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::borrow::Cow;
  12 use std::cmp::min;
  13
  14 use config::lists::*;
  15 use syntax::codemap::{BytePos, CodeMap, Span};
  16 use syntax::parse::token::DelimToken;
  17 use syntax::{ast, ptr};
  18
  19 use chains::rewrite_chain;
  20 use closures;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use comment::{
  23     combine_strs_with_missing_comments, contains_comment, recover_comment_removed, rewrite_comment,
  24     rewrite_missing_comment, CharClasses, FindUncommented,
  25 };
  26 use config::{Config, ControlBraceStyle, IndentStyle};
  27 use lists::{
  28     definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape,
  29     struct_lit_tactic, write_list, ListFormatting, ListItem, Separator,
  30 };
  31 use macros::{rewrite_macro, MacroArg, MacroPosition};
  32 use matches::rewrite_match;
  33 use overflow;
  34 use patterns::{can_be_overflowed_pat, is_short_pattern, TuplePatField};
  35 use rewrite::{Rewrite, RewriteContext};
  36 use shape::{Indent, Shape};
  37 use spanned::Spanned;
  38 use string::{rewrite_string, StringFormat};
  39 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  40 use utils::{
  41     colon_spaces, contains_skip, count_newlines, first_line_width, inner_attributes,
  42     last_line_extendable, last_line_width, mk_sp, outer_attributes, ptr_vec_to_ref_vec,
  43     semicolon_for_stmt, wrap_str,
  44 };
  45 use vertical::rewrite_with_alignment;
  46 use visitor::FmtVisitor;
  47
  48 impl Rewrite for ast::Expr {
  49     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  50         format_expr(self, ExprType::SubExpression, context, shape)
  51     }
  52 }
  53
  54 #[derive(Copy, Clone, PartialEq)]
  55 pub enum ExprType {
  56     Statement,
  57     SubExpression,
  58 }
  59
  60 pub fn format_expr(
  61     expr: &ast::Expr,
  62     expr_type: ExprType,
  63     context: &RewriteContext,
  64     shape: Shape,
  65 ) -> Option<String> {
  66     skip_out_of_file_lines_range!(context, expr.span);
  67
  68     if contains_skip(&*expr.attrs) {
  69         return Some(context.snippet(expr.span()).to_owned());
  70     }
  71
  72     let expr_rw = match expr.node {
  73         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  74             "",
  75             &ptr_vec_to_ref_vec(expr_vec),
  76             expr.span,
  77             context,
  78             shape,
  79             choose_separator_tactic(context, expr.span),
  80             None,
  81         ),
  82         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  83         ast::ExprKind::Call(ref callee, ref args) => {
  84             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  85             let callee_str = callee.rewrite(context, shape)?;
  86             rewrite_call(context, &callee_str, args, inner_span, shape)
  87         }
  88         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape, expr.span),
  89         ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
  90             // FIXME: format comments between operands and operator
  91             rewrite_simple_binaries(context, expr, shape, op).or_else(|| {
  92                 rewrite_pair(
  93                     &**lhs,
  94                     &**rhs,
  95                     PairParts::new("", &format!(" {} ", context.snippet(op.span)), ""),
  96                     context,
  97                     shape,
  98                     context.config.binop_separator(),
  99                 )
 100             })
 101         }
 102         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 103         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 104             context,
 105             path,
 106             fields,
 107             base.as_ref().map(|e| &**e),
 108             expr.span,
 109             shape,
 110         ),
 111         ast::ExprKind::Tup(ref items) => {
 112             rewrite_tuple(context, &ptr_vec_to_ref_vec(items), expr.span, shape)
 113         }
 114         ast::ExprKind::If(..)
 115         | ast::ExprKind::IfLet(..)
 116         | ast::ExprKind::ForLoop(..)
 117         | ast::ExprKind::Loop(..)
 118         | ast::ExprKind::While(..)
 119         | ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 120             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 121         ast::ExprKind::Block(ref block, opt_label) => {
 122             match expr_type {
 123                 ExprType::Statement => {
 124                     if is_unsafe_block(block) {
 125                         rewrite_block(block, Some(&expr.attrs), context, shape)
 126                     } else if let rw @ Some(_) =
 127                         rewrite_empty_block(context, block, Some(&expr.attrs), "", shape)
 128                     {
 129                         // Rewrite block without trying to put it in a single line.
 130                         rw
 131                     } else {
 132                         let prefix = block_prefix(context, block, shape)?;
 133                         let label_string = rewrite_label(opt_label);
 134
 135                         rewrite_block_with_visitor(
 136                             context,
 137                             &format!("{}{}", &prefix, &label_string),
 138                             block,
 139                             Some(&expr.attrs),
 140                             shape,
 141                             true,
 142                         )
 143                     }
 144                 }
 145                 ExprType::SubExpression => rewrite_block(block, Some(&expr.attrs), context, shape),
 146             }
 147         }
 148         ast::ExprKind::Match(ref cond, ref arms) => {
 149             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 150         }
 151         ast::ExprKind::Path(ref qself, ref path) => {
 152             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 153         }
 154         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 155             rewrite_assignment(context, lhs, rhs, None, shape)
 156         }
 157         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 158             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 159         }
 160         ast::ExprKind::Continue(ref opt_label) => {
 161             let id_str = match *opt_label {
 162                 Some(label) => format!(" {}", label.ident),
 163                 None => String::new(),
 164             };
 165             Some(format!("continue{}", id_str))
 166         }
 167         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 168             let id_str = match *opt_label {
 169                 Some(label) => format!(" {}", label.ident),
 170                 None => String::new(),
 171             };
 172
 173             if let Some(ref expr) = *opt_expr {
 174                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 175             } else {
 176                 Some(format!("break{}", id_str))
 177             }
 178         }
 179         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 180             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 181         } else {
 182             Some("yield".to_string())
 183         },
 184         ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) => {
 185             closures::rewrite_closure(
 186                 capture, movability, fn_decl, body, expr.span, context, shape,
 187             )
 188         }
 189         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 190             rewrite_chain(expr, context, shape)
 191         }
 192         ast::ExprKind::Mac(ref mac) => {
 193             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 194                 wrap_str(
 195                     context.snippet(expr.span).to_owned(),
 196                     context.config.max_width(),
 197                     shape,
 198                 )
 199             })
 200         }
 201         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 202         ast::ExprKind::Ret(Some(ref expr)) => {
 203             rewrite_unary_prefix(context, "return ", &**expr, shape)
 204         }
 205         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 206         ast::ExprKind::AddrOf(mutability, ref expr) => {
 207             rewrite_expr_addrof(context, mutability, expr, shape)
 208         }
 209         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 210             &**expr,
 211             &**ty,
 212             PairParts::new("", " as ", ""),
 213             context,
 214             shape,
 215             SeparatorPlace::Front,
 216         ),
 217         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 218             &**expr,
 219             &**ty,
 220             PairParts::new("", ": ", ""),
 221             context,
 222             shape,
 223             SeparatorPlace::Back,
 224         ),
 225         ast::ExprKind::Index(ref expr, ref index) => {
 226             rewrite_index(&**expr, &**index, context, shape)
 227         }
 228         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 229             &**expr,
 230             &**repeats,
 231             PairParts::new("[", "; ", "]"),
 232             context,
 233             shape,
 234             SeparatorPlace::Back,
 235         ),
 236         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 237             let delim = match limits {
 238                 ast::RangeLimits::HalfOpen => "..",
 239                 ast::RangeLimits::Closed => "..=",
 240             };
 241
 242             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 243                 match lhs.node {
 244                     ast::ExprKind::Lit(ref lit) => match lit.node {
 245                         ast::LitKind::FloatUnsuffixed(..) => {
 246                             context.snippet(lit.span).ends_with('.')
 247                         }
 248                         _ => false,
 249                     },
 250                     _ => false,
 251                 }
 252             }
 253
 254             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 255                 match rhs.node {
 256                     // Don't format `.. ..` into `....`, which is invalid.
