src/expr.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::borrow::Cow;
  12 use std::cmp::min;
  13
  14 use config::lists::*;
  15 use syntax::codemap::{BytePos, CodeMap, Span};
  16 use syntax::parse::token::DelimToken;
  17 use syntax::{ast, ptr};
  18
  19 use chains::rewrite_chain;
  20 use closures;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use comment::{
  23     combine_strs_with_missing_comments, contains_comment, recover_comment_removed, rewrite_comment,
  24     rewrite_missing_comment, CharClasses, FindUncommented,
  25 };
  26 use config::{Config, ControlBraceStyle, IndentStyle};
  27 use lists::{
  28     definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape,
  29     struct_lit_tactic, write_list, ListFormatting, ListItem, Separator,
  30 };
  31 use macros::{rewrite_macro, MacroArg, MacroPosition};
  32 use matches::rewrite_match;
  33 use overflow;
  34 use patterns::{can_be_overflowed_pat, is_short_pattern, TuplePatField};
  35 use rewrite::{Rewrite, RewriteContext};
  36 use shape::{Indent, Shape};
  37 use spanned::Spanned;
  38 use string::{rewrite_string, StringFormat};
  39 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  40 use utils::{
  41     colon_spaces, contains_skip, count_newlines, first_line_width, inner_attributes,
  42     last_line_extendable, last_line_width, mk_sp, outer_attributes, ptr_vec_to_ref_vec,
  43     semicolon_for_stmt, wrap_str,
  44 };
  45 use vertical::rewrite_with_alignment;
  46 use visitor::FmtVisitor;
  47
  48 impl Rewrite for ast::Expr {
  49     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  50         format_expr(self, ExprType::SubExpression, context, shape)
  51     }
  52 }
  53
  54 #[derive(Copy, Clone, PartialEq)]
  55 pub enum ExprType {
  56     Statement,
  57     SubExpression,
  58 }
  59
  60 pub fn format_expr(
  61     expr: &ast::Expr,
  62     expr_type: ExprType,
  63     context: &RewriteContext,
  64     shape: Shape,
  65 ) -> Option<String> {
  66     skip_out_of_file_lines_range!(context, expr.span);
  67
  68     if contains_skip(&*expr.attrs) {
  69         return Some(context.snippet(expr.span()).to_owned());
  70     }
  71
  72     let expr_rw = match expr.node {
  73         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  74             "",
  75             &ptr_vec_to_ref_vec(expr_vec),
  76             expr.span,
  77             context,
  78             shape,
  79             choose_separator_tactic(context, expr.span),
  80             None,
  81         ),
  82         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  83         ast::ExprKind::Call(ref callee, ref args) => {
  84             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  85             let callee_str = callee.rewrite(context, shape)?;
  86             rewrite_call(context, &callee_str, args, inner_span, shape)
  87         }
  88         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape, expr.span),
  89         ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
  90             // FIXME: format comments between operands and operator
  91             rewrite_simple_binaries(context, expr, shape, op).or_else(|| {
  92                 rewrite_pair(
  93                     &**lhs,
  94                     &**rhs,
  95                     PairParts::new("", &format!(" {} ", context.snippet(op.span)), ""),
  96                     context,
  97                     shape,
  98                     context.config.binop_separator(),
  99                 )
 100             })
 101         }
 102         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 103         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 104             context,
 105             path,
 106             fields,
 107             base.as_ref().map(|e| &**e),
 108             expr.span,
 109             shape,
 110         ),
 111         ast::ExprKind::Tup(ref items) => {
 112             rewrite_tuple(context, &ptr_vec_to_ref_vec(items), expr.span, shape)
 113         }
 114         ast::ExprKind::If(..)
 115         | ast::ExprKind::IfLet(..)
 116         | ast::ExprKind::ForLoop(..)
 117         | ast::ExprKind::Loop(..)
 118         | ast::ExprKind::While(..)
 119         | ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 120             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 121         ast::ExprKind::Block(ref block, opt_label) => {
 122             match expr_type {
 123                 ExprType::Statement => {
 124                     if is_unsafe_block(block) {
 125                         rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 126                     } else if let rw @ Some(_) =
 127                         rewrite_empty_block(context, block, Some(&expr.attrs), opt_label, "", shape)
 128                     {
 129                         // Rewrite block without trying to put it in a single line.
 130                         rw
 131                     } else {
 132                         let prefix = block_prefix(context, block, shape)?;
 133
 134                         rewrite_block_with_visitor(
 135                             context,
 136                             &prefix,
 137                             block,
 138                             Some(&expr.attrs),
 139                             opt_label,
 140                             shape,
 141                             true,
 142                         )
 143                     }
 144                 }
 145                 ExprType::SubExpression => {
 146                     rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 147                 }
 148             }
 149         }
 150         ast::ExprKind::Match(ref cond, ref arms) => {
 151             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 152         }
 153         ast::ExprKind::Path(ref qself, ref path) => {
 154             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 155         }
 156         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 157             rewrite_assignment(context, lhs, rhs, None, shape)
 158         }
 159         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 160             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 161         }
 162         ast::ExprKind::Continue(ref opt_label) => {
 163             let id_str = match *opt_label {
 164                 Some(label) => format!(" {}", label.ident),
 165                 None => String::new(),
 166             };
 167             Some(format!("continue{}", id_str))
 168         }
 169         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 170             let id_str = match *opt_label {
 171                 Some(label) => format!(" {}", label.ident),
 172                 None => String::new(),
 173             };
 174
 175             if let Some(ref expr) = *opt_expr {
 176                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 177             } else {
 178                 Some(format!("break{}", id_str))
 179             }
 180         }
 181         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 182             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 183         } else {
 184             Some("yield".to_string())
 185         },
 186         ast::ExprKind::Closure(capture, _, movability, ref fn_decl, ref body, _) => {
 187             closures::rewrite_closure(
 188                 capture, movability, fn_decl, body, expr.span, context, shape,
 189             )
 190         }
 191         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 192             rewrite_chain(expr, context, shape)
 193         }
 194         ast::ExprKind::Mac(ref mac) => {
 195             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 196                 wrap_str(
 197                     context.snippet(expr.span).to_owned(),
 198                     context.config.max_width(),
 199                     shape,
 200                 )
 201             })
 202         }
 203         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 204         ast::ExprKind::Ret(Some(ref expr)) => {
 205             rewrite_unary_prefix(context, "return ", &**expr, shape)
 206         }
 207         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 208         ast::ExprKind::AddrOf(mutability, ref expr) => {
 209             rewrite_expr_addrof(context, mutability, expr, shape)
 210         }
 211         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 212             &**expr,
 213             &**ty,
 214             PairParts::new("", " as ", ""),
 215             context,
 216             shape,
 217             SeparatorPlace::Front,
 218         ),
 219         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 220             &**expr,
 221             &**ty,
 222             PairParts::new("", ": ", ""),
 223             context,
 224             shape,
 225             SeparatorPlace::Back,
 226         ),
 227         ast::ExprKind::Index(ref expr, ref index) => {
 228             rewrite_index(&**expr, &**index, context, shape)
 229         }
 230         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 231             &**expr,
 232             &*repeats.value,
 233             PairParts::new("[", "; ", "]"),
 234             context,
 235             shape,
 236             SeparatorPlace::Back,
 237         ),
 238         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 239             let delim = match limits {
 240                 ast::RangeLimits::HalfOpen => "..",
 241                 ast::RangeLimits::Closed => "..=",
 242             };
 243
 244             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 245                 match lhs.node {
 246                     ast::ExprKind::Lit(ref lit) => match lit.node {
 247                         ast::LitKind::FloatUnsuffixed(..) => {
 248                             context.snippet(lit.span).ends_with('.')
 249                         }
 250                         _ => false,
 251                     },
 252                     _ => false,
 253                 }
 254             }
 255
 256             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 257                 match rhs.node {
 258                     // Don't format `.. ..` into `....`, which is invalid.
 259                     //
 260                     // This check is unnecessary for `lhs`, because a range
 261                     // starting from another range needs parentheses as `(x ..) ..`
 262                     // (`x .. ..` is a range from `x` to `..`).
