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 use string::{StringFormat, rewrite_string};
  18 use utils::{span_after, extra_offset, last_line_width, wrap_str, binary_search};
  19 use visitor::FmtVisitor;
  20 use config::{StructLitStyle, MultilineStyle};
  21 use comment::{FindUncommented, rewrite_comment, contains_comment};
  22 use types::rewrite_path;
  23 use items::{span_lo_for_arg, span_hi_for_arg};
  24 use chains::rewrite_chain;
  25 use macros::rewrite_macro;
  26
  27 use syntax::{ast, ptr};
  28 use syntax::codemap::{CodeMap, Span, BytePos, mk_sp};
  29 use syntax::visit::Visitor;
  30
  31 impl Rewrite for ast::Expr {
  32     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  33         match self.node {
  34             ast::Expr_::ExprVec(ref expr_vec) => {
  35                 rewrite_array(expr_vec.iter().map(|e| &**e),
  36                               self.span,
  37                               context,
  38                               width,
  39                               offset)
  40             }
  41             ast::Expr_::ExprLit(ref l) => {
  42                 match l.node {
  43                     ast::Lit_::LitStr(_, ast::StrStyle::CookedStr) => {
  44                         rewrite_string_lit(context, l.span, width, offset)
  45                     }
  46                     _ => {
  47                         wrap_str(context.snippet(self.span),
  48                                  context.config.max_width,
  49                                  width,
  50                                  offset)
  51                     }
  52                 }
  53             }
  54             ast::Expr_::ExprCall(ref callee, ref args) => {
  55                 let inner_span = mk_sp(callee.span.hi, self.span.hi);
  56                 rewrite_call(context, &**callee, args, inner_span, width, offset)
  57             }
  58             ast::Expr_::ExprParen(ref subexpr) => {
  59                 rewrite_paren(context, subexpr, width, offset)
  60             }
  61             ast::Expr_::ExprBinary(ref op, ref lhs, ref rhs) => {
  62                 rewrite_binary_op(context, op, lhs, rhs, width, offset)
  63             }
  64             ast::Expr_::ExprUnary(ref op, ref subexpr) => {
  65                 rewrite_unary_op(context, op, subexpr, width, offset)
  66             }
  67             ast::Expr_::ExprStruct(ref path, ref fields, ref base) => {
  68                 rewrite_struct_lit(context,
  69                                    path,
  70                                    fields,
  71                                    base.as_ref().map(|e| &**e),
  72                                    self.span,
  73                                    width,
  74                                    offset)
  75             }
  76             ast::Expr_::ExprTup(ref items) => {
  77                 rewrite_tuple_lit(context, items, self.span, width, offset)
  78             }
  79             ast::Expr_::ExprWhile(ref cond, ref block, label) => {
  80                 Loop::new_while(None, cond, block, label).rewrite(context, width, offset)
  81             }
  82             ast::Expr_::ExprWhileLet(ref pat, ref cond, ref block, label) => {
  83                 Loop::new_while(Some(pat), cond, block, label).rewrite(context, width, offset)
  84             }
  85             ast::Expr_::ExprForLoop(ref pat, ref cond, ref block, label) => {
  86                 Loop::new_for(pat, cond, block, label).rewrite(context, width, offset)
  87             }
  88             ast::Expr_::ExprLoop(ref block, label) => {
  89                 Loop::new_loop(block, label).rewrite(context, width, offset)
  90             }
  91             ast::Expr_::ExprBlock(ref block) => {
  92                 block.rewrite(context, width, offset)
  93             }
  94             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
  95                 rewrite_if_else(context,
  96                                 cond,
  97                                 if_block,
  98                                 else_block.as_ref().map(|e| &**e),
  99                                 None,
 100                                 width,
 101                                 offset,
 102                                 true)
 103             }
 104             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 105                 rewrite_if_else(context,
 106                                 cond,
 107                                 if_block,
 108                                 else_block.as_ref().map(|e| &**e),
 109                                 Some(pat),
 110                                 width,
 111                                 offset,
 112                                 true)
 113             }
 114             // We reformat it ourselves because rustc gives us a bad span
 115             // for ranges, see rust#27162
 116             ast::Expr_::ExprRange(ref left, ref right) => {
 117                 rewrite_range(context,
 118                               left.as_ref().map(|e| &**e),
 119                               right.as_ref().map(|e| &**e),
 120                               width,
 121                               offset)
 122             }
 123             ast::Expr_::ExprMatch(ref cond, ref arms, _) => {
 124                 rewrite_match(context, cond, arms, width, offset, self.span)
 125             }
 126             ast::Expr_::ExprPath(ref qself, ref path) => {
 127                 rewrite_path(context, qself.as_ref(), path, width, offset)
 128             }
 129             ast::Expr_::ExprAssign(ref lhs, ref rhs) => {
 130                 rewrite_assignment(context, lhs, rhs, None, width, offset)
 131             }
 132             ast::Expr_::ExprAssignOp(ref op, ref lhs, ref rhs) => {
 133                 rewrite_assignment(context, lhs, rhs, Some(op), width, offset)
 134             }
 135             ast::Expr_::ExprAgain(ref opt_ident) => {
 136                 let id_str = match *opt_ident {
 137                     Some(ident) => format!(" {}", ident.node),
 138                     None => String::new(),
 139                 };
 140                 Some(format!("continue{}", id_str))
 141             }
 142             ast::Expr_::ExprBreak(ref opt_ident) => {
 143                 let id_str = match *opt_ident {
 144                     Some(ident) => format!(" {}", ident.node),
 145                     None => String::new(),
 146                 };
 147                 Some(format!("break{}", id_str))
 148             }
 149             ast::Expr_::ExprClosure(capture, ref fn_decl, ref body) => {
 150                 rewrite_closure(capture, fn_decl, body, self.span, context, width, offset)
 151             }
 152             ast::Expr_::ExprField(..) |
 153             ast::Expr_::ExprTupField(..) |
 154             ast::Expr_::ExprMethodCall(..) => {
 155                 rewrite_chain(self, context, width, offset)
 156             }
 157             ast::Expr_::ExprMac(ref mac) => {
 158                 // Failure to rewrite a marco should not imply failure to
 159                 // rewrite the expression.
 160                 rewrite_macro(mac, context, width, offset).or_else(|| {
 161                     wrap_str(context.snippet(self.span),
 162                              context.config.max_width,
 163                              width,
 164                              offset)
 165                 })
 166             }
 167             ast::Expr_::ExprRet(None) => {
 168                 wrap_str("return".to_owned(),
 169                          context.config.max_width,
 170                          width,
 171                          offset)
 172             }
 173             ast::Expr_::ExprRet(Some(ref expr)) => {
 174                 rewrite_unary_prefix(context, "return ", expr, width, offset)
 175             }
 176             ast::Expr_::ExprBox(ref expr) => {
 177                 rewrite_unary_prefix(context, "box ", expr, width, offset)
 178             }
 179             ast::Expr_::ExprAddrOf(mutability, ref expr) => {
 180                 rewrite_expr_addrof(context, mutability, expr, width, offset)
 181             }
 182             ast::Expr_::ExprCast(ref expr, ref ty) => {
 183                 rewrite_cast(expr, ty, context, width, offset)
 184             }
 185             // We do not format these expressions yet, but they should still
 186             // satisfy our width restrictions.
