!("{}({})", callee_str, list_str))
1168 }
1169
1170 fn rewrite_paren(context: &RewriteContext,
1171                  subexpr: &ast::Expr,
1172                  width: usize,
1173                  offset: Indent)
1174                  -> Option<String> {
1175     debug!("rewrite_paren, width: {}, offset: {:?}", width, offset);
1176     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1177     // paren on the same line as the subexpr.
1178     let subexpr_str = subexpr.rewrite(context, try_opt!(width.checked_sub(2)), offset + 1);
1179     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1180     subexpr_str.map(|s| format!("({})", s))
1181 }
1182
1183 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1184                           path: &ast::Path,
1185                           fields: &'a [ast::Field],
1186                           base: Option<&'a ast::Expr>,
1187                           span: Span,
1188                           width: usize,
1189                           offset: Indent)
1190                           -> Option<String> {
1191     debug!("rewrite_struct_lit: width {}, offset {:?}",
1192            width,
1193            offset);
1194     assert!(!fields.is_empty() || base.is_some());
1195
1196     enum StructLitField<'a> {
1197         Regular(&'a ast::Field),
1198         Base(&'a ast::Expr),
1199     }
1200
1201     // 2 = " {".len()
1202     let path_budget = try_opt!(width.checked_sub(2));
1203     let path_str = try_opt!(path.rewrite(context, path_budget, offset));
1204
1205     // Foo { a: Foo } - indent is +3, width is -5.
1206     let h_budget = width.checked_sub(path_str.len() + 5).unwrap_or(0);
1207     let (indent, v_budget) = match context.config.struct_lit_style {
1208         StructLitStyle::Visual => {
1209             (offset + path_str.len() + 3, h_budget)
1210         }
1211         StructLitStyle::Block => {
1212             // If we are all on one line, then we'll ignore the indent, and we
1213             // have a smaller budget.
1214             let indent = context.block_indent.block_indent(context.config);
1215             let v_budget = context.config.max_width.checked_sub(indent.width()).unwrap_or(0);
1216             (indent, v_budget)
1217         }
1218     };
1219
1220     let field_iter = fields.into_iter()
1221                            .map(StructLitField::Regular)
1222                            .chain(base.into_iter().map(StructLitField::Base));
1223
1224     let inner_context = &RewriteContext { block_indent: indent, ..*context };
1225
1226     let items = itemize_list(context.codemap,
1227                              field_iter,
1228                              "}",
1229                              |item| {
1230                                  match *item {
1231                                      StructLitField::Regular(ref field) => field.span.lo,
1232                                      StructLitField::Base(ref expr) => {
1233                                          let last_field_hi = fields.last().map_or(span.lo,
1234                                                                                   |field| {
1235                                                                                       field.span.hi
1236                                                                                   });
1237                                          let snippet = context.snippet(mk_sp(last_field_hi,
1238                                                                              expr.span.lo));
1239                                          let pos = snippet.find_uncommented("..").unwrap();
1240                                          last_field_hi + BytePos(pos as u32)
1241                                      }
1242                                  }
1243                              },
1244                              |item| {
1245                                  match *item {
1246                                      StructLitField::Regular(ref field) => field.span.hi,
1247                                      StructLitField::Base(ref expr) => expr.span.hi,
1248                                  }
1249                              },
1250                              |item| {
1251                                  match *item {
1252                                      StructLitField::Regular(ref field) => {
1253                                          rewrite_field(inner_context, &field, v_budget, indent)
1254                                              .unwrap_or(context.snippet(field.span))
1255                                      }
1256                                      StructLitField::Base(ref expr) => {
1257                                          // 2 = ..
