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::cmp::min;
  12 use std::borrow::Cow;
  13 use std::iter::{repeat, ExactSizeIterator};
  14
  15 use syntax::{ast, ptr};
  16 use syntax::codemap::{BytePos, CodeMap, Span};
  17
  18 use spanned::Spanned;
  19 use chains::rewrite_chain;
  20 use closures;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use comment::{combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
  23               rewrite_comment, rewrite_missing_comment, FindUncommented};
  24 use config::{Config, ControlBraceStyle, IndentStyle};
  25 use lists::{definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting,
  26             struct_lit_shape, struct_lit_tactic, write_list, DefinitiveListTactic, ListFormatting,
  27             ListItem, ListTactic, Separator, SeparatorPlace, SeparatorTactic};
  28 use macros::{rewrite_macro, MacroArg, MacroPosition};
  29 use patterns::{can_be_overflowed_pat, TuplePatField};
  30 use rewrite::{Rewrite, RewriteContext};
  31 use shape::{Indent, Shape};
  32 use string::{rewrite_string, StringFormat};
  33 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  34 use utils::{colon_spaces, contains_skip, extra_offset, first_line_width, inner_attributes,
  35             last_line_extendable, last_line_width, mk_sp, outer_attributes, paren_overhead,
  36             ptr_vec_to_ref_vec, semicolon_for_stmt, trimmed_last_line_width, wrap_str};
  37 use vertical::rewrite_with_alignment;
  38 use visitor::FmtVisitor;
  39
  40 impl Rewrite for ast::Expr {
  41     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  42         format_expr(self, ExprType::SubExpression, context, shape)
  43     }
  44 }
  45
  46 #[derive(Copy, Clone, PartialEq)]
  47 pub enum ExprType {
  48     Statement,
  49     SubExpression,
  50 }
  51
  52 pub fn format_expr(
  53     expr: &ast::Expr,
  54     expr_type: ExprType,
  55     context: &RewriteContext,
  56     shape: Shape,
  57 ) -> Option<String> {
  58     skip_out_of_file_lines_range!(context, expr.span);
  59
  60     if contains_skip(&*expr.attrs) {
  61         return Some(context.snippet(expr.span()).to_owned());
  62     }
  63
  64     let expr_rw = match expr.node {
  65         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  66             &ptr_vec_to_ref_vec(expr_vec),
  67             mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi()),
  68             context,
  69             shape,
  70             false,
  71         ),
  72         ast::ExprKind::Lit(ref l) => rewrite_literal(context, l, shape),
  73         ast::ExprKind::Call(ref callee, ref args) => {
  74             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  75             let callee_str = callee.rewrite(context, shape)?;
  76             rewrite_call(context, &callee_str, args, inner_span, shape)
  77         }
  78         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
  79         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
  80             // FIXME: format comments between operands and operator
  81             rewrite_pair(
  82                 &**lhs,
  83                 &**rhs,
  84                 PairParts::new("", &format!(" {} ", context.snippet(op.span)), ""),
  85                 context,
  86                 shape,
  87                 context.config.binop_separator(),
  88             )
  89         }
  90         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
  91         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
  92             context,
  93             path,
  94             fields,
  95             base.as_ref().map(|e| &**e),
  96             expr.span,
  97             shape,
  98         ),
  99         ast::ExprKind::Tup(ref items) => {
 100             rewrite_tuple(context, &ptr_vec_to_ref_vec(items), expr.span, shape)
 101         }
 102         ast::ExprKind::If(..)
 103         | ast::ExprKind::IfLet(..)
 104         | ast::ExprKind::ForLoop(..)
 105         | ast::ExprKind::Loop(..)
 106         | ast::ExprKind::While(..)
 107         | ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 108             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 109         ast::ExprKind::Block(ref block) => {
 110             match expr_type {
 111                 ExprType::Statement => {
 112                     if is_unsafe_block(block) {
 113                         block.rewrite(context, shape)
 114                     } else if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 115                         // Rewrite block without trying to put it in a single line.
 116                         rw
 117                     } else {
 118                         let prefix = block_prefix(context, block, shape)?;
 119                         rewrite_block_with_visitor(context, &prefix, block, shape, true)
 120                     }
 121                 }
 122                 ExprType::SubExpression => block.rewrite(context, shape),
 123             }
 124         }
 125         ast::ExprKind::Match(ref cond, ref arms) => {
 126             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 127         }
 128         ast::ExprKind::Path(ref qself, ref path) => {
 129             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 130         }
 131         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 132             rewrite_assignment(context, lhs, rhs, None, shape)
 133         }
 134         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 135             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 136         }
 137         ast::ExprKind::Continue(ref opt_ident) => {
 138             let id_str = match *opt_ident {
 139                 Some(ident) => format!(" {}", ident.node),
 140                 None => String::new(),
 141             };
 142             Some(format!("continue{}", id_str))
 143         }
 144         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 145             let id_str = match *opt_ident {
 146                 Some(ident) => format!(" {}", ident.node),
 147                 None => String::new(),
 148             };
 149
 150             if let Some(ref expr) = *opt_expr {
 151                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 152             } else {
 153                 Some(format!("break{}", id_str))
 154             }
 155         }
 156         ast::ExprKind::Yield(ref opt_expr) => if let Some(ref expr) = *opt_expr {
 157             rewrite_unary_prefix(context, "yield ", &**expr, shape)
 158         } else {
 159             Some("yield".to_string())
 160         },
 161         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 162             closures::rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 163         }
 164         ast::ExprKind::Try(..)
 165         | ast::ExprKind::Field(..)
 166         | ast::ExprKind::TupField(..)
 167         | ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 168         ast::ExprKind::Mac(ref mac) => {
 169             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 170                 wrap_str(
 171                     context.snippet(expr.span).to_owned(),
 172                     context.config.max_width(),
 173                     shape,
 174                 )
 175             })
 176         }
 177         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 178         ast::ExprKind::Ret(Some(ref expr)) => {
 179             rewrite_unary_prefix(context, "return ", &**expr, shape)
 180         }
 181         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 182         ast::ExprKind::AddrOf(mutability, ref expr) => {
 183             rewrite_expr_addrof(context, mutability, expr, shape)
 184         }
 185         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 186             &**expr,
 187             &**ty,
 188             PairParts::new("", " as ", ""),
 189             context,
 190             shape,
 191             SeparatorPlace::Front,
 192         ),
 193         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 194             &**expr,
 195             &**ty,
 196             PairParts::new("", ": ", ""),
 197             context,
 198             shape,
 199             SeparatorPlace::Back,
 200         ),
 201         ast::ExprKind::Index(ref expr, ref index) => {
 202             rewrite_index(&**expr, &**index, context, shape)
 203         }
 204         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 205             let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
 206                 ("[ ", " ]")
 207             } else {
 208                 ("[", "]")
 209             };
 210             rewrite_pair(
 211                 &**expr,
 212                 &**repeats,
 213                 PairParts::new(lbr, "; ", rbr),
 214                 context,
 215                 shape,
 216                 SeparatorPlace::Back,
 217             )
 218         }
 219         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 220             let delim = match limits {
 221                 ast::RangeLimits::HalfOpen => "..",
 222                 ast::RangeLimits::Closed => "..=",
 223             };
 224
 225             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 226                 match lhs.node {
 227                     ast::ExprKind::Lit(ref lit) => match lit.node {
 228                         ast::LitKind::FloatUnsuffixed(..) => {
 229                             context.snippet(lit.span).ends_with('.')
 230                         }
 231                         _ => false,
 232                     },
 233                     _ => false,
 234                 }
 235             }
 236
 237             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 238                 (Some(lhs), Some(rhs)) => {
 239                     let sp_delim = if context.config.spaces_around_ranges() {
 240                         format!(" {} ", delim)
 241                     } else if needs_space_before_range(context, lhs) {
 242                         format!(" {}", delim)
 243                     } else {
 244                         delim.to_owned()
 245                     };
 246                     rewrite_pair(
 247                         &*lhs,
 248                         &*rhs,
 249                         PairParts::new("", &sp_delim, ""),
 250                         context,
 251                         shape,
 252                         SeparatorPlace::Front,
 253                     )
 254                 }
 255                 (None, Some(rhs)) => {
 256                     let sp_delim = if context.config.spaces_around_ranges() {
 257                         format!("{} ", delim)
 258                     } else {
 259                         delim.to_owned()
 260                     };
 261                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 262                 }
 263                 (Some(lhs), None) => {
 264                     let sp_delim = if context.config.spaces_around_ranges() {
 265                         format!(" {}", delim)
 266                     } else {
 267                         delim.to_owned()
 268                     };
 269                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 270                 }
 271                 (None, None) => Some(delim.to_owned()),
 272             }
 273         }
 274         // We do not format these expressions yet, but they should still
 275         // satisfy our width restrictions.
 276         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => {
 277             Some(context.snippet(expr.span).to_owned())
 278         }
 279         ast::ExprKind::Catch(ref block) => {
 280             if let rw @ Some(_) = rewrite_single_line_block(context, "do catch ", block, shape) {
 281                 rw
 282             } else {
 283                 // 9 = `do catch `
 284                 let budget = shape.width.checked_sub(9).unwrap_or(0);
 285                 Some(format!(
 286                     "{}{}",
 287                     "do catch ",
 288                     block.rewrite(context, Shape::legacy(budget, shape.indent))?
 289                 ))
 290             }
 291         }
 292     };
 293
 294     expr_rw
 295         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 296         .and_then(|expr_str| {
 297             let attrs = outer_attributes(&expr.attrs);
 298             let attrs_str = attrs.rewrite(context, shape)?;
 299             let span = mk_sp(
 300                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 301                 expr.span.lo(),
 302             );
 303             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 304         })
 305 }
 306
 307 #[derive(new, Clone, Copy)]
 308 pub struct PairParts<'a> {
 309     prefix: &'a str,
 310     infix: &'a str,
 311     suffix: &'a str,
 312 }
 313
 314 pub fn rewrite_pair<LHS, RHS>(
 315     lhs: &LHS,
 316     rhs: &RHS,
 317     pp: PairParts,
 318     context: &RewriteContext,
 319     shape: Shape,
 320     separator_place: SeparatorPlace,
 321 ) -> Option<String>
 322 where
 323     LHS: Rewrite,
 324     RHS: Rewrite,
 325 {
 326     let lhs_overhead = match separator_place {
 327         SeparatorPlace::Back => shape.used_width() + pp.prefix.len() + pp.infix.trim_right().len(),
 328         SeparatorPlace::Front => shape.used_width(),
 329     };
 330     let lhs_shape = Shape {
 331         width: context.budget(lhs_overhead),
 332         ..shape
 333     };
 334     let lhs_result = lhs.rewrite(context, lhs_shape)
 335         .map(|lhs_str| format!("{}{}", pp.prefix, lhs_str))?;
 336
 337     // Try to the both lhs and rhs on the same line.
 338     let rhs_orig_result = shape
 339         .offset_left(last_line_width(&lhs_result) + pp.infix.len())
 340         .and_then(|s| s.sub_width(pp.suffix.len()))
 341         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 342     if let Some(ref rhs_result) = rhs_orig_result {
 343         // If the rhs looks like block expression, we allow it to stay on the same line
 344         // with the lhs even if it is multi-lined.
