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, Ordering};
  12 use std::fmt::Write;
  13 use std::iter::ExactSizeIterator;
  14
  15 use syntax::{ast, ptr};
  16 use syntax::codemap::{BytePos, CodeMap, Span};
  17 use syntax::parse::classify;
  18
  19 use {Indent, Shape, Spanned};
  20 use chains::rewrite_chain;
  21 use codemap::SpanUtils;
  22 use comment::{contains_comment, recover_comment_removed, rewrite_comment, FindUncommented};
  23 use config::{Config, ControlBraceStyle, IndentStyle, MultilineStyle, Style};
  24 use items::{span_hi_for_arg, span_lo_for_arg};
  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, SeparatorTactic};
  28 use macros::{rewrite_macro, MacroPosition};
  29 use patterns::{can_be_overflowed_pat, TuplePatField};
  30 use rewrite::{Rewrite, RewriteContext};
  31 use string::{rewrite_string, StringFormat};
  32 use types::{can_be_overflowed_type, rewrite_path, PathContext};
  33 use utils::{binary_search, colon_spaces, contains_skip, extra_offset, first_line_width,
  34             last_line_extendable, last_line_width, left_most_sub_expr, mk_sp, paren_overhead,
  35             semicolon_for_stmt, stmt_expr, trimmed_last_line_width, wrap_str};
  36 use vertical::rewrite_with_alignment;
  37 use visitor::FmtVisitor;
  38
  39 impl Rewrite for ast::Expr {
  40     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  41         format_expr(self, ExprType::SubExpression, context, shape)
  42     }
  43 }
  44
  45 #[derive(PartialEq)]
  46 pub enum ExprType {
  47     Statement,
  48     SubExpression,
  49 }
  50
  51 fn combine_attr_and_expr(
  52     context: &RewriteContext,
  53     shape: Shape,
  54     expr: &ast::Expr,
  55     expr_str: &str,
  56 ) -> Option<String> {
  57     let attr_str = try_opt!((&*expr.attrs).rewrite(context, shape));
  58     let separator = if attr_str.is_empty() {
  59         String::new()
  60     } else {
  61         // Try to recover comments between the attributes and the expression if available.
  62         let missing_snippet = context.snippet(mk_sp(
  63             expr.attrs[expr.attrs.len() - 1].span.hi,
  64             expr.span.lo,
  65         ));
  66         let comment_opening_pos = missing_snippet.chars().position(|c| c == '/');
  67         let prefer_same_line = if let Some(pos) = comment_opening_pos {
  68             !missing_snippet[..pos].contains('\n')
  69         } else {
  70             !missing_snippet.contains('\n')
  71         };
  72
  73         let trimmed = missing_snippet.trim();
  74         let missing_comment = if trimmed.is_empty() {
  75             String::new()
  76         } else {
  77             try_opt!(rewrite_comment(&trimmed, false, shape, context.config))
  78         };
  79
  80         // 2 = ` ` + ` `
  81         let one_line_width =
  82             attr_str.len() + missing_comment.len() + 2 + first_line_width(expr_str);
  83         let attr_expr_separator = if prefer_same_line && !missing_comment.starts_with("//") &&
  84             one_line_width <= shape.width
  85         {
  86             String::from(" ")
  87         } else {
  88             format!("\n{}", shape.indent.to_string(context.config))
  89         };
  90
  91         if missing_comment.is_empty() {
  92             attr_expr_separator
  93         } else {
  94             // 1 = ` `
  95             let one_line_width =
  96                 last_line_width(&attr_str) + 1 + first_line_width(&missing_comment);
  97             let attr_comment_separator = if prefer_same_line && one_line_width <= shape.width {
  98                 String::from(" ")
  99             } else {
 100                 format!("\n{}", shape.indent.to_string(context.config))
 101             };
 102             attr_comment_separator + &missing_comment + &attr_expr_separator
 103         }
 104     };
 105     Some(format!("{}{}{}", attr_str, separator, expr_str))
 106 }
 107
 108 pub fn format_expr(
 109     expr: &ast::Expr,
 110     expr_type: ExprType,
 111     context: &RewriteContext,
 112     shape: Shape,
 113 ) -> Option<String> {
 114     if contains_skip(&*expr.attrs) {
 115         return Some(context.snippet(expr.span()));
 116     }
 117     let expr_rw = match expr.node {
 118         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
 119             expr_vec.iter().map(|e| &**e),
 120             mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi),
 121             context,
 122             shape,
 123             false,
 124         ),
 125         ast::ExprKind::Lit(ref l) => match l.node {
 126             ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
 127                 rewrite_string_lit(context, l.span, shape)
 128             }
 129             _ => wrap_str(
 130                 context.snippet(expr.span),
 131                 context.config.max_width(),
 132                 shape,
 133             ),
 134         },
 135         ast::ExprKind::Call(ref callee, ref args) => {
 136             let inner_span = mk_sp(callee.span.hi, expr.span.hi);
 137             rewrite_call_with_binary_search(
 138                 context,
 139                 &**callee,
 140                 &args.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 141                 inner_span,
 142                 shape,
 143             )
 144         }
 145         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
 146         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
 147             // FIXME: format comments between operands and operator
 148             rewrite_pair(
 149                 &**lhs,
 150                 &**rhs,
 151                 "",
 152                 &format!(" {} ", context.snippet(op.span)),
 153                 "",
 154                 context,
 155                 shape,
 156             )
 157         }
 158         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 159         ast::ExprKind::Struct(ref path, ref fields, ref base) => rewrite_struct_lit(
 160             context,
 161             path,
 162             fields,
 163             base.as_ref().map(|e| &**e),
 164             expr.span,
 165             shape,
 166         ),
 167         ast::ExprKind::Tup(ref items) => rewrite_tuple(
 168             context,
 169             &items.iter().map(|x| &**x).collect::<Vec<_>>()[..],
 170             expr.span,
 171             shape,
 172         ),
 173         ast::ExprKind::If(..) |
 174         ast::ExprKind::IfLet(..) |
 175         ast::ExprKind::ForLoop(..) |
 176         ast::ExprKind::Loop(..) |
 177         ast::ExprKind::While(..) |
 178         ast::ExprKind::WhileLet(..) => to_control_flow(expr, expr_type)
 179             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 180         ast::ExprKind::Block(ref block) => {
 181             match expr_type {
 182                 ExprType::Statement => {
 183                     if is_unsafe_block(block) {
 184                         block.rewrite(context, shape)
 185                     } else {
 186                         // Rewrite block without trying to put it in a single line.
 187                         if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 188                             return rw;
 189                         }
 190                         let prefix = try_opt!(block_prefix(context, block, shape));
 191                         rewrite_block_with_visitor(context, &prefix, block, shape)
 192                     }
 193                 }
 194                 ExprType::SubExpression => block.rewrite(context, shape),
 195             }
 196         }
 197         ast::ExprKind::Match(ref cond, ref arms) => {
 198             rewrite_match(context, cond, arms, shape, expr.span)
 199         }
 200         ast::ExprKind::Path(ref qself, ref path) => {
 201             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 202         }
 203         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 204             rewrite_assignment(context, lhs, rhs, None, shape)
 205         }
 206         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 207             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 208         }
 209         ast::ExprKind::Continue(ref opt_ident) => {
 210             let id_str = match *opt_ident {
 211                 Some(ident) => format!(" {}", ident.node),
 212                 None => String::new(),
 213             };
 214             wrap_str(
 215                 format!("continue{}", id_str),
 216                 context.config.max_width(),
 217                 shape,
 218             )
 219         }
 220         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 221             let id_str = match *opt_ident {
 222                 Some(ident) => format!(" {}", ident.node),
 223                 None => String::new(),
 224             };
 225
 226             if let Some(ref expr) = *opt_expr {
 227                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 228             } else {
 229                 wrap_str(
 230                     format!("break{}", id_str),
 231                     context.config.max_width(),
 232                     shape,
 233                 )
 234             }
 235         }
 236         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 237             rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 238         }
 239         ast::ExprKind::Try(..) |
 240         ast::ExprKind::Field(..) |
 241         ast::ExprKind::TupField(..) |
 242         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 243         ast::ExprKind::Mac(ref mac) => {
 244             // Failure to rewrite a marco should not imply failure to
 245             // rewrite the expression.
 246             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 247                 wrap_str(
 248                     context.snippet(expr.span),
 249                     context.config.max_width(),
 250                     shape,
 251                 )
 252             })
 253         }
 254         ast::ExprKind::Ret(None) => {
 255             wrap_str("return".to_owned(), context.config.max_width(), shape)
 256         }
 257         ast::ExprKind::Ret(Some(ref expr)) => {
 258             rewrite_unary_prefix(context, "return ", &**expr, shape)
 259         }
 260         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 261         ast::ExprKind::AddrOf(mutability, ref expr) => {
 262             rewrite_expr_addrof(context, mutability, expr, shape)
 263         }
 264         ast::ExprKind::Cast(ref expr, ref ty) => {
 265             rewrite_pair(&**expr, &**ty, "", " as ", "", context, shape)
 266         }
 267         ast::ExprKind::Type(ref expr, ref ty) => {
 268             rewrite_pair(&**expr, &**ty, "", ": ", "", context, shape)
 269         }
 270         ast::ExprKind::Index(ref expr, ref index) => {
 271             rewrite_index(&**expr, &**index, context, shape)
 272         }
 273         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 274             let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
 275                 ("[ ", " ]")
 276             } else {
 277                 ("[", "]")
 278             };
 279             rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, shape)
 280         }
 281         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 282             let delim = match limits {
 283                 ast::RangeLimits::HalfOpen => "..",
 284                 ast::RangeLimits::Closed => "...",
 285             };
 286
 287             fn needs_space_before_range(context: &RewriteContext, lhs: &ast::Expr) -> bool {
 288                 match lhs.node {
 289                     ast::ExprKind::Lit(ref lit) => match lit.node {
 290                         ast::LitKind::FloatUnsuffixed(..) => {
 291                             context.snippet(lit.span).ends_with('.')
 292                         }
 293                         _ => false,
 294                     },
 295                     _ => false,
 296                 }
 297             }
 298
 299             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 300                 (Some(ref lhs), Some(ref rhs)) => {
 301                     let sp_delim = if context.config.spaces_around_ranges() {
 302                         format!(" {} ", delim)
 303                     } else if needs_space_before_range(context, lhs) {
 304                         format!(" {}", delim)
 305                     } else {
 306                         delim.into()
 307                     };
 308                     rewrite_pair(&**lhs, &**rhs, "", &sp_delim, "", context, shape)
 309                 }
 310                 (None, Some(ref rhs)) => {
 311                     let sp_delim = if context.config.spaces_around_ranges() {
 312                         format!("{} ", delim)
 313                     } else {
 314                         delim.into()
 315                     };
 316                     rewrite_unary_prefix(context, &sp_delim, &**rhs, shape)
 317                 }
 318                 (Some(ref lhs), None) => {
 319                     let sp_delim = if context.config.spaces_around_ranges() {
 320                         format!(" {}", delim)
 321                     } else {
 322                         delim.into()
 323                     };
 324                     rewrite_unary_suffix(context, &sp_delim, &**lhs, shape)
 325                 }
 326                 (None, None) => wrap_str(delim.into(), context.config.max_width(), shape),
 327             }
 328         }
 329         // We do not format these expressions yet, but they should still
 330         // satisfy our width restrictions.
 331         ast::ExprKind::InPlace(..) | ast::ExprKind::InlineAsm(..) => wrap_str(
 332             context.snippet(expr.span),
 333             context.config.max_width(),
 334             shape,
 335         ),
 336         ast::ExprKind::Catch(ref block) => {
 337             if let rewrite @ Some(_) = rewrite_single_line_block(context, "do catch ", block, shape)
 338             {
 339                 return rewrite;
 340             }
 341             // 9 = `do catch `
 342             let budget = shape.width.checked_sub(9).unwrap_or(0);
 343             Some(format!(
 344                 "{}{}",
 345                 "do catch ",
 346                 try_opt!(block.rewrite(&context, Shape::legacy(budget, shape.indent)))
 347             ))
 348         }
 349     };
 350
 351     expr_rw
 352         .and_then(|expr_str| {
 353             recover_comment_removed(expr_str, expr.span, context, shape)
 354         })
 355         .and_then(|expr_str| {
 356             combine_attr_and_expr(context, shape, expr, &expr_str)
 357         })
 358 }
 359
 360 pub fn rewrite_pair<LHS, RHS>(
 361     lhs: &LHS,
 362     rhs: &RHS,
 363     prefix: &str,
 364     infix: &str,
 365     suffix: &str,
 366     context: &RewriteContext,
 367     shape: Shape,
 368 ) -> Option<String>
 369 where
 370     LHS: Rewrite,
 371     RHS: Rewrite,
 372 {
 373     let sep = if infix.ends_with(' ') { " " } else { "" };
 374     let infix = infix.trim_right();
 375     let lhs_overhead = shape.used_width() + prefix.len() + infix.len();
 376     let lhs_shape = Shape {
 377         width: try_opt!(context.config.max_width().checked_sub(lhs_overhead)),
 378         ..shape
 379     };
 380     let lhs_result = try_opt!(
 381         lhs.rewrite(context, lhs_shape)
 382             .map(|lhs_str| format!("{}{}{}", prefix, lhs_str, infix))
 383     );
 384
 385     // Try to the both lhs and rhs on the same line.
