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::{
  23     combine_strs_with_missing_comments, contains_comment, recover_comment_removed, rewrite_comment,
  24     rewrite_missing_comment, CharClasses, FindUncommented,
  25 };
  26 use config::{Config, ControlBraceStyle, IndentStyle};
  27 use lists::{
  28     definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape,
  29     struct_lit_tactic, write_list, ListFormatting, ListItem, Separator,
  30 };
  31 use macros::{rewrite_macro, MacroArg, MacroPosition};
  32 use matches::rewrite_match;
  33 use overflow;
  34 use patterns::{can_be_overflowed_pat, is_short_pattern, TuplePatField};
  35 use rewrite::{Rewrite, RewriteContext};
  36 use shape::{Indent, Shape};
  37 use spanned::Spanned;
  38 use string::{rewrite_string, StringFormat};
  39 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  40 use utils::{
  41     colon_spaces, contains_skip, count_newlines, first_line_width, inner_attributes,
  42     last_line_extendable, last_line_width, mk_sp, outer_attributes, paren_overhead,
  43     ptr_vec_to_ref_vec, semicolon_for_stmt, wrap_str,
  44 };
  45 use vertical::rewrite_with_alignment;
  46 use visitor::FmtVisitor;
  47
  48 impl Rewrite for ast::Expr {
  49     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  50         format_expr(self, ExprType::SubExpression, context, shape)
  51     }
  52 }
  53
  54 #[derive(Copy, Clone, PartialEq)]
  55 pub enum ExprType {
  56     Statement,
  57     SubExpression,
  58 }
  59
  60 pub fn format_expr(
  61     expr: &ast::Expr,
  62     expr_type: ExprType,
  63     context: &RewriteContext,
  64     shape: Shape,
  65 ) -> Option<String> {
  66     skip_out_of_file_lines_range!(context, expr.span);
  67
  68     if contains_skip(&*expr.attrs) {
  69         return Some(context.snippet(expr.span()).to_owned());
  70     }
  71
  72     let expr_rw = match expr.node {
  73         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  74             "",
  75             &ptr_vec_to_ref_vec(expr_vec),
  76             expr.span,
  77             context,
  78             shape,
  79             choose_separator_tactic(context, expr.span),
  80             None,
  81         ),
  82         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  83         ast::ExprKind::Call(ref callee, ref args) => {
  84             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  85             let callee_str = callee.rewrite(context, shape)?;
  86             rewrite_call(context, &callee_str, args, inner_span, shape)
  87         }
  88         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape, expr.span),
  89         ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
  90             // FIXME: format comments between operands and operator
  91             rewrite_simple_binaries(context, expr, shape, op).or_else(|| {
  92                 rewrite_pair(
  93                     &**lhs,
  94                     &**rhs,
  95                     PairParts::new("", &format!(" {} ", context.snippet(op.span)), ""),
  96                     context,
  97                     shape,
  98                     context.config.binop_separator(),
  99                 )
 100             })
 101         }
 102         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 103         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 104             context,
 105             path,
 106             fields,
 107             base.as_ref().map(|e| &**e),
 108             expr.span,
 109             shape,
 110         ),
 111         ast::ExprKind::Tup(ref items) => {
 112             rewrite_tuple(context, &ptr_vec_to_ref_vec(items), expr.span, shape)
 113         }
 114         ast::ExprKind::If(..)
 115         | ast::ExprKind::IfLet(..)
 116         | ast::ExprKind::ForLoop(..)
 117         | ast::ExprKind::Loop(..)
 118         | ast::ExprKind::While(..)
 119         | ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 120             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 121         ast::ExprKind::Block(ref block) => {
 122             match expr_type {
 123                 ExprType::Statement => {
 124                     if is_unsafe_block(block) {
 125                         rewrite_block(block, Some(&expr.attrs), context, shape)
 126                     } else if let rw @ Some(_) =
 127                         rewrite_empty_block(context, block, Some(&expr.attrs), "", shape)
 128                     {
 129                         // Rewrite block without trying to put it in a single line.
 130                         rw
 131                     } else {
 132                         let prefix = block_prefix(context, block, shape)?;
 133                         rewrite_block_with_visitor(
 134                             context,
 135                             &prefix,
 136                             block,
 137                             Some(&expr.attrs),
 138                             shape,
 139                             true,
 140                         )
 141                     }
 142                 }
 143                 ExprType::SubExpression => rewrite_block(block, Some(&expr.attrs), context, shape),
 144             }
 145         }
 146         ast::ExprKind::Match(ref cond, ref arms) => {
 147             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 148         }
 149         ast::ExprKind::Path(ref qself, ref path) => {
 150             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 151         }
 152         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 153             rewrite_assignment(context, lhs, rhs, None, shape)
 154         }
 155         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 156             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 157         }
 158         ast::ExprKind::Continue(ref opt_label) => {
 159             let id_str = match *opt_label {
 160                 Some(label) => format!(" {}", label.ident),
 161                 None => String::new(),
 162             };
 163             Some(format!("continue{}", id_str))
 164         }
 165         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 166             let id_str = match *opt_label {
 167                 Some(label) => format!(" {}", label.ident),
 168                 None => String::new(),
 169             };
 170
 171             if let Some(ref expr) = *opt_expr {
 172                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 173             } else {
 174                 Some(format!("break{}", id_str))
 175             }
 176         }
 177         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 178             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 179         } else {
 180             Some("yield".to_string())
 181         },
 182         ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) => {
 183             closures::rewrite_closure(
 184                 capture, movability, fn_decl, body, expr.span, context, shape,
 185             )
 186         }
 187         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 188             rewrite_chain(expr, context, shape)
 189         }
 190         ast::ExprKind::Mac(ref mac) => {
 191             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 192                 wrap_str(
 193                     context.snippet(expr.span).to_owned(),
 194                     context.config.max_width(),
 195                     shape,
 196                 )
 197             })
 198         }
 199         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 200         ast::ExprKind::Ret(Some(ref expr)) => {
 201             rewrite_unary_prefix(context, "return ", &**expr, shape)
 202         }
 203         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 204         ast::ExprKind::AddrOf(mutability, ref expr) => {
 205             rewrite_expr_addrof(context, mutability, expr, shape)
 206         }
 207         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 208             &**expr,
 209             &**ty,
 210             PairParts::new("", " as ", ""),
 211             context,
 212             shape,
 213             SeparatorPlace::Front,
 214         ),
 215         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 216             &**expr,
 217             &**ty,
 218             PairParts::new("", ": ", ""),
 219             context,
 220             shape,
 221             SeparatorPlace::Back,
 222         ),
 223         ast::ExprKind::Index(ref expr, ref index) => {
 224             rewrite_index(&**expr, &**index, context, shape)
 225         }
 226         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 227             let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
 228                 ("[ ", " ]")
 229             } else {
 230                 ("[", "]")
 231             };
 232             rewrite_pair(
 233                 &**expr,
 234                 &**repeats,
 235                 PairParts::new(lbr, "; ", rbr),
 236                 context,
 237                 shape,
 238                 SeparatorPlace::Back,
 239             )
 240         }
 241         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 242             let delim = match limits {
 243                 ast::RangeLimits::HalfOpen => "..",
 244                 ast::RangeLimits::Closed => "..=",
 245             };
 246
 247             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 248                 match lhs.node {
 249                     ast::ExprKind::Lit(ref lit) => match lit.node {
 250                         ast::LitKind::FloatUnsuffixed(..) => {
 251                             context.snippet(lit.span).ends_with('.')
 252                         }
 253                         _ => false,
 254                     },
 255                     _ => false,
 256                 }
 257             }
 258
 259             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 260                 match rhs.node {
 261                     // Don't format `.. ..` into `....`, which is invalid.
 262                     //
 263                     // This check is unnecessary for `lhs`, because a range
 264                     // starting from another range needs parentheses as `(x ..) ..`
 265                     // (`x .. ..` is a range from `x` to `..`).