1258                                          format!("..{}",
1259                                                  v_budget.checked_sub(2)
1260                                                          .and_then(|v_budget| {
1261                                                              expr.rewrite(inner_context,
1262                                                                           v_budget,
1263                                                                           indent + 2)
1264                                                          })
1265                                                          .unwrap_or(context.snippet(expr.span)))
1266                                      }
1267                                  }
1268                              },
1269                              span_after(span, "{", context.codemap),
1270                              span.hi);
1271     let item_vec = items.collect::<Vec<_>>();
1272
1273     let tactic = {
1274         let mut prelim_tactic = match (context.config.struct_lit_style, fields.len()) {
1275             (StructLitStyle::Visual, 1) => ListTactic::HorizontalVertical,
1276             _ => context.config.struct_lit_multiline_style.to_list_tactic(),
1277         };
1278
1279         if prelim_tactic == ListTactic::HorizontalVertical && fields.len() > 1 {
1280             prelim_tactic = ListTactic::LimitedHorizontalVertical(context.config.struct_lit_width);
1281         };
1282
1283         definitive_tactic(&item_vec, prelim_tactic, h_budget)
1284     };
1285
1286     let budget = match tactic {
1287         DefinitiveListTactic::Horizontal => h_budget,
1288         _ => v_budget,
1289     };
1290
1291     let fmt = ListFormatting {
1292         tactic: tactic,
1293         separator: ",",
1294         trailing_separator: if base.is_some() {
1295             SeparatorTactic::Never
1296         } else {
1297             context.config.struct_lit_trailing_comma
1298         },
1299         indent: indent,
1300         width: budget,
1301         ends_with_newline: false,
1302         config: context.config,
1303     };
1304     let fields_str = try_opt!(write_list(&item_vec, &fmt));
1305
1306     let format_on_newline = || {
1307         let inner_indent = context.block_indent
1308                                   .block_indent(context.config)
1309                                   .to_string(context.config);
1310         let outer_indent = context.block_indent.to_string(context.config);
1311         Some(format!("{} {{\n{}{}\n{}}}",
1312                      path_str,
1313                      inner_indent,
1314                      fields_str,
1315                      outer_indent))
1316     };
1317
1318     match (context.config.struct_lit_style,
1319            context.config.struct_lit_multiline_style) {
1320         (StructLitStyle::Block, _) if fields_str.contains('\n') || fields_str.len() > h_budget =>
1321             format_on_newline(),
1322         (StructLitStyle::Block, MultilineStyle::ForceMulti) => format_on_newline(),
1323         _ => Some(format!("{} {{ {} }}", path_str, fields_str)),
1324     }
1325
1326     // FIXME if context.config.struct_lit_style == Visual, but we run out
1327     // of space, we should fall back to BlockIndent.
1328 }
1329
1330 fn rewrite_field(context: &RewriteContext,
1331                  field: &ast::Field,
1332                  width: usize,
1333                  offset: Indent)
1334                  -> Option<String> {
1335     let name = &field.ident.node.to_string();
1336     let overhead = name.len() + 2;
1337     let expr = field.expr.rewrite(context,
1338                                   try_opt!(width.checked_sub(overhead)),
1339                                   offset + overhead);
1340     expr.map(|s| format!("{}: {}", name, s))
1341 }
1342
1343 fn rewrite_tuple_lit(context: &RewriteContext,
1344                      items: &[ptr::P<ast::Expr>],
1345                      span: Span,
1346                      width: usize,
1347                      offset: Indent)
1348                      -> Option<String> {
1349     debug!("rewrite_tuple_lit: width: {}, offset: {:?}",
1350            width,
1351            offset);
1352     let indent = offset + 1;
1353     // In case of length 1, need a trailing comma
1354     if items.len() == 1 {
1355         // 3 = "(" + ",)"
1356         let budget = try_opt!(width.checked_sub(3));
1357         return items[0].rewrite(context, budget, indent).map(|s| format!("({},)", s));
1358     }
1359
1360     let items = itemize_list(context.codemap,
1361                              items.iter(),
1362                              ")",
1363                              |item| item.span.lo,
1364                              |item| item.span.hi,
1365                              |item| {
1366                                  let inner_width = context.config.max_width - indent.width() - 1;
1367                                  item.rewrite(context, inner_width, indent)
1368                                      .unwrap_or(context.snippet(item.span))
1369                              },
1370                              span.lo + BytePos(1), // Remove parens
1371                              span.hi - BytePos(1));
1372     let budget = try_opt!(width.checked_sub(2));
1373     let list_str = try_opt!(::lists::format_fn_args(items, budget, indent, context.config));
1374
1375     Some(format!("({})", list_str))
1376 }
1377
1378 fn rewrite_binary_op(context: &RewriteContext,
1379                      op: &ast::BinOp,
1380                      lhs: &ast::Expr,
1381                      rhs: &ast::Expr,
1382                      width: usize,
1383                      offset: Indent)
1384                      -> Option<String> {
1385     // FIXME: format comments between operands and operator
1386
1387     let operator_str = context.snippet(op.span);
1388
1389     // Get "full width" rhs and see if it fits on the current line. This
1390     // usually works fairly well since it tends to place operands of
1391     // operations with high precendence close together.
1392     let rhs_result = try_opt!(rhs.rewrite(context, width, offset));
1393
1394     // Second condition is needed in case of line break not caused by a
1395     // shortage of space, but by end-of-line comments, for example.
1396     // Note that this is non-conservative, but its just to see if it's even
1397     // worth trying to put everything on one line.
