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