 266                     ast::ExprKind::Range(None, _, _) => true,
 267                     _ => false,
 268                 }
 269             }
 270
 271             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 272                 let space_if = |b: bool| if b { " " } else { "" };
 273
 274                 format!(
 275                     "{}{}{}",
 276                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 277                         .unwrap_or(""),
 278                     delim,
 279                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 280                         .unwrap_or(""),
 281                 )
 282             };
 283
 284             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 285                 (Some(lhs), Some(rhs)) => {
 286                     let sp_delim = if context.config.spaces_around_ranges() {
 287                         format!(" {} ", delim)
 288                     } else {
 289                         default_sp_delim(Some(lhs), Some(rhs))
 290                     };
 291                     rewrite_pair(
 292                         &*lhs,
 293                         &*rhs,
 294                         PairParts::new("", &sp_delim, ""),
 295                         context,
 296                         shape,
 297                         context.config.binop_separator(),
 298                     )
 299                 }
 300                 (None, Some(rhs)) => {
 301                     let sp_delim = if context.config.spaces_around_ranges() {
 302                         format!("{} ", delim)
 303                     } else {
 304                         default_sp_delim(None, Some(rhs))
 305                     };
 306                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 307                 }
 308                 (Some(lhs), None) => {
 309                     let sp_delim = if context.config.spaces_around_ranges() {
 310                         format!(" {}", delim)
 311                     } else {
 312                         default_sp_delim(Some(lhs), None)
 313                     };
 314                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 315                 }
 316                 (None, None) => Some(delim.to_owned()),
 317             }
 318         }
 319         // We do not format these expressions yet, but they should still
 320         // satisfy our width restrictions.
 321         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 322         ast::ExprKind::Catch(ref block) => {
 323             if let rw @ Some(_) =
 324                 rewrite_single_line_block(context, "do catch ", block, Some(&expr.attrs), shape)
 325             {
 326                 rw
 327             } else {
 328                 // 9 = `do catch `
 329                 let budget = shape.width.checked_sub(9).unwrap_or(0);
 330                 Some(format!(
 331                     "{}{}",
 332                     "do catch ",
 333                     rewrite_block(
 334                         block,
 335                         Some(&expr.attrs),
 336                         context,
 337                         Shape::legacy(budget, shape.indent)
 338                     )?
 339                 ))
 340             }
 341         }
 342     };
 343
 344     expr_rw
 345         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 346         .and_then(|expr_str| {
 347             let attrs = outer_attributes(&expr.attrs);
 348             let attrs_str = attrs.rewrite(context, shape)?;
 349             let span = mk_sp(
 350                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 351                 expr.span.lo(),
 352             );
 353             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 354         })
 355 }
 356
 357 /// Collect operands that appears in the given binary operator in the opposite order.
 358 /// e.g. `collect_binary_items(e, ||)` for `a && b || c || d` returns `[d, c, a && b]`.
 359 fn collect_binary_items<'a>(mut expr: &'a ast::Expr, binop: ast::BinOp) -> Vec<&'a ast::Expr> {
 360     let mut result = vec![];
 361     let mut prev_lhs = None;
 362     loop {
 363         match expr.node {
 364             ast::ExprKind::Binary(inner_binop, ref lhs, ref rhs)
 365                 if inner_binop.node == binop.node =>
 366             {
 367                 result.push(&**rhs);
 368                 expr = lhs;
 369                 prev_lhs = Some(lhs);
 370             }
 371             _ => {
 372                 if let Some(lhs) = prev_lhs {
 373                     result.push(lhs);
 374                 }
 375                 break;
 376             }
 377         }
 378     }
 379     result
 380 }
 381
 382 /// Rewrites a binary expression whose operands fits within a single line.
 383 fn rewrite_simple_binaries(
 384     context: &RewriteContext,
 385     expr: &ast::Expr,
 386     shape: Shape,
 387     op: ast::BinOp,
 388 ) -> Option<String> {
 389     let op_str = context.snippet(op.span);
 390
 391     // 2 = spaces around a binary operator.
 392     let sep_overhead = op_str.len() + 2;
 393     let nested_overhead = sep_overhead - 1;
 394
 395     let nested_shape = (match context.config.indent_style() {
 396         IndentStyle::Visual => shape.visual_indent(0),
 397         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 398     }).with_max_width(context.config);
 399     let nested_shape = match context.config.binop_separator() {
 400         SeparatorPlace::Back => nested_shape.sub_width(nested_overhead)?,
 401         SeparatorPlace::Front => nested_shape.offset_left(nested_overhead)?,
 402     };
 403
 404     let opt_rewrites: Option<Vec<_>> = collect_binary_items(expr, op)
 405         .iter()
 406         .rev()
 407         .map(|e| e.rewrite(context, nested_shape))
 408         .collect();
 409     if let Some(rewrites) = opt_rewrites {
 410         if rewrites.iter().all(|e| ::utils::is_single_line(e)) {
 411             let total_width = rewrites.iter().map(|s| s.len()).sum::<usize>()
 412                 + sep_overhead * (rewrites.len() - 1);
 413
 414             let sep_str = if total_width <= shape.width {
 415                 format!(" {} ", op_str)
 416             } else {
 417                 let indent_str = nested_shape.indent.to_string_with_newline(context.config);
 418                 match context.config.binop_separator() {
 419                     SeparatorPlace::Back => format!(" {}{}", op_str.trim_right(), indent_str),
 420                     SeparatorPlace::Front => format!("{}{} ", indent_str, op_str.trim_left()),
 421                 }
 422             };
 423
 424             return wrap_str(rewrites.join(&sep_str), context.config.max_width(), shape);
 425         }
 426     }
 427
 428     None
 429 }
 430
 431 #[derive(new, Clone, Copy)]
 432 pub struct PairParts<'a> {
 433     prefix: &'a str,
 434     infix: &'a str,
 435     suffix: &'a str,
 436 }
 437
 438 pub fn rewrite_pair<LHS, RHS>(
 439     lhs: &LHS,
 440     rhs: &RHS,
 441     pp: PairParts,
 442     context: &RewriteContext,
 443     shape: Shape,
 444     separator_place: SeparatorPlace,
 445 ) -> Option<String>
 446 where
 447     LHS: Rewrite,
 448     RHS: Rewrite,
 449 {
 450     let lhs_overhead = match separator_place {
 451         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 452         SeparatorPlace::Front => shape.used_width(),
 453     };
 454     let lhs_shape = Shape {
 455         width: context.budget(lhs_overhead),
 456         ..shape
 457     };
 458     let lhs_result = lhs.rewrite(context, lhs_shape)
 459         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 460
 461     // Try to put both lhs and rhs on the same line.
 462     let rhs_orig_result = shape
 463         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 464         .and_then(|s| s.sub_width(pp.suffix.len()))
 465         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 466     if let Some(ref rhs_result) = rhs_orig_result {
 467         // If the length of the lhs is equal to or shorter than the tab width or
 468         // the rhs looks like block expression, we put the rhs on the same
 469         // line with the lhs even if the rhs is multi-lined.
 470         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 471             || rhs_result
 472                 .lines()
 473                 .next()
 474                 .map(|first_line| first_line.ends_with('{'))
 475                 .unwrap_or(false);
 476         if !rhs_result.contains('\n') || allow_same_line {
 477             let one_line_width = last_line_width(&lhs_result)
 478                 + pp.infix.len()
 479                 + first_line_width(rhs_result)
 480                 + pp.suffix.len();
 481             if one_line_width <= shape.width {
 482                 return Some(format!(
 483                     "{}{}{}{}",
 484                     lhs_result, pp.infix, rhs_result, pp.suffix
 485                 ));
 486             }
 487         }
 488     }
 489
 490     // We have to use multiple lines.
 491     // Re-evaluate the rhs because we have more space now:
 492     let mut rhs_shape = match context.config.indent_style() {
 493         IndentStyle::Visual => shape
 494             .sub_width(pp.suffix.len() + pp.prefix.len())?
 495             .visual_indent(pp.prefix.len()),
 496         IndentStyle::Block => {
 497             // Try to calculate the initial constraint on the right hand side.
 498             let rhs_overhead = shape.rhs_overhead(context.config);
 499             Shape::indented(shape.indent.block_indent(context.config), context.config)
 500                 .sub_width(rhs_overhead)?
