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, min};
  12 use std::iter::ExactSizeIterator;
  13 use std::fmt::Write;
  14
  15 use {Indent, Shape, Spanned};
  16 use codemap::SpanUtils;
  17 use rewrite::{Rewrite, RewriteContext};
  18 use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic,
  19             DefinitiveListTactic, definitive_tactic, ListItem, struct_lit_shape,
  20             struct_lit_tactic, shape_for_tactic, struct_lit_formatting};
  21 use string::{StringFormat, rewrite_string};
  22 use utils::{extra_offset, last_line_width, wrap_str, binary_search, first_line_width,
  23             semicolon_for_stmt, trimmed_last_line_width, left_most_sub_expr, stmt_expr,
  24             colon_spaces, contains_skip, mk_sp, last_line_extendable, paren_overhead};
  25 use visitor::FmtVisitor;
  26 use config::{Config, IndentStyle, MultilineStyle, ControlBraceStyle, Style};
  27 use comment::{FindUncommented, rewrite_comment, contains_comment, recover_comment_removed};
  28 use types::{rewrite_path, PathContext, can_be_overflowed_type};
  29 use items::{span_lo_for_arg, span_hi_for_arg};
  30 use chains::rewrite_chain;
  31 use macros::{rewrite_macro, MacroPosition};
  32 use patterns::{TuplePatField, can_be_overflowed_pat};
  33 use vertical::rewrite_with_alignment;
  34
  35 use syntax::{ast, ptr};
  36 use syntax::codemap::{CodeMap, Span, BytePos};
  37 use syntax::parse::classify;
  38
  39 impl Rewrite for ast::Expr {
  40     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  41         format_expr(self, ExprType::SubExpression, context, shape)
  42     }
  43 }
  44
  45 #[derive(PartialEq)]
  46 pub enum ExprType {
  47     Statement,
  48     SubExpression,
  49 }
  50
  51 fn combine_attr_and_expr(
  52     context: &RewriteContext,
  53     shape: Shape,
  54     attr_str: &str,
  55     expr_str: &str,
  56 ) -> String {
  57     let separator = if attr_str.is_empty() {
  58         String::new()
  59     } else {
  60         if expr_str.contains('\n') || attr_str.contains('\n') ||
  61             attr_str.len() + expr_str.len() > shape.width
  62         {
  63             format!("\n{}", shape.indent.to_string(context.config))
  64         } else {
  65             String::from(" ")
  66         }
  67     };
  68     format!("{}{}{}", attr_str, separator, expr_str)
  69 }
  70
  71 pub fn format_expr(
  72     expr: &ast::Expr,
  73     expr_type: ExprType,
  74     context: &RewriteContext,
  75     shape: Shape,
  76 ) -> Option<String> {
  77     let attr_rw = (&*expr.attrs).rewrite(context, shape);
  78     if contains_skip(&*expr.attrs) {
  79         if let Some(attr_str) = attr_rw {
  80             return Some(combine_attr_and_expr(
  81                 context,
  82                 shape,
  83                 &attr_str,
  84                 &context.snippet(expr.span),
  85             ));
  86         } else {
  87             return Some(context.snippet(expr.span));
  88         }
  89     }
  90     let expr_rw = match expr.node {
  91         ast::ExprKind::Array(ref expr_vec) => {
  92             rewrite_array(
  93                 expr_vec.iter().map(|e| &**e),
  94                 mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi),
  95                 context,
  96                 shape,
  97                 false,
  98             )
  99         }
 100         ast::ExprKind::Lit(ref l) => {
 101             match l.node {
 102                 ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
 103                     rewrite_string_lit(context, l.span, shape)
 104                 }
 105                 _ => {
 106                     wrap_str(
 107                         context.snippet(expr.span),
 108                         context.config.max_width(),
 109                         shape,
 110                     )
 111                 }
 112             }
 113         }
 114         ast::ExprKind::Call(ref callee, ref args) => {
 115             let inner_span = mk_sp(callee.span.hi, expr.span.hi);
 116             rewrite_call_with_binary_search(
 117                 context,
 118                 &**callee,
 119                 &args.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 120                 inner_span,
 121                 shape,
 122             )
 123         }
 124         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
 125         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
 126             // FIXME: format comments between operands and operator
 127             rewrite_pair(
 128                 &**lhs,
 129                 &**rhs,
 130                 "",
 131                 &format!(" {} ", context.snippet(op.span)),
 132                 "",
 133                 context,
 134                 shape,
 135             )
 136         }
 137         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 138         ast::ExprKind::Struct(ref path, ref fields, ref base) => {
 139             rewrite_struct_lit(
 140                 context,
 141                 path,
 142                 fields,
 143                 base.as_ref().map(|e| &**e),
 144                 expr.span,
 145                 shape,
 146             )
 147         }
 148         ast::ExprKind::Tup(ref items) => {
 149             rewrite_tuple(
 150                 context,
 151                 &items.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 152                 expr.span,
 153                 shape,
 154             )
 155         }
 156         ast::ExprKind::If(..) |
 157         ast::ExprKind::IfLet(..) |
 158         ast::ExprKind::ForLoop(..) |
 159         ast::ExprKind::Loop(..) |
 160         ast::ExprKind::While(..) |
 161         ast::ExprKind::WhileLet(..) => {
 162             to_control_flow(expr, expr_type)
 163                 .and_then(|control_flow| control_flow.rewrite(context, shape))
 164         }
 165         ast::ExprKind::Block(ref block) => {
 166             match expr_type {
 167                 ExprType::Statement => {
 168                     if is_unsafe_block(block) {
 169                         block.rewrite(context, shape)
 170                     } else {
 171                         // Rewrite block without trying to put it in a single line.
 172                         if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 173                             return rw;
 174                         }
 175                         let prefix = try_opt!(block_prefix(context, block, shape));
 176                         rewrite_block_with_visitor(context, &prefix, block, shape)
 177                     }
 178                 }
 179                 ExprType::SubExpression => block.rewrite(context, shape),
 180             }
 181         }
 182         ast::ExprKind::Match(ref cond, ref arms) => {
 183             rewrite_match(context, cond, arms, shape, expr.span)
 184         }
 185         ast::ExprKind::Path(ref qself, ref path) => {
 186             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 187         }
 188         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 189             rewrite_assignment(context, lhs, rhs, None, shape)
 190         }
 191         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 192             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 193         }
 194         ast::ExprKind::Continue(ref opt_ident) => {
 195             let id_str = match *opt_ident {
 196                 Some(ident) => format!(" {}", ident.node),
 197                 None => String::new(),
 198             };
 199             wrap_str(
 200                 format!("continue{}", id_str),
 201                 context.config.max_width(),
 202                 shape,
 203             )
 204         }
 205         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 206             let id_str = match *opt_ident {
 207                 Some(ident) => format!(" {}", ident.node),
 208                 None => String::new(),
 209             };
 210
 211             if let Some(ref expr) = *opt_expr {
 212                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 213             } else {
 214                 wrap_str(
 215                     format!("break{}", id_str),
 216                     context.config.max_width(),
 217                     shape,
 218                 )
 219             }
 220         }
 221         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 222             rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 223         }
 224         ast::ExprKind::Try(..) |
 225         ast::ExprKind::Field(..) |
 226         ast::ExprKind::TupField(..) |
 227         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 228         ast::ExprKind::Mac(ref mac) => {
 229             // Failure to rewrite a marco should not imply failure to
 230             // rewrite the expression.
 231             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 232                 wrap_str(
 233                     context.snippet(expr.span),
 234                     context.config.max_width(),
 235                     shape,
 236                 )
 237             })
 238         }
 239         ast::ExprKind::Ret(None) => {
 240             wrap_str("return".to_owned(), context.config.max_width(), shape)
 241         }
 242         ast::ExprKind::Ret(Some(ref expr)) => {
 243             rewrite_unary_prefix(context, "return ", &**expr, shape)
 244         }
 245         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 246         ast::ExprKind::AddrOf(mutability, ref expr) => {
 247             rewrite_expr_addrof(context, mutability, expr, shape)
 248         }
 249         ast::ExprKind::Cast(ref expr, ref ty) => {
 250             rewrite_pair(&**expr, &**ty, "", " as ", "", context, shape)
 251         }
 252         ast::ExprKind::Type(ref expr, ref ty) => {
 253             rewrite_pair(&**expr, &**ty, "", ": ", "", context, shape)
 254         }
 255         ast::ExprKind::Index(ref expr, ref index) => {
 256             rewrite_index(&**expr, &**index, context, shape)
 257         }
 258         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 259             let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
 260                 ("[ ", " ]")
 261             } else {
 262                 ("[", "]")
 263             };
 264             rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, shape)
 265         }
 266         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 267             let delim = match limits {
 268                 ast::RangeLimits::HalfOpen => "..",
 269                 ast::RangeLimits::Closed => "...",
 270             };
 271
 272             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 273                 match lhs.node {
 274                     ast::ExprKind::Lit(ref lit) => {
 275                         match lit.node {
 276                             ast::LitKind::FloatUnsuffixed(..) => {
 277                                 context.snippet(lit.span).ends_with('.')
 278                             }
 279                             _ => false,
 280                         }
 281                     }
 282                     _ => false,
 283                 }
 284             }
 285
 286             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 287                 (Some(ref lhs), Some(ref rhs)) => {
 288                     let sp_delim = if context.config.spaces_around_ranges() {
 289                         format!(" {} ", delim)
 290                     } else if needs_space_before_range(context, lhs) {
 291                         format!(" {}", delim)
 292                     } else {
 293                         delim.into()
 294                     };
 295                     rewrite_pair(&**lhs, &**rhs, "", &sp_delim, "", context, shape)
 296                 }
 297                 (None, Some(ref rhs)) => {
 298                     let sp_delim = if context.config.spaces_around_ranges() {
 299                         format!("{} ", delim)
 300                     } else {
 301                         delim.into()
 302                     };
 303                     rewrite_unary_prefix(context, &sp_delim, &**rhs, shape)
 304                 }
 305                 (Some(ref lhs), None) => {
 306                     let sp_delim = if context.config.spaces_around_ranges() {
 307                         format!(" {}", delim)
 308                     } else {
 309                         delim.into()
 310                     };
 311                     rewrite_unary_suffix(context, &sp_delim, &**lhs, shape)
 312                 }
 313                 (None, None) => wrap_str(delim.into(), context.config.max_width(), shape),
 314             }
 315         }
 316         // We do not format these expressions yet, but they should still
 317         // satisfy our width restrictions.
 318         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => {
 319             wrap_str(
 320                 context.snippet(expr.span),
 321                 context.config.max_width(),
 322                 shape,
 323             )
 324         }
 325         ast::ExprKind::Catch(ref block) => {
 326             if let rewrite @ Some(_) =
 327                 rewrite_single_line_block(context, "do catch ", block, shape)
 328             {
 329                 return rewrite;
 330             }
 331             // 9 = `do catch `
 332             let budget = shape.width.checked_sub(9).unwrap_or(0);
 333             Some(format!(
 334                 "{}{}",
 335                 "do catch ",
 336                 try_opt!(block.rewrite(&context, Shape::legacy(budget, shape.indent)))
 337             ))
 338         }
 339     };
 340     match (attr_rw, expr_rw) {
 341         (Some(attr_str), Some(expr_str)) => {
 342             recover_comment_removed(
 343                 combine_attr_and_expr(context, shape, &attr_str, &expr_str),
 344                 expr.span,
 345                 context,
 346                 shape,
 347             )
 348         }
 349         _ => None,
 350     }
 351 }
 352
 353 pub fn rewrite_pair<LHS, RHS>(
 354     lhs: &LHS,
 355     rhs: &RHS,
 356     prefix: &str,
 357     infix: &str,
 358     suffix: &str,
 359     context: &RewriteContext,
 360     shape: Shape,
 361 ) -> Option<String>
 362 where
 363     LHS: Rewrite,
 364     RHS: Rewrite,
 365 {
 366     // Get "full width" rhs and see if it fits on the current line. This
 367     // usually works fairly well since it tends to place operands of
 368     // operations with high precendence close together.
