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
 459         .rewrite(context, lhs_shape)
 460         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 461
 462     // Try to put both lhs and rhs on the same line.
 463     let rhs_orig_result = shape
 464         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 465         .and_then(|s| s.sub_width(pp.suffix.len()))
 466         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 467     if let Some(ref rhs_result) = rhs_orig_result {
 468         // If the length of the lhs is equal to or shorter than the tab width or
 469         // the rhs looks like block expression, we put the rhs on the same
 470         // line with the lhs even if the rhs is multi-lined.
 471         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 472             || rhs_result
 473                 .lines()
 474                 .next()
 475                 .map(|first_line| first_line.ends_with('{'))
 476                 .unwrap_or(false);
 477         if !rhs_result.contains('\n') || allow_same_line {
 478             let one_line_width = last_line_width(&lhs_result)
 479                 + pp.infix.len()
 480                 + first_line_width(rhs_result)
 481                 + pp.suffix.len();
 482             if one_line_width <= shape.width {
 483                 return Some(format!(
 484                     "{}{}{}{}",
 485                     lhs_result, pp.infix, rhs_result, pp.suffix
 486                 ));
 487             }
 488         }
 489     }
 490
 491     // We have to use multiple lines.
 492     // Re-evaluate the rhs because we have more space now:
 493     let mut rhs_shape = match context.config.indent_style() {
 494         IndentStyle::Visual => shape
 495             .sub_width(pp.suffix.len() + pp.prefix.len())?
 496             .visual_indent(pp.prefix.len()),
 497         IndentStyle::Block => {
 498             // Try to calculate the initial constraint on the right hand side.
 499             let rhs_overhead = shape.rhs_overhead(context.config);
 500             Shape::indented(shape.indent.block_indent(context.config), context.config)
 501                 .sub_width(rhs_overhead)?
 502         }
 503     };
 504     let infix = match separator_place {
 505         SeparatorPlace::Back => pp.infix.trim_right(),
 506         SeparatorPlace::Front => pp.infix.trim_left(),
 507     };
 508     if separator_place == SeparatorPlace::Front {
 509         rhs_shape = rhs_shape.offset_left(infix.len())?;
 510     }
 511     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 512     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 513     let infix_with_sep = match separator_place {
 514         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 515         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 516     };
 517     Some(format!(
 518         "{}{}{}{}",
 519         lhs_result, infix_with_sep, rhs_result, pp.suffix
 520     ))
 521 }
 522
 523 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 524     name: &str,
 525     exprs: &[&T],
 526     span: Span,
 527     context: &RewriteContext,
 528     shape: Shape,
 529     force_separator_tactic: Option<SeparatorTactic>,
 530     delim_token: Option<DelimToken>,
 531 ) -> Option<String> {
 532     overflow::rewrite_with_square_brackets(
 533         context,
 534         name,
 535         exprs,
 536         shape,
 537         span,
 538         force_separator_tactic,
 539         delim_token,
 540     )
 541 }
 542
 543 fn rewrite_empty_block(
 544     context: &RewriteContext,
 545     block: &ast::Block,
 546     attrs: Option<&[ast::Attribute]>,
 547     prefix: &str,
 548     shape: Shape,
 549 ) -> Option<String> {
 550     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 551         return None;
 552     }
 553
 554     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 555     {
 556         return Some(format!("{}{{}}", prefix));
 557     }
 558
 559     // If a block contains only a single-line comment, then leave it on one line.
 560     let user_str = context.snippet(block.span);
 561     let user_str = user_str.trim();
 562     if user_str.starts_with('{') && user_str.ends_with('}') {
 563         let comment_str = user_str[1..user_str.len() - 1].trim();
 564         if block.stmts.is_empty()
 565             && !comment_str.contains('\n')
 566             && !comment_str.starts_with("//")
 567             && comment_str.len() + 4 <= shape.width
 568         {
 569             return Some(format!("{}{{ {} }}", prefix, comment_str));
 570         }
 571     }
 572
 573     None
 574 }
 575
 576 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 577     Some(match block.rules {
 578         ast::BlockCheckMode::Unsafe(..) => {
 579             let snippet = context.snippet(block.span);
 580             let open_pos = snippet.find_uncommented("{")?;
 581             // Extract comment between unsafe and block start.
 582             let trimmed = &snippet[6..open_pos].trim();
 583
 584             if !trimmed.is_empty() {
 585                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 586                 let budget = shape.width.checked_sub(9)?;
 587                 format!(
 588                     "unsafe {} ",
 589                     rewrite_comment(
 590                         trimmed,
 591                         true,
 592                         Shape::legacy(budget, shape.indent + 7),
 593                         context.config,
 594                     )?
 595                 )
 596             } else {
 597                 "unsafe ".to_owned()
 598             }
 599         }
 600         ast::BlockCheckMode::Default => String::new(),
 601     })
 602 }
 603
 604 fn rewrite_single_line_block(
 605     context: &RewriteContext,
 606     prefix: &str,
 607     block: &ast::Block,
 608     attrs: Option<&[ast::Attribute]>,
 609     shape: Shape,
 610 ) -> Option<String> {
 611     if is_simple_block(block, attrs, context.codemap) {
 612         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 613         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 614         let result = format!("{}{{ {} }}", prefix, expr_str);
 615         if result.len() <= shape.width && !result.contains('\n') {
 616             return Some(result);
 617         }
 618     }
 619     None
 620 }
 621
 622 pub fn rewrite_block_with_visitor(
 623     context: &RewriteContext,
 624     prefix: &str,
 625     block: &ast::Block,
 626     attrs: Option<&[ast::Attribute]>,
 627     shape: Shape,
 628     has_braces: bool,
 629 ) -> Option<String> {
 630     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, prefix, shape) {
 631         return rw;
 632     }
 633
 634     let mut visitor = FmtVisitor::from_context(context);
 635     visitor.block_indent = shape.indent;
 636     visitor.is_if_else_block = context.is_if_else_block();
 637     match block.rules {
 638         ast::BlockCheckMode::Unsafe(..) => {
 639             let snippet = context.snippet(block.span);
 640             let open_pos = snippet.find_uncommented("{")?;
 641             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 642         }
 643         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 644     }
 645
 646     let inner_attrs = attrs.map(inner_attributes);
 647     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 648     Some(format!("{}{}", prefix, visitor.buffer))
 649 }
 650
 651 impl Rewrite for ast::Block {
 652     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 653         rewrite_block(self, None, context, shape)
 654     }
 655 }
 656
 657 fn rewrite_block(
 658     block: &ast::Block,
 659     attrs: Option<&[ast::Attribute]>,
 660     context: &RewriteContext,
 661     shape: Shape,
 662 ) -> Option<String> {
 663     let prefix = block_prefix(context, block, shape)?;
 664
 665     // shape.width is used only for the single line case: either the empty block `{}`,
 666     // or an unsafe expression `unsafe { e }`.