 345         let allow_same_line = rhs_result
 346             .lines()
 347             .next()
 348             .map(|first_line| first_line.ends_with('{'))
 349             .unwrap_or(false);
 350         if !rhs_result.contains('\n') || allow_same_line {
 351             let one_line_width = last_line_width(&lhs_result) + pp.infix.len()
 352                 + first_line_width(rhs_result) + pp.suffix.len();
 353             if one_line_width <= shape.width {
 354                 return Some(format!(
 355                     "{}{}{}{}",
 356                     lhs_result, pp.infix, rhs_result, pp.suffix
 357                 ));
 358             }
 359         }
 360     }
 361
 362     // We have to use multiple lines.
 363     // Re-evaluate the rhs because we have more space now:
 364     let mut rhs_shape = match context.config.indent_style() {
 365         IndentStyle::Visual => shape
 366             .sub_width(pp.suffix.len() + pp.prefix.len())?
 367             .visual_indent(pp.prefix.len()),
 368         IndentStyle::Block => {
 369             // Try to calculate the initial constraint on the right hand side.
 370             let rhs_overhead = shape.rhs_overhead(context.config);
 371             Shape::indented(shape.indent.block_indent(context.config), context.config)
 372                 .sub_width(rhs_overhead)?
 373         }
 374     };
 375     let infix = match separator_place {
 376         SeparatorPlace::Back => pp.infix.trim_right(),
 377         SeparatorPlace::Front => pp.infix.trim_left(),
 378     };
 379     if separator_place == SeparatorPlace::Front {
 380         rhs_shape = rhs_shape.offset_left(infix.len())?;
 381     }
 382     let rhs_result = rhs.rewrite(context, rhs_shape)?;
 383     let indent_str = rhs_shape.indent.to_string(context.config);
 384     let infix_with_sep = match separator_place {
 385         SeparatorPlace::Back => format!("{}\n{}", infix, indent_str),
 386         SeparatorPlace::Front => format!("\n{}{}", indent_str, infix),
 387     };
 388     Some(format!(
 389         "{}{}{}{}",
 390         lhs_result, infix_with_sep, rhs_result, pp.suffix
 391     ))
 392 }
 393
 394 pub fn rewrite_array<T: Rewrite + Spanned + ToExpr>(
 395     exprs: &[&T],
 396     span: Span,
 397     context: &RewriteContext,
 398     shape: Shape,
 399     trailing_comma: bool,
 400 ) -> Option<String> {
 401     let bracket_size = if context.config.spaces_within_parens_and_brackets() {
 402         2 // "[ "
 403     } else {
 404         1 // "["
 405     };
 406
 407     let nested_shape = match context.config.indent_style() {
 408         IndentStyle::Block => shape
 409             .block()
 410             .block_indent(context.config.tab_spaces())
 411             .with_max_width(context.config)
 412             .sub_width(1)?,
 413         IndentStyle::Visual => shape
 414             .visual_indent(bracket_size)
 415             .sub_width(bracket_size * 2)?,
 416     };
 417
 418     let items = itemize_list(
 419         context.codemap,
 420         exprs.iter(),
 421         "]",
 422         ",",
 423         |item| item.span().lo(),
 424         |item| item.span().hi(),
 425         |item| item.rewrite(context, nested_shape),
 426         span.lo(),
 427         span.hi(),
 428         false,
 429     ).collect::<Vec<_>>();
 430
 431     if items.is_empty() {
 432         if context.config.spaces_within_parens_and_brackets() {
 433             return Some("[ ]".to_string());
 434         } else {
 435             return Some("[]".to_string());
 436         }
 437     }
 438
 439     let tactic = array_tactic(context, shape, nested_shape, exprs, &items, bracket_size);
 440     let ends_with_newline = tactic.ends_with_newline(context.config.indent_style());
 441
 442     let fmt = ListFormatting {
 443         tactic: tactic,
 444         separator: ",",
 445         trailing_separator: if trailing_comma {
 446             SeparatorTactic::Always
 447         } else if context.inside_macro && !exprs.is_empty() {
 448             let ends_with_bracket = context.snippet(span).ends_with(']');
 449             let bracket_offset = if ends_with_bracket { 1 } else { 0 };
 450             let snippet = context.snippet(mk_sp(span.lo(), span.hi() - BytePos(bracket_offset)));
 451             let last_char_index = snippet.rfind(|c: char| !c.is_whitespace())?;
 452             if &snippet[last_char_index..last_char_index + 1] == "," {
 453                 SeparatorTactic::Always
 454             } else {
 455                 SeparatorTactic::Never
 456             }
 457         } else if context.config.indent_style() == IndentStyle::Visual {
 458             SeparatorTactic::Never
 459         } else {
 460             SeparatorTactic::Vertical
 461         },
 462         separator_place: SeparatorPlace::Back,
 463         shape: nested_shape,
 464         ends_with_newline: ends_with_newline,
 465         preserve_newline: false,
 466         config: context.config,
 467     };
 468     let list_str = write_list(&items, &fmt)?;
 469
 470     let result = if context.config.indent_style() == IndentStyle::Visual
 471         || tactic == DefinitiveListTactic::Horizontal
 472     {
 473         if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
 474             format!("[ {} ]", list_str)
 475         } else {
 476             format!("[{}]", list_str)
 477         }
 478     } else {
 479         format!(
 480             "[\n{}{}\n{}]",
 481             nested_shape.indent.to_string(context.config),
 482             list_str,
 483             shape.block().indent.to_string(context.config)
 484         )
 485     };
 486
 487     Some(result)
 488 }
 489
 490 fn array_tactic<T: Rewrite + Spanned + ToExpr>(
 491     context: &RewriteContext,
 492     shape: Shape,
 493     nested_shape: Shape,
 494     exprs: &[&T],
 495     items: &[ListItem],
 496     bracket_size: usize,
 497 ) -> DefinitiveListTactic {
 498     let has_long_item = items
 499         .iter()
 500         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 501
 502     match context.config.indent_style() {
 503         IndentStyle::Block => {
 504             let tactic = match shape.width.checked_sub(2 * bracket_size) {
 505                 Some(width) => {
 506                     let tactic = ListTactic::LimitedHorizontalVertical(
 507                         context.config.width_heuristics().array_width,
 508                     );
 509                     definitive_tactic(items, tactic, Separator::Comma, width)
 510                 }
 511                 None => DefinitiveListTactic::Vertical,
 512             };
 513             if tactic == DefinitiveListTactic::Vertical && !has_long_item
 514                 && is_every_args_simple(exprs)
 515             {
 516                 DefinitiveListTactic::Mixed
 517             } else {
 518                 tactic
 519             }
 520         }
 521         IndentStyle::Visual => {
 522             if has_long_item || items.iter().any(ListItem::is_multiline) {
 523                 definitive_tactic(
 524                     items,
 525                     ListTactic::LimitedHorizontalVertical(
 526                         context.config.width_heuristics().array_width,
 527                     ),
 528                     Separator::Comma,
 529                     nested_shape.width,
 530                 )
 531             } else {
 532                 DefinitiveListTactic::Mixed
 533             }
 534         }
 535     }
 536 }
 537
 538 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 539     debug!("nop_block_collapse {:?} {}", block_str, budget);
 540     block_str.map(|block_str| {
 541         if block_str.starts_with('{') && budget >= 2
 542             && (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 543         {
 544             "{}".to_owned()
 545         } else {
 546             block_str.to_owned()
 547         }
 548     })
 549 }
 550
 551 fn rewrite_empty_block(
 552     context: &RewriteContext,
 553     block: &ast::Block,
 554     shape: Shape,
 555 ) -> Option<String> {
 556     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 557     {
 558         return Some("{}".to_owned());
 559     }
 560
 561     // If a block contains only a single-line comment, then leave it on one line.
 562     let user_str = context.snippet(block.span);
 563     let user_str = user_str.trim();
 564     if user_str.starts_with('{') && user_str.ends_with('}') {
 565         let comment_str = user_str[1..user_str.len() - 1].trim();
 566         if block.stmts.is_empty() && !comment_str.contains('\n') && !comment_str.starts_with("//")
 567             && comment_str.len() + 4 <= shape.width
 568         {
 569             return Some(format!("{{ {} }}", comment_str));
 570         }
 571     }
 572
 573     None
 574 }
 575
 576 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 577     Some(match block.rules {
 578         ast::BlockCheckMode::Unsafe(..) => {
 579             let snippet = context.snippet(block.span);
 580             let open_pos = snippet.find_uncommented("{")?;
 581             // Extract comment between unsafe and block start.
 582             let trimmed = &snippet[6..open_pos].trim();
 583
 584             if !trimmed.is_empty() {
 585                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 586                 let budget = shape.width.checked_sub(9)?;
 587                 format!(
 588                     "unsafe {} ",
 589                     rewrite_comment(
 590                         trimmed,
 591                         true,
 592                         Shape::legacy(budget, shape.indent + 7),
 593                         context.config,
 594                     )?
 595                 )
 596             } else {
 597                 "unsafe ".to_owned()
 598             }
 599         }
 600         ast::BlockCheckMode::Default => String::new(),
 601     })
 602 }
 603
 604 fn rewrite_single_line_block(
 605     context: &RewriteContext,
 606     prefix: &str,
 607     block: &ast::Block,
 608     shape: Shape,
 609 ) -> Option<String> {
 610     if is_simple_block(block, context.codemap) {
 611         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 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     shape: Shape,
 626     has_braces: bool,
 627 ) -> Option<String> {
 628     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 629         return rw;
 630     }
 631
 632     let mut visitor = FmtVisitor::from_context(context);
 633     visitor.block_indent = shape.indent;
 634     visitor.is_if_else_block = context.is_if_else_block;
 635     match block.rules {
 636         ast::BlockCheckMode::Unsafe(..) => {
 637             let snippet = context.snippet(block.span);
 638             let open_pos = snippet.find_uncommented("{")?;
 639             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 640         }
 641         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo(),
 642     }
 643
 644     visitor.visit_block(block, None, has_braces);
 645     Some(format!("{}{}", prefix, visitor.buffer))
 646 }
 647
 648 impl Rewrite for ast::Block {
 649     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 650         // shape.width is used only for the single line case: either the empty block `{}`,
 651         // or an unsafe expression `unsafe { e }`.
 652         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 653             return rw;
 654         }
 655
 656         let prefix = block_prefix(context, self, shape)?;
 657         let shape = shape.offset_left(last_line_width(&prefix))?;
 658
 659         let result = rewrite_block_with_visitor(context, &prefix, self, shape, true);
 660         if let Some(ref result_str) = result {
 661             if result_str.lines().count() <= 3 {
 662                 if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 663                     return rw;
 664                 }
 665             }
 666         }
 667
 668         result
 669     }
 670 }
 671
 672 impl Rewrite for ast::Stmt {
 673     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 674         skip_out_of_file_lines_range!(context, self.span());
 675
 676         let result = match self.node {
 677             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 678             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 679                 let suffix = if semicolon_for_stmt(context, self) {
 680                     ";"
 681                 } else {
 682                     ""
 683                 };
 684
 685                 let shape = shape.sub_width(suffix.len())?;
 686                 format_expr(ex, ExprType::Statement, context, shape).map(|s| s + suffix)
 687             }
 688             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 689         };
 690         result.and_then(|res| recover_comment_removed(res, self.span(), context))
 691     }
 692 }
 693
 694 // Rewrite condition if the given expression has one.