 369     // Note that this is non-conservative, but its just to see if it's even
 370     // worth trying to put everything on one line.
 371     let rhs_shape = try_opt!(shape.sub_width(suffix.len()));
 372     let rhs_result = rhs.rewrite(context, rhs_shape);
 373
 374     if let Some(rhs_result) = rhs_result {
 375         // This is needed in case of line break not caused by a
 376         // shortage of space, but by end-of-line comments, for example.
 377         if !rhs_result.contains('\n') {
 378             let lhs_shape =
 379                 try_opt!(try_opt!(shape.offset_left(prefix.len())).sub_width(infix.len()));
 380             let lhs_result = lhs.rewrite(context, lhs_shape);
 381             if let Some(lhs_result) = lhs_result {
 382                 let mut result = format!("{}{}{}", prefix, lhs_result, infix);
 383
 384                 let remaining_width = shape
 385                     .width
 386                     .checked_sub(last_line_width(&result) + suffix.len())
 387                     .unwrap_or(0);
 388
 389                 if rhs_result.len() <= remaining_width {
 390                     result.push_str(&rhs_result);
 391                     result.push_str(suffix);
 392                     return Some(result);
 393                 }
 394
 395                 // Try rewriting the rhs into the remaining space.
 396                 let rhs_shape = shape.shrink_left(last_line_width(&result) + suffix.len());
 397                 if let Some(rhs_shape) = rhs_shape {
 398                     if let Some(rhs_result) = rhs.rewrite(context, rhs_shape) {
 399                         // FIXME this should always hold.
 400                         if rhs_result.len() <= remaining_width {
 401                             result.push_str(&rhs_result);
 402                             result.push_str(suffix);
 403                             return Some(result);
 404                         }
 405                     }
 406                 }
 407             }
 408         }
 409     }
 410
 411     // We have to use multiple lines.
 412
 413     // Re-evaluate the rhs because we have more space now:
 414     let infix = infix.trim_right();
 415     let rhs_shape = match context.config.control_style() {
 416         Style::Legacy => {
 417             try_opt!(shape.sub_width(suffix.len() + prefix.len())).visual_indent(prefix.len())
 418         }
 419         Style::Rfc => {
 420             // Try to calculate the initial constraint on the right hand side.
 421             let rhs_overhead = shape.rhs_overhead(context.config);
 422             try_opt!(
 423                 Shape::indented(shape.indent.block_indent(context.config), context.config)
 424                     .sub_width(rhs_overhead)
 425             )
 426         }
 427     };
 428     let rhs_result = try_opt!(rhs.rewrite(context, rhs_shape));
 429     let lhs_overhead = shape.used_width() + prefix.len() + infix.len();
 430     let lhs_shape = Shape {
 431         width: try_opt!(context.config.max_width().checked_sub(lhs_overhead)),
 432         ..shape
 433     };
 434     let lhs_result = try_opt!(lhs.rewrite(context, lhs_shape));
 435     Some(format!(
 436         "{}{}{}\n{}{}{}",
 437         prefix,
 438         lhs_result,
 439         infix,
 440         rhs_shape.indent.to_string(context.config),
 441         rhs_result,
 442         suffix
 443     ))
 444 }
 445
 446 pub fn rewrite_array<'a, I>(
 447     expr_iter: I,
 448     span: Span,
 449     context: &RewriteContext,
 450     shape: Shape,
 451     trailing_comma: bool,
 452 ) -> Option<String>
 453 where
 454     I: Iterator<Item = &'a ast::Expr>,
 455 {
 456     let bracket_size = if context.config.spaces_within_square_brackets() {
 457         2 // "[ "
 458     } else {
 459         1 // "["
 460     };
 461
 462     let mut nested_shape = match context.config.array_layout() {
 463         IndentStyle::Block => {
 464             try_opt!(
 465                 shape
 466                     .block()
 467                     .block_indent(context.config.tab_spaces())
 468                     .with_max_width(context.config)
 469                     .sub_width(1)
 470             )
 471         }
 472         IndentStyle::Visual => {
 473             try_opt!(
 474                 shape
 475                     .visual_indent(bracket_size)
 476                     .sub_width(bracket_size * 2)
 477             )
 478         }
 479     };
 480
 481     let items = itemize_list(
 482         context.codemap,
 483         expr_iter,
 484         "]",
 485         |item| item.span.lo,
 486         |item| item.span.hi,
 487         |item| item.rewrite(context, nested_shape),
 488         span.lo,
 489         span.hi,
 490     ).collect::<Vec<_>>();
 491
 492     if items.is_empty() {
 493         if context.config.spaces_within_square_brackets() {
 494             return Some("[ ]".to_string());
 495         } else {
 496             return Some("[]".to_string());
 497         }
 498     }
 499
 500     let has_long_item = items
 501         .iter()
 502         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 503
 504     let mut tactic = match context.config.array_layout() {
 505         IndentStyle::Block => {
 506             // FIXME wrong shape in one-line case
 507             match shape.width.checked_sub(2 * bracket_size) {
 508                 Some(width) => {
 509                     let tactic =
 510                         ListTactic::LimitedHorizontalVertical(context.config.array_width());
 511                     definitive_tactic(&items, tactic, width)
 512                 }
 513                 None => DefinitiveListTactic::Vertical,
 514             }
 515         }
 516         IndentStyle::Visual => {
 517             if has_long_item || items.iter().any(ListItem::is_multiline) {
 518                 definitive_tactic(
 519                     &items,
 520                     ListTactic::LimitedHorizontalVertical(context.config.array_width()),
 521                     nested_shape.width,
 522                 )
 523             } else {
 524                 DefinitiveListTactic::Mixed
 525             }
 526         }
 527     };
 528     if context.config.array_horizontal_layout_threshold() > 0 &&
 529         items.len() > context.config.array_horizontal_layout_threshold()
 530     {
 531         tactic = DefinitiveListTactic::Mixed;
 532         if context.config.array_layout() == IndentStyle::Block {
 533             nested_shape = try_opt!(
 534                 shape
 535                     .visual_indent(bracket_size)
 536                     .sub_width(bracket_size * 2)
 537             );
 538         }
 539     }
 540
 541     let fmt = ListFormatting {
 542         tactic: tactic,
 543         separator: ",",
 544         trailing_separator: if trailing_comma {
 545             SeparatorTactic::Always
 546         } else if context.inside_macro || context.config.array_layout() == IndentStyle::Visual {
 547             SeparatorTactic::Never
 548         } else {
 549             SeparatorTactic::Vertical
 550         },
 551         shape: nested_shape,
 552         ends_with_newline: false,
 553         config: context.config,
 554     };
 555     let list_str = try_opt!(write_list(&items, &fmt));
 556
 557     let result = if context.config.array_layout() == IndentStyle::Visual ||
 558         tactic != DefinitiveListTactic::Vertical
 559     {
 560         if context.config.spaces_within_square_brackets() && list_str.len() > 0 {
 561             format!("[ {} ]", list_str)
 562         } else {
 563             format!("[{}]", list_str)
 564         }
 565     } else {
 566         format!(
 567             "[\n{}{}\n{}]",
 568             nested_shape.indent.to_string(context.config),
 569             list_str,
 570             shape.block().indent.to_string(context.config)
 571         )
 572     };
 573
 574     Some(result)
 575 }
 576
 577 // Return type is (prefix, extra_offset)
 578 fn rewrite_closure_fn_decl(
 579     capture: ast::CaptureBy,
 580     fn_decl: &ast::FnDecl,
 581     body: &ast::Expr,
 582     span: Span,
 583     context: &RewriteContext,
 584     shape: Shape,
 585 ) -> Option<(String, usize)> {
 586     let mover = if capture == ast::CaptureBy::Value {
 587         "move "
 588     } else {
 589         ""
 590     };
 591     // 4 = "|| {".len(), which is overconservative when the closure consists of
 592     // a single expression.
 593     let nested_shape = try_opt!(try_opt!(shape.shrink_left(mover.len())).sub_width(4));
 594
 595     // 1 = |
 596     let argument_offset = nested_shape.indent + 1;
 597     let arg_shape = try_opt!(nested_shape.shrink_left(1)).visual_indent(0);
 598     let ret_str = try_opt!(fn_decl.output.rewrite(context, arg_shape));
 599
 600     let arg_items = itemize_list(
 601         context.codemap,
 602         fn_decl.inputs.iter(),
 603         "|",
 604         |arg| span_lo_for_arg(arg),
 605         |arg| span_hi_for_arg(context, arg),
 606         |arg| arg.rewrite(context, arg_shape),
 607         context.codemap.span_after(span, "|"),
 608         body.span.lo,
 609     );
 610     let item_vec = arg_items.collect::<Vec<_>>();
 611     // 1 = space between arguments and return type.
 612     let horizontal_budget = nested_shape
 613         .width
 614         .checked_sub(ret_str.len() + 1)
 615         .unwrap_or(0);
 616     let tactic = definitive_tactic(&item_vec, ListTactic::HorizontalVertical, horizontal_budget);
 617     let arg_shape = match tactic {
 618         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 619         _ => arg_shape,
 620     };
 621
 622     let fmt = ListFormatting {
 623         tactic: tactic,
 624         separator: ",",
 625         trailing_separator: SeparatorTactic::Never,
 626         shape: arg_shape,
 627         ends_with_newline: false,
 628         config: context.config,
 629     };
 630     let list_str = try_opt!(write_list(&item_vec, &fmt));
 631     let mut prefix = format!("{}|{}|", mover, list_str);
 632     // 1 = space between `|...|` and body.
 633     let extra_offset = extra_offset(&prefix, shape) + 1;
 634
 635     if !ret_str.is_empty() {
 636         if prefix.contains('\n') {
 637             prefix.push('\n');
 638             prefix.push_str(&argument_offset.to_string(context.config));
 639         } else {
 640             prefix.push(' ');
 641         }
 642         prefix.push_str(&ret_str);
 643     }
 644
 645     Some((prefix, extra_offset))
 646 }
 647
 648 // This functions is pretty messy because of the rules around closures and blocks:
 649 // FIXME - the below is probably no longer true in full.
 650 //   * if there is a return type, then there must be braces,
 651 //   * given a closure with braces, whether that is parsed to give an inner block
 652 //     or not depends on if there is a return type and if there are statements
 653 //     in that block,
 654 //   * if the first expression in the body ends with a block (i.e., is a
 655 //     statement without needing a semi-colon), then adding or removing braces
 656 //     can change whether it is treated as an expression or statement.
 657 fn rewrite_closure(
 658     capture: ast::CaptureBy,
 659     fn_decl: &ast::FnDecl,
 660     body: &ast::Expr,
 661     span: Span,
 662     context: &RewriteContext,
 663     shape: Shape,
 664 ) -> Option<String> {
 665     let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
 666         capture,
 667         fn_decl,
 668         body,
 669         span,
 670         context,
 671         shape,
 672     ));
 673     // 1 = space between `|...|` and body.
 674     let body_shape = try_opt!(shape.offset_left(extra_offset));
 675
 676     if let ast::ExprKind::Block(ref block) = body.node {
 677         // The body of the closure is an empty block.
 678         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 679             return Some(format!("{} {{}}", prefix));
 680         }
 681
 682         // Figure out if the block is necessary.
 683         let needs_block = block.rules != ast::BlockCheckMode::Default ||
 684             block.stmts.len() > 1 || context.inside_macro ||
 685             block_contains_comment(block, context.codemap) ||
 686             prefix.contains('\n');
 687
 688         let no_return_type = if let ast::FunctionRetTy::Default(_) = fn_decl.output {
 689             true
 690         } else {
 691             false
 692         };
 693         if no_return_type && !needs_block {
 694             // lock.stmts.len() == 1
 695             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 696                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 697                     return Some(rw);
 698                 }
 699             }
 700         }
 701
 702         if !needs_block {
 703             // We need braces, but we might still prefer a one-liner.
