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