 386     let rhs_orig_result = shape
 387         .offset_left(last_line_width(&lhs_result) + suffix.len() + sep.len())
 388         .and_then(|rhs_shape| rhs.rewrite(context, rhs_shape));
 389     if let Some(ref rhs_result) = rhs_orig_result {
 390         // If the rhs looks like block expression, we allow it to stay on the same line
 391         // with the lhs even if it is multi-lined.
 392         let allow_same_line = rhs_result
 393             .lines()
 394             .next()
 395             .map(|first_line| first_line.ends_with('{'))
 396             .unwrap_or(false);
 397         if !rhs_result.contains('\n') || allow_same_line {
 398             return Some(format!("{}{}{}{}", lhs_result, sep, rhs_result, suffix));
 399         }
 400     }
 401
 402     // We have to use multiple lines.
 403     // Re-evaluate the rhs because we have more space now:
 404     let rhs_shape = match context.config.control_style() {
 405         Style::Legacy => {
 406             try_opt!(shape.sub_width(suffix.len() + prefix.len())).visual_indent(prefix.len())
 407         }
 408         Style::Rfc => {
 409             // Try to calculate the initial constraint on the right hand side.
 410             let rhs_overhead = shape.rhs_overhead(context.config);
 411             try_opt!(
 412                 Shape::indented(shape.indent.block_indent(context.config), context.config)
 413                     .sub_width(rhs_overhead)
 414             )
 415         }
 416     };
 417     let rhs_result = try_opt!(rhs.rewrite(context, rhs_shape));
 418     Some(format!(
 419         "{}\n{}{}{}",
 420         lhs_result,
 421         rhs_shape.indent.to_string(context.config),
 422         rhs_result,
 423         suffix
 424     ))
 425 }
 426
 427 pub fn rewrite_array<'a, I>(
 428     expr_iter: I,
 429     span: Span,
 430     context: &RewriteContext,
 431     shape: Shape,
 432     trailing_comma: bool,
 433 ) -> Option<String>
 434 where
 435     I: Iterator<Item = &'a ast::Expr>,
 436 {
 437     let bracket_size = if context.config.spaces_within_square_brackets() {
 438         2 // "[ "
 439     } else {
 440         1 // "["
 441     };
 442
 443     let mut nested_shape = match context.config.array_layout() {
 444         IndentStyle::Block => try_opt!(
 445             shape
 446                 .block()
 447                 .block_indent(context.config.tab_spaces())
 448                 .with_max_width(context.config)
 449                 .sub_width(1)
 450         ),
 451         IndentStyle::Visual => try_opt!(
 452             shape
 453                 .visual_indent(bracket_size)
 454                 .sub_width(bracket_size * 2)
 455         ),
 456     };
 457
 458     let items = itemize_list(
 459         context.codemap,
 460         expr_iter,
 461         "]",
 462         |item| item.span.lo,
 463         |item| item.span.hi,
 464         |item| item.rewrite(context, nested_shape),
 465         span.lo,
 466         span.hi,
 467     ).collect::<Vec<_>>();
 468
 469     if items.is_empty() {
 470         if context.config.spaces_within_square_brackets() {
 471             return Some("[ ]".to_string());
 472         } else {
 473             return Some("[]".to_string());
 474         }
 475     }
 476
 477     let has_long_item = items
 478         .iter()
 479         .any(|li| li.item.as_ref().map(|s| s.len() > 10).unwrap_or(false));
 480
 481     let mut tactic = match context.config.array_layout() {
 482         IndentStyle::Block => {
 483             // FIXME wrong shape in one-line case
 484             match shape.width.checked_sub(2 * bracket_size) {
 485                 Some(width) => {
 486                     let tactic =
 487                         ListTactic::LimitedHorizontalVertical(context.config.array_width());
 488                     definitive_tactic(&items, tactic, 2, width)
 489                 }
 490                 None => DefinitiveListTactic::Vertical,
 491             }
 492         }
 493         IndentStyle::Visual => if has_long_item || items.iter().any(ListItem::is_multiline) {
 494             definitive_tactic(
 495                 &items,
 496                 ListTactic::LimitedHorizontalVertical(context.config.array_width()),
 497                 2,
 498                 nested_shape.width,
 499             )
 500         } else {
 501             DefinitiveListTactic::Mixed
 502         },
 503     };
 504     let mut ends_with_newline = tactic.ends_with_newline(context.config.array_layout());
 505     if context.config.array_horizontal_layout_threshold() > 0 &&
 506         items.len() > context.config.array_horizontal_layout_threshold()
 507     {
 508         tactic = DefinitiveListTactic::Mixed;
 509         ends_with_newline = false;
 510         if context.config.array_layout() == IndentStyle::Block {
 511             nested_shape = try_opt!(
 512                 shape
 513                     .visual_indent(bracket_size)
 514                     .sub_width(bracket_size * 2)
 515             );
 516         }
 517     }
 518
 519     let fmt = ListFormatting {
 520         tactic: tactic,
 521         separator: ",",
 522         trailing_separator: if trailing_comma {
 523             SeparatorTactic::Always
 524         } else if context.inside_macro || context.config.array_layout() == IndentStyle::Visual {
 525             SeparatorTactic::Never
 526         } else {
 527             SeparatorTactic::Vertical
 528         },
 529         shape: nested_shape,
 530         ends_with_newline: ends_with_newline,
 531         preserve_newline: false,
 532         config: context.config,
 533     };
 534     let list_str = try_opt!(write_list(&items, &fmt));
 535
 536     let result = if context.config.array_layout() == IndentStyle::Visual ||
 537         tactic != DefinitiveListTactic::Vertical
 538     {
 539         if context.config.spaces_within_square_brackets() && list_str.len() > 0 {
 540             format!("[ {} ]", list_str)
 541         } else {
 542             format!("[{}]", list_str)
 543         }
 544     } else {
 545         format!(
 546             "[\n{}{}\n{}]",
 547             nested_shape.indent.to_string(context.config),
 548             list_str,
 549             shape.block().indent.to_string(context.config)
 550         )
 551     };
 552
 553     Some(result)
 554 }
 555
 556 // Return type is (prefix, extra_offset)
 557 fn rewrite_closure_fn_decl(
 558     capture: ast::CaptureBy,
 559     fn_decl: &ast::FnDecl,
 560     body: &ast::Expr,
 561     span: Span,
 562     context: &RewriteContext,
 563     shape: Shape,
 564 ) -> Option<(String, usize)> {
 565     let mover = if capture == ast::CaptureBy::Value {
 566         "move "
 567     } else {
 568         ""
 569     };
 570     // 4 = "|| {".len(), which is overconservative when the closure consists of
 571     // a single expression.
 572     let nested_shape = try_opt!(try_opt!(shape.shrink_left(mover.len())).sub_width(4));
 573
 574     // 1 = |
 575     let argument_offset = nested_shape.indent + 1;
 576     let arg_shape = try_opt!(nested_shape.offset_left(1)).visual_indent(0);
 577     let ret_str = try_opt!(fn_decl.output.rewrite(context, arg_shape));
 578
 579     let arg_items = itemize_list(
 580         context.codemap,
 581         fn_decl.inputs.iter(),
 582         "|",
 583         |arg| span_lo_for_arg(arg),
 584         |arg| span_hi_for_arg(context, arg),
 585         |arg| arg.rewrite(context, arg_shape),
 586         context.codemap.span_after(span, "|"),
 587         body.span.lo,
 588     );
 589     let item_vec = arg_items.collect::<Vec<_>>();
 590     // 1 = space between arguments and return type.
 591     let horizontal_budget = nested_shape
 592         .width
 593         .checked_sub(ret_str.len() + 1)
 594         .unwrap_or(0);
 595     let tactic = definitive_tactic(
 596         &item_vec,
 597         ListTactic::HorizontalVertical,
 598         2,
 599         horizontal_budget,
 600     );
 601     let arg_shape = match tactic {
 602         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 603         _ => arg_shape,
 604     };
 605
 606     let fmt = ListFormatting {
 607         tactic: tactic,
 608         separator: ",",
 609         trailing_separator: SeparatorTactic::Never,
 610         shape: arg_shape,
 611         ends_with_newline: false,
 612         preserve_newline: true,
 613         config: context.config,
 614     };
 615     let list_str = try_opt!(write_list(&item_vec, &fmt));
 616     let mut prefix = format!("{}|{}|", mover, list_str);
 617     // 1 = space between `|...|` and body.
 618     let extra_offset = extra_offset(&prefix, shape) + 1;
 619
 620     if !ret_str.is_empty() {
 621         if prefix.contains('\n') {
 622             prefix.push('\n');
 623             prefix.push_str(&argument_offset.to_string(context.config));
 624         } else {
 625             prefix.push(' ');
 626         }
 627         prefix.push_str(&ret_str);
 628     }
 629
 630     Some((prefix, extra_offset))
 631 }
 632
 633 // This functions is pretty messy because of the rules around closures and blocks:
 634 // FIXME - the below is probably no longer true in full.
 635 //   * if there is a return type, then there must be braces,
 636 //   * given a closure with braces, whether that is parsed to give an inner block
 637 //     or not depends on if there is a return type and if there are statements
 638 //     in that block,
 639 //   * if the first expression in the body ends with a block (i.e., is a
 640 //     statement without needing a semi-colon), then adding or removing braces
 641 //     can change whether it is treated as an expression or statement.
 642 fn rewrite_closure(
 643     capture: ast::CaptureBy,
 644     fn_decl: &ast::FnDecl,
 645     body: &ast::Expr,
 646     span: Span,
 647     context: &RewriteContext,
 648     shape: Shape,
 649 ) -> Option<String> {
 650     let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
 651         capture,
 652         fn_decl,
 653         body,
 654         span,
 655         context,
 656         shape,
 657     ));
 658     // 1 = space between `|...|` and body.
 659     let body_shape = try_opt!(shape.offset_left(extra_offset));
 660
 661     if let ast::ExprKind::Block(ref block) = body.node {
 662         // The body of the closure is an empty block.
 663         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 664             return Some(format!("{} {{}}", prefix));
 665         }
 666
 667         // Figure out if the block is necessary.
 668         let needs_block = block.rules != ast::BlockCheckMode::Default || block.stmts.len() > 1 ||
 669             context.inside_macro ||
 670             block_contains_comment(block, context.codemap) ||
 671             prefix.contains('\n');
 672
 673         let no_return_type = if let ast::FunctionRetTy::Default(_) = fn_decl.output {
 674             true
 675         } else {
 676             false
 677         };
 678         if no_return_type && !needs_block {
 679             // lock.stmts.len() == 1
 680             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 681                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 682                     return Some(rw);
 683                 }
 684             }
 685         }
 686
 687         if !needs_block {
 688             // We need braces, but we might still prefer a one-liner.
 689             let stmt = &block.stmts[0];
 690             // 4 = braces and spaces.
 691             if let Some(body_shape) = body_shape.sub_width(4) {
 692                 // Checks if rewrite succeeded and fits on a single line.
 693                 if let Some(rewrite) = and_one_line(stmt.rewrite(context, body_shape)) {
 694                     return Some(format!("{} {{ {} }}", prefix, rewrite));
 695                 }
 696             }
 697         }
 698
 699         // Either we require a block, or tried without and failed.
 700         rewrite_closure_block(&block, &prefix, context, body_shape)
 701     } else {
 702         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
 703             // The closure originally had a non-block expression, but we can't fit on
 704             // one line, so we'll insert a block.
 705             rewrite_closure_with_block(context, body_shape, &prefix, body)
 706         })
 707     }
 708 }
 709
 710 // Rewrite closure with a single expression wrapping its body with block.