 257                     //
 258                     // This check is unnecessary for `lhs`, because a range
 259                     // starting from another range needs parentheses as `(x ..) ..`
 260                     // (`x .. ..` is a range from `x` to `..`).
 261                     ast::ExprKind::Range(None, _, _) => true,
 262                     _ => false,
 263                 }
 264             }
 265
 266             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 267                 let space_if = |b: bool| if b { " " } else { "" };
 268
 269                 format!(
 270                     "{}{}{}",
 271                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 272                         .unwrap_or(""),
 273                     delim,
 274                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 275                         .unwrap_or(""),
 276                 )
 277             };
 278
 279             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 280                 (Some(lhs), Some(rhs)) => {
 281                     let sp_delim = if context.config.spaces_around_ranges() {
 282                         format!(" {} ", delim)
 283                     } else {
 284                         default_sp_delim(Some(lhs), Some(rhs))
 285                     };
 286                     rewrite_pair(
 287                         &*lhs,
 288                         &*rhs,
 289                         PairParts::new("", &sp_delim, ""),
 290                         context,
 291                         shape,
 292                         context.config.binop_separator(),
 293                     )
 294                 }
 295                 (None, Some(rhs)) => {
 296                     let sp_delim = if context.config.spaces_around_ranges() {
 297                         format!("{} ", delim)
 298                     } else {
 299                         default_sp_delim(None, Some(rhs))
 300                     };
 301                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 302                 }
 303                 (Some(lhs), None) => {
 304                     let sp_delim = if context.config.spaces_around_ranges() {
 305                         format!(" {}", delim)
 306                     } else {
 307                         default_sp_delim(Some(lhs), None)
 308                     };
 309                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 310                 }
 311                 (None, None) => Some(delim.to_owned()),
 312             }
 313         }
 314         // We do not format these expressions yet, but they should still
 315         // satisfy our width restrictions.
 316         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 317         ast::ExprKind::Catch(ref block) => {
 318             if let rw @ Some(_) =
 319                 rewrite_single_line_block(context, "do catch ", block, Some(&expr.attrs), shape)
 320             {
 321                 rw
 322             } else {
 323                 // 9 = `do catch `
 324                 let budget = shape.width.saturating_sub(9);
 325                 Some(format!(
 326                     "{}{}",
 327                     "do catch ",
 328                     rewrite_block(
 329                         block,
 330                         Some(&expr.attrs),
 331                         context,
 332                         Shape::legacy(budget, shape.indent)
 333                     )?
 334                 ))
 335             }
 336         }
 337     };
 338
 339     expr_rw
 340         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 341         .and_then(|expr_str| {
 342             let attrs = outer_attributes(&expr.attrs);
 343             let attrs_str = attrs.rewrite(context, shape)?;
 344             let span = mk_sp(
 345                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 346                 expr.span.lo(),
 347             );
 348             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 349         })
 350 }
 351
 352 /// Collect operands that appears in the given binary operator in the opposite order.
 353 /// e.g. `collect_binary_items(e, ||)` for `a && b || c || d` returns `[d, c, a && b]`.
 354 fn collect_binary_items<'a>(mut expr: &'a ast::Expr, binop: ast::BinOp) -> Vec<&'a ast::Expr> {
 355     let mut result = vec![];
 356     let mut prev_lhs = None;
 357     loop {
 358         match expr.node {
 359             ast::ExprKind::Binary(inner_binop, ref lhs, ref rhs)
 360                 if inner_binop.node == binop.node =>
 361             {
 362                 result.push(&**rhs);
 363                 expr = lhs;
 364                 prev_lhs = Some(lhs);
 365             }
 366             _ => {
 367                 if let Some(lhs) = prev_lhs {
 368                     result.push(lhs);
 369                 }
 370                 break;
 371             }
 372         }
 373     }
 374     result
 375 }
 376
 377 /// Rewrites a binary expression whose operands fits within a single line.
 378 fn rewrite_simple_binaries(
 379     context: &RewriteContext,
 380     expr: &ast::Expr,
 381     shape: Shape,
 382     op: ast::BinOp,
 383 ) -> Option<String> {
 384     let op_str = context.snippet(op.span);
 385
 386     // 2 = spaces around a binary operator.
 387     let sep_overhead = op_str.len() + 2;
 388     let nested_overhead = sep_overhead - 1;
 389
 390     let nested_shape = (match context.config.indent_style() {
 391         IndentStyle::Visual => shape.visual_indent(0),
 392         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 393     }).with_max_width(context.config);
 394     let nested_shape = match context.config.binop_separator() {
 395         SeparatorPlace::Back => nested_shape.sub_width(nested_overhead)?,
 396         SeparatorPlace::Front => nested_shape.offset_left(nested_overhead)?,
 397     };
 398
 399     let opt_rewrites: Option<Vec<_>> = collect_binary_items(expr, op)
 400         .iter()
 401         .rev()
 402         .map(|e| e.rewrite(context, nested_shape))
 403         .collect();
 404     if let Some(rewrites) = opt_rewrites {
 405         if rewrites.iter().all(|e| ::utils::is_single_line(e)) {
 406             let total_width = rewrites.iter().map(|s| s.len()).sum::<usize>()
 407                 + sep_overhead * (rewrites.len() - 1);
 408
 409             let sep_str = if total_width <= shape.width {
 410                 format!(" {} ", op_str)
 411             } else {
 412                 let indent_str = nested_shape.indent.to_string_with_newline(context.config);
 413                 match context.config.binop_separator() {
 414                     SeparatorPlace::Back => format!(" {}{}", op_str.trim_right(), indent_str),
 415                     SeparatorPlace::Front => format!("{}{} ", indent_str, op_str.trim_left()),
 416                 }
 417             };
 418
 419             return wrap_str(rewrites.join(&sep_str), context.config.max_width(), shape);
 420         }
 421     }
 422
 423     None
 424 }
 425
 426 #[derive(new, Clone, Copy)]
 427 pub struct PairParts<'a> {
 428     prefix: &'a str,
 429     infix: &'a str,
 430     suffix: &'a str,
 431 }
 432
 433 pub fn rewrite_pair<LHS, RHS>(
 434     lhs: &LHS,
 435     rhs: &RHS,
 436     pp: PairParts,
 437     context: &RewriteContext,
 438     shape: Shape,
 439     separator_place: SeparatorPlace,
 440 ) -> Option<String>
 441 where
 442     LHS: Rewrite,
 443     RHS: Rewrite,
 444 {
 445     let lhs_overhead = match separator_place {
 446         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 447         SeparatorPlace::Front => shape.used_width(),
 448     };
 449     let lhs_shape = Shape {
 450         width: context.budget(lhs_overhead),
 451         ..shape
 452     };
 453     let lhs_result = lhs
 454         .rewrite(context, lhs_shape)
 455         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 456
 457     // Try to put both lhs and rhs on the same line.
 458     let rhs_orig_result = shape
 459         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 460         .and_then(|s| s.sub_width(pp.suffix.len()))
 461         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 462     if let Some(ref rhs_result) = rhs_orig_result {
 463         // If the length of the lhs is equal to or shorter than the tab width or
 464         // the rhs looks like block expression, we put the rhs on the same
 465         // line with the lhs even if the rhs is multi-lined.
 466         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 467             || rhs_result
 468                 .lines()
 469                 .next()
 470                 .map(|first_line| first_line.ends_with('{'))
 471                 .unwrap_or(false);
 472         if !rhs_result.contains('\n') || allow_same_line {
 473             let one_line_width = last_line_width(&lhs_result)
 474                 + pp.infix.len()
 475                 + first_line_width(rhs_result)
 476                 + pp.suffix.len();
 477             if one_line_width <= shape.width {
 478                 return Some(format!(
 479                     "{}{}{}{}",
 480                     lhs_result, pp.infix, rhs_result, pp.suffix
 481                 ));
 482             }
 483         }
 484     }
 485
 486     // We have to use multiple lines.
 487     // Re-evaluate the rhs because we have more space now:
 488     let mut rhs_shape = match context.config.indent_style() {
 489         IndentStyle::Visual => shape
 490             .sub_width(pp.suffix.len() + pp.prefix.len())?