 667     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, &prefix, shape) {
 668         return rw;
 669     }
 670
 671     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, shape, true);
 672     if let Some(ref result_str) = result {
 673         if result_str.lines().count() <= 3 {
 674             if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, block, attrs, shape) {
 675                 return rw;
 676             }
 677         }
 678     }
 679
 680     result
 681 }
 682
 683 impl Rewrite for ast::Stmt {
 684     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 685         skip_out_of_file_lines_range!(context, self.span());
 686
 687         let result = match self.node {
 688             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 689             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 690                 let suffix = if semicolon_for_stmt(context, self) {
 691                     ";"
 692                 } else {
 693                     ""
 694                 };
 695
 696                 let shape = shape.sub_width(suffix.len())?;
 697                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 698             }
 699             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 700         };
 701         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 702     }
 703 }
 704
 705 // Rewrite condition if the given expression has one.
 706 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 707     match expr.node {
 708         ast::ExprKind::Match(ref cond, _) => {
 709             // `match `cond` {`
 710             let cond_shape = match context.config.indent_style() {
 711                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 712                 IndentStyle::Block => shape.offset_left(8)?,
 713             };
 714             cond.rewrite(context, cond_shape)
 715         }
 716         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 717             let alt_block_sep =
 718                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 719             control_flow
 720                 .rewrite_cond(context, shape, &alt_block_sep)
 721                 .and_then(|rw| Some(rw.0))
 722         }),
 723     }
 724 }
 725
 726 // Abstraction over control flow expressions
 727 #[derive(Debug)]
 728 struct ControlFlow<'a> {
 729     cond: Option<&'a ast::Expr>,
 730     block: &'a ast::Block,
 731     else_block: Option<&'a ast::Expr>,
 732     label: Option<ast::Label>,
 733     pats: Vec<&'a ast::Pat>,
 734     keyword: &'a str,
 735     matcher: &'a str,
 736     connector: &'a str,
 737     allow_single_line: bool,
 738     // True if this is an `if` expression in an `else if` :-( hacky
 739     nested_if: bool,
 740     span: Span,
 741 }
 742
 743 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 744     match expr.node {
 745         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 746             cond,
 747             vec![],
 748             if_block,
 749             else_block.as_ref().map(|e| &**e),
 750             expr_type == ExprType::SubExpression,
 751             false,
 752             expr.span,
 753         )),
 754         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 755             Some(ControlFlow::new_if(
 756                 cond,
 757                 ptr_vec_to_ref_vec(pat),
 758                 if_block,
 759                 else_block.as_ref().map(|e| &**e),
 760                 expr_type == ExprType::SubExpression,
 761                 false,
 762                 expr.span,
 763             ))
 764         }
 765         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 766             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 767         }
 768         ast::ExprKind::Loop(ref block, label) => {
 769             Some(ControlFlow::new_loop(block, label, expr.span))
 770         }
 771         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 772             vec![],
 773             cond,
 774             block,
 775             label,
 776             expr.span,
 777         )),
 778         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 779             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 780         ),
 781         _ => None,
 782     }
 783 }
 784
 785 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 786     if pats.is_empty() {
 787         ""
 788     } else {
 789         "let"
 790     }
 791 }
 792
 793 impl<'a> ControlFlow<'a> {
 794     fn new_if(
 795         cond: &'a ast::Expr,
 796         pats: Vec<&'a ast::Pat>,
 797         block: &'a ast::Block,
 798         else_block: Option<&'a ast::Expr>,
 799         allow_single_line: bool,
 800         nested_if: bool,
 801         span: Span,
 802     ) -> ControlFlow<'a> {
 803         let matcher = choose_matcher(&pats);
 804         ControlFlow {
 805             cond: Some(cond),
 806             block,
 807             else_block,
 808             label: None,
 809             pats,
 810             keyword: "if",
 811             matcher,
 812             connector: " =",
 813             allow_single_line,
 814             nested_if,
 815             span,
 816         }
 817     }
 818
 819     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 820         ControlFlow {
 821             cond: None,
 822             block,
 823             else_block: None,
 824             label,
 825             pats: vec![],
 826             keyword: "loop",
 827             matcher: "",
 828             connector: "",
 829             allow_single_line: false,
 830             nested_if: false,
 831             span,
 832         }
 833     }
 834
 835     fn new_while(
 836         pats: Vec<&'a ast::Pat>,
 837         cond: &'a ast::Expr,
 838         block: &'a ast::Block,
 839         label: Option<ast::Label>,
 840         span: Span,
 841     ) -> ControlFlow<'a> {
 842         let matcher = choose_matcher(&pats);
 843         ControlFlow {
 844             cond: Some(cond),
 845             block,
 846             else_block: None,
 847             label,
 848             pats,
 849             keyword: "while",
 850             matcher,
 851             connector: " =",
 852             allow_single_line: false,
 853             nested_if: false,
 854             span,
 855         }
 856     }
 857
 858     fn new_for(
 859         pat: &'a ast::Pat,
 860         cond: &'a ast::Expr,
 861         block: &'a ast::Block,
 862         label: Option<ast::Label>,
 863         span: Span,
 864     ) -> ControlFlow<'a> {
 865         ControlFlow {
 866             cond: Some(cond),
 867             block,
 868             else_block: None,
 869             label,
 870             pats: vec![pat],
 871             keyword: "for",
 872             matcher: "",
 873             connector: " in",
 874             allow_single_line: false,
 875             nested_if: false,
 876             span,
 877         }
 878     }
 879
 880     fn rewrite_single_line(
 881         &self,
 882         pat_expr_str: &str,
 883         context: &RewriteContext,
 884         width: usize,
 885     ) -> Option<String> {
 886         assert!(self.allow_single_line);
 887         let else_block = self.else_block?;
 888         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 889
 890         if let ast::ExprKind::Block(ref else_node) = else_block.node {
 891             if !is_simple_block(self.block, None, context.codemap)
 892                 || !is_simple_block(else_node, None, context.codemap)
 893                 || pat_expr_str.contains('\n')
 894             {
 895                 return None;
 896             }
 897
 898             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 899             let expr = &self.block.stmts[0];
 900             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 901
 902             let new_width = new_width.checked_sub(if_str.len())?;
 903             let else_expr = &else_node.stmts[0];
 904             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 905
 906             if if_str.contains('\n') || else_str.contains('\n') {
 907                 return None;
 908             }
 909
 910             let result = format!(
 911                 "{} {} {{ {} }} else {{ {} }}",
 912                 self.keyword, pat_expr_str, if_str, else_str
 913             );
 914
 915             if result.len() <= width {
 916                 return Some(result);
 917             }
 918         }
 919
 920         None
 921     }
 922 }
 923
 924 impl<'a> ControlFlow<'a> {
 925     fn rewrite_pat_expr(
 926         &self,
 927         context: &RewriteContext,
 928         expr: &ast::Expr,
 929         shape: Shape,
 930         offset: usize,
 931     ) -> Option<String> {
 932         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 933
 934         let cond_shape = shape.offset_left(offset)?;
 935         if !self.pats.is_empty() {
 936             let matcher = if self.matcher.is_empty() {
 937                 self.matcher.to_owned()
 938             } else {
 939                 format!("{} ", self.matcher)
 940             };
 941             let pat_shape = cond_shape
 942                 .offset_left(matcher.len())?
