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::{Ordering, min};
  12 use std::mem::swap;
  13 use std::ops::Deref;
  14 use std::iter::ExactSizeIterator;
  15 use std::fmt::Write;
  16
  17 use {Indent, Shape, Spanned};
  18 use codemap::SpanUtils;
  19 use rewrite::{Rewrite, RewriteContext};
  20 use lists::{write_list, itemize_list, ListFormatting, SeparatorTactic, ListTactic,
  21             DefinitiveListTactic, definitive_tactic, ListItem, format_item_list, struct_lit_shape,
  22             struct_lit_tactic, shape_for_tactic, struct_lit_formatting};
  23 use string::{StringFormat, rewrite_string};
  24 use utils::{extra_offset, last_line_width, wrap_str, binary_search, first_line_width,
  25             semicolon_for_stmt, trimmed_last_line_width, left_most_sub_expr, stmt_expr,
  26             colon_spaces};
  27 use visitor::FmtVisitor;
  28 use config::{Config, IndentStyle, MultilineStyle, ControlBraceStyle, Style};
  29 use comment::{FindUncommented, rewrite_comment, contains_comment, recover_comment_removed};
  30 use types::{rewrite_path, PathContext};
  31 use items::{span_lo_for_arg, span_hi_for_arg};
  32 use chains::rewrite_chain;
  33 use macros::{rewrite_macro, MacroPosition};
  34
  35 use syntax::{ast, ptr};
  36 use syntax::codemap::{CodeMap, Span, BytePos, mk_sp};
  37 use syntax::parse::classify;
  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 enum ExprType {
  47     Statement,
  48     SubExpression,
  49 }
  50
  51 fn format_expr(expr: &ast::Expr,
  52                expr_type: ExprType,
  53                context: &RewriteContext,
  54                shape: Shape)
  55                -> Option<String> {
  56     let result = match expr.node {
  57         ast::ExprKind::Array(ref expr_vec) => {
  58             rewrite_array(expr_vec.iter().map(|e| &**e),
  59                           mk_sp(context.codemap.span_after(expr.span, "["), expr.span.hi),
  60                           context,
  61                           shape)
  62         }
  63         ast::ExprKind::Lit(ref l) => {
  64             match l.node {
  65                 ast::LitKind::Str(_, ast::StrStyle::Cooked) => {
  66                     rewrite_string_lit(context, l.span, shape)
  67                 }
  68                 _ => wrap_str(context.snippet(expr.span), context.config.max_width, shape),
  69             }
  70         }
  71         ast::ExprKind::Call(ref callee, ref args) => {
  72             let inner_span = mk_sp(callee.span.hi, expr.span.hi);
  73             rewrite_call(context, &**callee, args, inner_span, shape)
  74         }
  75         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape),
  76         ast::ExprKind::Binary(ref op, ref lhs, ref rhs) => {
  77             // FIXME: format comments between operands and operator
  78             rewrite_pair(&**lhs,
  79                          &**rhs,
  80                          "",
  81                          &format!(" {} ", context.snippet(op.span)),
  82                          "",
  83                          context,
  84                          shape)
  85         }
  86         ast::ExprKind::Unary(ref op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
  87         ast::ExprKind::Struct(ref path, ref fields, ref base) => {
  88             rewrite_struct_lit(context,
  89                                path,
  90                                fields,
  91                                base.as_ref().map(|e| &**e),
  92                                expr.span,
  93                                shape)
  94         }
  95         ast::ExprKind::Tup(ref items) => {
  96             rewrite_tuple(context, items.iter().map(|x| &**x), expr.span, shape)
  97         }
  98         ast::ExprKind::While(ref cond, ref block, label) => {
  99             ControlFlow::new_while(None, cond, block, label, expr.span).rewrite(context, shape)
 100         }
 101         ast::ExprKind::WhileLet(ref pat, ref cond, ref block, label) => {
 102             ControlFlow::new_while(Some(pat), cond, block, label, expr.span).rewrite(context, shape)
 103         }
 104         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 105             ControlFlow::new_for(pat, cond, block, label, expr.span).rewrite(context, shape)
 106         }
 107         ast::ExprKind::Loop(ref block, label) => {
 108             ControlFlow::new_loop(block, label, expr.span).rewrite(context, shape)
 109         }
 110         ast::ExprKind::Block(ref block) => block.rewrite(context, shape),
 111         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => {
 112             ControlFlow::new_if(cond,
 113                                 None,
 114                                 if_block,
 115                                 else_block.as_ref().map(|e| &**e),
 116                                 expr_type == ExprType::SubExpression,
 117                                 false,
 118                                 expr.span)
 119                     .rewrite(context, shape)
 120         }
 121         ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref else_block) => {
 122             ControlFlow::new_if(cond,
 123                                 Some(pat),
 124                                 if_block,
 125                                 else_block.as_ref().map(|e| &**e),
 126                                 expr_type == ExprType::SubExpression,
 127                                 false,
 128                                 expr.span)
 129                     .rewrite(context, shape)
 130         }
 131         ast::ExprKind::Match(ref cond, ref arms) => {
 132             rewrite_match(context, cond, arms, shape, expr.span)
 133         }
 134         ast::ExprKind::Path(ref qself, ref path) => {
 135             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 136         }
 137         ast::ExprKind::Assign(ref lhs, ref rhs) => {
 138             rewrite_assignment(context, lhs, rhs, None, shape)
 139         }
 140         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 141             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 142         }
 143         ast::ExprKind::Continue(ref opt_ident) => {
 144             let id_str = match *opt_ident {
 145                 Some(ident) => format!(" {}", ident.node),
 146                 None => String::new(),
 147             };
 148             wrap_str(format!("continue{}", id_str),
 149                      context.config.max_width,
 150                      shape)
 151         }
 152         ast::ExprKind::Break(ref opt_ident, ref opt_expr) => {
 153             let id_str = match *opt_ident {
 154                 Some(ident) => format!(" {}", ident.node),
 155                 None => String::new(),
 156             };
 157
 158             if let Some(ref expr) = *opt_expr {
 159                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 160             } else {
 161                 wrap_str(format!("break{}", id_str), context.config.max_width, shape)
 162             }
 163         }
 164         ast::ExprKind::Closure(capture, ref fn_decl, ref body, _) => {
 165             rewrite_closure(capture, fn_decl, body, expr.span, context, shape)
 166         }
 167         ast::ExprKind::Try(..) |
 168         ast::ExprKind::Field(..) |
 169         ast::ExprKind::TupField(..) |
 170         ast::ExprKind::MethodCall(..) => rewrite_chain(expr, context, shape),
 171         ast::ExprKind::Mac(ref mac) => {
 172             // Failure to rewrite a marco should not imply failure to
 173             // rewrite the expression.
