src/expr.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::cmp::Ordering;
  12 use std::borrow::Borrow;
  13 use std::mem::swap;
  14 use std::ops::Deref;
  15 use std::iter::ExactSizeIterator;
  16 use std::fmt::Write;
  17
  18 use {Indent, Spanned};
  19 use rewrite::{Rewrite, RewriteContext};
  20 use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic,
  21             DefinitiveListTactic, definitive_tactic, ListItem, format_item_list};
  22 use string::{StringFormat, rewrite_string};
  23 use utils::{CodeMapSpanUtils, extra_offset, last_line_width, wrap_str, binary_search,
  24             first_line_width, semicolon_for_stmt, trimmed_last_line_width};
  25 use visitor::FmtVisitor;
  26 use config::{Config, StructLitStyle, MultilineStyle};
  27 use comment::{FindUncommented, rewrite_comment, contains_comment, recover_comment_removed};
  28 use types::rewrite_path;
  29 use items::{span_lo_for_arg, span_hi_for_arg};
  30 use chains::rewrite_chain;
  31 use macros::rewrite_macro;
  32
  33 use syntax::{ast, ptr};
  34 use syntax::codemap::{CodeMap, Span, BytePos, mk_sp};
  35 use syntax::visit::Visitor;
  36
  37 impl Rewrite for ast::Expr {
  38     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  39         let result = match self.node {
  40             ast::ExprKind::Vec(ref expr_vec) => {
  41                 rewrite_array(expr_vec.iter().map(|e| &**e),
  42                               mk_sp(context.codemap.span_after(self.span, "["), self.span.hi),
  43                               context,
  44                               width,
  45                               offset)
  46             }
  47             ast::ExprKind::Lit(ref l) => {
  48                 match l.node {
  49                     ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
  50                         rewrite_string_lit(context, l.span, width, offset)
  51                     }
  52                     _ => {
  53                         wrap_str(context.snippet(self.span),
  54                                  context.config.max_width,
  55                                  width,
  56                                  offset)
  57                     }
  58                 }
  59             }
  60             ast::ExprKind::Call(ref callee, ref args) => {
  61                 let inner_span = mk_sp(callee.span.hi, self.span.hi);
  62                 rewrite_call(context, &**callee, args, inner_span, width, offset)
  63             }
  64             ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, width, offset),
  65             ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
  66                 rewrite_binary_op(context, op, lhs, rhs, width, offset)
  67             }
  68             ast::ExprKind::Unary(ref op, ref subexpr) => {
  69                 rewrite_unary_op(context, op, subexpr, width, offset)
  70             }
  71             ast::ExprKind::Struct(ref path, ref fields, ref base) => {
  72                 rewrite_struct_lit(context,
  73                                    path,
  74                                    fields,
  75                                    base.as_ref().map(|e| &**e),
  76                                    self.span,
  77                                    width,
  78                                    offset)
  79             }
  80             ast::ExprKind::Tup(ref items) => {
  81                 rewrite_tuple(context,
  82                               items.iter().map(|x| &**x),
  83                               self.span,
  84                               width,
  85                               offset)
  86             }
  87             ast::ExprKind::While(ref cond, ref block, label) => {
  88                 Loop::new_while(None, cond, block, label).rewrite(context, width, offset)
  89             }
  90             ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => {
  91                 Loop::new_while(Some(pat), cond, block, label).rewrite(context, width, offset)
  92             }
  93             ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
  94                 Loop::new_for(pat, cond, block, label).rewrite(context, width, offset)
  95             }
  96             ast::ExprKind::Loop(ref block, label) => {
  97                 Loop::new_loop(block, label).rewrite(context, width, offset)
  98             }
  99             ast::ExprKind::Block(ref block) => block.rewrite(context, width, offset),
 100             ast::ExprKind::If(ref cond, ref if_block, ref else_block) => {
 101                 rewrite_if_else(context,
 102                                 cond,
 103                                 if_block,
 104                                 else_block.as_ref().map(|e| &**e),
 105                                 self.span,
 106                                 None,
 107                                 width,
 108                                 offset,
 109                                 true)
 110             }
 111             ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 112                 rewrite_if_else(context,
 113                                 cond,
 114                                 if_block,
 115                                 else_block.as_ref().map(|e| &**e),
 116                                 self.span,
 117                                 Some(pat),
 118                                 width,
 119                                 offset,
 120                                 true)
 121             }
 122             ast::ExprKind::Match(ref cond, ref arms) => {
 123                 rewrite_match(context, cond, arms, width, offset, self.span)
 124             }
 125             ast::ExprKind::Path(ref qself, ref path) => {
 126                 rewrite_path(context, true, qself.as_ref(), path, width, offset)
 127             }
 128             ast::ExprKind::Assign(ref lhs, ref rhs) => {
 129                 rewrite_assignment(context, lhs, rhs, None, width, offset)
 130             }
 131             ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 132                 rewrite_assignment(context, lhs, rhs, Some(op), width, offset)
 133             }
 134             ast::ExprKind::Again(ref opt_ident) => {
 135                 let id_str = match *opt_ident {
 136                     Some(ident) => format!(" {}", ident.node),
 137                     None => String::new(),
 138                 };
 139                 Some(format!("continue{}", id_str))
 140             }
 141             ast::ExprKind::Break(ref opt_ident) => {
 142                 let id_str = match *opt_ident {
 143                     Some(ident) => format!(" {}", ident.node),
 144                     None => String::new(),
 145                 };
 146                 Some(format!("break{}", id_str))
 147             }
 148             ast::ExprKind::Closure(capture, ref fn_decl, ref body) => {
 149                 rewrite_closure(capture, fn_decl, body, self.span, context, width, offset)
 150             }
 151             ast::ExprKind::Field(..) |
 152             ast::ExprKind::TupField(..) |
 153             ast::ExprKind::MethodCall(..) => rewrite_chain(self, context, width, offset),
 154             ast::ExprKind::Mac(ref mac) => {
 155                 // Failure to rewrite a marco should not imply failure to
 156                 // rewrite the expression.
 157                 rewrite_macro(mac, None, context, width, offset).or_else(|| {
 158                     wrap_str(context.snippet(self.span),
 159                              context.config.max_width,
 160                              width,
 161                              offset)
 162                 })
 163             }
 164             ast::ExprKind::Ret(None) => {
 165                 wrap_str("return".to_owned(), context.config.max_width, width, offset)
 166             }
 167             ast::ExprKind::Ret(Some(ref expr)) => {
 168                 rewrite_unary_prefix(context, "return ", &**expr, width, offset)
 169             }
 170             ast::ExprKind::Box(ref expr) => {
 171                 rewrite_unary_prefix(context, "box ", &**expr, width, offset)
 172             }
 173             ast::ExprKind::AddrOf(mutability, ref expr) => {
 174                 rewrite_expr_addrof(context, mutability, expr, width, offset)
 175             }
 176             ast::ExprKind::Cast(ref expr, ref ty) => {
 177                 rewrite_pair(&**expr, &**ty, "", " as ", "", context, width, offset)
 178             }
 179             ast::ExprKind::Index(ref expr, ref index) => {
 180                 rewrite_pair(&**expr, &**index, "", "[", "]", context, width, offset)
 181             }
 182             ast::ExprKind::Repeat(ref expr, ref repeats) => {
 183                 rewrite_pair(&**expr, &**repeats, "[", "; ", "]", context, width, offset)
 184             }
 185             ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 186                 let delim = match limits {
 187                     ast::RangeLimits::HalfOpen => "..",
 188                     ast::RangeLimits::Closed => "...",
 189                 };
 190
 191                 match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 192                     (Some(ref lhs), Some(ref rhs)) => {
 193                         rewrite_pair(&**lhs, &**rhs, "", delim, "", context, width, offset)
 194                     }
 195                     (None, Some(ref rhs)) => {
 196                         rewrite_unary_prefix(context, delim, &**rhs, width, offset)
 197                     }
 198                     (Some(ref lhs), None) => {
 199                         Some(format!("{}{}",
 200                                      try_opt!(lhs.rewrite(context,
 201                                                           try_opt!(width.checked_sub(delim.len())),
 202                                                           offset)),
 203                                      delim))
 204                     }
 205                     (None, None) => wrap_str(delim.into(), context.config.max_width, width, offset),
 206                 }
 207             }
 208             // We do not format these expressions yet, but they should still
 209             // satisfy our width restrictions.