 943                 .sub_width(self.connector.len())?;
 944             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 945             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 946             return rewrite_assign_rhs(context, result, expr, cond_shape);
 947         }
 948
 949         let expr_rw = expr.rewrite(context, cond_shape);
 950         // The expression may (partially) fit on the current line.
 951         // We do not allow splitting between `if` and condition.
 952         if self.keyword == "if" || expr_rw.is_some() {
 953             return expr_rw;
 954         }
 955
 956         // The expression won't fit on the current line, jump to next.
 957         let nested_shape = shape
 958             .block_indent(context.config.tab_spaces())
 959             .with_max_width(context.config);
 960         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 961         expr.rewrite(context, nested_shape)
 962             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 963     }
 964
 965     fn rewrite_cond(
 966         &self,
 967         context: &RewriteContext,
 968         shape: Shape,
 969         alt_block_sep: &str,
 970     ) -> Option<(String, usize)> {
 971         // Do not take the rhs overhead from the upper expressions into account
 972         // when rewriting pattern.
 973         let new_width = context.budget(shape.used_width());
 974         let fresh_shape = Shape {
 975             width: new_width,
 976             ..shape
 977         };
 978         let constr_shape = if self.nested_if {
 979             // We are part of an if-elseif-else chain. Our constraints are tightened.
 980             // 7 = "} else " .len()
 981             fresh_shape.offset_left(7)?
 982         } else {
 983             fresh_shape
 984         };
 985
 986         let label_string = rewrite_label(self.label);
 987         // 1 = space after keyword.
 988         let offset = self.keyword.len() + label_string.len() + 1;
 989
 990         let pat_expr_string = match self.cond {
 991             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 992             None => String::new(),
 993         };
 994
 995         let brace_overhead =
 996             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 997                 // 2 = ` {`
 998                 2
 999             } else {
1000                 0
1001             };
1002         let one_line_budget = context
1003             .config
1004             .max_width()
1005             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1006             .unwrap_or(0);
1007         let force_newline_brace = (pat_expr_string.contains('\n')
1008             || pat_expr_string.len() > one_line_budget)
1009             && !last_line_extendable(&pat_expr_string);
1010
1011         // Try to format if-else on single line.
1012         if self.allow_single_line
1013             && context
1014                 .config
1015                 .width_heuristics()
1016                 .single_line_if_else_max_width > 0
1017         {
1018             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1019
1020             if let Some(cond_str) = trial {
1021                 if cond_str.len()
1022                     <= context
1023                         .config
1024                         .width_heuristics()
1025                         .single_line_if_else_max_width
1026                 {
1027                     return Some((cond_str, 0));
1028                 }
1029             }
1030         }
1031
1032         let cond_span = if let Some(cond) = self.cond {
1033             cond.span
1034         } else {
1035             mk_sp(self.block.span.lo(), self.block.span.lo())
1036         };
1037
1038         // `for event in event`
1039         // Do not include label in the span.
1040         let lo = self
1041             .label
1042             .map_or(self.span.lo(), |label| label.ident.span.hi());
1043         let between_kwd_cond = mk_sp(
1044             context
1045                 .snippet_provider
1046                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1047             if self.pats.is_empty() {
1048                 cond_span.lo()
1049             } else if self.matcher.is_empty() {
1050                 self.pats[0].span.lo()
1051             } else {
1052                 context
1053                     .snippet_provider
1054                     .span_before(self.span, self.matcher.trim())
1055             },
1056         );
1057
1058         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1059
1060         let after_cond_comment =
1061             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1062
1063         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1064             ""
1065         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1066             || force_newline_brace
1067         {
1068             alt_block_sep
1069         } else {
1070             " "
1071         };
1072
1073         let used_width = if pat_expr_string.contains('\n') {
1074             last_line_width(&pat_expr_string)
1075         } else {
1076             // 2 = spaces after keyword and condition.
1077             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1078         };
1079
1080         Some((
1081             format!(
1082                 "{}{}{}{}{}",
1083                 label_string,
1084                 self.keyword,
1085                 between_kwd_cond_comment.as_ref().map_or(
1086                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1087                         ""
1088                     } else {
1089                         " "
1090                     },
1091                     |s| &**s,
1092                 ),
1093                 pat_expr_string,
1094                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1095             ),
1096             used_width,
1097         ))
1098     }
1099 }
1100
1101 impl<'a> Rewrite for ControlFlow<'a> {
1102     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1103         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1104
1105         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1106         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1107         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1108         if used_width == 0 {
1109             return Some(cond_str);
1110         }
1111
1112         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1113         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1114         // we should avoid the single line case.
1115         let block_width = if self.else_block.is_some() || self.nested_if {
1116             min(1, block_width)
1117         } else {
1118             block_width
1119         };
1120         let block_shape = Shape {
1121             width: block_width,
1122             ..shape
1123         };
1124         let block_str = {
1125             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1126             let result =
1127                 rewrite_block_with_visitor(context, "", self.block, None, block_shape, true);
1128             context.is_if_else_block.replace(old_val);
1129             result?