 263                     ast::ExprKind::Range(None, _, _) => true,
 264                     _ => false,
 265                 }
 266             }
 267
 268             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 269                 let space_if = |b: bool| if b { " " } else { "" };
 270
 271                 format!(
 272                     "{}{}{}",
 273                     lhs.map(|lhs| space_if(needs_space_before_range(context, lhs)))
 274                         .unwrap_or(""),
 275                     delim,
 276                     rhs.map(|rhs| space_if(needs_space_after_range(rhs)))
 277                         .unwrap_or(""),
 278                 )
 279             };
 280
 281             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 282                 (Some(lhs), Some(rhs)) => {
 283                     let sp_delim = if context.config.spaces_around_ranges() {
 284                         format!(" {} ", delim)
 285                     } else {
 286                         default_sp_delim(Some(lhs), Some(rhs))
 287                     };
 288                     rewrite_pair(
 289                         &*lhs,
 290                         &*rhs,
 291                         PairParts::new("", &sp_delim, ""),
 292                         context,
 293                         shape,
 294                         context.config.binop_separator(),
 295                     )
 296                 }
 297                 (None, Some(rhs)) => {
 298                     let sp_delim = if context.config.spaces_around_ranges() {
 299                         format!("{} ", delim)
 300                     } else {
 301                         default_sp_delim(None, Some(rhs))
 302                     };
 303                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 304                 }
 305                 (Some(lhs), None) => {
 306                     let sp_delim = if context.config.spaces_around_ranges() {
 307                         format!(" {}", delim)
 308                     } else {
 309                         default_sp_delim(Some(lhs), None)
 310                     };
 311                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 312                 }
 313                 (None, None) => Some(delim.to_owned()),
 314             }
 315         }
 316         // We do not format these expressions yet, but they should still
 317         // satisfy our width restrictions.
 318         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 319         ast::ExprKind::Catch(ref block) => {
 320             if let rw @ Some(_) = rewrite_single_line_block(
 321                 context,
 322                 "do catch ",
 323                 block,
 324                 Some(&expr.attrs),
 325                 None,
 326                 shape,
 327             ) {
 328                 rw
 329             } else {
 330                 // 9 = `do catch `
 331                 let budget = shape.width.saturating_sub(9);
 332                 Some(format!(
 333                     "{}{}",
 334                     "do catch ",
 335                     rewrite_block(
 336                         block,
 337                         Some(&expr.attrs),
 338                         None,
 339                         context,
 340                         Shape::legacy(budget, shape.indent)
 341                     )?
 342                 ))
 343             }
 344         }
 345         // FIXME(#2743)
 346         ast::ExprKind::ObsoleteInPlace(..) => unimplemented!(),
 347         // FIXME(topecongiro) Format async block.
 348         ast::ExprKind::Async(..) => None,
 349     };
 350
 351     expr_rw
 352         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 353         .and_then(|expr_str| {
 354             let attrs = outer_attributes(&expr.attrs);
 355             let attrs_str = attrs.rewrite(context, shape)?;
 356             let span = mk_sp(
 357                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 358                 expr.span.lo(),
 359             );
 360             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 361         })
 362 }
 363
 364 /// Collect operands that appears in the given binary operator in the opposite order.
 365 /// e.g. `collect_binary_items(e, ||)` for `a && b || c || d` returns `[d, c, a && b]`.
 366 fn collect_binary_items<'a>(mut expr: &'a ast::Expr, binop: ast::BinOp) -> Vec<&'a ast::Expr> {
 367     let mut result = vec![];
 368     let mut prev_lhs = None;
 369     loop {
 370         match expr.node {
 371             ast::ExprKind::Binary(inner_binop, ref lhs, ref rhs)
 372                 if inner_binop.node == binop.node =>
 373             {
 374                 result.push(&**rhs);
 375                 expr = lhs;
 376                 prev_lhs = Some(lhs);
 377             }
 378             _ => {
 379                 if let Some(lhs) = prev_lhs {
 380                     result.push(lhs);
 381                 }
 382                 break;
 383             }
 384         }
 385     }
 386     result
 387 }
 388
 389 /// Rewrites a binary expression whose operands fits within a single line.
 390 fn rewrite_simple_binaries(
 391     context: &RewriteContext,
 392     expr: &ast::Expr,
 393     shape: Shape,
 394     op: ast::BinOp,
 395 ) -> Option<String> {
 396     let op_str = context.snippet(op.span);
 397
 398     // 2 = spaces around a binary operator.
 399     let sep_overhead = op_str.len() + 2;
 400     let nested_overhead = sep_overhead - 1;
 401
 402     let nested_shape = (match context.config.indent_style() {
 403         IndentStyle::Visual => shape.visual_indent(0),
 404         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 405     }).with_max_width(context.config);
 406     let nested_shape = match context.config.binop_separator() {
 407         SeparatorPlace::Back => nested_shape.sub_width(nested_overhead)?,
 408         SeparatorPlace::Front => nested_shape.offset_left(nested_overhead)?,
 409     };
 410
 411     let opt_rewrites: Option<Vec<_>> = collect_binary_items(expr, op)
 412         .iter()
 413         .rev()
 414         .map(|e| e.rewrite(context, nested_shape))
 415         .collect();
 416     if let Some(rewrites) = opt_rewrites {
 417         if rewrites.iter().all(|e| ::utils::is_single_line(e)) {
 418             let total_width = rewrites.iter().map(|s| s.len()).sum::<usize>()
 419                 + sep_overhead * (rewrites.len() - 1);
 420
 421             let sep_str = if total_width <= shape.width {
 422                 format!(" {} ", op_str)
 423             } else {
 424                 let indent_str = nested_shape.indent.to_string_with_newline(context.config);
 425                 match context.config.binop_separator() {
 426                     SeparatorPlace::Back => format!(" {}{}", op_str.trim_right(), indent_str),
 427                     SeparatorPlace::Front => format!("{}{} ", indent_str, op_str.trim_left()),
 428                 }
 429             };
 430
 431             return wrap_str(rewrites.join(&sep_str), context.config.max_width(), shape);
 432         }
 433     }
 434
 435     None
 436 }
 437
 438 #[derive(new, Clone, Copy)]
 439 pub struct PairParts<'a> {
 440     prefix: &'a str,
 441     infix: &'a str,
 442     suffix: &'a str,
 443 }
 444
 445 pub fn rewrite_pair<LHS, RHS>(
 446     lhs: &LHS,
 447     rhs: &RHS,
 448     pp: PairParts,
 449     context: &RewriteContext,
 450     shape: Shape,
 451     separator_place: SeparatorPlace,
 452 ) -> Option<String>
 453 where
 454     LHS: Rewrite,
 455     RHS: Rewrite,
 456 {
 457     let lhs_overhead = match separator_place {
 458         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 459         SeparatorPlace::Front => shape.used_width(),
 460     };
 461     let lhs_shape = Shape {
 462         width: context.budget(lhs_overhead),
 463         ..shape
 464     };
 465     let lhs_result = lhs
 466         .rewrite(context, lhs_shape)
 467         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 468
 469     // Try to put both lhs and rhs on the same line.
 470     let rhs_orig_result = shape
 471         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 472         .and_then(|s| s.sub_width(pp.suffix.len()))
 473         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 474     if let Some(ref rhs_result) = rhs_orig_result {
 475         // If the length of the lhs is equal to or shorter than the tab width or
 476         // the rhs looks like block expression, we put the rhs on the same
 477         // line with the lhs even if the rhs is multi-lined.
 478         let allow_same_line = lhs_result.len() <= context.config.tab_spaces()
 479             || rhs_result
 480                 .lines()
 481                 .next()
 482                 .map(|first_line| first_line.ends_with('{'))
 483                 .unwrap_or(false);
 484         if !rhs_result.contains('\n') || allow_same_line {
 485             let one_line_width = last_line_width(&lhs_result)
 486                 + pp.infix.len()
 487                 + first_line_width(rhs_result)
 488                 + pp.suffix.len();
 489             if one_line_width <= shape.width {
 490                 return Some(format!(
 491                     "{}{}{}{}",
 492                     lhs_result, pp.infix, rhs_result, pp.suffix
 493                 ));
 494             }
 495         }
 496     }
 497
 498     // We have to use multiple lines.
 499     // Re-evaluate the rhs because we have more space now:
 500     let mut rhs_shape = match context.config.indent_style() {
 501         IndentStyle::Visual => shape
 502             .sub_width(pp.suffix.len() + pp.prefix.len())?
 503             .visual_indent(pp.prefix.len()),
 504         IndentStyle::Block => {
 505             // Try to calculate the initial constraint on the right hand side.
 506             let rhs_overhead = shape.rhs_overhead(context.config);
 507             Shape::indented(shape.indent.block_indent(context.config), context.config)
 508                 .sub_width(rhs_overhead)?