 704             let stmt = &block.stmts[0];
 705             // 4 = braces and spaces.
 706             if let Some(body_shape) = body_shape.sub_width(4) {
 707                 // Checks if rewrite succeeded and fits on a single line.
 708                 if let Some(rewrite) = and_one_line(stmt.rewrite(context, body_shape)) {
 709                     return Some(format!("{} {{ {} }}", prefix, rewrite));
 710                 }
 711             }
 712         }
 713
 714         // Either we require a block, or tried without and failed.
 715         rewrite_closure_block(&block, &prefix, context, body_shape)
 716     } else {
 717         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
 718             // The closure originally had a non-block expression, but we can't fit on
 719             // one line, so we'll insert a block.
 720             rewrite_closure_with_block(context, body_shape, &prefix, body)
 721         })
 722     }
 723 }
 724
 725 // Rewrite closure with a single expression wrapping its body with block.
 726 fn rewrite_closure_with_block(
 727     context: &RewriteContext,
 728     shape: Shape,
 729     prefix: &str,
 730     body: &ast::Expr,
 731 ) -> Option<String> {
 732     let block = ast::Block {
 733         stmts: vec![
 734             ast::Stmt {
 735                 id: ast::NodeId::new(0),
 736                 node: ast::StmtKind::Expr(ptr::P(body.clone())),
 737                 span: body.span,
 738             },
 739         ],
 740         id: ast::NodeId::new(0),
 741         rules: ast::BlockCheckMode::Default,
 742         span: body.span,
 743     };
 744     rewrite_closure_block(&block, prefix, context, shape)
 745 }
 746
 747 // Rewrite closure with a single expression without wrapping its body with block.
 748 fn rewrite_closure_expr(
 749     expr: &ast::Expr,
 750     prefix: &str,
 751     context: &RewriteContext,
 752     shape: Shape,
 753 ) -> Option<String> {
 754     let mut rewrite = expr.rewrite(context, shape);
 755     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 756         rewrite = and_one_line(rewrite);
 757     }
 758     rewrite.map(|rw| format!("{} {}", prefix, rw))
 759 }
 760
 761 // Rewrite closure whose body is block.
 762 fn rewrite_closure_block(
 763     block: &ast::Block,
 764     prefix: &str,
 765     context: &RewriteContext,
 766     shape: Shape,
 767 ) -> Option<String> {
 768     // Start with visual indent, then fall back to block indent if the
 769     // closure is large.
 770     let block_threshold = context.config.closure_block_indent_threshold();
 771     if block_threshold >= 0 {
 772         if let Some(block_str) = block.rewrite(&context, shape) {
 773             if block_str.matches('\n').count() <= block_threshold as usize &&
 774                 !need_block_indent(&block_str, shape)
 775             {
 776                 if let Some(block_str) = block_str.rewrite(context, shape) {
 777                     return Some(format!("{} {}", prefix, block_str));
 778                 }
 779             }
 780         }
 781     }
 782
 783     // The body of the closure is big enough to be block indented, that
 784     // means we must re-format.
 785     let block_shape = shape.block();
 786     let block_str = try_opt!(block.rewrite(&context, block_shape));
 787     Some(format!("{} {}", prefix, block_str))
 788 }
 789
 790 fn and_one_line(x: Option<String>) -> Option<String> {
 791     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 792 }
 793
 794 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 795     debug!("nop_block_collapse {:?} {}", block_str, budget);
 796     block_str.map(|block_str| {
 797         if block_str.starts_with('{') && budget >= 2 &&
 798             (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 799         {
 800             "{}".to_owned()
 801         } else {
 802             block_str.to_owned()
 803         }
 804     })
 805 }
 806
 807 fn rewrite_empty_block(
 808     context: &RewriteContext,
 809     block: &ast::Block,
 810     shape: Shape,
 811 ) -> Option<String> {
 812     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) &&
 813         shape.width >= 2
 814     {
 815         return Some("{}".to_owned());
 816     }
 817
 818     // If a block contains only a single-line comment, then leave it on one line.
 819     let user_str = context.snippet(block.span);
 820     let user_str = user_str.trim();
 821     if user_str.starts_with('{') && user_str.ends_with('}') {
 822         let comment_str = user_str[1..user_str.len() - 1].trim();
 823         if block.stmts.is_empty() && !comment_str.contains('\n') &&
 824             !comment_str.starts_with("//") && comment_str.len() + 4 <= shape.width
 825         {
 826             return Some(format!("{{ {} }}", comment_str));
 827         }
 828     }
 829
 830     None
 831 }
 832
 833 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 834     Some(match block.rules {
 835         ast::BlockCheckMode::Unsafe(..) => {
 836             let snippet = context.snippet(block.span);
 837             let open_pos = try_opt!(snippet.find_uncommented("{"));
 838             // Extract comment between unsafe and block start.
 839             let trimmed = &snippet[6..open_pos].trim();
 840
 841             if !trimmed.is_empty() {
 842                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 843                 let budget = try_opt!(shape.width.checked_sub(9));
 844                 format!(
 845                     "unsafe {} ",
 846                     try_opt!(rewrite_comment(
 847                         trimmed,
 848                         true,
 849                         Shape::legacy(budget, shape.indent + 7),
 850                         context.config,
 851                     ))
 852                 )
 853             } else {
 854                 "unsafe ".to_owned()
 855             }
 856         }
 857         ast::BlockCheckMode::Default => String::new(),
 858     })
 859 }
 860
 861 fn rewrite_single_line_block(
 862     context: &RewriteContext,
 863     prefix: &str,
 864     block: &ast::Block,
 865     shape: Shape,
 866 ) -> Option<String> {
 867     if is_simple_block(block, context.codemap) {
 868         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 869         let expr_str = try_opt!(block.stmts[0].rewrite(context, expr_shape));
 870         let result = format!("{}{{ {} }}", prefix, expr_str);
 871         if result.len() <= shape.width && !result.contains('\n') {
 872             return Some(result);
 873         }
 874     }
 875     None
 876 }
 877
 878 fn rewrite_block_with_visitor(
 879     context: &RewriteContext,
 880     prefix: &str,
 881     block: &ast::Block,
 882     shape: Shape,
 883 ) -> Option<String> {
 884     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 885         return rw;
 886     }
 887
 888     let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 889     visitor.block_indent = shape.indent;
 890     visitor.is_if_else_block = context.is_if_else_block;
 891     match block.rules {
 892         ast::BlockCheckMode::Unsafe(..) => {
 893             let snippet = context.snippet(block.span);
 894             let open_pos = try_opt!(snippet.find_uncommented("{"));
 895             visitor.last_pos = block.span.lo + BytePos(open_pos as u32)
 896         }
 897         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo,
 898     }
 899
 900     visitor.visit_block(block);
 901     if visitor.failed && shape.indent.alignment != 0 {
 902         block.rewrite(
 903             context,
 904             Shape::indented(shape.indent.block_only(), context.config),
 905         )
 906     } else {
 907         Some(format!("{}{}", prefix, visitor.buffer))
 908     }
 909 }
 910
 911 impl Rewrite for ast::Block {
 912     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 913         // shape.width is used only for the single line case: either the empty block `{}`,
 914         // or an unsafe expression `unsafe { e }`.
 915         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 916             return rw;
 917         }
 918
 919         let prefix = try_opt!(block_prefix(context, self, shape));
 920         if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 921             return rw;
 922         }
 923
 924         rewrite_block_with_visitor(context, &prefix, self, shape)
 925     }
 926 }
 927
 928 impl Rewrite for ast::Stmt {
 929     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 930         let result = match self.node {
 931             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 932             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 933                 let suffix = if semicolon_for_stmt(self) { ";" } else { "" };
 934
 935                 format_expr(
 936                     ex,
 937                     match self.node {
 938                         ast::StmtKind::Expr(_) => ExprType::SubExpression,
 939                         ast::StmtKind::Semi(_) => ExprType::Statement,
 940                         _ => unreachable!(),
 941                     },
 942                     context,
 943                     try_opt!(shape.sub_width(suffix.len())),
 944                 ).map(|s| s + suffix)
 945             }
 946             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 947         };
 948         result.and_then(|res| {
 949             recover_comment_removed(res, self.span, context, shape)
 950         })
 951     }
 952 }
 953
 954 // Rewrite condition if the given expression has one.
 955 fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 956     match expr.node {
 957         ast::ExprKind::Match(ref cond, _) => {
 958             // `match `cond` {`
 959             let cond_shape = match context.config.control_style() {
 960                 Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
 961                 Style::Rfc => try_opt!(shape.offset_left(8)),
 962             };
 963             cond.rewrite(context, cond_shape)
 964         }
 965         ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
 966             stmt_expr(&block.stmts[0]).and_then(|e| rewrite_cond(context, e, shape))
 967         }
 968         _ => {
 969             to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 970                 let alt_block_sep =
 971                     String::from("\n") + &shape.indent.block_only().to_string(context.config);
 972                 control_flow
 973                     .rewrite_cond(context, shape, &alt_block_sep)
 974                     .and_then(|rw| Some(rw.0))
 975             })
 976         }
 977     }
 978 }
 979
 980 // Abstraction over control flow expressions
 981 #[derive(Debug)]
 982 struct ControlFlow<'a> {
 983     cond: Option<&'a ast::Expr>,
 984     block: &'a ast::Block,
 985     else_block: Option<&'a ast::Expr>,
 986     label: Option<ast::SpannedIdent>,
 987     pat: Option<&'a ast::Pat>,
 988     keyword: &'a str,
 989     matcher: &'a str,
 990     connector: &'a str,
 991     allow_single_line: bool,
 992     // True if this is an `if` expression in an `else if` :-( hacky
 993     nested_if: bool,
 994     span: Span,
 995 }
 996
 997 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 998     match expr.node {
 999         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => {
1000             Some(ControlFlow::new_if(
1001                 cond,
1002                 None,
1003                 if_block,
1004                 else_block.as_ref().map(|e| &**e),
1005                 expr_type == ExprType::SubExpression,
1006                 false,
1007                 expr.span,
1008             ))
1009         }
1010         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
1011             Some(ControlFlow::new_if(
1012                 cond,
1013                 Some(pat),
1014                 if_block,
1015                 else_block.as_ref().map(|e| &**e),
1016                 expr_type == ExprType::SubExpression,
1017                 false,
1018                 expr.span,
1019             ))
1020         }
1021         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
1022             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
1023         }
1024         ast::ExprKind::Loop(ref block, label) => Some(
1025             ControlFlow::new_loop(block, label, expr.span),
1026         ),
1027         ast::ExprKind::While(ref cond, ref block, label) => Some(
1028             ControlFlow::new_while(None, cond, block, label, expr.span),
1029         ),
1030         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => {
1031             Some(ControlFlow::new_while(
1032                 Some(pat),
1033                 cond,
1034                 block,
1035                 label,
1036                 expr.span,
1037             ))
1038         }
1039         _ => None,
1040     }
1041 }
1042
1043 impl<'a> ControlFlow<'a> {
1044     fn new_if(
1045         cond: &'a ast::Expr,
1046         pat: Option<&'a ast::Pat>,
1047         block: &'a ast::Block,
1048         else_block: Option<&'a ast::Expr>,
1049         allow_single_line: bool,
1050         nested_if: bool,
1051         span: Span,
1052     ) -> ControlFlow<'a> {
1053         ControlFlow {
1054             cond: Some(cond),
1055             block: block,
1056             else_block: else_block,
1057             label: None,
1058             pat: pat,
1059             keyword: "if",
1060             matcher: match pat {
1061                 Some(..) => "let",
1062                 None => "",
1063             },
1064             connector: " =",
1065             allow_single_line: allow_single_line,
1066             nested_if: nested_if,
1067             span: span,
1068         }
1069     }
1070
1071     fn new_loop(
1072         block: &'a ast::Block,
1073         label: Option<ast::SpannedIdent>,
1074         span: Span,
1075     ) -> ControlFlow<'a> {
1076         ControlFlow {
1077             cond: None,
1078             block: block,
1079             else_block: None,
1080             label: label,
1081             pat: None,
1082             keyword: "loop",
1083             matcher: "",
1084             connector: "",
1085             allow_single_line: false,
1086             nested_if: false,
1087             span: span,
1088         }
1089     }
1090
1091     fn new_while(
1092         pat: Option<&'a ast::Pat>,
1093         cond: &'a ast::Expr,
1094         block: &'a ast::Block,
1095         label: Option<ast::SpannedIdent>,
1096         span: Span,
1097     ) -> ControlFlow<'a> {
1098         ControlFlow {
1099             cond: Some(cond),
1100             block: block,
1101             else_block: None,
1102             label: label,
1103             pat: pat,
1104             keyword: "while",
1105             matcher: match pat {
1106                 Some(..) => "let",
1107                 None => "",
1108             },
1109             connector: " =",
1110             allow_single_line: false,
1111             nested_if: false,
1112             span: span,
1113         }
1114     }
1115
1116     fn new_for(
1117         pat: &'a ast::Pat,
1118         cond: &'a ast::Expr,
1119         block: &'a ast::Block,
1120         label: Option<ast::SpannedIdent>,
1121         span: Span,
1122     ) -> ControlFlow<'a> {
1123         ControlFlow {
1124             cond: Some(cond),
1125             block: block,
1126             else_block: None,
1127             label: label,
1128             pat: Some(pat),
1129             keyword: "for",
1130             matcher: "",
1131             connector: " in",
1132             allow_single_line: false,
1133             nested_if: false,
1134             span: span,
1135         }
1136     }
1137
1138     fn rewrite_single_line(
1139         &self,
1140         pat_expr_str: &str,
1141         context: &RewriteContext,
1142         width: usize,
1143     ) -> Option<String> {
1144         assert!(self.allow_single_line);
1145         let else_block = try_opt!(self.else_block);
1146         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1147
1148         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1149             if !is_simple_block(self.block, context.codemap) ||
1150                 !is_simple_block(else_node, context.codemap) ||
1151                 pat_expr_str.contains('\n')
1152             {
1153                 return None;
1154             }
1155
1156             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
1157             let expr = &self.block.stmts[0];
1158             let if_str = try_opt!(expr.rewrite(
1159                 context,
1160                 Shape::legacy(new_width, Indent::empty()),
1161             ));
1162
1163             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
1164             let else_expr = &else_node.stmts[0];
1165             let else_str =
1166                 try_opt!(else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1167
1168             if if_str.contains('\n') || else_str.contains('\n') {
1169                 return None;
1170             }
1171
1172             let result = format!(
1173                 "{} {} {{ {} }} else {{ {} }}",
1174                 self.keyword,
1175                 pat_expr_str,
1176                 if_str,
1177                 else_str
1178             );
1179
1180             if result.len() <= width {
1181                 return Some(result);
1182             }
1183         }
1184
1185         None
1186     }
1187 }
1188
1189 impl<'a> ControlFlow<'a> {
1190     fn rewrite_cond(
1191         &self,
1192         context: &RewriteContext,
1193         shape: Shape,
1194         alt_block_sep: &str,
1195     ) -> Option<(String, usize)> {
1196         let constr_shape = if self.nested_if {
1197             // We are part of an if-elseif-else chain. Our constraints are tightened.