 187             ast::Expr_::ExprInPlace(..) |
 188             ast::Expr_::ExprIndex(..) |
 189             ast::Expr_::ExprInlineAsm(..) |
 190             ast::Expr_::ExprRepeat(..) => {
 191                 wrap_str(context.snippet(self.span),
 192                          context.config.max_width,
 193                          width,
 194                          offset)
 195             }
 196         }
 197     }
 198 }
 199
 200 fn rewrite_cast(expr: &ast::Expr,
 201                 ty: &ast::Ty,
 202                 context: &RewriteContext,
 203                 width: usize,
 204                 offset: Indent)
 205                 -> Option<String> {
 206     let max_width = try_opt!(width.checked_sub(" as ".len()));
 207
 208     binary_search(1,
 209                   max_width,
 210                   |expr_budget| {
 211                       let expr_str = match expr.rewrite(context, expr_budget, offset) {
 212                           Some(result) => result,
 213                           None => return Err(Ordering::Greater),
 214                       };
 215
 216                       let last_line_width = last_line_width(&expr_str);
 217                       let ty_budget = match max_width.checked_sub(last_line_width) {
 218                           Some(b) => b,
 219                           None => return Err(Ordering::Less),
 220                       };
 221                       let ty_indent = offset + last_line_width;
 222
 223                       let ty_str = match ty.rewrite(context, ty_budget, ty_indent) {
 224                           Some(result) => result,
 225                           None => return Err(Ordering::Less),
 226                       };
 227
 228                       Ok(format!("{} as {}", expr_str, ty_str))
 229                   })
 230 }
 231
 232 pub fn rewrite_array<'a, I>(expr_iter: I,
 233                             span: Span,
 234                             context: &RewriteContext,
 235                             width: usize,
 236                             offset: Indent)
 237                             -> Option<String>
 238     where I: Iterator<Item = &'a ast::Expr>
 239 {
 240     // 2 for brackets;
 241     let max_item_width = try_opt!(width.checked_sub(2));
 242     let items = itemize_list(context.codemap,
 243                              expr_iter,
 244                              "]",
 245                              |item| item.span.lo,
 246                              |item| item.span.hi,
 247                              // 1 = [
 248                              // FIXME(#133): itemize_list doesn't support
 249                              // rewrite failure. This may not be its
 250                              // responsibility, but that of write_list.
 251                              |item| {
 252                                  item.rewrite(context, max_item_width, offset + 1)
 253                                      .unwrap_or_else(|| context.snippet(item.span))
 254                              },
 255                              span_after(span, "[", context.codemap),
 256                              span.hi)
 257                     .collect::<Vec<_>>();
 258
 259     let tactic = if items.iter().any(|li| li.item.len() > 10 || li.is_multiline()) {
 260         ListTactic::HorizontalVertical
 261     } else {
 262         ListTactic::Mixed
 263     };
 264
 265     let fmt = ListFormatting {
 266         tactic: tactic,
 267         separator: ",",
 268         trailing_separator: SeparatorTactic::Never,
 269         indent: offset + 1,
 270         h_width: max_item_width,
 271         v_width: max_item_width,
 272         ends_with_newline: false,
 273         config: context.config,
 274     };
 275     let list_str = try_opt!(write_list(&items, &fmt));
 276
 277     Some(format!("[{}]", list_str))
 278 }
 279
 280 // This functions is pretty messy because of the wrapping and unwrapping of
 281 // expressions into and from blocks. See rust issue #27872.
 282 fn rewrite_closure(capture: ast::CaptureClause,
 283                    fn_decl: &ast::FnDecl,
 284                    body: &ast::Block,
 285                    span: Span,
 286                    context: &RewriteContext,
 287                    width: usize,
 288                    offset: Indent)
 289                    -> Option<String> {
 290     let mover = if capture == ast::CaptureClause::CaptureByValue {
 291         "move "
 292     } else {
 293         ""
 294     };
 295     let offset = offset + mover.len();
 296
 297     // 4 = "|| {".len(), which is overconservative when the closure consists of
 298     // a single expression.
 299     let budget = try_opt!(width.checked_sub(4 + mover.len()));
 300     // 1 = |
 301     let argument_offset = offset + 1;
 302     let ret_str = try_opt!(fn_decl.output.rewrite(context, budget, argument_offset));
 303     // 1 = space between arguments and return type.
 304     let horizontal_budget = budget.checked_sub(ret_str.len() + 1).unwrap_or(0);
 305
 306     let arg_items = itemize_list(context.codemap,
 307                                  fn_decl.inputs.iter(),
 308                                  "|",
 309                                  |arg| span_lo_for_arg(arg),
 310                                  |arg| span_hi_for_arg(arg),
 311                                  |arg| {
 312                                      // FIXME: we should just escalate failure
 313                                      // here, but itemize_list doesn't allow it.
 314                                      arg.rewrite(context, budget, argument_offset)
 315                                         .unwrap_or_else(|| {
 316                                             context.snippet(mk_sp(span_lo_for_arg(arg),
 317                                                                   span_hi_for_arg(arg)))
 318                                         })
 319                                  },
 320                                  span_after(span, "|", context.codemap),
 321                                  body.span.lo);
 322
 323     let fmt = ListFormatting {
 324         tactic: ListTactic::HorizontalVertical,
 325         separator: ",",
 326         trailing_separator: SeparatorTactic::Never,
 327         indent: argument_offset,
 328         h_width: horizontal_budget,
 329         v_width: budget,
 330         ends_with_newline: false,
 331         config: context.config,
 332     };
 333     let list_str = try_opt!(write_list(&arg_items.collect::<Vec<_>>(), &fmt));
 334     let mut prefix = format!("{}|{}|", mover, list_str);
 335
 336     if !ret_str.is_empty() {
 337         if prefix.contains('\n') {
 338             prefix.push('\n');
 339             prefix.push_str(&argument_offset.to_string(context.config));
 340         } else {
 341             prefix.push(' ');
 342         }
 343         prefix.push_str(&ret_str);
 344     }
 345
 346     // Try to format closure body as a single line expression without braces.
 347     if is_simple_block(body, context.codemap) && !prefix.contains('\n') {
 348         let (spacer, closer) = if ret_str.is_empty() {
 349             (" ", "")
 350         } else {
 351             (" { ", " }")
 352         };
 353         let expr = body.expr.as_ref().unwrap();
 354         // All closure bodies are blocks in the eyes of the AST, but we may not
 355         // want to unwrap them when they only contain a single expression.
 356         let inner_expr = match expr.node {
 357             ast::Expr_::ExprBlock(ref inner) if inner.stmts.is_empty() && inner.expr.is_some() &&
 358                                                 inner.rules ==
 359                                                 ast::BlockCheckMode::DefaultBlock => {
 360                 inner.expr.as_ref().unwrap()
 361             }
 362             _ => expr,
 363         };
 364         let extra_offset = extra_offset(&prefix, offset) + spacer.len();
 365         let budget = try_opt!(width.checked_sub(extra_offset + closer.len()));
 366         let rewrite = inner_expr.rewrite(context, budget, offset + extra_offset);
 367
 368         // Checks if rewrite succeeded and fits on a single line.