 509         }
 510     };
 511     let infix = match separator_place {
 512         SeparatorPlace::Back => pp.infix.trim_right(),
 513         SeparatorPlace::Front => pp.infix.trim_left(),
 514     };
 515     if separator_place == SeparatorPlace::Front {
 516         rhs_shape = rhs_shape.offset_left(infix.len())?;
 517     }
 518     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 519     let indent_str = rhs_shape.indent.to_string_with_newline(context.config);
 520     let infix_with_sep = match separator_place {
 521         SeparatorPlace::Back => format!("{}{}", infix, indent_str),
 522         SeparatorPlace::Front => format!("{}{}", indent_str, infix),
 523     };
 524     Some(format!(
 525         "{}{}{}{}",
 526         lhs_result, infix_with_sep, rhs_result, pp.suffix
 527     ))
 528 }
 529
 530 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 531     name: &str,
 532     exprs: &[&T],
 533     span: Span,
 534     context: &RewriteContext,
 535     shape: Shape,
 536     force_separator_tactic: Option<SeparatorTactic>,
 537     delim_token: Option<DelimToken>,
 538 ) -> Option<String> {
 539     overflow::rewrite_with_square_brackets(
 540         context,
 541         name,
 542         exprs,
 543         shape,
 544         span,
 545         force_separator_tactic,
 546         delim_token,
 547     )
 548 }
 549
 550 fn rewrite_empty_block(
 551     context: &RewriteContext,
 552     block: &ast::Block,
 553     attrs: Option<&[ast::Attribute]>,
 554     label: Option<ast::Label>,
 555     prefix: &str,
 556     shape: Shape,
 557 ) -> Option<String> {
 558     let label_str = rewrite_label(label);
 559     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 560         return None;
 561     }
 562
 563     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 564     {
 565         return Some(format!("{}{}{{}}", prefix, label_str));
 566     }
 567
 568     // If a block contains only a single-line comment, then leave it on one line.
 569     let user_str = context.snippet(block.span);
 570     let user_str = user_str.trim();
 571     if user_str.starts_with('{') && user_str.ends_with('}') {
 572         let comment_str = user_str[1..user_str.len() - 1].trim();
 573         if block.stmts.is_empty()
 574             && !comment_str.contains('\n')
 575             && !comment_str.starts_with("//")
 576             && comment_str.len() + 4 <= shape.width
 577         {
 578             return Some(format!("{}{}{{ {} }}", prefix, label_str, comment_str));
 579         }
 580     }
 581
 582     None
 583 }
 584
 585 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 586     Some(match block.rules {
 587         ast::BlockCheckMode::Unsafe(..) => {
 588             let snippet = context.snippet(block.span);
 589             let open_pos = snippet.find_uncommented("{")?;
 590             // Extract comment between unsafe and block start.
 591             let trimmed = &snippet[6..open_pos].trim();
 592
 593             if !trimmed.is_empty() {
 594                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 595                 let budget = shape.width.checked_sub(9)?;
 596                 format!(
 597                     "unsafe {} ",
 598                     rewrite_comment(
 599                         trimmed,
 600                         true,
 601                         Shape::legacy(budget, shape.indent + 7),
 602                         context.config,
 603                     )?
 604                 )
 605             } else {
 606                 "unsafe ".to_owned()
 607             }
 608         }
 609         ast::BlockCheckMode::Default => String::new(),
 610     })
 611 }
 612
 613 fn rewrite_single_line_block(
 614     context: &RewriteContext,
 615     prefix: &str,
 616     block: &ast::Block,
 617     attrs: Option<&[ast::Attribute]>,
 618     label: Option<ast::Label>,
 619     shape: Shape,
 620 ) -> Option<String> {
 621     if is_simple_block(block, attrs, context.codemap) {
 622         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 623         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 624         let label_str = rewrite_label(label);
 625         let result = format!("{}{}{{ {} }}", prefix, label_str, expr_str);
 626         if result.len() <= shape.width && !result.contains('\n') {
 627             return Some(result);
 628         }
 629     }
 630     None
 631 }
 632
 633 pub fn rewrite_block_with_visitor(
 634     context: &RewriteContext,
 635     prefix: &str,
 636     block: &ast::Block,
 637     attrs: Option<&[ast::Attribute]>,
 638     label: Option<ast::Label>,
 639     shape: Shape,
 640     has_braces: bool,
 641 ) -> Option<String> {
 642     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, prefix, shape) {
 643         return rw;
 644     }
 645
 646     let mut visitor = FmtVisitor::from_context(context);
 647     visitor.block_indent = shape.indent;
 648     visitor.is_if_else_block = context.is_if_else_block();
 649     match block.rules {
 650         ast::BlockCheckMode::Unsafe(..) => {
 651             let snippet = context.snippet(block.span);
 652             let open_pos = snippet.find_uncommented("{")?;
 653             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 654         }
 655         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 656     }
 657
 658     let inner_attrs = attrs.map(inner_attributes);
 659     let label_str = rewrite_label(label);
 660     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
 661     Some(format!("{}{}{}", prefix, label_str, visitor.buffer))
 662 }
 663
 664 impl Rewrite for ast::Block {
 665     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 666         rewrite_block(self, None, None, context, shape)
 667     }
 668 }
 669
 670 fn rewrite_block(
 671     block: &ast::Block,
 672     attrs: Option<&[ast::Attribute]>,
 673     label: Option<ast::Label>,
 674     context: &RewriteContext,
 675     shape: Shape,
 676 ) -> Option<String> {
 677     let prefix = block_prefix(context, block, shape)?;
 678
 679     // shape.width is used only for the single line case: either the empty block `{}`,
 680     // or an unsafe expression `unsafe { e }`.
 681     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, &prefix, shape) {
 682         return rw;
 683     }
 684
 685     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, label, shape, true);
 686     if let Some(ref result_str) = result {
 687         if result_str.lines().count() <= 3 {
 688             if let rw @ Some(_) =
 689                 rewrite_single_line_block(context, &prefix, block, attrs, label, shape)
 690             {
 691                 return rw;
 692             }
 693         }
 694     }
 695
 696     result
 697 }
 698
 699 impl Rewrite for ast::Stmt {
 700     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 701         skip_out_of_file_lines_range!(context, self.span());
 702
 703         let result = match self.node {
 704             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 705             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 706                 let suffix = if semicolon_for_stmt(context, self) {
 707                     ";"
 708                 } else {
 709                     ""
 710                 };
 711
 712                 let shape = shape.sub_width(suffix.len())?;
 713                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 714             }
 715             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 716         };
 717         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 718     }
 719 }
 720
 721 // Rewrite condition if the given expression has one.