 501         }
 502     };
 503     let infix = match separator_place {
 504         SeparatorPlace::Back => pp.infix.trim_right(),
 505         SeparatorPlace::Front => pp.infix.trim_left(),
 506     };
 507     if separator_place == SeparatorPlace::Front {
 508         rhs_shape = rhs_shape.offset_left(infix.len())?;
 509     }
 510     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 511     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 512     let infix_with_sep = match separator_place {
 513         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 514         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 515     };
 516     Some(format!(
 517         "{}{}{}{}",
 518         lhs_result, infix_with_sep, rhs_result, pp.suffix
 519     ))
 520 }
 521
 522 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 523     name: &str,
 524     exprs: &[&T],
 525     span: Span,
 526     context: &RewriteContext,
 527     shape: Shape,
 528     force_separator_tactic: Option<SeparatorTactic>,
 529     delim_token: Option<DelimToken>,
 530 ) -> Option<String> {
 531     overflow::rewrite_with_square_brackets(
 532         context,
 533         name,
 534         exprs,
 535         shape,
 536         span,
 537         force_separator_tactic,
 538         delim_token,
 539     )
 540 }
 541
 542 fn rewrite_empty_block(
 543     context: &RewriteContext,
 544     block: &ast::Block,
 545     attrs: Option<&[ast::Attribute]>,
 546     prefix: &str,
 547     shape: Shape,
 548 ) -> Option<String> {
 549     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 550         return None;
 551     }
 552
 553     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 554     {
 555         return Some(format!("{}{{}}", prefix));
 556     }
 557
 558     // If a block contains only a single-line comment, then leave it on one line.
 559     let user_str = context.snippet(block.span);
 560     let user_str = user_str.trim();
 561     if user_str.starts_with('{') && user_str.ends_with('}') {
 562         let comment_str = user_str[1..user_str.len() - 1].trim();
 563         if block.stmts.is_empty()
 564             && !comment_str.contains('\n')
 565             && !comment_str.starts_with("//")
 566             && comment_str.len() + 4 <= shape.width
 567         {
 568             return Some(format!("{}{{ {} }}", prefix, comment_str));
 569         }
 570     }
 571
 572     None
 573 }
 574
 575 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 576     Some(match block.rules {
 577         ast::BlockCheckMode::Unsafe(..) => {
 578             let snippet = context.snippet(block.span);
 579             let open_pos = snippet.find_uncommented("{")?;
 580             // Extract comment between unsafe and block start.
 581             let trimmed = &snippet[6..open_pos].trim();
 582
 583             if !trimmed.is_empty() {
 584                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 585                 let budget = shape.width.checked_sub(9)?;
 586                 format!(
 587                     "unsafe {} ",
 588                     rewrite_comment(
 589                         trimmed,
 590                         true,
 591                         Shape::legacy(budget, shape.indent + 7),
 592                         context.config,
 593                     )?
 594                 )
 595             } else {
 596                 "unsafe ".to_owned()
 597             }
 598         }
 599         ast::BlockCheckMode::Default => String::new(),
 600     })
 601 }
 602
 603 fn rewrite_single_line_block(
 604     context: &RewriteContext,
 605     prefix: &str,
 606     block: &ast::Block,
 607     attrs: Option<&[ast::Attribute]>,
 608     shape: Shape,
 609 ) -> Option<String> {
 610     if is_simple_block(block, attrs, context.codemap) {
 611         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 612         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 613         let result = format!("{}{{ {} }}", prefix, expr_str);
 614         if result.len() <= shape.width && !result.contains('\n') {
 615             return Some(result);
 616         }
 617     }
 618     None
 619 }
 620
 621 pub fn rewrite_block_with_visitor(
 622     context: &RewriteContext,
 623     prefix: &str,
 624     block: &ast::Block,
 625     attrs: Option<&[ast::Attribute]>,
 626     shape: Shape,
 627     has_braces: bool,
 628 ) -> Option<String> {
 629     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, prefix, shape) {
 630         return rw;
 631     }
 632
 633     let mut visitor = FmtVisitor::from_context(context);
 634     visitor.block_indent = shape.indent;
 635     visitor.is_if_else_block = context.is_if_else_block();
 636     match block.rules {
 637         ast::BlockCheckMode::Unsafe(..) => {
 638             let snippet = context.snippet(block.span);
 639             let open_pos = snippet.find_uncommented("{")?;
 640             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 641         }
 642         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 643     }
 644
 645     let inner_attrs = attrs.map(inner_attributes);
 646     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 647     Some(format!("{}{}", prefix, visitor.buffer))
 648 }
 649
 650 impl Rewrite for ast::Block {
 651     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 652         rewrite_block(self, None, context, shape)
 653     }
 654 }
 655
 656 fn rewrite_block(
 657     block: &ast::Block,
 658     attrs: Option<&[ast::Attribute]>,
 659     context: &RewriteContext,
 660     shape: Shape,
 661 ) -> Option<String> {
 662     let prefix = block_prefix(context, block, shape)?;
 663
 664     // shape.width is used only for the single line case: either the empty block `{}`,
 665     // or an unsafe expression `unsafe { e }`.
 666     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, &prefix, shape) {
 667         return rw;
 668     }
 669
 670     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, shape, true);
 671     if let Some(ref result_str) = result {
 672         if result_str.lines().count() <= 3 {
 673             if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, block, attrs, shape) {
 674                 return rw;
 675             }
 676         }
 677     }
 678
 679     result
 680 }
 681
 682 impl Rewrite for ast::Stmt {
 683     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 684         skip_out_of_file_lines_range!(context, self.span());
 685
 686         let result = match self.node {
 687             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 688             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 689                 let suffix = if semicolon_for_stmt(context, self) {
 690                     ";"
 691                 } else {
 692                     ""
 693                 };
 694
 695                 let shape = shape.sub_width(suffix.len())?;
 696                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 697             }
 698             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 699         };
 700         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 701     }
 702 }
 703
 704 // Rewrite condition if the given expression has one.