 369         let accept_rewrite = rewrite.as_ref().map(|result| !result.contains('\n')).unwrap_or(false);
 370
 371         if accept_rewrite {
 372             return Some(format!("{}{}{}{}", prefix, spacer, rewrite.unwrap(), closer));
 373         }
 374     }
 375
 376     // We couldn't format the closure body as a single line expression; fall
 377     // back to block formatting.
 378     let body_rewrite = body.expr
 379                            .as_ref()
 380                            .and_then(|body_expr| {
 381                                if let ast::Expr_::ExprBlock(ref inner) = body_expr.node {
 382                                    Some(inner.rewrite(&context, 2, Indent::empty()))
 383                                } else {
 384                                    None
 385                                }
 386                            })
 387                            .unwrap_or_else(|| body.rewrite(&context, 2, Indent::empty()));
 388
 389     Some(format!("{} {}", prefix, try_opt!(body_rewrite)))
 390 }
 391
 392 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 393     block_str.map(|block_str| {
 394         if block_str.starts_with("{") && budget >= 2 &&
 395            (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2) {
 396             "{}".to_owned()
 397         } else {
 398             block_str.to_owned()
 399         }
 400     })
 401 }
 402
 403 impl Rewrite for ast::Block {
 404     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 405         let user_str = context.snippet(self.span);
 406         if user_str == "{}" && width >= 2 {
 407             return Some(user_str);
 408         }
 409
 410         let mut visitor = FmtVisitor::from_codemap(context.codemap, context.config);
 411         visitor.block_indent = context.block_indent + context.overflow_indent;
 412
 413         let prefix = match self.rules {
 414             ast::BlockCheckMode::PushUnsafeBlock(..) |
 415             ast::BlockCheckMode::UnsafeBlock(..) => {
 416                 let snippet = context.snippet(self.span);
 417                 let open_pos = try_opt!(snippet.find_uncommented("{"));
 418                 visitor.last_pos = self.span.lo + BytePos(open_pos as u32);
 419
 420                 // Extract comment between unsafe and block start.
 421                 let trimmed = &snippet[6..open_pos].trim();
 422
 423                 let prefix = if !trimmed.is_empty() {
 424                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 425                     let budget = try_opt!(width.checked_sub(9));
 426                     format!("unsafe {} ",
 427                             try_opt!(rewrite_comment(trimmed,
 428                                                      true,
 429                                                      budget,
 430                                                      offset + 7,
 431                                                      context.config)))
 432                 } else {
 433                     "unsafe ".to_owned()
 434                 };
 435
 436                 if is_simple_block(self, context.codemap) && prefix.len() < width {
 437                     let body = self.expr
 438                                    .as_ref()
 439                                    .unwrap()
 440                                    .rewrite(context, width - prefix.len(), offset);
 441                     if let Some(ref expr_str) = body {
 442                         let result = format!("{}{{ {} }}", prefix, expr_str);
 443                         if result.len() <= width && !result.contains('\n') {
 444                             return Some(result);
 445                         }
 446                     }
 447                 }
 448
 449                 prefix
 450             }
 451             ast::BlockCheckMode::PopUnsafeBlock(..) |
 452             ast::BlockCheckMode::DefaultBlock => {
 453                 visitor.last_pos = self.span.lo;
 454
 455                 String::new()
 456             }
 457         };
 458
 459         visitor.visit_block(self);
 460
 461         // Push text between last block item and end of block
 462         let snippet = visitor.snippet(mk_sp(visitor.last_pos, self.span.hi));
 463         visitor.buffer.push_str(&snippet);
 464
 465         Some(format!("{}{}", prefix, visitor.buffer))
 466     }
 467 }
 468
 469 // FIXME(#18): implement pattern formatting
 470 impl Rewrite for ast::Pat {
 471     fn rewrite(&self, context: &RewriteContext, _: usize, _: Indent) -> Option<String> {
 472         Some(context.snippet(self.span))
 473     }
 474 }
 475
 476 // Abstraction over for, while and loop expressions
 477 struct Loop<'a> {
 478     cond: Option<&'a ast::Expr>,
 479     block: &'a ast::Block,
 480     label: Option<ast::Ident>,
 481     pat: Option<&'a ast::Pat>,
 482     keyword: &'a str,
 483     matcher: &'a str,
 484     connector: &'a str,
 485 }
 486
 487 impl<'a> Loop<'a> {
 488     fn new_loop(block: &'a ast::Block, label: Option<ast::Ident>) -> Loop<'a> {
 489         Loop {
 490             cond: None,
 491             block: block,
 492             label: label,
 493             pat: None,
 494             keyword: "loop",
 495             matcher: "",
 496             connector: "",
 497         }
 498     }
 499
 500     fn new_while(pat: Option<&'a ast::Pat>,
 501                  cond: &'a ast::Expr,
 502                  block: &'a ast::Block,
 503                  label: Option<ast::Ident>)
 504                  -> Loop<'a> {
 505         Loop {
 506             cond: Some(cond),
 507             block: block,
 508             label: label,
 509             pat: pat,
 510             keyword: "while ",
 511             matcher: match pat {
 512                 Some(..) => "let ",
 513                 None => "",
 514             },
 515             connector: " =",
 516         }
 517     }
 518
 519     fn new_for(pat: &'a ast::Pat,
 520                cond: &'a ast::Expr,
 521                block: &'a ast::Block,
 522                label: Option<ast::Ident>)
 523                -> Loop<'a> {
 524         Loop {
 525             cond: Some(cond),
 526             block: block,
 527             label: label,
 528             pat: Some(pat),
 529             keyword: "for ",
 530             matcher: "",
 531             connector: " in",
 532         }
 533     }
 534 }
 535
 536 impl<'a> Rewrite for Loop<'a> {
 537     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 538         let label_string = rewrite_label(self.label);
 539         // 2 = " {".len()
 540         let inner_width = try_opt!(width.checked_sub(self.keyword.len() + 2 + label_string.len()));
 541         let inner_offset = offset + self.keyword.len() + label_string.len();
 542
 543         let pat_expr_string = match self.cond {
 544             Some(cond) => try_opt!(rewrite_pat_expr(context,
 545                                                     self.pat,
 546                                                     cond,
 547                                                     self.matcher,
 548                                                     self.connector,
 549                                                     inner_width,
 550                                                     inner_offset)),
 551             None => String::new(),
 552         };
 553
 554         // FIXME: this drops any comment between "loop" and the block.
 555         self.block
 556             .rewrite(context, width, offset)
 557             .map(|result| {
 558                 format!("{}{}{} {}",
 559                         label_string,
 560                         self.keyword,
 561                         pat_expr_string,
 562                         result)
 563             })
 564     }
 565 }
 566
 567 fn rewrite_label(label: Option<ast::Ident>) -> String {
 568     match label {
 569         Some(ident) => format!("{}: ", ident),
 570         None => "".to_owned(),
 571     }
 572 }
 573
 574 // FIXME: this doesn't play well with line breaks
 575 fn rewrite_range(context: &RewriteContext,
 576                  left: Option<&ast::Expr>,
 577                  right: Option<&ast::Expr>,
 578                  width: usize,
 579                  offset: Indent)
 580                  -> Option<String> {
 581     let left_string = match left {
 582         Some(expr) => {
 583             // 2 = ..
