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