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