 210             ast::ExprKind::InPlace(..) |
 211             ast::ExprKind::InlineAsm(..) |
 212             // TODO(#848): Handle type ascription
 213             ast::ExprKind::Type(_, _) |
 214             // TODO(#867): Handle try shorthand
 215             ast::ExprKind::Try(_) => {
 216                 wrap_str(context.snippet(self.span),
 217                          context.config.max_width,
 218                          width,
 219                          offset)
 220             }
 221         };
 222         result.and_then(|res| recover_comment_removed(res, self.span, context, width, offset))
 223     }
 224 }
 225
 226 pub fn rewrite_pair<LHS, RHS>(lhs: &LHS,
 227                               rhs: &RHS,
 228                               prefix: &str,
 229                               infix: &str,
 230                               suffix: &str,
 231                               context: &RewriteContext,
 232                               width: usize,
 233                               offset: Indent)
 234                               -> Option<String>
 235     where LHS: Rewrite,
 236           RHS: Rewrite
 237 {
 238     let max_width = try_opt!(width.checked_sub(prefix.len() + infix.len() + suffix.len()));
 239
 240     binary_search(1, max_width, |lhs_budget| {
 241         let lhs_offset = offset + prefix.len();
 242         let lhs_str = match lhs.rewrite(context, lhs_budget, lhs_offset) {
 243             Some(result) => result,
 244             None => return Err(Ordering::Greater),
 245         };
 246
 247         let last_line_width = last_line_width(&lhs_str);
 248         let rhs_budget = match max_width.checked_sub(last_line_width) {
 249             Some(b) => b,
 250             None => return Err(Ordering::Less),
 251         };
 252         let rhs_indent = offset + last_line_width + prefix.len() + infix.len();
 253
 254         let rhs_str = match rhs.rewrite(context, rhs_budget, rhs_indent) {
 255             Some(result) => result,
 256             None => return Err(Ordering::Less),
 257         };
 258
 259         Ok(format!("{}{}{}{}{}", prefix, lhs_str, infix, rhs_str, suffix))
 260     })
 261 }
 262
 263 pub fn rewrite_array<'a, I>(expr_iter: I,
 264                             span: Span,
 265                             context: &RewriteContext,
 266                             width: usize,
 267                             offset: Indent)
 268                             -> Option<String>
 269     where I: Iterator<Item = &'a ast::Expr>
 270 {
 271     // 2 for brackets;
 272     let offset = offset + 1;
 273     let inner_context = &RewriteContext { block_indent: offset, ..*context };
 274     let max_item_width = try_opt!(width.checked_sub(2));
 275     let items = itemize_list(context.codemap,
 276                              expr_iter,
 277                              "]",
 278                              |item| item.span.lo,
 279                              |item| item.span.hi,
 280                              // 1 = [
 281                              |item| item.rewrite(&inner_context, max_item_width, offset),
 282                              span.lo,
 283                              span.hi)
 284                     .collect::<Vec<_>>();
 285
 286     let has_long_item = try_opt!(items.iter()
 287                                       .map(|li| li.item.as_ref().map(|s| s.len() > 10))
 288                                       .fold(Some(false),
 289                                             |acc, x| acc.and_then(|y| x.map(|x| x || y))));
 290
 291     let tactic = if has_long_item || items.iter().any(ListItem::is_multiline) {
 292         definitive_tactic(&items, ListTactic::HorizontalVertical, max_item_width)
 293     } else {
 294         DefinitiveListTactic::Mixed
 295     };
 296
 297     let fmt = ListFormatting {
 298         tactic: tactic,
 299         separator: ",",
 300         trailing_separator: SeparatorTactic::Never,
 301         indent: offset,
 302         width: max_item_width,
 303         ends_with_newline: false,
 304         config: context.config,
 305     };
 306     let list_str = try_opt!(write_list(&items, &fmt));
 307
 308     Some(format!("[{}]", list_str))
 309 }
 310
 311 // This functions is pretty messy because of the wrapping and unwrapping of
 312 // expressions into and from blocks. See rust issue #27872.
 313 fn rewrite_closure(capture: ast::CaptureBy,
 314                    fn_decl: &ast::FnDecl,
 315                    body: &ast::Block,
 316                    span: Span,
 317                    context: &RewriteContext,
 318                    width: usize,
 319                    offset: Indent)
 320                    -> Option<String> {
 321     let mover = if capture == ast::CaptureBy::Value {
 322         "move "
 323     } else {
 324         ""
 325     };
 326     let offset = offset + mover.len();
 327
 328     // 4 = "|| {".len(), which is overconservative when the closure consists of
 329     // a single expression.
 330     let budget = try_opt!(width.checked_sub(4 + mover.len()));
 331     // 1 = |
 332     let argument_offset = offset + 1;
 333     let ret_str = try_opt!(fn_decl.output.rewrite(context, budget, argument_offset));
 334     // 1 = space between arguments and return type.
 335     let horizontal_budget = budget.checked_sub(ret_str.len() + 1).unwrap_or(0);
 336
 337     let arg_items = itemize_list(context.codemap,
 338                                  fn_decl.inputs.iter(),
 339                                  "|",
 340                                  |arg| span_lo_for_arg(arg),
 341                                  |arg| span_hi_for_arg(arg),
 342                                  |arg| arg.rewrite(context, budget, argument_offset),
 343                                  context.codemap.span_after(span, "|"),
 344                                  body.span.lo);
 345     let item_vec = arg_items.collect::<Vec<_>>();
 346     let tactic = definitive_tactic(&item_vec, ListTactic::HorizontalVertical, horizontal_budget);
 347     let budget = match tactic {
 348         DefinitiveListTactic::Horizontal => horizontal_budget,
 349         _ => budget,
 350     };
 351
 352     let fmt = ListFormatting {
 353         tactic: tactic,
 354         separator: ",",
 355         trailing_separator: SeparatorTactic::Never,
 356         indent: argument_offset,
 357         width: budget,
 358         ends_with_newline: false,
 359         config: context.config,
 360     };
 361     let list_str = try_opt!(write_list(&item_vec, &fmt));
 362     let mut prefix = format!("{}|{}|", mover, list_str);
 363
 364     if !ret_str.is_empty() {
 365         if prefix.contains('\n') {
 366             prefix.push('\n');
 367             prefix.push_str(&argument_offset.to_string(context.config));
 368         } else {
 369             prefix.push(' ');
 370         }
 371         prefix.push_str(&ret_str);
 372     }
 373
 374     // Try to format closure body as a single line expression without braces.
 375     if is_simple_block(body, context.codemap) && !prefix.contains('\n') {
 376         let (spacer, closer) = if ret_str.is_empty() {
 377             (" ", "")
 378         } else {
 379             (" { ", " }")
 380         };
 381         let expr = body.expr.as_ref().unwrap();
 382         // All closure bodies are blocks in the eyes of the AST, but we may not
 383         // want to unwrap them when they only contain a single expression.
 384         let inner_expr = match expr.node {
 385             ast::ExprKind::Block(ref inner) if inner.stmts.is_empty() && inner.expr.is_some() &&
 386                                                inner.rules == ast::BlockCheckMode::Default => {
 387                 inner.expr.as_ref().unwrap()
 388             }
 389             _ => expr,
 390         };
 391         let extra_offset = extra_offset(&prefix, offset) + spacer.len();
 392         let budget = try_opt!(width.checked_sub(extra_offset + closer.len()));
 393         let rewrite = inner_expr.rewrite(context, budget, offset + extra_offset);
 394
 395         // Checks if rewrite succeeded and fits on a single line.
 396         let accept_rewrite = rewrite.as_ref().map_or(false, |result| !result.contains('\n'));
 397
 398         if accept_rewrite {
 399             return Some(format!("{}{}{}{}", prefix, spacer, rewrite.unwrap(), closer));
 400         }
 401     }
 402
 403     // We couldn't format the closure body as a single line expression; fall
 404     // back to block formatting.
