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