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), opt_label, 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
 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 => {
 145                     rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 146                 }
 147             }
 148         }
 149         ast::ExprKind::Match(ref cond, ref arms) => {
 150             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 151         }
 152         ast::ExprKind::Path(ref qself, ref path) => {
 153             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 154         }
 155         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 156             rewrite_assignment(context, lhs, rhs, None, shape)
 157         }
 158         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 159             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 160         }
 161         ast::ExprKind::Continue(ref opt_label) => {
 162             let id_str = match *opt_label {
 163                 Some(label) => format!(" {}", label.ident),
 164                 None => String::new(),
 165             };
 166             Some(format!("continue{}", id_str))
 167         }
 168         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 169             let id_str = match *opt_label {
 170                 Some(label) => format!(" {}", label.ident),
 171                 None => String::new(),
 172             };
 173
 174             if let Some(ref expr) = *opt_expr {
 175                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 176             } else {
 177                 Some(format!("break{}", id_str))
 178             }
 179         }
 180         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 181             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 182         } else {
 183             Some("yield".to_string())
 184         },
 185         ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) => {
 186             closures::rewrite_closure(
 187                 capture, movability, fn_decl, body, expr.span, context, shape,
 188             )
 189         }
 190         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 191             rewrite_chain(expr, context, shape)
 192         }
 193         ast::ExprKind::Mac(ref mac) => {
 194             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 195                 wrap_str(
 196                     context.snippet(expr.span).to_owned(),
 197                     context.config.max_width(),
 198                     shape,
 199                 )
 200             })
 201         }
 202         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 203         ast::ExprKind::Ret(Some(ref expr)) => {
 204             rewrite_unary_prefix(context, "return ", &**expr, shape)
 205         }
 206         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 207         ast::ExprKind::AddrOf(mutability, ref expr) => {
 208             rewrite_expr_addrof(context, mutability, expr, shape)
 209         }
 210         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 211             &**expr,
 212             &**ty,
 213             PairParts::new("", " as ", ""),
 214             context,
 215             shape,
 216             SeparatorPlace::Front,
 217         ),
 218         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 219             &**expr,
 220             &**ty,
 221             PairParts::new("", ": ", ""),
 222             context,
 223             shape,
 224             SeparatorPlace::Back,
 225         ),
 226         ast::ExprKind::Index(ref expr, ref index) => {
 227             rewrite_index(&**expr, &**index, context, shape)
 228         }
 229         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 230             &**expr,
 231             &**repeats,
 232             PairParts::new("[", "; ", "]"),
 233             context,
 234             shape,
 235             SeparatorPlace::Back,
 236         ),
 237         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 238             let delim = match limits {
 239                 ast::RangeLimits::HalfOpen => "..",
 240                 ast::RangeLimits::Closed => "..=",
 241             };
 242
 243             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 244                 match lhs.node {
 245                     ast::ExprKind::Lit(ref lit) => match lit.node {
 246                         ast::LitKind::FloatUnsuffixed(..) => {
 247                             context.snippet(lit.span).ends_with('.')
 248                         }
 249                         _ => false,
 250                     },
 251                     _ => false,
 252                 }
 253             }
 254
 255             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 256                 match rhs.node {
 257                     // Don't format `.. ..` into `....`, which is invalid.
 258                     //
 259                     // This check is unnecessary for `lhs`, because a range
 260                     // starting from another range needs parentheses as `(x ..) ..`
 261                     // (`x .. ..` is a range from `x` to `..`).
 262                     ast::ExprKind::Range(None, _, _) => true,
 263                     _ => false,
 264                 }
 265             }
 266
 267             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 268                 let space_if = |b: bool| if b { " " } else { "" };
 269
 270                 format!(
 271                     "{}{}{}",
 272                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 273                         .unwrap_or(""),
 274                     delim,
 275                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 276                         .unwrap_or(""),
 277                 )
 278             };
 279
 280             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 281                 (Some(lhs), Some(rhs)) => {
 282                     let sp_delim = if context.config.spaces_around_ranges() {
 283                         format!(" {} ", delim)
 284                     } else {
 285                         default_sp_delim(Some(lhs), Some(rhs))
 286                     };
 287                     rewrite_pair(
 288                         &*lhs,
 289                         &*rhs,
 290                         PairParts::new("", &sp_delim, ""),
 291                         context,
 292                         shape,
 293                         context.config.binop_separator(),
 294                     )
 295                 }
 296                 (None, Some(rhs)) => {
 297                     let sp_delim = if context.config.spaces_around_ranges() {
 298                         format!("{} ", delim)
 299                     } else {
 300                         default_sp_delim(None, Some(rhs))
 301                     };
 302                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 303                 }
 304                 (Some(lhs), None) => {
 305                     let sp_delim = if context.config.spaces_around_ranges() {
 306                         format!(" {}", delim)
 307                     } else {
 308                         default_sp_delim(Some(lhs), None)
 309                     };
 310                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 311                 }
 312                 (None, None) => Some(delim.to_owned()),
 313             }
 314         }
 315         // We do not format these expressions yet, but they should still
 316         // satisfy our width restrictions.
 317         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 318         ast::ExprKind::Catch(ref block) => {
 319             if let rw @ Some(_) =
 320                 rewrite_single_line_block(context, "do catch ", block, Some(&expr.attrs), shape)
 321             {
 322                 rw
 323             } else {
 324                 // 9 = `do catch `
 325                 let budget = shape.width.saturating_sub(9);
 326                 Some(format!(
 327                     "{}{}",
 328                     "do catch ",
 329                     rewrite_block(
 330                         block,
 331                         Some(&expr.attrs),
 332                         None,
 333                         context,
 334                         Shape::legacy(budget, shape.indent)
 335                     )?
 336                 ))
 337             }
 338         }
 339     };
 340
 341     expr_rw
 342         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 343         .and_then(|expr_str| {
 344             let attrs = outer_attributes(&expr.attrs);
 345             let attrs_str = attrs.rewrite(context, shape)?;
 346             let span = mk_sp(
 347                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 348                 expr.span.lo(),
 349             );
 350             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 351         })
 352 }
 353
 354 /// Collect operands that appears in the given binary operator in the opposite order.
 355 /// e.g. `collect_binary_items(e, ||)` for `a && b || c || d` returns `[d, c, a && b]`.
 356 fn collect_binary_items<'a>(mut expr: &'a ast::Expr, binop: ast::BinOp) -> Vec<&'a ast::Expr> {
 357     let mut result = vec![];
 358     let mut prev_lhs = None;
 359     loop {
 360         match expr.node {
 361             ast::ExprKind::Binary(inner_binop, ref lhs, ref rhs)
 362                 if inner_binop.node == binop.node =>
 363             {
 364                 result.push(&**rhs);
 365                 expr = lhs;
 366                 prev_lhs = Some(lhs);
 367             }
 368             _ => {
 369                 if let Some(lhs) = prev_lhs {
 370                     result.push(lhs);
 371                 }
 372                 break;
 373             }
 374         }
 375     }
 376     result
 377 }
 378
 379 /// Rewrites a binary expression whose operands fits within a single line.
 380 fn rewrite_simple_binaries(
 381     context: &RewriteContext,
 382     expr: &ast::Expr,
 383     shape: Shape,
 384     op: ast::BinOp,
 385 ) -> Option<String> {
 386     let op_str = context.snippet(op.span);
 387
 388     // 2 = spaces around a binary operator.