1130         };
1131
1132         let mut result = format!("{}{}", cond_str, block_str);
1133
1134         if let Some(else_block) = self.else_block {
1135             let shape = Shape::indented(shape.indent, context.config);
1136             let mut last_in_chain = false;
1137             let rewrite = match else_block.node {
1138                 // If the else expression is another if-else expression, prevent it
1139                 // from being formatted on a single line.
1140                 // Note how we're passing the original shape, as the
1141                 // cost of "else" should not cascade.
1142                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1143                     ControlFlow::new_if(
1144                         cond,
1145                         ptr_vec_to_ref_vec(pat),
1146                         if_block,
1147                         next_else_block.as_ref().map(|e| &**e),
1148                         false,
1149                         true,
1150                         mk_sp(else_block.span.lo(), self.span.hi()),
1151                     ).rewrite(context, shape)
1152                 }
1153                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1154                     ControlFlow::new_if(
1155                         cond,
1156                         vec![],
1157                         if_block,
1158                         next_else_block.as_ref().map(|e| &**e),
1159                         false,
1160                         true,
1161                         mk_sp(else_block.span.lo(), self.span.hi()),
1162                     ).rewrite(context, shape)
1163                 }
1164                 _ => {
1165                     last_in_chain = true;
1166                     // When rewriting a block, the width is only used for single line
1167                     // blocks, passing 1 lets us avoid that.
1168                     let else_shape = Shape {
1169                         width: min(1, shape.width),
1170                         ..shape
1171                     };
1172                     format_expr(else_block, ExprType::Statement, context, else_shape)
1173                 }
1174             };
1175
1176             let between_kwd_else_block = mk_sp(
1177                 self.block.span.hi(),
1178                 context
1179                     .snippet_provider
1180                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1181             );
1182             let between_kwd_else_block_comment =
1183                 extract_comment(between_kwd_else_block, context, shape);
1184
1185             let after_else = mk_sp(
1186                 context
1187                     .snippet_provider
1188                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1189                 else_block.span.lo(),
1190             );
1191             let after_else_comment = extract_comment(after_else, context, shape);
1192
1193             let between_sep = match context.config.control_brace_style() {
1194                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1195                     &*alt_block_sep
1196                 }
1197                 ControlBraceStyle::AlwaysSameLine => " ",
1198             };
1199             let after_sep = match context.config.control_brace_style() {
1200                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1201                 _ => " ",
1202             };
1203
1204             result.push_str(&format!(
1205                 "{}else{}",
1206                 between_kwd_else_block_comment
1207                     .as_ref()
1208                     .map_or(between_sep, |s| &**s),
1209                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1210             ));
1211             result.push_str(&rewrite?);
1212         }
1213
1214         Some(result)
1215     }
1216 }
1217
1218 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1219     match opt_label {
1220         Some(label) => Cow::from(format!("{}: ", label.ident)),
1221         None => Cow::from(""),
1222     }
1223 }
1224
1225 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1226     match rewrite_missing_comment(span, shape, context) {
1227         Some(ref comment) if !comment.is_empty() => Some(format!(
1228             "{indent}{}{indent}",
1229             comment,
1230             indent = shape.indent.to_string_with_newline(context.config)
1231         )),
1232         _ => None,
1233     }
1234 }
1235
1236 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1237     let snippet = codemap.span_to_snippet(block.span).unwrap();
1238     contains_comment(&snippet)
1239 }
1240
1241 // Checks that a block contains no statements, an expression and no comments or
1242 // attributes.
1243 // FIXME: incorrectly returns false when comment is contained completely within
1244 // the expression.
1245 pub fn is_simple_block(
1246     block: &ast::Block,
1247     attrs: Option<&[ast::Attribute]>,
1248     codemap: &CodeMap,
1249 ) -> bool {
1250     (block.stmts.len() == 1
1251         && stmt_is_expr(&block.stmts[0])
1252         && !block_contains_comment(block, codemap)
1253         && attrs.map_or(true, |a| a.is_empty()))
1254 }
1255
1256 /// Checks whether a block contains at most one statement or expression, and no
1257 /// comments or attributes.
1258 pub fn is_simple_block_stmt(
1259     block: &ast::Block,
1260     attrs: Option<&[ast::Attribute]>,
1261     codemap: &CodeMap,
1262 ) -> bool {
1263     block.stmts.len() <= 1
1264         && !block_contains_comment(block, codemap)
1265         && attrs.map_or(true, |a| a.is_empty())
1266 }
1267
1268 /// Checks whether a block contains no statements, expressions, comments, or
1269 /// inner attributes.
1270 pub fn is_empty_block(
1271     block: &ast::Block,
1272     attrs: Option<&[ast::Attribute]>,
1273     codemap: &CodeMap,
1274 ) -> bool {
1275     block.stmts.is_empty()
1276         && !block_contains_comment(block, codemap)
1277         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1278 }
1279
1280 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1281     match stmt.node {
1282         ast::StmtKind::Expr(..) => true,
1283         _ => false,
1284     }
1285 }
1286
1287 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1288     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1289         true
1290     } else {
1291         false
1292     }
1293 }
1294
1295 pub fn rewrite_multiple_patterns(
1296     context: &RewriteContext,
1297     pats: &[&ast::Pat],
1298     shape: Shape,
1299 ) -> Option<String> {
1300     let pat_strs = pats
1301         .iter()
1302         .map(|p| p.rewrite(context, shape))
1303         .collect::<Option<Vec<_>>>()?;
1304
1305     let use_mixed_layout = pats
1306         .iter()
1307         .zip(pat_strs.iter())
1308         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1309     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1310     let tactic = if use_mixed_layout {
1311         DefinitiveListTactic::Mixed
1312     } else {
1313         definitive_tactic(
1314             &items,
1315             ListTactic::HorizontalVertical,
1316             Separator::VerticalBar,
1317             shape.width,
1318         )
1319     };
1320     let fmt = ListFormatting {
1321         tactic,
1322         separator: " |",
1323         trailing_separator: SeparatorTactic::Never,
1324         separator_place: context.config.binop_separator(),
1325         shape,
1326         ends_with_newline: false,
1327         preserve_newline: false,
1328         config: context.config,
1329     };
1330     write_list(&items, &fmt)
1331 }
1332
1333 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1334     match l.node {
1335         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1336         _ => wrap_str(
1337             context.snippet(l.span).to_owned(),
1338             context.config.max_width(),
1339             shape,
1340         ),
1341     }
1342 }
1343
1344 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1345     let string_lit = context.snippet(span);
1346
1347     if !context.config.format_strings() {
1348         if string_lit
1349             .lines()
1350             .rev()
1351             .skip(1)
1352             .all(|line| line.ends_with('\\'))
1353         {
1354             let new_indent = shape.visual_indent(1).indent;
1355             let indented_string_lit = String::from(
1356                 string_lit
1357                     .lines()
1358                     .map(|line| {
1359                         format!(
1360                             "{}{}",
1361                             new_indent.to_string(context.config),
1362                             line.trim_left()
1363                         )
1364                     })
1365                     .collect::<Vec<_>>()
1366                     .join("\n")
1367                     .trim_left(),
1368             );
1369             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1370         } else {
1371             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1372         }
1373     }
1374
1375     // Remove the quote characters.