 174             rewrite_macro(mac, None, context, shape, MacroPosition::Expression)
 175                 .or_else(|| wrap_str(context.snippet(expr.span), context.config.max_width, shape))
 176         }
 177         ast::ExprKind::Ret(None) => wrap_str("return".to_owned(), context.config.max_width, shape),
 178         ast::ExprKind::Ret(Some(ref expr)) => {
 179             rewrite_unary_prefix(context, "return ", &**expr, shape)
 180         }
 181         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 182         ast::ExprKind::AddrOf(mutability, ref expr) => {
 183             rewrite_expr_addrof(context, mutability, expr, shape)
 184         }
 185         ast::ExprKind::Cast(ref expr, ref ty) => {
 186             rewrite_pair(&**expr, &**ty, "", " as ", "", context, shape)
 187         }
 188         ast::ExprKind::Type(ref expr, ref ty) => {
 189             rewrite_pair(&**expr, &**ty, "", ": ", "", context, shape)
 190         }
 191         ast::ExprKind::Index(ref expr, ref index) => {
 192             rewrite_index(&**expr, &**index, context, shape)
 193         }
 194         ast::ExprKind::Repeat(ref expr, ref repeats) => {
 195             let (lbr, rbr) = if context.config.spaces_within_square_brackets {
 196                 ("[ ", " ]")
 197             } else {
 198                 ("[", "]")
 199             };
 200             rewrite_pair(&**expr, &**repeats, lbr, "; ", rbr, context, shape)
 201         }
 202         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 203             let delim = match limits {
 204                 ast::RangeLimits::HalfOpen => "..",
 205                 ast::RangeLimits::Closed => "...",
 206             };
 207
 208             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 209                 (Some(ref lhs), Some(ref rhs)) => {
 210                     let sp_delim = if context.config.spaces_around_ranges {
 211                         format!(" {} ", delim)
 212                     } else {
 213                         delim.into()
 214                     };
 215                     rewrite_pair(&**lhs, &**rhs, "", &sp_delim, "", context, shape)
 216                 }
 217                 (None, Some(ref rhs)) => {
 218                     let sp_delim = if context.config.spaces_around_ranges {
 219                         format!("{} ", delim)
 220                     } else {
 221                         delim.into()
 222                     };
 223                     rewrite_unary_prefix(context, &sp_delim, &**rhs, shape)
 224                 }
 225                 (Some(ref lhs), None) => {
 226                     let sp_delim = if context.config.spaces_around_ranges {
 227                         format!(" {}", delim)
 228                     } else {
 229                         delim.into()
 230                     };
 231                     rewrite_unary_suffix(context, &sp_delim, &**lhs, shape)
 232                 }
 233                 (None, None) => wrap_str(delim.into(), context.config.max_width, shape),
 234             }
 235         }
 236         // We do not format these expressions yet, but they should still
 237         // satisfy our width restrictions.
 238         ast::ExprKind::InPlace(..) |
 239         ast::ExprKind::InlineAsm(..) => {
 240             wrap_str(context.snippet(expr.span), context.config.max_width, shape)
 241         }
 242     };
 243     result.and_then(|res| recover_comment_removed(res, expr.span, context, shape))
 244 }
 245
 246 pub fn rewrite_pair<LHS, RHS>(lhs: &LHS,
 247                               rhs: &RHS,
 248                               prefix: &str,
 249                               infix: &str,
 250                               suffix: &str,
 251                               context: &RewriteContext,
 252                               shape: Shape)
 253                               -> Option<String>
 254     where LHS: Rewrite,
 255           RHS: Rewrite
 256 {
 257     // Get "full width" rhs and see if it fits on the current line. This
 258     // usually works fairly well since it tends to place operands of
 259     // operations with high precendence close together.
 260     // Note that this is non-conservative, but its just to see if it's even
 261     // worth trying to put everything on one line.
 262     let rhs_shape = try_opt!(shape.sub_width(suffix.len()));
 263     let rhs_result = rhs.rewrite(context, rhs_shape);
 264
 265     if let Some(rhs_result) = rhs_result {
 266         // This is needed in case of line break not caused by a
 267         // shortage of space, but by end-of-line comments, for example.
 268         if !rhs_result.contains('\n') {
 269             let lhs_shape = try_opt!(shape.sub_width(prefix.len() + infix.len()));
 270             let lhs_result = lhs.rewrite(context, lhs_shape);
 271             if let Some(lhs_result) = lhs_result {
 272                 let mut result = format!("{}{}{}", prefix, lhs_result, infix);
 273
 274                 let remaining_width = shape
 275                     .width
 276                     .checked_sub(last_line_width(&result))
 277                     .unwrap_or(0);
 278
 279                 if rhs_result.len() <= remaining_width {
 280                     result.push_str(&rhs_result);
 281                     result.push_str(suffix);
 282                     return Some(result);
 283                 }
 284
 285                 // Try rewriting the rhs into the remaining space.
 286                 let rhs_shape = shape.shrink_left(last_line_width(&result) + suffix.len());
 287                 if let Some(rhs_shape) = rhs_shape {
 288                     if let Some(rhs_result) = rhs.rewrite(context, rhs_shape) {
 289                         // FIXME this should always hold.
 290                         if rhs_result.len() <= remaining_width {
 291                             result.push_str(&rhs_result);
 292                             result.push_str(suffix);
 293                             return Some(result);
 294                         }
 295                     }
 296                 }
 297             }
 298         }
 299     }
 300
 301     // We have to use multiple lines.
 302
 303     // Re-evaluate the rhs because we have more space now:
 304     let infix = infix.trim_right();
 305     let lhs_budget = try_opt!(context
 306                                   .config
 307                                   .max_width
 308                                   .checked_sub(shape.used_width() + prefix.len() +
 309                                                infix.len()));
 310     let rhs_shape = match context.config.control_style {
 311         Style::Default => {
 312             try_opt!(shape.sub_width(suffix.len() + prefix.len())).visual_indent(prefix.len())
 313         }
 314         Style::Rfc => try_opt!(shape.block_left(context.config.tab_spaces)),
 315     };
 316
 317     let rhs_result = try_opt!(rhs.rewrite(context, rhs_shape));
 318     let lhs_result = try_opt!(lhs.rewrite(context,
 319                                           Shape {
 320                                               width: lhs_budget,
 321                                               ..shape
 322                                           }));
 323     Some(format!("{}{}{}\n{}{}{}",
 324                  prefix,
 325                  lhs_result,
 326                  infix,
 327                  rhs_shape.indent.to_string(context.config),
 328                  rhs_result,
 329                  suffix))
 330 }
 331
 332 pub fn rewrite_array<'a, I>(expr_iter: I,
 333                             span: Span,
 334                             context: &RewriteContext,
 335                             shape: Shape)
 336                             -> Option<String>
 337     where I: Iterator<Item = &'a ast::Expr>
 338 {
 339     let bracket_size = if context.config.spaces_within_square_brackets {
 340         2 // "[ "
 341     } else {
 342         1 // "["
 343     };
 344
 345     let nested_shape = match context.config.array_layout {
 346         IndentStyle::Block => shape.block().block_indent(context.config.tab_spaces),
 347         IndentStyle::Visual => {
 348             try_opt!(shape
 349                          .visual_indent(bracket_size)
 350                          .sub_width(bracket_size * 2))
 351         }
 352     };
 353
 354     let items = itemize_list(context.codemap,
 355                              expr_iter,
 356                              "]",
 357                              |item| item.span.lo,
 358                              |item| item.span.hi,
 359                              |item| item.rewrite(context, nested_shape),
 360                              span.lo,
 361                              span.hi)
 362             .collect::<Vec<_>>();
 363
 364     if items.is_empty() {
 365         if context.config.spaces_within_square_brackets {
 366             return Some("[ ]".to_string());
 367         } else {
 368             return Some("[]".to_string());
 369         }
 370     }
 371
 372     let has_long_item = try_opt!(items
 373                                      .iter()
 374                                      .map(|li| li.item.as_ref().map(|s| s.len() > 10))
 375                                      .fold(Some(false),
 376                                            |acc, x| acc.and_then(|y| x.map(|x| x || y))));
 377
 378     let tactic = match context.config.array_layout {
 379         IndentStyle::Block => {
 380             // FIXME wrong shape in one-line case
 381             match shape.width.checked_sub(2 * bracket_size) {
 382                 Some(width) => {
 383                     let tactic = ListTactic::LimitedHorizontalVertical(context.config.array_width);
 384                     definitive_tactic(&items, tactic, width)
 385                 }
 386                 None => DefinitiveListTactic::Vertical,
 387             }
 388         }
 389         IndentStyle::Visual => {
 390             if has_long_item || items.iter().any(ListItem::is_multiline) {
 391                 definitive_tactic(&items,
 392                                   ListTactic::LimitedHorizontalVertical(context.config.array_width),
 393                                   nested_shape.width)
 394             } else {
 395                 DefinitiveListTactic::Mixed
 396             }
 397         }
 398     };
 399
 400     let fmt = ListFormatting {
 401         tactic: tactic,
 402         separator: ",",
 403         trailing_separator: SeparatorTactic::Never,
 404         shape: nested_shape,
 405         ends_with_newline: false,
 406         config: context.config,
 407     };
 408     let list_str = try_opt!(write_list(&items, &fmt));
 409
 410     let result = if context.config.array_layout == IndentStyle::Visual ||
 411                     tactic != DefinitiveListTactic::Vertical {
 412         if context.config.spaces_within_square_brackets && list_str.len() > 0 {
 413             format!("[ {} ]", list_str)
 414         } else {
 415             format!("[{}]", list_str)
 416         }
 417     } else {
 418         format!("[\n{}{},\n{}]",
 419                 nested_shape.indent.to_string(context.config),
 420                 list_str,
 421                 shape.block().indent.to_string(context.config))
 422     };
 423
 424     Some(result)
 425 }
 426
 427 // This functions is pretty messy because of the rules around closures and blocks:
 428 // FIXME - the below is probably no longer true in full.