1398     if rhs_result.len() + 2 + operator_str.len() < width && !rhs_result.contains('\n') {
1399         // 1 = space between lhs expr and operator
1400         if let Some(mut result) = lhs.rewrite(context, width - 1 - operator_str.len(), offset) {
1401             result.push(' ');
1402             result.push_str(&operator_str);
1403             result.push(' ');
1404
1405             let remaining_width = width.checked_sub(last_line_width(&result)).unwrap_or(0);
1406
1407             if rhs_result.len() <= remaining_width {
1408                 result.push_str(&rhs_result);
1409                 return Some(result);
1410             }
1411
1412             if let Some(rhs_result) = rhs.rewrite(context, remaining_width, offset + result.len()) {
1413                 if rhs_result.len() <= remaining_width {
1414                     result.push_str(&rhs_result);
1415                     return Some(result);
1416                 }
1417             }
1418         }
1419     }
1420
1421     // We have to use multiple lines.
1422
1423     // Re-evaluate the lhs because we have more space now:
1424     let budget = try_opt!(context.config
1425                                  .max_width
1426                                  .checked_sub(offset.width() + 1 + operator_str.len()));
1427     Some(format!("{} {}\n{}{}",
1428                  try_opt!(lhs.rewrite(context, budget, offset)),
1429                  operator_str,
1430                  offset.to_string(context.config),
1431                  rhs_result))
1432 }
1433
1434 fn rewrite_unary_prefix(context: &RewriteContext,
1435                         prefix: &str,
1436                         expr: &ast::Expr,
1437                         width: usize,
1438                         offset: Indent)
1439                         -> Option<String> {
1440     expr.rewrite(context,
1441                  try_opt!(width.checked_sub(prefix.len())),
1442                  offset + prefix.len())
1443         .map(|r| format!("{}{}", prefix, r))
1444 }
1445
1446 fn rewrite_unary_op(context: &RewriteContext,
1447                     op: &ast::UnOp,
1448                     expr: &ast::Expr,
1449                     width: usize,
1450                     offset: Indent)
1451                     -> Option<String> {
1452     // For some reason, an UnOp is not spanned like BinOp!
1453     let operator_str = match *op {
1454         ast::UnOp::UnDeref => "*",
1455         ast::UnOp::UnNot => "!",
1456         ast::UnOp::UnNeg => "-",
1457     };
1458     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1459 }
1460
1461 fn rewrite_assignment(context: &RewriteContext,
1462                       lhs: &ast::Expr,
1463                       rhs: &ast::Expr,
1464                       op: Option<&ast::BinOp>,
1465                       width: usize,
1466                       offset: Indent)
1467                       -> Option<String> {
1468     let operator_str = match op {
1469         Some(op) => context.snippet(op.span),
1470         None => "=".to_owned(),
1471     };
1472
1473     // 1 = space between lhs and operator.
1474     let max_width = try_opt!(width.checked_sub(operator_str.len() + 1));
1475     let lhs_str = format!("{} {}",
1476                           try_opt!(lhs.rewrite(context, max_width, offset)),
1477                           operator_str);
1478
1479     rewrite_assign_rhs(&context, lhs_str, rhs, width, offset)
1480 }
1481
1482 // The left hand side must contain everything up to, and including, the
1483 // assignment operator.
1484 pub fn rewrite_assign_rhs<S: Into<String>>(context: &RewriteContext,
1485                                            lhs: S,
1486                                            ex: &ast::Expr,
1487                                            width: usize,
1488                                            offset: Indent)
1489                                            -> Option<String> {
1490     let mut result = lhs.into();
1491
1492     // 1 = space between operator and rhs.
1493     let max_width = try_opt!(width.checked_sub(result.len() + 1));
1494     let rhs = ex.rewrite(&context, max_width, offset + result.len() + 1);
1495
1496     match rhs {
1497         Some(new_str) => {
1498             result.push(' ');
1499             result.push_str(&new_str)
1500         }
1501         None => {
1502             // Expression did not fit on the same line as the identifier. Retry
1503             // on the next line.
1504             let new_offset = offset.block_indent(context.config);
1505             result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1506
1507             // FIXME: we probably should related max_width to width instead of config.max_width
1508             // where is the 1 coming from anyway?
1509             let max_width = try_opt!(context.config.max_width.checked_sub(new_offset.width() + 1));
1510             let rhs_indent = Indent::new(context.config.tab_spaces, 0);
1511             let overflow_context = context.overflow_context(rhs_indent);
1512             let rhs = ex.rewrite(&overflow_context, max_width, new_offset);
1513
1514             result.push_str(&&try_opt!(rhs));
1515         }
1516     }
1517
1518     Some(result)
1519 }
1520
1521 fn rewrite_expr_addrof(context: &RewriteContext,
1522                        mutability: ast::Mutability,
1523                        expr: &ast::Expr,
1524                        width: usize,
1525                        offset: Indent)
1526                        -> Option<String> {
1527     let operator_str = match mutability {
1528         ast::Mutability::MutImmutable => "&",
1529         ast::Mutability::MutMutable => "&mut ",
1530     };
1531     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1532 }