1376     let str_lit = &string_lit[1..string_lit.len() - 1];
1377
1378     rewrite_string(
1379         str_lit,
1380         &StringFormat::new(shape.visual_indent(0), context.config),
1381         None,
1382     )
1383 }
1384
1385 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1386 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1387     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1388         .iter()
1389         .find(|&&(s, _)| s == callee_str)
1390     {
1391         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1392
1393         Some((all_simple, num_args_before))
1394     } else {
1395         None
1396     }
1397 }
1398
1399 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1400 /// format.
1401 ///
1402 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1403 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1404 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1405 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1406     // format! like macros
1407     // From the Rust Standard Library.
1408     ("eprint!", 0),
1409     ("eprintln!", 0),
1410     ("format!", 0),
1411     ("format_args!", 0),
1412     ("print!", 0),
1413     ("println!", 0),
1414     ("panic!", 0),
1415     ("unreachable!", 0),
1416     // From the `log` crate.
1417     ("debug!", 0),
1418     ("error!", 0),
1419     ("info!", 0),
1420     ("warn!", 0),
1421     // write! like macros
1422     ("assert!", 1),
1423     ("debug_assert!", 1),
1424     ("write!", 1),
1425     ("writeln!", 1),
1426     // assert_eq! like macros
1427     ("assert_eq!", 2),
1428     ("assert_ne!", 2),
1429     ("debug_assert_eq!", 2),
1430     ("debug_assert_ne!", 2),
1431 ];
1432
1433 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1434     if context.inside_macro() {
1435         if span_ends_with_comma(context, span) {
1436             Some(SeparatorTactic::Always)
1437         } else {
1438             Some(SeparatorTactic::Never)
1439         }
1440     } else {
1441         None
1442     }
1443 }
1444
1445 pub fn rewrite_call(
1446     context: &RewriteContext,
1447     callee: &str,
1448     args: &[ptr::P<ast::Expr>],
1449     span: Span,
1450     shape: Shape,
1451 ) -> Option<String> {
1452     overflow::rewrite_with_parens(
1453         context,
1454         callee,
1455         &ptr_vec_to_ref_vec(args),
1456         shape,
1457         span,
1458         context.config.width_heuristics().fn_call_width,
1459         choose_separator_tactic(context, span),
1460     )
1461 }
1462
1463 fn is_simple_expr(expr: &ast::Expr) -> bool {
1464     match expr.node {
1465         ast::ExprKind::Lit(..) => true,
1466         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1467         ast::ExprKind::AddrOf(_, ref expr)
1468         | ast::ExprKind::Box(ref expr)
1469         | ast::ExprKind::Cast(ref expr, _)
1470         | ast::ExprKind::Field(ref expr, _)
1471         | ast::ExprKind::Try(ref expr)
1472         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1473         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1474             is_simple_expr(lhs) && is_simple_expr(rhs)
1475         }
1476         _ => false,
1477     }
1478 }
1479
1480 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1481     lists
1482         .iter()
1483         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1484 }
1485
1486 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1487     match expr.node {
1488         ast::ExprKind::Match(..) => {
1489             (context.use_block_indent() && args_len == 1)
1490                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1491         }
1492         ast::ExprKind::If(..)
1493         | ast::ExprKind::IfLet(..)
1494         | ast::ExprKind::ForLoop(..)
1495         | ast::ExprKind::Loop(..)
1496         | ast::ExprKind::While(..)
1497         | ast::ExprKind::WhileLet(..) => {
1498             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1499         }
1500         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1501             context.use_block_indent()
1502                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1503         }
1504         ast::ExprKind::Array(..)
1505         | ast::ExprKind::Call(..)
1506         | ast::ExprKind::Mac(..)
1507         | ast::ExprKind::MethodCall(..)
1508         | ast::ExprKind::Struct(..)
1509         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
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, _) => can_be_overflowed_expr(context, expr, args_len),
1515         _ => false,
1516     }
1517 }
1518
1519 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1520     match expr.node {
1521         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1522         ast::ExprKind::AddrOf(_, ref expr)
1523         | ast::ExprKind::Box(ref expr)
1524         | ast::ExprKind::Try(ref expr)
1525         | ast::ExprKind::Unary(_, ref expr)
1526         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1527         _ => false,
1528     }
1529 }
1530
1531 /// Return true if a function call or a method call represented by the given span ends with a
1532 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1533 /// comma from macro can potentially break the code.
1534 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1535     let mut result: bool = Default::default();
1536     let mut prev_char: char = Default::default();
1537     let closing_delimiters = &[')', '}', ']'];
1538
1539     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1540         match c {
1541             _ if kind.is_comment() || c.is_whitespace() => continue,
1542             c if closing_delimiters.contains(&c) => {
1543                 result &= !closing_delimiters.contains(&prev_char);
1544             }
1545             ',' => result = true,
1546             _ => result = false,
1547         }
1548         prev_char = c;
1549     }
1550
1551     result
1552 }
1553
1554 fn rewrite_paren(
1555     context: &RewriteContext,
1556     mut subexpr: &ast::Expr,
1557     shape: Shape,
1558     mut span: Span,
1559 ) -> Option<String> {
1560     debug!("rewrite_paren, shape: {:?}", shape);
1561
1562     // Extract comments within parens.