 491             .visual_indent(pp.prefix.len()),
 492         IndentStyle::Block => {
 493             // Try to calculate the initial constraint on the right hand side.
 494             let rhs_overhead = shape.rhs_overhead(context.config);
 495             Shape::indented(shape.indent.block_indent(context.config), context.config)
 496                 .sub_width(rhs_overhead)?
 497         }
 498     };
 499     let infix = match separator_place {
 500         SeparatorPlace::Back => pp.infix.trim_right(),
 501         SeparatorPlace::Front => pp.infix.trim_left(),
 502     };
 503     if separator_place == SeparatorPlace::Front {
 504         rhs_shape = rhs_shape.offset_left(infix.len())?;
 505     }
 506     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 507     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 508     let infix_with_sep = match separator_place {
 509         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 510         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 511     };
 512     Some(format!(
 513         "{}{}{}{}",
 514         lhs_result, infix_with_sep, rhs_result, pp.suffix
 515     ))
 516 }
 517
 518 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 519     name: &str,
 520     exprs: &[&T],
 521     span: Span,
 522     context: &RewriteContext,
 523     shape: Shape,
 524     force_separator_tactic: Option<SeparatorTactic>,
 525     delim_token: Option<DelimToken>,
 526 ) -> Option<String> {
 527     overflow::rewrite_with_square_brackets(
 528         context,
 529         name,
 530         exprs,
 531         shape,
 532         span,
 533         force_separator_tactic,
 534         delim_token,
 535     )
 536 }
 537
 538 fn rewrite_empty_block(
 539     context: &RewriteContext,
 540     block: &ast::Block,
 541     attrs: Option<&[ast::Attribute]>,
 542     prefix: &str,
 543     shape: Shape,
 544 ) -> Option<String> {
 545     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 546         return None;
 547     }
 548
 549     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 550     {
 551         return Some(format!("{}{{}}", prefix));
 552     }
 553
 554     // If a block contains only a single-line comment, then leave it on one line.
 555     let user_str = context.snippet(block.span);
 556     let user_str = user_str.trim();
 557     if user_str.starts_with('{') && user_str.ends_with('}') {
 558         let comment_str = user_str[1..user_str.len() - 1].trim();
 559         if block.stmts.is_empty()
 560             && !comment_str.contains('\n')
 561             && !comment_str.starts_with("//")
 562             && comment_str.len() + 4 <= shape.width
 563         {
 564             return Some(format!("{}{{ {} }}", prefix, comment_str));
 565         }
 566     }
 567
 568     None
 569 }
 570
 571 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 572     Some(match block.rules {
 573         ast::BlockCheckMode::Unsafe(..) => {
 574             let snippet = context.snippet(block.span);
 575             let open_pos = snippet.find_uncommented("{")?;
 576             // Extract comment between unsafe and block start.
 577             let trimmed = &snippet[6..open_pos].trim();
 578
 579             if !trimmed.is_empty() {
 580                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 581                 let budget = shape.width.checked_sub(9)?;
 582                 format!(
 583                     "unsafe {} ",
 584                     rewrite_comment(
 585                         trimmed,
 586                         true,
 587                         Shape::legacy(budget, shape.indent + 7),
 588                         context.config,
 589                     )?
 590                 )
 591             } else {
 592                 "unsafe ".to_owned()
 593             }
 594         }
 595         ast::BlockCheckMode::Default => String::new(),
 596     })
 597 }
 598
 599 fn rewrite_single_line_block(
 600     context: &RewriteContext,
 601     prefix: &str,
 602     block: &ast::Block,
 603     attrs: Option<&[ast::Attribute]>,
 604     shape: Shape,
 605 ) -> Option<String> {
 606     if is_simple_block(block, attrs, context.codemap) {
 607         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 608         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 609         let result = format!("{}{{ {} }}", prefix, expr_str);
 610         if result.len() <= shape.width && !result.contains('\n') {
 611             return Some(result);
 612         }
 613     }
 614     None
 615 }
 616
 617 pub fn rewrite_block_with_visitor(
 618     context: &RewriteContext,
 619     prefix: &str,
 620     block: &ast::Block,
 621     attrs: Option<&[ast::Attribute]>,
 622     shape: Shape,
 623     has_braces: bool,
 624 ) -> Option<String> {
 625     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, prefix, shape) {
 626         return rw;
 627     }
 628
 629     let mut visitor = FmtVisitor::from_context(context);
 630     visitor.block_indent = shape.indent;
 631     visitor.is_if_else_block = context.is_if_else_block();
 632     match block.rules {
 633         ast::BlockCheckMode::Unsafe(..) => {
 634             let snippet = context.snippet(block.span);
 635             let open_pos = snippet.find_uncommented("{")?;
 636             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 637         }
 638         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 639     }
 640
 641     let inner_attrs = attrs.map(inner_attributes);
 642     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 643     Some(format!("{}{}", prefix, visitor.buffer))
 644 }
 645
 646 impl Rewrite for ast::Block {
 647     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 648         rewrite_block(self, None, context, shape)
 649     }
 650 }
 651
 652 fn rewrite_block(
 653     block: &ast::Block,
 654     attrs: Option<&[ast::Attribute]>,
 655     context: &RewriteContext,
 656     shape: Shape,
 657 ) -> Option<String> {
 658     let prefix = block_prefix(context, block, shape)?;
 659
 660     // shape.width is used only for the single line case: either the empty block `{}`,
 661     // or an unsafe expression `unsafe { e }`.
 662     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, &prefix, shape) {
 663         return rw;
 664     }
 665
 666     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, shape, true);
 667     if let Some(ref result_str) = result {
 668         if result_str.lines().count() <= 3 {
 669             if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, block, attrs, shape) {
 670                 return rw;
 671             }
 672         }
 673     }
 674
 675     result
 676 }
 677
 678 impl Rewrite for ast::Stmt {
 679     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 680         skip_out_of_file_lines_range!(context, self.span());
 681
 682         let result = match self.node {
 683             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 684             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 685                 let suffix = if semicolon_for_stmt(context, self) {
 686                     ";"
 687                 } else {
 688                     ""
 689                 };
 690
 691                 let shape = shape.sub_width(suffix.len())?;
 692                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 693             }
 694             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 695         };
 696         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 697     }
 698 }
 699
 700 // Rewrite condition if the given expression has one.