 405     let body_rewrite = body.expr
 406                            .as_ref()
 407                            .and_then(|body_expr| {
 408                                if let ast::ExprKind::Block(ref inner) = body_expr.node {
 409                                    Some(inner.rewrite(&context, 2, Indent::empty()))
 410                                } else {
 411                                    None
 412                                }
 413                            })
 414                            .unwrap_or_else(|| body.rewrite(&context, 2, Indent::empty()));
 415
 416     Some(format!("{} {}", prefix, try_opt!(body_rewrite)))
 417 }
 418
 419 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 420     block_str.map(|block_str| {
 421         if block_str.starts_with("{") && budget >= 2 &&
 422            (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2) {
 423             "{}".to_owned()
 424         } else {
 425             block_str.to_owned()
 426         }
 427     })
 428 }
 429
 430 impl Rewrite for ast::Block {
 431     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 432         let user_str = context.snippet(self.span);
 433         if user_str == "{}" && width >= 2 {
 434             return Some(user_str);
 435         }
 436
 437         let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 438         visitor.block_indent = context.block_indent;
 439
 440         let prefix = match self.rules {
 441             ast::BlockCheckMode::Unsafe(..) => {
 442                 let snippet = context.snippet(self.span);
 443                 let open_pos = try_opt!(snippet.find_uncommented("{"));
 444                 visitor.last_pos = self.span.lo + BytePos(open_pos as u32);
 445
 446                 // Extract comment between unsafe and block start.
 447                 let trimmed = &snippet[6..open_pos].trim();
 448
 449                 let prefix = if !trimmed.is_empty() {
 450                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 451                     let budget = try_opt!(width.checked_sub(9));
 452                     format!("unsafe {} ",
 453                             try_opt!(rewrite_comment(trimmed,
 454                                                      true,
 455                                                      budget,
 456                                                      offset + 7,
 457                                                      context.config)))
 458                 } else {
 459                     "unsafe ".to_owned()
 460                 };
 461
 462                 if is_simple_block(self, context.codemap) && prefix.len() < width {
 463                     let body = self.expr
 464                                    .as_ref()
 465                                    .unwrap()
 466                                    .rewrite(context, width - prefix.len(), offset);
 467                     if let Some(ref expr_str) = body {
 468                         let result = format!("{}{{ {} }}", prefix, expr_str);
 469                         if result.len() <= width && !result.contains('\n') {
 470                             return Some(result);
 471                         }
 472                     }
 473                 }
 474
 475                 prefix
 476             }
 477             ast::BlockCheckMode::Default => {
 478                 visitor.last_pos = self.span.lo;
 479
 480                 String::new()
 481             }
 482         };
 483
 484         visitor.visit_block(self);
 485
 486         Some(format!("{}{}", prefix, visitor.buffer))
 487     }
 488 }
 489
 490 impl Rewrite for ast::Stmt {
 491     fn rewrite(&self, context: &RewriteContext, _width: usize, offset: Indent) -> Option<String> {
 492         let result = match self.node {
 493             ast::StmtKind::Decl(ref decl, _) => {
 494                 if let ast::DeclKind::Local(ref local) = decl.node {
 495                     local.rewrite(context, context.config.max_width, offset)
 496                 } else {
 497                     None
 498                 }
 499             }
 500             ast::StmtKind::Expr(ref ex, _) |
 501             ast::StmtKind::Semi(ref ex, _) => {
 502                 let suffix = if semicolon_for_stmt(self) {
 503                     ";"
 504                 } else {
 505                     ""
 506                 };
 507
 508                 ex.rewrite(context,
 509                            context.config.max_width - offset.width() - suffix.len(),
 510                            offset)
 511                   .map(|s| s + suffix)
 512             }
 513             ast::StmtKind::Mac(..) => None,
 514         };
 515         result.and_then(|res| recover_comment_removed(res, self.span, context, _width, offset))
 516     }
 517 }
 518
 519 // Abstraction over for, while and loop expressions
 520 struct Loop<'a> {
 521     cond: Option<&'a ast::Expr>,
 522     block: &'a ast::Block,
 523     label: Option<ast::Ident>,
 524     pat: Option<&'a ast::Pat>,
 525     keyword: &'a str,
 526     matcher: &'a str,
 527     connector: &'a str,
 528 }
 529
 530 impl<'a> Loop<'a> {
 531     fn new_loop(block: &'a ast::Block, label: Option<ast::Ident>) -> Loop<'a> {
 532         Loop {
 533             cond: None,
 534             block: block,
 535             label: label,
 536             pat: None,
 537             keyword: "loop",
 538             matcher: "",
 539             connector: "",
 540         }
 541     }
 542
 543     fn new_while(pat: Option<&'a ast::Pat>,
 544                  cond: &'a ast::Expr,
 545                  block: &'a ast::Block,
 546                  label: Option<ast::Ident>)
 547                  -> Loop<'a> {
 548         Loop {
 549             cond: Some(cond),
 550             block: block,
 551             label: label,
 552             pat: pat,
 553             keyword: "while ",
 554             matcher: match pat {
 555                 Some(..) => "let ",
 556                 None => "",
 557             },
 558             connector: " =",
 559         }
 560     }
 561
 562     fn new_for(pat: &'a ast::Pat,
 563                cond: &'a ast::Expr,
 564                block: &'a ast::Block,
 565                label: Option<ast::Ident>)
 566                -> Loop<'a> {
 567         Loop {
 568             cond: Some(cond),
 569             block: block,
 570             label: label,
 571             pat: Some(pat),
 572             keyword: "for ",
 573             matcher: "",
 574             connector: " in",
 575         }
 576     }
 577 }
 578
 579 impl<'a> Rewrite for Loop<'a> {
 580     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 581         let label_string = rewrite_label(self.label);
 582         // 2 = " {".len()
 583         let inner_width = try_opt!(width.checked_sub(self.keyword.len() + 2 + label_string.len()));
 584         let inner_offset = offset + self.keyword.len() + label_string.len();
 585
 586         let pat_expr_string = match self.cond {
 587             Some(cond) => {
 588                 try_opt!(rewrite_pat_expr(context,
 589                                           self.pat,
 590                                           cond,
 591                                           self.matcher,
 592                                           self.connector,
 593                                           inner_width,
 594                                           inner_offset))
 595             }
 596             None => String::new(),
 597         };
 598
 599         // FIXME: this drops any comment between "loop" and the block.
 600         self.block
 601             .rewrite(context, width, offset)
 602             .map(|result| {
 603                 format!("{}{}{} {}",
 604                         label_string,
 605                         self.keyword,
 606                         pat_expr_string,
 607                         result)
 608             })
 609     }
 610 }
 611
 612 fn rewrite_label(label: Option<ast::Ident>) -> String {
 613     match label {
 614         Some(ident) => format!("{}: ", ident),
 615         None => "".to_owned(),
 616     }
 617 }
 618
 619 fn extract_comment(span: Span,
 620                    context: &RewriteContext,
 621                    offset: Indent,
 622                    width: usize)
 623                    -> Option<String> {
 624     let comment_str = context.snippet(span);
 625     if contains_comment(&comment_str) {
 626         let comment = try_opt!(rewrite_comment(comment_str.trim(),
 627                                                false,
 628                                                width,
 629                                                offset,
 630                                                context.config));
 631         Some(format!("\n{indent}{}\n{indent}",
 632                      comment,
 633                      indent = offset.to_string(context.config)))
 634     } else {
 635         None
 636     }
 637 }
 638
 639 // Rewrites if-else blocks. If let Some(_) = pat, the expression is
 640 // treated as an if-let-else expression.
 641 fn rewrite_if_else(context: &RewriteContext,
 642                    cond: &ast::Expr,
 643                    if_block: &ast::Block,
 644                    else_block_opt: Option<&ast::Expr>,
 645                    span: Span,
 646                    pat: Option<&ast::Pat>,
 647                    width: usize,
 648                    offset: Indent,
 649                    allow_single_line: bool)
 650                    -> Option<String> {
 651     // 3 = "if ", 2 = " {"
 652     let pat_expr_string = try_opt!(rewrite_pat_expr(context,
 653                                                     pat,
 654                                                     cond,
 655                                                     "let ",
 656                                                     " =",
 657                                                     try_opt!(width.checked_sub(3 + 2)),
 658                                                     offset + 3));
 659
 660     // Try to format if-else on single line.
