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, ptr_vec_to_ref_vec,
  43     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, opt_label) => {
 122             match expr_type {
 123                 ExprType::Statement => {
 124                     if is_unsafe_block(block) {
 125                         rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 126                     } else if let rw @ Some(_) =
 127                         rewrite_empty_block(context, block, Some(&expr.attrs), opt_label, "", 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
 134                         rewrite_block_with_visitor(
 135                             context,
 136                             &prefix,
 137                             block,
 138                             Some(&expr.attrs),
 139                             opt_label,
 140                             shape,
 141                             true,
 142                         )
 143                     }
 144                 }
 145                 ExprType::SubExpression => {
 146                     rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 147                 }
 148             }
 149         }
 150         ast::ExprKind::Match(ref cond, ref arms) => {
 151             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 152         }
 153         ast::ExprKind::Path(ref qself, ref path) => {
 154             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 155         }
 156         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 157             rewrite_assignment(context, lhs, rhs, None, shape)
 158         }
 159         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 160             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 161         }
 162         ast::ExprKind::Continue(ref opt_label) => {
 163             let id_str = match *opt_label {
 164                 Some(label) => format!(" {}", label.ident),
 165                 None => String::new(),
 166             };
 167             Some(format!("continue{}", id_str))
 168         }
 169         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 170             let id_str = match *opt_label {
 171                 Some(label) => format!(" {}", label.ident),
 172                 None => String::new(),
 173             };
 174
 175             if let Some(ref expr) = *opt_expr {
 176                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 177             } else {
 178                 Some(format!("break{}", id_str))
 179             }
 180         }
 181         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 182             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 183         } else {
 184             Some("yield".to_string())
 185         },
 186         ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) => {
 187             closures::rewrite_closure(
 188                 capture, movability, fn_decl, body, expr.span, context, shape,
 189             )
 190         }
 191         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 192             rewrite_chain(expr, context, shape)
 193         }
 194         ast::ExprKind::Mac(ref mac) => {
 195             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 196                 wrap_str(
 197                     context.snippet(expr.span).to_owned(),
 198                     context.config.max_width(),
 199                     shape,
 200                 )
 201             })
 202         }
 203         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 204         ast::ExprKind::Ret(Some(ref expr)) => {
 205             rewrite_unary_prefix(context, "return ", &**expr, shape)
 206         }
 207         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 208         ast::ExprKind::AddrOf(mutability, ref expr) => {
 209             rewrite_expr_addrof(context, mutability, expr, shape)
 210         }
 211         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 212             &**expr,
 213             &**ty,
 214             PairParts::new("", " as ", ""),
 215             context,
 216             shape,
 217             SeparatorPlace::Front,
 218         ),
 219         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 220             &**expr,
 221             &**ty,
 222             PairParts::new("", ": ", ""),
 223             context,
 224             shape,
 225             SeparatorPlace::Back,
 226         ),
 227         ast::ExprKind::Index(ref expr, ref index) => {
 228             rewrite_index(&**expr, &**index, context, shape)
 229         }
 230         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 231             &**expr,
 232             &*repeats.value,
 233             PairParts::new("[", "; ", "]"),
 234             context,
 235             shape,
 236             SeparatorPlace::Back,
 237         ),
 238         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 239             let delim = match limits {
 240                 ast::RangeLimits::HalfOpen => "..",
 241                 ast::RangeLimits::Closed => "..=",
 242             };
 243
 244             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 245                 match lhs.node {
 246                     ast::ExprKind::Lit(ref lit) => match lit.node {
 247                         ast::LitKind::FloatUnsuffixed(..) => {
 248                             context.snippet(lit.span).ends_with('.')
 249                         }
 250                         _ => false,
 251                     },
 252                     _ => false,
 253                 }
 254             }
 255
 256             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 257                 match rhs.node {
 258                     // Don't format `.. ..` into `....`, which is invalid.
 259                     //
 260                     // This check is unnecessary for `lhs`, because a range
 261                     // starting from another range needs parentheses as `(x ..) ..`
 262                     // (`x .. ..` is a range from `x` to `..`).
 263                     ast::ExprKind::Range(None, _, _) => true,
 264                     _ => false,
 265                 }
 266             }
 267
 268             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 269                 let space_if = |b: bool| if b { " " } else { "" };
 270
 271                 format!(
 272                     "{}{}{}",
 273                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 274                         .unwrap_or(""),
 275                     delim,
 276                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 277                         .unwrap_or(""),
 278                 )
 279             };
 280
 281             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 282                 (Some(lhs), Some(rhs)) => {
 283                     let sp_delim = if context.config.spaces_around_ranges() {
 284                         format!(" {} ", delim)
 285                     } else {
 286                         default_sp_delim(Some(lhs), Some(rhs))
 287                     };
 288                     rewrite_pair(
 289                         &*lhs,
 290                         &*rhs,
 291                         PairParts::new("", &sp_delim, ""),
 292                         context,
 293                         shape,
 294                         context.config.binop_separator(),
 295                     )
 296                 }
 297                 (None, Some(rhs)) => {
 298                     let sp_delim = if context.config.spaces_around_ranges() {
 299                         format!("{} ", delim)
 300                     } else {
 301                         default_sp_delim(None, Some(rhs))
 302                     };
 303                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 304                 }
 305                 (Some(lhs), None) => {
 306                     let sp_delim = if context.config.spaces_around_ranges() {
 307                         format!(" {}", delim)
 308                     } else {
 309                         default_sp_delim(Some(lhs), None)
 310                     };
 311                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 312                 }
 313                 (None, None) => Some(delim.to_owned()),
 314             }
 315         }
 316         // We do not format these expressions yet, but they should still
 317         // satisfy our width restrictions.
 318         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 319         ast::ExprKind::Catch(ref block) => {
 320             if let rw @ Some(_) = rewrite_single_line_block(
 321                 context,
 322                 "do catch ",
 323                 block,
 324                 Some(&expr.attrs),
 325                 None,
 326                 shape,
 327             ) {
 328                 rw
 329             } else {
 330                 // 9 = `do catch `
 331                 let budget = shape.width.saturating_sub(9);
 332                 Some(format!(
 333                     "{}{}",
 334                     "do catch ",
 335                     rewrite_block(
 336                         block,
 337                         Some(&expr.attrs),
 338                         None,
 339                         context,
 340                         Shape::legacy(budget, shape.indent)
 341                     )?
 342                 ))
 343             }
 344         }
 345         // FIXME(#2743)
 346         ast::ExprKind::ObsoleteInPlace(..) => unimplemented!(),
 347     };
 348
 349     expr_rw
 350         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 351         .and_then(|expr_str| {
 352             let attrs = outer_attributes(&expr.attrs);
 353             let attrs_str = attrs.rewrite(context, shape)?;
 354             let span = mk_sp(
 355                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 356                 expr.span.lo(),
 357             );
 358             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 359         })
 360 }
 361
 362 /// Collect operands that appears in the given binary operator in the opposite order.
 363 /// e.g. `collect_binary_items(e, ||)` for `a && b || c || d` returns `[d, c, a && b]`.
 364 fn collect_binary_items<'a>(mut expr: &'a ast::Expr, binop: ast::BinOp) -> Vec<&'a ast::Expr> {
 365     let mut result = vec![];
 366     let mut prev_lhs = None;
 367     loop {
 368         match expr.node {
 369             ast::ExprKind::Binary(inner_binop, ref lhs, ref rhs)
 370                 if inner_binop.node == binop.node =>
 371             {
 372                 result.push(&**rhs);
 373                 expr = lhs;
 374                 prev_lhs = Some(lhs);
 375             }
 376             _ => {
 377                 if let Some(lhs) = prev_lhs {
 378                     result.push(lhs);
 379                 }
 380                 break;
 381             }
 382         }
 383     }
 384     result
 385 }
 386
 387 /// Rewrites a binary expression whose operands fits within a single line.