 429 //   * if there is a return type, then there must be braces,
 430 //   * given a closure with braces, whether that is parsed to give an inner block
 431 //     or not depends on if there is a return type and if there are statements
 432 //     in that block,
 433 //   * if the first expression in the body ends with a block (i.e., is a
 434 //     statement without needing a semi-colon), then adding or removing braces
 435 //     can change whether it is treated as an expression or statement.
 436 fn rewrite_closure(capture: ast::CaptureBy,
 437                    fn_decl: &ast::FnDecl,
 438                    body: &ast::Expr,
 439                    span: Span,
 440                    context: &RewriteContext,
 441                    shape: Shape)
 442                    -> Option<String> {
 443     let mover = if capture == ast::CaptureBy::Value {
 444         "move "
 445     } else {
 446         ""
 447     };
 448     // 4 = "|| {".len(), which is overconservative when the closure consists of
 449     // a single expression.
 450     let nested_shape = try_opt!(try_opt!(shape.shrink_left(mover.len())).sub_width(4));
 451
 452     // 1 = |
 453     let argument_offset = nested_shape.indent + 1;
 454     let arg_shape = try_opt!(nested_shape.shrink_left(1)).visual_indent(0);
 455     let ret_str = try_opt!(fn_decl.output.rewrite(context, arg_shape));
 456
 457     let arg_items = itemize_list(context.codemap,
 458                                  fn_decl.inputs.iter(),
 459                                  "|",
 460                                  |arg| span_lo_for_arg(arg),
 461                                  |arg| span_hi_for_arg(arg),
 462                                  |arg| arg.rewrite(context, arg_shape),
 463                                  context.codemap.span_after(span, "|"),
 464                                  body.span.lo);
 465     let item_vec = arg_items.collect::<Vec<_>>();
 466     // 1 = space between arguments and return type.
 467     let horizontal_budget = nested_shape
 468         .width
 469         .checked_sub(ret_str.len() + 1)
 470         .unwrap_or(0);
 471     let tactic = definitive_tactic(&item_vec, ListTactic::HorizontalVertical, horizontal_budget);
 472     let arg_shape = match tactic {
 473         DefinitiveListTactic::Horizontal => try_opt!(arg_shape.sub_width(ret_str.len() + 1)),
 474         _ => arg_shape,
 475     };
 476
 477     let fmt = ListFormatting {
 478         tactic: tactic,
 479         separator: ",",
 480         trailing_separator: SeparatorTactic::Never,
 481         shape: arg_shape,
 482         ends_with_newline: false,
 483         config: context.config,
 484     };
 485     let list_str = try_opt!(write_list(&item_vec, &fmt));
 486     let mut prefix = format!("{}|{}|", mover, list_str);
 487
 488     if !ret_str.is_empty() {
 489         if prefix.contains('\n') {
 490             prefix.push('\n');
 491             prefix.push_str(&argument_offset.to_string(context.config));
 492         } else {
 493             prefix.push(' ');
 494         }
 495         prefix.push_str(&ret_str);
 496     }
 497
 498     // 1 = space between `|...|` and body.
 499     let extra_offset = extra_offset(&prefix, shape) + 1;
 500     let body_shape = try_opt!(shape.sub_width(extra_offset)).add_offset(extra_offset);
 501
 502     if let ast::ExprKind::Block(ref block) = body.node {
 503         // The body of the closure is an empty block.
 504         if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
 505             return Some(format!("{} {{}}", prefix));
 506         }
 507
 508         // Figure out if the block is necessary.
 509         let needs_block = block.rules != ast::BlockCheckMode::Default ||
 510                           block.stmts.len() > 1 || context.inside_macro ||
 511                           block_contains_comment(block, context.codemap) ||
 512                           prefix.contains('\n');
 513
 514         if ret_str.is_empty() && !needs_block {
 515             // lock.stmts.len() == 1
 516             if let Some(ref expr) = stmt_expr(&block.stmts[0]) {
 517                 if let Some(rw) = rewrite_closure_expr(expr, &prefix, context, body_shape) {
 518                     return Some(rw);
 519                 }
 520             }
 521         }
 522
 523         if !needs_block {
 524             // We need braces, but we might still prefer a one-liner.
 525             let stmt = &block.stmts[0];
 526             // 4 = braces and spaces.
 527             if let Some(body_shape) = body_shape.sub_width(4) {
 528                 // Checks if rewrite succeeded and fits on a single line.
 529                 if let Some(rewrite) = and_one_line(stmt.rewrite(context, body_shape)) {
 530                     return Some(format!("{} {{ {} }}", prefix, rewrite));
 531                 }
 532             }
 533         }
 534
 535         // Either we require a block, or tried without and failed.
 536         return rewrite_closure_block(&block, prefix, context, body_shape);
 537     }
 538
 539     if let Some(rw) = rewrite_closure_expr(body, &prefix, context, body_shape) {
 540         return Some(rw);
 541     }
 542
 543     // The closure originally had a non-block expression, but we can't fit on
 544     // one line, so we'll insert a block.
 545     let block = ast::Block {
 546         stmts: vec![ast::Stmt {
 547                         id: ast::NodeId::new(0),
 548                         node: ast::StmtKind::Expr(ptr::P(body.clone())),
 549                         span: body.span,
 550                     }],
 551         id: ast::NodeId::new(0),
 552         rules: ast::BlockCheckMode::Default,
 553         span: body.span,
 554     };
 555     return rewrite_closure_block(&block, prefix, context, body_shape);
 556
 557     fn rewrite_closure_expr(expr: &ast::Expr,
 558                             prefix: &str,
 559                             context: &RewriteContext,
 560                             shape: Shape)
 561                             -> Option<String> {
 562         let mut rewrite = expr.rewrite(context, shape);
 563         if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
 564             rewrite = and_one_line(rewrite);
 565         }
 566         rewrite.map(|rw| format!("{} {}", prefix, rw))
 567     }
 568
 569     fn rewrite_closure_block(block: &ast::Block,
 570                              prefix: String,
 571                              context: &RewriteContext,
 572                              shape: Shape)
 573                              -> Option<String> {
 574         // Start with visual indent, then fall back to block indent if the
 575         // closure is large.
 576         if let Some(block_str) = block.rewrite(&context, shape) {
 577             let block_threshold = context.config.closure_block_indent_threshold;
 578             if block_threshold < 0 || block_str.matches('\n').count() <= block_threshold as usize {
 579                 if let Some(block_str) = block_str.rewrite(context, shape) {
 580                     return Some(format!("{} {}", prefix, block_str));
 581                 }
 582             }
 583         }
 584
 585         // The body of the closure is big enough to be block indented, that
 586         // means we must re-format.