 695 pub fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 696     match expr.node {
 697         ast::ExprKind::Match(ref cond, _) => {
 698             // `match `cond` {`
 699             let cond_shape = match context.config.indent_style() {
 700                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 701                 IndentStyle::Block => shape.offset_left(8)?,
 702             };
 703             cond.rewrite(context, cond_shape)
 704         }
 705         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 706             let alt_block_sep =
 707                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 708             control_flow
 709                 .rewrite_cond(context, shape, &alt_block_sep)
 710                 .and_then(|rw| Some(rw.0))
 711         }),
 712     }
 713 }
 714
 715 // Abstraction over control flow expressions
 716 #[derive(Debug)]
 717 struct ControlFlow<'a> {
 718     cond: Option<&'a ast::Expr>,
 719     block: &'a ast::Block,
 720     else_block: Option<&'a ast::Expr>,
 721     label: Option<ast::SpannedIdent>,
 722     pat: Option<&'a ast::Pat>,
 723     keyword: &'a str,
 724     matcher: &'a str,
 725     connector: &'a str,
 726     allow_single_line: bool,
 727     // True if this is an `if` expression in an `else if` :-( hacky
 728     nested_if: bool,
 729     span: Span,
 730 }
 731
 732 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow> {
 733     match expr.node {
 734         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 735             cond,
 736             None,
 737             if_block,
 738             else_block.as_ref().map(|e| &**e),
 739             expr_type == ExprType::SubExpression,
 740             false,
 741             expr.span,
 742         )),
 743         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 744             Some(ControlFlow::new_if(
 745                 cond,
 746                 Some(pat),
 747                 if_block,
 748                 else_block.as_ref().map(|e| &**e),
 749                 expr_type == ExprType::SubExpression,
 750                 false,
 751                 expr.span,
 752             ))
 753         }
 754         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 755             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 756         }
 757         ast::ExprKind::Loop(ref block, label) => {
 758             Some(ControlFlow::new_loop(block, label, expr.span))
 759         }
 760         ast::ExprKind::While(ref cond, ref block, label) => {
 761             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
 762         }
 763         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
 764             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
 765         ),
 766         _ => None,
 767     }
 768 }
 769
 770 impl<'a> ControlFlow<'a> {
 771     fn new_if(
 772         cond: &'a ast::Expr,
 773         pat: Option<&'a ast::Pat>,
 774         block: &'a ast::Block,
 775         else_block: Option<&'a ast::Expr>,
 776         allow_single_line: bool,
 777         nested_if: bool,
 778         span: Span,
 779     ) -> ControlFlow<'a> {
 780         ControlFlow {
 781             cond: Some(cond),
 782             block: block,
 783             else_block: else_block,
 784             label: None,
 785             pat: pat,
 786             keyword: "if",
 787             matcher: match pat {
 788                 Some(..) => "let",
 789                 None => "",
 790             },
 791             connector: " =",
 792             allow_single_line: allow_single_line,
 793             nested_if: nested_if,
 794             span: span,
 795         }
 796     }
 797
 798     fn new_loop(
 799         block: &'a ast::Block,
 800         label: Option<ast::SpannedIdent>,
 801         span: Span,
 802     ) -> ControlFlow<'a> {
 803         ControlFlow {
 804             cond: None,
 805             block: block,
 806             else_block: None,
 807             label: label,
 808             pat: None,
 809             keyword: "loop",
 810             matcher: "",
 811             connector: "",
 812             allow_single_line: false,
 813             nested_if: false,
 814             span: span,
 815         }
 816     }
 817
 818     fn new_while(
 819         pat: Option<&'a ast::Pat>,
 820         cond: &'a ast::Expr,
 821         block: &'a ast::Block,
 822         label: Option<ast::SpannedIdent>,
 823         span: Span,
 824     ) -> ControlFlow<'a> {
 825         ControlFlow {
 826             cond: Some(cond),
 827             block: block,
 828             else_block: None,
 829             label: label,
 830             pat: pat,
 831             keyword: "while",
 832             matcher: match pat {
 833                 Some(..) => "let",
 834                 None => "",
 835             },
 836             connector: " =",
 837             allow_single_line: false,
 838             nested_if: false,
 839             span: span,
 840         }
 841     }
 842
 843     fn new_for(
 844         pat: &'a ast::Pat,
 845         cond: &'a ast::Expr,
 846         block: &'a ast::Block,
 847         label: Option<ast::SpannedIdent>,
 848         span: Span,
 849     ) -> ControlFlow<'a> {
 850         ControlFlow {
 851             cond: Some(cond),
 852             block: block,
 853             else_block: None,
 854             label: label,
 855             pat: Some(pat),
 856             keyword: "for",
 857             matcher: "",
 858             connector: " in",
 859             allow_single_line: false,
 860             nested_if: false,
 861             span: span,
 862         }
 863     }
 864
 865     fn rewrite_single_line(
 866         &self,
 867         pat_expr_str: &str,
 868         context: &RewriteContext,
 869         width: usize,
 870     ) -> Option<String> {
 871         assert!(self.allow_single_line);
 872         let else_block = self.else_block?;
 873         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 874
 875         if let ast::ExprKind::Block(ref else_node) = else_block.node {
 876             if !is_simple_block(self.block, context.codemap)
 877                 || !is_simple_block(else_node, context.codemap)
 878                 || pat_expr_str.contains('\n')
 879             {
 880                 return None;
 881             }
 882
 883             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 884             let expr = &self.block.stmts[0];
 885             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 886
 887             let new_width = new_width.checked_sub(if_str.len())?;
 888             let else_expr = &else_node.stmts[0];
 889             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 890
 891             if if_str.contains('\n') || else_str.contains('\n') {
 892                 return None;
 893             }
 894
 895             let result = format!(
 896                 "{} {} {{ {} }} else {{ {} }}",
 897                 self.keyword, pat_expr_str, if_str, else_str
 898             );
 899
 900             if result.len() <= width {
 901                 return Some(result);
 902             }
 903         }
 904
 905         None
 906     }
 907 }
 908
 909 impl<'a> ControlFlow<'a> {
 910     fn rewrite_cond(
 911         &self,
 912         context: &RewriteContext,
 913         shape: Shape,
 914         alt_block_sep: &str,
 915     ) -> Option<(String, usize)> {
 916         // Do not take the rhs overhead from the upper expressions into account
 917         // when rewriting pattern.
 918         let new_width = context
 919             .config
 920             .max_width()
 921             .checked_sub(shape.used_width())
 922             .unwrap_or(0);
 923         let fresh_shape = Shape {
 924             width: new_width,
 925             ..shape
 926         };
 927         let constr_shape = if self.nested_if {
 928             // We are part of an if-elseif-else chain. Our constraints are tightened.
 929             // 7 = "} else " .len()
 930             fresh_shape.offset_left(7)?
 931         } else {
 932             fresh_shape
 933         };
 934
 935         let label_string = rewrite_label(self.label);
 936         // 1 = space after keyword.
 937         let offset = self.keyword.len() + label_string.len() + 1;
 938
 939         let pat_expr_string = match self.cond {
 940             Some(cond) => rewrite_pat_expr(
 941                 context,
 942                 self.pat,
 943                 cond,
 944                 self.matcher,
 945                 self.connector,
 946                 self.keyword,
 947                 constr_shape,
 948                 offset,
 949             )?,
 950             None => String::new(),
 951         };
 952
 953         let brace_overhead =
 954             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 955                 // 2 = ` {`
 956                 2
 957             } else {
 958                 0
 959             };
 960         let one_line_budget = context
 961             .config
 962             .max_width()
 963             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
 964             .unwrap_or(0);
 965         let force_newline_brace = (pat_expr_string.contains('\n')
 966             || pat_expr_string.len() > one_line_budget)
 967             && !last_line_extendable(&pat_expr_string);
 968
 969         // Try to format if-else on single line.
 970         if self.allow_single_line
 971             && context
 972                 .config
 973                 .width_heuristics()
 974                 .single_line_if_else_max_width > 0
 975         {
 976             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
 977
 978             if let Some(cond_str) = trial {
 979                 if cond_str.len()
 980                     <= context
 981                         .config
 982                         .width_heuristics()
 983                         .single_line_if_else_max_width
 984                 {
 985                     return Some((cond_str, 0));
 986                 }
 987             }
 988         }
 989
 990         let cond_span = if let Some(cond) = self.cond {
 991             cond.span
 992         } else {
 993             mk_sp(self.block.span.lo(), self.block.span.lo())
 994         };
 995
 996         // `for event in event`
 997         // Do not include label in the span.
 998         let lo = self.label.map_or(self.span.lo(), |label| label.span.hi());
 999         let between_kwd_cond = mk_sp(
1000             context
1001                 .codemap
1002                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
1003             self.pat.map_or(cond_span.lo(), |p| {
1004                 if self.matcher.is_empty() {
1005                     p.span.lo()
1006                 } else {
1007                     context.codemap.span_before(self.span, self.matcher.trim())
1008                 }
1009             }),
1010         );
1011
1012         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1013
1014         let after_cond_comment =
1015             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
1016
1017         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1018             ""
1019         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
1020             || force_newline_brace
1021         {
1022             alt_block_sep
1023         } else {
1024             " "
1025         };
1026
1027         let used_width = if pat_expr_string.contains('\n') {
1028             last_line_width(&pat_expr_string)
1029         } else {
1030             // 2 = spaces after keyword and condition.
1031             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1032         };
1033
1034         Some((
1035             format!(
1036                 "{}{}{}{}{}",
1037                 label_string,
1038                 self.keyword,
1039                 between_kwd_cond_comment.as_ref().map_or(
1040                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1041                         ""
1042                     } else {
1043                         " "
1044                     },
1045                     |s| &**s,
1046                 ),
1047                 pat_expr_string,
1048                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1049             ),
1050             used_width,
1051         ))
1052     }
1053 }
1054
1055 impl<'a> Rewrite for ControlFlow<'a> {
1056     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1057         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1058
1059         let alt_block_sep = String::from("\n") + &shape.indent.to_string(context.config);
1060         let (cond_str, used_width) = self.rewrite_cond(context, shape, &alt_block_sep)?;
1061         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1062         if used_width == 0 {
1063             return Some(cond_str);
1064         }
1065
1066         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1067         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1068         // we should avoid the single line case.
1069         let block_width = if self.else_block.is_some() || self.nested_if {
1070             min(1, block_width)
1071         } else {
1072             block_width
1073         };
1074         let block_shape = Shape {
1075             width: block_width,
1076             ..shape
1077         };
1078         let mut block_context = context.clone();
1079         block_context.is_if_else_block = self.else_block.is_some();
1080         let block_str =
1081             rewrite_block_with_visitor(&block_context, "", self.block, block_shape, true)?;
1082
1083         let mut result = format!("{}{}", cond_str, block_str);
1084
1085         if let Some(else_block) = self.else_block {
1086             let shape = Shape::indented(shape.indent, context.config);
1087             let mut last_in_chain = false;
1088             let rewrite = match else_block.node {
1089                 // If the else expression is another if-else expression, prevent it
1090                 // from being formatted on a single line.
1091                 // Note how we're passing the original shape, as the
1092                 // cost of "else" should not cascade.
1093                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1094                     ControlFlow::new_if(
1095                         cond,
1096                         Some(pat),
1097                         if_block,
1098                         next_else_block.as_ref().map(|e| &**e),
1099                         false,
1100                         true,
1101                         mk_sp(else_block.span.lo(), self.span.hi()),
1102                     ).rewrite(context, shape)
1103                 }
1104                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1105                     ControlFlow::new_if(
1106                         cond,
1107                         None,
1108                         if_block,
1109                         next_else_block.as_ref().map(|e| &**e),
1110                         false,
1111                         true,
1112                         mk_sp(else_block.span.lo(), self.span.hi()),
1113                     ).rewrite(context, shape)
1114                 }
1115                 _ => {
1116                     last_in_chain = true;
1117                     // When rewriting a block, the width is only used for single line
1118                     // blocks, passing 1 lets us avoid that.