 701 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 702     match expr.node {
 703         ast::ExprKind::Match(ref cond, _) => {
 704             // `match `cond` {`
 705             let cond_shape = match context.config.indent_style() {
 706                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 707                 IndentStyle::Block => shape.offset_left(8)?,
 708             };
 709             cond.rewrite(context, cond_shape)
 710         }
 711         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 712             let alt_block_sep =
 713                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 714             control_flow
 715                 .rewrite_cond(context, shape, &alt_block_sep)
 716                 .and_then(|rw| Some(rw.0))
 717         }),
 718     }
 719 }
 720
 721 // Abstraction over control flow expressions
 722 #[derive(Debug)]
 723 struct ControlFlow<'a> {
 724     cond: Option<&'a ast::Expr>,
 725     block: &'a ast::Block,
 726     else_block: Option<&'a ast::Expr>,
 727     label: Option<ast::Label>,
 728     pats: Vec<&'a ast::Pat>,
 729     keyword: &'a str,
 730     matcher: &'a str,
 731     connector: &'a str,
 732     allow_single_line: bool,
 733     // True if this is an `if` expression in an `else if` :-( hacky
 734     nested_if: bool,
 735     span: Span,
 736 }
 737
 738 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 739     match expr.node {
 740         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 741             cond,
 742             vec![],
 743             if_block,
 744             else_block.as_ref().map(|e| &**e),
 745             expr_type == ExprType::SubExpression,
 746             false,
 747             expr.span,
 748         )),
 749         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 750             Some(ControlFlow::new_if(
 751                 cond,
 752                 ptr_vec_to_ref_vec(pat),
 753                 if_block,
 754                 else_block.as_ref().map(|e| &**e),
 755                 expr_type == ExprType::SubExpression,
 756                 false,
 757                 expr.span,
 758             ))
 759         }
 760         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 761             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 762         }
 763         ast::ExprKind::Loop(ref block, label) => {
 764             Some(ControlFlow::new_loop(block, label, expr.span))
 765         }
 766         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 767             vec![],
 768             cond,
 769             block,
 770             label,
 771             expr.span,
 772         )),
 773         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 774             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 775         ),
 776         _ => None,
 777     }
 778 }
 779
 780 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 781     if pats.is_empty() {
 782         ""
 783     } else {
 784         "let"
 785     }
 786 }
 787
 788 impl<'a> ControlFlow<'a> {
 789     fn new_if(
 790         cond: &'a ast::Expr,
 791         pats: Vec<&'a ast::Pat>,
 792         block: &'a ast::Block,
 793         else_block: Option<&'a ast::Expr>,
 794         allow_single_line: bool,
 795         nested_if: bool,
 796         span: Span,
 797     ) -> ControlFlow<'a> {
 798         let matcher = choose_matcher(&pats);
 799         ControlFlow {
 800             cond: Some(cond),
 801             block,
 802             else_block,
 803             label: None,
 804             pats,
 805             keyword: "if",
 806             matcher,
 807             connector: " =",
 808             allow_single_line,
 809             nested_if,
 810             span,
 811         }
 812     }
 813
 814     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 815         ControlFlow {
 816             cond: None,
 817             block,
 818             else_block: None,
 819             label,
 820             pats: vec![],
 821             keyword: "loop",
 822             matcher: "",
 823             connector: "",
 824             allow_single_line: false,
 825             nested_if: false,
 826             span,
 827         }
 828     }
 829
 830     fn new_while(
 831         pats: Vec<&'a ast::Pat>,
 832         cond: &'a ast::Expr,
 833         block: &'a ast::Block,
 834         label: Option<ast::Label>,
 835         span: Span,
 836     ) -> ControlFlow<'a> {
 837         let matcher = choose_matcher(&pats);
 838         ControlFlow {
 839             cond: Some(cond),
 840             block,
 841             else_block: None,
 842             label,
 843             pats,
 844             keyword: "while",
 845             matcher,
 846             connector: " =",
 847             allow_single_line: false,
 848             nested_if: false,
 849             span,
 850         }
 851     }
 852
 853     fn new_for(
 854         pat: &'a ast::Pat,
 855         cond: &'a ast::Expr,
 856         block: &'a ast::Block,
 857         label: Option<ast::Label>,
 858         span: Span,
 859     ) -> ControlFlow<'a> {
 860         ControlFlow {
 861             cond: Some(cond),
 862             block,
 863             else_block: None,
 864             label,
 865             pats: vec![pat],
 866             keyword: "for",
 867             matcher: "",
 868             connector: " in",
 869             allow_single_line: false,
 870             nested_if: false,
 871             span,
 872         }
 873     }
 874
 875     fn rewrite_single_line(
 876         &self,
 877         pat_expr_str: &str,
 878         context: &RewriteContext,
 879         width: usize,
 880     ) -> Option<String> {
 881         assert!(self.allow_single_line);
 882         let else_block = self.else_block?;
 883         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 884
 885         if let ast::ExprKind::Block(ref else_node, _) = else_block.node {
 886             if !is_simple_block(self.block, None, context.codemap)
 887                 || !is_simple_block(else_node, None, context.codemap)
 888                 || pat_expr_str.contains('\n')
 889             {
 890                 return None;
 891             }
 892
 893             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 894             let expr = &self.block.stmts[0];
 895             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 896
 897             let new_width = new_width.checked_sub(if_str.len())?;
 898             let else_expr = &else_node.stmts[0];
 899             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 900
 901             if if_str.contains('\n') || else_str.contains('\n') {
 902                 return None;
 903             }
 904
 905             let result = format!(
 906                 "{} {} {{ {} }} else {{ {} }}",
 907                 self.keyword, pat_expr_str, if_str, else_str
 908             );
 909
 910             if result.len() <= width {
 911                 return Some(result);
 912             }
 913         }
 914
 915         None
 916     }
 917 }
 918
 919 impl<'a> ControlFlow<'a> {
 920     fn rewrite_pat_expr(
 921         &self,
 922         context: &RewriteContext,
 923         expr: &ast::Expr,
 924         shape: Shape,
 925         offset: usize,
 926     ) -> Option<String> {
 927         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 928
 929         let cond_shape = shape.offset_left(offset)?;
 930         if !self.pats.is_empty() {
 931             let matcher = if self.matcher.is_empty() {
 932                 self.matcher.to_owned()
 933             } else {
 934                 format!("{} ", self.matcher)
 935             };
 936             let pat_shape = cond_shape
 937                 .offset_left(matcher.len())?
 938                 .sub_width(self.connector.len())?;
 939             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 940             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 941             return rewrite_assign_rhs(context, result, expr, cond_shape);
 942         }
 943
 944         let expr_rw = expr.rewrite(context, cond_shape);
 945         // The expression may (partially) fit on the current line.
 946         // We do not allow splitting between `if` and condition.
 947         if self.keyword == "if" || expr_rw.is_some() {
 948             return expr_rw;
 949         }
 950
 951         // The expression won't fit on the current line, jump to next.
 952         let nested_shape = shape
 953             .block_indent(context.config.tab_spaces())
 954             .with_max_width(context.config);
 955         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 956         expr.rewrite(context, nested_shape)
 957             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 958     }
 959
 960     fn rewrite_cond(
 961         &self,
 962         context: &RewriteContext,
 963         shape: Shape,
 964         alt_block_sep: &str,
 965     ) -> Option<(String, usize)> {
 966         // Do not take the rhs overhead from the upper expressions into account
 967         // when rewriting pattern.
 968         let new_width = context.budget(shape.used_width());
 969         let fresh_shape = Shape {
 970             width: new_width,
 971             ..shape
 972         };
 973         let constr_shape = if self.nested_if {
 974             // We are part of an if-elseif-else chain. Our constraints are tightened.
 975             // 7 = "} else " .len()
 976             fresh_shape.offset_left(7)?
 977         } else {
 978             fresh_shape
 979         };
 980
 981         let label_string = rewrite_label(self.label);
 982         // 1 = space after keyword.
 983         let offset = self.keyword.len() + label_string.len() + 1;
 984
 985         let pat_expr_string = match self.cond {
 986             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 987             None => String::new(),
 988         };
 989
 990         let brace_overhead =
 991             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 992                 // 2 = ` {`
 993                 2
 994             } else {
 995                 0
 996             };
 997         let one_line_budget = context
 998             .config
 999             .max_width()
1000             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
1001         let force_newline_brace = (pat_expr_string.contains('\n')
1002             || pat_expr_string.len() > one_line_budget)
1003             && !last_line_extendable(&pat_expr_string);
1004
1005         // Try to format if-else on single line.
1006         if self.allow_single_line
1007             && context
1008                 .config
1009                 .width_heuristics()
1010                 .single_line_if_else_max_width > 0
1011         {
1012             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1013
1014             if let Some(cond_str) = trial {
1015                 if cond_str.len()
1016                     <= context
1017                         .config
1018                         .width_heuristics()
1019                         .single_line_if_else_max_width
1020                 {
1021                     return Some((cond_str, 0));
1022                 }
1023             }
1024         }
1025
1026         let cond_span = if let Some(cond) = self.cond {
1027             cond.span
1028         } else {
1029             mk_sp(self.block.span.lo(), self.block.span.lo())
1030         };
1031
1032         // `for event in event`
1033         // Do not include label in the span.
1034         let lo = self
1035             .label
1036             .map_or(self.span.lo(), |label| label.ident.span.hi());
1037         let between_kwd_cond = mk_sp(
1038             context
1039                 .snippet_provider
1040                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1041             if self.pats.is_empty() {
1042                 cond_span.lo()
1043             } else if self.matcher.is_empty() {
1044                 self.pats[0].span.lo()
1045             } else {
1046                 context
1047                     .snippet_provider
1048                     .span_before(self.span, self.matcher.trim())
1049             },
1050         );
1051
1052         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1053
1054         let after_cond_comment =
1055             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1056
1057         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1058             ""
1059         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1060             || force_newline_brace
1061         {
1062             alt_block_sep
1063         } else {
1064             " "
1065         };
1066
1067         let used_width = if pat_expr_string.contains('\n') {
1068             last_line_width(&pat_expr_string)
1069         } else {
1070             // 2 = spaces after keyword and condition.
