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         // FIXME(topecongiro): Handle label on a block (#2722).
 122         ast::ExprKind::Block(ref block, _) => {
 123             match expr_type {
 124                 ExprType::Statement => {
 125                     if is_unsafe_block(block) {
 126                         rewrite_block(block, Some(&expr.attrs), context, shape)
 127                     } else if let rw @ Some(_) =
 128                         rewrite_empty_block(context, block, Some(&expr.attrs), "", shape)
 129                     {
 130                         // Rewrite block without trying to put it in a single line.
 131                         rw
 132                     } else {
 133                         let prefix = block_prefix(context, block, shape)?;
 134                         rewrite_block_with_visitor(
 135                             context,
 136                             &prefix,
 137                             block,
 138                             Some(&expr.attrs),
 139                             shape,
 140                             true,
 141                         )
 142                     }
 143                 }
 144                 ExprType::SubExpression => rewrite_block(block, Some(&expr.attrs), context, shape),
 145             }
 146         }
 147         ast::ExprKind::Match(ref cond, ref arms) => {
 148             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 149         }
 150         ast::ExprKind::Path(ref qself, ref path) => {
 151             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 152         }
 153         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 154             rewrite_assignment(context, lhs, rhs, None, shape)
 155         }
 156         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 157             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 158         }
 159         ast::ExprKind::Continue(ref opt_label) => {
 160             let id_str = match *opt_label {
 161                 Some(label) => format!(" {}", label.ident),
 162                 None => String::new(),
 163             };
 164             Some(format!("continue{}", id_str))
 165         }
 166         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 167             let id_str = match *opt_label {
 168                 Some(label) => format!(" {}", label.ident),
 169                 None => String::new(),
 170             };
 171
 172             if let Some(ref expr) = *opt_expr {
 173                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 174             } else {
 175                 Some(format!("break{}", id_str))
 176             }
 177         }
 178         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 179             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 180         } else {
 181             Some("yield".to_string())
 182         },
 183         ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) => {
 184             closures::rewrite_closure(
 185                 capture, movability, fn_decl, body, expr.span, context, shape,
 186             )
 187         }
 188         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 189             rewrite_chain(expr, context, shape)
 190         }
 191         ast::ExprKind::Mac(ref mac) => {
 192             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 193                 wrap_str(
 194                     context.snippet(expr.span).to_owned(),
 195                     context.config.max_width(),
 196                     shape,
 197                 )
 198             })
 199         }
 200         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 201         ast::ExprKind::Ret(Some(ref expr)) => {
 202             rewrite_unary_prefix(context, "return ", &**expr, shape)
 203         }
 204         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 205         ast::ExprKind::AddrOf(mutability, ref expr) => {
 206             rewrite_expr_addrof(context, mutability, expr, shape)
 207         }
 208         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 209             &**expr,
 210             &**ty,
 211             PairParts::new("", " as ", ""),
 212             context,
 213             shape,
 214             SeparatorPlace::Front,
 215         ),
 216         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 217             &**expr,
 218             &**ty,
 219             PairParts::new("", ": ", ""),
 220             context,
 221             shape,
 222             SeparatorPlace::Back,
 223         ),
 224         ast::ExprKind::Index(ref expr, ref index) => {
 225             rewrite_index(&**expr, &**index, context, shape)
 226         }
 227         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 228             &**expr,
 229             &**repeats,
 230             PairParts::new("[", "; ", "]"),
 231             context,
 232             shape,
 233             SeparatorPlace::Back,
 234         ),
 235         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 236             let delim = match limits {
 237                 ast::RangeLimits::HalfOpen => "..",
 238                 ast::RangeLimits::Closed => "..=",
 239             };
 240
 241             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 242                 match lhs.node {
 243                     ast::ExprKind::Lit(ref lit) => match lit.node {
 244                         ast::LitKind::FloatUnsuffixed(..) => {
 245                             context.snippet(lit.span).ends_with('.')
 246                         }
 247                         _ => false,
 248                     },
 249                     _ => false,
 250                 }
 251             }
 252
 253             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 254                 match rhs.node {
 255                     // Don't format `.. ..` into `....`, which is invalid.
 256                     //
 257                     // This check is unnecessary for `lhs`, because a range
 258                     // starting from another range needs parentheses as `(x ..) ..`
 259                     // (`x .. ..` is a range from `x` to `..`).
 260                     ast::ExprKind::Range(None, _, _) => true,
 261                     _ => false,
 262                 }
 263             }
 264
 265             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 266                 let space_if = |b: bool| if b { " " } else { "" };
 267
 268                 format!(
 269                     "{}{}{}",
 270                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 271                         .unwrap_or(""),
 272                     delim,
 273                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 274                         .unwrap_or(""),
 275                 )
 276             };
 277
 278             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 279                 (Some(lhs), Some(rhs)) => {
 280                     let sp_delim = if context.config.spaces_around_ranges() {
 281                         format!(" {} ", delim)
 282                     } else {
 283                         default_sp_delim(Some(lhs), Some(rhs))
 284                     };
 285                     rewrite_pair(
 286                         &*lhs,
 287                         &*rhs,
 288                         PairParts::new("", &sp_delim, ""),
 289                         context,
 290                         shape,
 291                         context.config.binop_separator(),
 292                     )
 293                 }
 294                 (None, Some(rhs)) => {
 295                     let sp_delim = if context.config.spaces_around_ranges() {
 296                         format!("{} ", delim)
 297                     } else {
 298                         default_sp_delim(None, Some(rhs))
 299                     };
 300                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 301                 }
 302                 (Some(lhs), None) => {
 303                     let sp_delim = if context.config.spaces_around_ranges() {
 304                         format!(" {}", delim)
 305                     } else {
 306                         default_sp_delim(Some(lhs), None)
 307                     };
 308                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 309                 }
 310                 (None, None) => Some(delim.to_owned()),
 311             }
 312         }
 313         // We do not format these expressions yet, but they should still
 314         // satisfy our width restrictions.
 315         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 316         ast::ExprKind::Catch(ref block) => {
 317             if let rw @ Some(_) =
 318                 rewrite_single_line_block(context, "do catch ", block, Some(&expr.attrs), shape)
 319             {
 320                 rw
 321             } else {
 322                 // 9 = `do catch `
 323                 let budget = shape.width.saturating_sub(9);
 324                 Some(format!(
 325                     "{}{}",
 326                     "do catch ",
 327                     rewrite_block(
 328                         block,
 329                         Some(&expr.attrs),
 330                         context,
 331                         Shape::legacy(budget, shape.indent)
 332                     )?
 333                 ))
 334             }
 335         }
 336     };
 337
 338     expr_rw
 339         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 340         .and_then(|expr_str| {
 341             let attrs = outer_attributes(&expr.attrs);
 342             let attrs_str = attrs.rewrite(context, shape)?;
 343             let span = mk_sp(
 344                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 345                 expr.span.lo(),
 346             );
 347             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 348         })
 349 }
 350
 351 /// Collect operands that appears in the given binary operator in the opposite order.
 352 /// e.g. `collect_binary_items(e, ||)` for `a && b || c || d` returns `[d, c, a && b]`.
 353 fn collect_binary_items<'a>(mut expr: &'a ast::Expr, binop: ast::BinOp) -> Vec<&'a ast::Expr> {
 354     let mut result = vec![];
 355     let mut prev_lhs = None;
 356     loop {
 357         match expr.node {
 358             ast::ExprKind::Binary(inner_binop, ref lhs, ref rhs)
 359                 if inner_binop.node == binop.node =>
 360             {
 361                 result.push(&**rhs);
 362                 expr = lhs;
 363                 prev_lhs = Some(lhs);
 364             }
 365             _ => {
 366                 if let Some(lhs) = prev_lhs {
 367                     result.push(lhs);
 368                 }
 369                 break;
 370             }
 371         }
 372     }
 373     result
 374 }
 375
 376 /// Rewrites a binary expression whose operands fits within a single line.
