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