 711 fn rewrite_closure_with_block(
 712     context: &RewriteContext,
 713     shape: Shape,
 714     prefix: &str,
 715     body: &ast::Expr,
 716 ) -> Option<String> {
 717     let block = ast::Block {
 718         stmts: vec![
 719             ast::Stmt {
 720                 id: ast::NodeId::new(0),
 721                 node: ast::StmtKind::Expr(ptr::P(body.clone())),
 722                 span: body.span,
 723             },
 724         ],
 725         id: ast::NodeId::new(0),
 726         rules: ast::BlockCheckMode::Default,
 727         span: body.span,
 728     };
 729     rewrite_closure_block(&block, prefix, context, shape)
 730 }
 731
 732 // Rewrite closure with a single expression without wrapping its body with block.
 733 fn rewrite_closure_expr(
 734     expr: &ast::Expr,
 735     prefix: &str,
 736     context: &RewriteContext,
 737     shape: Shape,
 738 ) -> Option<String> {
 739     let mut rewrite = expr.rewrite(context, shape);
 740     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 741         rewrite = and_one_line(rewrite);
 742     }
 743     rewrite.map(|rw| format!("{} {}", prefix, rw))
 744 }
 745
 746 // Rewrite closure whose body is block.
 747 fn rewrite_closure_block(
 748     block: &ast::Block,
 749     prefix: &str,
 750     context: &RewriteContext,
 751     shape: Shape,
 752 ) -> Option<String> {
 753     // Start with visual indent, then fall back to block indent if the
 754     // closure is large.
 755     let block_threshold = context.config.closure_block_indent_threshold();
 756     if block_threshold >= 0 {
 757         if let Some(block_str) = block.rewrite(&context, shape) {
 758             if block_str.matches('\n').count() <= block_threshold as usize &&
 759                 !need_block_indent(&block_str, shape)
 760             {
 761                 if let Some(block_str) = block_str.rewrite(context, shape) {
 762                     return Some(format!("{} {}", prefix, block_str));
 763                 }
 764             }
 765         }
 766     }
 767
 768     // The body of the closure is big enough to be block indented, that
 769     // means we must re-format.
 770     let block_shape = shape.block();
 771     let block_str = try_opt!(block.rewrite(&context, block_shape));
 772     Some(format!("{} {}", prefix, block_str))
 773 }
 774
 775 fn and_one_line(x: Option<String>) -> Option<String> {
 776     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 777 }
 778
 779 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 780     debug!("nop_block_collapse {:?} {}", block_str, budget);
 781     block_str.map(|block_str| {
 782         if block_str.starts_with('{') && budget >= 2 &&
 783             (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() == block_str.len() - 2)
 784         {
 785             "{}".to_owned()
 786         } else {
 787             block_str.to_owned()
 788         }
 789     })
 790 }
 791
 792 fn rewrite_empty_block(
 793     context: &RewriteContext,
 794     block: &ast::Block,
 795     shape: Shape,
 796 ) -> Option<String> {
 797     if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) && shape.width >= 2
 798     {
 799         return Some("{}".to_owned());
 800     }
 801
 802     // If a block contains only a single-line comment, then leave it on one line.
 803     let user_str = context.snippet(block.span);
 804     let user_str = user_str.trim();
 805     if user_str.starts_with('{') && user_str.ends_with('}') {
 806         let comment_str = user_str[1..user_str.len() - 1].trim();
 807         if block.stmts.is_empty() && !comment_str.contains('\n') &&
 808             !comment_str.starts_with("//") && comment_str.len() + 4 <= shape.width
 809         {
 810             return Some(format!("{{ {} }}", comment_str));
 811         }
 812     }
 813
 814     None
 815 }
 816
 817 fn block_prefix(context: &RewriteContext, block: &ast::Block, shape: Shape) -> Option<String> {
 818     Some(match block.rules {
 819         ast::BlockCheckMode::Unsafe(..) => {
 820             let snippet = context.snippet(block.span);
 821             let open_pos = try_opt!(snippet.find_uncommented("{"));
 822             // Extract comment between unsafe and block start.
 823             let trimmed = &snippet[6..open_pos].trim();
 824
 825             if !trimmed.is_empty() {
 826                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 827                 let budget = try_opt!(shape.width.checked_sub(9));
 828                 format!(
 829                     "unsafe {} ",
 830                     try_opt!(rewrite_comment(
 831                         trimmed,
 832                         true,
 833                         Shape::legacy(budget, shape.indent + 7),
 834                         context.config,
 835                     ))
 836                 )
 837             } else {
 838                 "unsafe ".to_owned()
 839             }
 840         }
 841         ast::BlockCheckMode::Default => String::new(),
 842     })
 843 }
 844
 845 fn rewrite_single_line_block(
 846     context: &RewriteContext,
 847     prefix: &str,
 848     block: &ast::Block,
 849     shape: Shape,
 850 ) -> Option<String> {
 851     if is_simple_block(block, context.codemap) {
 852         let expr_shape = Shape::legacy(shape.width - prefix.len(), shape.indent);
 853         let expr_str = try_opt!(block.stmts[0].rewrite(context, expr_shape));
 854         let result = format!("{}{{ {} }}", prefix, expr_str);
 855         if result.len() <= shape.width && !result.contains('\n') {
 856             return Some(result);
 857         }
 858     }
 859     None
 860 }
 861
 862 fn rewrite_block_with_visitor(
 863     context: &RewriteContext,
 864     prefix: &str,
 865     block: &ast::Block,
 866     shape: Shape,
 867 ) -> Option<String> {
 868     if let rw @ Some(_) = rewrite_empty_block(context, block, shape) {
 869         return rw;
 870     }
 871
 872     let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 873     visitor.block_indent = shape.indent;
 874     visitor.is_if_else_block = context.is_if_else_block;
 875     match block.rules {
 876         ast::BlockCheckMode::Unsafe(..) => {
 877             let snippet = context.snippet(block.span);
 878             let open_pos = try_opt!(snippet.find_uncommented("{"));
 879             visitor.last_pos = block.span.lo + BytePos(open_pos as u32)
 880         }
 881         ast::BlockCheckMode::Default => visitor.last_pos = block.span.lo,
 882     }
 883
 884     visitor.visit_block(block, None);
 885     Some(format!("{}{}", prefix, visitor.buffer))
 886 }
 887
 888 impl Rewrite for ast::Block {
 889     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 890         // shape.width is used only for the single line case: either the empty block `{}`,
 891         // or an unsafe expression `unsafe { e }`.
 892         if let rw @ Some(_) = rewrite_empty_block(context, self, shape) {
 893             return rw;
 894         }
 895
 896         let prefix = try_opt!(block_prefix(context, self, shape));
 897         if let rw @ Some(_) = rewrite_single_line_block(context, &prefix, self, shape) {
 898             return rw;
 899         }
 900
 901         rewrite_block_with_visitor(context, &prefix, self, shape)
 902     }
 903 }
 904
 905 impl Rewrite for ast::Stmt {
 906     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 907         let result = match self.node {
 908             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 909             ast::StmtKind::Expr(ref ex) | ast::StmtKind::Semi(ref ex) => {
 910                 let suffix = if semicolon_for_stmt(context, self) {
 911                     ";"
 912                 } else {
 913                     ""
 914                 };
 915
 916                 format_expr(
 917                     ex,
 918                     match self.node {
 919                         ast::StmtKind::Expr(_) => ExprType::SubExpression,
 920                         ast::StmtKind::Semi(_) => ExprType::Statement,
 921                         _ => unreachable!(),
 922                     },
 923                     context,
 924                     try_opt!(shape.sub_width(suffix.len())),
 925                 ).map(|s| s + suffix)
 926             }
 927             ast::StmtKind::Mac(..) | ast::StmtKind::Item(..) => None,
 928         };
 929         result.and_then(|res| {
 930             recover_comment_removed(res, self.span(), context, shape)
 931         })
 932     }
 933 }
 934
 935 // Rewrite condition if the given expression has one.
 936 fn rewrite_cond(context: &RewriteContext, expr: &ast::Expr, shape: Shape) -> Option<String> {
 937     match expr.node {
 938         ast::ExprKind::Match(ref cond, _) => {
 939             // `match `cond` {`
 940             let cond_shape = match context.config.control_style() {
 941                 Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
 942                 Style::Rfc => try_opt!(shape.offset_left(8)),
 943             };
 944             cond.rewrite(context, cond_shape)
 945         }
 946         ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
 947             stmt_expr(&block.stmts[0]).and_then(|e| rewrite_cond(context, e, shape))
 948         }
 949         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 950             let alt_block_sep =
 951                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 952             control_flow
 953                 .rewrite_cond(context, shape, &alt_block_sep)
 954                 .and_then(|rw| Some(rw.0))
 955         }),
 956     }
 957 }
 958
 959 // Abstraction over control flow expressions
 960 #[derive(Debug)]
 961 struct ControlFlow<'a> {
 962     cond: Option<&'a ast::Expr>,
 963     block: &'a ast::Block,
 964     else_block: Option<&'a ast::Expr>,
 965     label: Option<ast::SpannedIdent>,
 966     pat: Option<&'a ast::Pat>,
 967     keyword: &'a str,
 968     matcher: &'a str,
 969     connector: &'a str,
 970     allow_single_line: bool,
 971     // True if this is an `if` expression in an `else if` :-( hacky
 972     nested_if: bool,
 973     span: Span,
 974 }
 975
 976 fn to_control_flow<'a>(expr: &'a ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'a>> {
 977     match expr.node {
 978         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => Some(ControlFlow::new_if(
 979             cond,
 980             None,
 981             if_block,
 982             else_block.as_ref().map(|e| &**e),
 983             expr_type == ExprType::SubExpression,
 984             false,
 985             expr.span,
 986         )),
 987         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 988             Some(ControlFlow::new_if(
 989                 cond,
 990                 Some(pat),
 991                 if_block,
 992                 else_block.as_ref().map(|e| &**e),
 993                 expr_type == ExprType::SubExpression,
 994                 false,
 995                 expr.span,
 996             ))
 997         }
 998         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 999             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
1000         }
1001         ast::ExprKind::Loop(ref block, label) => {
1002             Some(ControlFlow::new_loop(block, label, expr.span))
1003         }
1004         ast::ExprKind::While(ref cond, ref block, label) => {
1005             Some(ControlFlow::new_while(None, cond, block, label, expr.span))
1006         }
1007         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => Some(
1008             ControlFlow::new_while(Some(pat), cond, block, label, expr.span),
1009         ),
1010         _ => None,
1011     }
1012 }
1013
1014 impl<'a> ControlFlow<'a> {
1015     fn new_if(
1016         cond: &'a ast::Expr,
1017         pat: Option<&'a ast::Pat>,
1018         block: &'a ast::Block,
1019         else_block: Option<&'a ast::Expr>,
1020         allow_single_line: bool,
1021         nested_if: bool,
1022         span: Span,
1023     ) -> ControlFlow<'a> {
1024         ControlFlow {
1025             cond: Some(cond),
1026             block: block,
1027             else_block: else_block,
1028             label: None,
1029             pat: pat,
1030             keyword: "if",
1031             matcher: match pat {
1032                 Some(..) => "let",
1033                 None => "",
1034             },
1035             connector: " =",
1036             allow_single_line: allow_single_line,
1037             nested_if: nested_if,
1038             span: span,
1039         }
1040     }
1041
1042     fn new_loop(
1043         block: &'a ast::Block,
1044         label: Option<ast::SpannedIdent>,
1045         span: Span,
1046     ) -> ControlFlow<'a> {
1047         ControlFlow {
1048             cond: None,
1049             block: block,
1050             else_block: None,
1051             label: label,
1052             pat: None,
1053             keyword: "loop",
1054             matcher: "",
1055             connector: "",
1056             allow_single_line: false,
1057             nested_if: false,
1058             span: span,
1059         }
1060     }
1061
1062     fn new_while(
1063         pat: Option<&'a ast::Pat>,
1064         cond: &'a ast::Expr,
1065         block: &'a ast::Block,
1066         label: Option<ast::SpannedIdent>,
1067         span: Span,
1068     ) -> ControlFlow<'a> {
1069         ControlFlow {
1070             cond: Some(cond),
1071             block: block,
1072             else_block: None,
1073             label: label,
1074             pat: pat,
1075             keyword: "while",
1076             matcher: match pat {
1077                 Some(..) => "let",
1078                 None => "",
1079             },
1080             connector: " =",
1081             allow_single_line: false,
1082             nested_if: false,
1083             span: span,
1084         }
1085     }
1086
1087     fn new_for(
1088         pat: &'a ast::Pat,
1089         cond: &'a ast::Expr,
1090         block: &'a ast::Block,
1091         label: Option<ast::SpannedIdent>,
1092         span: Span,
1093     ) -> ControlFlow<'a> {
1094         ControlFlow {
1095             cond: Some(cond),
1096             block: block,
1097             else_block: None,
1098             label: label,
1099             pat: Some(pat),
1100             keyword: "for",
1101             matcher: "",
1102             connector: " in",
1103             allow_single_line: false,
1104             nested_if: false,
1105             span: span,
1106         }
1107     }
1108
1109     fn rewrite_single_line(
1110         &self,
1111         pat_expr_str: &str,
1112         context: &RewriteContext,
1113         width: usize,
1114     ) -> Option<String> {
1115         assert!(self.allow_single_line);
1116         let else_block = try_opt!(self.else_block);
1117         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
1118
1119         if let ast::ExprKind::Block(ref else_node) = else_block.node {
1120             if !is_simple_block(self.block, context.codemap) ||
1121                 !is_simple_block(else_node, context.codemap) ||
1122                 pat_expr_str.contains('\n')
1123             {
1124                 return None;
1125             }
1126
1127             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
1128             let expr = &self.block.stmts[0];
1129             let if_str = try_opt!(expr.rewrite(
1130                 context,
1131                 Shape::legacy(new_width, Indent::empty()),
1132             ));
1133
1134             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
1135             let else_expr = &else_node.stmts[0];
1136             let else_str =
1137                 try_opt!(else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
1138
1139             if if_str.contains('\n') || else_str.contains('\n') {
1140                 return None;
1141             }
1142
1143             let result = format!(
1144                 "{} {} {{ {} }} else {{ {} }}",
1145                 self.keyword,
1146                 pat_expr_str,
1147                 if_str,
1148                 else_str
1149             );
1150
1151             if result.len() <= width {
1152                 return Some(result);
1153             }
1154         }
1155
1156         None
1157     }
1158 }
1159
1160 impl<'a> ControlFlow<'a> {
1161     fn rewrite_cond(
1162         &self,
1163         context: &RewriteContext,
1164         shape: Shape,
1165         alt_block_sep: &str,
1166     ) -> Option<(String, usize)> {
1167         // Do not take the rhs overhead from the upper expressions into account
1168         // when rewriting pattern.