 584             let max_width = try_opt!(width.checked_sub(2));
 585             try_opt!(expr.rewrite(context, max_width, offset))
 586         }
 587         None => String::new(),
 588     };
 589
 590     let right_string = match right {
 591         Some(expr) => {
 592             let max_width = try_opt!(width.checked_sub(left_string.len() + 2));
 593             try_opt!(expr.rewrite(context, max_width, offset + 2 + left_string.len()))
 594         }
 595         None => String::new(),
 596     };
 597
 598     Some(format!("{}..{}", left_string, right_string))
 599 }
 600
 601 // Rewrites if-else blocks. If let Some(_) = pat, the expression is
 602 // treated as an if-let-else expression.
 603 fn rewrite_if_else(context: &RewriteContext,
 604                    cond: &ast::Expr,
 605                    if_block: &ast::Block,
 606                    else_block_opt: Option<&ast::Expr>,
 607                    pat: Option<&ast::Pat>,
 608                    width: usize,
 609                    offset: Indent,
 610                    allow_single_line: bool)
 611                    -> Option<String> {
 612     // 3 = "if ", 2 = " {"
 613     let pat_expr_string = try_opt!(rewrite_pat_expr(context,
 614                                                     pat,
 615                                                     cond,
 616                                                     "let ",
 617                                                     " =",
 618                                                     try_opt!(width.checked_sub(3 + 2)),
 619                                                     offset + 3));
 620
 621     // Try to format if-else on single line.
 622     if allow_single_line && context.config.single_line_if_else {
 623         let trial = single_line_if_else(context, &pat_expr_string, if_block, else_block_opt, width);
 624
 625         if trial.is_some() {
 626             return trial;
 627         }
 628     }
 629
 630     let if_block_string = try_opt!(if_block.rewrite(context, width, offset));
 631     let mut result = format!("if {} {}", pat_expr_string, if_block_string);
 632
 633     if let Some(else_block) = else_block_opt {
 634         let rewrite = match else_block.node {
 635             // If the else expression is another if-else expression, prevent it
 636             // from being formatted on a single line.
 637             ast::Expr_::ExprIfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 638                 rewrite_if_else(context,
 639                                 cond,
 640                                 if_block,
 641                                 else_block.as_ref().map(|e| &**e),
 642                                 Some(pat),
 643                                 width,
 644                                 offset,
 645                                 false)
 646             }
 647             ast::Expr_::ExprIf(ref cond, ref if_block, ref else_block) => {
 648                 rewrite_if_else(context,
 649                                 cond,
 650                                 if_block,
 651                                 else_block.as_ref().map(|e| &**e),
 652                                 None,
 653                                 width,
 654                                 offset,
 655                                 false)
 656             }
 657             _ => else_block.rewrite(context, width, offset),
 658         };
 659
 660         result.push_str(" else ");
 661         result.push_str(&&try_opt!(rewrite));
 662     }
 663
 664     Some(result)
 665 }
 666
 667 fn single_line_if_else(context: &RewriteContext,
 668                        pat_expr_str: &str,
 669                        if_node: &ast::Block,
 670                        else_block_opt: Option<&ast::Expr>,
 671                        width: usize)
 672                        -> Option<String> {
 673     let else_block = try_opt!(else_block_opt);
 674     let fixed_cost = "if  {  } else {  }".len();
 675
 676     if let ast::ExprBlock(ref else_node) = else_block.node {
 677         if !is_simple_block(if_node, context.codemap) ||
 678            !is_simple_block(else_node, context.codemap) || pat_expr_str.contains('\n') {
 679             return None;
 680         }
 681
 682         let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 683         let if_expr = if_node.expr.as_ref().unwrap();
 684         let if_str = try_opt!(if_expr.rewrite(context, new_width, Indent::empty()));
 685
 686         let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 687         let else_expr = else_node.expr.as_ref().unwrap();
 688         let else_str = try_opt!(else_expr.rewrite(context, new_width, Indent::empty()));
 689
 690         // FIXME: this check shouldn't be necessary. Rewrites should either fail
 691         // or wrap to a newline when the object does not fit the width.
 692         let fits_line = fixed_cost + pat_expr_str.len() + if_str.len() + else_str.len() <= width;
 693
 694         if fits_line && !if_str.contains('\n') && !else_str.contains('\n') {
 695             return Some(format!("if {} {{ {} }} else {{ {} }}",
 696                                 pat_expr_str,
 697                                 if_str,
 698                                 else_str));
 699         }
 700     }
 701
 702     None
 703 }
 704
 705 // Checks that a block contains no statements, an expression and no comments.
 706 fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 707     if !block.stmts.is_empty() || block.expr.is_none() {
 708         return false;
 709     }
 710
 711     let snippet = codemap.span_to_snippet(block.span).unwrap();
 712
 713     !contains_comment(&snippet)
 714 }
 715
 716 // inter-match-arm-comment-rules:
 717 //  - all comments following a match arm before the start of the next arm
 718 //    are about the second arm
 719 fn rewrite_match_arm_comment(context: &RewriteContext,
 720                              missed_str: &str,
 721                              width: usize,
 722                              arm_indent: Indent,
 723                              arm_indent_str: &str)
 724                              -> Option<String> {
 725     // The leading "," is not part of the arm-comment
 726     let missed_str = match missed_str.find_uncommented(",") {
 727         Some(n) => &missed_str[n+1..],
 728         None => &missed_str[..],
 729     };
 730
 731     let mut result = String::new();
 732     // any text not preceeded by a newline is pushed unmodified to the block
 733     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
 734     result.push_str(&missed_str[..first_brk]);
 735     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
 736
 737     let first = missed_str.find(|c: char| !c.is_whitespace()).unwrap_or(missed_str.len());
 738     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
 739         // Excessive vertical whitespace before comment should be preserved
 740         // TODO handle vertical whitespace better
 741         result.push('\n');
 742     }
 743     let missed_str = missed_str[first..].trim();
 744     if !missed_str.is_empty() {
 745         let comment = try_opt!(rewrite_comment(&missed_str,
 746                                                false,
 747                                                width,
 748                                                arm_indent,
 749                                                context.config));
 750         result.push('\n');
 751         result.push_str(arm_indent_str);
 752         result.push_str(&comment);
 753     }
 754
 755     Some(result)
 756 }
 757
 758 fn rewrite_match(context: &RewriteContext,
 759                  cond: &ast::Expr,
 760                  arms: &[ast::Arm],
 761                  width: usize,
 762                  offset: Indent,
 763                  span: Span)
 764                  -> Option<String> {
 765     if arms.is_empty() {
 766         return None;
 767     }
 768
 769     // `match `cond` {`
 770     let cond_budget = try_opt!(width.checked_sub(8));
 771     let cond_str = try_opt!(cond.rewrite(context, cond_budget, offset + 6));
 772     let mut result = format!("match {} {{", cond_str);
 773
 774     let nested_context = context.nested_context();
 775     let arm_indent = nested_context.block_indent + context.overflow_indent;
 776     let arm_indent_str = arm_indent.to_string(context.config);
 777
 778     let open_brace_pos = span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])),
 779                                     "{",
 780                                     context.codemap);
 781
 782     for (i, arm) in arms.iter().enumerate() {
 783         // Make sure we get the stuff between arms.