1563     let mut pre_comment;
1564     let mut post_comment;
1565     let remove_nested_parens = context.config.remove_nested_parens();
1566     loop {
1567         // 1 = "(" or ")"
1568         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1569         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1570         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1571         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1572
1573         // Remove nested parens if there are no comments.
1574         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1575             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1576                 span = subexpr.span;
1577                 subexpr = subsubexpr;
1578                 continue;
1579             }
1580         }
1581
1582         break;
1583     }
1584
1585     let total_paren_overhead = paren_overhead(context);
1586     let paren_overhead = total_paren_overhead / 2;
1587     let sub_shape = shape
1588         .offset_left(paren_overhead)
1589         .and_then(|s| s.sub_width(paren_overhead))?;
1590
1591     let paren_wrapper = |s: &str| {
1592         if context.config.spaces_within_parens_and_brackets() && !s.is_empty() {
1593             format!("( {}{}{} )", pre_comment, s, post_comment)
1594         } else {
1595             format!("({}{}{})", pre_comment, s, post_comment)
1596         }
1597     };
1598
1599     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1600     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1601
1602     if subexpr_str.contains('\n')
1603         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
1604     {
1605         Some(paren_wrapper(&subexpr_str))
1606     } else {
1607         None
1608     }
1609 }
1610
1611 fn rewrite_index(
1612     expr: &ast::Expr,
1613     index: &ast::Expr,
1614     context: &RewriteContext,
1615     shape: Shape,
1616 ) -> Option<String> {
1617     let expr_str = expr.rewrite(context, shape)?;
1618
1619     let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
1620         ("[ ", " ]")
1621     } else {
1622         ("[", "]")
1623     };
1624
1625     let offset = last_line_width(&expr_str) + lbr.len();
1626     let rhs_overhead = shape.rhs_overhead(context.config);
1627     let index_shape = if expr_str.contains('\n') {
1628         Shape::legacy(context.config.max_width(), shape.indent)
1629             .offset_left(offset)
1630             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
1631     } else {
1632         shape.visual_indent(offset).sub_width(offset + rbr.len())
1633     };
1634     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1635
1636     // Return if index fits in a single line.
1637     match orig_index_rw {
1638         Some(ref index_str) if !index_str.contains('\n') => {
1639             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
1640         }
1641         _ => (),
1642     }
1643
1644     // Try putting index on the next line and see if it fits in a single line.
1645     let indent = shape.indent.block_indent(context.config);
1646     let index_shape = Shape::indented(indent, context.config).offset_left(lbr.len())?;
1647     let index_shape = index_shape.sub_width(rbr.len() + rhs_overhead)?;
1648     let new_index_rw = index.rewrite(context, index_shape);
1649     match (orig_index_rw, new_index_rw) {
1650         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1651             "{}{}{}{}{}",
1652             expr_str,
1653             indent.to_string_with_newline(context.config),
1654             lbr,
1655             new_index_str,
1656             rbr
1657         )),
1658         (None, Some(ref new_index_str)) => Some(format!(
1659             "{}{}{}{}{}",
1660             expr_str,
1661             indent.to_string_with_newline(context.config),
1662             lbr,
1663             new_index_str,
1664             rbr
1665         )),
1666         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
1667         _ => None,
1668     }
1669 }
1670
1671 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1672     if base.is_some() {
1673         return false;
1674     }
1675
1676     fields.iter().all(|field| !field.is_shorthand)
1677 }
1678
1679 fn rewrite_struct_lit<'a>(
1680     context: &RewriteContext,
1681     path: &ast::Path,
1682     fields: &'a [ast::Field],
1683     base: Option<&'a ast::Expr>,
1684     span: Span,
1685     shape: Shape,
1686 ) -> Option<String> {
1687     debug!("rewrite_struct_lit: shape {:?}", shape);
1688
1689     enum StructLitField<'a> {
1690         Regular(&'a ast::Field),
1691         Base(&'a ast::Expr),
1692     }
1693
1694     // 2 = " {".len()
1695     let path_shape = shape.sub_width(2)?;
1696     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1697
1698     if fields.is_empty() && base.is_none() {
1699         return Some(format!("{} {{}}", path_str));
1700     }
1701
1702     // Foo { a: Foo } - indent is +3, width is -5.
1703     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1704
1705     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1706     let body_lo = context.snippet_provider.span_after(span, "{");
1707     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1708         && context.config.struct_field_align_threshold() > 0
1709     {
1710         rewrite_with_alignment(
1711             fields,
1712             context,
1713             shape,
1714             mk_sp(body_lo, span.hi()),
1715             one_line_width,
1716         )?
1717     } else {
1718         let field_iter = fields
1719             .into_iter()
1720             .map(StructLitField::Regular)
1721             .chain(base.into_iter().map(StructLitField::Base));
1722
1723         let span_lo = |item: &StructLitField| match *item {
1724             StructLitField::Regular(field) => field.span().lo(),
1725             StructLitField::Base(expr) => {
1726                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1727                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1728                 let pos = snippet.find_uncommented("..").unwrap();
1729                 last_field_hi + BytePos(pos as u32)
1730             }
1731         };
1732         let span_hi = |item: &StructLitField| match *item {
1733             StructLitField::Regular(field) => field.span().hi(),
1734             StructLitField::Base(expr) => expr.span.hi(),
1735         };
1736         let rewrite = |item: &StructLitField| match *item {
1737             StructLitField::Regular(field) => {
1738                 // The 1 taken from the v_budget is for the comma.
1739                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1740             }
1741             StructLitField::Base(expr) => {
1742                 // 2 = ..
1743                 expr.rewrite(context, v_shape.offset_left(2)?)
1744                     .map(|s| format!("..{}", s))
1745             }
1746         };
1747
1748         let items = itemize_list(
1749             context.snippet_provider,
1750             field_iter,
1751             "}",
1752             ",",
1753             span_lo,
1754             span_hi,
1755             rewrite,
1756             body_lo,
1757             span.hi(),
1758             false,
1759         );
1760         let item_vec = items.collect::<Vec<_>>();
1761
1762         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1763         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1764
1765         let ends_with_comma = span_ends_with_comma(context, span);
1766         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1767
1768         let fmt = struct_lit_formatting(
1769             nested_shape,
1770             tactic,
1771             context,
1772             force_no_trailing_comma || base.is_some(),
1773         );
1774
1775         write_list(&item_vec, &fmt)?