1198             // 7 = "} else " .len()
1199             try_opt!(shape.shrink_left(7))
1200         } else {
1201             shape
1202         };
1203
1204         let label_string = rewrite_label(self.label);
1205         // 1 = space after keyword.
1206         let offset = self.keyword.len() + label_string.len() + 1;
1207
1208         let pat_expr_string = match self.cond {
1209             Some(cond) => {
1210                 let mut cond_shape = match context.config.control_style() {
1211                     Style::Legacy => try_opt!(constr_shape.shrink_left(offset)),
1212                     Style::Rfc => try_opt!(constr_shape.offset_left(offset)),
1213                 };
1214                 if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1215                     // 2 = " {".len()
1216                     cond_shape = try_opt!(cond_shape.sub_width(2));
1217                 }
1218
1219                 try_opt!(rewrite_pat_expr(
1220                     context,
1221                     self.pat,
1222                     cond,
1223                     self.matcher,
1224                     self.connector,
1225                     self.keyword,
1226                     cond_shape,
1227                 ))
1228             }
1229             None => String::new(),
1230         };
1231
1232         let force_newline_brace = context.config.control_style() == Style::Rfc &&
1233             pat_expr_string.contains('\n') &&
1234             !last_line_extendable(&pat_expr_string);
1235
1236         // Try to format if-else on single line.
1237         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1238             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1239
1240             if let Some(cond_str) = trial {
1241                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1242                     return Some((cond_str, 0));
1243                 }
1244             }
1245         }
1246
1247         let cond_span = if let Some(cond) = self.cond {
1248             cond.span
1249         } else {
1250             mk_sp(self.block.span.lo, self.block.span.lo)
1251         };
1252
1253         // for event in event
1254         let between_kwd_cond = mk_sp(
1255             context.codemap.span_after(self.span, self.keyword.trim()),
1256             self.pat.map_or(
1257                 cond_span.lo,
1258                 |p| if self.matcher.is_empty() {
1259                     p.span.lo
1260                 } else {
1261                     context.codemap.span_before(self.span, self.matcher.trim())
1262                 },
1263             ),
1264         );
1265
1266         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1267
1268         let after_cond_comment =
1269             extract_comment(mk_sp(cond_span.hi, self.block.span.lo), context, shape);
1270
1271         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1272             ""
1273         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine ||
1274                    force_newline_brace
1275         {
1276             alt_block_sep
1277         } else {
1278             " "
1279         };
1280
1281         let used_width = if pat_expr_string.contains('\n') {
1282             last_line_width(&pat_expr_string)
1283         } else {
1284             // 2 = spaces after keyword and condition.
1285             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1286         };
1287
1288         Some((
1289             format!(
1290                 "{}{}{}{}{}",
1291                 label_string,
1292                 self.keyword,
1293                 between_kwd_cond_comment.as_ref().map_or(
1294                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1295                         ""
1296                     } else {
1297                         " "
1298                     },
1299                     |s| &**s,
1300                 ),
1301                 pat_expr_string,
1302                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1303             ),
1304             used_width,
1305         ))
1306     }
1307 }
1308
1309 impl<'a> Rewrite for ControlFlow<'a> {
1310     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1311         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1312
1313         let alt_block_sep =
1314             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1315         let (cond_str, used_width) = try_opt!(self.rewrite_cond(context, shape, &alt_block_sep));
1316         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1317         if used_width == 0 {
1318             return Some(cond_str);
1319         }
1320
1321         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1322         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1323         // we should avoid the single line case.
1324         let block_width = if self.else_block.is_some() || self.nested_if {
1325             min(1, block_width)
1326         } else {
1327             block_width
1328         };
1329         let block_shape = Shape {
1330             width: block_width,
1331             ..shape
1332         };
1333         let mut block_context = context.clone();
1334         block_context.is_if_else_block = self.else_block.is_some();
1335         let block_str = try_opt!(rewrite_block_with_visitor(
1336             &block_context,
1337             "",
1338             self.block,
1339             block_shape,
1340         ));
1341
1342         let mut result = format!("{}{}", cond_str, block_str);
1343
1344         if let Some(else_block) = self.else_block {
1345             let shape = Shape::indented(shape.indent, context.config);
1346             let mut last_in_chain = false;
1347             let rewrite = match else_block.node {
1348                 // If the else expression is another if-else expression, prevent it
1349                 // from being formatted on a single line.
1350                 // Note how we're passing the original shape, as the
1351                 // cost of "else" should not cascade.
1352                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1353                     ControlFlow::new_if(
1354                         cond,
1355                         Some(pat),
1356                         if_block,
1357                         next_else_block.as_ref().map(|e| &**e),
1358                         false,
1359                         true,
1360                         mk_sp(else_block.span.lo, self.span.hi),
1361                     ).rewrite(context, shape)
1362                 }
1363                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1364                     ControlFlow::new_if(
1365                         cond,
1366                         None,
1367                         if_block,
1368                         next_else_block.as_ref().map(|e| &**e),
1369                         false,
1370                         true,
1371                         mk_sp(else_block.span.lo, self.span.hi),
1372                     ).rewrite(context, shape)
1373                 }
1374                 _ => {
1375                     last_in_chain = true;
1376                     // When rewriting a block, the width is only used for single line
1377                     // blocks, passing 1 lets us avoid that.
1378                     let else_shape = Shape {
1379                         width: min(1, shape.width),
1380                         ..shape
1381                     };
1382                     format_expr(else_block, ExprType::Statement, context, else_shape)
1383                 }
1384             };
1385
1386             let between_kwd_else_block = mk_sp(
1387                 self.block.span.hi,
1388                 context
1389                     .codemap
1390                     .span_before(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1391             );
1392             let between_kwd_else_block_comment =
1393                 extract_comment(between_kwd_else_block, context, shape);
1394
1395             let after_else = mk_sp(
1396                 context
1397                     .codemap
1398                     .span_after(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1399                 else_block.span.lo,
1400             );
1401             let after_else_comment = extract_comment(after_else, context, shape);
1402
1403             let between_sep = match context.config.control_brace_style() {
1404                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1405                     &*alt_block_sep
1406                 }
1407                 ControlBraceStyle::AlwaysSameLine => " ",
1408             };
1409             let after_sep = match context.config.control_brace_style() {
1410                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1411                 _ => " ",
1412             };
1413             try_opt!(
1414                 write!(
1415                     &mut result,
1416                     "{}else{}",
1417                     between_kwd_else_block_comment
1418                         .as_ref()
1419                         .map_or(between_sep, |s| &**s),
1420                     after_else_comment.as_ref().map_or(after_sep, |s| &**s)
1421                 ).ok()
1422             );
1423             result.push_str(&try_opt!(rewrite));
1424         }
1425
1426         Some(result)
1427     }
1428 }
1429
1430 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
1431     match label {
1432         Some(ident) => format!("{}: ", ident.node),
1433         None => "".to_owned(),
1434     }
1435 }
1436
1437 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1438     let comment_str = context.snippet(span);
1439     if contains_comment(&comment_str) {
1440         let comment = try_opt!(rewrite_comment(
1441             comment_str.trim(),
1442             false,
1443             shape,
1444             context.config,
1445         ));
1446         Some(format!(
1447             "\n{indent}{}\n{indent}",
1448             comment,
1449             indent = shape.indent.to_string(context.config)
1450         ))
1451     } else {
1452         None
1453     }
1454 }
1455
1456 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1457     let snippet = codemap.span_to_snippet(block.span).unwrap();
1458     contains_comment(&snippet)
1459 }
1460
1461 // Checks that a block contains no statements, an expression and no comments.
1462 // FIXME: incorrectly returns false when comment is contained completely within
1463 // the expression.
1464 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1465     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
1466          !block_contains_comment(block, codemap))
1467 }
1468
1469 /// Checks whether a block contains at most one statement or expression, and no comments.
1470 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1471     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1472 }
1473
1474 /// Checks whether a block contains no statements, expressions, or comments.