1169         let new_width = context
1170             .config
1171             .max_width()
1172             .checked_sub(shape.used_width())
1173             .unwrap_or(0);
1174         let fresh_shape = Shape {
1175             width: new_width,
1176             ..shape
1177         };
1178         let constr_shape = if self.nested_if {
1179             // We are part of an if-elseif-else chain. Our constraints are tightened.
1180             // 7 = "} else " .len()
1181             try_opt!(fresh_shape.offset_left(7))
1182         } else {
1183             fresh_shape
1184         };
1185
1186         let label_string = rewrite_label(self.label);
1187         // 1 = space after keyword.
1188         let offset = self.keyword.len() + label_string.len() + 1;
1189
1190         let pat_expr_string = match self.cond {
1191             Some(cond) => {
1192                 let cond_shape = match context.config.control_style() {
1193                     Style::Legacy => try_opt!(constr_shape.shrink_left(offset)),
1194                     Style::Rfc => try_opt!(constr_shape.offset_left(offset)),
1195                 };
1196                 try_opt!(rewrite_pat_expr(
1197                     context,
1198                     self.pat,
1199                     cond,
1200                     self.matcher,
1201                     self.connector,
1202                     self.keyword,
1203                     cond_shape,
1204                 ))
1205             }
1206             None => String::new(),
1207         };
1208
1209         let brace_overhead =
1210             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
1211                 // 2 = ` {`
1212                 2
1213             } else {
1214                 0
1215             };
1216         let one_line_budget = context
1217             .config
1218             .max_width()
1219             .checked_sub(constr_shape.used_width() + offset + brace_overhead)
1220             .unwrap_or(0);
1221         let force_newline_brace = context.config.control_style() == Style::Rfc &&
1222             (pat_expr_string.contains('\n') || pat_expr_string.len() > one_line_budget) &&
1223             !last_line_extendable(&pat_expr_string);
1224
1225         // Try to format if-else on single line.
1226         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
1227             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
1228
1229             if let Some(cond_str) = trial {
1230                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
1231                     return Some((cond_str, 0));
1232                 }
1233             }
1234         }
1235
1236         let cond_span = if let Some(cond) = self.cond {
1237             cond.span
1238         } else {
1239             mk_sp(self.block.span.lo, self.block.span.lo)
1240         };
1241
1242         // for event in event
1243         let between_kwd_cond = mk_sp(
1244             context.codemap.span_after(self.span, self.keyword.trim()),
1245             self.pat.map_or(
1246                 cond_span.lo,
1247                 |p| if self.matcher.is_empty() {
1248                     p.span.lo
1249                 } else {
1250                     context.codemap.span_before(self.span, self.matcher.trim())
1251                 },
1252             ),
1253         );
1254
1255         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
1256
1257         let after_cond_comment =
1258             extract_comment(mk_sp(cond_span.hi, self.block.span.lo), context, shape);
1259
1260         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
1261             ""
1262         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine ||
1263             force_newline_brace
1264         {
1265             alt_block_sep
1266         } else {
1267             " "
1268         };
1269
1270         let used_width = if pat_expr_string.contains('\n') {
1271             last_line_width(&pat_expr_string)
1272         } else {
1273             // 2 = spaces after keyword and condition.
1274             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
1275         };
1276
1277         Some((
1278             format!(
1279                 "{}{}{}{}{}",
1280                 label_string,
1281                 self.keyword,
1282                 between_kwd_cond_comment.as_ref().map_or(
1283                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
1284                         ""
1285                     } else {
1286                         " "
1287                     },
1288                     |s| &**s,
1289                 ),
1290                 pat_expr_string,
1291                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
1292             ),
1293             used_width,
1294         ))
1295     }
1296 }
1297
1298 impl<'a> Rewrite for ControlFlow<'a> {
1299     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1300         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
1301
1302         let alt_block_sep =
1303             String::from("\n") + &shape.indent.block_only().to_string(context.config);
1304         let (cond_str, used_width) = try_opt!(self.rewrite_cond(context, shape, &alt_block_sep));
1305         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1306         if used_width == 0 {
1307             return Some(cond_str);
1308         }
1309
1310         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
1311         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1312         // we should avoid the single line case.
1313         let block_width = if self.else_block.is_some() || self.nested_if {
1314             min(1, block_width)
1315         } else {
1316             block_width
1317         };
1318         let block_shape = Shape {
1319             width: block_width,
1320             ..shape
1321         };
1322         let mut block_context = context.clone();
1323         block_context.is_if_else_block = self.else_block.is_some();
1324         let block_str = try_opt!(rewrite_block_with_visitor(
1325             &block_context,
1326             "",
1327             self.block,
1328             block_shape,
1329         ));
1330
1331         let mut result = format!("{}{}", cond_str, block_str);
1332
1333         if let Some(else_block) = self.else_block {
1334             let shape = Shape::indented(shape.indent, context.config);
1335             let mut last_in_chain = false;
1336             let rewrite = match else_block.node {
1337                 // If the else expression is another if-else expression, prevent it
1338                 // from being formatted on a single line.
1339                 // Note how we're passing the original shape, as the
1340                 // cost of "else" should not cascade.
1341                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
1342                     ControlFlow::new_if(
1343                         cond,
1344                         Some(pat),
1345                         if_block,
1346                         next_else_block.as_ref().map(|e| &**e),
1347                         false,
1348                         true,
1349                         mk_sp(else_block.span.lo, self.span.hi),
1350                     ).rewrite(context, shape)
1351                 }
1352                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1353                     ControlFlow::new_if(
1354                         cond,
1355                         None,
1356                         if_block,
1357                         next_else_block.as_ref().map(|e| &**e),
1358                         false,
1359                         true,
1360                         mk_sp(else_block.span.lo, self.span.hi),
1361                     ).rewrite(context, shape)
1362                 }
1363                 _ => {
1364                     last_in_chain = true;
1365                     // When rewriting a block, the width is only used for single line
1366                     // blocks, passing 1 lets us avoid that.
1367                     let else_shape = Shape {
1368                         width: min(1, shape.width),
1369                         ..shape
1370                     };
1371                     format_expr(else_block, ExprType::Statement, context, else_shape)
1372                 }
1373             };
1374
1375             let between_kwd_else_block = mk_sp(
1376                 self.block.span.hi,
1377                 context
1378                     .codemap
1379                     .span_before(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1380             );
1381             let between_kwd_else_block_comment =
1382                 extract_comment(between_kwd_else_block, context, shape);
1383
1384             let after_else = mk_sp(
1385                 context
1386                     .codemap
1387                     .span_after(mk_sp(self.block.span.hi, else_block.span.lo), "else"),
1388                 else_block.span.lo,
1389             );
1390             let after_else_comment = extract_comment(after_else, context, shape);
1391
1392             let between_sep = match context.config.control_brace_style() {
1393                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1394                     &*alt_block_sep
1395                 }
1396                 ControlBraceStyle::AlwaysSameLine => " ",
1397             };
1398             let after_sep = match context.config.control_brace_style() {
1399                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1400                 _ => " ",
1401             };
1402             try_opt!(
1403                 write!(
1404                     &mut result,
1405                     "{}else{}",
1406                     between_kwd_else_block_comment
1407                         .as_ref()
1408                         .map_or(between_sep, |s| &**s),
1409                     after_else_comment.as_ref().map_or(after_sep, |s| &**s)
1410                 ).ok()
1411             );
1412             result.push_str(&try_opt!(rewrite));
1413         }
1414
1415         Some(result)
1416     }
1417 }
1418
1419 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
1420     match label {
1421         Some(ident) => format!("{}: ", ident.node),
1422         None => "".to_owned(),
1423     }
1424 }
1425
1426 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1427     let comment_str = context.snippet(span);
1428     if contains_comment(&comment_str) {
1429         let comment = try_opt!(rewrite_comment(
1430             comment_str.trim(),
1431             false,
1432             shape,
1433             context.config,
1434         ));
1435         Some(format!(
1436             "\n{indent}{}\n{indent}",
1437             comment,
1438             indent = shape.indent.to_string(context.config)
1439         ))
1440     } else {
1441         None
1442     }
1443 }
1444
1445 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1446     let snippet = codemap.span_to_snippet(block.span).unwrap();
1447     contains_comment(&snippet)
1448 }
1449
1450 // Checks that a block contains no statements, an expression and no comments.
1451 // FIXME: incorrectly returns false when comment is contained completely within
1452 // the expression.
1453 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1454     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
1455         !block_contains_comment(block, codemap))
1456 }
1457
1458 /// Checks whether a block contains at most one statement or expression, and no comments.
1459 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1460     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1461 }
1462
1463 /// Checks whether a block contains no statements, expressions, or comments.