1776     };
1777
1778     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1779     Some(format!("{} {{{}}}", path_str, fields_str))
1780
1781     // FIXME if context.config.indent_style() == Visual, but we run out
1782     // of space, we should fall back to BlockIndent.
1783 }
1784
1785 pub fn wrap_struct_field(
1786     context: &RewriteContext,
1787     fields_str: &str,
1788     shape: Shape,
1789     nested_shape: Shape,
1790     one_line_width: usize,
1791 ) -> String {
1792     if context.config.indent_style() == IndentStyle::Block
1793         && (fields_str.contains('\n')
1794             || !context.config.struct_lit_single_line()
1795             || fields_str.len() > one_line_width)
1796     {
1797         format!(
1798             "{}{}{}",
1799             nested_shape.indent.to_string_with_newline(context.config),
1800             fields_str,
1801             shape.indent.to_string_with_newline(context.config)
1802         )
1803     } else {
1804         // One liner or visual indent.
1805         format!(" {} ", fields_str)
1806     }
1807 }
1808
1809 pub fn struct_lit_field_separator(config: &Config) -> &str {
1810     colon_spaces(config.space_before_colon(), config.space_after_colon())
1811 }
1812
1813 pub fn rewrite_field(
1814     context: &RewriteContext,
1815     field: &ast::Field,
1816     shape: Shape,
1817     prefix_max_width: usize,
1818 ) -> Option<String> {
1819     if contains_skip(&field.attrs) {
1820         return Some(context.snippet(field.span()).to_owned());
1821     }
1822     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1823     if !attrs_str.is_empty() {
1824         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1825     };
1826     let name = &field.ident.name.to_string();
1827     if field.is_shorthand {
1828         Some(attrs_str + &name)
1829     } else {
1830         let mut separator = String::from(struct_lit_field_separator(context.config));
1831         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
1832             separator.push(' ');
1833         }
1834         let overhead = name.len() + separator.len();
1835         let expr_shape = shape.offset_left(overhead)?;
1836         let expr = field.expr.rewrite(context, expr_shape);
1837
1838         match expr {
1839             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1840                 Some(attrs_str + &name)
1841             }
1842             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1843             None => {
1844                 let expr_offset = shape.indent.block_indent(context.config);
1845                 let expr = field
1846                     .expr
1847                     .rewrite(context, Shape::indented(expr_offset, context.config));
1848                 expr.map(|s| {
1849                     format!(
1850                         "{}{}:\n{}{}",
1851                         attrs_str,
1852                         name,
1853                         expr_offset.to_string(context.config),
1854                         s
1855                     )
1856                 })
1857             }
1858         }
1859     }
1860 }
1861
1862 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1863     context: &RewriteContext,
1864     items: &[&T],
1865     span: Span,
1866     shape: Shape,
1867 ) -> Option<String>
1868 where
1869     T: Rewrite + Spanned + ToExpr + 'a,
1870 {
1871     let mut items = items.iter();
1872     // In case of length 1, need a trailing comma
1873     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1874     if items.len() == 1 {
1875         // 3 = "(" + ",)"
1876         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1877         return items
1878             .next()
1879             .unwrap()
1880             .rewrite(context, nested_shape)
1881             .map(|s| {
1882                 if context.config.spaces_within_parens_and_brackets() {
1883                     format!("( {}, )", s)
1884                 } else {
1885                     format!("({},)", s)
1886                 }
1887             });
1888     }
1889
1890     let list_lo = context.snippet_provider.span_after(span, "(");
1891     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1892     let items = itemize_list(
1893         context.snippet_provider,
1894         items,
1895         ")",
1896         ",",
1897         |item| item.span().lo(),
1898         |item| item.span().hi(),
1899         |item| item.rewrite(context, nested_shape),
1900         list_lo,
1901         span.hi() - BytePos(1),
1902         false,
1903     );
1904     let item_vec: Vec<_> = items.collect();
1905     let tactic = definitive_tactic(
1906         &item_vec,
1907         ListTactic::HorizontalVertical,
1908         Separator::Comma,
1909         nested_shape.width,
1910     );
1911     let fmt = ListFormatting {
1912         tactic,
1913         separator: ",",
1914         trailing_separator: SeparatorTactic::Never,
1915         separator_place: SeparatorPlace::Back,
1916         shape,
1917         ends_with_newline: false,
1918         preserve_newline: false,
1919         config: context.config,
1920     };
1921     let list_str = write_list(&item_vec, &fmt)?;
1922
1923     if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
1924         Some(format!("( {} )", list_str))
1925     } else {
1926         Some(format!("({})", list_str))
1927     }
1928 }
1929
1930 pub fn rewrite_tuple<'a, T>(
1931     context: &RewriteContext,
1932     items: &[&T],
1933     span: Span,
1934     shape: Shape,
1935 ) -> Option<String>
1936 where
1937     T: Rewrite + Spanned + ToExpr + 'a,
1938 {
1939     debug!("rewrite_tuple {:?}", shape);
1940     if context.use_block_indent() {
1941         // We use the same rule as function calls for rewriting tuples.
1942         let force_tactic = if context.inside_macro() {
1943             if span_ends_with_comma(context, span) {
1944                 Some(SeparatorTactic::Always)
1945             } else {
1946                 Some(SeparatorTactic::Never)
1947             }
1948         } else if items.len() == 1 {
1949             Some(SeparatorTactic::Always)
1950         } else {
1951             None
1952         };
1953         overflow::rewrite_with_parens(
1954             context,
1955             "",
1956             items,
1957             shape,
1958             span,
1959             context.config.width_heuristics().fn_call_width,
1960             force_tactic,
1961         )
1962     } else {
1963         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1964     }
1965 }
1966
1967 pub fn rewrite_unary_prefix<R: Rewrite>(
1968     context: &RewriteContext,
1969     prefix: &str,
1970     rewrite: &R,
1971     shape: Shape,
1972 ) -> Option<String> {
1973     rewrite
1974         .rewrite(context, shape.offset_left(prefix.len())?)
1975         .map(|r| format!("{}{}", prefix, r))
1976 }
1977
1978 // FIXME: this is probably not correct for multi-line Rewrites. we should
1979 // subtract suffix.len() from the last line budget, not the first!
1980 pub fn rewrite_unary_suffix<R: Rewrite>(
1981     context: &RewriteContext,
1982     suffix: &str,
1983     rewrite: &R,
1984     shape: Shape,
1985 ) -> Option<String> {
1986     rewrite
1987         .rewrite(context, shape.sub_width(suffix.len())?)