1119                     let else_shape = Shape {
1120                         width: min(1, shape.width),
1121                         ..shape
1122                     };
1123                     format_expr(else_block, ExprType::Statement, context, else_shape)
1124                 }
1125             };
1126
1127             let between_kwd_else_block = mk_sp(
1128                 self.block.span.hi(),
1129                 context
1130                     .codemap
1131                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1132             );
1133             let between_kwd_else_block_comment =
1134                 extract_comment(between_kwd_else_block, context, shape);
1135
1136             let after_else = mk_sp(
1137                 context
1138                     .codemap
1139                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1140                 else_block.span.lo(),
1141             );
1142             let after_else_comment = extract_comment(after_else, context, shape);
1143
1144             let between_sep = match context.config.control_brace_style() {
1145                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1146                     &*alt_block_sep
1147                 }
1148                 ControlBraceStyle::AlwaysSameLine => " ",
1149             };
1150             let after_sep = match context.config.control_brace_style() {
1151                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1152                 _ => " ",
1153             };
1154
1155             result.push_str(&format!(
1156                 "{}else{}",
1157                 between_kwd_else_block_comment
1158                     .as_ref()
1159                     .map_or(between_sep, |s| &**s),
1160                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1161             ));
1162             result.push_str(&rewrite?);
1163         }
1164
1165         Some(result)
1166     }
1167 }
1168
1169 fn rewrite_label(label: Option<ast::SpannedIdent>) -> Cow<'static, str> {
1170     match label {
1171         Some(ident) => Cow::from(format!("{}: ", ident.node)),
1172         None => Cow::from(""),
1173     }
1174 }
1175
1176 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1177     match rewrite_missing_comment(span, shape, context) {
1178         Some(ref comment) if !comment.is_empty() => Some(format!(
1179             "\n{indent}{}\n{indent}",
1180             comment,
1181             indent = shape.indent.to_string(context.config)
1182         )),
1183         _ => None,
1184     }
1185 }
1186
1187 pub fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1188     let snippet = codemap.span_to_snippet(block.span).unwrap();
1189     contains_comment(&snippet)
1190 }
1191
1192 // Checks that a block contains no statements, an expression and no comments.
1193 // FIXME: incorrectly returns false when comment is contained completely within
1194 // the expression.
1195 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1196     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0])
1197         && !block_contains_comment(block, codemap))
1198 }
1199
1200 /// Checks whether a block contains at most one statement or expression, and no comments.
1201 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1202     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1203 }
1204
1205 /// Checks whether a block contains no statements, expressions, or comments.
1206 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1207     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1208 }
1209
1210 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1211     match stmt.node {
1212         ast::StmtKind::Expr(..) => true,
1213         _ => false,
1214     }
1215 }
1216
1217 pub fn is_unsafe_block(block: &ast::Block) -> bool {
1218     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1219         true
1220     } else {
1221         false
1222     }
1223 }
1224
1225 // A simple wrapper type against ast::Arm. Used inside write_list().
1226 struct ArmWrapper<'a> {
1227     pub arm: &'a ast::Arm,
1228     // True if the arm is the last one in match expression. Used to decide on whether we should add
1229     // trailing comma to the match arm when `config.trailing_comma() == Never`.
1230     pub is_last: bool,
1231 }
1232
1233 impl<'a> ArmWrapper<'a> {
1234     pub fn new(arm: &'a ast::Arm, is_last: bool) -> ArmWrapper<'a> {
1235         ArmWrapper { arm, is_last }
1236     }
1237 }
1238
1239 impl<'a> Rewrite for ArmWrapper<'a> {
1240     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1241         rewrite_match_arm(context, self.arm, shape, self.is_last)
1242     }
1243 }
1244
1245 fn rewrite_match(
1246     context: &RewriteContext,
1247     cond: &ast::Expr,
1248     arms: &[ast::Arm],
1249     shape: Shape,
1250     span: Span,
1251     attrs: &[ast::Attribute],
1252 ) -> Option<String> {
1253     // Do not take the rhs overhead from the upper expressions into account
1254     // when rewriting match condition.
1255     let cond_shape = Shape {
1256         width: context.budget(shape.used_width()),
1257         ..shape
1258     };
1259     // 6 = `match `
1260     let cond_shape = match context.config.indent_style() {
1261         IndentStyle::Visual => cond_shape.shrink_left(6)?,
1262         IndentStyle::Block => cond_shape.offset_left(6)?,
1263     };
1264     let cond_str = cond.rewrite(context, cond_shape)?;
1265     let alt_block_sep = String::from("\n") + &shape.indent.to_string(context.config);
1266     let block_sep = match context.config.control_brace_style() {
1267         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1268         _ if last_line_extendable(&cond_str) => " ",
1269         // 2 = ` {`
1270         _ if cond_str.contains('\n') || cond_str.len() + 2 > cond_shape.width => &alt_block_sep,
1271         _ => " ",
1272     };
1273
1274     let nested_indent_str = shape
1275         .indent
1276         .block_indent(context.config)
1277         .to_string(context.config);
1278     // Inner attributes.
1279     let inner_attrs = &inner_attributes(attrs);
1280     let inner_attrs_str = if inner_attrs.is_empty() {
1281         String::new()
1282     } else {
1283         inner_attrs
1284             .rewrite(context, shape)
1285             .map(|s| format!("{}{}\n", nested_indent_str, s))?
1286     };
1287
1288     let open_brace_pos = if inner_attrs.is_empty() {
1289         let hi = if arms.is_empty() {
1290             span.hi()
1291         } else {
1292             arms[0].span().lo()
1293         };
1294         context.codemap.span_after(mk_sp(cond.span.hi(), hi), "{")
1295     } else {
1296         inner_attrs[inner_attrs.len() - 1].span().hi()
1297     };
1298
1299     if arms.is_empty() {
1300         let snippet = context.snippet(mk_sp(open_brace_pos, span.hi() - BytePos(1)));
1301         if snippet.trim().is_empty() {
1302             Some(format!("match {} {{}}", cond_str))
1303         } else {
1304             // Empty match with comments or inner attributes? We are not going to bother, sorry ;)
1305             Some(context.snippet(span).to_owned())
1306         }
1307     } else {
1308         Some(format!(
1309             "match {}{}{{\n{}{}{}\n{}}}",
1310             cond_str,
1311             block_sep,
1312             inner_attrs_str,
1313             nested_indent_str,
1314             rewrite_match_arms(context, arms, shape, span, open_brace_pos)?,
1315             shape.indent.to_string(context.config),
1316         ))
1317     }
1318 }
1319
1320 fn arm_comma(config: &Config, body: &ast::Expr, is_last: bool) -> &'static str {
1321     if is_last && config.trailing_comma() == SeparatorTactic::Never {
1322         ""
1323     } else if config.match_block_trailing_comma() {
1324         ","
1325     } else if let ast::ExprKind::Block(ref block) = body.node {
1326         if let ast::BlockCheckMode::Default = block.rules {
1327             ""
1328         } else {
1329             ","
1330         }
1331     } else {
1332         ","
1333     }
1334 }
1335
1336 fn rewrite_match_arms(
1337     context: &RewriteContext,
1338     arms: &[ast::Arm],
1339     shape: Shape,
1340     span: Span,
1341     open_brace_pos: BytePos,
1342 ) -> Option<String> {
1343     let arm_shape = shape
1344         .block_indent(context.config.tab_spaces())
1345         .with_max_width(context.config);
1346
1347     let arm_len = arms.len();
1348     let is_last_iter = repeat(false)
1349         .take(arm_len.checked_sub(1).unwrap_or(0))
1350         .chain(repeat(true));
1351     let items = itemize_list(
1352         context.codemap,
1353         arms.iter()
1354             .zip(is_last_iter)
1355             .map(|(arm, is_last)| ArmWrapper::new(arm, is_last)),
1356         "}",
1357         "|",
1358         |arm| arm.arm.span().lo(),
1359         |arm| arm.arm.span().hi(),
1360         |arm| arm.rewrite(context, arm_shape),
1361         open_brace_pos,
1362         span.hi(),
1363         false,
1364     );
1365     let arms_vec: Vec<_> = items.collect();
1366     let fmt = ListFormatting {
1367         tactic: DefinitiveListTactic::Vertical,
1368         // We will add/remove commas inside `arm.rewrite()`, and hence no separator here.
1369         separator: "",
1370         trailing_separator: SeparatorTactic::Never,
1371         separator_place: SeparatorPlace::Back,
1372         shape: arm_shape,
1373         ends_with_newline: true,
1374         preserve_newline: true,
1375         config: context.config,
1376     };
1377
1378     write_list(&arms_vec, &fmt)
1379 }
1380
1381 fn rewrite_match_arm(
1382     context: &RewriteContext,
1383     arm: &ast::Arm,
1384     shape: Shape,
1385     is_last: bool,
1386 ) -> Option<String> {
1387     let (missing_span, attrs_str) = if !arm.attrs.is_empty() {
1388         if contains_skip(&arm.attrs) {
1389             let (_, body) = flatten_arm_body(context, &arm.body);
1390             // `arm.span()` does not include trailing comma, add it manually.
1391             return Some(format!(
1392                 "{}{}",
1393                 context.snippet(arm.span()),
1394                 arm_comma(context.config, body, is_last),
1395             ));
1396         }
1397         let missing_span = mk_sp(
1398             arm.attrs[arm.attrs.len() - 1].span.hi(),
1399             arm.pats[0].span.lo(),
1400         );
1401         (missing_span, arm.attrs.rewrite(context, shape)?)
1402     } else {
1403         (mk_sp(arm.span().lo(), arm.span().lo()), String::new())
1404     };
1405     let pats_str =
1406         rewrite_match_pattern(context, &arm.pats, &arm.guard, shape).and_then(|pats_str| {
1407             combine_strs_with_missing_comments(
1408                 context,
1409                 &attrs_str,
1410                 &pats_str,
1411                 missing_span,
1412                 shape,
1413                 false,
1414             )
1415         })?;
1416     rewrite_match_body(
1417         context,
1418         &arm.body,
1419         &pats_str,
1420         shape,
1421         arm.guard.is_some(),
1422         is_last,
1423     )
1424 }
1425
1426 /// Returns true if the given pattern is short. A short pattern is defined by the following grammer:
1427 ///
1428 /// [small, ntp]:
1429 ///     - single token
1430 ///     - `&[single-line, ntp]`
1431 ///
1432 /// [small]:
1433 ///     - `[small, ntp]`
1434 ///     - unary tuple constructor `([small, ntp])`
1435 ///     - `&[small]`
1436 fn is_short_pattern(pat: &ast::Pat, pat_str: &str) -> bool {
1437     // We also require that the pattern is reasonably 'small' with its literal width.
1438     pat_str.len() <= 20 && !pat_str.contains('\n') && is_short_pattern_inner(pat)
1439 }
1440
1441 fn is_short_pattern_inner(pat: &ast::Pat) -> bool {
1442     match pat.node {
1443         ast::PatKind::Wild | ast::PatKind::Lit(_) => true,
1444         ast::PatKind::Ident(_, _, ref pat) => pat.is_none(),
1445         ast::PatKind::Struct(..)
1446         | ast::PatKind::Mac(..)
1447         | ast::PatKind::Slice(..)
1448         | ast::PatKind::Path(..)