1071             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1072         };
1073
1074         Some((
1075             format!(
1076                 "{}{}{}{}{}",
1077                 label_string,
1078                 self.keyword,
1079                 between_kwd_cond_comment.as_ref().map_or(
1080                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1081                         ""
1082                     } else {
1083                         " "
1084                     },
1085                     |s| &**s,
1086                 ),
1087                 pat_expr_string,
1088                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1089             ),
1090             used_width,
1091         ))
1092     }
1093 }
1094
1095 impl<'a> Rewrite for ControlFlow<'a> {
1096     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1097         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1098
1099         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1100         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1101         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1102         if used_width == 0 {
1103             return Some(cond_str);
1104         }
1105
1106         let block_width = shape.width.saturating_sub(used_width);
1107         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1108         // we should avoid the single line case.
1109         let block_width = if self.else_block.is_some() || self.nested_if {
1110             min(1, block_width)
1111         } else {
1112             block_width
1113         };
1114         let block_shape = Shape {
1115             width: block_width,
1116             ..shape
1117         };
1118         let block_str = {
1119             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1120             let result =
1121                 rewrite_block_with_visitor(context, "", self.block, None, block_shape, true);
1122             context.is_if_else_block.replace(old_val);
1123             result?
1124         };
1125
1126         let mut result = format!("{}{}", cond_str, block_str);
1127
1128         if let Some(else_block) = self.else_block {
1129             let shape = Shape::indented(shape.indent, context.config);
1130             let mut last_in_chain = false;
1131             let rewrite = match else_block.node {
1132                 // If the else expression is another if-else expression, prevent it
1133                 // from being formatted on a single line.
1134                 // Note how we're passing the original shape, as the
1135                 // cost of "else" should not cascade.
1136                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1137                     ControlFlow::new_if(
1138                         cond,
1139                         ptr_vec_to_ref_vec(pat),
1140                         if_block,
1141                         next_else_block.as_ref().map(|e| &**e),
1142                         false,
1143                         true,
1144                         mk_sp(else_block.span.lo(), self.span.hi()),
1145                     ).rewrite(context, shape)
1146                 }
1147                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1148                     ControlFlow::new_if(
1149                         cond,
1150                         vec![],
1151                         if_block,
1152                         next_else_block.as_ref().map(|e| &**e),
1153                         false,
1154                         true,
1155                         mk_sp(else_block.span.lo(), self.span.hi()),
1156                     ).rewrite(context, shape)
1157                 }
1158                 _ => {
1159                     last_in_chain = true;
1160                     // When rewriting a block, the width is only used for single line
1161                     // blocks, passing 1 lets us avoid that.
1162                     let else_shape = Shape {
1163                         width: min(1, shape.width),
1164                         ..shape
1165                     };
1166                     format_expr(else_block, ExprType::Statement, context, else_shape)
1167                 }
1168             };
1169
1170             let between_kwd_else_block = mk_sp(
1171                 self.block.span.hi(),
1172                 context
1173                     .snippet_provider
1174                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1175             );
1176             let between_kwd_else_block_comment =
1177                 extract_comment(between_kwd_else_block, context, shape);
1178
1179             let after_else = mk_sp(
1180                 context
1181                     .snippet_provider
1182                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1183                 else_block.span.lo(),
1184             );
1185             let after_else_comment = extract_comment(after_else, context, shape);
1186
1187             let between_sep = match context.config.control_brace_style() {
1188                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1189                     &*alt_block_sep
1190                 }
1191                 ControlBraceStyle::AlwaysSameLine => " ",
1192             };
1193             let after_sep = match context.config.control_brace_style() {
1194                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1195                 _ => " ",
1196             };
1197
1198             result.push_str(&format!(
1199                 "{}else{}",
1200                 between_kwd_else_block_comment
1201                     .as_ref()
1202                     .map_or(between_sep, |s| &**s),
1203                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1204             ));
1205             result.push_str(&rewrite?);
1206         }
1207
1208         Some(result)
1209     }
1210 }
1211
1212 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1213     match opt_label {
1214         Some(label) => Cow::from(format!("{}: ", label.ident)),
1215         None => Cow::from(""),
1216     }
1217 }
1218
1219 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1220     match rewrite_missing_comment(span, shape, context) {
1221         Some(ref comment) if !comment.is_empty() => Some(format!(
1222             "{indent}{}{indent}",
1223             comment,
1224             indent = shape.indent.to_string_with_newline(context.config)
1225         )),
1226         _ => None,
1227     }
1228 }
1229
1230 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1231     let snippet = codemap.span_to_snippet(block.span).unwrap();
1232     contains_comment(&snippet)
1233 }
1234
1235 // Checks that a block contains no statements, an expression and no comments or
1236 // attributes.
1237 // FIXME: incorrectly returns false when comment is contained completely within
1238 // the expression.
1239 pub fn is_simple_block(
1240     block: &ast::Block,
1241     attrs: Option<&[ast::Attribute]>,
1242     codemap: &CodeMap,
1243 ) -> bool {
1244     (block.stmts.len() == 1
1245         && stmt_is_expr(&block.stmts[0])
1246         && !block_contains_comment(block, codemap)
1247         && attrs.map_or(true, |a| a.is_empty()))
1248 }
1249
1250 /// Checks whether a block contains at most one statement or expression, and no
1251 /// comments or attributes.
1252 pub fn is_simple_block_stmt(
1253     block: &ast::Block,
1254     attrs: Option<&[ast::Attribute]>,
1255     codemap: &CodeMap,
1256 ) -> bool {
1257     block.stmts.len() <= 1
1258         && !block_contains_comment(block, codemap)
1259         && attrs.map_or(true, |a| a.is_empty())
1260 }
1261
1262 /// Checks whether a block contains no statements, expressions, comments, or
1263 /// inner attributes.
1264 pub fn is_empty_block(
1265     block: &ast::Block,
1266     attrs: Option<&[ast::Attribute]>,
1267     codemap: &CodeMap,
1268 ) -> bool {
1269     block.stmts.is_empty()
1270         && !block_contains_comment(block, codemap)
1271         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1272 }
1273
1274 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1275     match stmt.node {
1276         ast::StmtKind::Expr(..) => true,
1277         _ => false,
1278     }
1279 }
1280
1281 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1282     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1283         true
1284     } else {
1285         false
1286     }
1287 }
1288
1289 pub fn rewrite_multiple_patterns(
1290     context: &RewriteContext,
1291     pats: &[&ast::Pat],
1292     shape: Shape,
1293 ) -> Option<String> {
1294     let pat_strs = pats
1295         .iter()
1296         .map(|p| p.rewrite(context, shape))
1297         .collect::<Option<Vec<_>>>()?;
1298
1299     let use_mixed_layout = pats
1300         .iter()
1301         .zip(pat_strs.iter())
1302         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1303     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1304     let tactic = if use_mixed_layout {
1305         DefinitiveListTactic::Mixed
1306     } else {
1307         definitive_tactic(
1308             &items,
1309             ListTactic::HorizontalVertical,
1310             Separator::VerticalBar,
1311             shape.width,
1312         )
1313     };
1314     let fmt = ListFormatting {
1315         tactic,
1316         separator: " |",
1317         trailing_separator: SeparatorTactic::Never,
1318         separator_place: context.config.binop_separator(),
1319         shape,
1320         ends_with_newline: false,
1321         preserve_newline: false,
1322         config: context.config,
1323     };
1324     write_list(&items, &fmt)
1325 }
1326
1327 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1328     match l.node {
1329         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1330         _ => wrap_str(
1331             context.snippet(l.span).to_owned(),
1332             context.config.max_width(),
1333             shape,
1334         ),
1335     }
1336 }
1337
1338 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1339     let string_lit = context.snippet(span);
1340
1341     if !context.config.format_strings() {
1342         if string_lit
1343             .lines()
1344             .rev()
1345             .skip(1)
1346             .all(|line| line.ends_with('\\'))
1347         {
1348             let new_indent = shape.visual_indent(1).indent;
1349             let indented_string_lit = String::from(
1350                 string_lit
1351                     .lines()
1352                     .map(|line| {
1353                         format!(
1354                             "{}{}",
1355                             new_indent.to_string(context.config),
1356                             line.trim_left()
1357                         )
1358                     })
1359                     .collect::<Vec<_>>()
1360                     .join("\n")
1361                     .trim_left(),
1362             );
1363             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1364         } else {
1365             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1366         }
1367     }
1368
1369     // Remove the quote characters.