 784         let missed_str = if i == 0 {
 785             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
 786         } else {
 787             context.snippet(mk_sp(arm_end_pos(&arms[i-1]), arm_start_pos(arm)))
 788         };
 789         let comment = try_opt!(rewrite_match_arm_comment(context,
 790                                                          &missed_str,
 791                                                          width,
 792                                                          arm_indent,
 793                                                          &arm_indent_str));
 794         result.push_str(&comment);
 795         result.push('\n');
 796         result.push_str(&arm_indent_str);
 797
 798         let arm_str = arm.rewrite(&nested_context,
 799                                   context.config.max_width - arm_indent.width(),
 800                                   arm_indent);
 801         if let Some(ref arm_str) = arm_str {
 802             result.push_str(arm_str);
 803         } else {
 804             // We couldn't format the arm, just reproduce the source.
 805             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
 806             result.push_str(&snippet);
 807         }
 808     }
 809     // BytePos(1) = closing match brace.
 810     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]),
 811                           span.hi - BytePos(1));
 812     let last_comment = context.snippet(last_span);
 813     let comment = try_opt!(rewrite_match_arm_comment(context,
 814                                                      &last_comment,
 815                                                      width,
 816                                                      arm_indent,
 817                                                      &arm_indent_str));
 818     result.push_str(&comment);
 819     result.push('\n');
 820     result.push_str(&(context.block_indent + context.overflow_indent).to_string(context.config));
 821     result.push('}');
 822     Some(result)
 823 }
 824
 825 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
 826     let &ast::Arm { ref attrs, ref pats, .. } = arm;
 827     if !attrs.is_empty() {
 828         return attrs[0].span.lo
 829     }
 830
 831     pats[0].span.lo
 832 }
 833
 834 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
 835     arm.body.span.hi
 836 }
 837
 838 // Match arms.
 839 impl Rewrite for ast::Arm {
 840     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 841         let &ast::Arm { ref attrs, ref pats, ref guard, ref body } = self;
 842         let indent_str = offset.to_string(context.config);
 843
 844         // FIXME this is all a bit grotty, would be nice to abstract out the
 845         // treatment of attributes.
 846         let attr_str = if !attrs.is_empty() {
 847             // We only use this visitor for the attributes, should we use it for
 848             // more?
 849             let mut attr_visitor = FmtVisitor::from_codemap(context.codemap, context.config);
 850             attr_visitor.block_indent = context.block_indent;
 851             attr_visitor.last_pos = attrs[0].span.lo;
 852             if attr_visitor.visit_attrs(attrs) {
 853                 // Attributes included a skip instruction.
 854                 let snippet = context.snippet(mk_sp(attrs[0].span.lo, body.span.hi));
 855                 return Some(snippet);
 856             }
 857             attr_visitor.format_missing(pats[0].span.lo);
 858             attr_visitor.buffer.to_string()
 859         } else {
 860             String::new()
 861         };
 862
 863         // Patterns
 864         // 5 = ` => {`
 865         let pat_budget = try_opt!(width.checked_sub(5));
 866         let pat_strs = try_opt!(pats.iter()
 867                                     .map(|p| {
 868                                         p.rewrite(context,
 869                                                   pat_budget,
 870                                                   offset.block_indent(context.config))
 871                                     })
 872                                     .collect::<Option<Vec<_>>>());
 873
 874         let mut total_width = pat_strs.iter().fold(0, |a, p| a + p.len());
 875         // Add ` | `.len().
 876         total_width += (pat_strs.len() - 1) * 3;
 877
 878         let mut vertical = total_width > pat_budget || pat_strs.iter().any(|p| p.contains('\n'));
 879         if !vertical && context.config.take_source_hints {
 880             // If the patterns were previously stacked, keep them stacked.
 881             let pat_span = mk_sp(pats[0].span.lo, pats[pats.len() - 1].span.hi);
 882             let pat_str = context.snippet(pat_span);
 883             vertical = pat_str.find('\n').is_some();
 884         }
 885
 886         let pats_width = if vertical {
 887             pat_strs[pat_strs.len() - 1].len()
 888         } else {
 889             total_width
 890         };
 891
 892         let mut pats_str = String::new();
 893         for p in pat_strs {
 894             if !pats_str.is_empty() {
 895                 if vertical {
 896                     pats_str.push_str(" |\n");
 897                     pats_str.push_str(&indent_str);
 898                 } else {
 899                     pats_str.push_str(" | ");
 900                 }
 901             }
 902             pats_str.push_str(&p);
 903         }
 904
 905         let guard_str = try_opt!(rewrite_guard(context, guard, width, offset, pats_width));
 906
 907         let pats_str = format!("{}{}", pats_str, guard_str);
 908         // Where the next text can start.
 909         let mut line_start = last_line_width(&pats_str);
 910         if !pats_str.contains('\n') {
 911             line_start += offset.width();
 912         }
 913
 914         let comma = if let ast::ExprBlock(_) = body.node {
 915             ""
 916         } else {
 917             ","
 918         };
 919
 920         // Let's try and get the arm body on the same line as the condition.
 921         // 4 = ` => `.len()
 922         let same_line_body = if context.config.max_width > line_start + comma.len() + 4 {
 923             let budget = context.config.max_width - line_start - comma.len() - 4;
 924             let offset = Indent::new(offset.block_indent,
 925                                      line_start + 4 - offset.block_indent);
 926             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
 927
 928             match rewrite {
 929                 Some(ref body_str) if body_str.len() <= budget || comma.is_empty() =>
 930                     return Some(format!("{}{} => {}{}",
 931                                         attr_str.trim_left(),
 932                                         pats_str,
 933                                         body_str,
 934                                         comma)),
 935                 _ => rewrite,
 936             }
 937         } else {
 938             None
 939         };
 940
 941         if let ast::ExprBlock(_) = body.node {
 942             // We're trying to fit a block in, but it still failed, give up.
 943             return None;
 944         }
 945
 946         let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
 947         let next_line_body = nop_block_collapse(body.rewrite(context,
 948                                                              body_budget,
 949                                                              context.block_indent
 950                                                                     .block_indent(context.config)),
 951                                                 body_budget);
 952
 953         let body_str = try_opt!(match_arm_heuristic(same_line_body.as_ref().map(|x| &x[..]),
 954                                                     next_line_body.as_ref().map(|x| &x[..])));
 955
 956         let spacer = match same_line_body {
 957             Some(ref body) if body == body_str => " ".to_owned(),
 958             _ => format!("\n{}",
 959                          offset.block_indent(context.config).to_string(context.config)),
 960         };
 961
 962         Some(format!("{}{} =>{}{},",
 963                      attr_str.trim_left(),
 964                      pats_str,
 965                      spacer,
 966                      body_str))
 967     }
 968 }
 969
 970 // Takes two possible rewrites for the match arm body and chooses the "nicest".