1449         | ast::PatKind::Range(..) => false,
1450         ast::PatKind::Tuple(ref subpats, _) => subpats.len() <= 1,
1451         ast::PatKind::TupleStruct(ref path, ref subpats, _) => {
1452             path.segments.len() <= 1 && subpats.len() <= 1
1453         }
1454         ast::PatKind::Box(ref p) | ast::PatKind::Ref(ref p, _) => is_short_pattern_inner(&*p),
1455     }
1456 }
1457
1458 fn rewrite_match_pattern(
1459     context: &RewriteContext,
1460     pats: &[ptr::P<ast::Pat>],
1461     guard: &Option<ptr::P<ast::Expr>>,
1462     shape: Shape,
1463 ) -> Option<String> {
1464     // Patterns
1465     // 5 = ` => {`
1466     let pat_shape = shape.sub_width(5)?;
1467
1468     let pat_strs = pats.iter()
1469         .map(|p| p.rewrite(context, pat_shape))
1470         .collect::<Option<Vec<_>>>()?;
1471
1472     let use_mixed_layout = pats.iter()
1473         .zip(pat_strs.iter())
1474         .all(|(pat, pat_str)| is_short_pattern(pat, pat_str));
1475     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1476     let tactic = if use_mixed_layout {
1477         DefinitiveListTactic::Mixed
1478     } else {
1479         definitive_tactic(
1480             &items,
1481             ListTactic::HorizontalVertical,
1482             Separator::VerticalBar,
1483             pat_shape.width,
1484         )
1485     };
1486     let fmt = ListFormatting {
1487         tactic: tactic,
1488         separator: " |",
1489         trailing_separator: SeparatorTactic::Never,
1490         separator_place: context.config.binop_separator(),
1491         shape: pat_shape,
1492         ends_with_newline: false,
1493         preserve_newline: false,
1494         config: context.config,
1495     };
1496     let pats_str = write_list(&items, &fmt)?;
1497
1498     // Guard
1499     let guard_str = rewrite_guard(context, guard, shape, trimmed_last_line_width(&pats_str))?;
1500
1501     Some(format!("{}{}", pats_str, guard_str))
1502 }
1503
1504 // (extend, body)
1505 // @extend: true if the arm body can be put next to `=>`
1506 // @body: flattened body, if the body is block with a single expression
1507 fn flatten_arm_body<'a>(context: &'a RewriteContext, body: &'a ast::Expr) -> (bool, &'a ast::Expr) {
1508     match body.node {
1509         ast::ExprKind::Block(ref block)
1510             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1511         {
1512             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1513                 (
1514                     !context.config.force_multiline_blocks() && can_extend_match_arm_body(expr),
1515                     &*expr,
1516                 )
1517             } else {
1518                 (false, &*body)
1519             }
1520         }
1521         _ => (
1522             !context.config.force_multiline_blocks() && body.can_be_overflowed(context, 1),
1523             &*body,
1524         ),
1525     }
1526 }
1527
1528 fn rewrite_match_body(
1529     context: &RewriteContext,
1530     body: &ptr::P<ast::Expr>,
1531     pats_str: &str,
1532     shape: Shape,
1533     has_guard: bool,
1534     is_last: bool,
1535 ) -> Option<String> {
1536     let (extend, body) = flatten_arm_body(context, body);
1537     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1538         (true, is_empty_block(block, context.codemap))
1539     } else {
1540         (false, false)
1541     };
1542
1543     let comma = arm_comma(context.config, body, is_last);
1544     let alt_block_sep = String::from("\n") + &shape.indent.to_string(context.config);
1545     let alt_block_sep = alt_block_sep.as_str();
1546
1547     let combine_orig_body = |body_str: &str| {
1548         let block_sep = match context.config.control_brace_style() {
1549             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1550             _ => " ",
1551         };
1552
1553         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1554     };
1555
1556     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1557     let next_line_indent = if !is_block || is_empty_block {
1558         shape.indent.block_indent(context.config)
1559     } else {
1560         shape.indent
1561     };
1562     let combine_next_line_body = |body_str: &str| {
1563         if is_block {
1564             return Some(format!(
1565                 "{} =>\n{}{}",
1566                 pats_str,
1567                 next_line_indent.to_string(context.config),
1568                 body_str
1569             ));
1570         }
1571
1572         let indent_str = shape.indent.to_string(context.config);
1573         let nested_indent_str = next_line_indent.to_string(context.config);
1574         let (body_prefix, body_suffix) = if context.config.match_arm_blocks() {
1575             let comma = if context.config.match_block_trailing_comma() {
1576                 ","
1577             } else {
1578                 ""
1579             };
1580             ("{", format!("\n{}}}{}", indent_str, comma))
1581         } else {
1582             ("", String::from(","))
1583         };
1584
1585         let block_sep = match context.config.control_brace_style() {
1586             ControlBraceStyle::AlwaysNextLine => format!("{}{}\n", alt_block_sep, body_prefix),
1587             _ if body_prefix.is_empty() => "\n".to_owned(),
1588             _ if forbid_same_line => format!("{}{}\n", alt_block_sep, body_prefix),
1589             _ => format!(" {}\n", body_prefix),
1590         } + &nested_indent_str;
1591
1592         Some(format!(
1593             "{} =>{}{}{}",
1594             pats_str, block_sep, body_str, body_suffix
1595         ))
1596     };
1597
1598     // Let's try and get the arm body on the same line as the condition.
1599     // 4 = ` => `.len()
1600     let orig_body_shape = shape
1601         .offset_left(extra_offset(pats_str, shape) + 4)
1602         .and_then(|shape| shape.sub_width(comma.len()));
1603     let orig_body = if let Some(body_shape) = orig_body_shape {
1604         let rewrite = nop_block_collapse(
1605             format_expr(body, ExprType::Statement, context, body_shape),
1606             body_shape.width,
1607         );
1608
1609         match rewrite {
1610             Some(ref body_str)
1611                 if !forbid_same_line
1612                     && (is_block
1613                         || (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1614             {
1615                 return combine_orig_body(body_str);
1616             }
1617             _ => rewrite,
1618         }
1619     } else {
1620         None
1621     };
1622     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1623
1624     // Try putting body on the next line and see if it looks better.
1625     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1626     let next_line_body = nop_block_collapse(
1627         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1628         next_line_body_shape.width,
1629     );
1630     match (orig_body, next_line_body) {
1631         (Some(ref orig_str), Some(ref next_line_str))
1632             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1633         {
1634             combine_next_line_body(next_line_str)
1635         }
1636         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1637             combine_orig_body(orig_str)
1638         }
1639         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1640             combine_next_line_body(next_line_str)
1641         }
1642         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1643         (None, None) => None,
1644         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1645     }
1646 }
1647
1648 // The `if ...` guard on a match arm.
1649 fn rewrite_guard(
1650     context: &RewriteContext,
1651     guard: &Option<ptr::P<ast::Expr>>,
1652     shape: Shape,
1653     // The amount of space used up on this line for the pattern in
1654     // the arm (excludes offset).
1655     pattern_width: usize,
1656 ) -> Option<String> {
1657     if let Some(ref guard) = *guard {
1658         // First try to fit the guard string on the same line as the pattern.
1659         // 4 = ` if `, 5 = ` => {`
1660         let cond_shape = shape
1661             .offset_left(pattern_width + 4)
1662             .and_then(|s| s.sub_width(5));
1663         if let Some(cond_shape) = cond_shape {
1664             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1665                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1666                     return Some(format!(" if {}", cond_str));
1667                 }
1668             }
1669         }
1670
1671         // Not enough space to put the guard after the pattern, try a newline.
1672         // 3 = `if `, 5 = ` => {`
1673         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1674             .offset_left(3)
1675             .and_then(|s| s.sub_width(5));
1676         if let Some(cond_shape) = cond_shape {
1677             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1678                 return Some(format!(
1679                     "\n{}if {}",
1680                     cond_shape.indent.to_string(context.config),
1681                     cond_str
1682                 ));
1683             }
1684         }
1685
1686         None
1687     } else {
1688         Some(String::new())
1689     }
1690 }
1691
1692 fn rewrite_pat_expr(
1693     context: &RewriteContext,
1694     pat: Option<&ast::Pat>,
1695     expr: &ast::Expr,
1696     matcher: &str,
1697     // Connecting piece between pattern and expression,
1698     // *without* trailing space.
1699     connector: &str,
1700     keyword: &str,
1701     shape: Shape,
1702     offset: usize,
1703 ) -> Option<String> {
1704     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1705     let cond_shape = shape.offset_left(offset)?;
1706     if let Some(pat) = pat {
1707         let matcher = if matcher.is_empty() {
1708             matcher.to_owned()
1709         } else {
1710             format!("{} ", matcher)
1711         };
1712         let pat_shape = cond_shape
1713             .offset_left(matcher.len())?
1714             .sub_width(connector.len())?;
1715         let pat_string = pat.rewrite(context, pat_shape)?;
1716         let result = format!("{}{}{}", matcher, pat_string, connector);
1717         return rewrite_assign_rhs(context, result, expr, cond_shape);
1718     }
1719
1720     let expr_rw = expr.rewrite(context, cond_shape);
1721     // The expression may (partially) fit on the current line.
1722     // We do not allow splitting between `if` and condition.
1723     if keyword == "if" || expr_rw.is_some() {
1724         return expr_rw;
1725     }
1726
1727     // The expression won't fit on the current line, jump to next.
1728     let nested_shape = shape
1729         .block_indent(context.config.tab_spaces())
1730         .with_max_width(context.config);
1731     let nested_indent_str = nested_shape.indent.to_string(context.config);
1732     expr.rewrite(context, nested_shape)
1733         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1734 }
1735
1736 fn can_extend_match_arm_body(body: &ast::Expr) -> bool {
1737     match body.node {
1738         // We do not allow `if` to stay on the same line, since we could easily mistake
1739         // `pat => if cond { ... }` and `pat if cond => { ... }`.
1740         ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => false,
1741         ast::ExprKind::ForLoop(..)
1742         | ast::ExprKind::Loop(..)
1743         | ast::ExprKind::While(..)
1744         | ast::ExprKind::WhileLet(..)
1745         | ast::ExprKind::Match(..)
1746         | ast::ExprKind::Block(..)
1747         | ast::ExprKind::Closure(..)
1748         | ast::ExprKind::Array(..)
1749         | ast::ExprKind::Call(..)
1750         | ast::ExprKind::MethodCall(..)
1751         | ast::ExprKind::Mac(..)
1752         | ast::ExprKind::Struct(..)
1753         | ast::ExprKind::Tup(..) => true,
1754         ast::ExprKind::AddrOf(_, ref expr)
1755         | ast::ExprKind::Box(ref expr)
1756         | ast::ExprKind::Try(ref expr)
1757         | ast::ExprKind::Unary(_, ref expr)
1758         | ast::ExprKind::Cast(ref expr, _) => can_extend_match_arm_body(expr),
1759         _ => false,
1760     }
1761 }
1762
1763 pub fn rewrite_literal(context: &RewriteContext, l: &ast::Lit, shape: Shape) -> Option<String> {
1764     match l.node {
1765         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1766         _ => wrap_str(
1767             context.snippet(l.span).to_owned(),
1768             context.config.max_width(),
1769             shape,
1770         ),
1771     }
1772 }
1773
1774 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1775     let string_lit = context.snippet(span);
1776
1777     if !context.config.format_strings() {
1778         if string_lit
1779             .lines()
1780             .rev()
1781             .skip(1)
1782             .all(|line| line.ends_with('\\'))
1783         {
1784             let new_indent = shape.visual_indent(1).indent;
1785             let indented_string_lit = String::from(
1786                 string_lit
1787                     .lines()
1788                     .map(|line| {
1789                         format!(
1790                             "{}{}",
1791                             new_indent.to_string(context.config),
1792                             line.trim_left()
1793                         )
1794                     })
1795                     .collect::<Vec<_>>()
1796                     .join("\n")
1797                     .trim_left(),
1798             );
1799             return wrap_str(indented_string_lit, context.config.max_width(), shape);
1800         } else {
1801             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1802         }
1803     }
1804
1805     // Remove the quote characters.