 587         let block_shape = shape.block().with_max_width(context.config);
 588         let block_str = try_opt!(block.rewrite(&context, block_shape));
 589         Some(format!("{} {}",
 590                      prefix,
 591                      try_opt!(block_str.rewrite(context, block_shape))))
 592     }
 593 }
 594
 595 fn and_one_line(x: Option<String>) -> Option<String> {
 596     x.and_then(|x| if x.contains('\n') { None } else { Some(x) })
 597 }
 598
 599 fn nop_block_collapse(block_str: Option<String>, budget: usize) -> Option<String> {
 600     debug!("nop_block_collapse {:?} {}", block_str, budget);
 601     block_str.map(|block_str| if block_str.starts_with('{') && budget >= 2 &&
 602                                  (block_str[1..].find(|c: char| !c.is_whitespace()).unwrap() ==
 603                                   block_str.len() - 2) {
 604                       "{}".to_owned()
 605                   } else {
 606                       block_str.to_owned()
 607                   })
 608 }
 609
 610 impl Rewrite for ast::Block {
 611     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 612         // shape.width is used only for the single line case: either the empty block `{}`,
 613         // or an unsafe expression `unsafe { e }`.
 614
 615         if self.stmts.is_empty() && !block_contains_comment(self, context.codemap) &&
 616            shape.width >= 2 {
 617             return Some("{}".to_owned());
 618         }
 619
 620         // If a block contains only a single-line comment, then leave it on one line.
 621         let user_str = context.snippet(self.span);
 622         let user_str = user_str.trim();
 623         if user_str.starts_with('{') && user_str.ends_with('}') {
 624             let comment_str = user_str[1..user_str.len() - 1].trim();
 625             if self.stmts.is_empty() && !comment_str.contains('\n') &&
 626                !comment_str.starts_with("//") &&
 627                comment_str.len() + 4 <= shape.width {
 628                 return Some(format!("{{ {} }}", comment_str));
 629             }
 630         }
 631
 632         let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 633         visitor.block_indent = shape.indent;
 634
 635         let prefix = match self.rules {
 636             ast::BlockCheckMode::Unsafe(..) => {
 637                 let snippet = context.snippet(self.span);
 638                 let open_pos = try_opt!(snippet.find_uncommented("{"));
 639                 visitor.last_pos = self.span.lo + BytePos(open_pos as u32);
 640
 641                 // Extract comment between unsafe and block start.
 642                 let trimmed = &snippet[6..open_pos].trim();
 643
 644                 let prefix = if !trimmed.is_empty() {
 645                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 646                     let budget = try_opt!(shape.width.checked_sub(9));
 647                     format!("unsafe {} ",
 648                             try_opt!(rewrite_comment(trimmed,
 649                                                      true,
 650                                                      Shape::legacy(budget, shape.indent + 7),
 651                                                      context.config)))
 652                 } else {
 653                     "unsafe ".to_owned()
 654                 };
 655
 656                 if is_simple_block(self, context.codemap) && prefix.len() < shape.width {
 657                     let expr_str =
 658                         self.stmts[0].rewrite(context,
 659                                               Shape::legacy(shape.width - prefix.len(),
 660                                                             shape.indent));
 661                     let expr_str = try_opt!(expr_str);
 662                     let result = format!("{}{{ {} }}", prefix, expr_str);
 663                     if result.len() <= shape.width && !result.contains('\n') {
 664                         return Some(result);
 665                     }
 666                 }
 667
 668                 prefix
 669             }
 670             ast::BlockCheckMode::Default => {
 671                 visitor.last_pos = self.span.lo;
 672
 673                 String::new()
 674             }
 675         };
 676
 677         visitor.visit_block(self);
 678         if visitor.failed && shape.indent.alignment != 0 {
 679             self.rewrite(context,
 680                          Shape::indented(shape.indent.block_only(), context.config))
 681         } else {
 682             Some(format!("{}{}", prefix, visitor.buffer))
 683         }
 684     }
 685 }
 686
 687 impl Rewrite for ast::Stmt {
 688     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 689         let result = match self.node {
 690             ast::StmtKind::Local(ref local) => local.rewrite(context, shape),
 691             ast::StmtKind::Expr(ref ex) |
 692             ast::StmtKind::Semi(ref ex) => {
 693                 let suffix = if semicolon_for_stmt(self) { ";" } else { "" };
 694
 695                 format_expr(ex,
 696                             match self.node {
 697                                 ast::StmtKind::Expr(_) => ExprType::SubExpression,
 698                                 ast::StmtKind::Semi(_) => ExprType::Statement,
 699                                 _ => unreachable!(),
 700                             },
 701                             context,
 702                             try_opt!(shape.sub_width(suffix.len())))
 703                         .map(|s| s + suffix)
 704             }
 705             ast::StmtKind::Mac(..) |
 706             ast::StmtKind::Item(..) => None,
 707         };
 708         result.and_then(|res| recover_comment_removed(res, self.span, context, shape))
 709     }
 710 }
 711
 712 // Abstraction over control flow expressions
 713 #[derive(Debug)]
 714 struct ControlFlow<'a> {
 715     cond: Option<&'a ast::Expr>,
 716     block: &'a ast::Block,
 717     else_block: Option<&'a ast::Expr>,
 718     label: Option<ast::SpannedIdent>,
 719     pat: Option<&'a ast::Pat>,
 720     keyword: &'a str,
 721     matcher: &'a str,
 722     connector: &'a str,
 723     allow_single_line: bool,
 724     // True if this is an `if` expression in an `else if` :-( hacky
 725     nested_if: bool,
 726     span: Span,
 727 }
 728
 729 impl<'a> ControlFlow<'a> {
 730     fn new_if(cond: &'a ast::Expr,
 731               pat: Option<&'a ast::Pat>,
 732               block: &'a ast::Block,
 733               else_block: Option<&'a ast::Expr>,
 734               allow_single_line: bool,
 735               nested_if: bool,
 736               span: Span)
 737               -> ControlFlow<'a> {
 738         ControlFlow {
 739             cond: Some(cond),
 740             block: block,
 741             else_block: else_block,
 742             label: None,
 743             pat: pat,
 744             keyword: "if",
 745             matcher: match pat {
 746                 Some(..) => "let",
 747                 None => "",
 748             },
 749             connector: " =",
 750             allow_single_line: allow_single_line,
 751             nested_if: nested_if,
 752             span: span,
 753         }
 754     }
 755
 756     fn new_loop(block: &'a ast::Block,
 757                 label: Option<ast::SpannedIdent>,
 758                 span: Span)
 759                 -> ControlFlow<'a> {
 760         ControlFlow {
 761             cond: None,
 762             block: block,
 763             else_block: None,
 764             label: label,
 765             pat: None,
 766             keyword: "loop",
 767             matcher: "",
 768             connector: "",
 769             allow_single_line: false,
 770             nested_if: false,
 771             span: span,
 772         }
 773     }
 774
 775     fn new_while(pat: Option<&'a ast::Pat>,
 776                  cond: &'a ast::Expr,
 777                  block: &'a ast::Block,
 778                  label: Option<ast::SpannedIdent>,
 779                  span: Span)
 780                  -> ControlFlow<'a> {
 781         ControlFlow {
 782             cond: Some(cond),
 783             block: block,
 784             else_block: None,
 785             label: label,
 786             pat: pat,
 787             keyword: "while",
 788             matcher: match pat {
 789                 Some(..) => "let",
 790                 None => "",
 791             },
 792             connector: " =",
 793             allow_single_line: false,
 794             nested_if: false,
 795             span: span,
 796         }
 797     }
 798
 799     fn new_for(pat: &'a ast::Pat,
 800                cond: &'a ast::Expr,
 801                block: &'a ast::Block,
 802                label: Option<ast::SpannedIdent>,
 803                span: Span)
 804                -> ControlFlow<'a> {
 805         ControlFlow {
 806             cond: Some(cond),
 807             block: block,
 808             else_block: None,
 809             label: label,
 810             pat: Some(pat),
 811             keyword: "for",
 812             matcher: "",
 813             connector: " in",
 814             allow_single_line: false,
 815             nested_if: false,
 816             span: span,
 817         }
 818     }
 819
 820     fn rewrite_single_line(&self,
 821                            pat_expr_str: &str,
 822                            context: &RewriteContext,
 823                            width: usize)
 824                            -> Option<String> {
 825         assert!(self.allow_single_line);
 826         let else_block = try_opt!(self.else_block);
 827         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 828
 829         if let ast::ExprKind::Block(ref else_node) = else_block.node {
 830             if !is_simple_block(self.block, context.codemap) ||
 831                !is_simple_block(else_node, context.codemap) ||
 832                pat_expr_str.contains('\n') {
 833                 return None;
 834             }
 835
 836             let new_width = try_opt!(width.checked_sub(pat_expr_str.len() + fixed_cost));
 837             let expr = &self.block.stmts[0];
 838             let if_str = try_opt!(expr.rewrite(context, Shape::legacy(new_width, Indent::empty())));
 839
 840             let new_width = try_opt!(new_width.checked_sub(if_str.len()));
 841             let else_expr = &else_node.stmts[0];
 842             let else_str = try_opt!(else_expr.rewrite(context,
 843                                                       Shape::legacy(new_width, Indent::empty())));
 844
 845             if if_str.contains('\n') || else_str.contains('\n') {
 846                 return None;
 847             }
 848
 849             let result = format!("{} {} {{ {} }} else {{ {} }}",
 850                                  self.keyword,
 851                                  pat_expr_str,
 852                                  if_str,
 853                                  else_str);
 854
 855             if result.len() <= width {
 856                 return Some(result);
 857             }
 858         }
 859
 860         None
 861     }
 862 }
 863
 864 impl<'a> Rewrite for ControlFlow<'a> {
 865     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 866         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
 867         let constr_shape = if self.nested_if {
 868             // We are part of an if-elseif-else chain. Our constraints are tightened.