 722 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 723     match expr.node {
 724         ast::ExprKind::Match(ref cond, _) => {
 725             // `match `cond` {`
 726             let cond_shape = match context.config.indent_style() {
 727                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 728                 IndentStyle::Block => shape.offset_left(8)?,
 729             };
 730             cond.rewrite(context, cond_shape)
 731         }
 732         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 733             let alt_block_sep =
 734                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 735             control_flow
 736                 .rewrite_cond(context, shape, &alt_block_sep)
 737                 .and_then(|rw| Some(rw.0))
 738         }),
 739     }
 740 }
 741
 742 // Abstraction over control flow expressions
 743 #[derive(Debug)]
 744 struct ControlFlow<'a> {
 745     cond: Option<&'a ast::Expr>,
 746     block: &'a ast::Block,
 747     else_block: Option<&'a ast::Expr>,
 748     label: Option<ast::Label>,
 749     pats: Vec<&'a ast::Pat>,
 750     keyword: &'a str,
 751     matcher: &'a str,
 752     connector: &'a str,
 753     allow_single_line: bool,
 754     // True if this is an `if` expression in an `else if` :-( hacky
 755     nested_if: bool,
 756     span: Span,
 757 }
 758
 759 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 760     match expr.node {
 761         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 762             cond,
 763             vec![],
 764             if_block,
 765             else_block.as_ref().map(|e| &**e),
 766             expr_type == ExprType::SubExpression,
 767             false,
 768             expr.span,
 769         )),
 770         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 771             Some(ControlFlow::new_if(
 772                 cond,
 773                 ptr_vec_to_ref_vec(pat),
 774                 if_block,
 775                 else_block.as_ref().map(|e| &**e),
 776                 expr_type == ExprType::SubExpression,
 777                 false,
 778                 expr.span,
 779             ))
 780         }
 781         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 782             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 783         }
 784         ast::ExprKind::Loop(ref block, label) => {
 785             Some(ControlFlow::new_loop(block, label, expr.span))
 786         }
 787         ast::ExprKind::While(ref cond, ref block, label) => Some(ControlFlow::new_while(
 788             vec![],
 789             cond,
 790             block,
 791             label,
 792             expr.span,
 793         )),
 794         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 795             ControlFlow::new_while(ptr_vec_to_ref_vec(pat), cond, block, label, expr.span),
 796         ),
 797         _ => None,
 798     }
 799 }
 800
 801 fn choose_matcher(pats: &[&ast::Pat]) -> &'static str {
 802     if pats.is_empty() {
 803         ""
 804     } else {
 805         "let"
 806     }
 807 }
 808
 809 impl<'a> ControlFlow<'a> {
 810     fn new_if(
 811         cond: &'a ast::Expr,
 812         pats: Vec<&'a ast::Pat>,
 813         block: &'a ast::Block,
 814         else_block: Option<&'a ast::Expr>,
 815         allow_single_line: bool,
 816         nested_if: bool,
 817         span: Span,
 818     ) -> ControlFlow<'a> {
 819         let matcher = choose_matcher(&pats);
 820         ControlFlow {
 821             cond: Some(cond),
 822             block,
 823             else_block,
 824             label: None,
 825             pats,
 826             keyword: "if",
 827             matcher,
 828             connector: " =",
 829             allow_single_line,
 830             nested_if,
 831             span,
 832         }
 833     }
 834
 835     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 836         ControlFlow {
 837             cond: None,
 838             block,
 839             else_block: None,
 840             label,
 841             pats: vec![],
 842             keyword: "loop",
 843             matcher: "",
 844             connector: "",
 845             allow_single_line: false,
 846             nested_if: false,
 847             span,
 848         }
 849     }
 850
 851     fn new_while(
 852         pats: Vec<&'a ast::Pat>,
 853         cond: &'a ast::Expr,
 854         block: &'a ast::Block,
 855         label: Option<ast::Label>,
 856         span: Span,
 857     ) -> ControlFlow<'a> {
 858         let matcher = choose_matcher(&pats);
 859         ControlFlow {
 860             cond: Some(cond),
 861             block,
 862             else_block: None,
 863             label,
 864             pats,
 865             keyword: "while",
 866             matcher,
 867             connector: " =",
 868             allow_single_line: false,
 869             nested_if: false,
 870             span,
 871         }
 872     }
 873
 874     fn new_for(
 875         pat: &'a ast::Pat,
 876         cond: &'a ast::Expr,
 877         block: &'a ast::Block,
 878         label: Option<ast::Label>,
 879         span: Span,
 880     ) -> ControlFlow<'a> {
 881         ControlFlow {
 882             cond: Some(cond),
 883             block,
 884             else_block: None,
 885             label,
 886             pats: vec![pat],
 887             keyword: "for",
 888             matcher: "",
 889             connector: " in",
 890             allow_single_line: false,
 891             nested_if: false,
 892             span,
 893         }
 894     }
 895
 896     fn rewrite_single_line(
 897         &self,
 898         pat_expr_str: &str,
 899         context: &RewriteContext,
 900         width: usize,
 901     ) -> Option<String> {
 902         assert!(self.allow_single_line);
 903         let else_block = self.else_block?;
 904         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 905
 906         if let ast::ExprKind::Block(ref else_node, _) = else_block.node {
 907             if !is_simple_block(self.block, None, context.codemap)
 908                 || !is_simple_block(else_node, None, context.codemap)
 909                 || pat_expr_str.contains('\n')
 910             {
 911                 return None;
 912             }
 913
 914             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 915             let expr = &self.block.stmts[0];
 916             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 917
 918             let new_width = new_width.checked_sub(if_str.len())?;
 919             let else_expr = &else_node.stmts[0];
 920             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 921
 922             if if_str.contains('\n') || else_str.contains('\n') {
 923                 return None;
 924             }
 925
 926             let result = format!(
 927                 "{} {} {{ {} }} else {{ {} }}",
 928                 self.keyword, pat_expr_str, if_str, else_str
 929             );
 930
 931             if result.len() <= width {
 932                 return Some(result);
 933             }
 934         }
 935
 936         None
 937     }
 938 }
 939
 940 impl<'a> ControlFlow<'a> {
 941     fn rewrite_pat_expr(
 942         &self,
 943         context: &RewriteContext,
 944         expr: &ast::Expr,
 945         shape: Shape,
 946         offset: usize,
 947     ) -> Option<String> {
 948         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pats, expr);
 949
 950         let cond_shape = shape.offset_left(offset)?;
 951         if !self.pats.is_empty() {
 952             let matcher = if self.matcher.is_empty() {
 953                 self.matcher.to_owned()
 954             } else {
 955                 format!("{} ", self.matcher)
 956             };
 957             let pat_shape = cond_shape
 958                 .offset_left(matcher.len())?
 959                 .sub_width(self.connector.len())?;
 960             let pat_string = rewrite_multiple_patterns(context, &self.pats, pat_shape)?;
 961             let result = format!("{}{}{}", matcher, pat_string, self.connector);
 962             return rewrite_assign_rhs(context, result, expr, cond_shape);
 963         }
 964
 965         let expr_rw = expr.rewrite(context, cond_shape);
 966         // The expression may (partially) fit on the current line.
 967         // We do not allow splitting between `if` and condition.
 968         if self.keyword == "if" || expr_rw.is_some() {
 969             return expr_rw;
 970         }
 971
 972         // The expression won't fit on the current line, jump to next.
 973         let nested_shape = shape
 974             .block_indent(context.config.tab_spaces())
 975             .with_max_width(context.config);
 976         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 977         expr.rewrite(context, nested_shape)
 978             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 979     }
 980
 981     fn rewrite_cond(
 982         &self,
 983         context: &RewriteContext,
 984         shape: Shape,
 985         alt_block_sep: &str,
 986     ) -> Option<(String, usize)> {
 987         // Do not take the rhs overhead from the upper expressions into account
 988         // when rewriting pattern.
 989         let new_width = context.budget(shape.used_width());
 990         let fresh_shape = Shape {
 991             width: new_width,
 992             ..shape
 993         };
 994         let constr_shape = if self.nested_if {
 995             // We are part of an if-elseif-else chain. Our constraints are tightened.
 996             // 7 = "} else " .len()
 997             fresh_shape.offset_left(7)?
 998         } else {
 999             fresh_shape
1000         };
1001
1002         let label_string = rewrite_label(self.label);
1003         // 1 = space after keyword.
1004         let offset = self.keyword.len() + label_string.len() + 1;
1005
1006         let pat_expr_string = match self.cond {
1007             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
1008             None => String::new(),
1009         };
1010
1011         let brace_overhead =
1012             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1013                 // 2 = ` {`
1014                 2
1015             } else {
1016                 0
1017             };
1018         let one_line_budget = context
1019             .config
1020             .max_width()
1021             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
1022         let force_newline_brace = (pat_expr_string.contains('\n')
1023             || pat_expr_string.len() > one_line_budget)
1024             && !last_line_extendable(&pat_expr_string);
1025
1026         // Try to format if-else on single line.
1027         if self.allow_single_line
1028             && context
1029                 .config
1030                 .width_heuristics()
1031                 .single_line_if_else_max_width > 0
1032         {
1033             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1034
1035             if let Some(cond_str) = trial {
1036                 if cond_str.len()
1037                     <= context
1038                         .config
1039                         .width_heuristics()
1040                         .single_line_if_else_max_width
1041                 {
1042                     return Some((cond_str, 0));
1043                 }
1044             }
1045         }
1046
1047         let cond_span = if let Some(cond) = self.cond {
1048             cond.span
1049         } else {
1050             mk_sp(self.block.span.lo(), self.block.span.lo())
1051         };
1052
1053         // `for event in event`
1054         // Do not include label in the span.
1055         let lo = self
1056             .label
1057             .map_or(self.span.lo(), |label| label.ident.span.hi());
1058         let between_kwd_cond = mk_sp(
1059             context
1060                 .snippet_provider
1061                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1062             if self.pats.is_empty() {
1063                 cond_span.lo()
1064             } else if self.matcher.is_empty() {
1065                 self.pats[0].span.lo()
1066             } else {
1067                 context
1068                     .snippet_provider
1069                     .span_before(self.span, self.matcher.trim())
1070             },
1071         );
1072
1073         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1074
1075         let after_cond_comment =
1076             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1077
1078         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1079             ""
1080         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1081             || force_newline_brace
1082         {
1083             alt_block_sep
1084         } else {
1085             " "
1086         };
1087
1088         let used_width = if pat_expr_string.contains('\n') {
1089             last_line_width(&pat_expr_string)
1090         } else {
1091             // 2 = spaces after keyword and condition.