1806     let str_lit = &string_lit[1..string_lit.len() - 1];
1807
1808     rewrite_string(
1809         str_lit,
1810         &StringFormat::new(shape.visual_indent(0), context.config),
1811         None,
1812     )
1813 }
1814
1815 const FORMAT_LIKE_WHITELIST: &[&str] = &[
1816     // From the Rust Standard Library.
1817     "eprint!",
1818     "eprintln!",
1819     "format!",
1820     "format_args!",
1821     "print!",
1822     "println!",
1823     "panic!",
1824     "unreachable!",
1825     // From the `log` crate.
1826     "debug!",
1827     "error!",
1828     "info!",
1829     "warn!",
1830 ];
1831
1832 const WRITE_LIKE_WHITELIST: &[&str] = &["assert!", "write!", "writeln!"];
1833
1834 pub fn rewrite_call(
1835     context: &RewriteContext,
1836     callee: &str,
1837     args: &[ptr::P<ast::Expr>],
1838     span: Span,
1839     shape: Shape,
1840 ) -> Option<String> {
1841     let force_trailing_comma = if context.inside_macro {
1842         span_ends_with_comma(context, span)
1843     } else {
1844         false
1845     };
1846     rewrite_call_inner(
1847         context,
1848         callee,
1849         &ptr_vec_to_ref_vec(args),
1850         span,
1851         shape,
1852         context.config.width_heuristics().fn_call_width,
1853         force_trailing_comma,
1854     )
1855 }
1856
1857 pub fn rewrite_call_inner<'a, T>(
1858     context: &RewriteContext,
1859     callee_str: &str,
1860     args: &[&T],
1861     span: Span,
1862     shape: Shape,
1863     args_max_width: usize,
1864     force_trailing_comma: bool,
1865 ) -> Option<String>
1866 where
1867     T: Rewrite + Spanned + ToExpr + 'a,
1868 {
1869     // 2 = `( `, 1 = `(`
1870     let paren_overhead = if context.config.spaces_within_parens_and_brackets() {
1871         2
1872     } else {
1873         1
1874     };
1875     let used_width = extra_offset(callee_str, shape);
1876     let one_line_width = shape.width.checked_sub(used_width + 2 * paren_overhead)?;
1877
1878     // 1 = "(" or ")"
1879     let one_line_shape = shape
1880         .offset_left(last_line_width(callee_str) + 1)?
1881         .sub_width(1)?;
1882     let nested_shape = shape_from_indent_style(
1883         context,
1884         shape,
1885         used_width + 2 * paren_overhead,
1886         used_width + paren_overhead,
1887     )?;
1888
1889     let span_lo = context.codemap.span_after(span, "(");
1890     let args_span = mk_sp(span_lo, span.hi());
1891
1892     let (extendable, list_str) = rewrite_call_args(
1893         context,
1894         args,
1895         args_span,
1896         one_line_shape,
1897         nested_shape,
1898         one_line_width,
1899         args_max_width,
1900         force_trailing_comma,
1901         callee_str,
1902     )?;
1903
1904     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
1905         let mut new_context = context.clone();
1906         new_context.use_block = true;
1907         return rewrite_call_inner(
1908             &new_context,
1909             callee_str,
1910             args,
1911             span,
1912             shape,
1913             args_max_width,
1914             force_trailing_comma,
1915         );
1916     }
1917
1918     let args_shape = shape.sub_width(last_line_width(callee_str))?;
1919     Some(format!(
1920         "{}{}",
1921         callee_str,
1922         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
1923     ))
1924 }
1925
1926 fn need_block_indent(s: &str, shape: Shape) -> bool {
1927     s.lines().skip(1).any(|s| {
1928         s.find(|c| !char::is_whitespace(c))
1929             .map_or(false, |w| w + 1 < shape.indent.width())
1930     })
1931 }
1932
1933 fn rewrite_call_args<'a, T>(
1934     context: &RewriteContext,
1935     args: &[&T],
1936     span: Span,
1937     one_line_shape: Shape,
1938     nested_shape: Shape,
1939     one_line_width: usize,
1940     args_max_width: usize,
1941     force_trailing_comma: bool,
1942     callee_str: &str,
1943 ) -> Option<(bool, String)>
1944 where
1945     T: Rewrite + Spanned + ToExpr + 'a,
1946 {
1947     let items = itemize_list(
1948         context.codemap,
1949         args.iter(),
1950         ")",
1951         ",",
1952         |item| item.span().lo(),
1953         |item| item.span().hi(),
1954         |item| item.rewrite(context, nested_shape),
1955         span.lo(),
1956         span.hi(),
1957         true,
1958     );
1959     let mut item_vec: Vec<_> = items.collect();
1960
1961     // Try letting the last argument overflow to the next line with block
1962     // indentation. If its first line fits on one line with the other arguments,
1963     // we format the function arguments horizontally.
1964     let tactic = try_overflow_last_arg(
1965         context,
1966         &mut item_vec,
1967         &args[..],
1968         one_line_shape,
1969         nested_shape,
1970         one_line_width,
1971         args_max_width,
1972         callee_str,
1973     );
1974
1975     let fmt = ListFormatting {
1976         tactic: tactic,
1977         separator: ",",
1978         trailing_separator: if force_trailing_comma {
1979             SeparatorTactic::Always
1980         } else if context.inside_macro || !context.use_block_indent() {
1981             SeparatorTactic::Never
1982         } else {
1983             context.config.trailing_comma()
1984         },
1985         separator_place: SeparatorPlace::Back,
1986         shape: nested_shape,
1987         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
1988         preserve_newline: false,
1989         config: context.config,
1990     };
1991
1992     write_list(&item_vec, &fmt)
1993         .map(|args_str| (tactic == DefinitiveListTactic::Horizontal, args_str))
1994 }
1995
1996 fn try_overflow_last_arg<'a, T>(
1997     context: &RewriteContext,
1998     item_vec: &mut Vec<ListItem>,
1999     args: &[&T],
2000     one_line_shape: Shape,
2001     nested_shape: Shape,
2002     one_line_width: usize,
2003     args_max_width: usize,
2004     callee_str: &str,
2005 ) -> DefinitiveListTactic
2006 where
2007     T: Rewrite + Spanned + ToExpr + 'a,
2008 {
2009     // 1 = "("
2010     let combine_arg_with_callee =
2011         callee_str.len() + 1 <= context.config.tab_spaces() && args.len() == 1;
2012     let overflow_last = combine_arg_with_callee || can_be_overflowed(context, args);
2013
2014     // Replace the last item with its first line to see if it fits with
2015     // first arguments.
2016     let placeholder = if overflow_last {
2017         let mut context = context.clone();
2018         if !combine_arg_with_callee {
2019             if let Some(expr) = args[args.len() - 1].to_expr() {
2020                 if let ast::ExprKind::MethodCall(..) = expr.node {
2021                     context.force_one_line_chain = true;
2022                 }
2023             }
2024         }
2025         last_arg_shape(args, item_vec, one_line_shape, args_max_width).and_then(|arg_shape| {
2026             rewrite_last_arg_with_overflow(&context, args, &mut item_vec[args.len() - 1], arg_shape)
2027         })
2028     } else {
2029         None
2030     };
2031
2032     let mut tactic = definitive_tactic(
2033         &*item_vec,
2034         ListTactic::LimitedHorizontalVertical(args_max_width),
2035         Separator::Comma,
2036         one_line_width,
2037     );
2038
2039     // Replace the stub with the full overflowing last argument if the rewrite
2040     // succeeded and its first line fits with the other arguments.
2041     match (overflow_last, tactic, placeholder) {
2042         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2043             item_vec[args.len() - 1].item = placeholder;
2044         }
2045         _ if args.len() >= 1 => {
2046             item_vec[args.len() - 1].item = args.last()
2047                 .and_then(|last_arg| last_arg.rewrite(context, nested_shape));
2048
2049             let default_tactic = || {
2050                 definitive_tactic(
2051                     &*item_vec,
2052                     ListTactic::LimitedHorizontalVertical(args_max_width),
2053                     Separator::Comma,
2054                     one_line_width,
2055                 )
2056             };
2057
2058             // Use horizontal layout for a function with a single argument as long as
2059             // everything fits in a single line.
2060             if args.len() == 1
2061                 && args_max_width != 0 // Vertical layout is forced.
2062                 && !item_vec[0].has_comment()
2063                 && !item_vec[0].inner_as_ref().contains('\n')
2064                 && ::lists::total_item_width(&item_vec[0]) <= one_line_width
2065             {
2066                 tactic = DefinitiveListTactic::Horizontal;
2067             } else {
2068                 tactic = default_tactic();
2069
2070                 // For special-case macros, we may want to use different tactics.
2071                 let maybe_args_offset = maybe_get_args_offset(callee_str, args);
2072
2073                 if tactic == DefinitiveListTactic::Vertical && maybe_args_offset.is_some() {
2074                     let args_offset = maybe_args_offset.unwrap();
2075                     let args_tactic = definitive_tactic(
2076                         &item_vec[args_offset..],
2077                         ListTactic::HorizontalVertical,
2078                         Separator::Comma,
2079                         nested_shape.width,
2080                     );
2081
2082                     // Every argument is simple and fits on a single line.
2083                     if args_tactic == DefinitiveListTactic::Horizontal {
2084                         tactic = if args_offset == 1 {
2085                             DefinitiveListTactic::FormatCall
2086                         } else {
2087                             DefinitiveListTactic::WriteCall
2088                         };
2089                     }
2090                 }
2091             }
2092         }
2093         _ => (),
2094     }
2095
2096     tactic
2097 }
2098
2099 fn is_simple_arg(expr: &ast::Expr) -> bool {
2100     match expr.node {
2101         ast::ExprKind::Lit(..) => true,
2102         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
2103         ast::ExprKind::AddrOf(_, ref expr)
2104         | ast::ExprKind::Box(ref expr)
2105         | ast::ExprKind::Cast(ref expr, _)
2106         | ast::ExprKind::Field(ref expr, _)
2107         | ast::ExprKind::Try(ref expr)
2108         | ast::ExprKind::TupField(ref expr, _)
2109         | ast::ExprKind::Unary(_, ref expr) => is_simple_arg(expr),
2110         ast::ExprKind::Index(ref lhs, ref rhs) | ast::ExprKind::Repeat(ref lhs, ref rhs) => {
2111             is_simple_arg(lhs) && is_simple_arg(rhs)
2112         }
2113         _ => false,
2114     }
2115 }
2116
2117 fn is_every_args_simple<T: ToExpr>(lists: &[&T]) -> bool {
2118     lists
2119         .iter()
2120         .all(|arg| arg.to_expr().map_or(false, is_simple_arg))
2121 }
2122
2123 /// In case special-case style is required, returns an offset from which we start horizontal layout.
2124 fn maybe_get_args_offset<T: ToExpr>(callee_str: &str, args: &[&T]) -> Option<usize> {
2125     if FORMAT_LIKE_WHITELIST.iter().any(|s| *s == callee_str) && args.len() >= 1
2126         && is_every_args_simple(args)
2127     {
2128         Some(1)
2129     } else if WRITE_LIKE_WHITELIST.iter().any(|s| *s == callee_str) && args.len() >= 2
2130         && is_every_args_simple(args)
2131     {
2132         Some(2)
2133     } else {
2134         None
2135     }
2136 }
2137
2138 /// Returns a shape for the last argument which is going to be overflowed.