 971 fn match_arm_heuristic<'a>(former: Option<&'a str>, latter: Option<&'a str>) -> Option<&'a str> {
 972     match (former, latter) {
 973         (f @ Some(..), None) => f,
 974         (Some(f), Some(l)) if f.chars().filter(|&c| c == '\n').count() <=
 975                               l.chars().filter(|&c| c == '\n').count() => {
 976             Some(f)
 977         }
 978         (_, l) => l,
 979     }
 980 }
 981
 982 // The `if ...` guard on a match arm.
 983 fn rewrite_guard(context: &RewriteContext,
 984                  guard: &Option<ptr::P<ast::Expr>>,
 985                  width: usize,
 986                  offset: Indent,
 987                  // The amount of space used up on this line for the pattern in
 988                  // the arm (excludes offset).
 989                  pattern_width: usize)
 990                  -> Option<String> {
 991     if let &Some(ref guard) = guard {
 992         // First try to fit the guard string on the same line as the pattern.
 993         // 4 = ` if `, 5 = ` => {`
 994         let overhead = pattern_width + 4 + 5;
 995         if overhead < width {
 996             let cond_str = guard.rewrite(context, width - overhead, offset + pattern_width + 4);
 997             if let Some(cond_str) = cond_str {
 998                 return Some(format!(" if {}", cond_str));
 999             }
1000         }
1001
1002         // Not enough space to put the guard after the pattern, try a newline.
1003         let overhead = context.config.tab_spaces + 4 + 5;
1004         if overhead < width {
1005             let cond_str = guard.rewrite(context,
1006                                          width - overhead,
1007                                          offset.block_indent(context.config));
1008             if let Some(cond_str) = cond_str {
1009                 return Some(format!("\n{}if {}",
1010                                     offset.block_indent(context.config).to_string(context.config),
1011                                     cond_str));
1012             }
1013         }
1014
1015         None
1016     } else {
1017         Some(String::new())
1018     }
1019 }
1020
1021 fn rewrite_pat_expr(context: &RewriteContext,
1022                     pat: Option<&ast::Pat>,
1023                     expr: &ast::Expr,
1024                     matcher: &str,
1025                     // Connecting piece between pattern and expression,
1026                     // *without* trailing space.
1027                     connector: &str,
1028                     width: usize,
1029                     offset: Indent)
1030                     -> Option<String> {
1031     let pat_offset = offset + matcher.len();
1032     let mut result = match pat {
1033         Some(pat) => {
1034             let pat_budget = try_opt!(width.checked_sub(connector.len() + matcher.len()));
1035             let pat_string = try_opt!(pat.rewrite(context, pat_budget, pat_offset));
1036             format!("{}{}{}", matcher, pat_string, connector)
1037         }
1038         None => String::new(),
1039     };
1040
1041     // Consider only the last line of the pat string.
1042     let extra_offset = extra_offset(&result, offset);
1043
1044     // The expression may (partionally) fit on the current line.
1045     if width > extra_offset + 1 {
1046         let spacer = if pat.is_some() {
1047             " "
1048         } else {
1049             ""
1050         };
1051
1052         let expr_rewrite = expr.rewrite(context,
1053                                         width - extra_offset - spacer.len(),
1054                                         offset + extra_offset + spacer.len());
1055
1056         if let Some(expr_string) = expr_rewrite {
1057             result.push_str(spacer);
1058             result.push_str(&expr_string);
1059             return Some(result);
1060         }
1061     }
1062
1063     // The expression won't fit on the current line, jump to next.
1064     result.push('\n');
1065     result.push_str(&pat_offset.to_string(context.config));
1066
1067     let expr_rewrite = expr.rewrite(context,
1068                                     context.config.max_width - pat_offset.width(),
1069                                     pat_offset);
1070     result.push_str(&&try_opt!(expr_rewrite));
1071
1072     Some(result)
1073 }
1074
1075 fn rewrite_string_lit(context: &RewriteContext,
1076                       span: Span,
1077                       width: usize,
1078                       offset: Indent)
1079                       -> Option<String> {
1080     if !context.config.format_strings {
1081         return Some(context.snippet(span));
1082     }
1083
1084     let fmt = StringFormat {
1085         opener: "\"",
1086         closer: "\"",
1087         line_start: " ",
1088         line_end: "\\",
1089         width: width,
1090         offset: offset,
1091         trim_end: false,
1092         config: context.config,
1093     };
1094
1095     let string_lit = context.snippet(span);
1096     let str_lit = &string_lit[1..string_lit.len() - 1]; // Remove the quote characters.
1097
1098     rewrite_string(str_lit, &fmt)
1099 }
1100
1101 pub fn rewrite_call<R>(context: &RewriteContext,
1102                        callee: &R,
1103                        args: &[ptr::P<ast::Expr>],
1104                        span: Span,
1105                        width: usize,
1106                        offset: Indent)
1107                        -> Option<String>
1108     where R: Rewrite
1109 {
1110     let closure = |callee_max_width| {
1111         rewrite_call_inner(context, callee, callee_max_width, args, span, width, offset)
1112     };
1113
1114     // 2 is for parens
1115     let max_width = try_opt!(width.checked_sub(2));
1116     binary_search(1, max_width, closure)
1117 }
1118
1119 fn rewrite_call_inner<R>(context: &RewriteContext,
1120                          callee: &R,
1121                          max_callee_width: usize,
1122                          args: &[ptr::P<ast::Expr>],
1123                          span: Span,
1124                          width: usize,
1125                          offset: Indent)
1126                          -> Result<String, Ordering>
1127     where R: Rewrite
1128 {
1129     let callee = callee.borrow();
1130     // FIXME using byte lens instead of char lens (and probably all over the
1131     // place too)
1132     let callee_str = match callee.rewrite(context, max_callee_width, offset) {
1133         Some(string) => {
1134             if !string.contains('\n') && string.len() > max_callee_width {
1135                 panic!("{:?} {}", string, max_callee_width);
1136             } else {
1137                 string
1138             }
1139         }
1140         None => return Err(Ordering::Greater),
1141     };
1142
1143     let span_lo = span_after(span, "(", context.codemap);
1144     let span = mk_sp(span_lo, span.hi);
1145
1146     let extra_offset = extra_offset(&callee_str, offset);
1147     // 2 is for parens.
1148     let remaining_width = match width.checked_sub(extra_offset + 2) {
1149         Some(str) => str,
1150         None => return Err(Ordering::Greater),
1151     };
1152     let offset = offset + extra_offset + 1;
1153     let block_indent = if args.len() == 1 {
1154         context.block_indent
1155     } else {
1156         offset
1157     };
1158     let inner_context = &RewriteContext { block_indent: block_indent, ..*context };
1159
1160     let items = itemize_list(context.codemap,
1161                              args.iter(),
1162                              ")",
1163                              |item| item.span.lo,
1164                              |item| item.span.hi,
1165                              // Take old span when rewrite fails.