 377 fn rewrite_simple_binaries(
 378     context: &RewriteContext,
 379     expr: &ast::Expr,
 380     shape: Shape,
 381     op: ast::BinOp,
 382 ) -> Option<String> {
 383     let op_str = context.snippet(op.span);
 384
 385     // 2 = spaces around a binary operator.
 386     let sep_overhead = op_str.len() + 2;
 387     let nested_overhead = sep_overhead - 1;
 388
 389     let nested_shape = (match context.config.indent_style() {
 390         IndentStyle::Visual => shape.visual_indent(0),
 391         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 392     }).with_max_width(context.config);
 393     let nested_shape = match context.config.binop_separator() {
 394         SeparatorPlace::Back => nested_shape.sub_width(nested_overhead)?,
 395         SeparatorPlace::Front => nested_shape.offset_left(nested_overhead)?,
 396     };
 397
 398     let opt_rewrites: Option<Vec<_>> = collect_binary_items(expr, op)
 399         .iter()
 400         .rev()
 401         .map(|e| e.rewrite(context, nested_shape))
 402         .collect();
 403     if let Some(rewrites) = opt_rewrites {
 404         if rewrites.iter().all(|e| ::utils::is_single_line(e)) {
 405             let total_width = rewrites.iter().map(|s| s.len()).sum::<usize>()
 406                 + sep_overhead * (rewrites.len() - 1);
 407
 408             let sep_str = if total_width <= shape.width {
 409                 format!(" {} ", op_str)
 410             } else {
 411                 let indent_str = nested_shape.indent.to_string_with_newline(context.config);
 412                 match context.config.binop_separator() {
 413                     SeparatorPlace::Back => format!(" {}{}", op_str.trim_right(), indent_str),
 414                     SeparatorPlace::Front => format!("{}{} ", indent_str, op_str.trim_left()),
 415                 }
 416             };
 417
 418             return wrap_str(rewrites.join(&sep_str), context.config.max_width(), shape);
 419         }
 420     }
 421
 422     None
 423 }
 424
 425 #[derive(new, Clone, Copy)]
 426 pub struct PairParts<'a> {
 427     prefix: &'a str,
 428     infix: &'a str,
 429     suffix: &'a str,
 430 }
 431
 432 pub fn rewrite_pair<LHS, RHS>(
 433     lhs: &LHS,
 434     rhs: &RHS,
 435     pp: PairParts,
 436     context: &RewriteContext,
 437     shape: Shape,
 438     separator_place: SeparatorPlace,
 439 ) -> Option<String>
 440 where
 441     LHS: Rewrite,
 442     RHS: Rewrite,
 443 {
 444     let lhs_overhead = match separator_place {
 445         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 446         SeparatorPlace::Front => shape.used_width(),
 447     };
 448     let lhs_shape = Shape {
 449         width: context.budget(lhs_overhead),
 450         ..shape
 451     };
 452     let lhs_result = lhs
 453         .rewrite(context, lhs_shape)
 454         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 455
 456     // Try to put both lhs and rhs on the same line.
 457     let rhs_orig_result = shape
 458         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 459         .and_then(|s| s.sub_width(pp.suffix.len()))
 460         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 461     if let Some(ref rhs_result) = rhs_orig_result {
 462         // If the length of the lhs is equal to or shorter than the tab width or
 463         // the rhs looks like block expression, we put the rhs on the same
 464         // line with the lhs even if the rhs is multi-lined.
 465         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 466             || rhs_result
 467                 .lines()
 468                 .next()
 469                 .map(|first_line| first_line.ends_with('{'))
 470                 .unwrap_or(false);
 471         if !rhs_result.contains('\n') || allow_same_line {
 472             let one_line_width = last_line_width(&lhs_result)
 473                 + pp.infix.len()
 474                 + first_line_width(rhs_result)
 475                 + pp.suffix.len();
 476             if one_line_width <= shape.width {
 477                 return Some(format!(
 478                     "{}{}{}{}",
 479                     lhs_result, pp.infix, rhs_result, pp.suffix
 480                 ));
 481             }
 482         }
 483     }
 484
 485     // We have to use multiple lines.
 486     // Re-evaluate the rhs because we have more space now:
 487     let mut rhs_shape = match context.config.indent_style() {
 488         IndentStyle::Visual => shape
 489             .sub_width(pp.suffix.len() + pp.prefix.len())?
 490             .visual_indent(pp.prefix.len()),
 491         IndentStyle::Block => {
 492             // Try to calculate the initial constraint on the right hand side.
 493             let rhs_overhead = shape.rhs_overhead(context.config);
 494             Shape::indented(shape.indent.block_indent(context.config), context.config)
 495                 .sub_width(rhs_overhead)?
 496         }
 497     };
 498     let infix = match separator_place {
 499         SeparatorPlace::Back => pp.infix.trim_right(),
 500         SeparatorPlace::Front => pp.infix.trim_left(),
 501     };
 502     if separator_place == SeparatorPlace::Front {
 503         rhs_shape = rhs_shape.offset_left(infix.len())?;
 504     }
 505     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 506     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 507     let infix_with_sep = match separator_place {
 508         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 509         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 510     };
 511     Some(format!(
 512         "{}{}{}{}",
 513         lhs_result, infix_with_sep, rhs_result, pp.suffix
 514     ))
 515 }
 516
 517 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 518     name: &str,
 519     exprs: &[&T],
 520     span: Span,
 521     context: &RewriteContext,
 522     shape: Shape,
 523     force_separator_tactic: Option<SeparatorTactic>,
 524     delim_token: Option<DelimToken>,
 525 ) -> Option<String> {
 526     overflow::rewrite_with_square_brackets(
 527         context,
 528         name,
 529         exprs,
 530         shape,
 531         span,
 532         force_separator_tactic,
 533         delim_token,
 534     )
 535 }
 536
 537 fn rewrite_empty_block(
 538     context: &RewriteContext,
 539     block: &ast::Block,
 540     attrs: Option<&[ast::Attribute]>,
 541     prefix: &str,
 542     shape: Shape,
 543 ) -> Option<String> {
 544     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 545         return None;
 546     }
 547
 548     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 549     {
 550         return Some(format!("{}{{}}", prefix));
 551     }
 552
 553     // If a block contains only a single-line comment, then leave it on one line.
 554     let user_str = context.snippet(block.span);
 555     let user_str = user_str.trim();
 556     if user_str.starts_with('{') && user_str.ends_with('}') {
 557         let comment_str = user_str[1..user_str.len() - 1].trim();
 558         if block.stmts.is_empty()
 559             && !comment_str.contains('\n')
 560             && !comment_str.starts_with("//")
 561             && comment_str.len() + 4 <= shape.width
 562         {
 563             return Some(format!("{}{{ {} }}", prefix, comment_str));
 564         }
 565     }
 566
 567     None
 568 }
 569
 570 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 571     Some(match block.rules {
 572         ast::BlockCheckMode::Unsafe(..) => {
 573             let snippet = context.snippet(block.span);
 574             let open_pos = snippet.find_uncommented("{")?;
 575             // Extract comment between unsafe and block start.