 389     let sep_overhead = op_str.len() + 2;
 390     let nested_overhead = sep_overhead - 1;
 391
 392     let nested_shape = (match context.config.indent_style() {
 393         IndentStyle::Visual => shape.visual_indent(0),
 394         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 395     }).with_max_width(context.config);
 396     let nested_shape = match context.config.binop_separator() {
 397         SeparatorPlace::Back => nested_shape.sub_width(nested_overhead)?,
 398         SeparatorPlace::Front => nested_shape.offset_left(nested_overhead)?,
 399     };
 400
 401     let opt_rewrites: Option<Vec<_>> = collect_binary_items(expr, op)
 402         .iter()
 403         .rev()
 404         .map(|e| e.rewrite(context, nested_shape))
 405         .collect();
 406     if let Some(rewrites) = opt_rewrites {
 407         if rewrites.iter().all(|e| ::utils::is_single_line(e)) {
 408             let total_width = rewrites.iter().map(|s| s.len()).sum::<usize>()
 409                 + sep_overhead * (rewrites.len() - 1);
 410
 411             let sep_str = if total_width <= shape.width {
 412                 format!(" {} ", op_str)
 413             } else {
 414                 let indent_str = nested_shape.indent.to_string_with_newline(context.config);
 415                 match context.config.binop_separator() {
 416                     SeparatorPlace::Back => format!(" {}{}", op_str.trim_right(), indent_str),
 417                     SeparatorPlace::Front => format!("{}{} ", indent_str, op_str.trim_left()),
 418                 }
 419             };
 420
 421             return wrap_str(rewrites.join(&sep_str), context.config.max_width(), shape);
 422         }
 423     }
 424
 425     None
 426 }
 427
 428 #[derive(new, Clone, Copy)]
 429 pub struct PairParts<'a> {
 430     prefix: &'a str,
 431     infix: &'a str,
 432     suffix: &'a str,
 433 }
 434
 435 pub fn rewrite_pair<LHS, RHS>(
 436     lhs: &LHS,
 437     rhs: &RHS,
 438     pp: PairParts,
 439     context: &RewriteContext,
 440     shape: Shape,
 441     separator_place: SeparatorPlace,
 442 ) -> Option<String>
 443 where
 444     LHS: Rewrite,
 445     RHS: Rewrite,
 446 {
 447     let lhs_overhead = match separator_place {
 448         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 449         SeparatorPlace::Front => shape.used_width(),
 450     };
 451     let lhs_shape = Shape {
 452         width: context.budget(lhs_overhead),
 453         ..shape
 454     };
 455     let lhs_result = lhs
 456         .rewrite(context, lhs_shape)
 457         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 458
 459     // Try to put both lhs and rhs on the same line.
 460     let rhs_orig_result = shape
 461         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 462         .and_then(|s| s.sub_width(pp.suffix.len()))
 463         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 464     if let Some(ref rhs_result) = rhs_orig_result {
 465         // If the length of the lhs is equal to or shorter than the tab width or
 466         // the rhs looks like block expression, we put the rhs on the same
 467         // line with the lhs even if the rhs is multi-lined.
 468         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 469             || rhs_result
 470                 .lines()
 471                 .next()
 472                 .map(|first_line| first_line.ends_with('{'))
 473                 .unwrap_or(false);
 474         if !rhs_result.contains('\n') || allow_same_line {
 475             let one_line_width = last_line_width(&lhs_result)
 476                 + pp.infix.len()
 477                 + first_line_width(rhs_result)
 478                 + pp.suffix.len();
 479             if one_line_width <= shape.width {
 480                 return Some(format!(
 481                     "{}{}{}{}",
 482                     lhs_result, pp.infix, rhs_result, pp.suffix
 483                 ));
 484             }
 485         }
 486     }
 487
 488     // We have to use multiple lines.
 489     // Re-evaluate the rhs because we have more space now:
 490     let mut rhs_shape = match context.config.indent_style() {
 491         IndentStyle::Visual => shape
 492             .sub_width(pp.suffix.len() + pp.prefix.len())?
 493             .visual_indent(pp.prefix.len()),
 494         IndentStyle::Block => {
 495             // Try to calculate the initial constraint on the right hand side.
 496             let rhs_overhead = shape.rhs_overhead(context.config);
 497             Shape::indented(shape.indent.block_indent(context.config), context.config)
 498                 .sub_width(rhs_overhead)?
 499         }
 500     };
 501     let infix = match separator_place {
 502         SeparatorPlace::Back => pp.infix.trim_right(),
 503         SeparatorPlace::Front => pp.infix.trim_left(),
 504     };
 505     if separator_place == SeparatorPlace::Front {
 506         rhs_shape = rhs_shape.offset_left(infix.len())?;
 507     }
 508     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 509     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 510     let infix_with_sep = match separator_place {
 511         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 512         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 513     };
 514     Some(format!(
 515         "{}{}{}{}",
 516         lhs_result, infix_with_sep, rhs_result, pp.suffix
 517     ))
 518 }
 519
 520 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 521     name: &str,
 522     exprs: &[&T],
 523     span: Span,
 524     context: &RewriteContext,
 525     shape: Shape,
 526     force_separator_tactic: Option<SeparatorTactic>,
 527     delim_token: Option<DelimToken>,
 528 ) -> Option<String> {
 529     overflow::rewrite_with_square_brackets(
 530         context,
 531         name,
 532         exprs,
 533         shape,
 534         span,
 535         force_separator_tactic,
 536         delim_token,
 537     )
 538 }
 539
 540 fn rewrite_empty_block(
 541     context: &RewriteContext,
 542     block: &ast::Block,
 543     attrs: Option<&[ast::Attribute]>,
 544     prefix: &str,
 545     shape: Shape,
 546 ) -> Option<String> {
 547     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 548         return None;
 549     }
 550
 551     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 552     {
 553         return Some(format!("{}{{}}", prefix));
 554     }
 555
 556     // If a block contains only a single-line comment, then leave it on one line.
 557     let user_str = context.snippet(block.span);
 558     let user_str = user_str.trim();
 559     if user_str.starts_with('{') && user_str.ends_with('}') {
 560         let comment_str = user_str[1..user_str.len() - 1].trim();
 561         if block.stmts.is_empty()
 562             && !comment_str.contains('\n')
 563             && !comment_str.starts_with("//")
 564             && comment_str.len() + 4 <= shape.width
 565         {
 566             return Some(format!("{}{{ {} }}", prefix, comment_str));
 567         }
 568     }
 569
 570     None
 571 }
 572
 573 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 574     Some(match block.rules {
 575         ast::BlockCheckMode::Unsafe(..) => {
 576             let snippet = context.snippet(block.span);
 577             let open_pos = snippet.find_uncommented("{")?;
 578             // Extract comment between unsafe and block start.
 579             let trimmed = &snippet[6..open_pos].trim();
 580
 581             if !trimmed.is_empty() {
 582                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 583                 let budget = shape.width.checked_sub(9)?;
 584                 format!(
 585                     "unsafe {} ",
 586                     rewrite_comment(
 587                         trimmed,
 588                         true,
 589                         Shape::legacy(budget, shape.indent + 7),
 590                         context.config,
 591                     )?