1475 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1476     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1477 }
1478
1479 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1480     match stmt.node {
1481         ast::StmtKind::Expr(..) => true,
1482         _ => false,
1483     }
1484 }
1485
1486 fn is_unsafe_block(block: &ast::Block) -> bool {
1487     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1488         true
1489     } else {
1490         false
1491     }
1492 }
1493
1494 // inter-match-arm-comment-rules:
1495 //  - all comments following a match arm before the start of the next arm
1496 //    are about the second arm
1497 fn rewrite_match_arm_comment(
1498     context: &RewriteContext,
1499     missed_str: &str,
1500     shape: Shape,
1501     arm_indent_str: &str,
1502 ) -> Option<String> {
1503     // The leading "," is not part of the arm-comment
1504     let missed_str = match missed_str.find_uncommented(",") {
1505         Some(n) => &missed_str[n + 1..],
1506         None => &missed_str[..],
1507     };
1508
1509     let mut result = String::new();
1510     // any text not preceeded by a newline is pushed unmodified to the block
1511     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1512     result.push_str(&missed_str[..first_brk]);
1513     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1514
1515     let first = missed_str
1516         .find(|c: char| !c.is_whitespace())
1517         .unwrap_or(missed_str.len());
1518     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1519         // Excessive vertical whitespace before comment should be preserved
1520         // FIXME handle vertical whitespace better
1521         result.push('\n');
1522     }
1523     let missed_str = missed_str[first..].trim();
1524     if !missed_str.is_empty() {
1525         let comment = try_opt!(rewrite_comment(&missed_str, false, shape, context.config));
1526         result.push('\n');
1527         result.push_str(arm_indent_str);
1528         result.push_str(&comment);
1529     }
1530
1531     Some(result)
1532 }
1533
1534 fn rewrite_match(
1535     context: &RewriteContext,
1536     cond: &ast::Expr,
1537     arms: &[ast::Arm],
1538     shape: Shape,
1539     span: Span,
1540 ) -> Option<String> {
1541     if arms.is_empty() {
1542         return None;
1543     }
1544
1545     // `match `cond` {`
1546     let cond_shape = match context.config.control_style() {
1547         Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
1548         Style::Rfc => try_opt!(shape.offset_left(8)),
1549     };
1550     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1551     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1552     let block_sep = match context.config.control_brace_style() {
1553         ControlBraceStyle::AlwaysNextLine => alt_block_sep.as_str(),
1554         _ => " ",
1555     };
1556     let mut result = format!("match {}{}{{", cond_str, block_sep);
1557
1558     let arm_shape = if context.config.indent_match_arms() {
1559         shape.block_indent(context.config.tab_spaces())
1560     } else {
1561         shape.block_indent(0)
1562     };
1563
1564     let arm_indent_str = arm_shape.indent.to_string(context.config);
1565
1566     let open_brace_pos = context
1567         .codemap
1568         .span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])), "{");
1569
1570     let arm_num = arms.len();
1571     for (i, arm) in arms.iter().enumerate() {
1572         // Make sure we get the stuff between arms.
1573         let missed_str = if i == 0 {
1574             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
1575         } else {
1576             context.snippet(mk_sp(arm_end_pos(&arms[i - 1]), arm_start_pos(arm)))
1577         };
1578         let comment = try_opt!(rewrite_match_arm_comment(
1579             context,
1580             &missed_str,
1581             arm_shape,
1582             &arm_indent_str,
1583         ));
1584         result.push_str(&comment);
1585         result.push('\n');
1586         result.push_str(&arm_indent_str);
1587
1588         let arm_str = arm.rewrite(&context, arm_shape.with_max_width(context.config));
1589         if let Some(ref arm_str) = arm_str {
1590             // Trim the trailing comma if necessary.
1591             if i == arm_num - 1 && context.config.trailing_comma() == SeparatorTactic::Never &&
1592                 arm_str.ends_with(',')
1593             {
1594                 result.push_str(&arm_str[0..arm_str.len() - 1])
1595             } else {
1596                 result.push_str(arm_str)
1597             }
1598         } else {
1599             // We couldn't format the arm, just reproduce the source.
1600             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
1601             result.push_str(&snippet);
1602             if context.config.trailing_comma() != SeparatorTactic::Never {
1603                 result.push_str(arm_comma(context.config, &arm.body))
1604             }
1605         }
1606     }
1607     // BytePos(1) = closing match brace.
1608     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]), span.hi - BytePos(1));
1609     let last_comment = context.snippet(last_span);
1610     let comment = try_opt!(rewrite_match_arm_comment(
1611         context,
1612         &last_comment,
1613         arm_shape,
1614         &arm_indent_str,
1615     ));
1616     result.push_str(&comment);
1617     result.push('\n');
1618     result.push_str(&shape.indent.to_string(context.config));
1619     result.push('}');
1620     Some(result)
1621 }
1622
1623 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
1624     let &ast::Arm {
1625         ref attrs,
1626         ref pats,
1627         ..
1628     } = arm;
1629     if !attrs.is_empty() {
1630         return attrs[0].span.lo;
1631     }
1632
1633     pats[0].span.lo
1634 }
1635
1636 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
1637     arm.body.span.hi
1638 }
1639
1640 fn arm_comma(config: &Config, body: &ast::Expr) -> &'static str {
1641     if config.match_block_trailing_comma() {
1642         ","
1643     } else if let ast::ExprKind::Block(ref block) = body.node {
1644         if let ast::BlockCheckMode::Default = block.rules {
1645             ""
1646         } else {
1647             ","
1648         }
1649     } else {
1650         ","
1651     }
1652 }
1653
1654 // Match arms.
1655 impl Rewrite for ast::Arm {
1656     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1657         debug!("Arm::rewrite {:?} {:?}", self, shape);
1658         let &ast::Arm {
1659             ref attrs,
1660             ref pats,
1661             ref guard,
1662             ref body,
1663         } = self;
1664
1665         let attr_str = if !attrs.is_empty() {
1666             if contains_skip(attrs) {
1667                 return None;
1668             }
1669             format!(
1670                 "{}\n{}",
1671                 try_opt!(attrs.rewrite(context, shape)),
1672                 shape.indent.to_string(context.config)
1673             )
1674         } else {
1675             String::new()
1676         };
1677
1678         // Patterns
1679         // 5 = ` => {`
1680         let pat_shape = try_opt!(shape.sub_width(5));
1681
1682         let pat_strs = try_opt!(
1683             pats.iter()
1684                 .map(|p| p.rewrite(context, pat_shape))
1685                 .collect::<Option<Vec<_>>>()
1686         );
1687
1688         let all_simple = pat_strs.iter().all(|p| !p.contains('\n'));
1689         let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1690         let mut tactic = definitive_tactic(&items, ListTactic::HorizontalVertical, pat_shape.width);
1691         if tactic == DefinitiveListTactic::Horizontal && all_simple {
1692             tactic = DefinitiveListTactic::Mixed;
1693         }
1694         let fmt = ListFormatting {
1695             tactic: tactic,
1696             separator: " |",
1697             trailing_separator: SeparatorTactic::Never,
1698             shape: pat_shape,
1699             ends_with_newline: false,
1700             config: context.config,
1701         };
1702         let pats_str = try_opt!(write_list(&items, &fmt));
1703
1704         let guard_str = try_opt!(rewrite_guard(
1705             context,
1706             guard,
1707             shape,
1708             trimmed_last_line_width(&pats_str),
1709         ));
1710
1711         let pats_len = pats_str.len();
1712         let pats_str = format!("{}{}", pats_str, guard_str);
1713
1714         let (mut extend, body) = match body.node {
1715             ast::ExprKind::Block(ref block)
1716                 if !is_unsafe_block(block) && is_simple_block(block, context.codemap) &&
1717                        context.config.wrap_match_arms() => {
1718                 if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1719                     (false, &**expr)
1720                 } else {
1721                     (false, &**body)
1722                 }
1723             }
1724             ast::ExprKind::Call(_, ref args) => (args.len() == 1, &**body),
1725             ast::ExprKind::Closure(..) | ast::ExprKind::Struct(..) | ast::ExprKind::Tup(..) => (
1726                 true,
1727                 &**body,
1728             ),
1729             _ => (false, &**body),
1730         };
1731         extend &= context.use_block_indent();
1732
1733         let comma = arm_comma(&context.config, body);
1734         let alt_block_sep =
1735             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1736
1737         let pat_width = extra_offset(&pats_str, shape);
1738         // Let's try and get the arm body on the same line as the condition.
1739         // 4 = ` => `.len()
1740         if shape.width > pat_width + comma.len() + 4 {
1741             let arm_shape = shape
1742                 .offset_left(pat_width + 4)
1743                 .unwrap()
1744                 .sub_width(comma.len())
1745                 .unwrap();
1746             let rewrite = nop_block_collapse(
1747                 format_expr(body, ExprType::Statement, context, arm_shape),
1748                 arm_shape.width,
1749             );
1750             let is_block = if let ast::ExprKind::Block(..) = body.node {
1751                 true
1752             } else {
1753                 false
1754             };
1755
1756             match rewrite {
1757                 Some(ref body_str)
1758                     if (!body_str.contains('\n') && body_str.len() <= arm_shape.width) ||
1759                            !context.config.wrap_match_arms() ||
1760                            (extend && first_line_width(body_str) <= arm_shape.width) ||
1761                            is_block => {
1762                     let block_sep = match context.config.control_brace_style() {
1763                         ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep.as_str(),
1764                         _ if guard.is_some() && pats_str.contains('\n') && is_block &&
1765                             body_str != "{}" &&
1766                             pats_len > context.config.tab_spaces() => alt_block_sep.as_str(),
1767                         _ => " ",
1768                     };
1769
1770                     return Some(format!(
1771                         "{}{} =>{}{}{}",
1772                         attr_str.trim_left(),
1773                         pats_str,
1774                         block_sep,
1775                         body_str,
1776                         comma
1777                     ));
1778                 }
1779                 _ => {}
1780             }
1781         }
1782
1783         // FIXME: we're doing a second rewrite of the expr; This may not be
1784         // necessary.
1785         let body_shape = try_opt!(shape.block_left(context.config.tab_spaces()));
1786         let next_line_body = try_opt!(nop_block_collapse(
1787             format_expr(body, ExprType::Statement, context, body_shape),
1788             body_shape.width,
1789         ));
1790         let indent_str = shape
1791             .indent
1792             .block_indent(context.config)
1793             .to_string(context.config);
1794         let (body_prefix, body_suffix) = if context.config.wrap_match_arms() {
1795             if context.config.match_block_trailing_comma() {
1796                 ("{", "},")
1797             } else {
1798                 ("{", "}")
1799             }
1800         } else {
1801             ("", ",")
1802         };
1803
1804
1805         let block_sep = match context.config.control_brace_style() {
1806             ControlBraceStyle::AlwaysNextLine => alt_block_sep + body_prefix + "\n",
1807             _ if body_prefix.is_empty() => "\n".to_owned(),
1808             _ => " ".to_owned() + body_prefix + "\n",
1809         };
1810
1811         if context.config.wrap_match_arms() {
1812             Some(format!(
1813                 "{}{} =>{}{}{}\n{}{}",
1814                 attr_str.trim_left(),
1815                 pats_str,
1816                 block_sep,
1817                 indent_str,
1818                 next_line_body,
1819                 shape.indent.to_string(context.config),
1820                 body_suffix
1821             ))
1822         } else {
1823             Some(format!(
1824                 "{}{} =>{}{}{}{}",
1825                 attr_str.trim_left(),
1826                 pats_str,
1827                 block_sep,
1828                 indent_str,
1829                 next_line_body,
1830                 body_suffix
1831             ))
1832         }
1833     }
1834 }
1835
1836 // The `if ...` guard on a match arm.
1837 fn rewrite_guard(
1838     context: &RewriteContext,
1839     guard: &Option<ptr::P<ast::Expr>>,
1840     shape: Shape,
1841     // The amount of space used up on this line for the pattern in
1842     // the arm (excludes offset).
1843     pattern_width: usize,
1844 ) -> Option<String> {
1845     if let Some(ref guard) = *guard {
1846         // First try to fit the guard string on the same line as the pattern.
1847         // 4 = ` if `, 5 = ` => {`
1848         if let Some(cond_shape) = shape
1849             .offset_left(pattern_width + 4)
1850             .and_then(|s| s.sub_width(5))
1851         {
1852             if let Some(cond_str) = guard
1853                 .rewrite(context, cond_shape)
1854                 .and_then(|s| s.rewrite(context, cond_shape))
1855             {
1856                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1857                     return Some(format!(" if {}", cond_str));
1858                 }
1859             }
1860         }
1861
1862         // Not enough space to put the guard after the pattern, try a newline.