 576             let trimmed = &snippet[6..open_pos].trim();
 577
 578             if !trimmed.is_empty() {
 579                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 580                 let budget = shape.width.checked_sub(9)?;
 581                 format!(
 582                     "unsafe {} ",
 583                     rewrite_comment(
 584                         trimmed,
 585                         true,
 586                         Shape::legacy(budget, shape.indent + 7),
 587                         context.config,
 588                     )?
 589                 )
 590             } else {
 591                 "unsafe ".to_owned()
 592             }
 593         }
 594         ast::BlockCheckMode::Default => String::new(),
 595     })
 596 }
 597
 598 fn rewrite_single_line_block(
 599     context: &RewriteContext,
 600     prefix: &str,
 601     block: &ast::Block,
 602     attrs: Option<&[ast::Attribute]>,
 603     shape: Shape,
 604 ) -> Option<String> {
 605     if is_simple_block(block, attrs, context.codemap) {
 606         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 607         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 608         let result = format!("{}{{ {} }}", prefix, expr_str);
 609         if result.len() <= shape.width && !result.contains('\n') {
 610             return Some(result);
 611         }
 612     }
 613     None
 614 }
 615
 616 pub fn rewrite_block_with_visitor(
 617     context: &RewriteContext,
 618     prefix: &str,
 619     block: &ast::Block,
 620     attrs: Option<&[ast::Attribute]>,
 621     shape: Shape,
 622     has_braces: bool,
 623 ) -> Option<String> {
 624     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, prefix, shape) {
 625         return rw;
 626     }
 627
 628     let mut visitor = FmtVisitor::from_context(context);
 629     visitor.block_indent = shape.indent;
 630     visitor.is_if_else_block = context.is_if_else_block();
 631     match block.rules {
 632         ast::BlockCheckMode::Unsafe(..) => {
 633             let snippet = context.snippet(block.span);
 634             let open_pos = snippet.find_uncommented("{")?;
 635             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 636         }
 637         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 638     }
 639
 640     let inner_attrs = attrs.map(inner_attributes);
 641     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 642     Some(format!("{}{}", prefix, visitor.buffer))
 643 }
 644
 645 impl Rewrite for ast::Block {
 646     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 647         rewrite_block(self, None, context, shape)
 648     }
 649 }
 650
 651 fn rewrite_block(
 652     block: &ast::Block,
 653     attrs: Option<&[ast::Attribute]>,
 654     context: &RewriteContext,
 655     shape: Shape,
 656 ) -> Option<String> {
 657     let prefix = block_prefix(context, block, shape)?;
 658
 659     // shape.width is used only for the single line case: either the empty block `{}`,
 660     // or an unsafe expression `unsafe { e }`.
 661     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, &prefix, shape) {
 662         return rw;
 663     }
 664
 665     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, shape, true);
 666     if let Some(ref result_str) = result {
 667         if result_str.lines().count() <= 3 {
 668             if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, block, attrs, shape) {
 669                 return rw;
 670             }
 671         }
 672     }
 673
 674     result
 675 }
 676
 677 impl Rewrite for ast::Stmt {
 678     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 679         skip_out_of_file_lines_range!(context, self.span());
 680
 681         let result = match self.node {
 682             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 683             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 684                 let suffix = if semicolon_for_stmt(context, self) {
 685                     ";"
 686                 } else {
 687                     ""
 688                 };
 689
 690                 let shape = shape.sub_width(suffix.len())?;
 691                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 692             }
 693             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 694         };
 695         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 696     }
 697 }
 698
 699 // Rewrite condition if the given expression has one.
 700 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 701     match expr.node {
 702         ast::ExprKind::Match(ref cond, _) => {
 703             // `match `cond` {`
 704             let cond_shape = match context.config.indent_style() {
 705                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 706                 IndentStyle::Block => shape.offset_left(8)?,
 707             };
 708             cond.rewrite(context, cond_shape)
 709         }
 710         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 711             let alt_block_sep =
 712                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 713             control_flow
 714                 .rewrite_cond(context, shape, &alt_block_sep)
 715                 .and_then(|rw| Some(rw.0))
 716         }),
 717     }
 718 }
 719
 720 // Abstraction over control flow expressions
 721 #[derive(Debug)]
 722 struct ControlFlow<'a> {
 723     cond: Option<&'a ast::Expr>,
 724     block: &'a ast::Block,
 725     else_block: Option<&'a ast::Expr>,
 726     label: Option<ast::Label>,
 727     pats: Vec<&'a ast::Pat>,
 728     keyword: &'a str,
 729     matcher: &'a str,
 730     connector: &'a str,
 731     allow_single_line: bool,
 732     // True if this is an `if` expression in an `else if` :-( hacky
 733     nested_if: bool,
 734     span: Span,
 735 }
 736
 737 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 738     match expr.node {
 739         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 740             cond,
 741             vec![],
 742             if_block,
 743             else_block.as_ref().map(|e| &**e),
 744             expr_type == ExprType::SubExpression,
 745             false,
 746             expr.span,
 747         )),
 748         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 749             Some(ControlFlow::new_if(
 750                 cond,
 751                 ptr_vec_to_ref_vec(pat),
 752                 if_block,
 753                 else_block.as_ref().map(|e| &**e),
 754                 expr_type == ExprType::SubExpression,
 755                 false,
 756                 expr.span,
 757             ))
 758         }
 759         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 760             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 761         }
 762         ast::ExprKind::Loop(ref block, label) => {
 763             Some(ControlFlow::new_loop(block, label, expr.span))
 764         }
 765         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 766             vec![],
 767             cond,
 768             block,
 769             label,
 770             expr.span,
 771         )),
 772         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 773             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 774         ),
 775         _ => None,
 776     }
 777 }
 778
 779 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 780     if pats.is_empty() {
 781         ""
 782     } else {
 783         "let"
 784     }
 785 }
 786
 787 impl<'a> ControlFlow<'a> {
 788     fn new_if(
 789         cond: &'a ast::Expr,
 790         pats: Vec<&'a ast::Pat>,
 791         block: &'a ast::Block,
 792         else_block: Option<&'a ast::Expr>,
 793         allow_single_line: bool,
 794         nested_if: bool,
 795         span: Span,
 796     ) -> ControlFlow<'a> {
 797         let matcher = choose_matcher(&pats);
 798         ControlFlow {
 799             cond: Some(cond),
 800             block,
 801             else_block,
 802             label: None,
 803             pats,
 804             keyword: "if",
 805             matcher,
 806             connector: " =",
 807             allow_single_line,
 808             nested_if,
 809             span,
 810         }
 811     }
 812
 813     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 814         ControlFlow {
 815             cond: None,
 816             block,
 817             else_block: None,
 818             label,
 819             pats: vec![],
 820             keyword: "loop",
 821             matcher: "",
 822             connector: "",
 823             allow_single_line: false,
 824             nested_if: false,
 825             span,
 826         }
 827     }
 828
 829     fn new_while(
 830         pats: Vec<&'a ast::Pat>,
 831         cond: &'a ast::Expr,
 832         block: &'a ast::Block,
 833         label: Option<ast::Label>,
 834         span: Span,
 835     ) -> ControlFlow<'a> {
 836         let matcher = choose_matcher(&pats);
 837         ControlFlow {
 838             cond: Some(cond),
 839             block,
 840             else_block: None,
 841             label,
 842             pats,
 843             keyword: "while",
 844             matcher,
 845             connector: " =",
 846             allow_single_line: false,
 847             nested_if: false,
 848             span,
 849         }
 850     }
 851
 852     fn new_for(
 853         pat: &'a ast::Pat,
 854         cond: &'a ast::Expr,
 855         block: &'a ast::Block,
 856         label: Option<ast::Label>,
 857         span: Span,
 858     ) -> ControlFlow<'a> {
 859         ControlFlow {
 860             cond: Some(cond),
 861             block,
 862             else_block: None,
 863             label,
 864             pats: vec![pat],
 865             keyword: "for",
 866             matcher: "",
 867             connector: " in",
 868             allow_single_line: false,
 869             nested_if: false,
 870             span,
 871         }
 872     }
 873
 874     fn rewrite_single_line(
 875         &self,
 876         pat_expr_str: &str,
 877         context: &RewriteContext,
 878         width: usize,
 879     ) -> Option<String> {
 880         assert!(self.allow_single_line);
 881         let else_block = self.else_block?;
 882         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 883
 884         if let ast::ExprKind::Block(ref else_node, _) = else_block.node {
 885             if !is_simple_block(self.block, None, context.codemap)
 886                 || !is_simple_block(else_node, None, context.codemap)
 887                 || pat_expr_str.contains('\n')
 888             {
 889                 return None;
 890             }
 891
 892             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 893             let expr = &self.block.stmts[0];
 894             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 895
 896             let new_width = new_width.checked_sub(if_str.len())?;
 897             let else_expr = &else_node.stmts[0];
 898             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 899
 900             if if_str.contains('\n') || else_str.contains('\n') {
 901                 return None;
 902             }
 903
 904             let result = format!(
 905                 "{} {} {{ {} }} else {{ {} }}",
 906                 self.keyword, pat_expr_str, if_str, else_str
 907             );
 908
 909             if result.len() <= width {
 910                 return Some(result);
 911             }
 912         }
 913
 914         None
 915     }
 916 }
 917
 918 impl<'a> ControlFlow<'a> {
 919     fn rewrite_pat_expr(
 920         &self,
 921         context: &RewriteContext,
 922         expr: &ast::Expr,
 923         shape: Shape,
 924         offset: usize,
 925     ) -> Option<String> {
 926         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 927
 928         let cond_shape = shape.offset_left(offset)?;
 929         if !self.pats.is_empty() {
 930             let matcher = if self.matcher.is_empty() {
 931                 self.matcher.to_owned()
 932             } else {
 933                 format!("{} ", self.matcher)
 934             };
 935             let pat_shape = cond_shape
 936                 .offset_left(matcher.len())?