1092             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1093         };
1094
1095         Some((
1096             format!(
1097                 "{}{}{}{}{}",
1098                 label_string,
1099                 self.keyword,
1100                 between_kwd_cond_comment.as_ref().map_or(
1101                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1102                         ""
1103                     } else {
1104                         " "
1105                     },
1106                     |s| &**s,
1107                 ),
1108                 pat_expr_string,
1109                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1110             ),
1111             used_width,
1112         ))
1113     }
1114 }
1115
1116 impl<'a> Rewrite for ControlFlow<'a> {
1117     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1118         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1119
1120         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1121         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1122         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1123         if used_width == 0 {
1124             return Some(cond_str);
1125         }
1126
1127         let block_width = shape.width.saturating_sub(used_width);
1128         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1129         // we should avoid the single line case.
1130         let block_width = if self.else_block.is_some() || self.nested_if {
1131             min(1, block_width)
1132         } else {
1133             block_width
1134         };
1135         let block_shape = Shape {
1136             width: block_width,
1137             ..shape
1138         };
1139         let block_str = {
1140             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1141             let result =
1142                 rewrite_block_with_visitor(context, "", self.block, None, None, block_shape, true);
1143             context.is_if_else_block.replace(old_val);
1144             result?
1145         };
1146
1147         let mut result = format!("{}{}", cond_str, block_str);
1148
1149         if let Some(else_block) = self.else_block {
1150             let shape = Shape::indented(shape.indent, context.config);
1151             let mut last_in_chain = false;
1152             let rewrite = match else_block.node {
1153                 // If the else expression is another if-else expression, prevent it
1154                 // from being formatted on a single line.
1155                 // Note how we're passing the original shape, as the
1156                 // cost of "else" should not cascade.
1157                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1158                     ControlFlow::new_if(
1159                         cond,
1160                         ptr_vec_to_ref_vec(pat),
1161                         if_block,
1162                         next_else_block.as_ref().map(|e| &**e),
1163                         false,
1164                         true,
1165                         mk_sp(else_block.span.lo(), self.span.hi()),
1166                     ).rewrite(context, shape)
1167                 }
1168                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1169                     ControlFlow::new_if(
1170                         cond,
1171                         vec![],
1172                         if_block,
1173                         next_else_block.as_ref().map(|e| &**e),
1174                         false,
1175                         true,
1176                         mk_sp(else_block.span.lo(), self.span.hi()),
1177                     ).rewrite(context, shape)
1178                 }
1179                 _ => {
1180                     last_in_chain = true;
1181                     // When rewriting a block, the width is only used for single line
1182                     // blocks, passing 1 lets us avoid that.
1183                     let else_shape = Shape {
1184                         width: min(1, shape.width),
1185                         ..shape
1186                     };
1187                     format_expr(else_block, ExprType::Statement, context, else_shape)
1188                 }
1189             };
1190
1191             let between_kwd_else_block = mk_sp(
1192                 self.block.span.hi(),
1193                 context
1194                     .snippet_provider
1195                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1196             );
1197             let between_kwd_else_block_comment =
1198                 extract_comment(between_kwd_else_block, context, shape);
1199
1200             let after_else = mk_sp(
1201                 context
1202                     .snippet_provider
1203                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1204                 else_block.span.lo(),
1205             );
1206             let after_else_comment = extract_comment(after_else, context, shape);
1207
1208             let between_sep = match context.config.control_brace_style() {
1209                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1210                     &*alt_block_sep
1211                 }
1212                 ControlBraceStyle::AlwaysSameLine => " ",
1213             };
1214             let after_sep = match context.config.control_brace_style() {
1215                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1216                 _ => " ",
1217             };
1218
1219             result.push_str(&format!(
1220                 "{}else{}",
1221                 between_kwd_else_block_comment
1222                     .as_ref()
1223                     .map_or(between_sep, |s| &**s),
1224                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1225             ));
1226             result.push_str(&rewrite?);
1227         }
1228
1229         Some(result)
1230     }
1231 }
1232
1233 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1234     match opt_label {
1235         Some(label) => Cow::from(format!("{}: ", label.ident)),
1236         None => Cow::from(""),
1237     }
1238 }
1239
1240 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1241     match rewrite_missing_comment(span, shape, context) {
1242         Some(ref comment) if !comment.is_empty() => Some(format!(
1243             "{indent}{}{indent}",
1244             comment,
1245             indent = shape.indent.to_string_with_newline(context.config)
1246         )),
1247         _ => None,
1248     }
1249 }
1250
1251 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1252     let snippet = codemap.span_to_snippet(block.span).unwrap();
1253     contains_comment(&snippet)
1254 }
1255
1256 // Checks that a block contains no statements, an expression and no comments or
1257 // attributes.
1258 // FIXME: incorrectly returns false when comment is contained completely within
1259 // the expression.
1260 pub fn is_simple_block(
1261     block: &ast::Block,
1262     attrs: Option<&[ast::Attribute]>,
1263     codemap: &CodeMap,
1264 ) -> bool {
1265     (block.stmts.len() == 1
1266         && stmt_is_expr(&block.stmts[0])
1267         && !block_contains_comment(block, codemap)
1268         && attrs.map_or(true, |a| a.is_empty()))
1269 }
1270
1271 /// Checks whether a block contains at most one statement or expression, and no
1272 /// comments or attributes.
1273 pub fn is_simple_block_stmt(
1274     block: &ast::Block,
1275     attrs: Option<&[ast::Attribute]>,
1276     codemap: &CodeMap,
1277 ) -> bool {
1278     block.stmts.len() <= 1
1279         && !block_contains_comment(block, codemap)
1280         && attrs.map_or(true, |a| a.is_empty())
1281 }
1282
1283 /// Checks whether a block contains no statements, expressions, comments, or
1284 /// inner attributes.
1285 pub fn is_empty_block(
1286     block: &ast::Block,
1287     attrs: Option<&[ast::Attribute]>,
1288     codemap: &CodeMap,
1289 ) -> bool {
1290     block.stmts.is_empty()
1291         && !block_contains_comment(block, codemap)
1292         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1293 }
1294
1295 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1296     match stmt.node {
1297         ast::StmtKind::Expr(..) => true,
1298         _ => false,
1299     }
1300 }
1301
1302 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1303     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1304         true
1305     } else {
1306         false
1307     }
1308 }
1309
1310 pub fn rewrite_multiple_patterns(
1311     context: &RewriteContext,
1312     pats: &[&ast::Pat],
1313     shape: Shape,
1314 ) -> Option<String> {
1315     let pat_strs = pats
1316         .iter()
1317         .map(|p| p.rewrite(context, shape))
1318         .collect::<Option<Vec<_>>>()?;
1319
1320     let use_mixed_layout = pats
1321         .iter()
1322         .zip(pat_strs.iter())
1323         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1324     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1325     let tactic = if use_mixed_layout {
1326         DefinitiveListTactic::Mixed
1327     } else {
1328         definitive_tactic(
1329             &items,
1330             ListTactic::HorizontalVertical,
1331             Separator::VerticalBar,
1332             shape.width,
1333         )
1334     };
1335     let fmt = ListFormatting {
1336         tactic,
1337         separator: " |",
1338         trailing_separator: SeparatorTactic::Never,
1339         separator_place: context.config.binop_separator(),
1340         shape,
1341         ends_with_newline: false,
1342         preserve_newline: false,
1343         nested: false,
1344         config: context.config,
1345     };
1346     write_list(&items, &fmt)
1347 }
1348
1349 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1350     match l.node {
1351         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1352         _ => wrap_str(
1353             context.snippet(l.span).to_owned(),
1354             context.config.max_width(),
1355             shape,
1356         ),
1357     }
1358 }
1359
1360 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1361     let string_lit = context.snippet(span);
1362
1363     if !context.config.format_strings() {
1364         if string_lit
1365             .lines()
1366             .rev()
1367             .skip(1)
1368             .all(|line| line.ends_with('\\'))
1369         {
1370             let new_indent = shape.visual_indent(1).indent;
1371             let indented_string_lit = String::from(
1372                 string_lit
1373                     .lines()
1374                     .map(|line| {
1375                         format!(
1376                             "{}{}",
1377                             new_indent.to_string(context.config),
1378                             line.trim_left()
1379                         )
1380                     })
1381                     .collect::<Vec<_>>()
1382                     .join("\n")
1383                     .trim_left(),
1384             );
1385             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1386         } else {
1387             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1388         }
1389     }
1390
1391     // Remove the quote characters.