 705 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 706     match expr.node {
 707         ast::ExprKind::Match(ref cond, _) => {
 708             // `match `cond` {`
 709             let cond_shape = match context.config.indent_style() {
 710                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 711                 IndentStyle::Block => shape.offset_left(8)?,
 712             };
 713             cond.rewrite(context, cond_shape)
 714         }
 715         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 716             let alt_block_sep =
 717                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 718             control_flow
 719                 .rewrite_cond(context, shape, &alt_block_sep)
 720                 .and_then(|rw| Some(rw.0))
 721         }),
 722     }
 723 }
 724
 725 // Abstraction over control flow expressions
 726 #[derive(Debug)]
 727 struct ControlFlow<'a> {
 728     cond: Option<&'a ast::Expr>,
 729     block: &'a ast::Block,
 730     else_block: Option<&'a ast::Expr>,
 731     label: Option<ast::Label>,
 732     pats: Vec<&'a ast::Pat>,
 733     keyword: &'a str,
 734     matcher: &'a str,
 735     connector: &'a str,
 736     allow_single_line: bool,
 737     // True if this is an `if` expression in an `else if` :-( hacky
 738     nested_if: bool,
 739     span: Span,
 740 }
 741
 742 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 743     match expr.node {
 744         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 745             cond,
 746             vec![],
 747             if_block,
 748             else_block.as_ref().map(|e| &**e),
 749             expr_type == ExprType::SubExpression,
 750             false,
 751             expr.span,
 752         )),
 753         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 754             Some(ControlFlow::new_if(
 755                 cond,
 756                 ptr_vec_to_ref_vec(pat),
 757                 if_block,
 758                 else_block.as_ref().map(|e| &**e),
 759                 expr_type == ExprType::SubExpression,
 760                 false,
 761                 expr.span,
 762             ))
 763         }
 764         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 765             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 766         }
 767         ast::ExprKind::Loop(ref block, label) => {
 768             Some(ControlFlow::new_loop(block, label, expr.span))
 769         }
 770         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 771             vec![],
 772             cond,
 773             block,
 774             label,
 775             expr.span,
 776         )),
 777         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 778             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 779         ),
 780         _ => None,
 781     }
 782 }
 783
 784 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 785     if pats.is_empty() {
 786         ""
 787     } else {
 788         "let"
 789     }
 790 }
 791
 792 impl<'a> ControlFlow<'a> {
 793     fn new_if(
 794         cond: &'a ast::Expr,
 795         pats: Vec<&'a ast::Pat>,
 796         block: &'a ast::Block,
 797         else_block: Option<&'a ast::Expr>,
 798         allow_single_line: bool,
 799         nested_if: bool,
 800         span: Span,
 801     ) -> ControlFlow<'a> {
 802         let matcher = choose_matcher(&pats);
 803         ControlFlow {
 804             cond: Some(cond),
 805             block,
 806             else_block,
 807             label: None,
 808             pats,
 809             keyword: "if",
 810             matcher,
 811             connector: " =",
 812             allow_single_line,
 813             nested_if,
 814             span,
 815         }
 816     }
 817
 818     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 819         ControlFlow {
 820             cond: None,
 821             block,
 822             else_block: None,
 823             label,
 824             pats: vec![],
 825             keyword: "loop",
 826             matcher: "",
 827             connector: "",
 828             allow_single_line: false,
 829             nested_if: false,
 830             span,
 831         }
 832     }
 833
 834     fn new_while(
 835         pats: Vec<&'a ast::Pat>,
 836         cond: &'a ast::Expr,
 837         block: &'a ast::Block,
 838         label: Option<ast::Label>,
 839         span: Span,
 840     ) -> ControlFlow<'a> {
 841         let matcher = choose_matcher(&pats);
 842         ControlFlow {
 843             cond: Some(cond),
 844             block,
 845             else_block: None,
 846             label,
 847             pats,
 848             keyword: "while",
 849             matcher,
 850             connector: " =",
 851             allow_single_line: false,
 852             nested_if: false,
 853             span,
 854         }
 855     }
 856
 857     fn new_for(
 858         pat: &'a ast::Pat,
 859         cond: &'a ast::Expr,
 860         block: &'a ast::Block,
 861         label: Option<ast::Label>,
 862         span: Span,
 863     ) -> ControlFlow<'a> {
 864         ControlFlow {
 865             cond: Some(cond),
 866             block,
 867             else_block: None,
 868             label,
 869             pats: vec![pat],
 870             keyword: "for",
 871             matcher: "",
 872             connector: " in",
 873             allow_single_line: false,
 874             nested_if: false,
 875             span,
 876         }
 877     }
 878
 879     fn rewrite_single_line(
 880         &self,
 881         pat_expr_str: &str,
 882         context: &RewriteContext,
 883         width: usize,
 884     ) -> Option<String> {
 885         assert!(self.allow_single_line);
 886         let else_block = self.else_block?;
 887         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 888
 889         if let ast::ExprKind::Block(ref else_node) = else_block.node {
 890             if !is_simple_block(self.block, None, context.codemap)
 891                 || !is_simple_block(else_node, None, context.codemap)
 892                 || pat_expr_str.contains('\n')
 893             {
 894                 return None;
 895             }
 896
 897             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 898             let expr = &self.block.stmts[0];
 899             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 900
 901             let new_width = new_width.checked_sub(if_str.len())?;
 902             let else_expr = &else_node.stmts[0];
 903             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 904
 905             if if_str.contains('\n') || else_str.contains('\n') {
 906                 return None;
 907             }
 908
 909             let result = format!(
 910                 "{} {} {{ {} }} else {{ {} }}",
 911                 self.keyword, pat_expr_str, if_str, else_str
 912             );
 913
 914             if result.len() <= width {
 915                 return Some(result);
 916             }
 917         }
 918
 919         None
 920     }
 921 }
 922
 923 impl<'a> ControlFlow<'a> {
 924     fn rewrite_pat_expr(
 925         &self,
 926         context: &RewriteContext,
 927         expr: &ast::Expr,
 928         shape: Shape,
 929         offset: usize,
 930     ) -> Option<String> {
 931         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 932
 933         let cond_shape = shape.offset_left(offset)?;
 934         if !self.pats.is_empty() {
 935             let matcher = if self.matcher.is_empty() {
 936                 self.matcher.to_owned()
 937             } else {
 938                 format!("{} ", self.matcher)
 939             };
 940             let pat_shape = cond_shape
 941                 .offset_left(matcher.len())?
 942                 .sub_width(self.connector.len())?;
 943             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 944             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 945             return rewrite_assign_rhs(context, result, expr, cond_shape);
 946         }
 947
 948         let expr_rw = expr.rewrite(context, cond_shape);
 949         // The expression may (partially) fit on the current line.
 950         // We do not allow splitting between `if` and condition.
 951         if self.keyword == "if" || expr_rw.is_some() {
 952             return expr_rw;
 953         }
 954
 955         // The expression won't fit on the current line, jump to next.
 956         let nested_shape = shape
 957             .block_indent(context.config.tab_spaces())
 958             .with_max_width(context.config);
 959         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 960         expr.rewrite(context, nested_shape)
 961             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 962     }
 963
 964     fn rewrite_cond(
 965         &self,
 966         context: &RewriteContext,
 967         shape: Shape,
 968         alt_block_sep: &str,
 969     ) -> Option<(String, usize)> {
 970         // Do not take the rhs overhead from the upper expressions into account
 971         // when rewriting pattern.
 972         let new_width = context.budget(shape.used_width());
 973         let fresh_shape = Shape {
 974             width: new_width,
 975             ..shape
 976         };
 977         let constr_shape = if self.nested_if {
 978             // We are part of an if-elseif-else chain. Our constraints are tightened.
 979             // 7 = "} else " .len()
 980             fresh_shape.offset_left(7)?
 981         } else {
 982             fresh_shape
 983         };
 984
 985         let label_string = rewrite_label(self.label);
 986         // 1 = space after keyword.
 987         let offset = self.keyword.len() + label_string.len() + 1;
 988
 989         let pat_expr_string = match self.cond {
 990             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 991             None => String::new(),
 992         };
 993
 994         let brace_overhead =
 995             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 996                 // 2 = ` {`
 997                 2
 998             } else {
 999                 0
1000             };
1001         let one_line_budget = context
1002             .config
1003             .max_width()
1004             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1005             .unwrap_or(0);
1006         let force_newline_brace = (pat_expr_string.contains('\n')
1007             || pat_expr_string.len() > one_line_budget)
1008             && !last_line_extendable(&pat_expr_string);
1009
1010         // Try to format if-else on single line.
1011         if self.allow_single_line
1012             && context
1013                 .config
1014                 .width_heuristics()
1015                 .single_line_if_else_max_width > 0
1016         {
1017             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1018
1019             if let Some(cond_str) = trial {
1020                 if cond_str.len()
1021                     <= context
1022                         .config
1023                         .width_heuristics()
1024                         .single_line_if_else_max_width
1025                 {
1026                     return Some((cond_str, 0));
1027                 }
1028             }
1029         }
1030
1031         let cond_span = if let Some(cond) = self.cond {
1032             cond.span
1033         } else {
1034             mk_sp(self.block.span.lo(), self.block.span.lo())
1035         };
1036
1037         // `for event in event`
1038         // Do not include label in the span.
1039         let lo = self.label
1040             .map_or(self.span.lo(), |label| label.ident.span.hi());
1041         let between_kwd_cond = mk_sp(
1042             context
1043                 .snippet_provider
1044                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1045             if self.pats.is_empty() {
1046                 cond_span.lo()
1047             } else if self.matcher.is_empty() {
1048                 self.pats[0].span.lo()
1049             } else {
1050                 context
1051                     .snippet_provider
1052                     .span_before(self.span, self.matcher.trim())
1053             },
1054         );
1055
1056         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1057
1058         let after_cond_comment =
1059             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1060
1061         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1062             ""
1063         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1064             || force_newline_brace
1065         {
1066             alt_block_sep
1067         } else {
1068             " "
1069         };
1070
1071         let used_width = if pat_expr_string.contains('\n') {
1072             last_line_width(&pat_expr_string)
1073         } else {
1074             // 2 = spaces after keyword and condition.