 388 fn rewrite_simple_binaries(
 389     context: &RewriteContext,
 390     expr: &ast::Expr,
 391     shape: Shape,
 392     op: ast::BinOp,
 393 ) -> Option<String> {
 394     let op_str = context.snippet(op.span);
 395
 396     // 2 = spaces around a binary operator.
 397     let sep_overhead = op_str.len() + 2;
 398     let nested_overhead = sep_overhead - 1;
 399
 400     let nested_shape = (match context.config.indent_style() {
 401         IndentStyle::Visual => shape.visual_indent(0),
 402         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 403     }).with_max_width(context.config);
 404     let nested_shape = match context.config.binop_separator() {
 405         SeparatorPlace::Back => nested_shape.sub_width(nested_overhead)?,
 406         SeparatorPlace::Front => nested_shape.offset_left(nested_overhead)?,
 407     };
 408
 409     let opt_rewrites: Option<Vec<_>> = collect_binary_items(expr, op)
 410         .iter()
 411         .rev()
 412         .map(|e| e.rewrite(context, nested_shape))
 413         .collect();
 414     if let Some(rewrites) = opt_rewrites {
 415         if rewrites.iter().all(|e| ::utils::is_single_line(e)) {
 416             let total_width = rewrites.iter().map(|s| s.len()).sum::<usize>()
 417                 + sep_overhead * (rewrites.len() - 1);
 418
 419             let sep_str = if total_width <= shape.width {
 420                 format!(" {} ", op_str)
 421             } else {
 422                 let indent_str = nested_shape.indent.to_string_with_newline(context.config);
 423                 match context.config.binop_separator() {
 424                     SeparatorPlace::Back => format!(" {}{}", op_str.trim_right(), indent_str),
 425                     SeparatorPlace::Front => format!("{}{} ", indent_str, op_str.trim_left()),
 426                 }
 427             };
 428
 429             return wrap_str(rewrites.join(&sep_str), context.config.max_width(), shape);
 430         }
 431     }
 432
 433     None
 434 }
 435
 436 #[derive(new, Clone, Copy)]
 437 pub struct PairParts<'a> {
 438     prefix: &'a str,
 439     infix: &'a str,
 440     suffix: &'a str,
 441 }
 442
 443 pub fn rewrite_pair<LHS, RHS>(
 444     lhs: &LHS,
 445     rhs: &RHS,
 446     pp: PairParts,
 447     context: &RewriteContext,
 448     shape: Shape,
 449     separator_place: SeparatorPlace,
 450 ) -> Option<String>
 451 where
 452     LHS: Rewrite,
 453     RHS: Rewrite,
 454 {
 455     let lhs_overhead = match separator_place {
 456         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 457         SeparatorPlace::Front => shape.used_width(),
 458     };
 459     let lhs_shape = Shape {
 460         width: context.budget(lhs_overhead),
 461         ..shape
 462     };
 463     let lhs_result = lhs
 464         .rewrite(context, lhs_shape)
 465         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 466
 467     // Try to put both lhs and rhs on the same line.
 468     let rhs_orig_result = shape
 469         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 470         .and_then(|s| s.sub_width(pp.suffix.len()))
 471         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 472     if let Some(ref rhs_result) = rhs_orig_result {
 473         // If the length of the lhs is equal to or shorter than the tab width or
 474         // the rhs looks like block expression, we put the rhs on the same
 475         // line with the lhs even if the rhs is multi-lined.
 476         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 477             || rhs_result
 478                 .lines()
 479                 .next()
 480                 .map(|first_line| first_line.ends_with('{'))
 481                 .unwrap_or(false);
 482         if !rhs_result.contains('\n') || allow_same_line {
 483             let one_line_width = last_line_width(&lhs_result)
 484                 + pp.infix.len()
 485                 + first_line_width(rhs_result)
 486                 + pp.suffix.len();
 487             if one_line_width <= shape.width {
 488                 return Some(format!(
 489                     "{}{}{}{}",
 490                     lhs_result, pp.infix, rhs_result, pp.suffix
 491                 ));
 492             }
 493         }
 494     }
 495
 496     // We have to use multiple lines.
 497     // Re-evaluate the rhs because we have more space now:
 498     let mut rhs_shape = match context.config.indent_style() {
 499         IndentStyle::Visual => shape
 500             .sub_width(pp.suffix.len() + pp.prefix.len())?
 501             .visual_indent(pp.prefix.len()),
 502         IndentStyle::Block => {
 503             // Try to calculate the initial constraint on the right hand side.
 504             let rhs_overhead = shape.rhs_overhead(context.config);
 505             Shape::indented(shape.indent.block_indent(context.config), context.config)
 506                 .sub_width(rhs_overhead)?
 507         }
 508     };
 509     let infix = match separator_place {
 510         SeparatorPlace::Back => pp.infix.trim_right(),
 511         SeparatorPlace::Front => pp.infix.trim_left(),
 512     };
 513     if separator_place == SeparatorPlace::Front {
 514         rhs_shape = rhs_shape.offset_left(infix.len())?;
 515     }
 516     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 517     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 518     let infix_with_sep = match separator_place {
 519         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 520         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 521     };
 522     Some(format!(
 523         "{}{}{}{}",
 524         lhs_result, infix_with_sep, rhs_result, pp.suffix
 525     ))
 526 }
 527
 528 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 529     name: &str,
 530     exprs: &[&T],
 531     span: Span,
 532     context: &RewriteContext,
 533     shape: Shape,
 534     force_separator_tactic: Option<SeparatorTactic>,
 535     delim_token: Option<DelimToken>,
 536 ) -> Option<String> {
 537     overflow::rewrite_with_square_brackets(
 538         context,
 539         name,
 540         exprs,
 541         shape,
 542         span,
 543         force_separator_tactic,
 544         delim_token,
 545     )
 546 }
 547
 548 fn rewrite_empty_block(
 549     context: &RewriteContext,
 550     block: &ast::Block,
 551     attrs: Option<&[ast::Attribute]>,
 552     label: Option<ast::Label>,
 553     prefix: &str,
 554     shape: Shape,
 555 ) -> Option<String> {
 556     let label_str = rewrite_label(label);
 557     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 558         return None;
 559     }
 560
 561     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 562     {
 563         return Some(format!("{}{}{{}}", prefix, label_str));
 564     }
 565
 566     // If a block contains only a single-line comment, then leave it on one line.
 567     let user_str = context.snippet(block.span);
 568     let user_str = user_str.trim();
 569     if user_str.starts_with('{') && user_str.ends_with('}') {
 570         let comment_str = user_str[1..user_str.len() - 1].trim();
 571         if block.stmts.is_empty()
 572             && !comment_str.contains('\n')
 573             && !comment_str.starts_with("//")
 574             && comment_str.len() + 4 <= shape.width
 575         {
 576             return Some(format!("{}{}{{ {} }}", prefix, label_str, comment_str));
 577         }
 578     }
 579
 580     None
 581 }
 582
 583 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 584     Some(match block.rules {
 585         ast::BlockCheckMode::Unsafe(..) => {
 586             let snippet = context.snippet(block.span);
 587             let open_pos = snippet.find_uncommented("{")?;
 588             // Extract comment between unsafe and block start.
 589             let trimmed = &snippet[6..open_pos].trim();
 590
 591             if !trimmed.is_empty() {
 592                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 593                 let budget = shape.width.checked_sub(9)?;
 594                 format!(
 595                     "unsafe {} ",
 596                     rewrite_comment(
 597                         trimmed,
 598                         true,
 599                         Shape::legacy(budget, shape.indent + 7),
 600                         context.config,
 601                     )?