1166                              |item| {
1167                                  item.rewrite(&inner_context, remaining_width, offset)
1168                                      .unwrap_or(context.snippet(item.span))
1169                              },
1170                              span.lo,
1171                              span.hi);
1172
1173     let fmt = ListFormatting::for_fn(remaining_width, offset, context.config);
1174     let list_str = match write_list(&items.collect::<Vec<_>>(), &fmt) {
1175         Some(str) => str,
1176         None => return Err(Ordering::Less),
1177     };
1178
1179     Ok(format!("{}({})", callee_str, list_str))
1180 }
1181
1182 fn rewrite_paren(context: &RewriteContext,
1183                  subexpr: &ast::Expr,
1184                  width: usize,
1185                  offset: Indent)
1186                  -> Option<String> {
1187     debug!("rewrite_paren, width: {}, offset: {:?}",
1188            width,
1189            offset);
1190     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1191     // paren on the same line as the subexpr.
1192     let subexpr_str = subexpr.rewrite(context, try_opt!(width.checked_sub(2)), offset + 1);
1193     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1194     subexpr_str.map(|s| format!("({})", s))
1195 }
1196
1197 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1198                           path: &ast::Path,
1199                           fields: &'a [ast::Field],
1200                           base: Option<&'a ast::Expr>,
1201                           span: Span,
1202                           width: usize,
1203                           offset: Indent)
1204                           -> Option<String> {
1205     debug!("rewrite_struct_lit: width {}, offset {:?}",
1206            width,
1207            offset);
1208     assert!(!fields.is_empty() || base.is_some());
1209
1210     enum StructLitField<'a> {
1211         Regular(&'a ast::Field),
1212         Base(&'a ast::Expr),
1213     }
1214
1215     // 2 = " {".len()
1216     let path_budget = try_opt!(width.checked_sub(2));
1217     let path_str = try_opt!(path.rewrite(context, path_budget, offset));
1218
1219     // Foo { a: Foo } - indent is +3, width is -5.
1220     let h_budget = width.checked_sub(path_str.len() + 5).unwrap_or(0);
1221     let (indent, v_budget) = match context.config.struct_lit_style {
1222         StructLitStyle::Visual => {
1223             (offset + path_str.len() + 3, h_budget)
1224         }
1225         StructLitStyle::Block => {
1226             // If we are all on one line, then we'll ignore the indent, and we
1227             // have a smaller budget.
1228             let indent = context.block_indent.block_indent(context.config);
1229             let v_budget = context.config.max_width.checked_sub(indent.width()).unwrap_or(0);
1230             (indent, v_budget)
1231         }
1232     };
1233
1234     let field_iter = fields.into_iter()
1235                            .map(StructLitField::Regular)
1236                            .chain(base.into_iter().map(StructLitField::Base));
1237
1238     let inner_context = &RewriteContext { block_indent: indent, ..*context };
1239
1240     let items = itemize_list(context.codemap,
1241                              field_iter,
1242                              "}",
1243                              |item| {
1244                                  match *item {
1245                                      StructLitField::Regular(ref field) => field.span.lo,
1246                                      StructLitField::Base(ref expr) => {
1247                                          let last_field_hi = fields.last().map_or(span.lo,
1248                                                                                   |field| {
1249                                                                                       field.span.hi
1250                                                                                   });
1251                                          let snippet = context.snippet(mk_sp(last_field_hi,
1252                                                                              expr.span.lo));
1253                                          let pos = snippet.find_uncommented("..").unwrap();
1254                                          last_field_hi + BytePos(pos as u32)
1255                                      }
1256                                  }
1257                              },
1258                              |item| {
1259                                  match *item {
1260                                      StructLitField::Regular(ref field) => field.span.hi,
1261                                      StructLitField::Base(ref expr) => expr.span.hi,
1262                                  }
1263                              },
1264                              |item| {
1265                                  match *item {
1266                                      StructLitField::Regular(ref field) => {
1267                                          rewrite_field(inner_context, &field, v_budget, indent)
1268                                              .unwrap_or(context.snippet(field.span))
1269                                      }
1270                                      StructLitField::Base(ref expr) => {
1271                                          // 2 = ..
1272                                          format!("..{}",
1273                                                  v_budget.checked_sub(2)
1274                                                          .and_then(|v_budget| {
1275                                                              expr.rewrite(inner_context,
1276                                                                           v_budget,
1277                                                                           indent + 2)
1278                                                          })
1279                                                          .unwrap_or(context.snippet(expr.span)))
1280                                      }
1281                                  }
1282                              },
1283                              span_after(span, "{", context.codemap),
1284                              span.hi);
1285
1286     let mut tactic = match (context.config.struct_lit_style, fields.len()) {
1287         (StructLitStyle::Visual, 1) => ListTactic::HorizontalVertical,
1288         _ => context.config.struct_lit_multiline_style.to_list_tactic(),
1289     };
1290
1291     if tactic == ListTactic::HorizontalVertical && fields.len() > 1 {
1292         tactic = ListTactic::LimitedHorizontalVertical(context.config.struct_lit_width);
1293     }
1294
1295     let fmt = ListFormatting {
1296         tactic: tactic,
1297         separator: ",",
1298         trailing_separator: if base.is_some() {
1299             SeparatorTactic::Never
1300         } else {
1301             context.config.struct_lit_trailing_comma
1302         },
1303         indent: indent,
1304         h_width: h_budget,
1305         v_width: v_budget,
1306         ends_with_newline: false,
1307         config: context.config,
1308     };
1309     let fields_str = try_opt!(write_list(&items.collect::<Vec<_>>(), &fmt));
1310
1311     let format_on_newline = || {
1312         let inner_indent = context.block_indent
1313                                   .block_indent(context.config)
1314                                   .to_string(context.config);
1315         let outer_indent = context.block_indent.to_string(context.config);
1316         Some(format!("{} {{\n{}{}\n{}}}",
1317                      path_str,
1318                      inner_indent,
1319                      fields_str,
1320                      outer_indent))
1321     };
1322
1323     match (context.config.struct_lit_style,
1324            context.config.struct_lit_multiline_style) {
1325         (StructLitStyle::Block, _) if fields_str.contains('\n') || fields_str.len() > h_budget =>
1326             format_on_newline(),
1327         (StructLitStyle::Block, MultilineStyle::ForceMulti) => format_on_newline(),
1328         _ => Some(format!("{} {{ {} }}", path_str, fields_str)),
1329     }
1330
1331     // FIXME if context.config.struct_lit_style == Visual, but we run out
1332     // of space, we should fall back to BlockIndent.