 869             // 7 = "} else " .len()
 870             try_opt!(shape.shrink_left(7))
 871         } else {
 872             shape
 873         };
 874
 875         let label_string = rewrite_label(self.label);
 876         // 1 = space after keyword.
 877         let add_offset = self.keyword.len() + label_string.len() + 1;
 878
 879         let pat_expr_string = match self.cond {
 880             Some(cond) => {
 881                 let mut cond_shape = match context.config.control_style {
 882                     Style::Default => try_opt!(constr_shape.shrink_left(add_offset)),
 883                     Style::Rfc => constr_shape,
 884                 };
 885                 if context.config.control_brace_style != ControlBraceStyle::AlwaysNextLine {
 886                     // 2 = " {".len()
 887                     cond_shape = try_opt!(cond_shape.sub_width(2));
 888                 }
 889
 890                 try_opt!(rewrite_pat_expr(context,
 891                                           self.pat,
 892                                           cond,
 893                                           self.matcher,
 894                                           self.connector,
 895                                           cond_shape))
 896             }
 897             None => String::new(),
 898         };
 899
 900         let force_newline_brace = context.config.control_style == Style::Rfc &&
 901                                   pat_expr_string.contains('\n');
 902
 903         // Try to format if-else on single line.
 904         if self.allow_single_line && context.config.single_line_if_else_max_width > 0 {
 905             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
 906
 907             if trial.is_some() &&
 908                trial.as_ref().unwrap().len() <= context.config.single_line_if_else_max_width {
 909                 return trial;
 910             }
 911         }
 912
 913         let used_width = if pat_expr_string.contains('\n') {
 914             last_line_width(&pat_expr_string)
 915         } else {
 916             // 2 = spaces after keyword and condition.
 917             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
 918         };
 919
 920         let block_width = shape.width.checked_sub(used_width).unwrap_or(0);
 921         // This is used only for the empty block case: `{}`. So, we use 1 if we know
 922         // we should avoid the single line case.
 923         let block_width = if self.else_block.is_some() || self.nested_if {
 924             min(1, block_width)
 925         } else {
 926             block_width
 927         };
 928
 929         let block_shape = Shape {
 930             width: block_width,
 931             ..shape
 932         };
 933         let block_str = try_opt!(self.block.rewrite(context, block_shape));
 934
 935         let cond_span = if let Some(cond) = self.cond {
 936             cond.span
 937         } else {
 938             mk_sp(self.block.span.lo, self.block.span.lo)
 939         };
 940
 941         // for event in event
 942         let between_kwd_cond =
 943             mk_sp(context.codemap.span_after(self.span, self.keyword.trim()),
 944                   self.pat
 945                       .map_or(cond_span.lo, |p| if self.matcher.is_empty() {
 946                 p.span.lo
 947             } else {
 948                 context.codemap.span_before(self.span, self.matcher.trim())
 949             }));
 950
 951         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
 952
 953         let after_cond_comment =
 954             extract_comment(mk_sp(cond_span.hi, self.block.span.lo), context, shape);
 955
 956         let alt_block_sep = String::from("\n") +
 957                             &shape.indent.block_only().to_string(context.config);
 958         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
 959             ""
 960         } else if context.config.control_brace_style == ControlBraceStyle::AlwaysNextLine ||
 961                   force_newline_brace {
 962             alt_block_sep.as_str()
 963         } else {
 964             " "
 965         };
 966
 967         let mut result = format!("{}{}{}{}{}{}",
 968                                  label_string,
 969                                  self.keyword,
 970                                  between_kwd_cond_comment
 971                                      .as_ref()
 972                                      .map_or(if pat_expr_string.is_empty() ||
 973                                                 pat_expr_string.starts_with('\n') {
 974                                                  ""
 975                                              } else {
 976                                                  " "
 977                                              },
 978                                              |s| &**s),
 979                                  pat_expr_string,
 980                                  after_cond_comment.as_ref().map_or(block_sep, |s| &**s),
 981                                  block_str);
 982
 983         if let Some(else_block) = self.else_block {
 984             let shape = Shape::indented(shape.indent, context.config);
 985             let mut last_in_chain = false;
 986             let rewrite = match else_block.node {
 987                 // If the else expression is another if-else expression, prevent it
 988                 // from being formatted on a single line.
 989                 // Note how we're passing the original shape, as the
 990                 // cost of "else" should not cascade.
 991                 ast::ExprKind::IfLet(ref pat, ref cond, ref if_block, ref next_else_block) => {
 992                     ControlFlow::new_if(cond,
 993                                         Some(pat),
 994                                         if_block,
 995                                         next_else_block.as_ref().map(|e| &**e),
 996                                         false,
 997                                         true,
 998                                         mk_sp(else_block.span.lo, self.span.hi))
 999                             .rewrite(context, shape)
1000                 }
1001                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1002                     ControlFlow::new_if(cond,
1003                                         None,
1004                                         if_block,
1005                                         next_else_block.as_ref().map(|e| &**e),
1006                                         false,
1007                                         true,
1008                                         mk_sp(else_block.span.lo, self.span.hi))
1009                             .rewrite(context, shape)
1010                 }
1011                 _ => {
1012                     last_in_chain = true;
1013                     // When rewriting a block, the width is only used for single line
1014                     // blocks, passing 1 lets us avoid that.