 937                 .sub_width(self.connector.len())?;
 938             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 939             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 940             return rewrite_assign_rhs(context, result, expr, cond_shape);
 941         }
 942
 943         let expr_rw = expr.rewrite(context, cond_shape);
 944         // The expression may (partially) fit on the current line.
 945         // We do not allow splitting between `if` and condition.
 946         if self.keyword == "if" || expr_rw.is_some() {
 947             return expr_rw;
 948         }
 949
 950         // The expression won't fit on the current line, jump to next.
 951         let nested_shape = shape
 952             .block_indent(context.config.tab_spaces())
 953             .with_max_width(context.config);
 954         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 955         expr.rewrite(context, nested_shape)
 956             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 957     }
 958
 959     fn rewrite_cond(
 960         &self,
 961         context: &RewriteContext,
 962         shape: Shape,
 963         alt_block_sep: &str,
 964     ) -> Option<(String, usize)> {
 965         // Do not take the rhs overhead from the upper expressions into account
 966         // when rewriting pattern.
 967         let new_width = context.budget(shape.used_width());
 968         let fresh_shape = Shape {
 969             width: new_width,
 970             ..shape
 971         };
 972         let constr_shape = if self.nested_if {
 973             // We are part of an if-elseif-else chain. Our constraints are tightened.
 974             // 7 = "} else " .len()
 975             fresh_shape.offset_left(7)?
 976         } else {
 977             fresh_shape
 978         };
 979
 980         let label_string = rewrite_label(self.label);
 981         // 1 = space after keyword.
 982         let offset = self.keyword.len() + label_string.len() + 1;
 983
 984         let pat_expr_string = match self.cond {
 985             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 986             None => String::new(),
 987         };
 988
 989         let brace_overhead =
 990             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 991                 // 2 = ` {`
 992                 2
 993             } else {
 994                 0
 995             };
 996         let one_line_budget = context
 997             .config
 998             .max_width()
 999             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
1000         let force_newline_brace = (pat_expr_string.contains('\n')
1001             || pat_expr_string.len() > one_line_budget)
1002             && !last_line_extendable(&pat_expr_string);
1003
1004         // Try to format if-else on single line.
1005         if self.allow_single_line
1006             && context
1007                 .config
1008                 .width_heuristics()
1009                 .single_line_if_else_max_width > 0
1010         {
1011             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1012
1013             if let Some(cond_str) = trial {
1014                 if cond_str.len()
1015                     <= context
1016                         .config
1017                         .width_heuristics()
1018                         .single_line_if_else_max_width
1019                 {
1020                     return Some((cond_str, 0));
1021                 }
1022             }
1023         }
1024
1025         let cond_span = if let Some(cond) = self.cond {
1026             cond.span
1027         } else {
1028             mk_sp(self.block.span.lo(), self.block.span.lo())
1029         };
1030
1031         // `for event in event`
1032         // Do not include label in the span.
1033         let lo = self
1034             .label
1035             .map_or(self.span.lo(), |label| label.ident.span.hi());
1036         let between_kwd_cond = mk_sp(
1037             context
1038                 .snippet_provider
1039                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1040             if self.pats.is_empty() {
1041                 cond_span.lo()
1042             } else if self.matcher.is_empty() {
1043                 self.pats[0].span.lo()
1044             } else {
1045                 context
1046                     .snippet_provider
1047                     .span_before(self.span, self.matcher.trim())
1048             },
1049         );
1050
1051         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1052
1053         let after_cond_comment =
1054             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1055
1056         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1057             ""
1058         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1059             || force_newline_brace
1060         {
1061             alt_block_sep
1062         } else {
1063             " "
1064         };
1065
1066         let used_width = if pat_expr_string.contains('\n') {
1067             last_line_width(&pat_expr_string)
1068         } else {
1069             // 2 = spaces after keyword and condition.
1070             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1071         };
1072
1073         Some((
1074             format!(
1075                 "{}{}{}{}{}",
1076                 label_string,
1077                 self.keyword,
1078                 between_kwd_cond_comment.as_ref().map_or(
1079                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1080                         ""
1081                     } else {
1082                         " "
1083                     },
1084                     |s| &**s,
1085                 ),
1086                 pat_expr_string,
1087                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1088             ),
1089             used_width,
1090         ))
1091     }
1092 }
1093
1094 impl<'a> Rewrite for ControlFlow<'a> {
1095     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1096         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1097
1098         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1099         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1100         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1101         if used_width == 0 {
1102             return Some(cond_str);
1103         }
1104
1105         let block_width = shape.width.saturating_sub(used_width);
1106         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1107         // we should avoid the single line case.
1108         let block_width = if self.else_block.is_some() || self.nested_if {
1109             min(1, block_width)
1110         } else {
1111             block_width
1112         };
1113         let block_shape = Shape {
1114             width: block_width,
1115             ..shape
1116         };
1117         let block_str = {
1118             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1119             let result =
1120                 rewrite_block_with_visitor(context, "", self.block, None, block_shape, true);
1121             context.is_if_else_block.replace(old_val);
1122             result?
1123         };
1124
1125         let mut result = format!("{}{}", cond_str, block_str);
1126
1127         if let Some(else_block) = self.else_block {
1128             let shape = Shape::indented(shape.indent, context.config);
1129             let mut last_in_chain = false;
1130             let rewrite = match else_block.node {
1131                 // If the else expression is another if-else expression, prevent it
1132                 // from being formatted on a single line.