 592                 )
 593             } else {
 594                 "unsafe ".to_owned()
 595             }
 596         }
 597         ast::BlockCheckMode::Default => String::new(),
 598     })
 599 }
 600
 601 fn rewrite_single_line_block(
 602     context: &RewriteContext,
 603     prefix: &str,
 604     block: &ast::Block,
 605     attrs: Option<&[ast::Attribute]>,
 606     shape: Shape,
 607 ) -> Option<String> {
 608     if is_simple_block(block, attrs, context.codemap) {
 609         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 610         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 611         let result = format!("{}{{ {} }}", prefix, expr_str);
 612         if result.len() <= shape.width && !result.contains('\n') {
 613             return Some(result);
 614         }
 615     }
 616     None
 617 }
 618
 619 pub fn rewrite_block_with_visitor(
 620     context: &RewriteContext,
 621     prefix: &str,
 622     block: &ast::Block,
 623     attrs: Option<&[ast::Attribute]>,
 624     shape: Shape,
 625     has_braces: bool,
 626 ) -> Option<String> {
 627     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, prefix, shape) {
 628         return rw;
 629     }
 630
 631     let mut visitor = FmtVisitor::from_context(context);
 632     visitor.block_indent = shape.indent;
 633     visitor.is_if_else_block = context.is_if_else_block();
 634     match block.rules {
 635         ast::BlockCheckMode::Unsafe(..) => {
 636             let snippet = context.snippet(block.span);
 637             let open_pos = snippet.find_uncommented("{")?;
 638             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 639         }
 640         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 641     }
 642
 643     let inner_attrs = attrs.map(inner_attributes);
 644     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 645     Some(format!("{}{}", prefix, visitor.buffer))
 646 }
 647
 648 impl Rewrite for ast::Block {
 649     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 650         rewrite_block(self, None, None, context, shape)
 651     }
 652 }
 653
 654 fn rewrite_block(
 655     block: &ast::Block,
 656     attrs: Option<&[ast::Attribute]>,
 657     label: Option<ast::Label>,
 658     context: &RewriteContext,
 659     shape: Shape,
 660 ) -> Option<String> {
 661     let unsafe_string = block_prefix(context, block, shape)?;
 662     let label_string = rewrite_label(label);
 663     let prefix = format!("{}{}", unsafe_string, label_string);
 664
 665     // shape.width is used only for the single line case: either the empty block `{}`,
 666     // or an unsafe expression `unsafe { e }`.
 667     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, &prefix, shape) {
 668         return rw;
 669     }
 670
 671     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, shape, true);
 672     if let Some(ref result_str) = result {
 673         if result_str.lines().count() <= 3 {
 674             if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, block, attrs, shape) {
 675                 return rw;
 676             }
 677         }
 678     }
 679
 680     result
 681 }
 682
 683 impl Rewrite for ast::Stmt {
 684     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 685         skip_out_of_file_lines_range!(context, self.span());
 686
 687         let result = match self.node {
 688             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 689             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 690                 let suffix = if semicolon_for_stmt(context, self) {
 691                     ";"
 692                 } else {
 693                     ""
 694                 };
 695
 696                 let shape = shape.sub_width(suffix.len())?;
 697                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 698             }
 699             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 700         };
 701         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 702     }
 703 }
 704
 705 // Rewrite condition if the given expression has one.
 706 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 707     match expr.node {
 708         ast::ExprKind::Match(ref cond, _) => {
 709             // `match `cond` {`
 710             let cond_shape = match context.config.indent_style() {
 711                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 712                 IndentStyle::Block => shape.offset_left(8)?,
 713             };
 714             cond.rewrite(context, cond_shape)
 715         }
 716         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 717             let alt_block_sep =
 718                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 719             control_flow
 720                 .rewrite_cond(context, shape, &alt_block_sep)
 721                 .and_then(|rw| Some(rw.0))
 722         }),
 723     }
 724 }
 725
 726 // Abstraction over control flow expressions
 727 #[derive(Debug)]
 728 struct ControlFlow<'a> {
 729     cond: Option<&'a ast::Expr>,
 730     block: &'a ast::Block,
 731     else_block: Option<&'a ast::Expr>,
 732     label: Option<ast::Label>,
 733     pats: Vec<&'a ast::Pat>,
 734     keyword: &'a str,
 735     matcher: &'a str,
 736     connector: &'a str,
 737     allow_single_line: bool,
 738     // True if this is an `if` expression in an `else if` :-( hacky
 739     nested_if: bool,
 740     span: Span,
 741 }
 742
 743 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 744     match expr.node {
 745         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 746             cond,
 747             vec![],
 748             if_block,
 749             else_block.as_ref().map(|e| &**e),
 750             expr_type == ExprType::SubExpression,
 751             false,
 752             expr.span,
 753         )),
 754         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 755             Some(ControlFlow::new_if(
 756                 cond,
 757                 ptr_vec_to_ref_vec(pat),
 758                 if_block,
 759                 else_block.as_ref().map(|e| &**e),
 760                 expr_type == ExprType::SubExpression,
 761                 false,
 762                 expr.span,
 763             ))
 764         }
 765         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 766             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 767         }
 768         ast::ExprKind::Loop(ref block, label) => {
 769             Some(ControlFlow::new_loop(block, label, expr.span))
 770         }
 771         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 772             vec![],
 773             cond,
 774             block,
 775             label,
 776             expr.span,
 777         )),
 778         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 779             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 780         ),
 781         _ => None,
 782     }
 783 }
 784
 785 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 786     if pats.is_empty() {
 787         ""
 788     } else {
 789         "let"
 790     }
 791 }
 792
 793 impl<'a> ControlFlow<'a> {
 794     fn new_if(
 795         cond: &'a ast::Expr,
 796         pats: Vec<&'a ast::Pat>,
 797         block: &'a ast::Block,
 798         else_block: Option<&'a ast::Expr>,
 799         allow_single_line: bool,
 800         nested_if: bool,
 801         span: Span,
 802     ) -> ControlFlow<'a> {
 803         let matcher = choose_matcher(&pats);
 804         ControlFlow {
 805             cond: Some(cond),
 806             block,
 807             else_block,
 808             label: None,
 809             pats,
 810             keyword: "if",
 811             matcher,
 812             connector: " =",
 813             allow_single_line,
 814             nested_if,
 815             span,
 816         }
 817     }
 818
 819     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 820         ControlFlow {
 821             cond: None,
 822             block,
 823             else_block: None,
 824             label,
 825             pats: vec![],
 826             keyword: "loop",
 827             matcher: "",
 828             connector: "",
 829             allow_single_line: false,
 830             nested_if: false,
 831             span,
 832         }
 833     }
 834
 835     fn new_while(
 836         pats: Vec<&'a ast::Pat>,
 837         cond: &'a ast::Expr,
 838         block: &'a ast::Block,
 839         label: Option<ast::Label>,
 840         span: Span,
 841     ) -> ControlFlow<'a> {
 842         let matcher = choose_matcher(&pats);
 843         ControlFlow {
 844             cond: Some(cond),
 845             block,
 846             else_block: None,
 847             label,
 848             pats,
 849             keyword: "while",
 850             matcher,
 851             connector: " =",
 852             allow_single_line: false,
 853             nested_if: false,
 854             span,
 855         }
 856     }
 857
 858     fn new_for(
 859         pat: &'a ast::Pat,
 860         cond: &'a ast::Expr,
 861         block: &'a ast::Block,
 862         label: Option<ast::Label>,
 863         span: Span,
 864     ) -> ControlFlow<'a> {
 865         ControlFlow {
 866             cond: Some(cond),
 867             block,
 868             else_block: None,
 869             label,
 870             pats: vec![pat],
 871             keyword: "for",
 872             matcher: "",
 873             connector: " in",
 874             allow_single_line: false,
 875             nested_if: false,
 876             span,
 877         }
 878     }
 879
 880     fn rewrite_single_line(
 881         &self,
 882         pat_expr_str: &str,
 883         context: &RewriteContext,
 884         width: usize,
 885     ) -> Option<String> {
 886         assert!(self.allow_single_line);
 887         let else_block = self.else_block?;
 888         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 889
 890         if let ast::ExprKind::Block(ref else_node, _) = else_block.node {
 891             if !is_simple_block(self.block, None, context.codemap)
 892                 || !is_simple_block(else_node, None, context.codemap)
 893                 || pat_expr_str.contains('\n')
 894             {
 895                 return None;
 896             }
 897
 898             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 899             let expr = &self.block.stmts[0];
 900             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 901
 902             let new_width = new_width.checked_sub(if_str.len())?;
 903             let else_expr = &else_node.stmts[0];
 904             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 905
 906             if if_str.contains('\n') || else_str.contains('\n') {
 907                 return None;
 908             }
 909
 910             let result = format!(
 911                 "{} {} {{ {} }} else {{ {} }}",
 912                 self.keyword, pat_expr_str, if_str, else_str
 913             );
 914
 915             if result.len() <= width {
 916                 return Some(result);
 917             }
 918         }
 919
 920         None
 921     }
 922 }
 923
 924 impl<'a> ControlFlow<'a> {
 925     fn rewrite_pat_expr(
 926         &self,
 927         context: &RewriteContext,
 928         expr: &ast::Expr,
 929         shape: Shape,
 930         offset: usize,
 931     ) -> Option<String> {
 932         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 933
 934         let cond_shape = shape.offset_left(offset)?;
 935         if !self.pats.is_empty() {
 936             let matcher = if self.matcher.is_empty() {
 937                 self.matcher.to_owned()
 938             } else {
 939                 format!("{} ", self.matcher)
 940             };
 941             let pat_shape = cond_shape
 942                 .offset_left(matcher.len())?