 602                 )
 603             } else {
 604                 "unsafe ".to_owned()
 605             }
 606         }
 607         ast::BlockCheckMode::Default => String::new(),
 608     })
 609 }
 610
 611 fn rewrite_single_line_block(
 612     context: &RewriteContext,
 613     prefix: &str,
 614     block: &ast::Block,
 615     attrs: Option<&[ast::Attribute]>,
 616     label: Option<ast::Label>,
 617     shape: Shape,
 618 ) -> Option<String> {
 619     if is_simple_block(block, attrs, context.codemap) {
 620         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 621         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 622         let label_str = rewrite_label(label);
 623         let result = format!("{}{}{{ {} }}", prefix, label_str, expr_str);
 624         if result.len() <= shape.width && !result.contains('\n') {
 625             return Some(result);
 626         }
 627     }
 628     None
 629 }
 630
 631 pub fn rewrite_block_with_visitor(
 632     context: &RewriteContext,
 633     prefix: &str,
 634     block: &ast::Block,
 635     attrs: Option<&[ast::Attribute]>,
 636     label: Option<ast::Label>,
 637     shape: Shape,
 638     has_braces: bool,
 639 ) -> Option<String> {
 640     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, prefix, shape) {
 641         return rw;
 642     }
 643
 644     let mut visitor = FmtVisitor::from_context(context);
 645     visitor.block_indent = shape.indent;
 646     visitor.is_if_else_block = context.is_if_else_block();
 647     match block.rules {
 648         ast::BlockCheckMode::Unsafe(..) => {
 649             let snippet = context.snippet(block.span);
 650             let open_pos = snippet.find_uncommented("{")?;
 651             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 652         }
 653         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 654     }
 655
 656     let inner_attrs = attrs.map(inner_attributes);
 657     let label_str = rewrite_label(label);
 658     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 659     Some(format!("{}{}{}", prefix, label_str, visitor.buffer))
 660 }
 661
 662 impl Rewrite for ast::Block {
 663     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 664         rewrite_block(self, None, None, context, shape)
 665     }
 666 }
 667
 668 fn rewrite_block(
 669     block: &ast::Block,
 670     attrs: Option<&[ast::Attribute]>,
 671     label: Option<ast::Label>,
 672     context: &RewriteContext,
 673     shape: Shape,
 674 ) -> Option<String> {
 675     let prefix = block_prefix(context, block, shape)?;
 676
 677     // shape.width is used only for the single line case: either the empty block `{}`,
 678     // or an unsafe expression `unsafe { e }`.
 679     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, &prefix, shape) {
 680         return rw;
 681     }
 682
 683     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, label, shape, true);
 684     if let Some(ref result_str) = result {
 685         if result_str.lines().count() <= 3 {
 686             if let rw @ Some(_) =
 687                 rewrite_single_line_block(context, &prefix, block, attrs, label, shape)
 688             {
 689                 return rw;
 690             }
 691         }
 692     }
 693
 694     result
 695 }
 696
 697 impl Rewrite for ast::Stmt {
 698     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 699         skip_out_of_file_lines_range!(context, self.span());
 700
 701         let result = match self.node {
 702             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 703             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 704                 let suffix = if semicolon_for_stmt(context, self) {
 705                     ";"
 706                 } else {
 707                     ""
 708                 };
 709
 710                 let shape = shape.sub_width(suffix.len())?;
 711                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 712             }
 713             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 714         };
 715         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 716     }
 717 }
 718
 719 // Rewrite condition if the given expression has one.
 720 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 721     match expr.node {
 722         ast::ExprKind::Match(ref cond, _) => {
 723             // `match `cond` {`
 724             let cond_shape = match context.config.indent_style() {
 725                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 726                 IndentStyle::Block => shape.offset_left(8)?,
 727             };
 728             cond.rewrite(context, cond_shape)
 729         }
 730         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 731             let alt_block_sep =
 732                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 733             control_flow
 734                 .rewrite_cond(context, shape, &alt_block_sep)
 735                 .and_then(|rw| Some(rw.0))
 736         }),
 737     }
 738 }
 739
 740 // Abstraction over control flow expressions
 741 #[derive(Debug)]
 742 struct ControlFlow<'a> {
 743     cond: Option<&'a ast::Expr>,
 744     block: &'a ast::Block,
 745     else_block: Option<&'a ast::Expr>,
 746     label: Option<ast::Label>,
 747     pats: Vec<&'a ast::Pat>,
 748     keyword: &'a str,
 749     matcher: &'a str,
 750     connector: &'a str,
 751     allow_single_line: bool,
 752     // True if this is an `if` expression in an `else if` :-( hacky
 753     nested_if: bool,
 754     span: Span,
 755 }
 756
 757 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 758     match expr.node {
 759         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 760             cond,
 761             vec![],
 762             if_block,
 763             else_block.as_ref().map(|e| &**e),
 764             expr_type == ExprType::SubExpression,
 765             false,
 766             expr.span,
 767         )),
 768         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 769             Some(ControlFlow::new_if(
 770                 cond,
 771                 ptr_vec_to_ref_vec(pat),
 772                 if_block,
 773                 else_block.as_ref().map(|e| &**e),
 774                 expr_type == ExprType::SubExpression,
 775                 false,
 776                 expr.span,
 777             ))
 778         }
 779         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 780             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 781         }
 782         ast::ExprKind::Loop(ref block, label) => {
 783             Some(ControlFlow::new_loop(block, label, expr.span))
 784         }
 785         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 786             vec![],
 787             cond,
 788             block,
 789             label,
 790             expr.span,
 791         )),
 792         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 793             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 794         ),
 795         _ => None,
 796     }
 797 }
 798
 799 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 800     if pats.is_empty() {
 801         ""
 802     } else {
 803         "let"
 804     }
 805 }
 806
 807 impl<'a> ControlFlow<'a> {
 808     fn new_if(
 809         cond: &'a ast::Expr,
 810         pats: Vec<&'a ast::Pat>,
 811         block: &'a ast::Block,
 812         else_block: Option<&'a ast::Expr>,
 813         allow_single_line: bool,
 814         nested_if: bool,
 815         span: Span,
 816     ) -> ControlFlow<'a> {
 817         let matcher = choose_matcher(&pats);
 818         ControlFlow {
 819             cond: Some(cond),
 820             block,
 821             else_block,
 822             label: None,
 823             pats,
 824             keyword: "if",
 825             matcher,
 826             connector: " =",
 827             allow_single_line,
 828             nested_if,
 829             span,
 830         }
 831     }
 832
 833     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 834         ControlFlow {
 835             cond: None,
 836             block,
 837             else_block: None,
 838             label,
 839             pats: vec![],
 840             keyword: "loop",
 841             matcher: "",
 842             connector: "",
 843             allow_single_line: false,
 844             nested_if: false,
 845             span,
 846         }
 847     }
 848
 849     fn new_while(
 850         pats: Vec<&'a ast::Pat>,
 851         cond: &'a ast::Expr,
 852         block: &'a ast::Block,
 853         label: Option<ast::Label>,
 854         span: Span,
 855     ) -> ControlFlow<'a> {
 856         let matcher = choose_matcher(&pats);
 857         ControlFlow {
 858             cond: Some(cond),
 859             block,
 860             else_block: None,
 861             label,
 862             pats,
 863             keyword: "while",
 864             matcher,
 865             connector: " =",
 866             allow_single_line: false,
 867             nested_if: false,
 868             span,
 869         }
 870     }
 871
 872     fn new_for(
 873         pat: &'a ast::Pat,
 874         cond: &'a ast::Expr,
 875         block: &'a ast::Block,
 876         label: Option<ast::Label>,
 877         span: Span,
 878     ) -> ControlFlow<'a> {
 879         ControlFlow {
 880             cond: Some(cond),
 881             block,
 882             else_block: None,
 883             label,
 884             pats: vec![pat],
 885             keyword: "for",
 886             matcher: "",
 887             connector: " in",
 888             allow_single_line: false,
 889             nested_if: false,
 890             span,
 891         }
 892     }
 893
 894     fn rewrite_single_line(
 895         &self,
 896         pat_expr_str: &str,
 897         context: &RewriteContext,
 898         width: usize,
 899     ) -> Option<String> {
 900         assert!(self.allow_single_line);
 901         let else_block = self.else_block?;
 902         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 903
 904         if let ast::ExprKind::Block(ref else_node, _) = else_block.node {
 905             if !is_simple_block(self.block, None, context.codemap)
 906                 || !is_simple_block(else_node, None, context.codemap)
 907                 || pat_expr_str.contains('\n')
 908             {
 909                 return None;
 910             }
 911
 912             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 913             let expr = &self.block.stmts[0];
 914             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 915
 916             let new_width = new_width.checked_sub(if_str.len())?;
 917             let else_expr = &else_node.stmts[0];
 918             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 919
 920             if if_str.contains('\n') || else_str.contains('\n') {
 921                 return None;
 922             }
 923
 924             let result = format!(
 925                 "{} {} {{ {} }} else {{ {} }}",
 926                 self.keyword, pat_expr_str, if_str, else_str
 927             );
 928
 929             if result.len() <= width {
 930                 return Some(result);
 931             }
 932         }
 933
 934         None
 935     }
 936 }
 937
 938 impl<'a> ControlFlow<'a> {
 939     fn rewrite_pat_expr(
 940         &self,
 941         context: &RewriteContext,
 942         expr: &ast::Expr,
 943         shape: Shape,
 944         offset: usize,
 945     ) -> Option<String> {
 946         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 947
 948         let cond_shape = shape.offset_left(offset)?;
 949         if !self.pats.is_empty() {
 950             let matcher = if self.matcher.is_empty() {
 951                 self.matcher.to_owned()
 952             } else {
 953                 format!("{} ", self.matcher)
 954             };
 955             let pat_shape = cond_shape
 956                 .offset_left(matcher.len())?