1464 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1465     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1466 }
1467
1468 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1469     match stmt.node {
1470         ast::StmtKind::Expr(..) => true,
1471         _ => false,
1472     }
1473 }
1474
1475 fn is_unsafe_block(block: &ast::Block) -> bool {
1476     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1477         true
1478     } else {
1479         false
1480     }
1481 }
1482
1483 // inter-match-arm-comment-rules:
1484 //  - all comments following a match arm before the start of the next arm
1485 //    are about the second arm
1486 fn rewrite_match_arm_comment(
1487     context: &RewriteContext,
1488     missed_str: &str,
1489     shape: Shape,
1490     arm_indent_str: &str,
1491 ) -> Option<String> {
1492     // The leading "," is not part of the arm-comment
1493     let missed_str = match missed_str.find_uncommented(",") {
1494         Some(n) => &missed_str[n + 1..],
1495         None => &missed_str[..],
1496     };
1497
1498     let mut result = String::new();
1499     // any text not preceeded by a newline is pushed unmodified to the block
1500     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1501     result.push_str(&missed_str[..first_brk]);
1502     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1503
1504     let first = missed_str
1505         .find(|c: char| !c.is_whitespace())
1506         .unwrap_or(missed_str.len());
1507     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1508         // Excessive vertical whitespace before comment should be preserved
1509         // FIXME handle vertical whitespace better
1510         result.push('\n');
1511     }
1512     let missed_str = missed_str[first..].trim();
1513     if !missed_str.is_empty() {
1514         let comment = try_opt!(rewrite_comment(&missed_str, false, shape, context.config));
1515         result.push('\n');
1516         result.push_str(arm_indent_str);
1517         result.push_str(&comment);
1518     }
1519
1520     Some(result)
1521 }
1522
1523 fn rewrite_match(
1524     context: &RewriteContext,
1525     cond: &ast::Expr,
1526     arms: &[ast::Arm],
1527     shape: Shape,
1528     span: Span,
1529 ) -> Option<String> {
1530     if arms.is_empty() {
1531         return None;
1532     }
1533
1534     // 6 = `match `, 2 = ` {`
1535     let cond_shape = match context.config.control_style() {
1536         Style::Legacy => try_opt!(shape.shrink_left(6).and_then(|s| s.sub_width(2))),
1537         Style::Rfc => try_opt!(shape.offset_left(6).and_then(|s| s.sub_width(2))),
1538     };
1539     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1540     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1541     let block_sep = match context.config.control_brace_style() {
1542         ControlBraceStyle::AlwaysNextLine => &alt_block_sep,
1543         _ if last_line_extendable(&cond_str) => " ",
1544         _ if cond_str.contains('\n') => &alt_block_sep,
1545         _ => " ",
1546     };
1547
1548     Some(format!(
1549         "match {}{}{{{}\n{}}}",
1550         cond_str,
1551         block_sep,
1552         try_opt!(rewrite_match_arms(context, arms, shape, span, cond.span.hi)),
1553         shape.indent.to_string(context.config),
1554     ))
1555 }
1556
1557 fn arm_comma(config: &Config, body: &ast::Expr) -> &'static str {
1558     if config.match_block_trailing_comma() {
1559         ","
1560     } else if let ast::ExprKind::Block(ref block) = body.node {
1561         if let ast::BlockCheckMode::Default = block.rules {
1562             ""
1563         } else {
1564             ","
1565         }
1566     } else {
1567         ","
1568     }
1569 }
1570
1571 fn rewrite_match_arms(
1572     context: &RewriteContext,
1573     arms: &[ast::Arm],
1574     shape: Shape,
1575     span: Span,
1576     cond_end_pos: BytePos,
1577 ) -> Option<String> {
1578     let mut result = String::new();
1579
1580     let arm_shape = if context.config.indent_match_arms() {
1581         shape.block_indent(context.config.tab_spaces())
1582     } else {
1583         shape.block_indent(0)
1584     }.with_max_width(context.config);
1585     let arm_indent_str = arm_shape.indent.to_string(context.config);
1586
1587     let open_brace_pos = context
1588         .codemap
1589         .span_after(mk_sp(cond_end_pos, arms[0].span().lo), "{");
1590
1591     let arm_num = arms.len();
1592     for (i, arm) in arms.iter().enumerate() {
1593         // Make sure we get the stuff between arms.
1594         let missed_str = if i == 0 {
1595             context.snippet(mk_sp(open_brace_pos, arm.span().lo))
1596         } else {
1597             context.snippet(mk_sp(arms[i - 1].span().hi, arm.span().lo))
1598         };
1599         let comment = try_opt!(rewrite_match_arm_comment(
1600             context,
1601             &missed_str,
1602             arm_shape,
1603             &arm_indent_str,
1604         ));
1605         result.push_str(&comment);
1606         result.push('\n');
1607         result.push_str(&arm_indent_str);
1608
1609         let arm_str = rewrite_match_arm(context, arm, arm_shape);
1610         if let Some(ref arm_str) = arm_str {
1611             // Trim the trailing comma if necessary.
1612             if i == arm_num - 1 && context.config.trailing_comma() == SeparatorTactic::Never &&
1613                 arm_str.ends_with(',')
1614             {
1615                 result.push_str(&arm_str[0..arm_str.len() - 1])
1616             } else {
1617                 result.push_str(arm_str)
1618             }
1619         } else {
1620             // We couldn't format the arm, just reproduce the source.
1621             let snippet = context.snippet(arm.span());
1622             result.push_str(&snippet);
1623             if context.config.trailing_comma() != SeparatorTactic::Never {
1624                 result.push_str(arm_comma(context.config, &arm.body))
1625             }
1626         }
1627     }
1628     // BytePos(1) = closing match brace.
1629     let last_span = mk_sp(arms[arms.len() - 1].span().hi, span.hi - BytePos(1));
1630     let last_comment = context.snippet(last_span);
1631     let comment = try_opt!(rewrite_match_arm_comment(
1632         context,
1633         &last_comment,
1634         arm_shape,
1635         &arm_indent_str,
1636     ));
1637     result.push_str(&comment);
1638
1639     Some(result)
1640 }
1641
1642 fn rewrite_match_arm(context: &RewriteContext, arm: &ast::Arm, shape: Shape) -> Option<String> {
1643     let attr_str = if !arm.attrs.is_empty() {
1644         if contains_skip(&arm.attrs) {
1645             return None;
1646         }
1647         format!(
1648             "{}\n{}",
1649             try_opt!(arm.attrs.rewrite(context, shape)),
1650             shape.indent.to_string(context.config)
1651         )
1652     } else {
1653         String::new()
1654     };
1655     let pats_str = try_opt!(rewrite_match_pattern(context, &arm.pats, &arm.guard, shape));
1656     let pats_str = attr_str + &pats_str;
1657     rewrite_match_body(context, &arm.body, &pats_str, shape, arm.guard.is_some())
1658 }
1659
1660 fn rewrite_match_pattern(
1661     context: &RewriteContext,
1662     pats: &Vec<ptr::P<ast::Pat>>,
1663     guard: &Option<ptr::P<ast::Expr>>,
1664     shape: Shape,
1665 ) -> Option<String> {
1666     // Patterns
1667     // 5 = ` => {`
1668     let pat_shape = try_opt!(shape.sub_width(5));
1669
1670     let pat_strs = try_opt!(
1671         pats.iter()
1672             .map(|p| p.rewrite(context, pat_shape))
1673             .collect::<Option<Vec<_>>>()
1674     );
1675
1676     let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1677     let tactic = definitive_tactic(&items, ListTactic::HorizontalVertical, 3, pat_shape.width);
1678     let fmt = ListFormatting {
1679         tactic: tactic,
1680         separator: " |",
1681         trailing_separator: SeparatorTactic::Never,
1682         shape: pat_shape,
1683         ends_with_newline: false,
1684         preserve_newline: false,
1685         config: context.config,
1686     };
1687     let pats_str = try_opt!(write_list(&items, &fmt));
1688
1689     // Guard
1690     let guard_str = try_opt!(rewrite_guard(
1691         context,
1692         guard,
1693         shape,
1694         trimmed_last_line_width(&pats_str),
1695     ));
1696
1697     Some(format!("{}{}", pats_str, guard_str))
1698 }
1699
1700 fn rewrite_match_body(
1701     context: &RewriteContext,
1702     body: &ptr::P<ast::Expr>,
1703     pats_str: &str,
1704     shape: Shape,
1705     has_guard: bool,
1706 ) -> Option<String> {
1707     let (extend, body) = match body.node {
1708         ast::ExprKind::Block(ref block)
1709             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
1710         {
1711             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1712                 (expr.can_be_overflowed(context, 1), &**expr)
1713             } else {
1714                 (false, &**body)
1715             }
1716         }
1717         _ => (body.can_be_overflowed(context, 1), &**body),
1718     };
1719
1720     let comma = arm_comma(&context.config, body);
1721     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1722     let alt_block_sep = alt_block_sep.as_str();
1723     let (is_block, is_empty_block) = if let ast::ExprKind::Block(ref block) = body.node {
1724         (true, is_empty_block(block, context.codemap))
1725     } else {
1726         (false, false)
1727     };
1728
1729     let combine_orig_body = |body_str: &str| {
1730         let block_sep = match context.config.control_brace_style() {
1731             ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep,
1732             _ => " ",
1733         };
1734
1735         Some(format!("{} =>{}{}{}", pats_str, block_sep, body_str, comma))
1736     };
1737
1738     let forbid_same_line = has_guard && pats_str.contains('\n') && !is_empty_block;
1739     let next_line_indent = if is_block {
1740         shape.indent
1741     } else {
1742         shape.indent.block_indent(context.config)
1743     };
1744     let combine_next_line_body = |body_str: &str| {
1745         if is_block {
1746             return Some(format!(
1747                 "{} =>\n{}{}",
1748                 pats_str,
1749                 next_line_indent.to_string(context.config),
1750                 body_str
1751             ));
1752         }
1753
1754         let indent_str = shape.indent.to_string(context.config);
1755         let nested_indent_str = next_line_indent.to_string(context.config);
1756         let (body_prefix, body_suffix) = if context.config.wrap_match_arms() {
1757             let comma = if context.config.match_block_trailing_comma() {
1758                 ","
1759             } else {
1760                 ""
1761             };
1762             ("{", format!("\n{}}}{}", indent_str, comma))
1763         } else {
1764             ("", String::from(","))
1765         };
1766
1767         let block_sep = match context.config.control_brace_style() {
1768             ControlBraceStyle::AlwaysNextLine => format!("{}{}\n", alt_block_sep, body_prefix),
1769             _ if body_prefix.is_empty() => "\n".to_owned(),
1770             _ if forbid_same_line => format!("{}{}\n", alt_block_sep, body_prefix),
1771             _ => format!(" {}\n", body_prefix),
1772         } + &nested_indent_str;
1773
1774         Some(format!(
1775             "{} =>{}{}{}",
1776             pats_str,
1777             block_sep,
1778             body_str,
1779             body_suffix
1780         ))
1781     };
1782
1783     // Let's try and get the arm body on the same line as the condition.
1784     // 4 = ` => `.len()
1785     let orig_body_shape = shape
1786         .offset_left(extra_offset(&pats_str, shape) + 4)
1787         .and_then(|shape| shape.sub_width(comma.len()));
1788     let orig_body = if let Some(body_shape) = orig_body_shape {
1789         let rewrite = nop_block_collapse(
1790             format_expr(body, ExprType::Statement, context, body_shape),
1791             body_shape.width,
1792         );
1793
1794         match rewrite {
1795             Some(ref body_str)
1796                 if !forbid_same_line &&
1797                     (is_block ||
1798                         (!body_str.contains('\n') && body_str.len() <= body_shape.width)) =>
1799             {
1800                 return combine_orig_body(body_str);
1801             }
1802             _ => rewrite,
1803         }
1804     } else {
1805         None
1806     };
1807     let orig_budget = orig_body_shape.map_or(0, |shape| shape.width);
1808
1809     // Try putting body on the next line and see if it looks better.
1810     let next_line_body_shape = Shape::indented(next_line_indent, context.config);
1811     let next_line_body = nop_block_collapse(
1812         format_expr(body, ExprType::Statement, context, next_line_body_shape),
1813         next_line_body_shape.width,
1814     );
1815     match (orig_body, next_line_body) {
1816         (Some(ref orig_str), Some(ref next_line_str))
1817             if forbid_same_line || prefer_next_line(orig_str, next_line_str) =>
1818         {
1819             combine_next_line_body(next_line_str)
1820         }
1821         (Some(ref orig_str), _) if extend && first_line_width(orig_str) <= orig_budget => {
1822             combine_orig_body(orig_str)
1823         }
1824         (Some(ref orig_str), Some(ref next_line_str)) if orig_str.contains('\n') => {
1825             combine_next_line_body(next_line_str)
1826         }
1827         (None, Some(ref next_line_str)) => combine_next_line_body(next_line_str),
1828         (None, None) => None,
1829         (Some(ref orig_str), _) => combine_orig_body(orig_str),
1830     }
1831 }
1832
1833 // The `if ...` guard on a match arm.
1834 fn rewrite_guard(
1835     context: &RewriteContext,
1836     guard: &Option<ptr::P<ast::Expr>>,
1837     shape: Shape,
1838     // The amount of space used up on this line for the pattern in
1839     // the arm (excludes offset).
1840     pattern_width: usize,
1841 ) -> Option<String> {
1842     if let Some(ref guard) = *guard {
1843         // First try to fit the guard string on the same line as the pattern.
1844         // 4 = ` if `, 5 = ` => {`
1845         let cond_shape = shape
1846             .offset_left(pattern_width + 4)
1847             .and_then(|s| s.sub_width(5));
1848         if let Some(cond_shape) = cond_shape {
1849             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1850                 if !cond_str.contains('\n') || pattern_width <= context.config.tab_spaces() {
1851                     return Some(format!(" if {}", cond_str));
1852                 }
1853             }
1854         }
1855
1856         // Not enough space to put the guard after the pattern, try a newline.
1857         // 3 = `if `, 5 = ` => {`
1858         let cond_shape = Shape::indented(shape.indent.block_indent(context.config), context.config)
1859             .offset_left(3)
1860             .and_then(|s| s.sub_width(5));
1861         if let Some(cond_shape) = cond_shape {
1862             if let Some(cond_str) = guard.rewrite(context, cond_shape) {
1863                 return Some(format!(
1864                     "\n{}if {}",
1865                     cond_shape.indent.to_string(context.config),
1866                     cond_str
1867                 ));
1868             }
1869         }
1870
1871         None
1872     } else {
1873         Some(String::new())
1874     }
1875 }
1876
1877 fn rewrite_pat_expr(
1878     context: &RewriteContext,
1879     pat: Option<&ast::Pat>,
1880     expr: &ast::Expr,
1881     matcher: &str,
1882     // Connecting piece between pattern and expression,
1883     // *without* trailing space.