 661     if allow_single_line && context.config.single_line_if_else {
 662         let trial = single_line_if_else(context, &pat_expr_string, if_block, else_block_opt, width);
 663
 664         if trial.is_some() {
 665             return trial;
 666         }
 667     }
 668
 669     let if_block_string = try_opt!(if_block.rewrite(context, width, offset));
 670
 671     let between_if_cond = mk_sp(context.codemap.span_after(span, "if"),
 672                                 pat.map_or(cond.span.lo,
 673                                            |_| context.codemap.span_before(span, "let")));
 674
 675     let between_if_cond_comment = extract_comment(between_if_cond, &context, offset, width);
 676
 677     let after_cond_comment = extract_comment(mk_sp(cond.span.hi, if_block.span.lo),
 678                                              context,
 679                                              offset,
 680                                              width);
 681
 682     let mut result = format!("if{}{}{}{}",
 683                              between_if_cond_comment.as_ref().map_or(" ", |str| &**str),
 684                              pat_expr_string,
 685                              after_cond_comment.as_ref().map_or(" ", |str| &**str),
 686                              if_block_string);
 687
 688     if let Some(else_block) = else_block_opt {
 689         let rewrite = match else_block.node {
 690             // If the else expression is another if-else expression, prevent it
 691             // from being formatted on a single line.
 692             ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
 693                 rewrite_if_else(context,
 694                                 cond,
 695                                 if_block,
 696                                 next_else_block.as_ref().map(|e| &**e),
 697                                 mk_sp(else_block.span.lo, span.hi),
 698                                 Some(pat),
 699                                 width,
 700                                 offset,
 701                                 false)
 702             }
 703             ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
 704                 rewrite_if_else(context,
 705                                 cond,
 706                                 if_block,
 707                                 next_else_block.as_ref().map(|e| &**e),
 708                                 mk_sp(else_block.span.lo, span.hi),
 709                                 None,
 710                                 width,
 711                                 offset,
 712                                 false)
 713             }
 714             _ => else_block.rewrite(context, width, offset),
 715         };
 716
 717         let between_if_else_block = mk_sp(if_block.span.hi,
 718                                           context.codemap.span_before(mk_sp(if_block.span.hi,
 719                                                                             else_block.span.lo),
 720                                                                       "else"));
 721         let between_if_else_block_comment = extract_comment(between_if_else_block,
 722                                                             &context,
 723                                                             offset,
 724                                                             width);
 725
 726         let after_else = mk_sp(context.codemap
 727                                       .span_after(mk_sp(if_block.span.hi, else_block.span.lo),
 728                                                   "else"),
 729                                else_block.span.lo);
 730         let after_else_comment = extract_comment(after_else, &context, offset, width);
 731
 732         try_opt!(write!(&mut result,
 733                         "{}else{}",
 734                         between_if_else_block_comment.as_ref().map_or(" ", |str| &**str),
 735                         after_else_comment.as_ref().map_or(" ", |str| &**str))
 736                      .ok());
 737         result.push_str(&&try_opt!(rewrite));
 738     }
 739
 740     Some(result)
 741 }
 742
 743 fn single_line_if_else(context: &RewriteContext,
 744                        pat_expr_str: &str,
 745                        if_node: &ast::Block,
 746                        else_block_opt: Option<&ast::Expr>,
 747                        width: usize)
 748                        -> Option<String> {
 749     let else_block = try_opt!(else_block_opt);
 750     let fixed_cost = "if  {  } else {  }".len();
 751
 752     if let ast::ExprKind::Block(ref else_node) = else_block.node {
 753         if !is_simple_block(if_node, context.codemap) ||
 754            !is_simple_block(else_node, context.codemap) || pat_expr_str.contains('\n') {
 755             return None;
 756         }
 757
 758         let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 759         let if_expr = if_node.expr.as_ref().unwrap();
 760         let if_str = try_opt!(if_expr.rewrite(context, new_width, Indent::empty()));
 761
 762         let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 763         let else_expr = else_node.expr.as_ref().unwrap();
 764         let else_str = try_opt!(else_expr.rewrite(context, new_width, Indent::empty()));
 765
 766         // FIXME: this check shouldn't be necessary. Rewrites should either fail
 767         // or wrap to a newline when the object does not fit the width.
 768         let fits_line = fixed_cost + pat_expr_str.len() + if_str.len() + else_str.len() <= width;
 769
 770         if fits_line && !if_str.contains('\n') && !else_str.contains('\n') {
 771             return Some(format!("if {} {{ {} }} else {{ {} }}",
 772                                 pat_expr_str,
 773                                 if_str,
 774                                 else_str));
 775         }
 776     }
 777
 778     None
 779 }
 780
 781 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
 782     let snippet = codemap.span_to_snippet(block.span).unwrap();
 783     contains_comment(&snippet)
 784 }
 785
 786 // Checks that a block contains no statements, an expression and no comments.
 787 // FIXME: incorrectly returns false when comment is contained completely within
 788 // the expression.
 789 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 790     block.stmts.is_empty() && block.expr.is_some() && !block_contains_comment(block, codemap)
 791 }
 792
 793 /// Checks whether a block contains at most one statement or expression, and no comments.
 794 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
 795     (block.stmts.is_empty() || (block.stmts.len() == 1 && block.expr.is_none())) &&
 796     !block_contains_comment(block, codemap)
 797 }
 798
 799 /// Checks whether a block contains no statements, expressions, or comments.
 800 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
 801     block.stmts.is_empty() && block.expr.is_none() && !block_contains_comment(block, codemap)
 802 }
 803
 804 fn is_unsafe_block(block: &ast::Block) -> bool {
 805     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
 806         true
 807     } else {
 808         false
 809     }
 810 }
 811
 812 // inter-match-arm-comment-rules:
 813 //  - all comments following a match arm before the start of the next arm
 814 //    are about the second arm
 815 fn rewrite_match_arm_comment(context: &RewriteContext,
 816                              missed_str: &str,
 817                              width: usize,
 818                              arm_indent: Indent,
 819                              arm_indent_str: &str)
 820                              -> Option<String> {
 821     // The leading "," is not part of the arm-comment
 822     let missed_str = match missed_str.find_uncommented(",") {
 823         Some(n) => &missed_str[n + 1..],
 824         None => &missed_str[..],
 825     };
 826
 827     let mut result = String::new();
 828     // any text not preceeded by a newline is pushed unmodified to the block
 829     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
 830     result.push_str(&missed_str[..first_brk]);
 831     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
 832
 833     let first = missed_str.find(|c: char| !c.is_whitespace()).unwrap_or(missed_str.len());
 834     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
 835         // Excessive vertical whitespace before comment should be preserved
 836         // TODO handle vertical whitespace better
 837         result.push('\n');
 838     }
 839     let missed_str = missed_str[first..].trim();
 840     if !missed_str.is_empty() {
 841         let comment = try_opt!(rewrite_comment(&missed_str,
 842                                                false,
 843                                                width,
 844                                                arm_indent,
 845                                                context.config));
 846         result.push('\n');
 847         result.push_str(arm_indent_str);
 848         result.push_str(&comment);
 849     }
 850
 851     Some(result)
 852 }
 853
 854 fn rewrite_match(context: &RewriteContext,
 855                  cond: &ast::Expr,
 856                  arms: &[ast::Arm],
 857                  width: usize,
 858                  offset: Indent,
 859                  span: Span)
 860                  -> Option<String> {
 861     if arms.is_empty() {
 862         return None;
 863     }
 864
 865     // `match `cond` {`
 866     let cond_budget = try_opt!(width.checked_sub(8));
 867     let cond_str = try_opt!(cond.rewrite(context, cond_budget, offset + 6));
 868     let mut result = format!("match {} {{", cond_str);
 869
 870     let nested_context = context.nested_context();
 871     let arm_indent = nested_context.block_indent;
 872     let arm_indent_str = arm_indent.to_string(context.config);
 873
 874     let open_brace_pos = context.codemap
 875                                 .span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])), "{");
 876
 877     for (i, arm) in arms.iter().enumerate() {
 878         // Make sure we get the stuff between arms.