 957                 .sub_width(self.connector.len())?;
 958             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 959             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 960             return rewrite_assign_rhs(context, result, expr, cond_shape);
 961         }
 962
 963         let expr_rw = expr.rewrite(context, cond_shape);
 964         // The expression may (partially) fit on the current line.
 965         // We do not allow splitting between `if` and condition.
 966         if self.keyword == "if" || expr_rw.is_some() {
 967             return expr_rw;
 968         }
 969
 970         // The expression won't fit on the current line, jump to next.
 971         let nested_shape = shape
 972             .block_indent(context.config.tab_spaces())
 973             .with_max_width(context.config);
 974         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 975         expr.rewrite(context, nested_shape)
 976             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 977     }
 978
 979     fn rewrite_cond(
 980         &self,
 981         context: &RewriteContext,
 982         shape: Shape,
 983         alt_block_sep: &str,
 984     ) -> Option<(String, usize)> {
 985         // Do not take the rhs overhead from the upper expressions into account
 986         // when rewriting pattern.
 987         let new_width = context.budget(shape.used_width());
 988         let fresh_shape = Shape {
 989             width: new_width,
 990             ..shape
 991         };
 992         let constr_shape = if self.nested_if {
 993             // We are part of an if-elseif-else chain. Our constraints are tightened.
 994             // 7 = "} else " .len()
 995             fresh_shape.offset_left(7)?
 996         } else {
 997             fresh_shape
 998         };
 999
1000         let label_string = rewrite_label(self.label);
1001         // 1 = space after keyword.
1002         let offset = self.keyword.len() + label_string.len() + 1;
1003
1004         let pat_expr_string = match self.cond {
1005             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
1006             None => String::new(),
1007         };
1008
1009         let brace_overhead =
1010             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1011                 // 2 = ` {`
1012                 2
1013             } else {
1014                 0
1015             };
1016         let one_line_budget = context
1017             .config
1018             .max_width()
1019             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
1020         let force_newline_brace = (pat_expr_string.contains('\n')
1021             || pat_expr_string.len() > one_line_budget)
1022             && !last_line_extendable(&pat_expr_string);
1023
1024         // Try to format if-else on single line.
1025         if self.allow_single_line
1026             && context
1027                 .config
1028                 .width_heuristics()
1029                 .single_line_if_else_max_width > 0
1030         {
1031             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1032
1033             if let Some(cond_str) = trial {
1034                 if cond_str.len()
1035                     <= context
1036                         .config
1037                         .width_heuristics()
1038                         .single_line_if_else_max_width
1039                 {
1040                     return Some((cond_str, 0));
1041                 }
1042             }
1043         }
1044
1045         let cond_span = if let Some(cond) = self.cond {
1046             cond.span
1047         } else {
1048             mk_sp(self.block.span.lo(), self.block.span.lo())
1049         };
1050
1051         // `for event in event`
1052         // Do not include label in the span.
1053         let lo = self
1054             .label
1055             .map_or(self.span.lo(), |label| label.ident.span.hi());
1056         let between_kwd_cond = mk_sp(
1057             context
1058                 .snippet_provider
1059                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1060             if self.pats.is_empty() {
1061                 cond_span.lo()
1062             } else if self.matcher.is_empty() {
1063                 self.pats[0].span.lo()
1064             } else {
1065                 context
1066                     .snippet_provider
1067                     .span_before(self.span, self.matcher.trim())
1068             },
1069         );
1070
1071         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1072
1073         let after_cond_comment =
1074             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1075
1076         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1077             ""
1078         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1079             || force_newline_brace
1080         {
1081             alt_block_sep
1082         } else {
1083             " "
1084         };
1085
1086         let used_width = if pat_expr_string.contains('\n') {
1087             last_line_width(&pat_expr_string)
1088         } else {
1089             // 2 = spaces after keyword and condition.
1090             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1091         };
1092
1093         Some((
1094             format!(
1095                 "{}{}{}{}{}",
1096                 label_string,
1097                 self.keyword,
1098                 between_kwd_cond_comment.as_ref().map_or(
1099                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1100                         ""
1101                     } else {
1102                         " "
1103                     },
1104                     |s| &**s,
1105                 ),
1106                 pat_expr_string,
1107                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1108             ),
1109             used_width,
1110         ))
1111     }
1112 }
1113
1114 impl<'a> Rewrite for ControlFlow<'a> {
1115     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1116         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1117
1118         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1119         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1120         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1121         if used_width == 0 {
1122             return Some(cond_str);
1123         }
1124
1125         let block_width = shape.width.saturating_sub(used_width);
1126         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1127         // we should avoid the single line case.
1128         let block_width = if self.else_block.is_some() || self.nested_if {
1129             min(1, block_width)
1130         } else {
1131             block_width
1132         };
1133         let block_shape = Shape {
1134             width: block_width,
1135             ..shape
1136         };
1137         let block_str = {
1138             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1139             let result =
1140                 rewrite_block_with_visitor(context, "", self.block, None, None, block_shape, true);
1141             context.is_if_else_block.replace(old_val);
1142             result?
1143         };
1144
1145         let mut result = format!("{}{}", cond_str, block_str);
1146
1147         if let Some(else_block) = self.else_block {
1148             let shape = Shape::indented(shape.indent, context.config);
1149             let mut last_in_chain = false;
1150             let rewrite = match else_block.node {
1151                 // If the else expression is another if-else expression, prevent it
1152                 // from being formatted on a single line.