1075             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1076         };
1077
1078         Some((
1079             format!(
1080                 "{}{}{}{}{}",
1081                 label_string,
1082                 self.keyword,
1083                 between_kwd_cond_comment.as_ref().map_or(
1084                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1085                         ""
1086                     } else {
1087                         " "
1088                     },
1089                     |s| &**s,
1090                 ),
1091                 pat_expr_string,
1092                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1093             ),
1094             used_width,
1095         ))
1096     }
1097 }
1098
1099 impl<'a> Rewrite for ControlFlow<'a> {
1100     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1101         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1102
1103         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1104         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1105         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1106         if used_width == 0 {
1107             return Some(cond_str);
1108         }
1109
1110         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1111         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1112         // we should avoid the single line case.
1113         let block_width = if self.else_block.is_some() || self.nested_if {
1114             min(1, block_width)
1115         } else {
1116             block_width
1117         };
1118         let block_shape = Shape {
1119             width: block_width,
1120             ..shape
1121         };
1122         let block_str = {
1123             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1124             let result =
1125                 rewrite_block_with_visitor(context, "", self.block, None, block_shape, true);
1126             context.is_if_else_block.replace(old_val);
1127             result?
1128         };
1129
1130         let mut result = format!("{}{}", cond_str, block_str);
1131
1132         if let Some(else_block) = self.else_block {
1133             let shape = Shape::indented(shape.indent, context.config);
1134             let mut last_in_chain = false;
1135             let rewrite = match else_block.node {
1136                 // If the else expression is another if-else expression, prevent it
1137                 // from being formatted on a single line.
1138                 // Note how we're passing the original shape, as the
1139                 // cost of "else" should not cascade.
1140                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1141                     ControlFlow::new_if(
1142                         cond,
1143                         ptr_vec_to_ref_vec(pat),
1144                         if_block,
1145                         next_else_block.as_ref().map(|e| &**e),
1146                         false,
1147                         true,
1148                         mk_sp(else_block.span.lo(), self.span.hi()),
1149                     ).rewrite(context, shape)
1150                 }
1151                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1152                     ControlFlow::new_if(
1153                         cond,
1154                         vec![],
1155                         if_block,
1156                         next_else_block.as_ref().map(|e| &**e),
1157                         false,
1158                         true,
1159                         mk_sp(else_block.span.lo(), self.span.hi()),
1160                     ).rewrite(context, shape)
1161                 }
1162                 _ => {
1163                     last_in_chain = true;
1164                     // When rewriting a block, the width is only used for single line
1165                     // blocks, passing 1 lets us avoid that.
1166                     let else_shape = Shape {
1167                         width: min(1, shape.width),
1168                         ..shape
1169                     };
1170                     format_expr(else_block, ExprType::Statement, context, else_shape)
1171                 }
1172             };
1173
1174             let between_kwd_else_block = mk_sp(
1175                 self.block.span.hi(),
1176                 context
1177                     .snippet_provider
1178                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1179             );
1180             let between_kwd_else_block_comment =
1181                 extract_comment(between_kwd_else_block, context, shape);
1182
1183             let after_else = mk_sp(
1184                 context
1185                     .snippet_provider
1186                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1187                 else_block.span.lo(),
1188             );
1189             let after_else_comment = extract_comment(after_else, context, shape);
1190
1191             let between_sep = match context.config.control_brace_style() {
1192                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1193                     &*alt_block_sep
1194                 }
1195                 ControlBraceStyle::AlwaysSameLine => " ",
1196             };
1197             let after_sep = match context.config.control_brace_style() {
1198                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1199                 _ => " ",
1200             };
1201
1202             result.push_str(&format!(
1203                 "{}else{}",
1204                 between_kwd_else_block_comment
1205                     .as_ref()
1206                     .map_or(between_sep, |s| &**s),
1207                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1208             ));
1209             result.push_str(&rewrite?);
1210         }
1211
1212         Some(result)
1213     }
1214 }
1215
1216 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1217     match opt_label {
1218         Some(label) => Cow::from(format!("{}: ", label.ident)),
1219         None => Cow::from(""),
1220     }
1221 }
1222
1223 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1224     match rewrite_missing_comment(span, shape, context) {
1225         Some(ref comment) if !comment.is_empty() => Some(format!(
1226             "{indent}{}{indent}",
1227             comment,
1228             indent = shape.indent.to_string_with_newline(context.config)
1229         )),
1230         _ => None,
1231     }
1232 }
1233
1234 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1235     let snippet = codemap.span_to_snippet(block.span).unwrap();
1236     contains_comment(&snippet)
1237 }
1238
1239 // Checks that a block contains no statements, an expression and no comments or
1240 // attributes.
1241 // FIXME: incorrectly returns false when comment is contained completely within
1242 // the expression.
1243 pub fn is_simple_block(
1244     block: &ast::Block,
1245     attrs: Option<&[ast::Attribute]>,
1246     codemap: &CodeMap,
1247 ) -> bool {
1248     (block.stmts.len() == 1
1249         && stmt_is_expr(&block.stmts[0])
1250         && !block_contains_comment(block, codemap)
1251         && attrs.map_or(true, |a| a.is_empty()))
1252 }
1253
1254 /// Checks whether a block contains at most one statement or expression, and no
1255 /// comments or attributes.
1256 pub fn is_simple_block_stmt(
1257     block: &ast::Block,
1258     attrs: Option<&[ast::Attribute]>,
1259     codemap: &CodeMap,
1260 ) -> bool {
1261     block.stmts.len() <= 1
1262         && !block_contains_comment(block, codemap)
1263         && attrs.map_or(true, |a| a.is_empty())
1264 }
1265
1266 /// Checks whether a block contains no statements, expressions, comments, or
1267 /// inner attributes.
1268 pub fn is_empty_block(
1269     block: &ast::Block,
1270     attrs: Option<&[ast::Attribute]>,
1271     codemap: &CodeMap,
1272 ) -> bool {
1273     block.stmts.is_empty()
1274         && !block_contains_comment(block, codemap)
1275         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1276 }
1277
1278 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1279     match stmt.node {
1280         ast::StmtKind::Expr(..) => true,
1281         _ => false,
1282     }
1283 }
1284
1285 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1286     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1287         true
1288     } else {
1289         false
1290     }
1291 }
1292
1293 pub fn rewrite_multiple_patterns(
1294     context: &RewriteContext,
1295     pats: &[&ast::Pat],
1296     shape: Shape,
1297 ) -> Option<String> {
1298     let pat_strs = pats.iter()
1299         .map(|p| p.rewrite(context, shape))
1300         .collect::<Option<Vec<_>>>()?;
1301
1302     let use_mixed_layout = pats.iter()
1303         .zip(pat_strs.iter())
1304         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1305     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1306     let tactic = if use_mixed_layout {
1307         DefinitiveListTactic::Mixed
1308     } else {
1309         definitive_tactic(
1310             &items,
1311             ListTactic::HorizontalVertical,
1312             Separator::VerticalBar,
1313             shape.width,
1314         )
1315     };
1316     let fmt = ListFormatting {
1317         tactic,
1318         separator: " |",
1319         trailing_separator: SeparatorTactic::Never,
1320         separator_place: context.config.binop_separator(),
1321         shape,
1322         ends_with_newline: false,
1323         preserve_newline: false,
1324         config: context.config,
1325     };
1326     write_list(&items, &fmt)
1327 }
1328
1329 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1330     match l.node {
1331         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1332         _ => wrap_str(
1333             context.snippet(l.span).to_owned(),
1334             context.config.max_width(),
1335             shape,
1336         ),
1337     }
1338 }
1339
1340 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1341     let string_lit = context.snippet(span);
1342
1343     if !context.config.format_strings() {
1344         if string_lit
1345             .lines()
1346             .rev()
1347             .skip(1)
1348             .all(|line| line.ends_with('\\'))
1349         {
1350             let new_indent = shape.visual_indent(1).indent;
1351             let indented_string_lit = String::from(
1352                 string_lit
1353                     .lines()
1354                     .map(|line| {
1355                         format!(
1356                             "{}{}",
1357                             new_indent.to_string(context.config),
1358                             line.trim_left()
1359                         )
1360                     })
1361                     .collect::<Vec<_>>()
1362                     .join("\n")
1363                     .trim_left(),
1364             );
1365             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1366         } else {
1367             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1368         }
1369     }
1370
1371     // Remove the quote characters.