 879         let missed_str = if i == 0 {
 880             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
 881         } else {
 882             context.snippet(mk_sp(arm_end_pos(&arms[i - 1]), arm_start_pos(arm)))
 883         };
 884         let comment = try_opt!(rewrite_match_arm_comment(context,
 885                                                          &missed_str,
 886                                                          width,
 887                                                          arm_indent,
 888                                                          &arm_indent_str));
 889         result.push_str(&comment);
 890         result.push('\n');
 891         result.push_str(&arm_indent_str);
 892
 893         let arm_str = arm.rewrite(&nested_context,
 894                                   context.config.max_width - arm_indent.width(),
 895                                   arm_indent);
 896         if let Some(ref arm_str) = arm_str {
 897             result.push_str(arm_str);
 898         } else {
 899             // We couldn't format the arm, just reproduce the source.
 900             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
 901             result.push_str(&snippet);
 902             result.push_str(arm_comma(&context.config, &arm, &arm.body));
 903         }
 904     }
 905     // BytePos(1) = closing match brace.
 906     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]), span.hi - BytePos(1));
 907     let last_comment = context.snippet(last_span);
 908     let comment = try_opt!(rewrite_match_arm_comment(context,
 909                                                      &last_comment,
 910                                                      width,
 911                                                      arm_indent,
 912                                                      &arm_indent_str));
 913     result.push_str(&comment);
 914     result.push('\n');
 915     result.push_str(&context.block_indent.to_string(context.config));
 916     result.push('}');
 917     Some(result)
 918 }
 919
 920 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
 921     let &ast::Arm { ref attrs, ref pats, .. } = arm;
 922     if !attrs.is_empty() {
 923         return attrs[0].span.lo;
 924     }
 925
 926     pats[0].span.lo
 927 }
 928
 929 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
 930     arm.body.span.hi
 931 }
 932
 933 fn arm_comma(config: &Config, arm: &ast::Arm, body: &ast::Expr) -> &'static str {
 934     if !config.match_wildcard_trailing_comma {
 935         if arm.pats.len() == 1 && arm.pats[0].node == ast::PatKind::Wild && arm.guard.is_none() {
 936             return "";
 937         }
 938     }
 939
 940     if config.match_block_trailing_comma {
 941         ","
 942     } else if let ast::ExprKind::Block(ref block) = body.node {
 943         if let ast::BlockCheckMode::Default = block.rules {
 944             ""
 945         } else {
 946             ","
 947         }
 948     } else {
 949         ","
 950     }
 951 }
 952
 953 // Match arms.
 954 impl Rewrite for ast::Arm {
 955     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 956         let &ast::Arm { ref attrs, ref pats, ref guard, ref body } = self;
 957
 958         // FIXME this is all a bit grotty, would be nice to abstract out the
 959         // treatment of attributes.
 960         let attr_str = if !attrs.is_empty() {
 961             // We only use this visitor for the attributes, should we use it for
 962             // more?
 963             let mut attr_visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 964             attr_visitor.block_indent = context.block_indent;
 965             attr_visitor.last_pos = attrs[0].span.lo;
 966             if attr_visitor.visit_attrs(attrs) {
 967                 // Attributes included a skip instruction.
 968                 return None;
 969             }
 970             attr_visitor.format_missing(pats[0].span.lo);
 971             attr_visitor.buffer.to_string()
 972         } else {
 973             String::new()
 974         };
 975
 976         // Patterns
 977         // 5 = ` => {`
 978         let pat_budget = try_opt!(width.checked_sub(5));
 979         let pat_strs = try_opt!(pats.iter()
 980                                     .map(|p| p.rewrite(context, pat_budget, offset))
 981                                     .collect::<Option<Vec<_>>>());
 982
 983         let all_simple = pat_strs.iter().all(|p| pat_is_simple(&p));
 984         let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
 985         let fmt = ListFormatting {
 986             tactic: if all_simple {
 987                 DefinitiveListTactic::Mixed
 988             } else {
 989                 DefinitiveListTactic::Vertical
 990             },
 991             separator: " |",
 992             trailing_separator: SeparatorTactic::Never,
 993             indent: offset,
 994             width: pat_budget,
 995             ends_with_newline: false,
 996             config: context.config,
 997         };
 998         let pats_str = try_opt!(write_list(items, &fmt));
 999
1000         let budget = if pats_str.contains('\n') {
1001             context.config.max_width - offset.width()
1002         } else {
1003             width
1004         };
1005
1006         let guard_str = try_opt!(rewrite_guard(context,
1007                                                guard,
1008                                                budget,
1009                                                offset,
1010                                                trimmed_last_line_width(&pats_str)));
1011
1012         let pats_str = format!("{}{}", pats_str, guard_str);
1013         // Where the next text can start.
1014         let mut line_start = last_line_width(&pats_str);
1015         if !pats_str.contains('\n') {
1016             line_start += offset.width();
1017         }
1018
1019         let body = match **body {
1020             ast::Expr { node: ast::ExprKind::Block(ref block), .. }
1021                 if !is_unsafe_block(block) && is_simple_block(block, context.codemap) &&
1022                    context.config.wrap_match_arms => block.expr.as_ref().map(|e| &**e).unwrap(),
1023             ref x => x,
1024         };
1025
1026         let comma = arm_comma(&context.config, self, body);
1027
1028         // Let's try and get the arm body on the same line as the condition.
1029         // 4 = ` => `.len()
1030         if context.config.max_width > line_start + comma.len() + 4 {
1031             let budget = context.config.max_width - line_start - comma.len() - 4;
1032             let offset = Indent::new(offset.block_indent, line_start + 4 - offset.block_indent);
1033             let rewrite = nop_block_collapse(body.rewrite(context, budget, offset), budget);
1034             let is_block = if let ast::ExprKind::Block(..) = body.node {
1035                 true
1036             } else {
1037                 false
1038             };
1039
1040             match rewrite {
1041                 Some(ref body_str) if !body_str.contains('\n') || !context.config.wrap_match_arms ||
1042                                       is_block => {
1043                     return Some(format!("{}{} => {}{}",
1044                                         attr_str.trim_left(),
1045                                         pats_str,
1046                                         body_str,
1047                                         comma));
1048                 }
1049                 _ => {}
1050             }
1051         }
1052
1053         // FIXME: we're doing a second rewrite of the expr; This may not be
1054         // necessary.
1055         let body_budget = try_opt!(width.checked_sub(context.config.tab_spaces));
1056         let indent = context.block_indent.block_indent(context.config);
1057         let inner_context = &RewriteContext { block_indent: indent, ..*context };
1058         let next_line_body = try_opt!(nop_block_collapse(body.rewrite(inner_context,
1059                                                                       body_budget,
1060                                                                       indent),
1061                                                          body_budget));
1062         let indent_str = offset.block_indent(context.config).to_string(context.config);
1063         let (body_prefix, body_suffix) = if context.config.wrap_match_arms {
1064             if context.config.match_block_trailing_comma {
1065                 (" {", "},")
1066             } else {
1067                 (" {", "}")
1068             }
1069         } else {
1070             ("", "")
1071         };
1072
1073         Some(format!("{}{} =>{}\n{}{}\n{}{}",
1074                      attr_str.trim_left(),
1075                      pats_str,
1076                      body_prefix,
1077                      indent_str,
1078                      next_line_body,
1079                      offset.to_string(context.config),
1080                      body_suffix))
1081     }
1082 }
1083
1084 // A pattern is simple if it is very short or it is short-ish and just a path.
1085 // E.g. `Foo::Bar` is simple, but `Foo(..)` is not.
1086 fn pat_is_simple(pat_str: &str) -> bool {
1087     pat_str.len() <= 16 ||
1088     (pat_str.len() <= 24 && pat_str.chars().all(|c| c.is_alphabetic() || c == ':'))
1089 }
1090
1091 // The `if ...` guard on a match arm.
1092 fn rewrite_guard(context: &RewriteContext,
1093                  guard: &Option<ptr::P<ast::Expr>>,
1094                  width: usize,
1095                  offset: Indent,
1096                  // The amount of space used up on this line for the pattern in
1097                  // the arm (excludes offset).