1370     let str_lit = &string_lit[1..string_lit.len() - 1];
1371
1372     rewrite_string(
1373         str_lit,
1374         &StringFormat::new(shape.visual_indent(0), context.config),
1375         None,
1376     )
1377 }
1378
1379 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1380 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1381     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1382         .iter()
1383         .find(|&&(s, _)| s == callee_str)
1384     {
1385         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1386
1387         Some((all_simple, num_args_before))
1388     } else {
1389         None
1390     }
1391 }
1392
1393 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1394 /// format.
1395 ///
1396 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1397 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1398 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1399 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1400     // format! like macros
1401     // From the Rust Standard Library.
1402     ("eprint!", 0),
1403     ("eprintln!", 0),
1404     ("format!", 0),
1405     ("format_args!", 0),
1406     ("print!", 0),
1407     ("println!", 0),
1408     ("panic!", 0),
1409     ("unreachable!", 0),
1410     // From the `log` crate.
1411     ("debug!", 0),
1412     ("error!", 0),
1413     ("info!", 0),
1414     ("warn!", 0),
1415     // write! like macros
1416     ("assert!", 1),
1417     ("debug_assert!", 1),
1418     ("write!", 1),
1419     ("writeln!", 1),
1420     // assert_eq! like macros
1421     ("assert_eq!", 2),
1422     ("assert_ne!", 2),
1423     ("debug_assert_eq!", 2),
1424     ("debug_assert_ne!", 2),
1425 ];
1426
1427 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1428     if context.inside_macro() {
1429         if span_ends_with_comma(context, span) {
1430             Some(SeparatorTactic::Always)
1431         } else {
1432             Some(SeparatorTactic::Never)
1433         }
1434     } else {
1435         None
1436     }
1437 }
1438
1439 pub fn rewrite_call(
1440     context: &RewriteContext,
1441     callee: &str,
1442     args: &[ptr::P<ast::Expr>],
1443     span: Span,
1444     shape: Shape,
1445 ) -> Option<String> {
1446     overflow::rewrite_with_parens(
1447         context,
1448         callee,
1449         &ptr_vec_to_ref_vec(args),
1450         shape,
1451         span,
1452         context.config.width_heuristics().fn_call_width,
1453         choose_separator_tactic(context, span),
1454     )
1455 }
1456
1457 fn is_simple_expr(expr: &ast::Expr) -> bool {
1458     match expr.node {
1459         ast::ExprKind::Lit(..) => true,
1460         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1461         ast::ExprKind::AddrOf(_, ref expr)
1462         | ast::ExprKind::Box(ref expr)
1463         | ast::ExprKind::Cast(ref expr, _)
1464         | ast::ExprKind::Field(ref expr, _)
1465         | ast::ExprKind::Try(ref expr)
1466         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1467         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1468             is_simple_expr(lhs) && is_simple_expr(rhs)
1469         }
1470         _ => false,
1471     }
1472 }
1473
1474 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1475     lists
1476         .iter()
1477         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1478 }
1479
1480 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1481     match expr.node {
1482         ast::ExprKind::Match(..) => {
1483             (context.use_block_indent() && args_len == 1)
1484                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1485         }
1486         ast::ExprKind::If(..)
1487         | ast::ExprKind::IfLet(..)
1488         | ast::ExprKind::ForLoop(..)
1489         | ast::ExprKind::Loop(..)
1490         | ast::ExprKind::While(..)
1491         | ast::ExprKind::WhileLet(..) => {
1492             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1493         }
1494         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1495             context.use_block_indent()
1496                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1497         }
1498         ast::ExprKind::Array(..)
1499         | ast::ExprKind::Call(..)
1500         | ast::ExprKind::Mac(..)
1501         | ast::ExprKind::MethodCall(..)
1502         | ast::ExprKind::Struct(..)
1503         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1504         ast::ExprKind::AddrOf(_, ref expr)
1505         | ast::ExprKind::Box(ref expr)
1506         | ast::ExprKind::Try(ref expr)
1507         | ast::ExprKind::Unary(_, ref expr)
1508         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1509         _ => false,
1510     }
1511 }
1512
1513 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1514     match expr.node {
1515         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1516         ast::ExprKind::AddrOf(_, ref expr)
1517         | ast::ExprKind::Box(ref expr)
1518         | ast::ExprKind::Try(ref expr)
1519         | ast::ExprKind::Unary(_, ref expr)
1520         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1521         _ => false,
1522     }
1523 }
1524
1525 /// Return true if a function call or a method call represented by the given span ends with a
1526 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1527 /// comma from macro can potentially break the code.
1528 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1529     let mut result: bool = Default::default();
1530     let mut prev_char: char = Default::default();
1531     let closing_delimiters = &[')', '}', ']'];
1532
1533     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1534         match c {
1535             _ if kind.is_comment() || c.is_whitespace() => continue,
1536             c if closing_delimiters.contains(&c) => {
1537                 result &= !closing_delimiters.contains(&prev_char);
1538             }
1539             ',' => result = true,
1540             _ => result = false,
1541         }
1542         prev_char = c;
1543     }
1544
1545     result
1546 }
1547
1548 fn rewrite_paren(
1549     context: &RewriteContext,
1550     mut subexpr: &ast::Expr,
1551     shape: Shape,
1552     mut span: Span,
1553 ) -> Option<String> {
1554     debug!("rewrite_paren, shape: {:?}", shape);
1555
1556     // Extract comments within parens.
1557     let mut pre_comment;
1558     let mut post_comment;
1559     let remove_nested_parens = context.config.remove_nested_parens();
1560     loop {
1561         // 1 = "(" or ")"
1562         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1563         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1564         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1565         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1566
1567         // Remove nested parens if there are no comments.
1568         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1569             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1570                 span = subexpr.span;
1571                 subexpr = subsubexpr;
1572                 continue;
1573             }
1574         }
1575
1576         break;
1577     }
1578
1579     // 1 `(`
1580     let sub_shape = shape.offset_left(1).and_then(|s| s.sub_width(1))?;
1581
1582     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1583     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1584
1585     // 2 = `()`
1586     if subexpr_str.contains('\n') || first_line_width(&subexpr_str) + 2 <= shape.width {
1587         Some(format!("({}{}{})", pre_comment, &subexpr_str, post_comment))
1588     } else {
1589         None
1590     }
1591 }
1592
1593 fn rewrite_index(
1594     expr: &ast::Expr,
1595     index: &ast::Expr,
1596     context: &RewriteContext,
1597     shape: Shape,
1598 ) -> Option<String> {
1599     let expr_str = expr.rewrite(context, shape)?;
1600
1601     let offset = last_line_width(&expr_str) + 1;
1602     let rhs_overhead = shape.rhs_overhead(context.config);
1603     let index_shape = if expr_str.contains('\n') {
1604         Shape::legacy(context.config.max_width(), shape.indent)
1605             .offset_left(offset)
1606             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1607     } else {
1608         shape.visual_indent(offset).sub_width(offset + 1)
1609     };
1610     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1611
1612     // Return if index fits in a single line.
1613     match orig_index_rw {
1614         Some(ref index_str) if !index_str.contains('\n') => {
1615             return Some(format!("{}[{}]", expr_str, index_str));
1616         }
1617         _ => (),
1618     }
1619
1620     // Try putting index on the next line and see if it fits in a single line.