1372     let str_lit = &string_lit[1..string_lit.len() - 1];
1373
1374     rewrite_string(
1375         str_lit,
1376         &StringFormat::new(shape.visual_indent(0), context.config),
1377         None,
1378     )
1379 }
1380
1381 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1382 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1383     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1384         .iter()
1385         .find(|&&(s, _)| s == callee_str)
1386     {
1387         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1388
1389         Some((all_simple, num_args_before))
1390     } else {
1391         None
1392     }
1393 }
1394
1395 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1396 /// format.
1397 ///
1398 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1399 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1400 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1401 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1402     // format! like macros
1403     // From the Rust Standard Library.
1404     ("eprint!", 0),
1405     ("eprintln!", 0),
1406     ("format!", 0),
1407     ("format_args!", 0),
1408     ("print!", 0),
1409     ("println!", 0),
1410     ("panic!", 0),
1411     ("unreachable!", 0),
1412     // From the `log` crate.
1413     ("debug!", 0),
1414     ("error!", 0),
1415     ("info!", 0),
1416     ("warn!", 0),
1417     // write! like macros
1418     ("assert!", 1),
1419     ("debug_assert!", 1),
1420     ("write!", 1),
1421     ("writeln!", 1),
1422     // assert_eq! like macros
1423     ("assert_eq!", 2),
1424     ("assert_ne!", 2),
1425     ("debug_assert_eq!", 2),
1426     ("debug_assert_ne!", 2),
1427 ];
1428
1429 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1430     if context.inside_macro() {
1431         if span_ends_with_comma(context, span) {
1432             Some(SeparatorTactic::Always)
1433         } else {
1434             Some(SeparatorTactic::Never)
1435         }
1436     } else {
1437         None
1438     }
1439 }
1440
1441 pub fn rewrite_call(
1442     context: &RewriteContext,
1443     callee: &str,
1444     args: &[ptr::P<ast::Expr>],
1445     span: Span,
1446     shape: Shape,
1447 ) -> Option<String> {
1448     overflow::rewrite_with_parens(
1449         context,
1450         callee,
1451         &ptr_vec_to_ref_vec(args),
1452         shape,
1453         span,
1454         context.config.width_heuristics().fn_call_width,
1455         choose_separator_tactic(context, span),
1456     )
1457 }
1458
1459 fn is_simple_expr(expr: &ast::Expr) -> bool {
1460     match expr.node {
1461         ast::ExprKind::Lit(..) => true,
1462         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1463         ast::ExprKind::AddrOf(_, ref expr)
1464         | ast::ExprKind::Box(ref expr)
1465         | ast::ExprKind::Cast(ref expr, _)
1466         | ast::ExprKind::Field(ref expr, _)
1467         | ast::ExprKind::Try(ref expr)
1468         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1469         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1470             is_simple_expr(lhs) && is_simple_expr(rhs)
1471         }
1472         _ => false,
1473     }
1474 }
1475
1476 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1477     lists
1478         .iter()
1479         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1480 }
1481
1482 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1483     match expr.node {
1484         ast::ExprKind::Match(..) => {
1485             (context.use_block_indent() && args_len == 1)
1486                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1487         }
1488         ast::ExprKind::If(..)
1489         | ast::ExprKind::IfLet(..)
1490         | ast::ExprKind::ForLoop(..)
1491         | ast::ExprKind::Loop(..)
1492         | ast::ExprKind::While(..)
1493         | ast::ExprKind::WhileLet(..) => {
1494             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1495         }
1496         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1497             context.use_block_indent()
1498                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1499         }
1500         ast::ExprKind::Array(..)
1501         | ast::ExprKind::Call(..)
1502         | ast::ExprKind::Mac(..)
1503         | ast::ExprKind::MethodCall(..)
1504         | ast::ExprKind::Struct(..)
1505         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1506         ast::ExprKind::AddrOf(_, ref expr)
1507         | ast::ExprKind::Box(ref expr)
1508         | ast::ExprKind::Try(ref expr)
1509         | ast::ExprKind::Unary(_, ref expr)
1510         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1511         _ => false,
1512     }
1513 }
1514
1515 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1516     match expr.node {
1517         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1518         ast::ExprKind::AddrOf(_, ref expr)
1519         | ast::ExprKind::Box(ref expr)
1520         | ast::ExprKind::Try(ref expr)
1521         | ast::ExprKind::Unary(_, ref expr)
1522         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1523         _ => false,
1524     }
1525 }
1526
1527 /// Return true if a function call or a method call represented by the given span ends with a
1528 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1529 /// comma from macro can potentially break the code.
1530 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1531     let mut result: bool = Default::default();
1532     let mut prev_char: char = Default::default();
1533     let closing_delimiters = &[')', '}', ']'];
1534
1535     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1536         match c {
1537             _ if kind.is_comment() || c.is_whitespace() => continue,
1538             c if closing_delimiters.contains(&c) => {
1539                 result &= !closing_delimiters.contains(&prev_char);
1540             }
1541             ',' => result = true,
1542             _ => result = false,
1543         }
1544         prev_char = c;
1545     }
1546
1547     result
1548 }
1549
1550 fn rewrite_paren(
1551     context: &RewriteContext,
1552     mut subexpr: &ast::Expr,
1553     shape: Shape,
1554     mut span: Span,
1555 ) -> Option<String> {
1556     debug!("rewrite_paren, shape: {:?}", shape);
1557
1558     // Extract comments within parens.
1559     let mut pre_comment;
1560     let mut post_comment;
1561     let remove_nested_parens = context.config.remove_nested_parens();
1562     loop {
1563         // 1 = "(" or ")"
1564         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1565         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1566         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1567         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1568
1569         // Remove nested parens if there are no comments.
1570         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1571             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1572                 span = subexpr.span;
1573                 subexpr = subsubexpr;
1574                 continue;
1575             }
1576         }
1577
1578         break;
1579     }
1580
1581     let total_paren_overhead = paren_overhead(context);
1582     let paren_overhead = total_paren_overhead / 2;
1583     let sub_shape = shape
1584         .offset_left(paren_overhead)
1585         .and_then(|s| s.sub_width(paren_overhead))?;
1586
1587     let paren_wrapper = |s: &str| {
1588         if context.config.spaces_within_parens_and_brackets() && !s.is_empty() {
1589             format!("( {}{}{} )", pre_comment, s, post_comment)
1590         } else {
1591             format!("({}{}{})", pre_comment, s, post_comment)
1592         }
1593     };
1594
1595     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1596     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1597
1598     if subexpr_str.contains('\n')
1599         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
1600     {
1601         Some(paren_wrapper(&subexpr_str))
1602     } else {
1603         None
1604     }
1605 }
1606
1607 fn rewrite_index(
1608     expr: &ast::Expr,
1609     index: &ast::Expr,
1610     context: &RewriteContext,
1611     shape: Shape,
1612 ) -> Option<String> {
1613     let expr_str = expr.rewrite(context, shape)?;
1614
1615     let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
1616         ("[ ", " ]")
1617     } else {
1618         ("[", "]")
1619     };
1620
1621     let offset = last_line_width(&expr_str) + lbr.len();
1622     let rhs_overhead = shape.rhs_overhead(context.config);
1623     let index_shape = if expr_str.contains('\n') {
1624         Shape::legacy(context.config.max_width(), shape.indent)
1625             .offset_left(offset)
1626             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
1627     } else {
1628         shape.visual_indent(offset).sub_width(offset + rbr.len())
1629     };
1630     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1631
1632     // Return if index fits in a single line.
1633     match orig_index_rw {
1634         Some(ref index_str) if !index_str.contains('\n') => {
1635             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
1636         }
1637         _ => (),
1638     }
1639
1640     // Try putting index on the next line and see if it fits in a single line.