1133                 // Note how we're passing the original shape, as the
1134                 // cost of "else" should not cascade.
1135                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1136                     ControlFlow::new_if(
1137                         cond,
1138                         ptr_vec_to_ref_vec(pat),
1139                         if_block,
1140                         next_else_block.as_ref().map(|e| &**e),
1141                         false,
1142                         true,
1143                         mk_sp(else_block.span.lo(), self.span.hi()),
1144                     ).rewrite(context, shape)
1145                 }
1146                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1147                     ControlFlow::new_if(
1148                         cond,
1149                         vec![],
1150                         if_block,
1151                         next_else_block.as_ref().map(|e| &**e),
1152                         false,
1153                         true,
1154                         mk_sp(else_block.span.lo(), self.span.hi()),
1155                     ).rewrite(context, shape)
1156                 }
1157                 _ => {
1158                     last_in_chain = true;
1159                     // When rewriting a block, the width is only used for single line
1160                     // blocks, passing 1 lets us avoid that.
1161                     let else_shape = Shape {
1162                         width: min(1, shape.width),
1163                         ..shape
1164                     };
1165                     format_expr(else_block, ExprType::Statement, context, else_shape)
1166                 }
1167             };
1168
1169             let between_kwd_else_block = mk_sp(
1170                 self.block.span.hi(),
1171                 context
1172                     .snippet_provider
1173                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1174             );
1175             let between_kwd_else_block_comment =
1176                 extract_comment(between_kwd_else_block, context, shape);
1177
1178             let after_else = mk_sp(
1179                 context
1180                     .snippet_provider
1181                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1182                 else_block.span.lo(),
1183             );
1184             let after_else_comment = extract_comment(after_else, context, shape);
1185
1186             let between_sep = match context.config.control_brace_style() {
1187                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1188                     &*alt_block_sep
1189                 }
1190                 ControlBraceStyle::AlwaysSameLine => " ",
1191             };
1192             let after_sep = match context.config.control_brace_style() {
1193                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1194                 _ => " ",
1195             };
1196
1197             result.push_str(&format!(
1198                 "{}else{}",
1199                 between_kwd_else_block_comment
1200                     .as_ref()
1201                     .map_or(between_sep, |s| &**s),
1202                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1203             ));
1204             result.push_str(&rewrite?);
1205         }
1206
1207         Some(result)
1208     }
1209 }
1210
1211 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1212     match opt_label {
1213         Some(label) => Cow::from(format!("{}: ", label.ident)),
1214         None => Cow::from(""),
1215     }
1216 }
1217
1218 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1219     match rewrite_missing_comment(span, shape, context) {
1220         Some(ref comment) if !comment.is_empty() => Some(format!(
1221             "{indent}{}{indent}",
1222             comment,
1223             indent = shape.indent.to_string_with_newline(context.config)
1224         )),
1225         _ => None,
1226     }
1227 }
1228
1229 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1230     let snippet = codemap.span_to_snippet(block.span).unwrap();
1231     contains_comment(&snippet)
1232 }
1233
1234 // Checks that a block contains no statements, an expression and no comments or
1235 // attributes.
1236 // FIXME: incorrectly returns false when comment is contained completely within
1237 // the expression.
1238 pub fn is_simple_block(
1239     block: &ast::Block,
1240     attrs: Option<&[ast::Attribute]>,
1241     codemap: &CodeMap,
1242 ) -> bool {
1243     (block.stmts.len() == 1
1244         && stmt_is_expr(&block.stmts[0])
1245         && !block_contains_comment(block, codemap)
1246         && attrs.map_or(true, |a| a.is_empty()))
1247 }
1248
1249 /// Checks whether a block contains at most one statement or expression, and no
1250 /// comments or attributes.
1251 pub fn is_simple_block_stmt(
1252     block: &ast::Block,
1253     attrs: Option<&[ast::Attribute]>,
1254     codemap: &CodeMap,
1255 ) -> bool {
1256     block.stmts.len() <= 1
1257         && !block_contains_comment(block, codemap)
1258         && attrs.map_or(true, |a| a.is_empty())
1259 }
1260
1261 /// Checks whether a block contains no statements, expressions, comments, or
1262 /// inner attributes.
1263 pub fn is_empty_block(
1264     block: &ast::Block,
1265     attrs: Option<&[ast::Attribute]>,
1266     codemap: &CodeMap,
1267 ) -> bool {
1268     block.stmts.is_empty()
1269         && !block_contains_comment(block, codemap)
1270         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1271 }
1272
1273 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1274     match stmt.node {
1275         ast::StmtKind::Expr(..) => true,
1276         _ => false,
1277     }
1278 }
1279
1280 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1281     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1282         true
1283     } else {
1284         false
1285     }
1286 }
1287
1288 pub fn rewrite_multiple_patterns(
1289     context: &RewriteContext,
1290     pats: &[&ast::Pat],
1291     shape: Shape,
1292 ) -> Option<String> {
1293     let pat_strs = pats
1294         .iter()
1295         .map(|p| p.rewrite(context, shape))
1296         .collect::<Option<Vec<_>>>()?;
1297
1298     let use_mixed_layout = pats
1299         .iter()
1300         .zip(pat_strs.iter())
1301         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1302     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1303     let tactic = if use_mixed_layout {
1304         DefinitiveListTactic::Mixed
1305     } else {
1306         definitive_tactic(
1307             &items,
1308             ListTactic::HorizontalVertical,
1309             Separator::VerticalBar,
1310             shape.width,
1311         )
1312     };
1313     let fmt = ListFormatting {
1314         tactic,
1315         separator: " |",
1316         trailing_separator: SeparatorTactic::Never,
1317         separator_place: context.config.binop_separator(),
1318         shape,
1319         ends_with_newline: false,
1320         preserve_newline: false,
1321         config: context.config,
1322     };
1323     write_list(&items, &fmt)
1324 }
1325
1326 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1327     match l.node {
1328         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1329         _ => wrap_str(
1330             context.snippet(l.span).to_owned(),
1331             context.config.max_width(),
1332             shape,
1333         ),
1334     }
1335 }
1336
1337 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1338     let string_lit = context.snippet(span);
1339
1340     if !context.config.format_strings() {
1341         if string_lit
1342             .lines()
1343             .rev()
1344             .skip(1)
1345             .all(|line| line.ends_with('\\'))
1346         {
1347             let new_indent = shape.visual_indent(1).indent;
1348             let indented_string_lit = String::from(
1349                 string_lit
1350                     .lines()
1351                     .map(|line| {
1352                         format!(
1353                             "{}{}",
1354                             new_indent.to_string(context.config),
1355                             line.trim_left()
1356                         )
1357                     })
1358                     .collect::<Vec<_>>()
1359                     .join("\n")
1360                     .trim_left(),
1361             );
1362             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1363         } else {
1364             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1365         }
1366     }
1367
1368     // Remove the quote characters.
1369     let str_lit = &string_lit[1..string_lit.len() - 1];
1370
1371     rewrite_string(
1372         str_lit,
1373         &StringFormat::new(shape.visual_indent(0), context.config),
1374         None,
1375     )
1376 }
1377
1378 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1379 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1380     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1381         .iter()
1382         .find(|&&(s, _)| s == callee_str)
1383     {
1384         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1385
1386         Some((all_simple, num_args_before))
1387     } else {
1388         None
1389     }
1390 }
1391
1392 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1393 /// format.
1394 ///
1395 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1396 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1397 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1398 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1399     // format! like macros
1400     // From the Rust Standard Library.