1621     let indent = shape.indent.block_indent(context.config);
1622     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1623     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1624     let new_index_rw = index.rewrite(context, index_shape);
1625     match (orig_index_rw, new_index_rw) {
1626         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1627             "{}{}[{}]",
1628             expr_str,
1629             indent.to_string_with_newline(context.config),
1630             new_index_str,
1631         )),
1632         (None, Some(ref new_index_str)) => Some(format!(
1633             "{}{}[{}]",
1634             expr_str,
1635             indent.to_string_with_newline(context.config),
1636             new_index_str,
1637         )),
1638         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1639         _ => None,
1640     }
1641 }
1642
1643 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1644     if base.is_some() {
1645         return false;
1646     }
1647
1648     fields.iter().all(|field| !field.is_shorthand)
1649 }
1650
1651 fn rewrite_struct_lit<'a>(
1652     context: &RewriteContext,
1653     path: &ast::Path,
1654     fields: &'a [ast::Field],
1655     base: Option<&'a ast::Expr>,
1656     span: Span,
1657     shape: Shape,
1658 ) -> Option<String> {
1659     debug!("rewrite_struct_lit: shape {:?}", shape);
1660
1661     enum StructLitField<'a> {
1662         Regular(&'a ast::Field),
1663         Base(&'a ast::Expr),
1664     }
1665
1666     // 2 = " {".len()
1667     let path_shape = shape.sub_width(2)?;
1668     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1669
1670     if fields.is_empty() && base.is_none() {
1671         return Some(format!("{} {{}}", path_str));
1672     }
1673
1674     // Foo { a: Foo } - indent is +3, width is -5.
1675     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1676
1677     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1678     let body_lo = context.snippet_provider.span_after(span, "{");
1679     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1680         && context.config.struct_field_align_threshold() > 0
1681     {
1682         rewrite_with_alignment(
1683             fields,
1684             context,
1685             shape,
1686             mk_sp(body_lo, span.hi()),
1687             one_line_width,
1688         )?
1689     } else {
1690         let field_iter = fields
1691             .into_iter()
1692             .map(StructLitField::Regular)
1693             .chain(base.into_iter().map(StructLitField::Base));
1694
1695         let span_lo = |item: &StructLitField| match *item {
1696             StructLitField::Regular(field) => field.span().lo(),
1697             StructLitField::Base(expr) => {
1698                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1699                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1700                 let pos = snippet.find_uncommented("..").unwrap();
1701                 last_field_hi + BytePos(pos as u32)
1702             }
1703         };
1704         let span_hi = |item: &StructLitField| match *item {
1705             StructLitField::Regular(field) => field.span().hi(),
1706             StructLitField::Base(expr) => expr.span.hi(),
1707         };
1708         let rewrite = |item: &StructLitField| match *item {
1709             StructLitField::Regular(field) => {
1710                 // The 1 taken from the v_budget is for the comma.
1711                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1712             }
1713             StructLitField::Base(expr) => {
1714                 // 2 = ..
1715                 expr.rewrite(context, v_shape.offset_left(2)?)
1716                     .map(|s| format!("..{}", s))
1717             }
1718         };
1719
1720         let items = itemize_list(
1721             context.snippet_provider,
1722             field_iter,
1723             "}",
1724             ",",
1725             span_lo,
1726             span_hi,
1727             rewrite,
1728             body_lo,
1729             span.hi(),
1730             false,
1731         );
1732         let item_vec = items.collect::<Vec<_>>();
1733
1734         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1735         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1736
1737         let ends_with_comma = span_ends_with_comma(context, span);
1738         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1739
1740         let fmt = struct_lit_formatting(
1741             nested_shape,
1742             tactic,
1743             context,
1744             force_no_trailing_comma || base.is_some(),
1745         );
1746
1747         write_list(&item_vec, &fmt)?
1748     };
1749
1750     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1751     Some(format!("{} {{{}}}", path_str, fields_str))
1752
1753     // FIXME if context.config.indent_style() == Visual, but we run out
1754     // of space, we should fall back to BlockIndent.
1755 }
1756
1757 pub fn wrap_struct_field(
1758     context: &RewriteContext,
1759     fields_str: &str,
1760     shape: Shape,
1761     nested_shape: Shape,
1762     one_line_width: usize,
1763 ) -> String {
1764     if context.config.indent_style() == IndentStyle::Block
1765         && (fields_str.contains('\n')
1766             || !context.config.struct_lit_single_line()
1767             || fields_str.len() > one_line_width)
1768     {
1769         format!(
1770             "{}{}{}",
1771             nested_shape.indent.to_string_with_newline(context.config),
1772             fields_str,
1773             shape.indent.to_string_with_newline(context.config)
1774         )
1775     } else {
1776         // One liner or visual indent.
1777         format!(" {} ", fields_str)
1778     }
1779 }
1780
1781 pub fn struct_lit_field_separator(config: &Config) -> &str {
1782     colon_spaces(config.space_before_colon(), config.space_after_colon())
1783 }
1784
1785 pub fn rewrite_field(
1786     context: &RewriteContext,
1787     field: &ast::Field,
1788     shape: Shape,
1789     prefix_max_width: usize,
1790 ) -> Option<String> {
1791     if contains_skip(&field.attrs) {
1792         return Some(context.snippet(field.span()).to_owned());
1793     }
1794     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1795     if !attrs_str.is_empty() {
1796         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1797     };
1798     let name = &field.ident.name.to_string();
1799     if field.is_shorthand {
1800         Some(attrs_str + &name)
1801     } else {
1802         let mut separator = String::from(struct_lit_field_separator(context.config));
1803         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1804             separator.push(' ');
1805         }
1806         let overhead = name.len() + separator.len();
1807         let expr_shape = shape.offset_left(overhead)?;
1808         let expr = field.expr.rewrite(context, expr_shape);
1809
1810         match expr {
1811             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1812                 Some(attrs_str + &name)
1813             }
1814             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1815             None => {
1816                 let expr_offset = shape.indent.block_indent(context.config);
1817                 let expr = field
1818                     .expr
1819                     .rewrite(context, Shape::indented(expr_offset, context.config));
1820                 expr.map(|s| {
1821                     format!(
1822                         "{}{}:\n{}{}",
1823                         attrs_str,
1824                         name,
1825                         expr_offset.to_string(context.config),
1826                         s
1827                     )
1828                 })
1829             }
1830         }
1831     }
1832 }
1833
1834 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1835     context: &RewriteContext,
1836     items: &[&T],
1837     span: Span,
1838     shape: Shape,
1839 ) -> Option<String>
1840 where
1841     T: Rewrite + Spanned + ToExpr + 'a,
1842 {
1843     let mut items = items.iter();
1844     // In case of length 1, need a trailing comma
1845     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1846     if items.len() == 1 {
1847         // 3 = "(" + ",)"
1848         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1849         return items
1850             .next()
1851             .unwrap()
1852             .rewrite(context, nested_shape)
1853             .map(|s| format!("({},)", s));
1854     }
1855
1856     let list_lo = context.snippet_provider.span_after(span, "(");
1857     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1858     let items = itemize_list(
1859         context.snippet_provider,
1860         items,
1861         ")",
1862         ",",
1863         |item| item.span().lo(),
1864         |item| item.span().hi(),
1865         |item| item.rewrite(context, nested_shape),
1866         list_lo,
1867         span.hi() - BytePos(1),
1868         false,
1869     );
1870     let item_vec: Vec<_> = items.collect();
1871     let tactic = definitive_tactic(
1872         &item_vec,
1873         ListTactic::HorizontalVertical,
1874         Separator::Comma,
1875         nested_shape.width,
1876     );
1877     let fmt = ListFormatting {
1878         tactic,
1879         separator: ",",
1880         trailing_separator: SeparatorTactic::Never,
1881         separator_place: SeparatorPlace::Back,
1882         shape,
1883         ends_with_newline: false,
1884         preserve_newline: false,
1885         config: context.config,
1886     };
1887     let list_str = write_list(&item_vec, &fmt)?;
1888
1889     Some(format!("({})", list_str))
1890 }
1891
1892 pub fn rewrite_tuple<'a, T>(
1893     context: &RewriteContext,
1894     items: &[&T],
1895     span: Span,
1896     shape: Shape,
1897 ) -> Option<String>
1898 where
1899     T: Rewrite + Spanned + ToExpr + 'a,
1900 {
1901     debug!("rewrite_tuple {:?}", shape);
1902     if context.use_block_indent() {
1903         // We use the same rule as function calls for rewriting tuples.
