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