1401     ("eprint!", 0),
1402     ("eprintln!", 0),
1403     ("format!", 0),
1404     ("format_args!", 0),
1405     ("print!", 0),
1406     ("println!", 0),
1407     ("panic!", 0),
1408     ("unreachable!", 0),
1409     // From the `log` crate.
1410     ("debug!", 0),
1411     ("error!", 0),
1412     ("info!", 0),
1413     ("warn!", 0),
1414     // write! like macros
1415     ("assert!", 1),
1416     ("debug_assert!", 1),
1417     ("write!", 1),
1418     ("writeln!", 1),
1419     // assert_eq! like macros
1420     ("assert_eq!", 2),
1421     ("assert_ne!", 2),
1422     ("debug_assert_eq!", 2),
1423     ("debug_assert_ne!", 2),
1424 ];
1425
1426 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1427     if context.inside_macro() {
1428         if span_ends_with_comma(context, span) {
1429             Some(SeparatorTactic::Always)
1430         } else {
1431             Some(SeparatorTactic::Never)
1432         }
1433     } else {
1434         None
1435     }
1436 }
1437
1438 pub fn rewrite_call(
1439     context: &RewriteContext,
1440     callee: &str,
1441     args: &[ptr::P<ast::Expr>],
1442     span: Span,
1443     shape: Shape,
1444 ) -> Option<String> {
1445     overflow::rewrite_with_parens(
1446         context,
1447         callee,
1448         &ptr_vec_to_ref_vec(args),
1449         shape,
1450         span,
1451         context.config.width_heuristics().fn_call_width,
1452         choose_separator_tactic(context, span),
1453     )
1454 }
1455
1456 fn is_simple_expr(expr: &ast::Expr) -> bool {
1457     match expr.node {
1458         ast::ExprKind::Lit(..) => true,
1459         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1460         ast::ExprKind::AddrOf(_, ref expr)
1461         | ast::ExprKind::Box(ref expr)
1462         | ast::ExprKind::Cast(ref expr, _)
1463         | ast::ExprKind::Field(ref expr, _)
1464         | ast::ExprKind::Try(ref expr)
1465         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1466         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1467             is_simple_expr(lhs) && is_simple_expr(rhs)
1468         }
1469         _ => false,
1470     }
1471 }
1472
1473 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1474     lists
1475         .iter()
1476         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1477 }
1478
1479 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1480     match expr.node {
1481         ast::ExprKind::Match(..) => {
1482             (context.use_block_indent() && args_len == 1)
1483                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1484         }
1485         ast::ExprKind::If(..)
1486         | ast::ExprKind::IfLet(..)
1487         | ast::ExprKind::ForLoop(..)
1488         | ast::ExprKind::Loop(..)
1489         | ast::ExprKind::While(..)
1490         | ast::ExprKind::WhileLet(..) => {
1491             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1492         }
1493         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1494             context.use_block_indent()
1495                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1496         }
1497         ast::ExprKind::Array(..)
1498         | ast::ExprKind::Call(..)
1499         | ast::ExprKind::Mac(..)
1500         | ast::ExprKind::MethodCall(..)
1501         | ast::ExprKind::Struct(..)
1502         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1503         ast::ExprKind::AddrOf(_, ref expr)
1504         | ast::ExprKind::Box(ref expr)
1505         | ast::ExprKind::Try(ref expr)
1506         | ast::ExprKind::Unary(_, ref expr)
1507         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1508         _ => false,
1509     }
1510 }
1511
1512 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1513     match expr.node {
1514         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1515         ast::ExprKind::AddrOf(_, ref expr)
1516         | ast::ExprKind::Box(ref expr)
1517         | ast::ExprKind::Try(ref expr)
1518         | ast::ExprKind::Unary(_, ref expr)
1519         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1520         _ => false,
1521     }
1522 }
1523
1524 /// Return true if a function call or a method call represented by the given span ends with a
1525 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1526 /// comma from macro can potentially break the code.
1527 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1528     let mut result: bool = Default::default();
1529     let mut prev_char: char = Default::default();
1530     let closing_delimiters = &[')', '}', ']'];
1531
1532     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1533         match c {
1534             _ if kind.is_comment() || c.is_whitespace() => continue,
1535             c if closing_delimiters.contains(&c) => {
1536                 result &= !closing_delimiters.contains(&prev_char);
1537             }
1538             ',' => result = true,
1539             _ => result = false,
1540         }
1541         prev_char = c;
1542     }
1543
1544     result
1545 }
1546
1547 fn rewrite_paren(
1548     context: &RewriteContext,
1549     mut subexpr: &ast::Expr,
1550     shape: Shape,
1551     mut span: Span,
1552 ) -> Option<String> {
1553     debug!("rewrite_paren, shape: {:?}", shape);
1554
1555     // Extract comments within parens.
1556     let mut pre_comment;
1557     let mut post_comment;
1558     let remove_nested_parens = context.config.remove_nested_parens();
1559     loop {
1560         // 1 = "(" or ")"
1561         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1562         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1563         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1564         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1565
1566         // Remove nested parens if there are no comments.
1567         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1568             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1569                 span = subexpr.span;
1570                 subexpr = subsubexpr;
1571                 continue;
1572             }
1573         }
1574
1575         break;
1576     }
1577
1578     // 1 `(`
1579     let sub_shape = shape.offset_left(1).and_then(|s| s.sub_width(1))?;
1580
1581     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1582     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1583
1584     // 2 = `()`
1585     if subexpr_str.contains('\n') || first_line_width(&subexpr_str) + 2 <= shape.width {
1586         Some(format!("({}{}{})", pre_comment, &subexpr_str, post_comment))
1587     } else {
1588         None
1589     }
1590 }
1591
1592 fn rewrite_index(
1593     expr: &ast::Expr,
1594     index: &ast::Expr,
1595     context: &RewriteContext,
1596     shape: Shape,
1597 ) -> Option<String> {
1598     let expr_str = expr.rewrite(context, shape)?;
1599
1600     let offset = last_line_width(&expr_str) + 1;
1601     let rhs_overhead = shape.rhs_overhead(context.config);
1602     let index_shape = if expr_str.contains('\n') {
1603         Shape::legacy(context.config.max_width(), shape.indent)
1604             .offset_left(offset)
1605             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1606     } else {
1607         shape.visual_indent(offset).sub_width(offset + 1)
1608     };
1609     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1610
1611     // Return if index fits in a single line.
1612     match orig_index_rw {
1613         Some(ref index_str) if !index_str.contains('\n') => {
1614             return Some(format!("{}[{}]", expr_str, index_str));
1615         }
1616         _ => (),
1617     }
1618
1619     // Try putting index on the next line and see if it fits in a single line.
1620     let indent = shape.indent.block_indent(context.config);
1621     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1622     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1623     let new_index_rw = index.rewrite(context, index_shape);
1624     match (orig_index_rw, new_index_rw) {
1625         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1626             "{}{}[{}]",
1627             expr_str,
1628             indent.to_string_with_newline(context.config),
1629             new_index_str,
1630         )),
1631         (None, Some(ref new_index_str)) => Some(format!(
1632             "{}{}[{}]",
1633             expr_str,
1634             indent.to_string_with_newline(context.config),
1635             new_index_str,
1636         )),
1637         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1638         _ => None,
1639     }
1640 }
1641
1642 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1643     if base.is_some() {
1644         return false;
1645     }
1646
1647     fields.iter().all(|field| !field.is_shorthand)
1648 }
1649
1650 fn rewrite_struct_lit<'a>(
1651     context: &RewriteContext,
1652     path: &ast::Path,
1653     fields: &'a [ast::Field],
1654     base: Option<&'a ast::Expr>,
1655     span: Span,
1656     shape: Shape,
1657 ) -> Option<String> {
1658     debug!("rewrite_struct_lit: shape {:?}", shape);
1659
1660     enum StructLitField<'a> {
1661         Regular(&'a ast::Field),
1662         Base(&'a ast::Expr),
1663     }
1664
1665     // 2 = " {".len()
1666     let path_shape = shape.sub_width(2)?;
1667     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1668
1669     if fields.is_empty() && base.is_none() {
1670         return Some(format!("{} {{}}", path_str));
1671     }
1672
1673     // Foo { a: Foo } - indent is +3, width is -5.