1988         .map(|mut r| {
1989             r.push_str(suffix);
1990             r
1991         })
1992 }
1993
1994 fn rewrite_unary_op(
1995     context: &RewriteContext,
1996     op: &ast::UnOp,
1997     expr: &ast::Expr,
1998     shape: Shape,
1999 ) -> Option<String> {
2000     // For some reason, an UnOp is not spanned like BinOp!
2001     let operator_str = match *op {
2002         ast::UnOp::Deref => "*",
2003         ast::UnOp::Not => "!",
2004         ast::UnOp::Neg => "-",
2005     };
2006     rewrite_unary_prefix(context, operator_str, expr, shape)
2007 }
2008
2009 fn rewrite_assignment(
2010     context: &RewriteContext,
2011     lhs: &ast::Expr,
2012     rhs: &ast::Expr,
2013     op: Option<&ast::BinOp>,
2014     shape: Shape,
2015 ) -> Option<String> {
2016     let operator_str = match op {
2017         Some(op) => context.snippet(op.span),
2018         None => "=",
2019     };
2020
2021     // 1 = space between lhs and operator.
2022     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2023     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2024
2025     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2026 }
2027
2028 /// Controls where to put the rhs.
2029 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
2030 pub enum RhsTactics {
2031     /// Use heuristics.
2032     Default,
2033     /// Put the rhs on the next line if it uses multiple line.
2034     ForceNextLine,
2035 }
2036
2037 // The left hand side must contain everything up to, and including, the
2038 // assignment operator.
2039 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2040     context: &RewriteContext,
2041     lhs: S,
2042     ex: &R,
2043     shape: Shape,
2044 ) -> Option<String> {
2045     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2046 }
2047
2048 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2049     context: &RewriteContext,
2050     lhs: S,
2051     ex: &R,
2052     shape: Shape,
2053     rhs_tactics: RhsTactics,
2054 ) -> Option<String> {
2055     let lhs = lhs.into();
2056     let last_line_width = last_line_width(&lhs)
2057         .checked_sub(if lhs.contains('\n') {
2058             shape.indent.width()
2059         } else {
2060             0
2061         })
2062         .unwrap_or(0);
2063     // 1 = space between operator and rhs.
2064     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2065         width: 0,
2066         offset: shape.offset + last_line_width + 1,
2067         ..shape
2068     });
2069     let rhs = choose_rhs(
2070         context,
2071         ex,
2072         orig_shape,
2073         ex.rewrite(context, orig_shape),
2074         rhs_tactics,
2075     )?;
2076     Some(lhs + &rhs)
2077 }
2078
2079 fn choose_rhs<R: Rewrite>(
2080     context: &RewriteContext,
2081     expr: &R,
2082     shape: Shape,
2083     orig_rhs: Option<String>,
2084     rhs_tactics: RhsTactics,
2085 ) -> Option<String> {
2086     match orig_rhs {
2087         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2088             Some(format!(" {}", new_str))
2089         }
2090         _ => {
2091             // Expression did not fit on the same line as the identifier.
2092             // Try splitting the line and see if that works better.
2093             let new_shape =
2094                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2095                     .sub_width(shape.rhs_overhead(context.config))?;
2096             let new_rhs = expr.rewrite(context, new_shape);
2097             let new_indent_str = &new_shape.indent.to_string_with_newline(context.config);
2098
2099             match (orig_rhs, new_rhs) {
2100                 (Some(ref orig_rhs), Some(ref new_rhs))
2101                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2102                         .is_none() =>
2103                 {
2104                     Some(format!(" {}", orig_rhs))
2105                 }
2106                 (Some(ref orig_rhs), Some(ref new_rhs))
2107                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2108                 {
2109                     Some(format!("{}{}", new_indent_str, new_rhs))
2110                 }
2111                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2112                 (None, None) => None,
2113                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2114             }
2115         }
2116     }
2117 }
2118
2119 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2120     rhs_tactics == RhsTactics::ForceNextLine
2121         || !next_line_rhs.contains('\n')
2122         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2123 }
2124
2125 fn rewrite_expr_addrof(
2126     context: &RewriteContext,
2127     mutability: ast::Mutability,
2128     expr: &ast::Expr,
2129     shape: Shape,
2130 ) -> Option<String> {
2131     let operator_str = match mutability {
2132         ast::Mutability::Immutable => "&",
2133         ast::Mutability::Mutable => "&mut ",
2134     };
2135     rewrite_unary_prefix(context, operator_str, expr, shape)
2136 }
2137
2138 pub trait ToExpr {
2139     fn to_expr(&self) -> Option<&ast::Expr>;
2140     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2141 }
2142
2143 impl ToExpr for ast::Expr {
2144     fn to_expr(&self) -> Option<&ast::Expr> {
2145         Some(self)
2146     }
2147
2148     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2149         can_be_overflowed_expr(context, self, len)
2150     }
2151 }
2152
2153 impl ToExpr for ast::Ty {
2154     fn to_expr(&self) -> Option<&ast::Expr> {
2155         None
2156     }
2157
2158     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2159         can_be_overflowed_type(context, self, len)
2160     }
2161 }
2162
2163 impl<'a> ToExpr for TuplePatField<'a> {
2164     fn to_expr(&self) -> Option<&ast::Expr> {
2165         None
2166     }
2167
2168     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2169         can_be_overflowed_pat(context, self, len)
2170     }
2171 }
2172
2173 impl<'a> ToExpr for ast::StructField {
2174     fn to_expr(&self) -> Option<&ast::Expr> {
2175         None
2176     }
2177
2178     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2179         false
2180     }
2181 }
2182
2183 impl<'a> ToExpr for MacroArg {
2184     fn to_expr(&self) -> Option<&ast::Expr> {
2185         match *self {
2186             MacroArg::Expr(ref expr) => Some(expr),
2187             _ => None,
2188         }
2189     }
2190
2191     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2192         match *self {
2193             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2194             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2195             MacroArg::Pat(..) => false,
2196             MacroArg::Item(..) => len == 1,
2197         }
2198     }
2199 }
2200
2201 impl ToExpr for ast::GenericParam {
2202     fn to_expr(&self) -> Option<&ast::Expr> {
2203         None
2204     }
2205
2206     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2207         false
2208     }
2209 }