 943                 .sub_width(self.connector.len())?;
 944             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 945             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 946             return rewrite_assign_rhs(context, result, expr, cond_shape);
 947         }
 948
 949         let expr_rw = expr.rewrite(context, cond_shape);
 950         // The expression may (partially) fit on the current line.
 951         // We do not allow splitting between `if` and condition.
 952         if self.keyword == "if" || expr_rw.is_some() {
 953             return expr_rw;
 954         }
 955
 956         // The expression won't fit on the current line, jump to next.
 957         let nested_shape = shape
 958             .block_indent(context.config.tab_spaces())
 959             .with_max_width(context.config);
 960         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 961         expr.rewrite(context, nested_shape)
 962             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 963     }
 964
 965     fn rewrite_cond(
 966         &self,
 967         context: &RewriteContext,
 968         shape: Shape,
 969         alt_block_sep: &str,
 970     ) -> Option<(String, usize)> {
 971         // Do not take the rhs overhead from the upper expressions into account
 972         // when rewriting pattern.
 973         let new_width = context.budget(shape.used_width());
 974         let fresh_shape = Shape {
 975             width: new_width,
 976             ..shape
 977         };
 978         let constr_shape = if self.nested_if {
 979             // We are part of an if-elseif-else chain. Our constraints are tightened.
 980             // 7 = "} else " .len()
 981             fresh_shape.offset_left(7)?
 982         } else {
 983             fresh_shape
 984         };
 985
 986         let label_string = rewrite_label(self.label);
 987         // 1 = space after keyword.
 988         let offset = self.keyword.len() + label_string.len() + 1;
 989
 990         let pat_expr_string = match self.cond {
 991             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 992             None => String::new(),
 993         };
 994
 995         let brace_overhead =
 996             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 997                 // 2 = ` {`
 998                 2
 999             } else {
1000                 0
1001             };
1002         let one_line_budget = context
1003             .config
1004             .max_width()
1005             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
1006         let force_newline_brace = (pat_expr_string.contains('\n')
1007             || pat_expr_string.len() > one_line_budget)
1008             && !last_line_extendable(&pat_expr_string);
1009
1010         // Try to format if-else on single line.
1011         if self.allow_single_line
1012             && context
1013                 .config
1014                 .width_heuristics()
1015                 .single_line_if_else_max_width > 0
1016         {
1017             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1018
1019             if let Some(cond_str) = trial {
1020                 if cond_str.len()
1021                     <= context
1022                         .config
1023                         .width_heuristics()
1024                         .single_line_if_else_max_width
1025                 {
1026                     return Some((cond_str, 0));
1027                 }
1028             }
1029         }
1030
1031         let cond_span = if let Some(cond) = self.cond {
1032             cond.span
1033         } else {
1034             mk_sp(self.block.span.lo(), self.block.span.lo())
1035         };
1036
1037         // `for event in event`
1038         // Do not include label in the span.
1039         let lo = self
1040             .label
1041             .map_or(self.span.lo(), |label| label.ident.span.hi());
1042         let between_kwd_cond = mk_sp(
1043             context
1044                 .snippet_provider
1045                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1046             if self.pats.is_empty() {
1047                 cond_span.lo()
1048             } else if self.matcher.is_empty() {
1049                 self.pats[0].span.lo()
1050             } else {
1051                 context
1052                     .snippet_provider
1053                     .span_before(self.span, self.matcher.trim())
1054             },
1055         );
1056
1057         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1058
1059         let after_cond_comment =
1060             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1061
1062         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1063             ""
1064         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1065             || force_newline_brace
1066         {
1067             alt_block_sep
1068         } else {
1069             " "
1070         };
1071
1072         let used_width = if pat_expr_string.contains('\n') {
1073             last_line_width(&pat_expr_string)
1074         } else {
1075             // 2 = spaces after keyword and condition.
1076             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1077         };
1078
1079         Some((
1080             format!(
1081                 "{}{}{}{}{}",
1082                 label_string,
1083                 self.keyword,
1084                 between_kwd_cond_comment.as_ref().map_or(
1085                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1086                         ""
1087                     } else {
1088                         " "
1089                     },
1090                     |s| &**s,
1091                 ),
1092                 pat_expr_string,
1093                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1094             ),
1095             used_width,
1096         ))
1097     }
1098 }
1099
1100 impl<'a> Rewrite for ControlFlow<'a> {
1101     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1102         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1103
1104         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1105         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1106         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1107         if used_width == 0 {
1108             return Some(cond_str);
1109         }
1110
1111         let block_width = shape.width.saturating_sub(used_width);
1112         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1113         // we should avoid the single line case.
1114         let block_width = if self.else_block.is_some() || self.nested_if {
1115             min(1, block_width)
1116         } else {
1117             block_width
1118         };
1119         let block_shape = Shape {
1120             width: block_width,
1121             ..shape
1122         };
1123         let block_str = {
1124             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1125             let result =
1126                 rewrite_block_with_visitor(context, "", self.block, None, block_shape, true);
1127             context.is_if_else_block.replace(old_val);
1128             result?
1129         };
1130
1131         let mut result = format!("{}{}", cond_str, block_str);
1132
1133         if let Some(else_block) = self.else_block {
1134             let shape = Shape::indented(shape.indent, context.config);
1135             let mut last_in_chain = false;
1136             let rewrite = match else_block.node {
1137                 // If the else expression is another if-else expression, prevent it
1138                 // from being formatted on a single line.
1139                 // Note how we're passing the original shape, as the
1140                 // cost of "else" should not cascade.