1863         // 3 = `if `, 5 = ` => {`
1864         if let Some(cond_shape) =
1865             Shape::indented(shape.indent.block_indent(context.config), context.config)
1866                 .offset_left(3)
1867                 .and_then(|s| s.sub_width(5))
1868         {
1869             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1870                 return Some(format!(
1871                     "\n{}if {}",
1872                     cond_shape.indent.to_string(context.config),
1873                     cond_str
1874                 ));
1875             }
1876         }
1877
1878         None
1879     } else {
1880         Some(String::new())
1881     }
1882 }
1883
1884 fn rewrite_pat_expr(
1885     context: &RewriteContext,
1886     pat: Option<&ast::Pat>,
1887     expr: &ast::Expr,
1888     matcher: &str,
1889     // Connecting piece between pattern and expression,
1890     // *without* trailing space.
1891     connector: &str,
1892     keyword: &str,
1893     shape: Shape,
1894 ) -> Option<String> {
1895     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1896     if let Some(pat) = pat {
1897         let matcher = if matcher.is_empty() {
1898             matcher.to_owned()
1899         } else {
1900             format!("{} ", matcher)
1901         };
1902         let pat_shape =
1903             try_opt!(try_opt!(shape.offset_left(matcher.len())).sub_width(connector.len()));
1904         let pat_string = try_opt!(pat.rewrite(context, pat_shape));
1905         let result = format!("{}{}{}", matcher, pat_string, connector);
1906         return rewrite_assign_rhs(context, result, expr, shape);
1907     }
1908
1909     let expr_rw = expr.rewrite(context, shape);
1910     // The expression may (partially) fit on the current line.
1911     // We do not allow splitting between `if` and condition.
1912     if keyword == "if" || expr_rw.is_some() {
1913         return expr_rw;
1914     }
1915
1916     // The expression won't fit on the current line, jump to next.
1917     let nested_shape = shape
1918         .block_indent(context.config.tab_spaces())
1919         .with_max_width(context.config);
1920     let nested_indent_str = nested_shape.indent.to_string(context.config);
1921     expr.rewrite(context, nested_shape)
1922         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1923 }
1924
1925 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1926     let string_lit = context.snippet(span);
1927
1928     if !context.config.format_strings() && !context.config.force_format_strings() {
1929         if string_lit
1930             .lines()
1931             .rev()
1932             .skip(1)
1933             .all(|line| line.ends_with('\\'))
1934         {
1935             let new_indent = shape.visual_indent(1).indent;
1936             return Some(String::from(
1937                 string_lit
1938                     .lines()
1939                     .map(|line| {
1940                         new_indent.to_string(context.config) + line.trim_left()
1941                     })
1942                     .collect::<Vec<_>>()
1943                     .join("\n")
1944                     .trim_left(),
1945             ));
1946         } else {
1947             return Some(string_lit);
1948         }
1949     }
1950
1951     if !context.config.force_format_strings() &&
1952         !string_requires_rewrite(context, span, &string_lit, shape)
1953     {
1954         return Some(string_lit);
1955     }
1956
1957     let fmt = StringFormat {
1958         opener: "\"",
1959         closer: "\"",
1960         line_start: " ",
1961         line_end: "\\",
1962         shape: shape,
1963         trim_end: false,
1964         config: context.config,
1965     };
1966
1967     // Remove the quote characters.
1968     let str_lit = &string_lit[1..string_lit.len() - 1];
1969
1970     rewrite_string(str_lit, &fmt)
1971 }
1972
1973 fn string_requires_rewrite(
1974     context: &RewriteContext,
1975     span: Span,
1976     string: &str,
1977     shape: Shape,
1978 ) -> bool {
1979     if context.codemap.lookup_char_pos(span.lo).col.0 != shape.indent.width() {
1980         return true;
1981     }
1982
1983     for (i, line) in string.lines().enumerate() {
1984         if i == 0 {
1985             if line.len() > shape.width {
1986                 return true;
1987             }
1988         } else {
1989             if line.len() > shape.width + shape.indent.width() {
1990                 return true;
1991             }
1992         }
1993     }
1994
1995     false
1996 }
1997
1998 pub fn rewrite_call_with_binary_search<R>(
1999     context: &RewriteContext,
2000     callee: &R,
2001     args: &[&ast::Expr],
2002     span: Span,
2003     shape: Shape,
2004 ) -> Option<String>
2005 where
2006     R: Rewrite,
2007 {
2008     let force_trailing_comma = if context.inside_macro {
2009         span_ends_with_comma(context, span)
2010     } else {
2011         false
2012     };
2013     let closure = |callee_max_width| {
2014         // FIXME using byte lens instead of char lens (and probably all over the
2015         // place too)
2016         let callee_shape = Shape {
2017             width: callee_max_width,
2018             ..shape
2019         };
2020         let callee_str = callee
2021             .rewrite(context, callee_shape)
2022             .ok_or(Ordering::Greater)?;
2023
2024         rewrite_call_inner(
2025             context,
2026             &callee_str,
2027             args,
2028             span,
2029             shape,
2030             context.config.fn_call_width(),
2031             force_trailing_comma,
2032         )
2033     };
2034
2035     binary_search(1, shape.width, closure)
2036 }
2037
2038 pub fn rewrite_call(
2039     context: &RewriteContext,
2040     callee: &str,
2041     args: &[ptr::P<ast::Expr>],
2042     span: Span,
2043     shape: Shape,
2044 ) -> Option<String> {
2045     let force_trailing_comma = if context.inside_macro {
2046         span_ends_with_comma(context, span)
2047     } else {
2048         false
2049     };
2050     rewrite_call_inner(
2051         context,
2052         &callee,
2053         &args.iter().map(|x| &**x).collect::<Vec<_>>(),
2054         span,
2055         shape,
2056         context.config.fn_call_width(),
2057         force_trailing_comma,
2058     ).ok()
2059 }
2060
2061 pub fn rewrite_call_inner<'a, T>(
2062     context: &RewriteContext,
2063     callee_str: &str,
2064     args: &[&T],
2065     span: Span,
2066     shape: Shape,
2067     args_max_width: usize,
2068     force_trailing_comma: bool,
2069 ) -> Result<String, Ordering>
2070 where
2071     T: Rewrite + Spanned + ToExpr + 'a,
2072 {
2073     // 2 = `( `, 1 = `(`
2074     let paren_overhead = if context.config.spaces_within_parens() {
2075         2
2076     } else {
2077         1
2078     };
2079     let used_width = extra_offset(&callee_str, shape);
2080     let one_line_width = shape
2081         .width
2082         .checked_sub(used_width + 2 * paren_overhead)
2083         .ok_or(Ordering::Greater)?;
2084
2085     let nested_shape = shape_from_fn_call_style(
2086         context,
2087         shape,
2088         used_width + 2 * paren_overhead,
2089         used_width + paren_overhead,
2090     ).ok_or(Ordering::Greater)?;
2091
2092     let span_lo = context.codemap.span_after(span, "(");
2093     let args_span = mk_sp(span_lo, span.hi);
2094
2095     let (extendable, list_str) = rewrite_call_args(
2096         context,
2097         args,
2098         args_span,
2099         nested_shape,
2100         one_line_width,
2101         args_max_width,
2102         force_trailing_comma,
2103     ).or_else(|| if context.use_block_indent() {
2104         rewrite_call_args(
2105             context,
2106             args,
2107             args_span,
2108             Shape::indented(
2109                 shape.block().indent.block_indent(context.config),
2110                 context.config,
2111             ),
2112             0,
2113             0,
2114             force_trailing_comma,
2115         )
2116     } else {
2117         None
2118     })
2119         .ok_or(Ordering::Less)?;
2120
2121     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2122         let mut new_context = context.clone();
2123         new_context.use_block = true;
2124         return rewrite_call_inner(
2125             &new_context,
2126             callee_str,
2127             args,
2128             span,
2129             shape,
2130             args_max_width,
2131             force_trailing_comma,
2132         );
2133     }
2134
2135     let args_shape = shape
2136         .sub_width(last_line_width(&callee_str))
2137         .ok_or(Ordering::Less)?;
2138     Ok(format!(
2139         "{}{}",
2140         callee_str,
2141         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2142     ))
2143 }
2144
2145 fn need_block_indent(s: &str, shape: Shape) -> bool {
2146     s.lines().skip(1).any(|s| {
2147         s.find(|c| !char::is_whitespace(c))
2148             .map_or(false, |w| w + 1 < shape.indent.width())
2149     })
2150 }
2151
2152 fn rewrite_call_args<'a, T>(
2153     context: &RewriteContext,
2154     args: &[&T],
2155     span: Span,
2156     shape: Shape,
2157     one_line_width: usize,
2158     args_max_width: usize,
2159     force_trailing_comma: bool,
2160 ) -> Option<(bool, String)>
2161 where
2162     T: Rewrite + Spanned + ToExpr + 'a,
2163 {
2164     let items = itemize_list(
2165         context.codemap,
2166         args.iter(),
2167         ")",
2168         |item| item.span().lo,
2169         |item| item.span().hi,
2170         |item| item.rewrite(context, shape),
2171         span.lo,
2172         span.hi,
2173     );
2174     let mut item_vec: Vec<_> = items.collect();
2175
2176     // Try letting the last argument overflow to the next line with block
2177     // indentation. If its first line fits on one line with the other arguments,
2178     // we format the function arguments horizontally.
2179     let tactic = try_overflow_last_arg(
2180         context,
2181         &mut item_vec,
2182         &args[..],
2183         shape,
2184         one_line_width,
2185         args_max_width,
2186     );
2187
2188     let fmt = ListFormatting {
2189         tactic: tactic,
2190         separator: ",",
2191         trailing_separator: if force_trailing_comma {
2192             SeparatorTactic::Always
2193         } else if context.inside_macro || !context.use_block_indent() {
2194             SeparatorTactic::Never
2195         } else {
2196             context.config.trailing_comma()
2197         },
2198         shape: shape,
2199         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2200         config: context.config,
2201     };
2202
2203     write_list(&item_vec, &fmt).map(|args_str| {
2204         (tactic != DefinitiveListTactic::Vertical, args_str)
2205     })
2206 }
2207
2208 fn try_overflow_last_arg<'a, T>(
2209     context: &RewriteContext,
2210     item_vec: &mut Vec<ListItem>,
2211     args: &[&T],
2212     shape: Shape,
2213     one_line_width: usize,
2214     args_max_width: usize,
2215 ) -> DefinitiveListTactic
2216 where
2217     T: Rewrite + Spanned + ToExpr + 'a,
2218 {
2219     let overflow_last = can_be_overflowed(&context, args);
2220
2221     // Replace the last item with its first line to see if it fits with
2222     // first arguments.
2223     let (orig_last, placeholder) = if overflow_last {
2224         let mut context = context.clone();
2225         if let Some(expr) = args[args.len() - 1].to_expr() {
2226             match expr.node {
2227                 ast::ExprKind::MethodCall(..) => context.force_one_line_chain = true,
2228                 _ => (),
2229             }
2230         }
2231         last_arg_shape(&context, &item_vec, shape, args_max_width)
2232             .map_or((None, None), |arg_shape| {
2233                 rewrite_last_arg_with_overflow(
2234                     &context,
2235                     args,
2236                     &mut item_vec[args.len() - 1],
2237                     arg_shape,
2238                 )
2239             })
2240     } else {
2241         (None, None)
2242     };
2243
2244     let tactic = definitive_tactic(
2245         &*item_vec,
2246         ListTactic::LimitedHorizontalVertical(args_max_width),
2247         one_line_width,
2248     );
2249
2250     // Replace the stub with the full overflowing last argument if the rewrite
2251     // succeeded and its first line fits with the other arguments.