1884     connector: &str,
1885     keyword: &str,
1886     shape: Shape,
1887 ) -> Option<String> {
1888     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1889     if let Some(pat) = pat {
1890         let matcher = if matcher.is_empty() {
1891             matcher.to_owned()
1892         } else {
1893             format!("{} ", matcher)
1894         };
1895         let pat_shape =
1896             try_opt!(try_opt!(shape.offset_left(matcher.len())).sub_width(connector.len()));
1897         let pat_string = try_opt!(pat.rewrite(context, pat_shape));
1898         let result = format!("{}{}{}", matcher, pat_string, connector);
1899         return rewrite_assign_rhs(context, result, expr, shape);
1900     }
1901
1902     let expr_rw = expr.rewrite(context, shape);
1903     // The expression may (partially) fit on the current line.
1904     // We do not allow splitting between `if` and condition.
1905     if keyword == "if" || expr_rw.is_some() {
1906         return expr_rw;
1907     }
1908
1909     // The expression won't fit on the current line, jump to next.
1910     let nested_shape = shape
1911         .block_indent(context.config.tab_spaces())
1912         .with_max_width(context.config);
1913     let nested_indent_str = nested_shape.indent.to_string(context.config);
1914     expr.rewrite(context, nested_shape)
1915         .map(|expr_rw| format!("\n{}{}", nested_indent_str, expr_rw))
1916 }
1917
1918 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1919     let string_lit = context.snippet(span);
1920
1921     if !context.config.format_strings() && !context.config.force_format_strings() {
1922         if string_lit
1923             .lines()
1924             .rev()
1925             .skip(1)
1926             .all(|line| line.ends_with('\\'))
1927         {
1928             let new_indent = shape.visual_indent(1).indent;
1929             return Some(String::from(
1930                 string_lit
1931                     .lines()
1932                     .map(|line| {
1933                         new_indent.to_string(context.config) + line.trim_left()
1934                     })
1935                     .collect::<Vec<_>>()
1936                     .join("\n")
1937                     .trim_left(),
1938             ));
1939         } else {
1940             return Some(string_lit);
1941         }
1942     }
1943
1944     if !context.config.force_format_strings() &&
1945         !string_requires_rewrite(context, span, &string_lit, shape)
1946     {
1947         return Some(string_lit);
1948     }
1949
1950     let fmt = StringFormat {
1951         opener: "\"",
1952         closer: "\"",
1953         line_start: " ",
1954         line_end: "\\",
1955         shape: shape,
1956         trim_end: false,
1957         config: context.config,
1958     };
1959
1960     // Remove the quote characters.
1961     let str_lit = &string_lit[1..string_lit.len() - 1];
1962
1963     rewrite_string(str_lit, &fmt)
1964 }
1965
1966 fn string_requires_rewrite(
1967     context: &RewriteContext,
1968     span: Span,
1969     string: &str,
1970     shape: Shape,
1971 ) -> bool {
1972     if context.codemap.lookup_char_pos(span.lo).col.0 != shape.indent.width() {
1973         return true;
1974     }
1975
1976     for (i, line) in string.lines().enumerate() {
1977         if i == 0 {
1978             if line.len() > shape.width {
1979                 return true;
1980             }
1981         } else {
1982             if line.len() > shape.width + shape.indent.width() {
1983                 return true;
1984             }
1985         }
1986     }
1987
1988     false
1989 }
1990
1991 pub fn rewrite_call_with_binary_search<R>(
1992     context: &RewriteContext,
1993     callee: &R,
1994     args: &[&ast::Expr],
1995     span: Span,
1996     shape: Shape,
1997 ) -> Option<String>
1998 where
1999     R: Rewrite,
2000 {
2001     let force_trailing_comma = if context.inside_macro {
2002         span_ends_with_comma(context, span)
2003     } else {
2004         false
2005     };
2006     let closure = |callee_max_width| {
2007         // FIXME using byte lens instead of char lens (and probably all over the
2008         // place too)
2009         let callee_shape = Shape {
2010             width: callee_max_width,
2011             ..shape
2012         };
2013         let callee_str = callee
2014             .rewrite(context, callee_shape)
2015             .ok_or(Ordering::Greater)?;
2016
2017         rewrite_call_inner(
2018             context,
2019             &callee_str,
2020             args,
2021             span,
2022             shape,
2023             context.config.fn_call_width(),
2024             force_trailing_comma,
2025         )
2026     };
2027
2028     binary_search(1, shape.width, closure)
2029 }
2030
2031 pub fn rewrite_call(
2032     context: &RewriteContext,
2033     callee: &str,
2034     args: &[ptr::P<ast::Expr>],
2035     span: Span,
2036     shape: Shape,
2037 ) -> Option<String> {
2038     let force_trailing_comma = if context.inside_macro {
2039         span_ends_with_comma(context, span)
2040     } else {
2041         false
2042     };
2043     rewrite_call_inner(
2044         context,
2045         &callee,
2046         &args.iter().map(|x| &**x).collect::<Vec<_>>(),
2047         span,
2048         shape,
2049         context.config.fn_call_width(),
2050         force_trailing_comma,
2051     ).ok()
2052 }
2053
2054 pub fn rewrite_call_inner<'a, T>(
2055     context: &RewriteContext,
2056     callee_str: &str,
2057     args: &[&T],
2058     span: Span,
2059     shape: Shape,
2060     args_max_width: usize,
2061     force_trailing_comma: bool,
2062 ) -> Result<String, Ordering>
2063 where
2064     T: Rewrite + Spanned + ToExpr + 'a,
2065 {
2066     // 2 = `( `, 1 = `(`
2067     let paren_overhead = if context.config.spaces_within_parens() {
2068         2
2069     } else {
2070         1
2071     };
2072     let used_width = extra_offset(&callee_str, shape);
2073     let one_line_width = shape
2074         .width
2075         .checked_sub(used_width + 2 * paren_overhead)
2076         .ok_or(Ordering::Greater)?;
2077
2078     let nested_shape = shape_from_fn_call_style(
2079         context,
2080         shape,
2081         used_width + 2 * paren_overhead,
2082         used_width + paren_overhead,
2083     ).ok_or(Ordering::Greater)?;
2084
2085     let span_lo = context.codemap.span_after(span, "(");
2086     let args_span = mk_sp(span_lo, span.hi);
2087
2088     let (extendable, list_str) = rewrite_call_args(
2089         context,
2090         args,
2091         args_span,
2092         nested_shape,
2093         one_line_width,
2094         args_max_width,
2095         force_trailing_comma,
2096     ).ok_or(Ordering::Less)?;
2097
2098     if !context.use_block_indent() && need_block_indent(&list_str, nested_shape) && !extendable {
2099         let mut new_context = context.clone();
2100         new_context.use_block = true;
2101         return rewrite_call_inner(
2102             &new_context,
2103             callee_str,
2104             args,
2105             span,
2106             shape,
2107             args_max_width,
2108             force_trailing_comma,
2109         );
2110     }
2111
2112     let args_shape = shape
2113         .sub_width(last_line_width(&callee_str))
2114         .ok_or(Ordering::Less)?;
2115     Ok(format!(
2116         "{}{}",
2117         callee_str,
2118         wrap_args_with_parens(context, &list_str, extendable, args_shape, nested_shape)
2119     ))
2120 }
2121
2122 fn need_block_indent(s: &str, shape: Shape) -> bool {
2123     s.lines().skip(1).any(|s| {
2124         s.find(|c| !char::is_whitespace(c))
2125             .map_or(false, |w| w + 1 < shape.indent.width())
2126     })
2127 }
2128
2129 fn rewrite_call_args<'a, T>(
2130     context: &RewriteContext,
2131     args: &[&T],
2132     span: Span,
2133     shape: Shape,
2134     one_line_width: usize,
2135     args_max_width: usize,
2136     force_trailing_comma: bool,
2137 ) -> Option<(bool, String)>
2138 where
2139     T: Rewrite + Spanned + ToExpr + 'a,
2140 {
2141     let items = itemize_list(
2142         context.codemap,
2143         args.iter(),
2144         ")",
2145         |item| item.span().lo,
2146         |item| item.span().hi,
2147         |item| item.rewrite(context, shape),
2148         span.lo,
2149         span.hi,
2150     );
2151     let mut item_vec: Vec<_> = items.collect();
2152
2153     // Try letting the last argument overflow to the next line with block
2154     // indentation. If its first line fits on one line with the other arguments,
2155     // we format the function arguments horizontally.
2156     let tactic = try_overflow_last_arg(
2157         context,
2158         &mut item_vec,
2159         &args[..],
2160         shape,
2161         one_line_width,
2162         args_max_width,
2163     );
2164
2165     let fmt = ListFormatting {
2166         tactic: tactic,
2167         separator: ",",
2168         trailing_separator: if force_trailing_comma {
2169             SeparatorTactic::Always
2170         } else if context.inside_macro || !context.use_block_indent() {
2171             SeparatorTactic::Never
2172         } else {
2173             context.config.trailing_comma()
2174         },
2175         shape: shape,
2176         ends_with_newline: context.use_block_indent() && tactic == DefinitiveListTactic::Vertical,
2177         preserve_newline: false,
2178         config: context.config,
2179     };
2180
2181     write_list(&item_vec, &fmt).map(|args_str| {
2182         (tactic != DefinitiveListTactic::Vertical, args_str)
2183     })
2184 }
2185
2186 fn try_overflow_last_arg<'a, T>(
2187     context: &RewriteContext,
2188     item_vec: &mut Vec<ListItem>,
2189     args: &[&T],
2190     shape: Shape,
2191     one_line_width: usize,
2192     args_max_width: usize,
2193 ) -> DefinitiveListTactic
2194 where
2195     T: Rewrite + Spanned + ToExpr + 'a,
2196 {
2197     let overflow_last = can_be_overflowed(&context, args);
2198
2199     // Replace the last item with its first line to see if it fits with
2200     // first arguments.
2201     let (orig_last, placeholder) = if overflow_last {
2202         let mut context = context.clone();
2203         if let Some(expr) = args[args.len() - 1].to_expr() {
2204             match expr.node {
2205                 ast::ExprKind::MethodCall(..) => context.force_one_line_chain = true,
2206                 _ => (),
2207             }
2208         }
2209         last_arg_shape(&context, &item_vec, shape, args_max_width)
2210             .map_or((None, None), |arg_shape| {
2211                 rewrite_last_arg_with_overflow(
2212                     &context,
2213                     args,
2214                     &mut item_vec[args.len() - 1],
2215                     arg_shape,
2216                 )
2217             })
2218     } else {
2219         (None, None)
2220     };
2221
2222     let tactic = definitive_tactic(
2223         &*item_vec,
2224         ListTactic::LimitedHorizontalVertical(args_max_width),
2225         2,
2226         one_line_width,
2227     );
2228
2229     // Replace the stub with the full overflowing last argument if the rewrite
2230     // succeeded and its first line fits with the other arguments.
2231     match (overflow_last, tactic, placeholder) {
2232         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
2233             item_vec[args.len() - 1].item = placeholder;
2234         }
2235         (true, _, _) => {
2236             item_vec[args.len() - 1].item = orig_last;
2237         }
2238         (false, _, _) => {}
2239     }
2240
2241     tactic
2242 }
2243
2244 fn last_arg_shape(
2245     context: &RewriteContext,
2246     items: &Vec<ListItem>,
2247     shape: Shape,
2248     args_max_width: usize,
2249 ) -> Option<Shape> {
2250     let overhead = items.iter().rev().skip(1).fold(0, |acc, i| {
2251         acc + i.item.as_ref().map_or(0, |s| first_line_width(&s))
2252     });
2253     let max_width = min(args_max_width, shape.width);
2254     let arg_indent = if context.use_block_indent() {
2255         shape.block().indent.block_unindent(context.config)
2256     } else {
2257         shape.block().indent
2258     };
2259     Some(Shape {
2260         width: try_opt!(max_width.checked_sub(overhead)),
2261         indent: arg_indent,
2262         offset: 0,
2263     })
2264 }
2265
2266 // Rewriting closure which is placed at the end of the function call's arg.
2267 // Returns `None` if the reformatted closure 'looks bad'.