2139 fn last_arg_shape<T>(
2140     lists: &[&T],
2141     items: &[ListItem],
2142     shape: Shape,
2143     args_max_width: usize,
2144 ) -> Option<Shape>
2145 where
2146     T: Rewrite + Spanned + ToExpr,
2147 {
2148     let is_nested_call = lists
2149         .iter()
2150         .next()
2151         .and_then(|item| item.to_expr())
2152         .map_or(false, is_nested_call);
2153     if items.len() == 1 && !is_nested_call {
2154         return Some(shape);
2155     }
2156     let offset = items.iter().rev().skip(1).fold(0, |acc, i| {
2157         // 2 = ", "
2158         acc + 2 + i.inner_as_ref().len()
2159     });
2160     Shape {
2161         width: min(args_max_width, shape.width),
2162         ..shape
2163     }.offset_left(offset)
2164 }
2165
2166 fn rewrite_last_arg_with_overflow<'a, T>(
2167     context: &RewriteContext,
2168     args: &[&T],
2169     last_item: &mut ListItem,
2170     shape: Shape,
2171 ) -> Option<String>
2172 where
2173     T: Rewrite + Spanned + ToExpr + 'a,
2174 {
2175     let last_arg = args[args.len() - 1];
2176     let rewrite = if let Some(expr) = last_arg.to_expr() {
2177         match expr.node {
2178             // When overflowing the closure which consists of a single control flow expression,
2179             // force to use block if its condition uses multi line.
2180             ast::ExprKind::Closure(..) => {
2181                 // If the argument consists of multiple closures, we do not overflow
2182                 // the last closure.
2183                 if closures::args_have_many_closure(args) {
2184                     None
2185                 } else {
2186                     closures::rewrite_last_closure(context, expr, shape)
2187                 }
2188             }
2189             _ => expr.rewrite(context, shape),
2190         }
2191     } else {
2192         last_arg.rewrite(context, shape)
2193     };
2194
2195     if let Some(rewrite) = rewrite {
2196         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2197         last_item.item = rewrite_first_line;
2198         Some(rewrite)
2199     } else {
2200         None
2201     }
2202 }
2203
2204 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2205 where
2206     T: Rewrite + Spanned + ToExpr + 'a,
2207 {
2208     args.last()
2209         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2210 }
2211
2212 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2213     match expr.node {
2214         ast::ExprKind::Match(..) => {
2215             (context.use_block_indent() && args_len == 1)
2216                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
2217         }
2218         ast::ExprKind::If(..)
2219         | ast::ExprKind::IfLet(..)
2220         | ast::ExprKind::ForLoop(..)
2221         | ast::ExprKind::Loop(..)
2222         | ast::ExprKind::While(..)
2223         | ast::ExprKind::WhileLet(..) => {
2224             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2225         }
2226         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2227             context.use_block_indent()
2228                 || context.config.indent_style() == IndentStyle::Visual && args_len > 1
2229         }
2230         ast::ExprKind::Array(..)
2231         | ast::ExprKind::Call(..)
2232         | ast::ExprKind::Mac(..)
2233         | ast::ExprKind::MethodCall(..)
2234         | ast::ExprKind::Struct(..)
2235         | ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2236         ast::ExprKind::AddrOf(_, ref expr)
2237         | ast::ExprKind::Box(ref expr)
2238         | ast::ExprKind::Try(ref expr)
2239         | ast::ExprKind::Unary(_, ref expr)
2240         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2241         _ => false,
2242     }
2243 }
2244
2245 fn is_nested_call(expr: &ast::Expr) -> bool {
2246     match expr.node {
2247         ast::ExprKind::Call(..) | ast::ExprKind::Mac(..) => true,
2248         ast::ExprKind::AddrOf(_, ref expr)
2249         | ast::ExprKind::Box(ref expr)
2250         | ast::ExprKind::Try(ref expr)
2251         | ast::ExprKind::Unary(_, ref expr)
2252         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
2253         _ => false,
2254     }
2255 }
2256
2257 pub fn wrap_args_with_parens(
2258     context: &RewriteContext,
2259     args_str: &str,
2260     is_extendable: bool,
2261     shape: Shape,
2262     nested_shape: Shape,
2263 ) -> String {
2264     if !context.use_block_indent()
2265         || (context.inside_macro && !args_str.contains('\n')
2266             && args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2267     {
2268         if context.config.spaces_within_parens_and_brackets() && !args_str.is_empty() {
2269             format!("( {} )", args_str)
2270         } else {
2271             format!("({})", args_str)
2272         }
2273     } else {
2274         format!(
2275             "(\n{}{}\n{})",
2276             nested_shape.indent.to_string(context.config),
2277             args_str,
2278             shape.block().indent.to_string(context.config)
2279         )
2280     }
2281 }
2282
2283 /// Return true if a function call or a method call represented by the given span ends with a
2284 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
2285 /// comma from macro can potentially break the code.
2286 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2287     let mut encountered_closing_paren = false;
2288     for c in context.snippet(span).chars().rev() {
2289         match c {
2290             ',' => return true,
2291             ')' => if encountered_closing_paren {
2292                 return false;
2293             } else {
2294                 encountered_closing_paren = true;
2295             },
2296             _ if c.is_whitespace() => continue,
2297             _ => return false,
2298         }
2299     }
2300     false
2301 }
2302
2303 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2304     debug!("rewrite_paren, shape: {:?}", shape);
2305     let total_paren_overhead = paren_overhead(context);
2306     let paren_overhead = total_paren_overhead / 2;
2307     let sub_shape = shape
2308         .offset_left(paren_overhead)
2309         .and_then(|s| s.sub_width(paren_overhead))?;
2310
2311     let paren_wrapper = |s: &str| {
2312         if context.config.spaces_within_parens_and_brackets() && !s.is_empty() {
2313             format!("( {} )", s)
2314         } else {
2315             format!("({})", s)
2316         }
2317     };
2318
2319     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
2320     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2321
2322     if subexpr_str.contains('\n')
2323         || first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2324     {
2325         Some(paren_wrapper(&subexpr_str))
2326     } else {
2327         None
2328     }
2329 }
2330
2331 fn rewrite_index(
2332     expr: &ast::Expr,
2333     index: &ast::Expr,
2334     context: &RewriteContext,
2335     shape: Shape,
2336 ) -> Option<String> {
2337     let expr_str = expr.rewrite(context, shape)?;
2338
2339     let (lbr, rbr) = if context.config.spaces_within_parens_and_brackets() {
2340         ("[ ", " ]")
2341     } else {
2342         ("[", "]")
2343     };
2344
2345     let offset = last_line_width(&expr_str) + lbr.len();
2346     let rhs_overhead = shape.rhs_overhead(context.config);
2347     let index_shape = if expr_str.contains('\n') {
2348         Shape::legacy(context.config.max_width(), shape.indent)
2349             .offset_left(offset)
2350             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2351     } else {
2352         shape.visual_indent(offset).sub_width(offset + rbr.len())
2353     };
2354     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2355
2356     // Return if index fits in a single line.
2357     match orig_index_rw {
2358         Some(ref index_str) if !index_str.contains('\n') => {
2359             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2360         }
2361         _ => (),
2362     }
2363
2364     // Try putting index on the next line and see if it fits in a single line.
2365     let indent = shape.indent.block_indent(context.config);
2366     let index_shape = Shape::indented(indent, context.config).offset_left(lbr.len())?;
2367     let index_shape = index_shape.sub_width(rbr.len() + rhs_overhead)?;
2368     let new_index_rw = index.rewrite(context, index_shape);
2369     match (orig_index_rw, new_index_rw) {
2370         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2371             "{}\n{}{}{}{}",
2372             expr_str,
2373             indent.to_string(context.config),
2374             lbr,
2375             new_index_str,
2376             rbr
2377         )),
2378         (None, Some(ref new_index_str)) => Some(format!(
2379             "{}\n{}{}{}{}",
2380             expr_str,
2381             indent.to_string(context.config),
2382             lbr,
2383             new_index_str,
2384             rbr
2385         )),
2386         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2387         _ => None,
2388     }
2389 }
2390
2391 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2392     if base.is_some() {
2393         return false;
2394     }
2395
2396     fields.iter().all(|field| !field.is_shorthand)
2397 }
2398
2399 fn rewrite_struct_lit<'a>(
2400     context: &RewriteContext,
2401     path: &ast::Path,
2402     fields: &'a [ast::Field],
2403     base: Option<&'a ast::Expr>,
2404     span: Span,
2405     shape: Shape,
2406 ) -> Option<String> {
2407     debug!("rewrite_struct_lit: shape {:?}", shape);
2408
2409     enum StructLitField<'a> {
2410         Regular(&'a ast::Field),
2411         Base(&'a ast::Expr),
2412     }
2413
2414     // 2 = " {".len()
2415     let path_shape = shape.sub_width(2)?;
2416     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
2417
2418     if fields.is_empty() && base.is_none() {
2419         return Some(format!("{} {{}}", path_str));
2420     }
2421
2422     // Foo { a: Foo } - indent is +3, width is -5.
2423     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
2424
2425     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2426     let body_lo = context.codemap.span_after(span, "{");
2427     let fields_str = if struct_lit_can_be_aligned(fields, &base)
2428         && context.config.struct_field_align_threshold() > 0
2429     {
2430         rewrite_with_alignment(
2431             fields,
2432             context,
2433             shape,
2434             mk_sp(body_lo, span.hi()),
2435             one_line_width,
2436         )?
2437     } else {
2438         let field_iter = fields
2439             .into_iter()
2440             .map(StructLitField::Regular)
2441             .chain(base.into_iter().map(StructLitField::Base));
2442
2443         let span_lo = |item: &StructLitField| match *item {
2444             StructLitField::Regular(field) => field.span().lo(),
2445             StructLitField::Base(expr) => {
2446                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
2447                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
2448                 let pos = snippet.find_uncommented("..").unwrap();
2449                 last_field_hi + BytePos(pos as u32)
2450             }
2451         };
2452         let span_hi = |item: &StructLitField| match *item {
2453             StructLitField::Regular(field) => field.span().hi(),
2454             StructLitField::Base(expr) => expr.span.hi(),
2455         };
2456         let rewrite = |item: &StructLitField| match *item {
2457             StructLitField::Regular(field) => {
2458                 // The 1 taken from the v_budget is for the comma.
2459                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
2460             }
2461             StructLitField::Base(expr) => {
2462                 // 2 = ..
2463                 expr.rewrite(context, v_shape.offset_left(2)?)
2464                     .map(|s| format!("..{}", s))
2465             }
2466         };
2467
2468         let items = itemize_list(
2469             context.codemap,
2470             field_iter,
2471             "}",
2472             ",",
2473             span_lo,
2474             span_hi,
2475             rewrite,
2476             body_lo,
2477             span.hi(),
2478             false,
2479         );
2480         let item_vec = items.collect::<Vec<_>>();
2481
2482         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2483         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2484         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2485
2486         write_list(&item_vec, &fmt)?
2487     };
2488
2489     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2490     Some(format!("{} {{{}}}", path_str, fields_str))
2491
2492     // FIXME if context.config.indent_style() == Visual, but we run out
2493     // of space, we should fall back to BlockIndent.
2494 }
2495
2496 pub fn wrap_struct_field(
2497     context: &RewriteContext,
2498     fields_str: &str,
2499     shape: Shape,
2500     nested_shape: Shape,
2501     one_line_width: usize,
2502 ) -> String {
2503     if context.config.indent_style() == IndentStyle::Block
2504         && (fields_str.contains('\n') || !context.config.struct_lit_single_line()
2505             || fields_str.len() > one_line_width)
2506     {
2507         format!(
2508             "\n{}{}\n{}",
2509             nested_shape.indent.to_string(context.config),
2510             fields_str,
2511             shape.indent.to_string(context.config)
2512         )
2513     } else {
2514         // One liner or visual indent.