1015                     let else_shape = Shape {
1016                         width: min(1, shape.width),
1017                         ..shape
1018                     };
1019                     else_block.rewrite(context, else_shape)
1020                 }
1021             };
1022
1023             let between_kwd_else_block =
1024                 mk_sp(self.block.span.hi,
1025                       context
1026                           .codemap
1027                           .span_before(mk_sp(self.block.span.hi, else_block.span.lo), "else"));
1028             let between_kwd_else_block_comment =
1029                 extract_comment(between_kwd_else_block, context, shape);
1030
1031             let after_else = mk_sp(context.codemap.span_after(mk_sp(self.block.span.hi,
1032                                                                     else_block.span.lo),
1033                                                               "else"),
1034                                    else_block.span.lo);
1035             let after_else_comment = extract_comment(after_else, context, shape);
1036
1037             let between_sep = match context.config.control_brace_style {
1038                 ControlBraceStyle::AlwaysNextLine |
1039                 ControlBraceStyle::ClosingNextLine => &*alt_block_sep,
1040                 ControlBraceStyle::AlwaysSameLine => " ",
1041             };
1042             let after_sep = match context.config.control_brace_style {
1043                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1044                 _ => " ",
1045             };
1046             try_opt!(write!(&mut result,
1047                             "{}else{}",
1048                             between_kwd_else_block_comment
1049                                 .as_ref()
1050                                 .map_or(between_sep, |s| &**s),
1051                             after_else_comment.as_ref().map_or(after_sep, |s| &**s))
1052                              .ok());
1053             result.push_str(&try_opt!(rewrite));
1054         }
1055
1056         Some(result)
1057     }
1058 }
1059
1060 fn rewrite_label(label: Option<ast::SpannedIdent>) -> String {
1061     match label {
1062         Some(ident) => format!("{}: ", ident.node),
1063         None => "".to_owned(),
1064     }
1065 }
1066
1067 fn extract_comment(span: Span, context: &RewriteContext, shape: Shape) -> Option<String> {
1068     let comment_str = context.snippet(span);
1069     if contains_comment(&comment_str) {
1070         let comment = try_opt!(rewrite_comment(comment_str.trim(), false, shape, context.config));
1071         Some(format!("\n{indent}{}\n{indent}",
1072                      comment,
1073                      indent = shape.indent.to_string(context.config)))
1074     } else {
1075         None
1076     }
1077 }
1078
1079 fn block_contains_comment(block: &ast::Block, codemap: &CodeMap) -> bool {
1080     let snippet = codemap.span_to_snippet(block.span).unwrap();
1081     contains_comment(&snippet)
1082 }
1083
1084 // Checks that a block contains no statements, an expression and no comments.
1085 // FIXME: incorrectly returns false when comment is contained completely within
1086 // the expression.
1087 pub fn is_simple_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1088     (block.stmts.len() == 1 && stmt_is_expr(&block.stmts[0]) &&
1089      !block_contains_comment(block, codemap))
1090 }
1091
1092 /// Checks whether a block contains at most one statement or expression, and no comments.
1093 pub fn is_simple_block_stmt(block: &ast::Block, codemap: &CodeMap) -> bool {
1094     block.stmts.len() <= 1 && !block_contains_comment(block, codemap)
1095 }
1096
1097 /// Checks whether a block contains no statements, expressions, or comments.
1098 pub fn is_empty_block(block: &ast::Block, codemap: &CodeMap) -> bool {
1099     block.stmts.is_empty() && !block_contains_comment(block, codemap)
1100 }
1101
1102 pub fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1103     match stmt.node {
1104         ast::StmtKind::Expr(..) => true,
1105         _ => false,
1106     }
1107 }
1108
1109 fn is_unsafe_block(block: &ast::Block) -> bool {
1110     if let ast::BlockCheckMode::Unsafe(..) = block.rules {
1111         true
1112     } else {
1113         false
1114     }
1115 }
1116
1117 // inter-match-arm-comment-rules:
1118 //  - all comments following a match arm before the start of the next arm
1119 //    are about the second arm
1120 fn rewrite_match_arm_comment(context: &RewriteContext,
1121                              missed_str: &str,
1122                              shape: Shape,
1123                              arm_indent_str: &str)
1124                              -> Option<String> {
1125     // The leading "," is not part of the arm-comment
1126     let missed_str = match missed_str.find_uncommented(",") {
1127         Some(n) => &missed_str[n + 1..],
1128         None => &missed_str[..],
1129     };
1130
1131     let mut result = String::new();
1132     // any text not preceeded by a newline is pushed unmodified to the block
1133     let first_brk = missed_str.find(|c: char| c == '\n').unwrap_or(0);
1134     result.push_str(&missed_str[..first_brk]);
1135     let missed_str = &missed_str[first_brk..]; // If missed_str had one newline, it starts with it
1136
1137     let first = missed_str
1138         .find(|c: char| !c.is_whitespace())
1139         .unwrap_or(missed_str.len());
1140     if missed_str[..first].chars().filter(|c| c == &'\n').count() >= 2 {
1141         // Excessive vertical whitespace before comment should be preserved
1142         // FIXME handle vertical whitespace better
1143         result.push('\n');
1144     }
1145     let missed_str = missed_str[first..].trim();
1146     if !missed_str.is_empty() {
1147         let comment = try_opt!(rewrite_comment(&missed_str, false, shape, context.config));
1148         result.push('\n');
1149         result.push_str(arm_indent_str);
1150         result.push_str(&comment);
1151     }
1152
1153     Some(result)
1154 }
1155
1156 fn rewrite_match(context: &RewriteContext,
1157                  cond: &ast::Expr,
1158                  arms: &[ast::Arm],
1159                  shape: Shape,
1160                  span: Span)
1161                  -> Option<String> {
1162     if arms.is_empty() {
1163         return None;
1164     }
1165
1166     // `match `cond` {`
1167     let cond_shape = try_opt!(shape.shrink_left(6));
1168     let cond_shape = try_opt!(cond_shape.sub_width(2));
1169     let cond_str = try_opt!(cond.rewrite(context, cond_shape));
1170     let alt_block_sep = String::from("\n") + &shape.indent.block_only().to_string(context.config);
1171     let block_sep = match context.config.control_brace_style {
1172         ControlBraceStyle::AlwaysSameLine => " ",
1173         _ => alt_block_sep.as_str(),
1174     };
1175     let mut result = format!("match {}{}{{", cond_str, block_sep);
1176
1177     let arm_shape = if context.config.indent_match_arms {
1178         shape.block_indent(context.config.tab_spaces)
1179     } else {
1180         shape.block_indent(0)
1181     };
1182
1183     let arm_indent_str = arm_shape.indent.to_string(context.config);
1184
1185     let open_brace_pos = context
1186         .codemap
1187         .span_after(mk_sp(cond.span.hi, arm_start_pos(&arms[0])), "{");
1188
1189     for (i, arm) in arms.iter().enumerate() {
1190         // Make sure we get the stuff between arms.
1191         let missed_str = if i == 0 {
1192             context.snippet(mk_sp(open_brace_pos, arm_start_pos(arm)))
1193         } else {
1194             context.snippet(mk_sp(arm_end_pos(&arms[i - 1]), arm_start_pos(arm)))
1195         };
1196         let comment =
1197             try_opt!(rewrite_match_arm_comment(context, &missed_str, arm_shape, &arm_indent_str));
1198         result.push_str(&comment);
1199         result.push('\n');
1200         result.push_str(&arm_indent_str);
1201
1202         let arm_str = arm.rewrite(&context, arm_shape.with_max_width(context.config));
1203         if let Some(ref arm_str) = arm_str {
1204             result.push_str(arm_str);
1205         } else {
1206             // We couldn't format the arm, just reproduce the source.
1207             let snippet = context.snippet(mk_sp(arm_start_pos(arm), arm_end_pos(arm)));
1208             result.push_str(&snippet);
1209             result.push_str(arm_comma(context.config, &arm.body));
1210         }
1211     }
1212     // BytePos(1) = closing match brace.