1098                  pattern_width: usize)
1099                  -> Option<String> {
1100     if let Some(ref guard) = *guard {
1101         // First try to fit the guard string on the same line as the pattern.
1102         // 4 = ` if `, 5 = ` => {`
1103         let overhead = pattern_width + 4 + 5;
1104         if overhead < width {
1105             let cond_str = guard.rewrite(context, width - overhead, offset + pattern_width + 4);
1106             if let Some(cond_str) = cond_str {
1107                 return Some(format!(" if {}", cond_str));
1108             }
1109         }
1110
1111         // Not enough space to put the guard after the pattern, try a newline.
1112         let overhead = offset.block_indent(context.config).width() + 4 + 5;
1113         if overhead < width {
1114             let cond_str = guard.rewrite(context,
1115                                          width - overhead,
1116                                          // 3 == `if `
1117                                          offset.block_indent(context.config) + 3);
1118             if let Some(cond_str) = cond_str {
1119                 return Some(format!("\n{}if {}",
1120                                     offset.block_indent(context.config).to_string(context.config),
1121                                     cond_str));
1122             }
1123         }
1124
1125         None
1126     } else {
1127         Some(String::new())
1128     }
1129 }
1130
1131 fn rewrite_pat_expr(context: &RewriteContext,
1132                     pat: Option<&ast::Pat>,
1133                     expr: &ast::Expr,
1134                     matcher: &str,
1135                     // Connecting piece between pattern and expression,
1136                     // *without* trailing space.
1137                     connector: &str,
1138                     width: usize,
1139                     offset: Indent)
1140                     -> Option<String> {
1141     let pat_offset = offset + matcher.len();
1142     let mut result = match pat {
1143         Some(pat) => {
1144             let pat_budget = try_opt!(width.checked_sub(connector.len() + matcher.len()));
1145             let pat_string = try_opt!(pat.rewrite(context, pat_budget, pat_offset));
1146             format!("{}{}{}", matcher, pat_string, connector)
1147         }
1148         None => String::new(),
1149     };
1150
1151     // Consider only the last line of the pat string.
1152     let extra_offset = extra_offset(&result, offset);
1153
1154     // The expression may (partionally) fit on the current line.
1155     if width > extra_offset + 1 {
1156         let spacer = if pat.is_some() {
1157             " "
1158         } else {
1159             ""
1160         };
1161
1162         let expr_rewrite = expr.rewrite(context,
1163                                         width - extra_offset - spacer.len(),
1164                                         offset + extra_offset + spacer.len());
1165
1166         if let Some(expr_string) = expr_rewrite {
1167             result.push_str(spacer);
1168             result.push_str(&expr_string);
1169             return Some(result);
1170         }
1171     }
1172
1173     // The expression won't fit on the current line, jump to next.
1174     result.push('\n');
1175     result.push_str(&pat_offset.to_string(context.config));
1176
1177     let expr_rewrite = expr.rewrite(context,
1178                                     context.config.max_width - pat_offset.width(),
1179                                     pat_offset);
1180     result.push_str(&&try_opt!(expr_rewrite));
1181
1182     Some(result)
1183 }
1184
1185 fn rewrite_string_lit(context: &RewriteContext,
1186                       span: Span,
1187                       width: usize,
1188                       offset: Indent)
1189                       -> Option<String> {
1190     let string_lit = context.snippet(span);
1191
1192     if !context.config.format_strings && !context.config.force_format_strings {
1193         return Some(string_lit);
1194     }
1195
1196     if !context.config.force_format_strings &&
1197        !string_requires_rewrite(context, span, &string_lit, width, offset) {
1198         return Some(string_lit);
1199     }
1200
1201     let fmt = StringFormat {
1202         opener: "\"",
1203         closer: "\"",
1204         line_start: " ",
1205         line_end: "\\",
1206         width: width,
1207         offset: offset,
1208         trim_end: false,
1209         config: context.config,
1210     };
1211
1212     // Remove the quote characters.
1213     let str_lit = &string_lit[1..string_lit.len() - 1];
1214
1215     rewrite_string(str_lit, &fmt)
1216 }
1217
1218 fn string_requires_rewrite(context: &RewriteContext,
1219                            span: Span,
1220                            string: &str,
1221                            width: usize,
1222                            offset: Indent)
1223                            -> bool {
1224     if context.codemap.lookup_char_pos(span.lo).col.0 != offset.width() {
1225         return true;
1226     }
1227
1228     for (i, line) in string.lines().enumerate() {
1229         if i == 0 {
1230             if line.len() > width {
1231                 return true;
1232             }
1233         } else {
1234             if line.len() > width + offset.width() {
1235                 return true;
1236             }
1237         }
1238     }
1239
1240     false
1241 }
1242
1243 pub fn rewrite_call<R>(context: &RewriteContext,
1244                        callee: &R,
1245                        args: &[ptr::P<ast::Expr>],
1246                        span: Span,
1247                        width: usize,
1248                        offset: Indent)
1249                        -> Option<String>
1250     where R: Rewrite
1251 {
1252     let closure = |callee_max_width| {
1253         rewrite_call_inner(context, callee, callee_max_width, args, span, width, offset)
1254     };
1255
1256     // 2 is for parens
1257     let max_width = try_opt!(width.checked_sub(2));
1258     binary_search(1, max_width, closure)
1259 }
1260
1261 fn rewrite_call_inner<R>(context: &RewriteContext,
1262                          callee: &R,
1263                          max_callee_width: usize,
1264                          args: &[ptr::P<ast::Expr>],
1265                          span: Span,
1266                          width: usize,
1267                          offset: Indent)
1268                          -> Result<String, Ordering>
1269     where R: Rewrite
1270 {
1271     let callee = callee.borrow();
1272     // FIXME using byte lens instead of char lens (and probably all over the
1273     // place too)
1274     let callee_str = match callee.rewrite(context, max_callee_width, offset) {
1275         Some(string) => {
1276             if !string.contains('\n') && string.len() > max_callee_width {
1277                 panic!("{:?} {}", string, max_callee_width);
1278             } else {
1279                 string
1280             }
1281         }
1282         None => return Err(Ordering::Greater),
1283     };
1284
1285     let span_lo = context.codemap.span_after(span, "(");
1286     let span = mk_sp(span_lo, span.hi);
1287
1288     let extra_offset = extra_offset(&callee_str, offset);
1289     // 2 is for parens.
1290     let remaining_width = match width.checked_sub(extra_offset + 2) {
1291         Some(str) => str,
1292         None => return Err(Ordering::Greater),
1293     };
1294     let offset = offset + extra_offset + 1;
1295     let arg_count = args.len();
1296     let block_indent = if arg_count == 1 {
1297         context.block_indent
1298     } else {
1299         offset
1300     };
1301     let inner_context = &RewriteContext { block_indent: block_indent, ..*context };
1302
1303     let items = itemize_list(context.codemap,
1304                              args.iter(),
1305                              ")",
1306                              |item| item.span.lo,
1307                              |item| item.span.hi,
1308                              |item| item.rewrite(&inner_context, remaining_width, offset),
1309                              span.lo,
1310                              span.hi);
1311     let mut item_vec: Vec<_> = items.collect();
1312
1313     // Try letting the last argument overflow to the next line with block
1314     // indentation. If its first line fits on one line with the other arguments,
1315     // we format the function arguments horizontally.
1316     let overflow_last = match args.last().map(|x| &x.node) {
1317         Some(&ast::ExprKind::Closure(..)) |
1318         Some(&ast::ExprKind::Block(..)) if arg_count > 1 => true,
1319         _ => false,
1320     } && context.config.chains_overflow_last;
1321
1322     let mut orig_last = None;
1323     let mut placeholder = None;
1324
1325     // Replace the last item with its first line to see if it fits with
1326     // first arguments.