1333 }
1334
1335 fn rewrite_field(context: &RewriteContext,
1336                  field: &ast::Field,
1337                  width: usize,
1338                  offset: Indent)
1339                  -> Option<String> {
1340     let name = &field.ident.node.to_string();
1341     let overhead = name.len() + 2;
1342     let expr = field.expr.rewrite(context,
1343                                   try_opt!(width.checked_sub(overhead)),
1344                                   offset + overhead);
1345     expr.map(|s| format!("{}: {}", name, s))
1346 }
1347
1348 fn rewrite_tuple_lit(context: &RewriteContext,
1349                      items: &[ptr::P<ast::Expr>],
1350                      span: Span,
1351                      width: usize,
1352                      offset: Indent)
1353                      -> Option<String> {
1354     debug!("rewrite_tuple_lit: width: {}, offset: {:?}",
1355            width,
1356            offset);
1357     let indent = offset + 1;
1358     // In case of length 1, need a trailing comma
1359     if items.len() == 1 {
1360         // 3 = "(" + ",)"
1361         let budget = try_opt!(width.checked_sub(3));
1362         return items[0].rewrite(context, budget, indent).map(|s| format!("({},)", s));
1363     }
1364
1365     let items = itemize_list(context.codemap,
1366                              items.iter(),
1367                              ")",
1368                              |item| item.span.lo,
1369                              |item| item.span.hi,
1370                              |item| {
1371                                  let inner_width = context.config.max_width - indent.width() - 1;
1372                                  item.rewrite(context, inner_width, indent)
1373                                      .unwrap_or(context.snippet(item.span))
1374                              },
1375                              span.lo + BytePos(1), // Remove parens
1376                              span.hi - BytePos(1));
1377
1378     let budget = try_opt!(width.checked_sub(2));
1379     let fmt = ListFormatting::for_fn(budget, indent, context.config);
1380     let list_str = try_opt!(write_list(&items.collect::<Vec<_>>(), &fmt));
1381
1382     Some(format!("({})", list_str))
1383 }
1384
1385 fn rewrite_binary_op(context: &RewriteContext,
1386                      op: &ast::BinOp,
1387                      lhs: &ast::Expr,
1388                      rhs: &ast::Expr,
1389                      width: usize,
1390                      offset: Indent)
1391                      -> Option<String> {
1392     // FIXME: format comments between operands and operator
1393
1394     let operator_str = context.snippet(op.span);
1395
1396     // Get "full width" rhs and see if it fits on the current line. This
1397     // usually works fairly well since it tends to place operands of
1398     // operations with high precendence close together.
1399     let rhs_result = try_opt!(rhs.rewrite(context, width, offset));
1400
1401     // Second condition is needed in case of line break not caused by a
1402     // shortage of space, but by end-of-line comments, for example.
1403     // Note that this is non-conservative, but its just to see if it's even
1404     // worth trying to put everything on one line.
1405     if rhs_result.len() + 2 + operator_str.len() < width && !rhs_result.contains('\n') {
1406         // 1 = space between lhs expr and operator
1407         if let Some(mut result) = lhs.rewrite(context, width - 1 - operator_str.len(), offset) {
1408             result.push(' ');
1409             result.push_str(&operator_str);
1410             result.push(' ');
1411
1412             let remaining_width = width.checked_sub(last_line_width(&result)).unwrap_or(0);
1413
1414             if rhs_result.len() <= remaining_width {
1415                 result.push_str(&rhs_result);
1416                 return Some(result);
1417             }
1418
1419             if let Some(rhs_result) = rhs.rewrite(context, remaining_width, offset + result.len()) {
1420                 if rhs_result.len() <= remaining_width {
1421                     result.push_str(&rhs_result);
1422                     return Some(result);
1423                 }
1424             }
1425         }
1426     }
1427
1428     // We have to use multiple lines.
1429
1430     // Re-evaluate the lhs because we have more space now:
1431     let budget = try_opt!(context.config
1432                                  .max_width
1433                                  .checked_sub(offset.width() + 1 + operator_str.len()));
1434     Some(format!("{} {}\n{}{}",
1435                  try_opt!(lhs.rewrite(context, budget, offset)),
1436                  operator_str,
1437                  offset.to_string(context.config),
1438                  rhs_result))
1439 }
1440
1441 fn rewrite_unary_prefix(context: &RewriteContext,
1442                         prefix: &str,
1443                         expr: &ast::Expr,
1444                         width: usize,
1445                         offset: Indent)
1446                         -> Option<String> {
1447     expr.rewrite(context,
1448                  try_opt!(width.checked_sub(prefix.len())),
1449                  offset + prefix.len())
1450         .map(|r| format!("{}{}", prefix, r))
1451 }
1452
1453 fn rewrite_unary_op(context: &RewriteContext,
1454                     op: &ast::UnOp,
1455                     expr: &ast::Expr,
1456                     width: usize,
1457                     offset: Indent)
1458                     -> Option<String> {
1459     // For some reason, an UnOp is not spanned like BinOp!
1460     let operator_str = match *op {
1461         ast::UnOp::UnDeref => "*",
1462         ast::UnOp::UnNot => "!",
1463         ast::UnOp::UnNeg => "-",
1464     };
1465     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1466 }
1467
1468 fn rewrite_assignment(context: &RewriteContext,
1469                       lhs: &ast::Expr,
1470                       rhs: &ast::Expr,
1471                       op: Option<&ast::BinOp>,
1472                       width: usize,
1473                       offset: Indent)
1474                       -> Option<String> {
1475     let operator_str = match op {
1476         Some(op) => context.snippet(op.span),
1477         None => "=".to_owned(),
1478     };
1479
1480     // 1 = space between lhs and operator.
1481     let max_width = try_opt!(width.checked_sub(operator_str.len() + 1));
1482     let lhs_str = format!("{} {}",
1483                           try_opt!(lhs.rewrite(context, max_width, offset)),
1484                           operator_str);
1485
1486     rewrite_assign_rhs(&context, lhs_str, rhs, width, offset)
1487 }
1488
1489 // The left hand side must contain everything up to, and including, the
1490 // assignment operator.
1491 pub fn rewrite_assign_rhs<S: Into<String>>(context: &RewriteContext,
1492                                            lhs: S,
1493                                            ex: &ast::Expr,
1494                                            width: usize,
1495                                            offset: Indent)
1496                                            -> Option<String> {
1497     let mut result = lhs.into();
1498
1499     // 1 = space between operator and rhs.
1500     let max_width = try_opt!(width.checked_sub(result.len() + 1));
1501     let rhs = ex.rewrite(&context, max_width, offset + result.len() + 1);
1502
1503     match rhs {
1504         Some(new_str) => {
1505             result.push(' ');
1506             result.push_str(&new_str)
1507         }
1508         None => {
1509             // Expression did not fit on the same line as the identifier. Retry
1510             // on the next line.
1511             let new_offset = offset.block_indent(context.config);
1512             result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1513
1514             // FIXME: we probably should related max_width to width instead of config.max_width
1515             // where is the 1 coming from anyway?
1516             let max_width = try_opt!(context.config.max_width.checked_sub(new_offset.width() + 1));
1517             let rhs_indent = Indent::new(context.config.tab_spaces, 0);
1518             let overflow_context = context.overflow_context(rhs_indent);
1519             let rhs = ex.rewrite(&overflow_context, max_width, new_offset);
1520
1521             result.push_str(&&try_opt!(rhs));
1522         }
1523     }
1524
1525     Some(result)
1526 }
1527
1528 fn rewrite_expr_addrof(context: &RewriteContext,
1529                        mutability: ast::Mutability,
1530                        expr: &ast::Expr,
1531                        width: usize,
1532                        offset: Indent)
1533                        -> Option<String> {
1534     let operator_str = match mutability {
1535         ast::Mutability::MutImmutable => "&",
1536         ast::Mutability::MutMutable => "&mut ",
1537     };
1538     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1539 }