1141                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1142                     ControlFlow::new_if(
1143                         cond,
1144                         ptr_vec_to_ref_vec(pat),
1145                         if_block,
1146                         next_else_block.as_ref().map(|e| &**e),
1147                         false,
1148                         true,
1149                         mk_sp(else_block.span.lo(), self.span.hi()),
1150                     ).rewrite(context, shape)
1151                 }
1152                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1153                     ControlFlow::new_if(
1154                         cond,
1155                         vec![],
1156                         if_block,
1157                         next_else_block.as_ref().map(|e| &**e),
1158                         false,
1159                         true,
1160                         mk_sp(else_block.span.lo(), self.span.hi()),
1161                     ).rewrite(context, shape)
1162                 }
1163                 _ => {
1164                     last_in_chain = true;
1165                     // When rewriting a block, the width is only used for single line
1166                     // blocks, passing 1 lets us avoid that.
1167                     let else_shape = Shape {
1168                         width: min(1, shape.width),
1169                         ..shape
1170                     };
1171                     format_expr(else_block, ExprType::Statement, context, else_shape)
1172                 }
1173             };
1174
1175             let between_kwd_else_block = mk_sp(
1176                 self.block.span.hi(),
1177                 context
1178                     .snippet_provider
1179                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1180             );
1181             let between_kwd_else_block_comment =
1182                 extract_comment(between_kwd_else_block, context, shape);
1183
1184             let after_else = mk_sp(
1185                 context
1186                     .snippet_provider
1187                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1188                 else_block.span.lo(),
1189             );
1190             let after_else_comment = extract_comment(after_else, context, shape);
1191
1192             let between_sep = match context.config.control_brace_style() {
1193                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1194                     &*alt_block_sep
1195                 }
1196                 ControlBraceStyle::AlwaysSameLine => " ",
1197             };
1198             let after_sep = match context.config.control_brace_style() {
1199                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1200                 _ => " ",
1201             };
1202
1203             result.push_str(&format!(
1204                 "{}else{}",
1205                 between_kwd_else_block_comment
1206                     .as_ref()
1207                     .map_or(between_sep, |s| &**s),
1208                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1209             ));
1210             result.push_str(&rewrite?);
1211         }
1212
1213         Some(result)
1214     }
1215 }
1216
1217 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1218     match opt_label {
1219         Some(label) => Cow::from(format!("{}: ", label.ident)),
1220         None => Cow::from(""),
1221     }
1222 }
1223
1224 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1225     match rewrite_missing_comment(span, shape, context) {
1226         Some(ref comment) if !comment.is_empty() => Some(format!(
1227             "{indent}{}{indent}",
1228             comment,
1229             indent = shape.indent.to_string_with_newline(context.config)
1230         )),
1231         _ => None,
1232     }
1233 }
1234
1235 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1236     let snippet = codemap.span_to_snippet(block.span).unwrap();
1237     contains_comment(&snippet)
1238 }
1239
1240 // Checks that a block contains no statements, an expression and no comments or
1241 // attributes.
1242 // FIXME: incorrectly returns false when comment is contained completely within
1243 // the expression.
1244 pub fn is_simple_block(
1245     block: &ast::Block,
1246     attrs: Option<&[ast::Attribute]>,
1247     codemap: &CodeMap,
1248 ) -> bool {
1249     (block.stmts.len() == 1
1250         && stmt_is_expr(&block.stmts[0])
1251         && !block_contains_comment(block, codemap)
1252         && attrs.map_or(true, |a| a.is_empty()))
1253 }
1254
1255 /// Checks whether a block contains at most one statement or expression, and no
1256 /// comments or attributes.
1257 pub fn is_simple_block_stmt(
1258     block: &ast::Block,
1259     attrs: Option<&[ast::Attribute]>,
1260     codemap: &CodeMap,
1261 ) -> bool {
1262     block.stmts.len() <= 1
1263         && !block_contains_comment(block, codemap)
1264         && attrs.map_or(true, |a| a.is_empty())
1265 }
1266
1267 /// Checks whether a block contains no statements, expressions, comments, or
1268 /// inner attributes.
1269 pub fn is_empty_block(
1270     block: &ast::Block,
1271     attrs: Option<&[ast::Attribute]>,
1272     codemap: &CodeMap,
1273 ) -> bool {
1274     block.stmts.is_empty()
1275         && !block_contains_comment(block, codemap)
1276         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1277 }
1278
1279 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1280     match stmt.node {
1281         ast::StmtKind::Expr(..) => true,
1282         _ => false,
1283     }
1284 }
1285
1286 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1287     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1288         true
1289     } else {
1290         false
1291     }
1292 }
1293
1294 pub fn rewrite_multiple_patterns(
1295     context: &RewriteContext,
1296     pats: &[&ast::Pat],
1297     shape: Shape,
1298 ) -> Option<String> {
1299     let pat_strs = pats
1300         .iter()
1301         .map(|p| p.rewrite(context, shape))
1302         .collect::<Option<Vec<_>>>()?;
1303
1304     let use_mixed_layout = pats
1305         .iter()
1306         .zip(pat_strs.iter())
1307         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1308     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1309     let tactic = if use_mixed_layout {
1310         DefinitiveListTactic::Mixed
1311     } else {
1312         definitive_tactic(
1313             &items,
1314             ListTactic::HorizontalVertical,
1315             Separator::VerticalBar,
1316             shape.width,
1317         )
1318     };
1319     let fmt = ListFormatting {
1320         tactic,
1321         separator: " |",
1322         trailing_separator: SeparatorTactic::Never,
1323         separator_place: context.config.binop_separator(),
1324         shape,
1325         ends_with_newline: false,
1326         preserve_newline: false,
1327         config: context.config,
1328     };
1329     write_list(&items, &fmt)
1330 }
1331
1332 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1333     match l.node {
1334         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1335         _ => wrap_str(
1336             context.snippet(l.span).to_owned(),
1337             context.config.max_width(),
1338             shape,
1339         ),
1340     }
1341 }
1342
1343 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1344     let string_lit = context.snippet(span);
1345
1346     if !context.config.format_strings() {
1347         if string_lit
1348             .lines()
1349             .rev()
1350             .skip(1)
1351             .all(|line| line.ends_with('\\'))
1352         {
1353             let new_indent = shape.visual_indent(1).indent;
1354             let indented_string_lit = String::from(
1355                 string_lit
1356                     .lines()
1357                     .map(|line| {
1358                         format!(
1359                             "{}{}",
1360                             new_indent.to_string(context.config),
1361                             line.trim_left()
1362                         )
1363                     })
1364                     .collect::<Vec<_>>()
1365                     .join("\n")
1366                     .trim_left(),
1367             );
1368             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1369         } else {
1370             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1371         }
1372     }
1373
1374     // Remove the quote characters.
1375     let str_lit = &string_lit[1..string_lit.len() - 1];
1376
1377     rewrite_string(
1378         str_lit,
1379         &StringFormat::new(shape.visual_indent(0), context.config),
1380         None,
1381     )
1382 }
1383
1384 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1385 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1386     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1387         .iter()
1388         .find(|&&(s, _)| s == callee_str)
1389     {
1390         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1391
1392         Some((all_simple, num_args_before))
1393     } else {
1394         None
1395     }
1396 }
1397
1398 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1399 /// format.
1400 ///
1401 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1402 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1403 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1404 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1405     // format! like macros
1406     // From the Rust Standard Library.
1407     ("eprint!", 0),
1408     ("eprintln!", 0),
1409     ("format!", 0),
1410     ("format_args!", 0),
1411     ("print!", 0),
1412     ("println!", 0),
1413     ("panic!", 0),
1414     ("unreachable!", 0),
1415     // From the `log` crate.