1213     let last_span = mk_sp(arm_end_pos(&arms[arms.len() - 1]), span.hi - BytePos(1));
1214     let last_comment = context.snippet(last_span);
1215     let comment =
1216         try_opt!(rewrite_match_arm_comment(context, &last_comment, arm_shape, &arm_indent_str));
1217     result.push_str(&comment);
1218     result.push('\n');
1219     result.push_str(&shape.indent.to_string(context.config));
1220     result.push('}');
1221     Some(result)
1222 }
1223
1224 fn arm_start_pos(arm: &ast::Arm) -> BytePos {
1225     let &ast::Arm {
1226         ref attrs,
1227         ref pats,
1228         ..
1229     } = arm;
1230     if !attrs.is_empty() {
1231         return attrs[0].span.lo;
1232     }
1233
1234     pats[0].span.lo
1235 }
1236
1237 fn arm_end_pos(arm: &ast::Arm) -> BytePos {
1238     arm.body.span.hi
1239 }
1240
1241 fn arm_comma(config: &Config, body: &ast::Expr) -> &'static str {
1242     if config.match_block_trailing_comma {
1243         ","
1244     } else if let ast::ExprKind::Block(ref block) = body.node {
1245         if let ast::BlockCheckMode::Default = block.rules {
1246             ""
1247         } else {
1248             ","
1249         }
1250     } else {
1251         ","
1252     }
1253 }
1254
1255 // Match arms.
1256 impl Rewrite for ast::Arm {
1257     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1258         debug!("Arm::rewrite {:?} {:?}", self, shape);
1259         let &ast::Arm {
1260             ref attrs,
1261             ref pats,
1262             ref guard,
1263             ref body,
1264         } = self;
1265
1266         // FIXME this is all a bit grotty, would be nice to abstract out the
1267         // treatment of attributes.
1268         let attr_str = if !attrs.is_empty() {
1269             // We only use this visitor for the attributes, should we use it for
1270             // more?
1271             let mut attr_visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
1272             attr_visitor.block_indent = shape.indent.block_only();
1273             attr_visitor.last_pos = attrs[0].span.lo;
1274             if attr_visitor.visit_attrs(attrs) {
1275                 // Attributes included a skip instruction.
1276                 return None;
1277             }
1278             attr_visitor.format_missing(pats[0].span.lo);
1279             attr_visitor.buffer.to_string()
1280         } else {
1281             String::new()
1282         };
1283
1284         // Patterns
1285         // 5 = ` => {`
1286         let pat_shape = try_opt!(shape.sub_width(5));
1287
1288         let pat_strs = try_opt!(pats.iter()
1289                                     .map(|p| p.rewrite(context, pat_shape))
1290                                     .collect::<Option<Vec<_>>>());
1291
1292         let all_simple = pat_strs.iter().all(|p| pat_is_simple(p));
1293         let items: Vec<_> = pat_strs.into_iter().map(ListItem::from_str).collect();
1294         let fmt = ListFormatting {
1295             tactic: if all_simple {
1296                 DefinitiveListTactic::Mixed
1297             } else {
1298                 DefinitiveListTactic::Vertical
1299             },
1300             separator: " |",
1301             trailing_separator: SeparatorTactic::Never,
1302             shape: pat_shape,
1303             ends_with_newline: false,
1304             config: context.config,
1305         };
1306         let pats_str = try_opt!(write_list(items, &fmt));
1307
1308         let guard_shape = if pats_str.contains('\n') {
1309             shape.with_max_width(context.config)
1310         } else {
1311             shape
1312         };
1313
1314         let guard_str = try_opt!(rewrite_guard(context,
1315                                                guard,
1316                                                guard_shape,
1317                                                trimmed_last_line_width(&pats_str)));
1318
1319         let pats_str = format!("{}{}", pats_str, guard_str);
1320
1321         let body = match body.node {
1322             ast::ExprKind::Block(ref block) if !is_unsafe_block(block) &&
1323                                                is_simple_block(block, context.codemap) &&
1324                                                context.config.wrap_match_arms => {
1325                 if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
1326                     expr
1327                 } else {
1328                     &**body
1329                 }
1330             }
1331             _ => &**body,
1332         };
1333
1334         let comma = arm_comma(&context.config, body);
1335         let alt_block_sep = String::from("\n") +
1336                             &shape.indent.block_only().to_string(context.config);
1337
1338         let pat_width = extra_offset(&pats_str, shape);
1339         // Let's try and get the arm body on the same line as the condition.
1340         // 4 = ` => `.len()
1341         if shape.width > pat_width + comma.len() + 4 {
1342             let arm_shape = shape
1343                 .offset_left(pat_width + 4)
1344                 .unwrap()
1345                 .sub_width(comma.len())
1346                 .unwrap();
1347             let rewrite = nop_block_collapse(body.rewrite(context, arm_shape), arm_shape.width);
1348             let is_block = if let ast::ExprKind::Block(..) = body.node {
1349                 true
1350             } else {
1351                 false
1352             };
1353
1354             match rewrite {
1355                 Some(ref body_str) if (!body_str.contains('\n') &&
1356                                        body_str.len() <= arm_shape.width) ||
1357                                       !context.config.wrap_match_arms ||
1358                                       is_block => {
1359                     let block_sep = match context.config.control_brace_style {
1360                         ControlBraceStyle::AlwaysNextLine if is_block => alt_block_sep.as_str(),
1361                         _ => " ",
1362                     };
1363
1364                     return Some(format!("{}{} =>{}{}{}",
1365                                         attr_str.trim_left(),
1366                                         pats_str,
1367                                         block_sep,
1368                                         body_str,
1369                                         comma));
1370                 }
1371                 _ => {}
1372             }
1373         }
1374
1375         // FIXME: we're doing a second rewrite of the expr; This may not be
1376         // necessary.
1377         let body_shape = try_opt!(shape.sub_width(context.config.tab_spaces))
1378             .block_indent(context.config.tab_spaces);
1379         let next_line_body = try_opt!(nop_block_collapse(body.rewrite(context, body_shape),
1380                                                          body_shape.width));
1381         let indent_str = shape
1382             .indent
1383             .block_indent(context.config)
1384             .to_string(context.config);
1385         let (body_prefix, body_suffix) = if context.config.wrap_match_arms {
1386             if context.config.match_block_trailing_comma {
1387                 ("{", "},")
1388             } else {
1389                 ("{", "}")
1390             }
1391         } else {
1392             ("", ",")
1393         };
1394
1395
1396         let block_sep = match context.config.control_brace_style {
1397             ControlBraceStyle::AlwaysNextLine => alt_block_sep + body_prefix + "\n",
1398             _ if body_prefix.is_empty() => "\n".to_owned(),
1399             _ => " ".to_owned() + body_prefix + "\n",
1400         };
1401
1402         if context.config.wrap_match_arms {
1403             Some(format!("{}{} =>{}{}{}\n{}{}",
1404                          attr_str.trim_left(),
1405                          pats_str,
1406                          block_sep,
1407                          indent_str,
1408                          next_line_body,
1409                          shape.indent.to_string(context.config),
1410                          body_suffix))
1411         } else {
1412             Some(format!("{}{} =>{}{}{}{}",
1413                          attr_str.trim_left(),
1414                          pats_str,
1415                          block_sep,
1416                          indent_str,
1417                          next_line_body,
1418                          body_suffix))
1419         }
1420     }
1421 }
1422
1423 // A pattern is simple if it is very short or it is short-ish and just a path.
1424 // E.g. `Foo::Bar` is simple, but `Foo(..)` is not.
1425 fn pat_is_simple(pat_str: &str) -> bool {
1426     pat_str.len() <= 16 ||
1427     (pat_str.len() <= 24 && pat_str.chars().all(|c| c.is_alphabetic() || c == ':'))
1428 }
1429
1430 // The `if ...` guard on a match arm.
1431 fn rewrite_guard(context: &RewriteContext,
1432                  guard: &Option<ptr::P<ast::Expr>>,
1433                  shape: Shape,
1434                  // The amount of space used up on this line for the pattern in
1435                  // the arm (excludes offset).