1674     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1675
1676     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1677     let body_lo = context.snippet_provider.span_after(span, "{");
1678     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1679         && context.config.struct_field_align_threshold() > 0
1680     {
1681         rewrite_with_alignment(
1682             fields,
1683             context,
1684             shape,
1685             mk_sp(body_lo, span.hi()),
1686             one_line_width,
1687         )?
1688     } else {
1689         let field_iter = fields
1690             .into_iter()
1691             .map(StructLitField::Regular)
1692             .chain(base.into_iter().map(StructLitField::Base));
1693
1694         let span_lo = |item: &StructLitField| match *item {
1695             StructLitField::Regular(field) => field.span().lo(),
1696             StructLitField::Base(expr) => {
1697                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1698                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1699                 let pos = snippet.find_uncommented("..").unwrap();
1700                 last_field_hi + BytePos(pos as u32)
1701             }
1702         };
1703         let span_hi = |item: &StructLitField| match *item {
1704             StructLitField::Regular(field) => field.span().hi(),
1705             StructLitField::Base(expr) => expr.span.hi(),
1706         };
1707         let rewrite = |item: &StructLitField| match *item {
1708             StructLitField::Regular(field) => {
1709                 // The 1 taken from the v_budget is for the comma.
1710                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1711             }
1712             StructLitField::Base(expr) => {
1713                 // 2 = ..
1714                 expr.rewrite(context, v_shape.offset_left(2)?)
1715                     .map(|s| format!("..{}", s))
1716             }
1717         };
1718
1719         let items = itemize_list(
1720             context.snippet_provider,
1721             field_iter,
1722             "}",
1723             ",",
1724             span_lo,
1725             span_hi,
1726             rewrite,
1727             body_lo,
1728             span.hi(),
1729             false,
1730         );
1731         let item_vec = items.collect::<Vec<_>>();
1732
1733         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1734         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1735
1736         let ends_with_comma = span_ends_with_comma(context, span);
1737         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1738
1739         let fmt = struct_lit_formatting(
1740             nested_shape,
1741             tactic,
1742             context,
1743             force_no_trailing_comma || base.is_some(),
1744         );
1745
1746         write_list(&item_vec, &fmt)?
1747     };
1748
1749     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1750     Some(format!("{} {{{}}}", path_str, fields_str))
1751
1752     // FIXME if context.config.indent_style() == Visual, but we run out
1753     // of space, we should fall back to BlockIndent.
1754 }
1755
1756 pub fn wrap_struct_field(
1757     context: &RewriteContext,
1758     fields_str: &str,
1759     shape: Shape,
1760     nested_shape: Shape,
1761     one_line_width: usize,
1762 ) -> String {
1763     if context.config.indent_style() == IndentStyle::Block
1764         && (fields_str.contains('\n')
1765             || !context.config.struct_lit_single_line()
1766             || fields_str.len() > one_line_width)
1767     {
1768         format!(
1769             "{}{}{}",
1770             nested_shape.indent.to_string_with_newline(context.config),
1771             fields_str,
1772             shape.indent.to_string_with_newline(context.config)
1773         )
1774     } else {
1775         // One liner or visual indent.
1776         format!(" {} ", fields_str)
1777     }
1778 }
1779
1780 pub fn struct_lit_field_separator(config: &Config) -> &str {
1781     colon_spaces(config.space_before_colon(), config.space_after_colon())
1782 }
1783
1784 pub fn rewrite_field(
1785     context: &RewriteContext,
1786     field: &ast::Field,
1787     shape: Shape,
1788     prefix_max_width: usize,
1789 ) -> Option<String> {
1790     if contains_skip(&field.attrs) {
1791         return Some(context.snippet(field.span()).to_owned());
1792     }
1793     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1794     if !attrs_str.is_empty() {
1795         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1796     };
1797     let name = &field.ident.name.to_string();
1798     if field.is_shorthand {
1799         Some(attrs_str + &name)
1800     } else {
1801         let mut separator = String::from(struct_lit_field_separator(context.config));
1802         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1803             separator.push(' ');
1804         }
1805         let overhead = name.len() + separator.len();
1806         let expr_shape = shape.offset_left(overhead)?;
1807         let expr = field.expr.rewrite(context, expr_shape);
1808
1809         match expr {
1810             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1811                 Some(attrs_str + &name)
1812             }
1813             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1814             None => {
1815                 let expr_offset = shape.indent.block_indent(context.config);
1816                 let expr = field
1817                     .expr
1818                     .rewrite(context, Shape::indented(expr_offset, context.config));
1819                 expr.map(|s| {
1820                     format!(
1821                         "{}{}:\n{}{}",
1822                         attrs_str,
1823                         name,
1824                         expr_offset.to_string(context.config),
1825                         s
1826                     )
1827                 })
1828             }
1829         }
1830     }
1831 }
1832
1833 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1834     context: &RewriteContext,
1835     items: &[&T],
1836     span: Span,
1837     shape: Shape,
1838 ) -> Option<String>
1839 where
1840     T: Rewrite + Spanned + ToExpr + 'a,
1841 {
1842     let mut items = items.iter();
1843     // In case of length 1, need a trailing comma
1844     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1845     if items.len() == 1 {
1846         // 3 = "(" + ",)"
1847         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1848         return items
1849             .next()
1850             .unwrap()
1851             .rewrite(context, nested_shape)
1852             .map(|s| format!("({},)", s));
1853     }
1854
1855     let list_lo = context.snippet_provider.span_after(span, "(");
1856     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1857     let items = itemize_list(
1858         context.snippet_provider,
1859         items,
1860         ")",
1861         ",",
1862         |item| item.span().lo(),
1863         |item| item.span().hi(),
1864         |item| item.rewrite(context, nested_shape),
1865         list_lo,
1866         span.hi() - BytePos(1),
1867         false,
1868     );
1869     let item_vec: Vec<_> = items.collect();
1870     let tactic = definitive_tactic(
1871         &item_vec,
1872         ListTactic::HorizontalVertical,
1873         Separator::Comma,
1874         nested_shape.width,
1875     );
1876     let fmt = ListFormatting {
1877         tactic,
1878         separator: ",",
1879         trailing_separator: SeparatorTactic::Never,
1880         separator_place: SeparatorPlace::Back,
1881         shape,
1882         ends_with_newline: false,
1883         preserve_newline: false,
1884         config: context.config,
1885     };
1886     let list_str = write_list(&item_vec, &fmt)?;
1887
1888     Some(format!("({})", list_str))
1889 }
1890
1891 pub fn rewrite_tuple<'a, T>(
1892     context: &RewriteContext,
1893     items: &[&T],
1894     span: Span,
1895     shape: Shape,
1896 ) -> Option<String>
1897 where
1898     T: Rewrite + Spanned + ToExpr + 'a,
1899 {
1900     debug!("rewrite_tuple {:?}", shape);
1901     if context.use_block_indent() {
1902         // We use the same rule as function calls for rewriting tuples.