2515         format!(" {} ", fields_str)
2516     }
2517 }
2518
2519 pub fn struct_lit_field_separator(config: &Config) -> &str {
2520     colon_spaces(config.space_before_colon(), config.space_after_colon())
2521 }
2522
2523 pub fn rewrite_field(
2524     context: &RewriteContext,
2525     field: &ast::Field,
2526     shape: Shape,
2527     prefix_max_width: usize,
2528 ) -> Option<String> {
2529     if contains_skip(&field.attrs) {
2530         return Some(context.snippet(field.span()).to_owned());
2531     }
2532     let name = &field.ident.node.to_string();
2533     if field.is_shorthand {
2534         Some(name.to_string())
2535     } else {
2536         let mut separator = String::from(struct_lit_field_separator(context.config));
2537         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2538             separator.push(' ');
2539         }
2540         let overhead = name.len() + separator.len();
2541         let expr_shape = shape.offset_left(overhead)?;
2542         let expr = field.expr.rewrite(context, expr_shape);
2543
2544         let mut attrs_str = field.attrs.rewrite(context, shape)?;
2545         if !attrs_str.is_empty() {
2546             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2547         };
2548
2549         match expr {
2550             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2551             None => {
2552                 let expr_offset = shape.indent.block_indent(context.config);
2553                 let expr = field
2554                     .expr
2555                     .rewrite(context, Shape::indented(expr_offset, context.config));
2556                 expr.map(|s| {
2557                     format!(
2558                         "{}{}:\n{}{}",
2559                         attrs_str,
2560                         name,
2561                         expr_offset.to_string(context.config),
2562                         s
2563                     )
2564                 })
2565             }
2566         }
2567     }
2568 }
2569
2570 fn shape_from_indent_style(
2571     context: &RewriteContext,
2572     shape: Shape,
2573     overhead: usize,
2574     offset: usize,
2575 ) -> Option<Shape> {
2576     if context.use_block_indent() {
2577         // 1 = ","
2578         shape
2579             .block()
2580             .block_indent(context.config.tab_spaces())
2581             .with_max_width(context.config)
2582             .sub_width(1)
2583     } else {
2584         shape.visual_indent(offset).sub_width(overhead)
2585     }
2586 }
2587
2588 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2589     context: &RewriteContext,
2590     items: &[&T],
2591     span: Span,
2592     shape: Shape,
2593 ) -> Option<String>
2594 where
2595     T: Rewrite + Spanned + ToExpr + 'a,
2596 {
2597     let mut items = items.iter();
2598     // In case of length 1, need a trailing comma
2599     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2600     if items.len() == 1 {
2601         // 3 = "(" + ",)"
2602         let nested_shape = shape.sub_width(3)?.visual_indent(1);
2603         return items
2604             .next()
2605             .unwrap()
2606             .rewrite(context, nested_shape)
2607             .map(|s| {
2608                 if context.config.spaces_within_parens_and_brackets() {
2609                     format!("( {}, )", s)
2610                 } else {
2611                     format!("({},)", s)
2612                 }
2613             });
2614     }
2615
2616     let list_lo = context.codemap.span_after(span, "(");
2617     let nested_shape = shape.sub_width(2)?.visual_indent(1);
2618     let items = itemize_list(
2619         context.codemap,
2620         items,
2621         ")",
2622         ",",
2623         |item| item.span().lo(),
2624         |item| item.span().hi(),
2625         |item| item.rewrite(context, nested_shape),
2626         list_lo,
2627         span.hi() - BytePos(1),
2628         false,
2629     );
2630     let item_vec: Vec<_> = items.collect();
2631     let tactic = definitive_tactic(
2632         &item_vec,
2633         ListTactic::HorizontalVertical,
2634         Separator::Comma,
2635         nested_shape.width,
2636     );
2637     let fmt = ListFormatting {
2638         tactic: tactic,
2639         separator: ",",
2640         trailing_separator: SeparatorTactic::Never,
2641         separator_place: SeparatorPlace::Back,
2642         shape: shape,
2643         ends_with_newline: false,
2644         preserve_newline: false,
2645         config: context.config,
2646     };
2647     let list_str = write_list(&item_vec, &fmt)?;
2648
2649     if context.config.spaces_within_parens_and_brackets() && !list_str.is_empty() {
2650         Some(format!("( {} )", list_str))
2651     } else {
2652         Some(format!("({})", list_str))
2653     }
2654 }
2655
2656 pub fn rewrite_tuple<'a, T>(
2657     context: &RewriteContext,
2658     items: &[&T],
2659     span: Span,
2660     shape: Shape,
2661 ) -> Option<String>
2662 where
2663     T: Rewrite + Spanned + ToExpr + 'a,
2664 {
2665     debug!("rewrite_tuple {:?}", shape);
2666     if context.use_block_indent() {
2667         // We use the same rule as function calls for rewriting tuples.
2668         let force_trailing_comma = if context.inside_macro {
2669             span_ends_with_comma(context, span)
2670         } else {
2671             items.len() == 1
2672         };
2673         rewrite_call_inner(
2674             context,
2675             &String::new(),
2676             items,
2677             span,
2678             shape,
2679             context.config.width_heuristics().fn_call_width,
2680             force_trailing_comma,
2681         )
2682     } else {
2683         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2684     }
2685 }
2686
2687 pub fn rewrite_unary_prefix<R: Rewrite>(
2688     context: &RewriteContext,
2689     prefix: &str,
2690     rewrite: &R,
2691     shape: Shape,
2692 ) -> Option<String> {
2693     rewrite
2694         .rewrite(context, shape.offset_left(prefix.len())?)
2695         .map(|r| format!("{}{}", prefix, r))
2696 }
2697
2698 // FIXME: this is probably not correct for multi-line Rewrites. we should
2699 // subtract suffix.len() from the last line budget, not the first!
2700 pub fn rewrite_unary_suffix<R: Rewrite>(
2701     context: &RewriteContext,
2702     suffix: &str,
2703     rewrite: &R,
2704     shape: Shape,
2705 ) -> Option<String> {
2706     rewrite
2707         .rewrite(context, shape.sub_width(suffix.len())?)
2708         .map(|mut r| {
2709             r.push_str(suffix);
2710             r
2711         })
2712 }
2713
2714 fn rewrite_unary_op(
2715     context: &RewriteContext,
2716     op: &ast::UnOp,
2717     expr: &ast::Expr,
2718     shape: Shape,
2719 ) -> Option<String> {
2720     // For some reason, an UnOp is not spanned like BinOp!
2721     let operator_str = match *op {
2722         ast::UnOp::Deref => "*",
2723         ast::UnOp::Not => "!",
2724         ast::UnOp::Neg => "-",
2725     };
2726     rewrite_unary_prefix(context, operator_str, expr, shape)
2727 }
2728
2729 fn rewrite_assignment(
2730     context: &RewriteContext,
2731     lhs: &ast::Expr,
2732     rhs: &ast::Expr,
2733     op: Option<&ast::BinOp>,
2734     shape: Shape,
2735 ) -> Option<String> {
2736     let operator_str = match op {
2737         Some(op) => context.snippet(op.span),
2738         None => "=",
2739     };
2740
2741     // 1 = space between lhs and operator.
2742     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
2743     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
2744
2745     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2746 }
2747
2748 // The left hand side must contain everything up to, and including, the
2749 // assignment operator.
2750 pub fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
2751     context: &RewriteContext,
2752     lhs: S,
2753     ex: &R,
2754     shape: Shape,
2755 ) -> Option<String> {
2756     let lhs = lhs.into();
2757     let last_line_width = last_line_width(&lhs)
2758         .checked_sub(if lhs.contains('\n') {
2759             shape.indent.width()
2760         } else {
2761             0
2762         })
2763         .unwrap_or(0);
2764     // 1 = space between operator and rhs.
2765     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
2766         width: 0,
2767         offset: shape.offset + last_line_width + 1,
2768         ..shape
2769     });
2770     let rhs = choose_rhs(context, ex, orig_shape, ex.rewrite(context, orig_shape))?;
2771     Some(lhs + &rhs)
2772 }
2773
2774 pub fn choose_rhs<R: Rewrite>(
2775     context: &RewriteContext,
2776     expr: &R,
2777     shape: Shape,
2778     orig_rhs: Option<String>,
2779 ) -> Option<String> {
2780     match orig_rhs {
2781         Some(ref new_str) if !new_str.contains('\n') && new_str.len() <= shape.width => {
2782             Some(format!(" {}", new_str))
2783         }
2784         _ => {
2785             // Expression did not fit on the same line as the identifier.
2786             // Try splitting the line and see if that works better.
2787             let new_shape =
2788                 Shape::indented(shape.indent.block_indent(context.config), context.config)
2789                     .sub_width(shape.rhs_overhead(context.config))?;
2790             let new_rhs = expr.rewrite(context, new_shape);
2791             let new_indent_str = &new_shape.indent.to_string(context.config);
2792
2793             match (orig_rhs, new_rhs) {
2794                 (Some(ref orig_rhs), Some(ref new_rhs))
2795                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2796                         .is_none() =>
2797                 {
2798                     Some(format!(" {}", orig_rhs))
2799                 }
2800                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2801                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2802                 }
2803                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2804                 (None, None) => None,
2805                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2806             }
2807         }
2808     }
2809 }
2810
2811 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2812     use utils::count_newlines;
2813     !next_line_rhs.contains('\n') || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2814 }
2815
2816 fn rewrite_expr_addrof(
2817     context: &RewriteContext,
2818     mutability: ast::Mutability,
2819     expr: &ast::Expr,
2820     shape: Shape,
2821 ) -> Option<String> {
2822     let operator_str = match mutability {
2823         ast::Mutability::Immutable => "&",
2824         ast::Mutability::Mutable => "&mut ",
2825     };
2826     rewrite_unary_prefix(context, operator_str, expr, shape)
2827 }
2828
2829 pub trait ToExpr {
2830     fn to_expr(&self) -> Option<&ast::Expr>;
2831     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2832 }
2833
2834 impl ToExpr for ast::Expr {
2835     fn to_expr(&self) -> Option<&ast::Expr> {
2836         Some(self)
2837     }
2838
2839     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2840         can_be_overflowed_expr(context, self, len)
2841     }
2842 }
2843
2844 impl ToExpr for ast::Ty {
2845     fn to_expr(&self) -> Option<&ast::Expr> {
2846         None
2847     }
2848
2849     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2850         can_be_overflowed_type(context, self, len)
2851     }
2852 }
2853
2854 impl<'a> ToExpr for TuplePatField<'a> {
2855     fn to_expr(&self) -> Option<&ast::Expr> {
2856         None
2857     }
2858
2859     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2860         can_be_overflowed_pat(context, self, len)
2861     }
2862 }
2863
2864 impl<'a> ToExpr for ast::StructField {
2865     fn to_expr(&self) -> Option<&ast::Expr> {
2866         None
2867     }
2868
2869     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
2870         false
2871     }
2872 }
2873
2874 impl<'a> ToExpr for MacroArg {
2875     fn to_expr(&self) -> Option<&ast::Expr> {
2876         match *self {
2877             MacroArg::Expr(ref expr) => Some(expr),
2878             _ => None,
2879         }
2880     }
2881
2882     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2883         match *self {
2884             MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
2885             MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
2886             MacroArg::Pat(..) => false,
2887         }
2888     }
2889 }