1416     ("debug!", 0),
1417     ("error!", 0),
1418     ("info!", 0),
1419     ("warn!", 0),
1420     // write! like macros
1421     ("assert!", 1),
1422     ("debug_assert!", 1),
1423     ("write!", 1),
1424     ("writeln!", 1),
1425     // assert_eq! like macros
1426     ("assert_eq!", 2),
1427     ("assert_ne!", 2),
1428     ("debug_assert_eq!", 2),
1429     ("debug_assert_ne!", 2),
1430 ];
1431
1432 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1433     if context.inside_macro() {
1434         if span_ends_with_comma(context, span) {
1435             Some(SeparatorTactic::Always)
1436         } else {
1437             Some(SeparatorTactic::Never)
1438         }
1439     } else {
1440         None
1441     }
1442 }
1443
1444 pub fn rewrite_call(
1445     context: &RewriteContext,
1446     callee: &str,
1447     args: &[ptr::P<ast::Expr>],
1448     span: Span,
1449     shape: Shape,
1450 ) -> Option<String> {
1451     overflow::rewrite_with_parens(
1452         context,
1453         callee,
1454         &ptr_vec_to_ref_vec(args),
1455         shape,
1456         span,
1457         context.config.width_heuristics().fn_call_width,
1458         choose_separator_tactic(context, span),
1459     )
1460 }
1461
1462 fn is_simple_expr(expr: &ast::Expr) -> bool {
1463     match expr.node {
1464         ast::ExprKind::Lit(..) => true,
1465         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1466         ast::ExprKind::AddrOf(_, ref expr)
1467         | ast::ExprKind::Box(ref expr)
1468         | ast::ExprKind::Cast(ref expr, _)
1469         | ast::ExprKind::Field(ref expr, _)
1470         | ast::ExprKind::Try(ref expr)
1471         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1472         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1473             is_simple_expr(lhs) && is_simple_expr(rhs)
1474         }
1475         _ => false,
1476     }
1477 }
1478
1479 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1480     lists
1481         .iter()
1482         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1483 }
1484
1485 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1486     match expr.node {
1487         ast::ExprKind::Match(..) => {
1488             (context.use_block_indent() && args_len == 1)
1489                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1490         }
1491         ast::ExprKind::If(..)
1492         | ast::ExprKind::IfLet(..)
1493         | ast::ExprKind::ForLoop(..)
1494         | ast::ExprKind::Loop(..)
1495         | ast::ExprKind::While(..)
1496         | ast::ExprKind::WhileLet(..) => {
1497             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1498         }
1499         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1500             context.use_block_indent()
1501                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1502         }
1503         ast::ExprKind::Array(..)
1504         | ast::ExprKind::Call(..)
1505         | ast::ExprKind::Mac(..)
1506         | ast::ExprKind::MethodCall(..)
1507         | ast::ExprKind::Struct(..)
1508         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1509         ast::ExprKind::AddrOf(_, ref expr)
1510         | ast::ExprKind::Box(ref expr)
1511         | ast::ExprKind::Try(ref expr)
1512         | ast::ExprKind::Unary(_, ref expr)
1513         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1514         _ => false,
1515     }
1516 }
1517
1518 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1519     match expr.node {
1520         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1521         ast::ExprKind::AddrOf(_, ref expr)
1522         | ast::ExprKind::Box(ref expr)
1523         | ast::ExprKind::Try(ref expr)
1524         | ast::ExprKind::Unary(_, ref expr)
1525         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1526         _ => false,
1527     }
1528 }
1529
1530 /// Return true if a function call or a method call represented by the given span ends with a
1531 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1532 /// comma from macro can potentially break the code.
1533 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1534     let mut result: bool = Default::default();
1535     let mut prev_char: char = Default::default();
1536     let closing_delimiters = &[')', '}', ']'];
1537
1538     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1539         match c {
1540             _ if kind.is_comment() || c.is_whitespace() => continue,
1541             c if closing_delimiters.contains(&c) => {
1542                 result &= !closing_delimiters.contains(&prev_char);
1543             }
1544             ',' => result = true,
1545             _ => result = false,
1546         }
1547         prev_char = c;
1548     }
1549
1550     result
1551 }
1552
1553 fn rewrite_paren(
1554     context: &RewriteContext,
1555     mut subexpr: &ast::Expr,
1556     shape: Shape,
1557     mut span: Span,
1558 ) -> Option<String> {
1559     debug!("rewrite_paren, shape: {:?}", shape);
1560
1561     // Extract comments within parens.
1562     let mut pre_comment;
1563     let mut post_comment;
1564     let remove_nested_parens = context.config.remove_nested_parens();
1565     loop {
1566         // 1 = "(" or ")"
1567         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1568         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1569         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1570         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1571
1572         // Remove nested parens if there are no comments.
1573         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1574             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1575                 span = subexpr.span;
1576                 subexpr = subsubexpr;
1577                 continue;
1578             }
1579         }
1580
1581         break;
1582     }
1583
1584     // 1 `(`
1585     let sub_shape = shape.offset_left(1).and_then(|s| s.sub_width(1))?;
1586
1587     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1588     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1589
1590     // 2 = `()`
1591     if subexpr_str.contains('\n') || first_line_width(&subexpr_str) + 2 <= shape.width {
1592         Some(format!("({}{}{})", pre_comment, &subexpr_str, post_comment))
1593     } else {
1594         None
1595     }
1596 }
1597
1598 fn rewrite_index(
1599     expr: &ast::Expr,
1600     index: &ast::Expr,
1601     context: &RewriteContext,
1602     shape: Shape,
1603 ) -> Option<String> {
1604     let expr_str = expr.rewrite(context, shape)?;
1605
1606     let offset = last_line_width(&expr_str) + 1;
1607     let rhs_overhead = shape.rhs_overhead(context.config);
1608     let index_shape = if expr_str.contains('\n') {
1609         Shape::legacy(context.config.max_width(), shape.indent)
1610             .offset_left(offset)
1611             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1612     } else {
1613         shape.visual_indent(offset).sub_width(offset + 1)
1614     };
1615     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1616
1617     // Return if index fits in a single line.
1618     match orig_index_rw {
1619         Some(ref index_str) if !index_str.contains('\n') => {
1620             return Some(format!("{}[{}]", expr_str, index_str));
1621         }
1622         _ => (),
1623     }
1624
1625     // Try putting index on the next line and see if it fits in a single line.
1626     let indent = shape.indent.block_indent(context.config);
1627     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1628     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1629     let new_index_rw = index.rewrite(context, index_shape);
1630     match (orig_index_rw, new_index_rw) {
1631         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1632             "{}{}[{}]",
1633             expr_str,
1634             indent.to_string_with_newline(context.config),
1635             new_index_str,
1636         )),
1637         (None, Some(ref new_index_str)) => Some(format!(
1638             "{}{}[{}]",
1639             expr_str,
1640             indent.to_string_with_newline(context.config),
1641             new_index_str,
1642         )),
1643         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1644         _ => None,
1645     }
1646 }
1647
1648 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1649     if base.is_some() {
1650         return false;
1651     }
1652
1653     fields.iter().all(|field| !field.is_shorthand)
1654 }
1655
1656 fn rewrite_struct_lit<'a>(
1657     context: &RewriteContext,
1658     path: &ast::Path,
1659     fields: &'a [ast::Field],
1660     base: Option<&'a ast::Expr>,
1661     span: Span,
1662     shape: Shape,
1663 ) -> Option<String> {
1664     debug!("rewrite_struct_lit: shape {:?}", shape);
1665
1666     enum StructLitField<'a> {
1667         Regular(&'a ast::Field),
1668         Base(&'a ast::Expr),
1669     }
1670
1671     // 2 = " {".len()
1672     let path_shape = shape.sub_width(2)?;
1673     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1674
1675     if fields.is_empty() && base.is_none() {
1676         return Some(format!("{} {{}}", path_str));
1677     }
1678
1679     // Foo { a: Foo } - indent is +3, width is -5.