1153                 // Note how we're passing the original shape, as the
1154                 // cost of "else" should not cascade.
1155                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1156                     ControlFlow::new_if(
1157                         cond,
1158                         ptr_vec_to_ref_vec(pat),
1159                         if_block,
1160                         next_else_block.as_ref().map(|e| &**e),
1161                         false,
1162                         true,
1163                         mk_sp(else_block.span.lo(), self.span.hi()),
1164                     ).rewrite(context, shape)
1165                 }
1166                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1167                     ControlFlow::new_if(
1168                         cond,
1169                         vec![],
1170                         if_block,
1171                         next_else_block.as_ref().map(|e| &**e),
1172                         false,
1173                         true,
1174                         mk_sp(else_block.span.lo(), self.span.hi()),
1175                     ).rewrite(context, shape)
1176                 }
1177                 _ => {
1178                     last_in_chain = true;
1179                     // When rewriting a block, the width is only used for single line
1180                     // blocks, passing 1 lets us avoid that.
1181                     let else_shape = Shape {
1182                         width: min(1, shape.width),
1183                         ..shape
1184                     };
1185                     format_expr(else_block, ExprType::Statement, context, else_shape)
1186                 }
1187             };
1188
1189             let between_kwd_else_block = mk_sp(
1190                 self.block.span.hi(),
1191                 context
1192                     .snippet_provider
1193                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1194             );
1195             let between_kwd_else_block_comment =
1196                 extract_comment(between_kwd_else_block, context, shape);
1197
1198             let after_else = mk_sp(
1199                 context
1200                     .snippet_provider
1201                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1202                 else_block.span.lo(),
1203             );
1204             let after_else_comment = extract_comment(after_else, context, shape);
1205
1206             let between_sep = match context.config.control_brace_style() {
1207                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1208                     &*alt_block_sep
1209                 }
1210                 ControlBraceStyle::AlwaysSameLine => " ",
1211             };
1212             let after_sep = match context.config.control_brace_style() {
1213                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1214                 _ => " ",
1215             };
1216
1217             result.push_str(&format!(
1218                 "{}else{}",
1219                 between_kwd_else_block_comment
1220                     .as_ref()
1221                     .map_or(between_sep, |s| &**s),
1222                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1223             ));
1224             result.push_str(&rewrite?);
1225         }
1226
1227         Some(result)
1228     }
1229 }
1230
1231 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1232     match opt_label {
1233         Some(label) => Cow::from(format!("{}: ", label.ident)),
1234         None => Cow::from(""),
1235     }
1236 }
1237
1238 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1239     match rewrite_missing_comment(span, shape, context) {
1240         Some(ref comment) if !comment.is_empty() => Some(format!(
1241             "{indent}{}{indent}",
1242             comment,
1243             indent = shape.indent.to_string_with_newline(context.config)
1244         )),
1245         _ => None,
1246     }
1247 }
1248
1249 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1250     let snippet = codemap.span_to_snippet(block.span).unwrap();
1251     contains_comment(&snippet)
1252 }
1253
1254 // Checks that a block contains no statements, an expression and no comments or
1255 // attributes.
1256 // FIXME: incorrectly returns false when comment is contained completely within
1257 // the expression.
1258 pub fn is_simple_block(
1259     block: &ast::Block,
1260     attrs: Option<&[ast::Attribute]>,
1261     codemap: &CodeMap,
1262 ) -> bool {
1263     (block.stmts.len() == 1
1264         && stmt_is_expr(&block.stmts[0])
1265         && !block_contains_comment(block, codemap)
1266         && attrs.map_or(true, |a| a.is_empty()))
1267 }
1268
1269 /// Checks whether a block contains at most one statement or expression, and no
1270 /// comments or attributes.
1271 pub fn is_simple_block_stmt(
1272     block: &ast::Block,
1273     attrs: Option<&[ast::Attribute]>,
1274     codemap: &CodeMap,
1275 ) -> bool {
1276     block.stmts.len() <= 1
1277         && !block_contains_comment(block, codemap)
1278         && attrs.map_or(true, |a| a.is_empty())
1279 }
1280
1281 /// Checks whether a block contains no statements, expressions, comments, or
1282 /// inner attributes.
1283 pub fn is_empty_block(
1284     block: &ast::Block,
1285     attrs: Option<&[ast::Attribute]>,
1286     codemap: &CodeMap,
1287 ) -> bool {
1288     block.stmts.is_empty()
1289         && !block_contains_comment(block, codemap)
1290         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1291 }
1292
1293 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1294     match stmt.node {
1295         ast::StmtKind::Expr(..) => true,
1296         _ => false,
1297     }
1298 }
1299
1300 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1301     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1302         true
1303     } else {
1304         false
1305     }
1306 }
1307
1308 pub fn rewrite_multiple_patterns(
1309     context: &RewriteContext,
1310     pats: &[&ast::Pat],
1311     shape: Shape,
1312 ) -> Option<String> {
1313     let pat_strs = pats
1314         .iter()
1315         .map(|p| p.rewrite(context, shape))
1316         .collect::<Option<Vec<_>>>()?;
1317
1318     let use_mixed_layout = pats
1319         .iter()
1320         .zip(pat_strs.iter())
1321         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1322     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1323     let tactic = if use_mixed_layout {
1324         DefinitiveListTactic::Mixed
1325     } else {
1326         definitive_tactic(
1327             &items,
1328             ListTactic::HorizontalVertical,
1329             Separator::VerticalBar,
1330             shape.width,
1331         )
1332     };
1333     let fmt = ListFormatting {
1334         tactic,
1335         separator: " |",
1336         trailing_separator: SeparatorTactic::Never,
1337         separator_place: context.config.binop_separator(),
1338         shape,
1339         ends_with_newline: false,
1340         preserve_newline: false,
1341         nested: false,
1342         config: context.config,
1343     };
1344     write_list(&items, &fmt)
1345 }
1346
1347 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1348     match l.node {
1349         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1350         _ => wrap_str(
1351             context.snippet(l.span).to_owned(),
1352             context.config.max_width(),
1353             shape,
1354         ),
1355     }
1356 }
1357
1358 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1359     let string_lit = context.snippet(span);
1360
1361     if !context.config.format_strings() {
1362         if string_lit
1363             .lines()
1364             .rev()
1365             .skip(1)
1366             .all(|line| line.ends_with('\\'))
1367         {
1368             let new_indent = shape.visual_indent(1).indent;
1369             let indented_string_lit = String::from(
1370                 string_lit
1371                     .lines()
1372                     .map(|line| {
1373                         format!(
1374                             "{}{}",
1375                             new_indent.to_string(context.config),
1376                             line.trim_left()
1377                         )
1378                     })
1379                     .collect::<Vec<_>>()
1380                     .join("\n")
1381                     .trim_left(),
1382             );
1383             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1384         } else {
1385             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1386         }
1387     }
1388
1389     // Remove the quote characters.
1390     let str_lit = &string_lit[1..string_lit.len() - 1];
1391
1392     rewrite_string(
1393         str_lit,
1394         &StringFormat::new(shape.visual_indent(0), context.config),
1395         None,
1396     )
1397 }
1398
1399 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1400 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1401     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1402         .iter()
1403         .find(|&&(s, _)| s == callee_str)
1404     {
1405         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1406
1407         Some((all_simple, num_args_before))
1408     } else {
1409         None
1410     }
1411 }
1412
1413 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1414 /// format.
1415 ///
1416 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1417 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1418 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1419 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1420     // format! like macros
1421     // From the Rust Standard Library.
1422     ("eprint!", 0),
1423     ("eprintln!", 0),
1424     ("format!", 0),
1425     ("format_args!", 0),
1426     ("print!", 0),
1427     ("println!", 0),
1428     ("panic!", 0),
1429     ("unreachable!", 0),
1430     // From the `log` crate.