1327     if overflow_last {
1328         let inner_context = &RewriteContext { block_indent: context.block_indent, ..*context };
1329         let rewrite = args.last().unwrap().rewrite(&inner_context, remaining_width, offset);
1330
1331         if let Some(rewrite) = rewrite {
1332             let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
1333             placeholder = Some(rewrite);
1334
1335             swap(&mut item_vec[arg_count - 1].item, &mut orig_last);
1336             item_vec[arg_count - 1].item = rewrite_first_line;
1337         }
1338     }
1339
1340     let tactic = definitive_tactic(&item_vec,
1341                                    ListTactic::LimitedHorizontalVertical(context.config
1342                                                                                 .fn_call_width),
1343                                    remaining_width);
1344
1345     // Replace the stub with the full overflowing last argument if the rewrite
1346     // succeeded and its first line fits with the other arguments.
1347     match (overflow_last, tactic, placeholder) {
1348         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
1349             item_vec[arg_count - 1].item = placeholder;
1350         }
1351         (true, _, _) => {
1352             item_vec[arg_count - 1].item = orig_last;
1353         }
1354         (false, _, _) => {}
1355     }
1356
1357     let fmt = ListFormatting {
1358         tactic: tactic,
1359         separator: ",",
1360         trailing_separator: SeparatorTactic::Never,
1361         indent: offset,
1362         width: width,
1363         ends_with_newline: false,
1364         config: context.config,
1365     };
1366
1367     let list_str = match write_list(&item_vec, &fmt) {
1368         Some(str) => str,
1369         None => return Err(Ordering::Less),
1370     };
1371
1372     Ok(format!("{}({})", callee_str, list_str))
1373 }
1374
1375 fn rewrite_paren(context: &RewriteContext,
1376                  subexpr: &ast::Expr,
1377                  width: usize,
1378                  offset: Indent)
1379                  -> Option<String> {
1380     debug!("rewrite_paren, width: {}, offset: {:?}", width, offset);
1381     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1382     // paren on the same line as the subexpr.
1383     let subexpr_str = subexpr.rewrite(context, try_opt!(width.checked_sub(2)), offset + 1);
1384     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1385     subexpr_str.map(|s| format!("({})", s))
1386 }
1387
1388 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1389                           path: &ast::Path,
1390                           fields: &'a [ast::Field],
1391                           base: Option<&'a ast::Expr>,
1392                           span: Span,
1393                           width: usize,
1394                           offset: Indent)
1395                           -> Option<String> {
1396     debug!("rewrite_struct_lit: width {}, offset {:?}", width, offset);
1397
1398     enum StructLitField<'a> {
1399         Regular(&'a ast::Field),
1400         Base(&'a ast::Expr),
1401     }
1402
1403     // 2 = " {".len()
1404     let path_budget = try_opt!(width.checked_sub(2));
1405     let path_str = try_opt!(rewrite_path(context, true, None, path, path_budget, offset));
1406
1407     // Foo { a: Foo } - indent is +3, width is -5.
1408     let h_budget = width.checked_sub(path_str.len() + 5).unwrap_or(0);
1409     // The 1 taken from the v_budget is for the comma.
1410     let (indent, v_budget) = match context.config.struct_lit_style {
1411         StructLitStyle::Visual => (offset + path_str.len() + 3, h_budget),
1412         StructLitStyle::Block => {
1413             // If we are all on one line, then we'll ignore the indent, and we
1414             // have a smaller budget.
1415             let indent = context.block_indent.block_indent(context.config);
1416             let v_budget = context.config.max_width.checked_sub(indent.width()).unwrap_or(0);
1417             (indent, v_budget)
1418         }
1419     };
1420
1421     let field_iter = fields.into_iter()
1422                            .map(StructLitField::Regular)
1423                            .chain(base.into_iter().map(StructLitField::Base));
1424
1425     let inner_context = &RewriteContext { block_indent: indent, ..*context };
1426
1427     let items = itemize_list(context.codemap,
1428                              field_iter,
1429                              "}",
1430                              |item| {
1431                                  match *item {
1432                                      StructLitField::Regular(ref field) => field.span.lo,
1433                                      StructLitField::Base(ref expr) => {
1434                                          let last_field_hi = fields.last().map_or(span.lo,
1435                                                                                   |field| {
1436                                                                                       field.span.hi
1437                                                                                   });
1438                                          let snippet = context.snippet(mk_sp(last_field_hi,
1439                                                                              expr.span.lo));
1440                                          let pos = snippet.find_uncommented("..").unwrap();
1441                                          last_field_hi + BytePos(pos as u32)
1442                                      }
1443                                  }
1444                              },
1445                              |item| {
1446                                  match *item {
1447                                      StructLitField::Regular(ref field) => field.span.hi,
1448                                      StructLitField::Base(ref expr) => expr.span.hi,
1449                                  }
1450                              },
1451                              |item| {
1452                                  match *item {
1453                                      StructLitField::Regular(ref field) => {
1454                                          rewrite_field(inner_context,
1455                                                        &field,
1456                                                        v_budget.checked_sub(1).unwrap_or(0),
1457                                                        indent)
1458                                      }
1459                                      StructLitField::Base(ref expr) => {
1460                                          // 2 = ..
1461                                          expr.rewrite(inner_context,
1462                                                       try_opt!(v_budget.checked_sub(2)),
1463                                                       indent + 2)
1464                                              .map(|s| format!("..{}", s))
1465                                      }
1466                                  }
1467                              },
1468                              context.codemap.span_after(span, "{"),
1469                              span.hi);
1470     let item_vec = items.collect::<Vec<_>>();
1471
1472     let tactic = {
1473         let mut prelim_tactic = match (context.config.struct_lit_style, fields.len()) {
1474             (StructLitStyle::Visual, 1) => ListTactic::HorizontalVertical,
1475             _ => context.config.struct_lit_multiline_style.to_list_tactic(),
1476         };
1477
1478         if prelim_tactic == ListTactic::HorizontalVertical && fields.len() > 1 {
1479             prelim_tactic = ListTactic::LimitedHorizontalVertical(context.config.struct_lit_width);
1480         }
1481
1482         definitive_tactic(&item_vec, prelim_tactic, h_budget)
1483     };
1484
1485     let budget = match tactic {
1486         DefinitiveListTactic::Horizontal => h_budget,
1487         _ => v_budget,
1488     };
1489
1490     let ends_with_newline = context.config.struct_lit_style != StructLitStyle::Visual &&
1491                             tactic == DefinitiveListTactic::Vertical;
1492
1493     let fmt = ListFormatting {
1494         tactic: tactic,
1495         separator: ",",
1496         trailing_separator: if base.is_some() {
1497             SeparatorTactic::Never
1498         } else {
1499             context.config.struct_lit_trailing_comma
1500         },
1501         indent: indent,
1502         width: budget,
1503         ends_with_newline: ends_with_newline,
1504         config: context.config,
1505     };
1506     let fields_str = try_opt!(write_list(&item_vec, &fmt));
1507
1508     if fields_str.is_empty() {
1509         return Some(format!("{} {{}}", path_str));
1510     }
1511
1512     let format_on_newline = || {
1513         let inner_indent = context.block_indent
1514                                   .block_indent(context.config)
1515                                   .to_string(context.config);
1516         let outer_indent = context.block_indent.to_string(context.config);
1517         Some(format!("{} {{\n{}{}\n{}}}",
1518                      path_str,
1519                      inner_indent,
1520                      fields_str,
1521                      outer_indent))
1522     };
1523
1524     match (context.config.struct_lit_style, context.config.struct_lit_multiline_style) {
1525         (StructLitStyle::Block, _) if fields_str.contains('\n') || fields_str.len() > h_budget => {
1526             format_on_newline()
1527         }
1528         (StructLitStyle::Block, MultilineStyle::ForceMulti) => format_on_newline(),
1529         _ => Some(format!("{} {{ {} }}", path_str, fields_str)),
1530     }
1531
1532     // FIXME if context.config.struct_lit_style == Visual, but we run out
1533     // of space, we should fall back to BlockIndent.