2268 fn rewrite_last_closure(
2269     context: &RewriteContext,
2270     expr: &ast::Expr,
2271     shape: Shape,
2272 ) -> Option<String> {
2273     if let ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) = expr.node {
2274         let body = match body.node {
2275             ast::ExprKind::Block(ref block) if block.stmts.len() == 1 => {
2276                 stmt_expr(&block.stmts[0]).unwrap_or(body)
2277             }
2278             _ => body,
2279         };
2280         let (prefix, extra_offset) = try_opt!(rewrite_closure_fn_decl(
2281             capture,
2282             fn_decl,
2283             body,
2284             expr.span,
2285             context,
2286             shape,
2287         ));
2288         // If the closure goes multi line before its body, do not overflow the closure.
2289         if prefix.contains('\n') {
2290             return None;
2291         }
2292         let body_shape = try_opt!(shape.offset_left(extra_offset));
2293         // When overflowing the closure which consists of a single control flow expression,
2294         // force to use block if its condition uses multi line.
2295         let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
2296             .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
2297             .unwrap_or(false);
2298         if is_multi_lined_cond {
2299             return rewrite_closure_with_block(context, body_shape, &prefix, body);
2300         }
2301
2302         // Seems fine, just format the closure in usual manner.
2303         return expr.rewrite(context, shape);
2304     }
2305     None
2306 }
2307
2308 fn rewrite_last_arg_with_overflow<'a, T>(
2309     context: &RewriteContext,
2310     args: &[&T],
2311     last_item: &mut ListItem,
2312     shape: Shape,
2313 ) -> (Option<String>, Option<String>)
2314 where
2315     T: Rewrite + Spanned + ToExpr + 'a,
2316 {
2317     let last_arg = args[args.len() - 1];
2318     let rewrite = if let Some(expr) = last_arg.to_expr() {
2319         match expr.node {
2320             // When overflowing the closure which consists of a single control flow expression,
2321             // force to use block if its condition uses multi line.
2322             ast::ExprKind::Closure(..) => {
2323                 // If the argument consists of multiple closures, we do not overflow
2324                 // the last closure.
2325                 if args.len() > 1 &&
2326                     args.iter()
2327                         .rev()
2328                         .skip(1)
2329                         .filter_map(|arg| arg.to_expr())
2330                         .any(|expr| match expr.node {
2331                             ast::ExprKind::Closure(..) => true,
2332                             _ => false,
2333                         }) {
2334                     None
2335                 } else {
2336                     rewrite_last_closure(context, expr, shape)
2337                 }
2338             }
2339             _ => expr.rewrite(context, shape),
2340         }
2341     } else {
2342         last_arg.rewrite(context, shape)
2343     };
2344     let orig_last = last_item.item.clone();
2345
2346     if let Some(rewrite) = rewrite {
2347         let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
2348         last_item.item = rewrite_first_line;
2349         (orig_last, Some(rewrite))
2350     } else {
2351         (orig_last, None)
2352     }
2353 }
2354
2355 fn can_be_overflowed<'a, T>(context: &RewriteContext, args: &[&T]) -> bool
2356 where
2357     T: Rewrite + Spanned + ToExpr + 'a,
2358 {
2359     args.last()
2360         .map_or(false, |x| x.can_be_overflowed(context, args.len()))
2361 }
2362
2363 pub fn can_be_overflowed_expr(context: &RewriteContext, expr: &ast::Expr, args_len: usize) -> bool {
2364     match expr.node {
2365         ast::ExprKind::Match(..) => {
2366             (context.use_block_indent() && args_len == 1) ||
2367                 (context.config.fn_call_style() == IndentStyle::Visual && args_len > 1)
2368         }
2369         ast::ExprKind::If(..) |
2370         ast::ExprKind::IfLet(..) |
2371         ast::ExprKind::ForLoop(..) |
2372         ast::ExprKind::Loop(..) |
2373         ast::ExprKind::While(..) |
2374         ast::ExprKind::WhileLet(..) => {
2375             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
2376         }
2377         ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => {
2378             context.use_block_indent() ||
2379                 context.config.fn_call_style() == IndentStyle::Visual && args_len > 1
2380         }
2381         ast::ExprKind::Array(..) |
2382         ast::ExprKind::Call(..) |
2383         ast::ExprKind::Mac(..) |
2384         ast::ExprKind::MethodCall(..) |
2385         ast::ExprKind::Struct(..) |
2386         ast::ExprKind::Tup(..) => context.use_block_indent() && args_len == 1,
2387         ast::ExprKind::AddrOf(_, ref expr) |
2388         ast::ExprKind::Box(ref expr) |
2389         ast::ExprKind::Try(ref expr) |
2390         ast::ExprKind::Unary(_, ref expr) |
2391         ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
2392         _ => false,
2393     }
2394 }
2395
2396 pub fn wrap_args_with_parens(
2397     context: &RewriteContext,
2398     args_str: &str,
2399     is_extendable: bool,
2400     shape: Shape,
2401     nested_shape: Shape,
2402 ) -> String {
2403     if !context.use_block_indent() ||
2404         (context.inside_macro && !args_str.contains('\n') &&
2405             args_str.len() + paren_overhead(context) <= shape.width) || is_extendable
2406     {
2407         if context.config.spaces_within_parens() && args_str.len() > 0 {
2408             format!("( {} )", args_str)
2409         } else {
2410             format!("({})", args_str)
2411         }
2412     } else {
2413         format!(
2414             "(\n{}{}\n{})",
2415             nested_shape.indent.to_string(context.config),
2416             args_str,
2417             shape.block().indent.to_string(context.config)
2418         )
2419     }
2420 }
2421
2422 fn span_ends_with_comma(context: &RewriteContext, span: Span) -> bool {
2423     let snippet = context.snippet(span);
2424     snippet
2425         .trim_right_matches(|c: char| c == ')' || c.is_whitespace())
2426         .ends_with(',')
2427 }
2428
2429 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
2430     debug!("rewrite_paren, shape: {:?}", shape);
2431     let total_paren_overhead = paren_overhead(context);
2432     let paren_overhead = total_paren_overhead / 2;
2433     let sub_shape = try_opt!(
2434         shape
2435             .offset_left(paren_overhead)
2436             .and_then(|s| s.sub_width(paren_overhead))
2437     );
2438
2439     let paren_wrapper = |s: &str| if context.config.spaces_within_parens() && s.len() > 0 {
2440         format!("( {} )", s)
2441     } else {
2442         format!("({})", s)
2443     };
2444
2445     let subexpr_str = try_opt!(subexpr.rewrite(context, sub_shape));
2446     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
2447
2448     if subexpr_str.contains('\n') ||
2449         first_line_width(&subexpr_str) + total_paren_overhead <= shape.width
2450     {
2451         Some(paren_wrapper(&subexpr_str))
2452     } else {
2453         None
2454     }
2455 }
2456
2457 fn rewrite_index(
2458     expr: &ast::Expr,
2459     index: &ast::Expr,
2460     context: &RewriteContext,
2461     shape: Shape,
2462 ) -> Option<String> {
2463     let expr_str = try_opt!(expr.rewrite(context, shape));
2464
2465     let (lbr, rbr) = if context.config.spaces_within_square_brackets() {
2466         ("[ ", " ]")
2467     } else {
2468         ("[", "]")
2469     };
2470
2471     let offset = last_line_width(&expr_str) + lbr.len();
2472     let rhs_overhead = shape.rhs_overhead(context.config);
2473     let index_shape = if expr_str.contains('\n') {
2474         Shape::legacy(context.config.max_width(), shape.indent)
2475             .offset_left(offset)
2476             .and_then(|shape| shape.sub_width(rbr.len() + rhs_overhead))
2477     } else {
2478         shape.visual_indent(offset).sub_width(offset + rbr.len())
2479     };
2480     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
2481
2482     // Return if index fits in a single line.
2483     match orig_index_rw {
2484         Some(ref index_str) if !index_str.contains('\n') => {
2485             return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
2486         }
2487         _ => (),
2488     }
2489
2490     // Try putting index on the next line and see if it fits in a single line.
2491     let indent = shape.indent.block_indent(context.config);
2492     let index_shape = try_opt!(Shape::indented(indent, context.config).offset_left(lbr.len()));
2493     let index_shape = try_opt!(index_shape.sub_width(rbr.len() + rhs_overhead));
2494     let new_index_rw = index.rewrite(context, index_shape);
2495     match (orig_index_rw, new_index_rw) {
2496         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
2497             "{}\n{}{}{}{}",
2498             expr_str,
2499             indent.to_string(&context.config),
2500             lbr,
2501             new_index_str,
2502             rbr
2503         )),
2504         (None, Some(ref new_index_str)) => Some(format!(
2505             "{}\n{}{}{}{}",
2506             expr_str,
2507             indent.to_string(&context.config),
2508             lbr,
2509             new_index_str,
2510             rbr
2511         )),
2512         (Some(ref index_str), _) => Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr)),
2513         _ => None,
2514     }
2515 }
2516
2517 fn struct_lit_can_be_aligned(fields: &[ast::Field], base: &Option<&ast::Expr>) -> bool {
2518     if base.is_some() {
2519         return false;
2520     }
2521
2522     fields.iter().all(|field| !field.is_shorthand)
2523 }
2524
2525 fn rewrite_struct_lit<'a>(
2526     context: &RewriteContext,
2527     path: &ast::Path,
2528     fields: &'a [ast::Field],
2529     base: Option<&'a ast::Expr>,
2530     span: Span,
2531     shape: Shape,
2532 ) -> Option<String> {
2533     debug!("rewrite_struct_lit: shape {:?}", shape);
2534
2535     enum StructLitField<'a> {
2536         Regular(&'a ast::Field),
2537         Base(&'a ast::Expr),
2538     }
2539
2540     // 2 = " {".len()
2541     let path_shape = try_opt!(shape.sub_width(2));
2542     let path_str = try_opt!(rewrite_path(
2543         context,
2544         PathContext::Expr,
2545         None,
2546         path,
2547         path_shape,
2548     ));
2549
2550     if fields.len() == 0 && base.is_none() {
2551         return Some(format!("{} {{}}", path_str));
2552     }
2553
2554     // Foo { a: Foo } - indent is +3, width is -5.
2555     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
2556
2557     let one_line_width = h_shape.map_or(0, |shape| shape.width);
2558     let body_lo = context.codemap.span_after(span, "{");
2559     let fields_str = if struct_lit_can_be_aligned(fields, &base) &&
2560         context.config.struct_field_align_threshold() > 0
2561     {
2562         try_opt!(rewrite_with_alignment(
2563             fields,
2564             context,
2565             shape,
2566             mk_sp(body_lo, span.hi),
2567             one_line_width,
2568         ))
2569     } else {
2570         let field_iter = fields
2571             .into_iter()
2572             .map(StructLitField::Regular)
2573             .chain(base.into_iter().map(StructLitField::Base));
2574
2575         let span_lo = |item: &StructLitField| match *item {
2576             StructLitField::Regular(field) => field.span().lo,
2577             StructLitField::Base(expr) => {
2578                 let last_field_hi = fields.last().map_or(span.lo, |field| field.span.hi);
2579                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo));
2580                 let pos = snippet.find_uncommented("..").unwrap();
2581                 last_field_hi + BytePos(pos as u32)
2582             }
2583         };
2584         let span_hi = |item: &StructLitField| match *item {
2585             StructLitField::Regular(field) => field.span().hi,
2586             StructLitField::Base(expr) => expr.span.hi,
2587         };
2588         let rewrite = |item: &StructLitField| match *item {
2589             StructLitField::Regular(field) => {
2590                 // The 1 taken from the v_budget is for the comma.
2591                 rewrite_field(context, field, try_opt!(v_shape.sub_width(1)), 0)
2592             }
2593             StructLitField::Base(expr) => {
2594                 // 2 = ..
2595                 expr.rewrite(context, try_opt!(v_shape.offset_left(2)))
2596                     .map(|s| format!("..{}", s))
2597             }
2598         };
2599
2600         let items = itemize_list(
2601             context.codemap,
2602             field_iter,
2603             "}",
2604             span_lo,
2605             span_hi,
2606             rewrite,
2607             body_lo,
2608             span.hi,
2609         );
2610         let item_vec = items.collect::<Vec<_>>();
2611
2612         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
2613         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
2614         let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
2615
2616         try_opt!(write_list(&item_vec, &fmt))
2617     };
2618
2619     let fields_str = wrap_struct_field(context, &fields_str, shape, v_shape, one_line_width);
2620     Some(format!("{} {{{}}}", path_str, fields_str))
2621
2622     // FIXME if context.config.struct_lit_style() == Visual, but we run out
2623     // of space, we should fall back to BlockIndent.
