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