2252     match (overflow_last, tactic, placeholder) {
2253         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2254             item_vec[args.len() - 1].item = placeholder;
2255         }
2256         (true, _, _) => {
2257             item_vec[args.len() - 1].item = orig_last;
2258         }
2259         (false, _, _) => {}
2260     }
2261
2262     tactic
2263 }
2264
2265 fn last_arg_shape(
2266     context: &RewriteContext,
2267     items: &Vec<ListItem>,
2268     shape: Shape,
2269     args_max_width: usize,
2270 ) -> Option<Shape> {
2271     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2272         acc + i.item.as_ref().map_or(0, |s| first_line_width(&s))
2273     });
2274     let max_width = min(args_max_width, shape.width);
2275     let arg_indent = if context.use_block_indent() {
2276         shape.block().indent.block_unindent(context.config)
2277     } else {
2278         shape.block().indent
2279     };
2280     Some(Shape {
2281         width: try_opt!(max_width.checked_sub(overhead)),
2282         indent: arg_indent,
2283         offset: 0,
2284     })
2285 }
2286
2287 // Rewriting closure which is placed at the end of the function call's arg.
2288 // Returns `None` if the reformatted closure 'looks bad'.
2289 fn rewrite_last_closure(
2290     context: &RewriteContext,
2291     expr: &ast::Expr,
2292     shape: Shape,
2293 ) -> Option<String> {
2294     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2295         let body = match body.node {
2296             ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
2297                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2298             }
2299             _ => body,
2300         };
2301         let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
2302             capture,
2303             fn_decl,
2304             body,
2305             expr.span,
2306             context,
2307             shape,
2308         ));
2309         // If the closure goes multi line before its body, do not overflow the closure.
2310         if prefix.contains('\n') {
2311             return None;
2312         }
2313         let body_shape = try_opt!(shape.offset_left(extra_offset));
2314         // When overflowing the closure which consists of a single control flow expression,
2315         // force to use block if its condition uses multi line.
2316         if rewrite_cond(context, body, body_shape)
2317             .map(|cond| cond.contains('\n'))
2318             .unwrap_or(false)
2319         {
2320             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2321         }
2322
2323         // Seems fine, just format the closure in usual manner.
2324         return expr.rewrite(context, shape);
2325     }
2326     None
2327 }
2328
2329 fn rewrite_last_arg_with_overflow<'a, T>(
2330     context: &RewriteContext,
2331     args: &[&T],
2332     last_item: &mut ListItem,
2333     shape: Shape,
2334 ) -> (Option<String>, Option<String>)
2335 where
2336     T: Rewrite + Spanned + ToExpr + 'a,
2337 {
2338     let last_arg = args[args.len() - 1];
2339     let rewrite = if let Some(expr) = last_arg.to_expr() {
2340         match expr.node {
2341             // When overflowing the closure which consists of a single control flow expression,
2342             // force to use block if its condition uses multi line.
2343             ast::ExprKind::Closure(..) => {
2344                 // If the argument consists of multiple closures, we do not overflow
2345                 // the last closure.
2346                 if args.len() > 1 &&
2347                     args.iter()
2348                         .rev()
2349                         .skip(1)
2350                         .filter_map(|arg| arg.to_expr())
2351                         .any(|expr| match expr.node {
2352                             ast::ExprKind::Closure(..) => true,
2353                             _ => false,
2354                         }) {
2355                     None
2356                 } else {
2357                     rewrite_last_closure(context, expr, shape)
2358                 }
2359             }
2360             _ => expr.rewrite(context, shape),
2361         }
2362     } else {
2363         last_arg.rewrite(context, shape)
2364     };
2365     let orig_last = last_item.item.clone();
2366
2367     if let Some(rewrite) = rewrite {
2368         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2369         last_item.item = rewrite_first_line;
2370         (orig_last, Some(rewrite))
2371     } else {
2372         (orig_last, None)
2373     }
2374 }
2375
2376 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2377 where
2378     T: Rewrite + Spanned + ToExpr + 'a,
2379 {
2380     args.last()
2381         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2382 }
2383
2384 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2385     match expr.node {
2386         ast::ExprKind::Match(..) => {
2387             (context.use_block_indent() && args_len == 1) ||
2388                 (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2389         }
2390         ast::ExprKind::If(..) |
2391         ast::ExprKind::IfLet(..) |
2392         ast::ExprKind::ForLoop(..) |
2393         ast::ExprKind::Loop(..) |
2394         ast::ExprKind::While(..) |
2395         ast::ExprKind::WhileLet(..) => {
2396             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2397         }
2398         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2399             context.use_block_indent() ||
2400                 context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2401         }
2402         ast::ExprKind::Array(..) |
2403         ast::ExprKind::Call(..) |
2404         ast::ExprKind::Mac(..) |
2405         ast::ExprKind::MethodCall(..) |
2406         ast::ExprKind::Struct(..) |
2407         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2408         ast::ExprKind::AddrOf(_, ref expr) |
2409         ast::ExprKind::Box(ref expr) |
2410         ast::ExprKind::Try(ref expr) |
2411         ast::ExprKind::Unary(_, ref expr) |
2412         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2413         _ => false,
2414     }
2415 }
2416
2417 pub fn wrap_args_with_parens(
2418     context: &RewriteContext,
2419     args_str: &str,
2420     is_extendable: bool,
2421     shape: Shape,
2422     nested_shape: Shape,
2423 ) -> String {
2424     if !context.use_block_indent() ||
2425         (context.inside_macro && !args_str.contains('\n') &&
2426              args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2427     {
2428         if context.config.spaces_within_parens() && args_str.len() > 0 {
2429             format!("( {} )", args_str)
2430         } else {
2431             format!("({})", args_str)
2432         }
2433     } else {
2434         format!(
2435             "(\n{}{}\n{})",
2436             nested_shape.indent.to_string(context.config),
2437             args_str,
2438             shape.block().indent.to_string(context.config)
2439         )
2440     }
2441 }
2442
2443 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2444     let snippet = context.snippet(span);
2445     snippet
2446         .trim_right_matches(|c: char| c == ')' || c.is_whitespace())
2447         .ends_with(',')
2448 }
2449
2450 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2451     debug!("rewrite_paren, shape: {:?}", shape);
2452     let paren_overhead = paren_overhead(context);
2453     let sub_shape = try_opt!(shape.sub_width(paren_overhead / 2)).visual_indent(paren_overhead / 2);
2454
2455     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && s.len() > 0 {
2456         format!("( {} )", s)
2457     } else {
2458         format!("({})", s)
2459     };
2460
2461     let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2462     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2463
2464     if subexpr_str.contains('\n') {
2465         Some(paren_wrapper(&subexpr_str))
2466     } else {
2467         if subexpr_str.len() + paren_overhead <= shape.width {
2468             Some(paren_wrapper(&subexpr_str))
2469         } else {
2470             let sub_shape = try_opt!(shape.offset_left(2));
2471             let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2472             Some(paren_wrapper(&subexpr_str))
2473         }
2474     }
2475 }
2476
2477 fn rewrite_index(
2478     expr: &ast::Expr,
2479     index: &ast::Expr,
2480     context: &RewriteContext,
2481     shape: Shape,
2482 ) -> Option<String> {
2483     let expr_str = try_opt!(expr.rewrite(context, shape));
2484
2485     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2486         ("[ ", " ]")
2487     } else {
2488         ("[", "]")
2489     };
2490
2491     let offset = expr_str.len() + lbr.len();
2492     let orig_index_rw = shape
2493         .visual_indent(offset)
2494         .sub_width(offset + rbr.len())
2495         .and_then(|index_shape| index.rewrite(context, index_shape));
2496
2497     // Return if everything fits in a single line.
2498     match orig_index_rw {
2499         Some(ref index_str) if !index_str.contains('\n') => {
2500             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2501         }
2502         _ => (),
2503     }
2504
2505     // Try putting index on the next line and see if it fits in a single line.
2506     let indent = shape.indent.block_indent(context.config);
2507     let rhs_overhead = shape.rhs_overhead(context.config);
2508     let index_shape = try_opt!(Shape::indented(indent, context.config).offset_left(lbr.len()));
2509     let index_shape = try_opt!(index_shape.sub_width(rbr.len() + rhs_overhead));
2510     let new_index_rw = index.rewrite(context, index_shape);
2511     match (orig_index_rw, new_index_rw) {
2512         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => {
2513             Some(format!(
2514                 "{}\n{}{}{}{}",
2515                 expr_str,
2516                 indent.to_string(&context.config),
2517                 lbr,
2518                 new_index_str,
2519                 rbr
2520             ))
2521         }
2522         (None, Some(ref new_index_str)) => {
2523             Some(format!(
2524                 "{}\n{}{}{}{}",
2525                 expr_str,
2526                 indent.to_string(&context.config),
2527                 lbr,
2528                 new_index_str,
2529                 rbr
2530             ))
2531         }
2532         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2533         _ => None,
2534     }
2535 }
2536
2537 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2538     if base.is_some() {
2539         return false;
2540     }
2541
2542     fields.iter().all(|field| !field.is_shorthand)
2543 }
2544
2545 fn rewrite_struct_lit<'a>(
2546     context: &RewriteContext,
2547     path: &ast::Path,
2548     fields: &'a [ast::Field],
2549     base: Option<&'a ast::Expr>,
2550     span: Span,
2551     shape: Shape,
2552 ) -> Option<String> {
2553     debug!("rewrite_struct_lit: shape {:?}", shape);
2554
2555     enum StructLitField<'a> {
2556         Regular(&'a ast::Field),
2557         Base(&'a ast::Expr),
2558     }
2559
2560     // 2 = " {".len()
2561     let path_shape = try_opt!(shape.sub_width(2));
2562     let path_str = try_opt!(rewrite_path(
2563         context,
2564         PathContext::Expr,
2565         None,
2566         path,
2567         path_shape,
2568     ));
2569
2570     if fields.len() == 0 && base.is_none() {
2571         return Some(format!("{} {{}}", path_str));
2572     }
2573
2574     // Foo { a: Foo } - indent is +3, width is -5.
2575     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
2576
2577     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2578     let body_lo = context.codemap.span_after(span, "{");
2579     let fields_str = if struct_lit_can_be_aligned(fields, &base) &&
2580         context.config.struct_field_align_threshold() > 0
2581     {
2582         try_opt!(rewrite_with_alignment(
2583             fields,
2584             context,
2585             shape,
2586             mk_sp(body_lo, span.hi),
2587             one_line_width,
2588         ))
2589     } else {
2590         let field_iter = fields
2591             .into_iter()
2592             .map(StructLitField::Regular)
2593             .chain(base.into_iter().map(StructLitField::Base));
2594
2595         let span_lo = |item: &StructLitField| match *item {
2596             StructLitField::Regular(field) => field.span().lo,
2597             StructLitField::Base(expr) => {
2598                 let last_field_hi = fields.last().map_or(span.lo, |field| field.span.hi);
2599                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo));
2600                 let pos = snippet.find_uncommented("..").unwrap();
2601                 last_field_hi + BytePos(pos as u32)
2602             }
2603         };
2604         let span_hi = |item: &StructLitField| match *item {
2605             StructLitField::Regular(field) => field.span().hi,
2606             StructLitField::Base(expr) => expr.span.hi,
2607         };
2608         let rewrite = |item: &StructLitField| match *item {
2609             StructLitField::Regular(field) => {
2610                 // The 1 taken from the v_budget is for the comma.
2611                 rewrite_field(context, field, try_opt!(v_shape.sub_width(1)), 0)
2612             }
2613             StructLitField::Base(expr) => {
2614                 // 2 = ..
2615                 expr.rewrite(context, try_opt!(v_shape.shrink_left(2)))
2616                     .map(|s| format!("..{}", s))
2617             }
2618         };
2619
2620         let items = itemize_list(
2621             context.codemap,
2622             field_iter,
2623             "}",
2624             span_lo,
2625             span_hi,
2626             rewrite,
2627             body_lo,
2628             span.hi,
2629         );
2630         let item_vec = items.collect::<Vec<_>>();
2631
2632         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2633         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2634         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2635
2636         try_opt!(write_list(&item_vec, &fmt))
2637     };
2638
2639     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2640     Some(format!("{} {{{}}}", path_str, fields_str))
2641
2642     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2643     // of space, we should fall back to BlockIndent.