1904         let force_tactic = if context.inside_macro() {
1905             if span_ends_with_comma(context, span) {
1906                 Some(SeparatorTactic::Always)
1907             } else {
1908                 Some(SeparatorTactic::Never)
1909             }
1910         } else if items.len() == 1 {
1911             Some(SeparatorTactic::Always)
1912         } else {
1913             None
1914         };
1915         overflow::rewrite_with_parens(
1916             context,
1917             "",
1918             items,
1919             shape,
1920             span,
1921             context.config.width_heuristics().fn_call_width,
1922             force_tactic,
1923         )
1924     } else {
1925         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1926     }
1927 }
1928
1929 pub fn rewrite_unary_prefix<R: Rewrite>(
1930     context: &RewriteContext,
1931     prefix: &str,
1932     rewrite: &R,
1933     shape: Shape,
1934 ) -> Option<String> {
1935     rewrite
1936         .rewrite(context, shape.offset_left(prefix.len())?)
1937         .map(|r| format!("{}{}", prefix, r))
1938 }
1939
1940 // FIXME: this is probably not correct for multi-line Rewrites. we should
1941 // subtract suffix.len() from the last line budget, not the first!
1942 pub fn rewrite_unary_suffix<R: Rewrite>(
1943     context: &RewriteContext,
1944     suffix: &str,
1945     rewrite: &R,
1946     shape: Shape,
1947 ) -> Option<String> {
1948     rewrite
1949         .rewrite(context, shape.sub_width(suffix.len())?)
1950         .map(|mut r| {
1951             r.push_str(suffix);
1952             r
1953         })
1954 }
1955
1956 fn rewrite_unary_op(
1957     context: &RewriteContext,
1958     op: &ast::UnOp,
1959     expr: &ast::Expr,
1960     shape: Shape,
1961 ) -> Option<String> {
1962     // For some reason, an UnOp is not spanned like BinOp!
1963     let operator_str = match *op {
1964         ast::UnOp::Deref => "*",
1965         ast::UnOp::Not => "!",
1966         ast::UnOp::Neg => "-",
1967     };
1968     rewrite_unary_prefix(context, operator_str, expr, shape)
1969 }
1970
1971 fn rewrite_assignment(
1972     context: &RewriteContext,
1973     lhs: &ast::Expr,
1974     rhs: &ast::Expr,
1975     op: Option<&ast::BinOp>,
1976     shape: Shape,
1977 ) -> Option<String> {
1978     let operator_str = match op {
1979         Some(op) => context.snippet(op.span),
1980         None => "=",
1981     };
1982
1983     // 1 = space between lhs and operator.
1984     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
1985     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
1986
1987     rewrite_assign_rhs(context, lhs_str, rhs, shape)
1988 }
1989
1990 /// Controls where to put the rhs.
1991 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1992 pub enum RhsTactics {
1993     /// Use heuristics.
1994     Default,
1995     /// Put the rhs on the next line if it uses multiple line.
1996     ForceNextLine,
1997 }
1998
1999 // The left hand side must contain everything up to, and including, the
2000 // assignment operator.
2001 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2002     context: &RewriteContext,
2003     lhs: S,
2004     ex: &R,
2005     shape: Shape,
2006 ) -> Option<String> {
2007     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2008 }
2009
2010 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2011     context: &RewriteContext,
2012     lhs: S,
2013     ex: &R,
2014     shape: Shape,
2015     rhs_tactics: RhsTactics,
2016 ) -> Option<String> {
2017     let lhs = lhs.into();
2018     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
2019         shape.indent.width()
2020     } else {
2021         0
2022     });
2023     // 1 = space between operator and rhs.
2024     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2025         width: 0,
2026         offset: shape.offset + last_line_width + 1,
2027         ..shape
2028     });
2029     let rhs = choose_rhs(
2030         context,
2031         ex,
2032         orig_shape,
2033         ex.rewrite(context, orig_shape),
2034         rhs_tactics,
2035     )?;
2036     Some(lhs + &rhs)
2037 }
2038
2039 fn choose_rhs<R: Rewrite>(
2040     context: &RewriteContext,
2041     expr: &R,
2042     shape: Shape,
2043     orig_rhs: Option<String>,
2044     rhs_tactics: RhsTactics,
2045 ) -> Option<String> {
2046     match orig_rhs {
2047         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2048             Some(format!(" {}", new_str))
2049         }
2050         _ => {
2051             // Expression did not fit on the same line as the identifier.
2052             // Try splitting the line and see if that works better.
2053             let new_shape =
2054                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2055                     .sub_width(shape.rhs_overhead(context.config))?;
2056             let new_rhs = expr.rewrite(context, new_shape);
2057             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2058
2059             match (orig_rhs, new_rhs) {
2060                 (Some(ref orig_rhs), Some(ref new_rhs))
2061                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2062                         .is_none() =>
2063                 {
2064                     Some(format!(" {}", orig_rhs))
2065                 }
2066                 (Some(ref orig_rhs), Some(ref new_rhs))
2067                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2068                 {
2069                     Some(format!("{}{}", new_indent_str, new_rhs))
2070                 }
2071                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2072                 (None, None) => None,
2073                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2074             }
2075         }
2076     }
2077 }
2078
2079 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2080     rhs_tactics == RhsTactics::ForceNextLine
2081         || !next_line_rhs.contains('\n')
2082         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2083 }
2084
2085 fn rewrite_expr_addrof(
2086     context: &RewriteContext,
2087     mutability: ast::Mutability,
2088     expr: &ast::Expr,
2089     shape: Shape,
2090 ) -> Option<String> {
2091     let operator_str = match mutability {
2092         ast::Mutability::Immutable => "&",
2093         ast::Mutability::Mutable => "&mut ",
2094     };
2095     rewrite_unary_prefix(context, operator_str, expr, shape)
2096 }
2097
2098 pub trait ToExpr {
2099     fn to_expr(&self) -> Option<&ast::Expr>;
2100     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2101 }
2102
2103 impl ToExpr for ast::Expr {
2104     fn to_expr(&self) -> Option<&ast::Expr> {
2105         Some(self)
2106     }
2107
2108     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2109         can_be_overflowed_expr(context, self, len)
2110     }
2111 }
2112
2113 impl ToExpr for ast::Ty {
2114     fn to_expr(&self) -> Option<&ast::Expr> {
2115         None
2116     }
2117
2118     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2119         can_be_overflowed_type(context, self, len)
2120     }
2121 }
2122
2123 impl<'a> ToExpr for TuplePatField<'a> {
2124     fn to_expr(&self) -> Option<&ast::Expr> {
2125         None
2126     }
2127
2128     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2129         can_be_overflowed_pat(context, self, len)
2130     }
2131 }
2132
2133 impl<'a> ToExpr for ast::StructField {
2134     fn to_expr(&self) -> Option<&ast::Expr> {
2135         None
2136     }
2137
2138     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2139         false
2140     }
2141 }
2142
2143 impl<'a> ToExpr for MacroArg {
2144     fn to_expr(&self) -> Option<&ast::Expr> {
2145         match *self {
2146             MacroArg::Expr(ref expr) => Some(expr),
2147             _ => None,
2148         }
2149     }
2150
2151     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2152         match *self {
2153             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2154             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2155             MacroArg::Pat(..) => false,
2156             MacroArg::Item(..) => len == 1,
2157         }
2158     }
2159 }
2160
2161 impl ToExpr for ast::GenericParam {
2162     fn to_expr(&self) -> Option<&ast::Expr> {
2163         None
2164     }
2165
2166     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2167         false
2168     }
2169 }