1680     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1681
1682     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1683     let body_lo = context.snippet_provider.span_after(span, "{");
1684     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1685         && context.config.struct_field_align_threshold() > 0
1686     {
1687         rewrite_with_alignment(
1688             fields,
1689             context,
1690             shape,
1691             mk_sp(body_lo, span.hi()),
1692             one_line_width,
1693         )?
1694     } else {
1695         let field_iter = fields
1696             .into_iter()
1697             .map(StructLitField::Regular)
1698             .chain(base.into_iter().map(StructLitField::Base));
1699
1700         let span_lo = |item: &StructLitField| match *item {
1701             StructLitField::Regular(field) => field.span().lo(),
1702             StructLitField::Base(expr) => {
1703                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1704                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1705                 let pos = snippet.find_uncommented("..").unwrap();
1706                 last_field_hi + BytePos(pos as u32)
1707             }
1708         };
1709         let span_hi = |item: &StructLitField| match *item {
1710             StructLitField::Regular(field) => field.span().hi(),
1711             StructLitField::Base(expr) => expr.span.hi(),
1712         };
1713         let rewrite = |item: &StructLitField| match *item {
1714             StructLitField::Regular(field) => {
1715                 // The 1 taken from the v_budget is for the comma.
1716                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1717             }
1718             StructLitField::Base(expr) => {
1719                 // 2 = ..
1720                 expr.rewrite(context, v_shape.offset_left(2)?)
1721                     .map(|s| format!("..{}", s))
1722             }
1723         };
1724
1725         let items = itemize_list(
1726             context.snippet_provider,
1727             field_iter,
1728             "}",
1729             ",",
1730             span_lo,
1731             span_hi,
1732             rewrite,
1733             body_lo,
1734             span.hi(),
1735             false,
1736         );
1737         let item_vec = items.collect::<Vec<_>>();
1738
1739         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1740         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1741
1742         let ends_with_comma = span_ends_with_comma(context, span);
1743         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1744
1745         let fmt = struct_lit_formatting(
1746             nested_shape,
1747             tactic,
1748             context,
1749             force_no_trailing_comma || base.is_some(),
1750         );
1751
1752         write_list(&item_vec, &fmt)?
1753     };
1754
1755     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1756     Some(format!("{} {{{}}}", path_str, fields_str))
1757
1758     // FIXME if context.config.indent_style() == Visual, but we run out
1759     // of space, we should fall back to BlockIndent.
1760 }
1761
1762 pub fn wrap_struct_field(
1763     context: &RewriteContext,
1764     fields_str: &str,
1765     shape: Shape,
1766     nested_shape: Shape,
1767     one_line_width: usize,
1768 ) -> String {
1769     if context.config.indent_style() == IndentStyle::Block
1770         && (fields_str.contains('\n')
1771             || !context.config.struct_lit_single_line()
1772             || fields_str.len() > one_line_width)
1773     {
1774         format!(
1775             "{}{}{}",
1776             nested_shape.indent.to_string_with_newline(context.config),
1777             fields_str,
1778             shape.indent.to_string_with_newline(context.config)
1779         )
1780     } else {
1781         // One liner or visual indent.
1782         format!(" {} ", fields_str)
1783     }
1784 }
1785
1786 pub fn struct_lit_field_separator(config: &Config) -> &str {
1787     colon_spaces(config.space_before_colon(), config.space_after_colon())
1788 }
1789
1790 pub fn rewrite_field(
1791     context: &RewriteContext,
1792     field: &ast::Field,
1793     shape: Shape,
1794     prefix_max_width: usize,
1795 ) -> Option<String> {
1796     if contains_skip(&field.attrs) {
1797         return Some(context.snippet(field.span()).to_owned());
1798     }
1799     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1800     if !attrs_str.is_empty() {
1801         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1802     };
1803     let name = &field.ident.name.to_string();
1804     if field.is_shorthand {
1805         Some(attrs_str + &name)
1806     } else {
1807         let mut separator = String::from(struct_lit_field_separator(context.config));
1808         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1809             separator.push(' ');
1810         }
1811         let overhead = name.len() + separator.len();
1812         let expr_shape = shape.offset_left(overhead)?;
1813         let expr = field.expr.rewrite(context, expr_shape);
1814
1815         match expr {
1816             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1817                 Some(attrs_str + &name)
1818             }
1819             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1820             None => {
1821                 let expr_offset = shape.indent.block_indent(context.config);
1822                 let expr = field
1823                     .expr
1824                     .rewrite(context, Shape::indented(expr_offset, context.config));
1825                 expr.map(|s| {
1826                     format!(
1827                         "{}{}:\n{}{}",
1828                         attrs_str,
1829                         name,
1830                         expr_offset.to_string(context.config),
1831                         s
1832                     )
1833                 })
1834             }
1835         }
1836     }
1837 }
1838
1839 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1840     context: &RewriteContext,
1841     items: &[&T],
1842     span: Span,
1843     shape: Shape,
1844 ) -> Option<String>
1845 where
1846     T: Rewrite + Spanned + ToExpr + 'a,
1847 {
1848     let mut items = items.iter();
1849     // In case of length 1, need a trailing comma
1850     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1851     if items.len() == 1 {
1852         // 3 = "(" + ",)"
1853         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1854         return items
1855             .next()
1856             .unwrap()
1857             .rewrite(context, nested_shape)
1858             .map(|s| format!("({},)", s));
1859     }
1860
1861     let list_lo = context.snippet_provider.span_after(span, "(");
1862     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1863     let items = itemize_list(
1864         context.snippet_provider,
1865         items,
1866         ")",
1867         ",",
1868         |item| item.span().lo(),
1869         |item| item.span().hi(),
1870         |item| item.rewrite(context, nested_shape),
1871         list_lo,
1872         span.hi() - BytePos(1),
1873         false,
1874     );
1875     let item_vec: Vec<_> = items.collect();
1876     let tactic = definitive_tactic(
1877         &item_vec,
1878         ListTactic::HorizontalVertical,
1879         Separator::Comma,
1880         nested_shape.width,
1881     );
1882     let fmt = ListFormatting {
1883         tactic,
1884         separator: ",",
1885         trailing_separator: SeparatorTactic::Never,
1886         separator_place: SeparatorPlace::Back,
1887         shape,
1888         ends_with_newline: false,
1889         preserve_newline: false,
1890         config: context.config,
1891     };
1892     let list_str = write_list(&item_vec, &fmt)?;
1893
1894     Some(format!("({})", list_str))
1895 }
1896
1897 pub fn rewrite_tuple<'a, T>(
1898     context: &RewriteContext,
1899     items: &[&T],
1900     span: Span,
1901     shape: Shape,
1902 ) -> Option<String>
1903 where
1904     T: Rewrite + Spanned + ToExpr + 'a,
1905 {
1906     debug!("rewrite_tuple {:?}", shape);
1907     if context.use_block_indent() {
1908         // We use the same rule as function calls for rewriting tuples.