2644 }
2645
2646 pub fn wrap_struct_field(
2647     context: &RewriteContext,
2648     fields_str: &str,
2649     shape: Shape,
2650     nested_shape: Shape,
2651     one_line_width: usize,
2652 ) -> String {
2653     if context.config.struct_lit_style() == IndentStyle::Block &&
2654         (fields_str.contains('\n') ||
2655              context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti ||
2656              fields_str.len() > one_line_width)
2657     {
2658         format!(
2659             "\n{}{}\n{}",
2660             nested_shape.indent.to_string(context.config),
2661             fields_str,
2662             shape.indent.to_string(context.config)
2663         )
2664     } else {
2665         // One liner or visual indent.
2666         format!(" {} ", fields_str)
2667     }
2668 }
2669
2670 pub fn struct_lit_field_separator(config: &Config) -> &str {
2671     colon_spaces(
2672         config.space_before_struct_lit_field_colon(),
2673         config.space_after_struct_lit_field_colon(),
2674     )
2675 }
2676
2677 pub fn rewrite_field(
2678     context: &RewriteContext,
2679     field: &ast::Field,
2680     shape: Shape,
2681     prefix_max_width: usize,
2682 ) -> Option<String> {
2683     if contains_skip(&field.attrs) {
2684         return wrap_str(
2685             context.snippet(field.span()),
2686             context.config.max_width(),
2687             shape,
2688         );
2689     }
2690     let name = &field.ident.node.to_string();
2691     if field.is_shorthand {
2692         Some(name.to_string())
2693     } else {
2694         let mut separator = String::from(struct_lit_field_separator(context.config));
2695         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2696             separator.push(' ');
2697         }
2698         let overhead = name.len() + separator.len();
2699         let expr_shape = try_opt!(shape.offset_left(overhead));
2700         let expr = field.expr.rewrite(context, expr_shape);
2701
2702         let mut attrs_str = try_opt!(field.attrs.rewrite(context, shape));
2703         if !attrs_str.is_empty() {
2704             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2705         };
2706
2707         match expr {
2708             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2709             None => {
2710                 let expr_offset = shape.indent.block_indent(context.config);
2711                 let expr = field
2712                     .expr
2713                     .rewrite(context, Shape::indented(expr_offset, context.config));
2714                 expr.map(|s| {
2715                     format!(
2716                         "{}{}:\n{}{}",
2717                         attrs_str,
2718                         name,
2719                         expr_offset.to_string(&context.config),
2720                         s
2721                     )
2722                 })
2723             }
2724         }
2725     }
2726 }
2727
2728 fn shape_from_fn_call_style(
2729     context: &RewriteContext,
2730     shape: Shape,
2731     overhead: usize,
2732     offset: usize,
2733 ) -> Option<Shape> {
2734     if context.use_block_indent() {
2735         // 1 = ","
2736         shape
2737             .block()
2738             .block_indent(context.config.tab_spaces())
2739             .with_max_width(context.config)
2740             .sub_width(1)
2741     } else {
2742         shape.visual_indent(offset).sub_width(overhead)
2743     }
2744 }
2745
2746 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2747     context: &RewriteContext,
2748     items: &[&T],
2749     span: Span,
2750     shape: Shape,
2751 ) -> Option<String>
2752 where
2753     T: Rewrite + Spanned + ToExpr + 'a,
2754 {
2755     let mut items = items.iter();
2756     // In case of length 1, need a trailing comma
2757     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2758     if items.len() == 1 {
2759         // 3 = "(" + ",)"
2760         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
2761         return items.next().unwrap().rewrite(context, nested_shape).map(
2762             |s| if context.config.spaces_within_parens() {
2763                 format!("( {}, )", s)
2764             } else {
2765                 format!("({},)", s)
2766             },
2767         );
2768     }
2769
2770     let list_lo = context.codemap.span_after(span, "(");
2771     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
2772     let items = itemize_list(
2773         context.codemap,
2774         items,
2775         ")",
2776         |item| item.span().lo,
2777         |item| item.span().hi,
2778         |item| item.rewrite(context, nested_shape),
2779         list_lo,
2780         span.hi - BytePos(1),
2781     );
2782     let item_vec: Vec<_> = items.collect();
2783     let tactic = definitive_tactic(
2784         &item_vec,
2785         ListTactic::HorizontalVertical,
2786         nested_shape.width,
2787     );
2788     let fmt = ListFormatting {
2789         tactic: tactic,
2790         separator: ",",
2791         trailing_separator: SeparatorTactic::Never,
2792         shape: shape,
2793         ends_with_newline: false,
2794         config: context.config,
2795     };
2796     let list_str = try_opt!(write_list(&item_vec, &fmt));
2797
2798     if context.config.spaces_within_parens() && list_str.len() > 0 {
2799         Some(format!("( {} )", list_str))
2800     } else {
2801         Some(format!("({})", list_str))
2802     }
2803 }
2804
2805 pub fn rewrite_tuple<'a, T>(
2806     context: &RewriteContext,
2807     items: &[&T],
2808     span: Span,
2809     shape: Shape,
2810 ) -> Option<String>
2811 where
2812     T: Rewrite + Spanned + ToExpr + 'a,
2813 {
2814     debug!("rewrite_tuple {:?}", shape);
2815     if context.use_block_indent() {
2816         // We use the same rule as funcation call for rewriting tuple.
2817         let force_trailing_comma = if context.inside_macro {
2818             span_ends_with_comma(context, span)
2819         } else {
2820             items.len() == 1
2821         };
2822         rewrite_call_inner(
2823             context,
2824             &String::new(),
2825             items,
2826             span,
2827             shape,
2828             context.config.fn_call_width(),
2829             force_trailing_comma,
2830         ).ok()
2831     } else {
2832         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2833     }
2834 }
2835
2836 pub fn rewrite_unary_prefix<R: Rewrite>(
2837     context: &RewriteContext,
2838     prefix: &str,
2839     rewrite: &R,
2840     shape: Shape,
2841 ) -> Option<String> {
2842     rewrite
2843         .rewrite(context, try_opt!(shape.offset_left(prefix.len())))
2844         .map(|r| format!("{}{}", prefix, r))
2845 }
2846
2847 // FIXME: this is probably not correct for multi-line Rewrites. we should
2848 // subtract suffix.len() from the last line budget, not the first!
2849 pub fn rewrite_unary_suffix<R: Rewrite>(
2850     context: &RewriteContext,
2851     suffix: &str,
2852     rewrite: &R,
2853     shape: Shape,
2854 ) -> Option<String> {
2855     rewrite
2856         .rewrite(context, try_opt!(shape.sub_width(suffix.len())))
2857         .map(|mut r| {
2858             r.push_str(suffix);
2859             r
2860         })
2861 }
2862
2863 fn rewrite_unary_op(
2864     context: &RewriteContext,
2865     op: &ast::UnOp,
2866     expr: &ast::Expr,
2867     shape: Shape,
2868 ) -> Option<String> {
2869     // For some reason, an UnOp is not spanned like BinOp!
2870     let operator_str = match *op {
2871         ast::UnOp::Deref => "*",
2872         ast::UnOp::Not => "!",
2873         ast::UnOp::Neg => "-",
2874     };
2875     rewrite_unary_prefix(context, operator_str, expr, shape)
2876 }
2877
2878 fn rewrite_assignment(
2879     context: &RewriteContext,
2880     lhs: &ast::Expr,
2881     rhs: &ast::Expr,
2882     op: Option<&ast::BinOp>,
2883     shape: Shape,
2884 ) -> Option<String> {
2885     let operator_str = match op {
2886         Some(op) => context.snippet(op.span),
2887         None => "=".to_owned(),
2888     };
2889
2890     // 1 = space between lhs and operator.
2891     let lhs_shape = try_opt!(shape.sub_width(operator_str.len() + 1));
2892     let lhs_str = format!(
2893         "{} {}",
2894         try_opt!(lhs.rewrite(context, lhs_shape)),
2895         operator_str
2896     );
2897
2898     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2899 }
2900
2901 // The left hand side must contain everything up to, and including, the
2902 // assignment operator.
2903 pub fn rewrite_assign_rhs<S: Into<String>>(
2904     context: &RewriteContext,
2905     lhs: S,
2906     ex: &ast::Expr,
2907     shape: Shape,
2908 ) -> Option<String> {
2909     let lhs = lhs.into();
2910     let last_line_width = last_line_width(&lhs) -
2911         if lhs.contains('\n') {
2912             shape.indent.width()
2913         } else {
2914             0
2915         };
2916     // 1 = space between operator and rhs.
2917     let orig_shape = try_opt!(shape.offset_left(last_line_width + 1));
2918     let rhs = try_opt!(choose_rhs(
2919         context,
2920         ex,
2921         shape,
2922         ex.rewrite(context, orig_shape)
2923     ));
2924     Some(lhs + &rhs)
2925 }
2926
2927 fn choose_rhs(
2928     context: &RewriteContext,
2929     expr: &ast::Expr,
2930     shape: Shape,
2931     orig_rhs: Option<String>,
2932 ) -> Option<String> {
2933     match orig_rhs {
2934         Some(ref new_str) if !new_str.contains('\n') => Some(format!(" {}", new_str)),
2935         _ => {
2936             // Expression did not fit on the same line as the identifier.
2937             // Try splitting the line and see if that works better.
2938             let new_shape = try_opt!(
2939                 Shape::indented(
2940                     shape.block().indent.block_indent(context.config),
2941                     context.config,
2942                 ).sub_width(shape.rhs_overhead(context.config))
2943             );
2944             let new_rhs = expr.rewrite(context, new_shape);
2945             let new_indent_str = &new_shape.indent.to_string(context.config);
2946
2947             match (orig_rhs, new_rhs) {
2948                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2949                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2950                 }
2951                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2952                 (None, None) => None,
2953                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2954             }
2955         }
2956     }
2957 }
2958
2959 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2960
2961     fn count_line_breaks(src: &str) -> usize {
2962         src.chars().filter(|&x| x == '\n').count()
2963     }
2964
2965     !next_line_rhs.contains('\n') ||
2966         count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2967 }
2968
2969 fn rewrite_expr_addrof(
2970     context: &RewriteContext,
2971     mutability: ast::Mutability,
2972     expr: &ast::Expr,
2973     shape: Shape,
2974 ) -> Option<String> {
2975     let operator_str = match mutability {
2976         ast::Mutability::Immutable => "&",
2977         ast::Mutability::Mutable => "&mut ",
2978     };
2979     rewrite_unary_prefix(context, operator_str, expr, shape)
2980 }
2981
2982 pub trait ToExpr {
2983     fn to_expr(&self) -> Option<&ast::Expr>;
2984     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2985 }
2986
2987 impl ToExpr for ast::Expr {
2988     fn to_expr(&self) -> Option<&ast::Expr> {
2989         Some(self)
2990     }
2991
2992     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2993         can_be_overflowed_expr(context, self, len)
2994     }
2995 }
2996
2997 impl ToExpr for ast::Ty {
2998     fn to_expr(&self) -> Option<&ast::Expr> {
2999         None
3000     }
3001
3002     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3003         can_be_overflowed_type(context, self, len)
3004     }
3005 }
3006
3007 impl<'a> ToExpr for TuplePatField<'a> {
3008     fn to_expr(&self) -> Option<&ast::Expr> {
3009         None
3010     }
3011
3012     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
3013         can_be_overflowed_pat(context, self, len)
3014     }
3015 }
3016
3017 impl<'a> ToExpr for ast::StructField {
3018     fn to_expr(&self) -> Option<&ast::Expr> {
3019         None
3020     }
3021
3022     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
3023         false
3024     }
3025 }