1392     let str_lit = &string_lit[1..string_lit.len() - 1];
1393
1394     rewrite_string(
1395         str_lit,
1396         &StringFormat::new(shape.visual_indent(0), context.config),
1397         None,
1398     )
1399 }
1400
1401 /// In case special-case style is required, returns an offset from which we start horizontal layout.
1402 pub fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<(bool, usize)> {
1403     if let Some(&(_, num_args_before)) = SPECIAL_MACRO_WHITELIST
1404         .iter()
1405         .find(|&&(s, _)| s == callee_str)
1406     {
1407         let all_simple = args.len() > num_args_before && is_every_expr_simple(args);
1408
1409         Some((all_simple, num_args_before))
1410     } else {
1411         None
1412     }
1413 }
1414
1415 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
1416 /// format.
1417 ///
1418 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
1419 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
1420 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
1421 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
1422     // format! like macros
1423     // From the Rust Standard Library.
1424     ("eprint!", 0),
1425     ("eprintln!", 0),
1426     ("format!", 0),
1427     ("format_args!", 0),
1428     ("print!", 0),
1429     ("println!", 0),
1430     ("panic!", 0),
1431     ("unreachable!", 0),
1432     // From the `log` crate.
1433     ("debug!", 0),
1434     ("error!", 0),
1435     ("info!", 0),
1436     ("warn!", 0),
1437     // write! like macros
1438     ("assert!", 1),
1439     ("debug_assert!", 1),
1440     ("write!", 1),
1441     ("writeln!", 1),
1442     // assert_eq! like macros
1443     ("assert_eq!", 2),
1444     ("assert_ne!", 2),
1445     ("debug_assert_eq!", 2),
1446     ("debug_assert_ne!", 2),
1447 ];
1448
1449 fn choose_separator_tactic(context: &RewriteContext, span: Span) -> Option<SeparatorTactic> {
1450     if context.inside_macro() {
1451         if span_ends_with_comma(context, span) {
1452             Some(SeparatorTactic::Always)
1453         } else {
1454             Some(SeparatorTactic::Never)
1455         }
1456     } else {
1457         None
1458     }
1459 }
1460
1461 pub fn rewrite_call(
1462     context: &RewriteContext,
1463     callee: &str,
1464     args: &[ptr::P<ast::Expr>],
1465     span: Span,
1466     shape: Shape,
1467 ) -> Option<String> {
1468     overflow::rewrite_with_parens(
1469         context,
1470         callee,
1471         &ptr_vec_to_ref_vec(args),
1472         shape,
1473         span,
1474         context.config.width_heuristics().fn_call_width,
1475         choose_separator_tactic(context, span),
1476     )
1477 }
1478
1479 fn is_simple_expr(expr: &ast::Expr) -> bool {
1480     match expr.node {
1481         ast::ExprKind::Lit(..) => true,
1482         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1483         ast::ExprKind::AddrOf(_, ref expr)
1484         | ast::ExprKind::Box(ref expr)
1485         | ast::ExprKind::Cast(ref expr, _)
1486         | ast::ExprKind::Field(ref expr, _)
1487         | ast::ExprKind::Try(ref expr)
1488         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1489         ast::ExprKind::Index(ref lhs, ref rhs) => is_simple_expr(lhs) && is_simple_expr(rhs),
1490         ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1491             is_simple_expr(lhs) && is_simple_expr(&*rhs.value)
1492         }
1493         _ => false,
1494     }
1495 }
1496
1497 pub fn is_every_expr_simple<T: ToExpr>(lists: &[&T]) -> bool {
1498     lists
1499         .iter()
1500         .all(|arg| arg.to_expr().map_or(false, is_simple_expr))
1501 }
1502
1503 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
1504     match expr.node {
1505         ast::ExprKind::Match(..) => {
1506             (context.use_block_indent() && args_len == 1)
1507                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1508         }
1509         ast::ExprKind::If(..)
1510         | ast::ExprKind::IfLet(..)
1511         | ast::ExprKind::ForLoop(..)
1512         | ast::ExprKind::Loop(..)
1513         | ast::ExprKind::While(..)
1514         | ast::ExprKind::WhileLet(..) => {
1515             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1516         }
1517         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
1518             context.use_block_indent()
1519                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
1520         }
1521         ast::ExprKind::Array(..)
1522         | ast::ExprKind::Call(..)
1523         | ast::ExprKind::Mac(..)
1524         | ast::ExprKind::MethodCall(..)
1525         | ast::ExprKind::Struct(..)
1526         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
1527         ast::ExprKind::AddrOf(_, ref expr)
1528         | ast::ExprKind::Box(ref expr)
1529         | ast::ExprKind::Try(ref expr)
1530         | ast::ExprKind::Unary(_, ref expr)
1531         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1532         _ => false,
1533     }
1534 }
1535
1536 pub fn is_nested_call(expr: &ast::Expr) -> bool {
1537     match expr.node {
1538         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
1539         ast::ExprKind::AddrOf(_, ref expr)
1540         | ast::ExprKind::Box(ref expr)
1541         | ast::ExprKind::Try(ref expr)
1542         | ast::ExprKind::Unary(_, ref expr)
1543         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1544         _ => false,
1545     }
1546 }
1547
1548 /// Return true if a function call or a method call represented by the given span ends with a
1549 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1550 /// comma from macro can potentially break the code.
1551 pub fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
1552     let mut result: bool = Default::default();
1553     let mut prev_char: char = Default::default();
1554     let closing_delimiters = &[')', '}', ']'];
1555
1556     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1557         match c {
1558             _ if kind.is_comment() || c.is_whitespace() => continue,
1559             c if closing_delimiters.contains(&c) => {
1560                 result &= !closing_delimiters.contains(&prev_char);
1561             }
1562             ',' => result = true,
1563             _ => result = false,
1564         }
1565         prev_char = c;
1566     }
1567
1568     result
1569 }
1570
1571 fn rewrite_paren(
1572     context: &RewriteContext,
1573     mut subexpr: &ast::Expr,
1574     shape: Shape,
1575     mut span: Span,
1576 ) -> Option<String> {
1577     debug!("rewrite_paren, shape: {:?}", shape);
1578
1579     // Extract comments within parens.
1580     let mut pre_comment;
1581     let mut post_comment;
1582     let remove_nested_parens = context.config.remove_nested_parens();
1583     loop {
1584         // 1 = "(" or ")"
1585         let pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1586         let post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1587         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1588         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1589
1590         // Remove nested parens if there are no comments.
1591         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.node {
1592             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1593                 span = subexpr.span;
1594                 subexpr = subsubexpr;
1595                 continue;
1596             }
1597         }
1598
1599         break;
1600     }
1601
1602     // 1 `(`
1603     let sub_shape = shape.offset_left(1).and_then(|s| s.sub_width(1))?;
1604
1605     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1606     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1607
1608     // 2 = `()`
1609     if subexpr_str.contains('\n') || first_line_width(&subexpr_str) + 2 <= shape.width {
1610         Some(format!("({}{}{})", pre_comment, &subexpr_str, post_comment))
1611     } else {
1612         None
1613     }
1614 }
1615
1616 fn rewrite_index(
1617     expr: &ast::Expr,
1618     index: &ast::Expr,
1619     context: &RewriteContext,
1620     shape: Shape,
1621 ) -> Option<String> {
1622     let expr_str = expr.rewrite(context, shape)?;
1623
1624     let offset = last_line_width(&expr_str) + 1;
1625     let rhs_overhead = shape.rhs_overhead(context.config);
1626     let index_shape = if expr_str.contains('\n') {
1627         Shape::legacy(context.config.max_width(), shape.indent)
1628             .offset_left(offset)
1629             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1630     } else {
1631         shape.visual_indent(offset).sub_width(offset + 1)
1632     };
1633     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1634
1635     // Return if index fits in a single line.
1636     match orig_index_rw {
1637         Some(ref index_str) if !index_str.contains('\n') => {
1638             return Some(format!("{}[{}]", expr_str, index_str));
1639         }
1640         _ => (),
1641     }
1642
1643     // Try putting index on the next line and see if it fits in a single line.