1903         let force_tactic = if context.inside_macro() {
1904             if span_ends_with_comma(context, span) {
1905                 Some(SeparatorTactic::Always)
1906             } else {
1907                 Some(SeparatorTactic::Never)
1908             }
1909         } else if items.len() == 1 {
1910             Some(SeparatorTactic::Always)
1911         } else {
1912             None
1913         };
1914         overflow::rewrite_with_parens(
1915             context,
1916             "",
1917             items,
1918             shape,
1919             span,
1920             context.config.width_heuristics().fn_call_width,
1921             force_tactic,
1922         )
1923     } else {
1924         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1925     }
1926 }
1927
1928 pub fn rewrite_unary_prefix<R: Rewrite>(
1929     context: &RewriteContext,
1930     prefix: &str,
1931     rewrite: &R,
1932     shape: Shape,
1933 ) -> Option<String> {
1934     rewrite
1935         .rewrite(context, shape.offset_left(prefix.len())?)
1936         .map(|r| format!("{}{}", prefix, r))
1937 }
1938
1939 // FIXME: this is probably not correct for multi-line Rewrites. we should
1940 // subtract suffix.len() from the last line budget, not the first!
1941 pub fn rewrite_unary_suffix<R: Rewrite>(
1942     context: &RewriteContext,
1943     suffix: &str,
1944     rewrite: &R,
1945     shape: Shape,
1946 ) -> Option<String> {
1947     rewrite
1948         .rewrite(context, shape.sub_width(suffix.len())?)
1949         .map(|mut r| {
1950             r.push_str(suffix);
1951             r
1952         })
1953 }
1954
1955 fn rewrite_unary_op(
1956     context: &RewriteContext,
1957     op: &ast::UnOp,
1958     expr: &ast::Expr,
1959     shape: Shape,
1960 ) -> Option<String> {
1961     // For some reason, an UnOp is not spanned like BinOp!
1962     let operator_str = match *op {
1963         ast::UnOp::Deref => "*",
1964         ast::UnOp::Not => "!",
1965         ast::UnOp::Neg => "-",
1966     };
1967     rewrite_unary_prefix(context, operator_str, expr, shape)
1968 }
1969
1970 fn rewrite_assignment(
1971     context: &RewriteContext,
1972     lhs: &ast::Expr,
1973     rhs: &ast::Expr,
1974     op: Option<&ast::BinOp>,
1975     shape: Shape,
1976 ) -> Option<String> {
1977     let operator_str = match op {
1978         Some(op) => context.snippet(op.span),
1979         None => "=",
1980     };
1981
1982     // 1 = space between lhs and operator.
1983     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
1984     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
1985
1986     rewrite_assign_rhs(context, lhs_str, rhs, shape)
1987 }
1988
1989 /// Controls where to put the rhs.
1990 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1991 pub enum RhsTactics {
1992     /// Use heuristics.
1993     Default,
1994     /// Put the rhs on the next line if it uses multiple line.
1995     ForceNextLine,
1996 }
1997
1998 // The left hand side must contain everything up to, and including, the
1999 // assignment operator.
2000 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2001     context: &RewriteContext,
2002     lhs: S,
2003     ex: &R,
2004     shape: Shape,
2005 ) -> Option<String> {
2006     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2007 }
2008
2009 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2010     context: &RewriteContext,
2011     lhs: S,
2012     ex: &R,
2013     shape: Shape,
2014     rhs_tactics: RhsTactics,
2015 ) -> Option<String> {
2016     let lhs = lhs.into();
2017     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
2018         shape.indent.width()
2019     } else {
2020         0
2021     });
2022     // 1 = space between operator and rhs.
2023     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2024         width: 0,
2025         offset: shape.offset + last_line_width + 1,
2026         ..shape
2027     });
2028     let rhs = choose_rhs(
2029         context,
2030         ex,
2031         orig_shape,
2032         ex.rewrite(context, orig_shape),
2033         rhs_tactics,
2034     )?;
2035     Some(lhs + &rhs)
2036 }
2037
2038 fn choose_rhs<R: Rewrite>(
2039     context: &RewriteContext,
2040     expr: &R,
2041     shape: Shape,
2042     orig_rhs: Option<String>,
2043     rhs_tactics: RhsTactics,
2044 ) -> Option<String> {
2045     match orig_rhs {
2046         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2047             Some(format!(" {}", new_str))
2048         }
2049         _ => {
2050             // Expression did not fit on the same line as the identifier.
2051             // Try splitting the line and see if that works better.
2052             let new_shape =
2053                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2054                     .sub_width(shape.rhs_overhead(context.config))?;
2055             let new_rhs = expr.rewrite(context, new_shape);
2056             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2057
2058             match (orig_rhs, new_rhs) {
2059                 (Some(ref orig_rhs), Some(ref new_rhs))
2060                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2061                         .is_none() =>
2062                 {
2063                     Some(format!(" {}", orig_rhs))
2064                 }
2065                 (Some(ref orig_rhs), Some(ref new_rhs))
2066                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2067                 {
2068                     Some(format!("{}{}", new_indent_str, new_rhs))
2069                 }
2070                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2071                 (None, None) => None,
2072                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2073             }
2074         }
2075     }
2076 }
2077
2078 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2079     rhs_tactics == RhsTactics::ForceNextLine
2080         || !next_line_rhs.contains('\n')
2081         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2082 }
2083
2084 fn rewrite_expr_addrof(
2085     context: &RewriteContext,
2086     mutability: ast::Mutability,
2087     expr: &ast::Expr,
2088     shape: Shape,
2089 ) -> Option<String> {
2090     let operator_str = match mutability {
2091         ast::Mutability::Immutable => "&",
2092         ast::Mutability::Mutable => "&mut ",
2093     };
2094     rewrite_unary_prefix(context, operator_str, expr, shape)
2095 }
2096
2097 pub trait ToExpr {
2098     fn to_expr(&self) -> Option<&ast::Expr>;
2099     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2100 }
2101
2102 impl ToExpr for ast::Expr {
2103     fn to_expr(&self) -> Option<&ast::Expr> {
2104         Some(self)
2105     }
2106
2107     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2108         can_be_overflowed_expr(context, self, len)
2109     }
2110 }
2111
2112 impl ToExpr for ast::Ty {
2113     fn to_expr(&self) -> Option<&ast::Expr> {
2114         None
2115     }
2116
2117     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2118         can_be_overflowed_type(context, self, len)
2119     }
2120 }
2121
2122 impl<'a> ToExpr for TuplePatField<'a> {
2123     fn to_expr(&self) -> Option<&ast::Expr> {
2124         None
2125     }
2126
2127     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2128         can_be_overflowed_pat(context, self, len)
2129     }
2130 }
2131
2132 impl<'a> ToExpr for ast::StructField {
2133     fn to_expr(&self) -> Option<&ast::Expr> {
2134         None
2135     }
2136
2137     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2138         false
2139     }
2140 }
2141
2142 impl<'a> ToExpr for MacroArg {
2143     fn to_expr(&self) -> Option<&ast::Expr> {
2144         match *self {
2145             MacroArg::Expr(ref expr) => Some(expr),
2146             _ => None,
2147         }
2148     }
2149
2150     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2151         match *self {
2152             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2153             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2154             MacroArg::Pat(..) => false,
2155             MacroArg::Item(..) => len == 1,
2156         }
2157     }
2158 }
2159
2160 impl ToExpr for ast::GenericParam {
2161     fn to_expr(&self) -> Option<&ast::Expr> {
2162         None
2163     }
2164
2165     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2166         false
2167     }
2168 }