1641     let indent = shape.indent.block_indent(context.config);
1642     let index_shape = Shape::indented(indent, context.config).offset_left(lbr.len())?;
1643     let index_shape = index_shape.sub_width(rbr.len() + rhs_overhead)?;
1644     let new_index_rw = index.rewrite(context, index_shape);
1645     match (orig_index_rw, new_index_rw) {
1646         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1647             "{}{}{}{}{}",
1648             expr_str,
1649             indent.to_string_with_newline(context.config),
1650             lbr,
1651             new_index_str,
1652             rbr
1653         )),
1654         (None, Some(ref new_index_str)) => Some(format!(
1655             "{}{}{}{}{}",
1656             expr_str,
1657             indent.to_string_with_newline(context.config),
1658             lbr,
1659             new_index_str,
1660             rbr
1661         )),
1662         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
1663         _ => None,
1664     }
1665 }
1666
1667 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1668     if base.is_some() {
1669         return false;
1670     }
1671
1672     fields.iter().all(|field| !field.is_shorthand)
1673 }
1674
1675 fn rewrite_struct_lit<'a>(
1676     context: &RewriteContext,
1677     path: &ast::Path,
1678     fields: &'a [ast::Field],
1679     base: Option<&'a ast::Expr>,
1680     span: Span,
1681     shape: Shape,
1682 ) -> Option<String> {
1683     debug!("rewrite_struct_lit: shape {:?}", shape);
1684
1685     enum StructLitField<'a> {
1686         Regular(&'a ast::Field),
1687         Base(&'a ast::Expr),
1688     }
1689
1690     // 2 = " {".len()
1691     let path_shape = shape.sub_width(2)?;
1692     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1693
1694     if fields.is_empty() && base.is_none() {
1695         return Some(format!("{} {{}}", path_str));
1696     }
1697
1698     // Foo { a: Foo } - indent is +3, width is -5.
1699     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1700
1701     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1702     let body_lo = context.snippet_provider.span_after(span, "{");
1703     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1704         && context.config.struct_field_align_threshold() > 0
1705     {
1706         rewrite_with_alignment(
1707             fields,
1708             context,
1709             shape,
1710             mk_sp(body_lo, span.hi()),
1711             one_line_width,
1712         )?
1713     } else {
1714         let field_iter = fields
1715             .into_iter()
1716             .map(StructLitField::Regular)
1717             .chain(base.into_iter().map(StructLitField::Base));
1718
1719         let span_lo = |item: &StructLitField| match *item {
1720             StructLitField::Regular(field) => field.span().lo(),
1721             StructLitField::Base(expr) => {
1722                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1723                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1724                 let pos = snippet.find_uncommented("..").unwrap();
1725                 last_field_hi + BytePos(pos as u32)
1726             }
1727         };
1728         let span_hi = |item: &StructLitField| match *item {
1729             StructLitField::Regular(field) => field.span().hi(),
1730             StructLitField::Base(expr) => expr.span.hi(),
1731         };
1732         let rewrite = |item: &StructLitField| match *item {
1733             StructLitField::Regular(field) => {
1734                 // The 1 taken from the v_budget is for the comma.
1735                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1736             }
1737             StructLitField::Base(expr) => {
1738                 // 2 = ..
1739                 expr.rewrite(context, v_shape.offset_left(2)?)
1740                     .map(|s| format!("..{}", s))
1741             }
1742         };
1743
1744         let items = itemize_list(
1745             context.snippet_provider,
1746             field_iter,
1747             "}",
1748             ",",
1749             span_lo,
1750             span_hi,
1751             rewrite,
1752             body_lo,
1753             span.hi(),
1754             false,
1755         );
1756         let item_vec = items.collect::<Vec<_>>();
1757
1758         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1759         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1760
1761         let ends_with_comma = span_ends_with_comma(context, span);
1762         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1763
1764         let fmt = struct_lit_formatting(
1765             nested_shape,
1766             tactic,
1767             context,
1768             force_no_trailing_comma || base.is_some(),
1769         );
1770
1771         write_list(&item_vec, &fmt)?
1772     };
1773
1774     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1775     Some(format!("{} {{{}}}", path_str, fields_str))
1776
1777     // FIXME if context.config.indent_style() == Visual, but we run out
1778     // of space, we should fall back to BlockIndent.
1779 }
1780
1781 pub fn wrap_struct_field(
1782     context: &RewriteContext,
1783     fields_str: &str,
1784     shape: Shape,
1785     nested_shape: Shape,
1786     one_line_width: usize,
1787 ) -> String {
1788     if context.config.indent_style() == IndentStyle::Block
1789         && (fields_str.contains('\n')
1790             || !context.config.struct_lit_single_line()
1791             || fields_str.len() > one_line_width)
1792     {
1793         format!(
1794             "{}{}{}",
1795             nested_shape.indent.to_string_with_newline(context.config),
1796             fields_str,
1797             shape.indent.to_string_with_newline(context.config)
1798         )
1799     } else {
1800         // One liner or visual indent.
1801         format!(" {} ", fields_str)
1802     }
1803 }
1804
1805 pub fn struct_lit_field_separator(config: &Config) -> &str {
1806     colon_spaces(config.space_before_colon(), config.space_after_colon())
1807 }
1808
1809 pub fn rewrite_field(
1810     context: &RewriteContext,
1811     field: &ast::Field,
1812     shape: Shape,
1813     prefix_max_width: usize,
1814 ) -> Option<String> {
1815     if contains_skip(&field.attrs) {
1816         return Some(context.snippet(field.span()).to_owned());
1817     }
1818     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1819     if !attrs_str.is_empty() {
1820         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1821     };
1822     let name = &field.ident.name.to_string();
1823     if field.is_shorthand {
1824         Some(attrs_str + &name)
1825     } else {
1826         let mut separator = String::from(struct_lit_field_separator(context.config));
1827         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
1828             separator.push(' ');
1829         }
1830         let overhead = name.len() + separator.len();
1831         let expr_shape = shape.offset_left(overhead)?;
1832         let expr = field.expr.rewrite(context, expr_shape);
1833
1834         match expr {
1835             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1836                 Some(attrs_str + &name)
1837             }
1838             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1839             None => {
1840                 let expr_offset = shape.indent.block_indent(context.config);
1841                 let expr = field
1842                     .expr
1843                     .rewrite(context, Shape::indented(expr_offset, context.config));
1844                 expr.map(|s| {
1845                     format!(
1846                         "{}{}:\n{}{}",
1847                         attrs_str,
1848                         name,
1849                         expr_offset.to_string(context.config),
1850                         s
1851                     )
1852                 })
1853             }
1854         }
1855     }
1856 }
1857
1858 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1859     context: &RewriteContext,
1860     items: &[&T],
1861     span: Span,
1862     shape: Shape,
1863 ) -> Option<String>
1864 where
1865     T: Rewrite + Spanned + ToExpr + 'a,
1866 {
1867     let mut items = items.iter();
1868     // In case of length 1, need a trailing comma
1869     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1870     if items.len() == 1 {
1871         // 3 = "(" + ",)"
1872         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1873         return items
1874             .next()
1875             .unwrap()
1876             .rewrite(context, nested_shape)
1877             .map(|s| {
1878                 if context.config.spaces_within_parens_and_brackets() {
1879                     format!("( {}, )", s)
1880                 } else {
1881                     format!("({},)", s)
1882                 }
1883             });
1884     }
1885
1886     let list_lo = context.snippet_provider.span_after(span, "(");
1887     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1888     let items = itemize_list(
1889         context.snippet_provider,
1890         items,
1891         ")",
1892         ",",
1893         |item| item.span().lo(),
1894         |item| item.span().hi(),
1895         |item| item.rewrite(context, nested_shape),
1896         list_lo,
1897         span.hi() - BytePos(1),
1898         false,
1899     );
1900     let item_vec: Vec<_> = items.collect();
1901     let tactic = definitive_tactic(
1902         &item_vec,
1903         ListTactic::HorizontalVertical,
1904         Separator::Comma,
1905         nested_shape.width,
1906     );
1907     let fmt = ListFormatting {
1908         tactic,
1909         separator: ",",
1910         trailing_separator: SeparatorTactic::Never,
1911         separator_place: SeparatorPlace::Back,
1912         shape,
1913         ends_with_newline: false,
1914         preserve_newline: false,
1915         config: context.config,
1916     };
1917     let list_str = write_list(&item_vec, &fmt)?;
1918
1919     if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
1920         Some(format!("( {} )", list_str))
1921     } else {
1922         Some(format!("({})", list_str))
1923     }
1924 }
1925
1926 pub fn rewrite_tuple<'a, T>(
1927     context: &RewriteContext,
1928     items: &[&T],
1929     span: Span,
1930     shape: Shape,
1931 ) -> Option<String>
1932 where
1933     T: Rewrite + Spanned + ToExpr + 'a,
1934 {
1935     debug!("rewrite_tuple {:?}", shape);
1936     if context.use_block_indent() {
1937         // We use the same rule as function calls for rewriting tuples.