1644     let indent = shape.indent.block_indent(context.config);
1645     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1646     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1647     let new_index_rw = index.rewrite(context, index_shape);
1648     match (orig_index_rw, new_index_rw) {
1649         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1650             "{}{}[{}]",
1651             expr_str,
1652             indent.to_string_with_newline(context.config),
1653             new_index_str,
1654         )),
1655         (None, Some(ref new_index_str)) => Some(format!(
1656             "{}{}[{}]",
1657             expr_str,
1658             indent.to_string_with_newline(context.config),
1659             new_index_str,
1660         )),
1661         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1662         _ => None,
1663     }
1664 }
1665
1666 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
1667     if base.is_some() {
1668         return false;
1669     }
1670
1671     fields.iter().all(|field| !field.is_shorthand)
1672 }
1673
1674 fn rewrite_struct_lit<'a>(
1675     context: &RewriteContext,
1676     path: &ast::Path,
1677     fields: &'a [ast::Field],
1678     base: Option<&'a ast::Expr>,
1679     span: Span,
1680     shape: Shape,
1681 ) -> Option<String> {
1682     debug!("rewrite_struct_lit: shape {:?}", shape);
1683
1684     enum StructLitField<'a> {
1685         Regular(&'a ast::Field),
1686         Base(&'a ast::Expr),
1687     }
1688
1689     // 2 = " {".len()
1690     let path_shape = shape.sub_width(2)?;
1691     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1692
1693     if fields.is_empty() && base.is_none() {
1694         return Some(format!("{} {{}}", path_str));
1695     }
1696
1697     // Foo { a: Foo } - indent is +3, width is -5.
1698     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1699
1700     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1701     let body_lo = context.snippet_provider.span_after(span, "{");
1702     let fields_str = if struct_lit_can_be_aligned(fields, &base)
1703         && context.config.struct_field_align_threshold() > 0
1704     {
1705         rewrite_with_alignment(
1706             fields,
1707             context,
1708             shape,
1709             mk_sp(body_lo, span.hi()),
1710             one_line_width,
1711         )?
1712     } else {
1713         let field_iter = fields
1714             .into_iter()
1715             .map(StructLitField::Regular)
1716             .chain(base.into_iter().map(StructLitField::Base));
1717
1718         let span_lo = |item: &StructLitField| match *item {
1719             StructLitField::Regular(field) => field.span().lo(),
1720             StructLitField::Base(expr) => {
1721                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1722                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1723                 let pos = snippet.find_uncommented("..").unwrap();
1724                 last_field_hi + BytePos(pos as u32)
1725             }
1726         };
1727         let span_hi = |item: &StructLitField| match *item {
1728             StructLitField::Regular(field) => field.span().hi(),
1729             StructLitField::Base(expr) => expr.span.hi(),
1730         };
1731         let rewrite = |item: &StructLitField| match *item {
1732             StructLitField::Regular(field) => {
1733                 // The 1 taken from the v_budget is for the comma.
1734                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1735             }
1736             StructLitField::Base(expr) => {
1737                 // 2 = ..
1738                 expr.rewrite(context, v_shape.offset_left(2)?)
1739                     .map(|s| format!("..{}", s))
1740             }
1741         };
1742
1743         let items = itemize_list(
1744             context.snippet_provider,
1745             field_iter,
1746             "}",
1747             ",",
1748             span_lo,
1749             span_hi,
1750             rewrite,
1751             body_lo,
1752             span.hi(),
1753             false,
1754         );
1755         let item_vec = items.collect::<Vec<_>>();
1756
1757         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1758         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1759
1760         let ends_with_comma = span_ends_with_comma(context, span);
1761         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1762
1763         let fmt = struct_lit_formatting(
1764             nested_shape,
1765             tactic,
1766             context,
1767             force_no_trailing_comma || base.is_some(),
1768         );
1769
1770         write_list(&item_vec, &fmt)?
1771     };
1772
1773     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
1774     Some(format!("{} {{{}}}", path_str, fields_str))
1775
1776     // FIXME if context.config.indent_style() == Visual, but we run out
1777     // of space, we should fall back to BlockIndent.
1778 }
1779
1780 pub fn wrap_struct_field(
1781     context: &RewriteContext,
1782     fields_str: &str,
1783     shape: Shape,
1784     nested_shape: Shape,
1785     one_line_width: usize,
1786 ) -> String {
1787     if context.config.indent_style() == IndentStyle::Block
1788         && (fields_str.contains('\n')
1789             || !context.config.struct_lit_single_line()
1790             || fields_str.len() > one_line_width)
1791     {
1792         format!(
1793             "{}{}{}",
1794             nested_shape.indent.to_string_with_newline(context.config),
1795             fields_str,
1796             shape.indent.to_string_with_newline(context.config)
1797         )
1798     } else {
1799         // One liner or visual indent.
1800         format!(" {} ", fields_str)
1801     }
1802 }
1803
1804 pub fn struct_lit_field_separator(config: &Config) -> &str {
1805     colon_spaces(config.space_before_colon(), config.space_after_colon())
1806 }
1807
1808 pub fn rewrite_field(
1809     context: &RewriteContext,
1810     field: &ast::Field,
1811     shape: Shape,
1812     prefix_max_width: usize,
1813 ) -> Option<String> {
1814     if contains_skip(&field.attrs) {
1815         return Some(context.snippet(field.span()).to_owned());
1816     }
1817     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1818     if !attrs_str.is_empty() {
1819         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1820     };
1821     let name = &field.ident.name.to_string();
1822     if field.is_shorthand {
1823         Some(attrs_str + &name)
1824     } else {
1825         let mut separator = String::from(struct_lit_field_separator(context.config));
1826         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1827             separator.push(' ');
1828         }
1829         let overhead = name.len() + separator.len();
1830         let expr_shape = shape.offset_left(overhead)?;
1831         let expr = field.expr.rewrite(context, expr_shape);
1832
1833         match expr {
1834             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1835                 Some(attrs_str + &name)
1836             }
1837             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1838             None => {
1839                 let expr_offset = shape.indent.block_indent(context.config);
1840                 let expr = field
1841                     .expr
1842                     .rewrite(context, Shape::indented(expr_offset, context.config));
1843                 expr.map(|s| {
1844                     format!(
1845                         "{}{}:\n{}{}",
1846                         attrs_str,
1847                         name,
1848                         expr_offset.to_string(context.config),
1849                         s
1850                     )
1851                 })
1852             }
1853         }
1854     }
1855 }
1856
1857 fn rewrite_tuple_in_visual_indent_style<'a, T>(
1858     context: &RewriteContext,
1859     items: &[&T],
1860     span: Span,
1861     shape: Shape,
1862 ) -> Option<String>
1863 where
1864     T: Rewrite + Spanned + ToExpr + 'a,
1865 {
1866     let mut items = items.iter();
1867     // In case of length 1, need a trailing comma
1868     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1869     if items.len() == 1 {
1870         // 3 = "(" + ",)"
1871         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1872         return items
1873             .next()
1874             .unwrap()
1875             .rewrite(context, nested_shape)
1876             .map(|s| format!("({},)", s));
1877     }
1878
1879     let list_lo = context.snippet_provider.span_after(span, "(");
1880     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1881     let items = itemize_list(
1882         context.snippet_provider,
1883         items,
1884         ")",
1885         ",",
1886         |item| item.span().lo(),
1887         |item| item.span().hi(),
1888         |item| item.rewrite(context, nested_shape),
1889         list_lo,
1890         span.hi() - BytePos(1),
1891         false,
1892     );
1893     let item_vec: Vec<_> = items.collect();
1894     let tactic = definitive_tactic(
1895         &item_vec,
1896         ListTactic::HorizontalVertical,
1897         Separator::Comma,
1898         nested_shape.width,
1899     );
1900     let fmt = ListFormatting {
1901         tactic,
1902         separator: ",",
1903         trailing_separator: SeparatorTactic::Never,
1904         separator_place: SeparatorPlace::Back,
1905         shape,
1906         ends_with_newline: false,
1907         preserve_newline: false,
1908         nested: false,
1909         config: context.config,
1910     };
1911     let list_str = write_list(&item_vec, &fmt)?;
1912
1913     Some(format!("({})", list_str))
1914 }
1915
1916 pub fn rewrite_tuple<'a, T>(
1917     context: &RewriteContext,
1918     items: &[&T],
1919     span: Span,
1920     shape: Shape,
1921 ) -> Option<String>
1922 where
1923     T: Rewrite + Spanned + ToExpr + 'a,
1924 {
1925     debug!("rewrite_tuple {:?}", shape);
1926     if context.use_block_indent() {
1927         // We use the same rule as function calls for rewriting tuples.