1431     ("debug!", 0),
1432     ("error!", 0),
1433     ("info!", 0),
1434     ("warn!", 0),
1435     // write! like macros
1436     ("assert!", 1),
1437     ("debug_assert!", 1),
1438     ("write!", 1),
1439     ("writeln!", 1),
1440     // assert_eq! like macros
1441     ("assert_eq!", 2),
1442     ("assert_ne!", 2),
1443     ("debug_assert_eq!", 2),
1444     ("debug_assert_ne!", 2),
1445 ];
1446
1447 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1448     if context.inside_macro() {
1449         if span_ends_with_comma(context, span) {
1450             Some(SeparatorTactic::Always)
1451         } else {
1452             Some(SeparatorTactic::Never)
1453         }
1454     } else {
1455         None
1456     }
1457 }
1458
1459 pub fn rewrite_call(
1460     context: &RewriteContext,
1461     callee: &str,
1462     args: &[ptr::P<ast::Expr>],
1463     span: Span,
1464     shape: Shape,
1465 ) -> Option<String> {
1466     overflow::rewrite_with_parens(
1467         context,
1468         callee,
1469         &ptr_vec_to_ref_vec(args),
1470         shape,
1471         span,
1472         context.config.width_heuristics().fn_call_width,
1473         choose_separator_tactic(context, span),
1474     )
1475 }
1476
1477 fn is_simple_expr(expr: &ast::Expr) -> bool {
1478     match expr.node {
1479         ast::ExprKind::Lit(..) => true,
1480         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1481         ast::ExprKind::AddrOf(_, ref expr)
1482         | ast::ExprKind::Box(ref expr)
1483         | ast::ExprKind::Cast(ref expr, _)
1484         | ast::ExprKind::Field(ref expr, _)
1485         | ast::ExprKind::Try(ref expr)
1486         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1487         ast::ExprKind::Index(ref lhs, ref rhs) => is_simple_expr(lhs) && is_simple_expr(rhs),
1488         ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1489             is_simple_expr(lhs) && is_simple_expr(&*rhs.value)
1490         }
1491         _ => false,
1492     }
1493 }
1494
1495 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1496     lists
1497         .iter()
1498         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1499 }
1500
1501 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1502     match expr.node {
1503         ast::ExprKind::Match(..) => {
1504             (context.use_block_indent() && args_len == 1)
1505                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1506         }
1507         ast::ExprKind::If(..)
1508         | ast::ExprKind::IfLet(..)
1509         | ast::ExprKind::ForLoop(..)
1510         | ast::ExprKind::Loop(..)
1511         | ast::ExprKind::While(..)
1512         | ast::ExprKind::WhileLet(..) => {
1513             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1514         }
1515         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1516             context.use_block_indent()
1517                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1518         }
1519         ast::ExprKind::Array(..)
1520         | ast::ExprKind::Call(..)
1521         | ast::ExprKind::Mac(..)
1522         | ast::ExprKind::MethodCall(..)
1523         | ast::ExprKind::Struct(..)
1524         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1525         ast::ExprKind::AddrOf(_, ref expr)
1526         | ast::ExprKind::Box(ref expr)
1527         | ast::ExprKind::Try(ref expr)
1528         | ast::ExprKind::Unary(_, ref expr)
1529         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1530         _ => false,
1531     }
1532 }
1533
1534 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1535     match expr.node {
1536         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1537         ast::ExprKind::AddrOf(_, ref expr)
1538         | ast::ExprKind::Box(ref expr)
1539         | ast::ExprKind::Try(ref expr)
1540         | ast::ExprKind::Unary(_, ref expr)
1541         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1542         _ => false,
1543     }
1544 }
1545
1546 /// Return true if a function call or a method call represented by the given span ends with a
1547 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1548 /// comma from macro can potentially break the code.
1549 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1550     let mut result: bool = Default::default();
1551     let mut prev_char: char = Default::default();
1552     let closing_delimiters = &[')', '}', ']'];
1553
1554     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1555         match c {
1556             _ if kind.is_comment() || c.is_whitespace() => continue,
1557             c if closing_delimiters.contains(&c) => {
1558                 result &= !closing_delimiters.contains(&prev_char);
1559             }
1560             ',' => result = true,
1561             _ => result = false,
1562         }
1563         prev_char = c;
1564     }
1565
1566     result
1567 }
1568
1569 fn rewrite_paren(
1570     context: &RewriteContext,
1571     mut subexpr: &ast::Expr,
1572     shape: Shape,
1573     mut span: Span,
1574 ) -> Option<String> {
1575     debug!("rewrite_paren, shape: {:?}", shape);
1576
1577     // Extract comments within parens.
1578     let mut pre_comment;
1579     let mut post_comment;
1580     let remove_nested_parens = context.config.remove_nested_parens();
1581     loop {
1582         // 1 = "(" or ")"
1583         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1584         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1585         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1586         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1587
1588         // Remove nested parens if there are no comments.
1589         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1590             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1591                 span = subexpr.span;
1592                 subexpr = subsubexpr;
1593                 continue;
1594             }
1595         }
1596
1597         break;
1598     }
1599
1600     // 1 `(`
1601     let sub_shape = shape.offset_left(1).and_then(|s| s.sub_width(1))?;
1602
1603     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1604     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1605
1606     // 2 = `()`
1607     if subexpr_str.contains('\n') || first_line_width(&subexpr_str) + 2 <= shape.width {
1608         Some(format!("({}{}{})", pre_comment, &subexpr_str, post_comment))
1609     } else {
1610         None
1611     }
1612 }
1613
1614 fn rewrite_index(
1615     expr: &ast::Expr,
1616     index: &ast::Expr,
1617     context: &RewriteContext,
1618     shape: Shape,
1619 ) -> Option<String> {
1620     let expr_str = expr.rewrite(context, shape)?;
1621
1622     let offset = last_line_width(&expr_str) + 1;
1623     let rhs_overhead = shape.rhs_overhead(context.config);
1624     let index_shape = if expr_str.contains('\n') {
1625         Shape::legacy(context.config.max_width(), shape.indent)
1626             .offset_left(offset)
1627             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1628     } else {
1629         shape.visual_indent(offset).sub_width(offset + 1)
1630     };
1631     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1632
1633     // Return if index fits in a single line.
1634     match orig_index_rw {
1635         Some(ref index_str) if !index_str.contains('\n') => {
1636             return Some(format!("{}[{}]", expr_str, index_str));
1637         }
1638         _ => (),
1639     }
1640
1641     // Try putting index on the next line and see if it fits in a single line.
1642     let indent = shape.indent.block_indent(context.config);
1643     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1644     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1645     let new_index_rw = index.rewrite(context, index_shape);
1646     match (orig_index_rw, new_index_rw) {
1647         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1648             "{}{}[{}]",
1649             expr_str,
1650             indent.to_string_with_newline(context.config),
1651             new_index_str,
1652         )),
1653         (None, Some(ref new_index_str)) => Some(format!(
1654             "{}{}[{}]",
1655             expr_str,
1656             indent.to_string_with_newline(context.config),
1657             new_index_str,
1658         )),
1659         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1660         _ => None,
1661     }
1662 }
1663
1664 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1665     if base.is_some() {
1666         return false;
1667     }
1668
1669     fields.iter().all(|field| !field.is_shorthand)
1670 }
1671
1672 fn rewrite_struct_lit<'a>(
1673     context: &RewriteContext,
1674     path: &ast::Path,
1675     fields: &'a [ast::Field],
1676     base: Option<&'a ast::Expr>,
1677     span: Span,
1678     shape: Shape,
1679 ) -> Option<String> {
1680     debug!("rewrite_struct_lit: shape {:?}", shape);
1681
1682     enum StructLitField<'a> {
1683         Regular(&'a ast::Field),
1684         Base(&'a ast::Expr),
1685     }
1686
1687     // 2 = " {".len()
1688     let path_shape = shape.sub_width(2)?;
1689     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1690
1691     if fields.is_empty() && base.is_none() {
1692         return Some(format!("{} {{}}", path_str));
1693     }
1694
1695     // Foo { a: Foo } - indent is +3, width is -5.