1534 }
1535
1536 fn rewrite_field(context: &RewriteContext,
1537                  field: &ast::Field,
1538                  width: usize,
1539                  offset: Indent)
1540                  -> Option<String> {
1541     let name = &field.ident.node.to_string();
1542     let overhead = name.len() + 2;
1543     let expr = field.expr.rewrite(context,
1544                                   try_opt!(width.checked_sub(overhead)),
1545                                   offset + overhead);
1546
1547     match expr {
1548         Some(e) => Some(format!("{}: {}", name, e)),
1549         None => {
1550             let expr_offset = offset.block_indent(&context.config);
1551             let expr = field.expr.rewrite(context,
1552                                           try_opt!(context.config
1553                                                           .max_width
1554                                                           .checked_sub(expr_offset.width())),
1555                                           expr_offset);
1556             expr.map(|s| format!("{}:\n{}{}", name, expr_offset.to_string(&context.config), s))
1557         }
1558     }
1559 }
1560
1561 pub fn rewrite_tuple<'a, I>(context: &RewriteContext,
1562                             mut items: I,
1563                             span: Span,
1564                             width: usize,
1565                             offset: Indent)
1566                             -> Option<String>
1567     where I: ExactSizeIterator,
1568           <I as Iterator>::Item: Deref,
1569           <I::Item as Deref>::Target: Rewrite + Spanned + 'a
1570 {
1571     let indent = offset + 1;
1572     // In case of length 1, need a trailing comma
1573     if items.len() == 1 {
1574         // 3 = "(" + ",)"
1575         let budget = try_opt!(width.checked_sub(3));
1576         return items.next().unwrap().rewrite(context, budget, indent).map(|s| format!("({},)", s));
1577     }
1578
1579     let list_lo = context.codemap.span_after(span, "(");
1580     let items = itemize_list(context.codemap,
1581                              items,
1582                              ")",
1583                              |item| item.span().lo,
1584                              |item| item.span().hi,
1585                              |item| {
1586                                  let inner_width = try_opt!(context.config
1587                                                                    .max_width
1588                                                                    .checked_sub(indent.width() +
1589                                                                                 1));
1590                                  item.rewrite(context, inner_width, indent)
1591                              },
1592                              list_lo,
1593                              span.hi - BytePos(1));
1594     let budget = try_opt!(width.checked_sub(2));
1595     let list_str = try_opt!(format_item_list(items, budget, indent, context.config));
1596
1597     Some(format!("({})", list_str))
1598 }
1599
1600 fn rewrite_binary_op(context: &RewriteContext,
1601                      op: &ast::BinOp,
1602                      lhs: &ast::Expr,
1603                      rhs: &ast::Expr,
1604                      width: usize,
1605                      offset: Indent)
1606                      -> Option<String> {
1607     // FIXME: format comments between operands and operator
1608
1609     let operator_str = context.snippet(op.span);
1610
1611     // Get "full width" rhs and see if it fits on the current line. This
1612     // usually works fairly well since it tends to place operands of
1613     // operations with high precendence close together.
1614     let rhs_result = try_opt!(rhs.rewrite(context, width, offset));
1615
1616     // Second condition is needed in case of line break not caused by a
1617     // shortage of space, but by end-of-line comments, for example.
1618     // Note that this is non-conservative, but its just to see if it's even
1619     // worth trying to put everything on one line.
1620     if rhs_result.len() + 2 + operator_str.len() < width && !rhs_result.contains('\n') {
1621         // 1 = space between lhs expr and operator
1622         if let Some(mut result) = lhs.rewrite(context, width - 1 - operator_str.len(), offset) {
1623             result.push(' ');
1624             result.push_str(&operator_str);
1625             result.push(' ');
1626
1627             let remaining_width = width.checked_sub(last_line_width(&result)).unwrap_or(0);
1628
1629             if rhs_result.len() <= remaining_width {
1630                 result.push_str(&rhs_result);
1631                 return Some(result);
1632             }
1633
1634             if let Some(rhs_result) = rhs.rewrite(context, remaining_width, offset + result.len()) {
1635                 if rhs_result.len() <= remaining_width {
1636                     result.push_str(&rhs_result);
1637                     return Some(result);
1638                 }
1639             }
1640         }
1641     }
1642
1643     // We have to use multiple lines.
1644
1645     // Re-evaluate the lhs because we have more space now:
1646     let budget = try_opt!(context.config
1647                                  .max_width
1648                                  .checked_sub(offset.width() + 1 + operator_str.len()));
1649     Some(format!("{} {}\n{}{}",
1650                  try_opt!(lhs.rewrite(context, budget, offset)),
1651                  operator_str,
1652                  offset.to_string(context.config),
1653                  rhs_result))
1654 }
1655
1656 pub fn rewrite_unary_prefix<R: Rewrite>(context: &RewriteContext,
1657                                         prefix: &str,
1658                                         rewrite: &R,
1659                                         width: usize,
1660                                         offset: Indent)
1661                                         -> Option<String> {
1662     rewrite.rewrite(context,
1663                     try_opt!(width.checked_sub(prefix.len())),
1664                     offset + prefix.len())
1665            .map(|r| format!("{}{}", prefix, r))
1666 }
1667
1668 fn rewrite_unary_op(context: &RewriteContext,
1669                     op: &ast::UnOp,
1670                     expr: &ast::Expr,
1671                     width: usize,
1672                     offset: Indent)
1673                     -> Option<String> {
1674     // For some reason, an UnOp is not spanned like BinOp!
1675     let operator_str = match *op {
1676         ast::UnOp::Deref => "*",
1677         ast::UnOp::Not => "!",
1678         ast::UnOp::Neg => "-",
1679     };
1680     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1681 }
1682
1683 fn rewrite_assignment(context: &RewriteContext,
1684                       lhs: &ast::Expr,
1685                       rhs: &ast::Expr,
1686                       op: Option<&ast::BinOp>,
1687                       width: usize,
1688                       offset: Indent)
1689                       -> Option<String> {
1690     let operator_str = match op {
1691         Some(op) => context.snippet(op.span),
1692         None => "=".to_owned(),
1693     };
1694
1695     // 1 = space between lhs and operator.
1696     let max_width = try_opt!(width.checked_sub(operator_str.len() + 1));
1697     let lhs_str = format!("{} {}",
1698                           try_opt!(lhs.rewrite(context, max_width, offset)),
1699                           operator_str);
1700
1701     rewrite_assign_rhs(&context, lhs_str, rhs, width, offset)
1702 }
1703
1704 // The left hand side must contain everything up to, and including, the
1705 // assignment operator.
1706 pub fn rewrite_assign_rhs<S: Into<String>>(context: &RewriteContext,
1707                                            lhs: S,
1708                                            ex: &ast::Expr,
1709                                            width: usize,
1710                                            offset: Indent)
1711                                            -> Option<String> {
1712     let mut result = lhs.into();
1713     let last_line_width = last_line_width(&result) -
1714                           if result.contains('\n') {
1715         offset.width()
1716     } else {
1717         0
1718     };
1719     // 1 = space between operator and rhs.
1720     let max_width = try_opt!(width.checked_sub(last_line_width + 1));
1721     let rhs = ex.rewrite(&context, max_width, offset + last_line_width + 1);
1722
1723     match rhs {
1724         Some(new_str) => {
1725             result.push(' ');
1726             result.push_str(&new_str)
1727         }
1728         None => {
1729             // Expression did not fit on the same line as the identifier. Retry
1730             // on the next line.
1731             let new_offset = offset.block_indent(context.config);
1732             result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
1733
1734             // FIXME: we probably should related max_width to width instead of
1735             // config.max_width where is the 1 coming from anyway?
1736             let max_width = try_opt!(context.config.max_width.checked_sub(new_offset.width() + 1));
1737             let inner_context = context.nested_context();
1738             let rhs = ex.rewrite(&inner_context, max_width, new_offset);
1739
1740             result.push_str(&&try_opt!(rhs));
1741         }
1742     }
1743
1744     Some(result)
1745 }
1746
1747 fn rewrite_expr_addrof(context: &RewriteContext,
1748                        mutability: ast::Mutability,
1749                        expr: &ast::Expr,
1750                        width: usize,
1751                        offset: Indent)
1752                        -> Option<String> {
1753     let operator_str = match mutability {
1754         ast::Mutability::Immutable => "&",
1755         ast::Mutability::Mutable => "&mut ",
1756     };
1757     rewrite_unary_prefix(context, operator_str, expr, width, offset)
1758 }