2624 }
2625
2626 pub fn wrap_struct_field(
2627     context: &RewriteContext,
2628     fields_str: &str,
2629     shape: Shape,
2630     nested_shape: Shape,
2631     one_line_width: usize,
2632 ) -> String {
2633     if context.config.struct_lit_style() == IndentStyle::Block &&
2634         (fields_str.contains('\n') ||
2635             context.config.struct_lit_multiline_style() == MultilineStyle::ForceMulti ||
2636             fields_str.len() > one_line_width)
2637     {
2638         format!(
2639             "\n{}{}\n{}",
2640             nested_shape.indent.to_string(context.config),
2641             fields_str,
2642             shape.indent.to_string(context.config)
2643         )
2644     } else {
2645         // One liner or visual indent.
2646         format!(" {} ", fields_str)
2647     }
2648 }
2649
2650 pub fn struct_lit_field_separator(config: &Config) -> &str {
2651     colon_spaces(
2652         config.space_before_struct_lit_field_colon(),
2653         config.space_after_struct_lit_field_colon(),
2654     )
2655 }
2656
2657 pub fn rewrite_field(
2658     context: &RewriteContext,
2659     field: &ast::Field,
2660     shape: Shape,
2661     prefix_max_width: usize,
2662 ) -> Option<String> {
2663     if contains_skip(&field.attrs) {
2664         return wrap_str(
2665             context.snippet(field.span()),
2666             context.config.max_width(),
2667             shape,
2668         );
2669     }
2670     let name = &field.ident.node.to_string();
2671     if field.is_shorthand {
2672         Some(name.to_string())
2673     } else {
2674         let mut separator = String::from(struct_lit_field_separator(context.config));
2675         for _ in 0..prefix_max_width.checked_sub(name.len()).unwrap_or(0) {
2676             separator.push(' ');
2677         }
2678         let overhead = name.len() + separator.len();
2679         let expr_shape = try_opt!(shape.offset_left(overhead));
2680         let expr = field.expr.rewrite(context, expr_shape);
2681
2682         let mut attrs_str = try_opt!(field.attrs.rewrite(context, shape));
2683         if !attrs_str.is_empty() {
2684             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
2685         };
2686
2687         match expr {
2688             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
2689             None => {
2690                 let expr_offset = shape.indent.block_indent(context.config);
2691                 let expr = field
2692                     .expr
2693                     .rewrite(context, Shape::indented(expr_offset, context.config));
2694                 expr.map(|s| {
2695                     format!(
2696                         "{}{}:\n{}{}",
2697                         attrs_str,
2698                         name,
2699                         expr_offset.to_string(&context.config),
2700                         s
2701                     )
2702                 })
2703             }
2704         }
2705     }
2706 }
2707
2708 fn shape_from_fn_call_style(
2709     context: &RewriteContext,
2710     shape: Shape,
2711     overhead: usize,
2712     offset: usize,
2713 ) -> Option<Shape> {
2714     if context.use_block_indent() {
2715         // 1 = ","
2716         shape
2717             .block()
2718             .block_indent(context.config.tab_spaces())
2719             .with_max_width(context.config)
2720             .sub_width(1)
2721     } else {
2722         shape.visual_indent(offset).sub_width(overhead)
2723     }
2724 }
2725
2726 fn rewrite_tuple_in_visual_indent_style<'a, T>(
2727     context: &RewriteContext,
2728     items: &[&T],
2729     span: Span,
2730     shape: Shape,
2731 ) -> Option<String>
2732 where
2733     T: Rewrite + Spanned + ToExpr + 'a,
2734 {
2735     let mut items = items.iter();
2736     // In case of length 1, need a trailing comma
2737     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
2738     if items.len() == 1 {
2739         // 3 = "(" + ",)"
2740         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
2741         return items.next().unwrap().rewrite(context, nested_shape).map(
2742             |s| if context.config.spaces_within_parens() {
2743                 format!("( {}, )", s)
2744             } else {
2745                 format!("({},)", s)
2746             },
2747         );
2748     }
2749
2750     let list_lo = context.codemap.span_after(span, "(");
2751     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
2752     let items = itemize_list(
2753         context.codemap,
2754         items,
2755         ")",
2756         |item| item.span().lo,
2757         |item| item.span().hi,
2758         |item| item.rewrite(context, nested_shape),
2759         list_lo,
2760         span.hi - BytePos(1),
2761     );
2762     let item_vec: Vec<_> = items.collect();
2763     let tactic = definitive_tactic(
2764         &item_vec,
2765         ListTactic::HorizontalVertical,
2766         2,
2767         nested_shape.width,
2768     );
2769     let fmt = ListFormatting {
2770         tactic: tactic,
2771         separator: ",",
2772         trailing_separator: SeparatorTactic::Never,
2773         shape: shape,
2774         ends_with_newline: false,
2775         preserve_newline: false,
2776         config: context.config,
2777     };
2778     let list_str = try_opt!(write_list(&item_vec, &fmt));
2779
2780     if context.config.spaces_within_parens() && list_str.len() > 0 {
2781         Some(format!("( {} )", list_str))
2782     } else {
2783         Some(format!("({})", list_str))
2784     }
2785 }
2786
2787 pub fn rewrite_tuple<'a, T>(
2788     context: &RewriteContext,
2789     items: &[&T],
2790     span: Span,
2791     shape: Shape,
2792 ) -> Option<String>
2793 where
2794     T: Rewrite + Spanned + ToExpr + 'a,
2795 {
2796     debug!("rewrite_tuple {:?}", shape);
2797     if context.use_block_indent() {
2798         // We use the same rule as funcation call for rewriting tuple.
2799         let force_trailing_comma = if context.inside_macro {
2800             span_ends_with_comma(context, span)
2801         } else {
2802             items.len() == 1
2803         };
2804         rewrite_call_inner(
2805             context,
2806             &String::new(),
2807             items,
2808             span,
2809             shape,
2810             context.config.fn_call_width(),
2811             force_trailing_comma,
2812         ).ok()
2813     } else {
2814         rewrite_tuple_in_visual_indent_style(context, items, span, shape)
2815     }
2816 }
2817
2818 pub fn rewrite_unary_prefix<R: Rewrite>(
2819     context: &RewriteContext,
2820     prefix: &str,
2821     rewrite: &R,
2822     shape: Shape,
2823 ) -> Option<String> {
2824     rewrite
2825         .rewrite(context, try_opt!(shape.offset_left(prefix.len())))
2826         .map(|r| format!("{}{}", prefix, r))
2827 }
2828
2829 // FIXME: this is probably not correct for multi-line Rewrites. we should
2830 // subtract suffix.len() from the last line budget, not the first!
2831 pub fn rewrite_unary_suffix<R: Rewrite>(
2832     context: &RewriteContext,
2833     suffix: &str,
2834     rewrite: &R,
2835     shape: Shape,
2836 ) -> Option<String> {
2837     rewrite
2838         .rewrite(context, try_opt!(shape.sub_width(suffix.len())))
2839         .map(|mut r| {
2840             r.push_str(suffix);
2841             r
2842         })
2843 }
2844
2845 fn rewrite_unary_op(
2846     context: &RewriteContext,
2847     op: &ast::UnOp,
2848     expr: &ast::Expr,
2849     shape: Shape,
2850 ) -> Option<String> {
2851     // For some reason, an UnOp is not spanned like BinOp!
2852     let operator_str = match *op {
2853         ast::UnOp::Deref => "*",
2854         ast::UnOp::Not => "!",
2855         ast::UnOp::Neg => "-",
2856     };
2857     rewrite_unary_prefix(context, operator_str, expr, shape)
2858 }
2859
2860 fn rewrite_assignment(
2861     context: &RewriteContext,
2862     lhs: &ast::Expr,
2863     rhs: &ast::Expr,
2864     op: Option<&ast::BinOp>,
2865     shape: Shape,
2866 ) -> Option<String> {
2867     let operator_str = match op {
2868         Some(op) => context.snippet(op.span),
2869         None => "=".to_owned(),
2870     };
2871
2872     // 1 = space between lhs and operator.
2873     let lhs_shape = try_opt!(shape.sub_width(operator_str.len() + 1));
2874     let lhs_str = format!(
2875         "{} {}",
2876         try_opt!(lhs.rewrite(context, lhs_shape)),
2877         operator_str
2878     );
2879
2880     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2881 }
2882
2883 // The left hand side must contain everything up to, and including, the
2884 // assignment operator.
2885 pub fn rewrite_assign_rhs<S: Into<String>>(
2886     context: &RewriteContext,
2887     lhs: S,
2888     ex: &ast::Expr,
2889     shape: Shape,
2890 ) -> Option<String> {
2891     let lhs = lhs.into();
2892     let last_line_width = last_line_width(&lhs) - if lhs.contains('\n') {
2893         shape.indent.width()
2894     } else {
2895         0
2896     };
2897     // 1 = space between operator and rhs.
2898     let orig_shape = try_opt!(shape.offset_left(last_line_width + 1));
2899     let rhs = try_opt!(choose_rhs(
2900         context,
2901         ex,
2902         shape,
2903         ex.rewrite(context, orig_shape)
2904     ));
2905     Some(lhs + &rhs)
2906 }
2907
2908 fn choose_rhs(
2909     context: &RewriteContext,
2910     expr: &ast::Expr,
2911     shape: Shape,
2912     orig_rhs: Option<String>,
2913 ) -> Option<String> {
2914     match orig_rhs {
2915         Some(ref new_str) if !new_str.contains('\n') => Some(format!(" {}", new_str)),
2916         _ => {
2917             // Expression did not fit on the same line as the identifier.
2918             // Try splitting the line and see if that works better.
2919             let new_shape = try_opt!(
2920                 Shape::indented(
2921                     shape.block().indent.block_indent(context.config),
2922                     context.config,
2923                 ).sub_width(shape.rhs_overhead(context.config))
2924             );
2925             let new_rhs = expr.rewrite(context, new_shape);
2926             let new_indent_str = &new_shape.indent.to_string(context.config);
2927
2928             match (orig_rhs, new_rhs) {
2929                 (Some(ref orig_rhs), Some(ref new_rhs)) if prefer_next_line(orig_rhs, new_rhs) => {
2930                     Some(format!("\n{}{}", new_indent_str, new_rhs))
2931                 }
2932                 (None, Some(ref new_rhs)) => Some(format!("\n{}{}", new_indent_str, new_rhs)),
2933                 (None, None) => None,
2934                 (Some(ref orig_rhs), _) => Some(format!(" {}", orig_rhs)),
2935             }
2936         }
2937     }
2938 }
2939
2940 fn prefer_next_line(orig_rhs: &str, next_line_rhs: &str) -> bool {
2941
2942     fn count_line_breaks(src: &str) -> usize {
2943         src.chars().filter(|&x| x == '\n').count()
2944     }
2945
2946     !next_line_rhs.contains('\n') ||
2947         count_line_breaks(orig_rhs) > count_line_breaks(next_line_rhs) + 1
2948 }
2949
2950 fn rewrite_expr_addrof(
2951     context: &RewriteContext,
2952     mutability: ast::Mutability,
2953     expr: &ast::Expr,
2954     shape: Shape,
2955 ) -> Option<String> {
2956     let operator_str = match mutability {
2957         ast::Mutability::Immutable => "&",
2958         ast::Mutability::Mutable => "&mut ",
2959     };
2960     rewrite_unary_prefix(context, operator_str, expr, shape)
2961 }
2962
2963 pub trait ToExpr {
2964     fn to_expr(&self) -> Option<&ast::Expr>;
2965     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool;
2966 }
2967
2968 impl ToExpr for ast::Expr {
2969     fn to_expr(&self) -> Option<&ast::Expr> {
2970         Some(self)
2971     }
2972
2973     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2974         can_be_overflowed_expr(context, self, len)
2975     }
2976 }
2977
2978 impl ToExpr for ast::Ty {
2979     fn to_expr(&self) -> Option<&ast::Expr> {
2980         None
2981     }
2982
2983     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2984         can_be_overflowed_type(context, self, len)
2985     }
2986 }
2987
2988 impl<'a> ToExpr for TuplePatField<'a> {
2989     fn to_expr(&self) -> Option<&ast::Expr> {
2990         None
2991     }
2992
2993     fn can_be_overflowed(&self, context: &RewriteContext, len: usize) -> bool {
2994         can_be_overflowed_pat(context, self, len)
2995     }
2996 }
2997
2998 impl<'a> ToExpr for ast::StructField {
2999     fn to_expr(&self) -> Option<&ast::Expr> {
3000         None
3001     }
3002
3003     fn can_be_overflowed(&self, _: &RewriteContext, _: usize) -> bool {
3004         false
3005     }
3006 }