1909         let force_tactic = if context.inside_macro() {
1910             if span_ends_with_comma(context, span) {
1911                 Some(SeparatorTactic::Always)
1912             } else {
1913                 Some(SeparatorTactic::Never)
1914             }
1915         } else if items.len() == 1 {
1916             Some(SeparatorTactic::Always)
1917         } else {
1918             None
1919         };
1920         overflow::rewrite_with_parens(
1921             context,
1922             "",
1923             items,
1924             shape,
1925             span,
1926             context.config.width_heuristics().fn_call_width,
1927             force_tactic,
1928         )
1929     } else {
1930         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1931     }
1932 }
1933
1934 pub fn rewrite_unary_prefix<R: Rewrite>(
1935     context: &RewriteContext,
1936     prefix: &str,
1937     rewrite: &R,
1938     shape: Shape,
1939 ) -> Option<String> {
1940     rewrite
1941         .rewrite(context, shape.offset_left(prefix.len())?)
1942         .map(|r| format!("{}{}", prefix, r))
1943 }
1944
1945 // FIXME: this is probably not correct for multi-line Rewrites. we should
1946 // subtract suffix.len() from the last line budget, not the first!
1947 pub fn rewrite_unary_suffix<R: Rewrite>(
1948     context: &RewriteContext,
1949     suffix: &str,
1950     rewrite: &R,
1951     shape: Shape,
1952 ) -> Option<String> {
1953     rewrite
1954         .rewrite(context, shape.sub_width(suffix.len())?)
1955         .map(|mut r| {
1956             r.push_str(suffix);
1957             r
1958         })
1959 }
1960
1961 fn rewrite_unary_op(
1962     context: &RewriteContext,
1963     op: &ast::UnOp,
1964     expr: &ast::Expr,
1965     shape: Shape,
1966 ) -> Option<String> {
1967     // For some reason, an UnOp is not spanned like BinOp!
1968     let operator_str = match *op {
1969         ast::UnOp::Deref => "*",
1970         ast::UnOp::Not => "!",
1971         ast::UnOp::Neg => "-",
1972     };
1973     rewrite_unary_prefix(context, operator_str, expr, shape)
1974 }
1975
1976 fn rewrite_assignment(
1977     context: &RewriteContext,
1978     lhs: &ast::Expr,
1979     rhs: &ast::Expr,
1980     op: Option<&ast::BinOp>,
1981     shape: Shape,
1982 ) -> Option<String> {
1983     let operator_str = match op {
1984         Some(op) => context.snippet(op.span),
1985         None => "=",
1986     };
1987
1988     // 1 = space between lhs and operator.
1989     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
1990     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
1991
1992     rewrite_assign_rhs(context, lhs_str, rhs, shape)
1993 }
1994
1995 /// Controls where to put the rhs.
1996 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1997 pub enum RhsTactics {
1998     /// Use heuristics.
1999     Default,
2000     /// Put the rhs on the next line if it uses multiple line.
2001     ForceNextLine,
2002 }
2003
2004 // The left hand side must contain everything up to, and including, the
2005 // assignment operator.
2006 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2007     context: &RewriteContext,
2008     lhs: S,
2009     ex: &R,
2010     shape: Shape,
2011 ) -> Option<String> {
2012     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2013 }
2014
2015 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2016     context: &RewriteContext,
2017     lhs: S,
2018     ex: &R,
2019     shape: Shape,
2020     rhs_tactics: RhsTactics,
2021 ) -> Option<String> {
2022     let lhs = lhs.into();
2023     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
2024         shape.indent.width()
2025     } else {
2026         0
2027     });
2028     // 1 = space between operator and rhs.
2029     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2030         width: 0,
2031         offset: shape.offset + last_line_width + 1,
2032         ..shape
2033     });
2034     let rhs = choose_rhs(
2035         context,
2036         ex,
2037         orig_shape,
2038         ex.rewrite(context, orig_shape),
2039         rhs_tactics,
2040     )?;
2041     Some(lhs + &rhs)
2042 }
2043
2044 fn choose_rhs<R: Rewrite>(
2045     context: &RewriteContext,
2046     expr: &R,
2047     shape: Shape,
2048     orig_rhs: Option<String>,
2049     rhs_tactics: RhsTactics,
2050 ) -> Option<String> {
2051     match orig_rhs {
2052         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2053             Some(format!(" {}", new_str))
2054         }
2055         _ => {
2056             // Expression did not fit on the same line as the identifier.
2057             // Try splitting the line and see if that works better.
2058             let new_shape =
2059                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2060                     .sub_width(shape.rhs_overhead(context.config))?;
2061             let new_rhs = expr.rewrite(context, new_shape);
2062             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2063
2064             match (orig_rhs, new_rhs) {
2065                 (Some(ref orig_rhs), Some(ref new_rhs))
2066                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2067                         .is_none() =>
2068                 {
2069                     Some(format!(" {}", orig_rhs))
2070                 }
2071                 (Some(ref orig_rhs), Some(ref new_rhs))
2072                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2073                 {
2074                     Some(format!("{}{}", new_indent_str, new_rhs))
2075                 }
2076                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2077                 (None, None) => None,
2078                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2079             }
2080         }
2081     }
2082 }
2083
2084 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2085     rhs_tactics == RhsTactics::ForceNextLine
2086         || !next_line_rhs.contains('\n')
2087         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2088 }
2089
2090 fn rewrite_expr_addrof(
2091     context: &RewriteContext,
2092     mutability: ast::Mutability,
2093     expr: &ast::Expr,
2094     shape: Shape,
2095 ) -> Option<String> {
2096     let operator_str = match mutability {
2097         ast::Mutability::Immutable => "&",
2098         ast::Mutability::Mutable => "&mut ",
2099     };
2100     rewrite_unary_prefix(context, operator_str, expr, shape)
2101 }
2102
2103 pub trait ToExpr {
2104     fn to_expr(&self) -> Option<&ast::Expr>;
2105     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2106 }
2107
2108 impl ToExpr for ast::Expr {
2109     fn to_expr(&self) -> Option<&ast::Expr> {
2110         Some(self)
2111     }
2112
2113     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2114         can_be_overflowed_expr(context, self, len)
2115     }
2116 }
2117
2118 impl ToExpr for ast::Ty {
2119     fn to_expr(&self) -> Option<&ast::Expr> {
2120         None
2121     }
2122
2123     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2124         can_be_overflowed_type(context, self, len)
2125     }
2126 }
2127
2128 impl<'a> ToExpr for TuplePatField<'a> {
2129     fn to_expr(&self) -> Option<&ast::Expr> {
2130         None
2131     }
2132
2133     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2134         can_be_overflowed_pat(context, self, len)
2135     }
2136 }
2137
2138 impl<'a> ToExpr for ast::StructField {
2139     fn to_expr(&self) -> Option<&ast::Expr> {
2140         None
2141     }
2142
2143     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2144         false
2145     }
2146 }
2147
2148 impl<'a> ToExpr for MacroArg {
2149     fn to_expr(&self) -> Option<&ast::Expr> {
2150         match *self {
2151             MacroArg::Expr(ref expr) => Some(expr),
2152             _ => None,
2153         }
2154     }
2155
2156     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2157         match *self {
2158             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2159             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2160             MacroArg::Pat(..) => false,
2161             MacroArg::Item(..) => len == 1,
2162         }
2163     }
2164 }
2165
2166 impl ToExpr for ast::GenericParam {
2167     fn to_expr(&self) -> Option<&ast::Expr> {
2168         None
2169     }
2170
2171     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2172         false
2173     }
2174 }
2175
2176 pub fn is_method_call(expr: &ast::Expr) -> bool {
2177     match expr.node {
2178         ast::ExprKind::MethodCall(..) => true,
2179         ast::ExprKind::AddrOf(_, ref expr)
2180         | ast::ExprKind::Box(ref expr)
2181         | ast::ExprKind::Cast(ref expr, _)
2182         | ast::ExprKind::Try(ref expr)
2183         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),
2184         _ => false,
2185     }
2186 }