1938         let force_tactic = if context.inside_macro() {
1939             if span_ends_with_comma(context, span) {
1940                 Some(SeparatorTactic::Always)
1941             } else {
1942                 Some(SeparatorTactic::Never)
1943             }
1944         } else if items.len() == 1 {
1945             Some(SeparatorTactic::Always)
1946         } else {
1947             None
1948         };
1949         overflow::rewrite_with_parens(
1950             context,
1951             "",
1952             items,
1953             shape,
1954             span,
1955             context.config.width_heuristics().fn_call_width,
1956             force_tactic,
1957         )
1958     } else {
1959         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1960     }
1961 }
1962
1963 pub fn rewrite_unary_prefix<R: Rewrite>(
1964     context: &RewriteContext,
1965     prefix: &str,
1966     rewrite: &R,
1967     shape: Shape,
1968 ) -> Option<String> {
1969     rewrite
1970         .rewrite(context, shape.offset_left(prefix.len())?)
1971         .map(|r| format!("{}{}", prefix, r))
1972 }
1973
1974 // FIXME: this is probably not correct for multi-line Rewrites. we should
1975 // subtract suffix.len() from the last line budget, not the first!
1976 pub fn rewrite_unary_suffix<R: Rewrite>(
1977     context: &RewriteContext,
1978     suffix: &str,
1979     rewrite: &R,
1980     shape: Shape,
1981 ) -> Option<String> {
1982     rewrite
1983         .rewrite(context, shape.sub_width(suffix.len())?)
1984         .map(|mut r| {
1985             r.push_str(suffix);
1986             r
1987         })
1988 }
1989
1990 fn rewrite_unary_op(
1991     context: &RewriteContext,
1992     op: &ast::UnOp,
1993     expr: &ast::Expr,
1994     shape: Shape,
1995 ) -> Option<String> {
1996     // For some reason, an UnOp is not spanned like BinOp!
1997     let operator_str = match *op {
1998         ast::UnOp::Deref => "*",
1999         ast::UnOp::Not => "!",
2000         ast::UnOp::Neg => "-",
2001     };
2002     rewrite_unary_prefix(context, operator_str, expr, shape)
2003 }
2004
2005 fn rewrite_assignment(
2006     context: &RewriteContext,
2007     lhs: &ast::Expr,
2008     rhs: &ast::Expr,
2009     op: Option<&ast::BinOp>,
2010     shape: Shape,
2011 ) -> Option<String> {
2012     let operator_str = match op {
2013         Some(op) => context.snippet(op.span),
2014         None => "=",
2015     };
2016
2017     // 1 = space between lhs and operator.
2018     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2019     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2020
2021     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2022 }
2023
2024 /// Controls where to put the rhs.
2025 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
2026 pub enum RhsTactics {
2027     /// Use heuristics.
2028     Default,
2029     /// Put the rhs on the next line if it uses multiple line.
2030     ForceNextLine,
2031 }
2032
2033 // The left hand side must contain everything up to, and including, the
2034 // assignment operator.
2035 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2036     context: &RewriteContext,
2037     lhs: S,
2038     ex: &R,
2039     shape: Shape,
2040 ) -> Option<String> {
2041     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2042 }
2043
2044 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2045     context: &RewriteContext,
2046     lhs: S,
2047     ex: &R,
2048     shape: Shape,
2049     rhs_tactics: RhsTactics,
2050 ) -> Option<String> {
2051     let lhs = lhs.into();
2052     let last_line_width = last_line_width(&lhs)
2053         .checked_sub(if lhs.contains('\n') {
2054             shape.indent.width()
2055         } else {
2056             0
2057         })
2058         .unwrap_or(0);
2059     // 1 = space between operator and rhs.
2060     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2061         width: 0,
2062         offset: shape.offset + last_line_width + 1,
2063         ..shape
2064     });
2065     let rhs = choose_rhs(
2066         context,
2067         ex,
2068         orig_shape,
2069         ex.rewrite(context, orig_shape),
2070         rhs_tactics,
2071     )?;
2072     Some(lhs + &rhs)
2073 }
2074
2075 fn choose_rhs<R: Rewrite>(
2076     context: &RewriteContext,
2077     expr: &R,
2078     shape: Shape,
2079     orig_rhs: Option<String>,
2080     rhs_tactics: RhsTactics,
2081 ) -> Option<String> {
2082     match orig_rhs {
2083         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2084             Some(format!(" {}", new_str))
2085         }
2086         _ => {
2087             // Expression did not fit on the same line as the identifier.
2088             // Try splitting the line and see if that works better.
2089             let new_shape =
2090                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2091                     .sub_width(shape.rhs_overhead(context.config))?;
2092             let new_rhs = expr.rewrite(context, new_shape);
2093             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2094
2095             match (orig_rhs, new_rhs) {
2096                 (Some(ref orig_rhs), Some(ref new_rhs))
2097                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2098                         .is_none() =>
2099                 {
2100                     Some(format!(" {}", orig_rhs))
2101                 }
2102                 (Some(ref orig_rhs), Some(ref new_rhs))
2103                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2104                 {
2105                     Some(format!("{}{}", new_indent_str, new_rhs))
2106                 }
2107                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2108                 (None, None) => None,
2109                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2110             }
2111         }
2112     }
2113 }
2114
2115 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2116     rhs_tactics == RhsTactics::ForceNextLine
2117         || !next_line_rhs.contains('\n')
2118         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2119 }
2120
2121 fn rewrite_expr_addrof(
2122     context: &RewriteContext,
2123     mutability: ast::Mutability,
2124     expr: &ast::Expr,
2125     shape: Shape,
2126 ) -> Option<String> {
2127     let operator_str = match mutability {
2128         ast::Mutability::Immutable => "&",
2129         ast::Mutability::Mutable => "&mut ",
2130     };
2131     rewrite_unary_prefix(context, operator_str, expr, shape)
2132 }
2133
2134 pub trait ToExpr {
2135     fn to_expr(&self) -> Option<&ast::Expr>;
2136     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2137 }
2138
2139 impl ToExpr for ast::Expr {
2140     fn to_expr(&self) -> Option<&ast::Expr> {
2141         Some(self)
2142     }
2143
2144     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2145         can_be_overflowed_expr(context, self, len)
2146     }
2147 }
2148
2149 impl ToExpr for ast::Ty {
2150     fn to_expr(&self) -> Option<&ast::Expr> {
2151         None
2152     }
2153
2154     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2155         can_be_overflowed_type(context, self, len)
2156     }
2157 }
2158
2159 impl<'a> ToExpr for TuplePatField<'a> {
2160     fn to_expr(&self) -> Option<&ast::Expr> {
2161         None
2162     }
2163
2164     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2165         can_be_overflowed_pat(context, self, len)
2166     }
2167 }
2168
2169 impl<'a> ToExpr for ast::StructField {
2170     fn to_expr(&self) -> Option<&ast::Expr> {
2171         None
2172     }
2173
2174     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2175         false
2176     }
2177 }
2178
2179 impl<'a> ToExpr for MacroArg {
2180     fn to_expr(&self) -> Option<&ast::Expr> {
2181         match *self {
2182             MacroArg::Expr(ref expr) => Some(expr),
2183             _ => None,
2184         }
2185     }
2186
2187     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2188         match *self {
2189             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2190             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2191             MacroArg::Pat(..) => false,
2192             MacroArg::Item(..) => len == 1,
2193         }
2194     }
2195 }
2196
2197 impl ToExpr for ast::GenericParam {
2198     fn to_expr(&self) -> Option<&ast::Expr> {
2199         None
2200     }
2201
2202     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2203         false
2204     }
2205 }