1696     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1697
1698     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1699     let body_lo = context.snippet_provider.span_after(span, "{");
1700     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1701         && context.config.struct_field_align_threshold() > 0
1702     {
1703         rewrite_with_alignment(
1704             fields,
1705             context,
1706             shape,
1707             mk_sp(body_lo, span.hi()),
1708             one_line_width,
1709         )?
1710     } else {
1711         let field_iter = fields
1712             .into_iter()
1713             .map(StructLitField::Regular)
1714             .chain(base.into_iter().map(StructLitField::Base));
1715
1716         let span_lo = |item: &StructLitField| match *item {
1717             StructLitField::Regular(field) => field.span().lo(),
1718             StructLitField::Base(expr) => {
1719                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1720                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1721                 let pos = snippet.find_uncommented("..").unwrap();
1722                 last_field_hi + BytePos(pos as u32)
1723             }
1724         };
1725         let span_hi = |item: &StructLitField| match *item {
1726             StructLitField::Regular(field) => field.span().hi(),
1727             StructLitField::Base(expr) => expr.span.hi(),
1728         };
1729         let rewrite = |item: &StructLitField| match *item {
1730             StructLitField::Regular(field) => {
1731                 // The 1 taken from the v_budget is for the comma.
1732                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1733             }
1734             StructLitField::Base(expr) => {
1735                 // 2 = ..
1736                 expr.rewrite(context, v_shape.offset_left(2)?)
1737                     .map(|s| format!("..{}", s))
1738             }
1739         };
1740
1741         let items = itemize_list(
1742             context.snippet_provider,
1743             field_iter,
1744             "}",
1745             ",",
1746             span_lo,
1747             span_hi,
1748             rewrite,
1749             body_lo,
1750             span.hi(),
1751             false,
1752         );
1753         let item_vec = items.collect::<Vec<_>>();
1754
1755         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1756         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1757
1758         let ends_with_comma = span_ends_with_comma(context, span);
1759         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1760
1761         let fmt = struct_lit_formatting(
1762             nested_shape,
1763             tactic,
1764             context,
1765             force_no_trailing_comma || base.is_some(),
1766         );
1767
1768         write_list(&item_vec, &fmt)?
1769     };
1770
1771     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1772     Some(format!("{} {{{}}}", path_str, fields_str))
1773
1774     // FIXME if context.config.indent_style() == Visual, but we run out
1775     // of space, we should fall back to BlockIndent.
1776 }
1777
1778 pub fn wrap_struct_field(
1779     context: &RewriteContext,
1780     fields_str: &str,
1781     shape: Shape,
1782     nested_shape: Shape,
1783     one_line_width: usize,
1784 ) -> String {
1785     if context.config.indent_style() == IndentStyle::Block
1786         && (fields_str.contains('\n')
1787             || !context.config.struct_lit_single_line()
1788             || fields_str.len() > one_line_width)
1789     {
1790         format!(
1791             "{}{}{}",
1792             nested_shape.indent.to_string_with_newline(context.config),
1793             fields_str,
1794             shape.indent.to_string_with_newline(context.config)
1795         )
1796     } else {
1797         // One liner or visual indent.
1798         format!(" {} ", fields_str)
1799     }
1800 }
1801
1802 pub fn struct_lit_field_separator(config: &Config) -> &str {
1803     colon_spaces(config.space_before_colon(), config.space_after_colon())
1804 }
1805
1806 pub fn rewrite_field(
1807     context: &RewriteContext,
1808     field: &ast::Field,
1809     shape: Shape,
1810     prefix_max_width: usize,
1811 ) -> Option<String> {
1812     if contains_skip(&field.attrs) {
1813         return Some(context.snippet(field.span()).to_owned());
1814     }
1815     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1816     if !attrs_str.is_empty() {
1817         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1818     };
1819     let name = &field.ident.name.to_string();
1820     if field.is_shorthand {
1821         Some(attrs_str + &name)
1822     } else {
1823         let mut separator = String::from(struct_lit_field_separator(context.config));
1824         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1825             separator.push(' ');
1826         }
1827         let overhead = name.len() + separator.len();
1828         let expr_shape = shape.offset_left(overhead)?;
1829         let expr = field.expr.rewrite(context, expr_shape);
1830
1831         match expr {
1832             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1833                 Some(attrs_str + &name)
1834             }
1835             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1836             None => {
1837                 let expr_offset = shape.indent.block_indent(context.config);
1838                 let expr = field
1839                     .expr
1840                     .rewrite(context, Shape::indented(expr_offset, context.config));
1841                 expr.map(|s| {
1842                     format!(
1843                         "{}{}:\n{}{}",
1844                         attrs_str,
1845                         name,
1846                         expr_offset.to_string(context.config),
1847                         s
1848                     )
1849                 })
1850             }
1851         }
1852     }
1853 }
1854
1855 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1856     context: &RewriteContext,
1857     items: &[&T],
1858     span: Span,
1859     shape: Shape,
1860 ) -> Option<String>
1861 where
1862     T: Rewrite + Spanned + ToExpr + 'a,
1863 {
1864     let mut items = items.iter();
1865     // In case of length 1, need a trailing comma
1866     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1867     if items.len() == 1 {
1868         // 3 = "(" + ",)"
1869         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1870         return items
1871             .next()
1872             .unwrap()
1873             .rewrite(context, nested_shape)
1874             .map(|s| format!("({},)", s));
1875     }
1876
1877     let list_lo = context.snippet_provider.span_after(span, "(");
1878     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1879     let items = itemize_list(
1880         context.snippet_provider,
1881         items,
1882         ")",
1883         ",",
1884         |item| item.span().lo(),
1885         |item| item.span().hi(),
1886         |item| item.rewrite(context, nested_shape),
1887         list_lo,
1888         span.hi() - BytePos(1),
1889         false,
1890     );
1891     let item_vec: Vec<_> = items.collect();
1892     let tactic = definitive_tactic(
1893         &item_vec,
1894         ListTactic::HorizontalVertical,
1895         Separator::Comma,
1896         nested_shape.width,
1897     );
1898     let fmt = ListFormatting {
1899         tactic,
1900         separator: ",",
1901         trailing_separator: SeparatorTactic::Never,
1902         separator_place: SeparatorPlace::Back,
1903         shape,
1904         ends_with_newline: false,
1905         preserve_newline: false,
1906         nested: false,
1907         config: context.config,
1908     };
1909     let list_str = write_list(&item_vec, &fmt)?;
1910
1911     Some(format!("({})", list_str))
1912 }
1913
1914 pub fn rewrite_tuple<'a, T>(
1915     context: &RewriteContext,
1916     items: &[&T],
1917     span: Span,
1918     shape: Shape,
1919 ) -> Option<String>
1920 where
1921     T: Rewrite + Spanned + ToExpr + 'a,
1922 {
1923     debug!("rewrite_tuple {:?}", shape);
1924     if context.use_block_indent() {
1925         // We use the same rule as function calls for rewriting tuples.