1928         let force_tactic = if context.inside_macro() {
1929             if span_ends_with_comma(context, span) {
1930                 Some(SeparatorTactic::Always)
1931             } else {
1932                 Some(SeparatorTactic::Never)
1933             }
1934         } else if items.len() == 1 {
1935             Some(SeparatorTactic::Always)
1936         } else {
1937             None
1938         };
1939         overflow::rewrite_with_parens(
1940             context,
1941             "",
1942             items,
1943             shape,
1944             span,
1945             context.config.width_heuristics().fn_call_width,
1946             force_tactic,
1947         )
1948     } else {
1949         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
1950     }
1951 }
1952
1953 pub fn rewrite_unary_prefix<R: Rewrite>(
1954     context: &RewriteContext,
1955     prefix: &str,
1956     rewrite: &R,
1957     shape: Shape,
1958 ) -> Option<String> {
1959     rewrite
1960         .rewrite(context, shape.offset_left(prefix.len())?)
1961         .map(|r| format!("{}{}", prefix, r))
1962 }
1963
1964 // FIXME: this is probably not correct for multi-line Rewrites. we should
1965 // subtract suffix.len() from the last line budget, not the first!
1966 pub fn rewrite_unary_suffix<R: Rewrite>(
1967     context: &RewriteContext,
1968     suffix: &str,
1969     rewrite: &R,
1970     shape: Shape,
1971 ) -> Option<String> {
1972     rewrite
1973         .rewrite(context, shape.sub_width(suffix.len())?)
1974         .map(|mut r| {
1975             r.push_str(suffix);
1976             r
1977         })
1978 }
1979
1980 fn rewrite_unary_op(
1981     context: &RewriteContext,
1982     op: &ast::UnOp,
1983     expr: &ast::Expr,
1984     shape: Shape,
1985 ) -> Option<String> {
1986     // For some reason, an UnOp is not spanned like BinOp!
1987     let operator_str = match *op {
1988         ast::UnOp::Deref => "*",
1989         ast::UnOp::Not => "!",
1990         ast::UnOp::Neg => "-",
1991     };
1992     rewrite_unary_prefix(context, operator_str, expr, shape)
1993 }
1994
1995 fn rewrite_assignment(
1996     context: &RewriteContext,
1997     lhs: &ast::Expr,
1998     rhs: &ast::Expr,
1999     op: Option<&ast::BinOp>,
2000     shape: Shape,
2001 ) -> Option<String> {
2002     let operator_str = match op {
2003         Some(op) => context.snippet(op.span),
2004         None => "=",
2005     };
2006
2007     // 1 = space between lhs and operator.
2008     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2009     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2010
2011     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2012 }
2013
2014 /// Controls where to put the rhs.
2015 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
2016 pub enum RhsTactics {
2017     /// Use heuristics.
2018     Default,
2019     /// Put the rhs on the next line if it uses multiple line, without extra indentation.
2020     ForceNextLineWithoutIndent,
2021 }
2022
2023 // The left hand side must contain everything up to, and including, the
2024 // assignment operator.
2025 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2026     context: &RewriteContext,
2027     lhs: S,
2028     ex: &R,
2029     shape: Shape,
2030 ) -> Option<String> {
2031     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
2032 }
2033
2034 pub fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
2035     context: &RewriteContext,
2036     lhs: S,
2037     ex: &R,
2038     shape: Shape,
2039     rhs_tactics: RhsTactics,
2040 ) -> Option<String> {
2041     let lhs = lhs.into();
2042     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
2043         shape.indent.width()
2044     } else {
2045         0
2046     });
2047     // 1 = space between operator and rhs.
2048     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2049         width: 0,
2050         offset: shape.offset + last_line_width + 1,
2051         ..shape
2052     });
2053     let rhs = choose_rhs(
2054         context,
2055         ex,
2056         orig_shape,
2057         ex.rewrite(context, orig_shape),
2058         rhs_tactics,
2059     )?;
2060     Some(lhs + &rhs)
2061 }
2062
2063 fn choose_rhs<R: Rewrite>(
2064     context: &RewriteContext,
2065     expr: &R,
2066     shape: Shape,
2067     orig_rhs: Option<String>,
2068     rhs_tactics: RhsTactics,
2069 ) -> Option<String> {
2070     match orig_rhs {
2071         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2072             Some(format!(" {}", new_str))
2073         }
2074         _ => {
2075             // Expression did not fit on the same line as the identifier.
2076             // Try splitting the line and see if that works better.
2077             let new_shape = shape_from_rhs_tactic(context, shape, rhs_tactics)?;
2078             let new_rhs = expr.rewrite(context, new_shape);
2079             let new_indent_str = &shape
2080                 .indent
2081                 .block_indent(context.config)
2082                 .to_string_with_newline(context.config);
2083
2084             match (orig_rhs, new_rhs) {
2085                 (Some(ref orig_rhs), Some(ref new_rhs))
2086                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2087                         .is_none() =>
2088                 {
2089                     Some(format!(" {}", orig_rhs))
2090                 }
2091                 (Some(ref orig_rhs), Some(ref new_rhs))
2092                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2093                 {
2094                     Some(format!("{}{}", new_indent_str, new_rhs))
2095                 }
2096                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2097                 (None, None) => None,
2098                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2099             }
2100         }
2101     }
2102 }
2103
2104 fn shape_from_rhs_tactic(
2105     context: &RewriteContext,
2106     shape: Shape,
2107     rhs_tactic: RhsTactics,
2108 ) -> Option<Shape> {
2109     match rhs_tactic {
2110         RhsTactics::ForceNextLineWithoutIndent => Some(shape.with_max_width(context.config)),
2111         RhsTactics::Default => {
2112             Shape::indented(shape.indent.block_indent(context.config), context.config)
2113                 .sub_width(shape.rhs_overhead(context.config))
2114         }
2115     }
2116 }
2117
2118 pub fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str, rhs_tactics: RhsTactics) -> bool {
2119     rhs_tactics == RhsTactics::ForceNextLineWithoutIndent
2120         || !next_line_rhs.contains('\n')
2121         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2122 }
2123
2124 fn rewrite_expr_addrof(
2125     context: &RewriteContext,
2126     mutability: ast::Mutability,
2127     expr: &ast::Expr,
2128     shape: Shape,
2129 ) -> Option<String> {
2130     let operator_str = match mutability {
2131         ast::Mutability::Immutable => "&",
2132         ast::Mutability::Mutable => "&mut ",
2133     };
2134     rewrite_unary_prefix(context, operator_str, expr, shape)
2135 }
2136
2137 pub trait ToExpr {
2138     fn to_expr(&self) -> Option<&ast::Expr>;
2139     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2140 }
2141
2142 impl ToExpr for ast::Expr {
2143     fn to_expr(&self) -> Option<&ast::Expr> {
2144         Some(self)
2145     }
2146
2147     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2148         can_be_overflowed_expr(context, self, len)
2149     }
2150 }
2151
2152 impl ToExpr for ast::Ty {
2153     fn to_expr(&self) -> Option<&ast::Expr> {
2154         None
2155     }
2156
2157     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2158         can_be_overflowed_type(context, self, len)
2159     }
2160 }
2161
2162 impl<'a> ToExpr for TuplePatField<'a> {
2163     fn to_expr(&self) -> Option<&ast::Expr> {
2164         None
2165     }
2166
2167     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2168         can_be_overflowed_pat(context, self, len)
2169     }
2170 }
2171
2172 impl<'a> ToExpr for ast::StructField {
2173     fn to_expr(&self) -> Option<&ast::Expr> {
2174         None
2175     }
2176
2177     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2178         false
2179     }
2180 }
2181
2182 impl<'a> ToExpr for MacroArg {
2183     fn to_expr(&self) -> Option<&ast::Expr> {
2184         match *self {
2185             MacroArg::Expr(ref expr) => Some(expr),
2186             _ => None,
2187         }
2188     }
2189
2190     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2191         match *self {
2192             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2193             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2194             MacroArg::Pat(..) => false,
2195             MacroArg::Item(..) => len == 1,
2196         }
2197     }
2198 }
2199
2200 impl ToExpr for ast::GenericParam {
2201     fn to_expr(&self) -> Option<&ast::Expr> {
2202         None
2203     }
2204
2205     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2206         false
2207     }
2208 }
2209
2210 pub fn is_method_call(expr: &ast::Expr) -> bool {
2211     match expr.node {
2212         ast::ExprKind::MethodCall(..) => true,
2213         ast::ExprKind::AddrOf(_, ref expr)
2214         | ast::ExprKind::Box(ref expr)
2215         | ast::ExprKind::Cast(ref expr, _)
2216         | ast::ExprKind::Try(ref expr)
2217         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),
2218         _ => false,
2219     }
2220 }