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