1926         let force_tactic = if context.inside_macro() {
1927             if span_ends_with_comma(context, span) {
1928                 Some(SeparatorTactic::Always)
1929             } else {
1930                 Some(SeparatorTactic::Never)
1931             }
1932         } else if items.len() == 1 {
1933             Some(SeparatorTactic::Always)
1934         } else {
1935             None
1936         };
1937         overflow::rewrite_with_parens(
1938             context,
1939             "",
1940             items,
1941             shape,
1942             span,
1943             context.config.width_heuristics().fn_call_width,
1944             force_tactic,
1945         )
1946     } else {
1947         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1948     }
1949 }
1950
1951 pub fn rewrite_unary_prefix<R: Rewrite>(
1952     context: &RewriteContext,
1953     prefix: &str,
1954     rewrite: &R,
1955     shape: Shape,
1956 ) -> Option<String> {
1957     rewrite
1958         .rewrite(context, shape.offset_left(prefix.len())?)
1959         .map(|r| format!("{}{}", prefix, r))
1960 }
1961
1962 // FIXME: this is probably not correct for multi-line Rewrites. we should
1963 // subtract suffix.len() from the last line budget, not the first!
1964 pub fn rewrite_unary_suffix<R: Rewrite>(
1965     context: &RewriteContext,
1966     suffix: &str,
1967     rewrite: &R,
1968     shape: Shape,
1969 ) -> Option<String> {
1970     rewrite
1971         .rewrite(context, shape.sub_width(suffix.len())?)
1972         .map(|mut r| {
1973             r.push_str(suffix);
1974             r
1975         })
1976 }
1977
1978 fn rewrite_unary_op(
1979     context: &RewriteContext,
1980     op: &ast::UnOp,
1981     expr: &ast::Expr,
1982     shape: Shape,
1983 ) -> Option<String> {
1984     // For some reason, an UnOp is not spanned like BinOp!
1985     let operator_str = match *op {
1986         ast::UnOp::Deref => "*",
1987         ast::UnOp::Not => "!",
1988         ast::UnOp::Neg => "-",
1989     };
1990     rewrite_unary_prefix(context, operator_str, expr, shape)
1991 }
1992
1993 fn rewrite_assignment(
1994     context: &RewriteContext,
1995     lhs: &ast::Expr,
1996     rhs: &ast::Expr,
1997     op: Option<&ast::BinOp>,
1998     shape: Shape,
1999 ) -> Option<String> {
2000     let operator_str = match op {
2001         Some(op) => context.snippet(op.span),
2002         None => "=",
2003     };
2004
2005     // 1 = space between lhs and operator.
2006     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2007     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2008
2009     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2010 }
2011
2012 /// Controls where to put the rhs.
2013 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
2014 pub enum RhsTactics {
2015     /// Use heuristics.
2016     Default,
2017     /// Put the rhs on the next line if it uses multiple line.
2018     ForceNextLine,
2019 }
2020
2021 // The left hand side must contain everything up to, and including, the
2022 // assignment operator.
2023 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2024     context: &RewriteContext,
2025     lhs: S,
2026     ex: &R,
2027     shape: Shape,
2028 ) -> Option<String> {
2029     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2030 }
2031
2032 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2033     context: &RewriteContext,
2034     lhs: S,
2035     ex: &R,
2036     shape: Shape,
2037     rhs_tactics: RhsTactics,
2038 ) -> Option<String> {
2039     let lhs = lhs.into();
2040     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
2041         shape.indent.width()
2042     } else {
2043         0
2044     });
2045     // 1 = space between operator and rhs.
2046     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2047         width: 0,
2048         offset: shape.offset + last_line_width + 1,
2049         ..shape
2050     });
2051     let rhs = choose_rhs(
2052         context,
2053         ex,
2054         orig_shape,
2055         ex.rewrite(context, orig_shape),
2056         rhs_tactics,
2057     )?;
2058     Some(lhs + &rhs)
2059 }
2060
2061 fn choose_rhs<R: Rewrite>(
2062     context: &RewriteContext,
2063     expr: &R,
2064     shape: Shape,
2065     orig_rhs: Option<String>,
2066     rhs_tactics: RhsTactics,
2067 ) -> Option<String> {
2068     match orig_rhs {
2069         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2070             Some(format!(" {}", new_str))
2071         }
2072         _ => {
2073             // Expression did not fit on the same line as the identifier.
2074             // Try splitting the line and see if that works better.
2075             let new_shape =
2076                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2077                     .sub_width(shape.rhs_overhead(context.config))?;
2078             let new_rhs = expr.rewrite(context, new_shape);
2079             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2080
2081             match (orig_rhs, new_rhs) {
2082                 (Some(ref orig_rhs), Some(ref new_rhs))
2083                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2084                         .is_none() =>
2085                 {
2086                     Some(format!(" {}", orig_rhs))
2087                 }
2088                 (Some(ref orig_rhs), Some(ref new_rhs))
2089                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2090                 {
2091                     Some(format!("{}{}", new_indent_str, new_rhs))
2092                 }
2093                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2094                 (None, None) => None,
2095                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2096             }
2097         }
2098     }
2099 }
2100
2101 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2102     rhs_tactics == RhsTactics::ForceNextLine
2103         || !next_line_rhs.contains('\n')
2104         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2105 }
2106
2107 fn rewrite_expr_addrof(
2108     context: &RewriteContext,
2109     mutability: ast::Mutability,
2110     expr: &ast::Expr,
2111     shape: Shape,
2112 ) -> Option<String> {
2113     let operator_str = match mutability {
2114         ast::Mutability::Immutable => "&",
2115         ast::Mutability::Mutable => "&mut ",
2116     };
2117     rewrite_unary_prefix(context, operator_str, expr, shape)
2118 }
2119
2120 pub trait ToExpr {
2121     fn to_expr(&self) -> Option<&ast::Expr>;
2122     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2123 }
2124
2125 impl ToExpr for ast::Expr {
2126     fn to_expr(&self) -> Option<&ast::Expr> {
2127         Some(self)
2128     }
2129
2130     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2131         can_be_overflowed_expr(context, self, len)
2132     }
2133 }
2134
2135 impl ToExpr for ast::Ty {
2136     fn to_expr(&self) -> Option<&ast::Expr> {
2137         None
2138     }
2139
2140     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2141         can_be_overflowed_type(context, self, len)
2142     }
2143 }
2144
2145 impl<'a> ToExpr for TuplePatField<'a> {
2146     fn to_expr(&self) -> Option<&ast::Expr> {
2147         None
2148     }
2149
2150     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2151         can_be_overflowed_pat(context, self, len)
2152     }
2153 }
2154
2155 impl<'a> ToExpr for ast::StructField {
2156     fn to_expr(&self) -> Option<&ast::Expr> {
2157         None
2158     }
2159
2160     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2161         false
2162     }
2163 }
2164
2165 impl<'a> ToExpr for MacroArg {
2166     fn to_expr(&self) -> Option<&ast::Expr> {
2167         match *self {
2168             MacroArg::Expr(ref expr) => Some(expr),
2169             _ => None,
2170         }
2171     }
2172
2173     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2174         match *self {
2175             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2176             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2177             MacroArg::Pat(..) => false,
2178             MacroArg::Item(..) => len == 1,
2179         }
2180     }
2181 }
2182
2183 impl ToExpr for ast::GenericParam {
2184     fn to_expr(&self) -> Option<&ast::Expr> {
2185         None
2186     }
2187
2188     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2189         false
2190     }
2191 }
2192
2193 pub fn is_method_call(expr: &ast::Expr) -> bool {
2194     match expr.node {
2195         ast::ExprKind::MethodCall(..) => true,
2196         ast::ExprKind::AddrOf(_, ref expr)
2197         | ast::ExprKind::Box(ref expr)
2198         | ast::ExprKind::Cast(ref expr, _)
2199         | ast::ExprKind::Try(ref expr)
2200         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),
2201         _ => false,
2202     }
2203 }