1436                  pattern_width: usize)
1437                  -> Option<String> {
1438     if let Some(ref guard) = *guard {
1439         // First try to fit the guard string on the same line as the pattern.
1440         // 4 = ` if `, 5 = ` => {`
1441         let overhead = pattern_width + 4 + 5;
1442         if overhead < shape.width {
1443             let cond_shape = shape
1444                 .shrink_left(pattern_width + 4)
1445                 .unwrap()
1446                 .sub_width(5)
1447                 .unwrap();
1448             let cond_str = guard.rewrite(context, cond_shape);
1449             if let Some(cond_str) = cond_str {
1450                 return Some(format!(" if {}", cond_str));
1451             }
1452         }
1453
1454         // Not enough space to put the guard after the pattern, try a newline.
1455         let overhead = shape.indent.block_indent(context.config).width() + 4 + 5;
1456         if overhead < shape.width {
1457             let cond_str = guard.rewrite(context,
1458                                          Shape::legacy(shape.width - overhead,
1459                                                        // 3 == `if `
1460                                                        shape.indent.block_indent(context.config) +
1461                                                        3));
1462             if let Some(cond_str) = cond_str {
1463                 return Some(format!("\n{}if {}",
1464                                     shape
1465                                         .indent
1466                                         .block_indent(context.config)
1467                                         .to_string(context.config),
1468                                     cond_str));
1469             }
1470         }
1471
1472         None
1473     } else {
1474         Some(String::new())
1475     }
1476 }
1477
1478 fn rewrite_pat_expr(context: &RewriteContext,
1479                     pat: Option<&ast::Pat>,
1480                     expr: &ast::Expr,
1481                     matcher: &str,
1482                     // Connecting piece between pattern and expression,
1483                     // *without* trailing space.
1484                     connector: &str,
1485                     shape: Shape)
1486                     -> Option<String> {
1487     debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, pat, expr);
1488     let mut pat_string = String::new();
1489     let mut result = match pat {
1490         Some(pat) => {
1491             let matcher = if matcher.is_empty() {
1492                 matcher.to_owned()
1493             } else {
1494                 format!("{} ", matcher)
1495             };
1496             let pat_shape = try_opt!(try_opt!(shape.shrink_left(matcher.len()))
1497                                          .sub_width(connector.len()));
1498             pat_string = try_opt!(pat.rewrite(context, pat_shape));
1499             format!("{}{}{}", matcher, pat_string, connector)
1500         }
1501         None => String::new(),
1502     };
1503
1504     // Consider only the last line of the pat string.
1505     let extra_offset = extra_offset(&result, shape);
1506
1507     // The expression may (partially) fit on the current line.
1508     if shape.width > extra_offset + 1 {
1509         let spacer = if pat.is_some() { " " } else { "" };
1510
1511         let expr_shape = try_opt!(shape.offset_left(extra_offset + spacer.len()));
1512         let expr_rewrite = expr.rewrite(context, expr_shape);
1513
1514         if let Some(expr_string) = expr_rewrite {
1515             if pat.is_none() || pat_is_simple(&pat_string) || !expr_string.contains('\n') {
1516                 result.push_str(spacer);
1517                 result.push_str(&expr_string);
1518                 return Some(result);
1519             }
1520         }
1521     }
1522
1523     let nested_indent = shape.indent.block_only().block_indent(context.config);
1524
1525     // The expression won't fit on the current line, jump to next.
1526     result.push('\n');
1527     result.push_str(&nested_indent.to_string(context.config));
1528
1529     let expr_rewrite = expr.rewrite(&context, Shape::indented(nested_indent, context.config));
1530     result.push_str(&try_opt!(expr_rewrite));
1531
1532     Some(result)
1533 }
1534
1535 fn rewrite_string_lit(context: &RewriteContext, span: Span, shape: Shape) -> Option<String> {
1536     let string_lit = context.snippet(span);
1537
1538     if !context.config.format_strings && !context.config.force_format_strings {
1539         return Some(string_lit);
1540     }
1541
1542     if !context.config.force_format_strings &&
1543        !string_requires_rewrite(context, span, &string_lit, shape) {
1544         return Some(string_lit);
1545     }
1546
1547     let fmt = StringFormat {
1548         opener: "\"",
1549         closer: "\"",
1550         line_start: " ",
1551         line_end: "\\",
1552         shape: shape,
1553         trim_end: false,
1554         config: context.config,
1555     };
1556
1557     // Remove the quote characters.
1558     let str_lit = &string_lit[1..string_lit.len() - 1];
1559
1560     rewrite_string(str_lit, &fmt)
1561 }
1562
1563 fn string_requires_rewrite(context: &RewriteContext,
1564                            span: Span,
1565                            string: &str,
1566                            shape: Shape)
1567                            -> bool {
1568     if context.codemap.lookup_char_pos(span.lo).col.0 != shape.indent.width() {
1569         return true;
1570     }
1571
1572     for (i, line) in string.lines().enumerate() {
1573         if i == 0 {
1574             if line.len() > shape.width {
1575                 return true;
1576             }
1577         } else {
1578             if line.len() > shape.width + shape.indent.width() {
1579                 return true;
1580             }
1581         }
1582     }
1583
1584     false
1585 }
1586
1587 pub fn rewrite_call<R>(context: &RewriteContext,
1588                        callee: &R,
1589                        args: &[ptr::P<ast::Expr>],
1590                        span: Span,
1591                        shape: Shape)
1592                        -> Option<String>
1593     where R: Rewrite
1594 {
1595     let closure =
1596         |callee_max_width| rewrite_call_inner(context, callee, callee_max_width, args, span, shape);
1597
1598     // 2 is for parens
1599     let max_width = try_opt!(shape.width.checked_sub(2));
1600     binary_search(1, max_width, closure)
1601 }
1602
1603 fn rewrite_call_inner<R>(context: &RewriteContext,
1604                          callee: &R,
1605                          max_callee_width: usize,
1606                          args: &[ptr::P<ast::Expr>],
1607                          span: Span,
1608                          shape: Shape)
1609                          -> Result<String, Ordering>
1610     where R: Rewrite
1611 {
1612     // FIXME using byte lens instead of char lens (and probably all over the
1613     // place too)
1614     let callee_shape = Shape {
1615         width: max_callee_width,
1616         ..shape
1617     };
1618     let callee_str = callee
1619         .rewrite(context, callee_shape)
1620         .ok_or(Ordering::Greater)?;
1621
1622     // 4 = `(  )`, 2 = `()`
1623     let paren_overhead = if context.config.spaces_within_parens {
1624         4
1625     } else {
1626         2
1627     };
1628     let used_width = extra_offset(&callee_str, shape);
1629     let one_line_width = shape
1630         .width
1631         .checked_sub(used_width + paren_overhead)
1632         .ok_or(Ordering::Greater)?;
1633
1634     let nested_shape = match context.config.fn_call_style {
1635             IndentStyle::Block => shape.block().block_left(context.config.tab_spaces),
1636             // 1 = (
1637             IndentStyle::Visual => {
1638                 shape
1639                     .visual_indent(used_width + 1)
1640                     .sub_width(used_width + paren_overhead)
1641             }
1642         }
1643         .ok_or(Ordering::Greater)?;
1644
1645     let span_lo = context.codemap.span_after(span, "(");
1646     let span = mk_sp(span_lo, span.hi);
1647
1648     let list_str = rewrite_call_args(context, args, span, nested_shape, one_line_width)
1649         .ok_or(Ordering::Less)?;
1650
1651     let result = if context.config.fn_call_style == IndentStyle::Visual ||
1652                     (!list_str.contains('\n') && list_str.chars().last().unwrap_or(' ') != ',') {
1653         if context.config.spaces_within_parens && list_str.len() > 0 {
1654             format!("{}( {} )", callee_str, list_str)
1655         } else {
1656             format!("{}({})", callee_str, list_str)
1657         }
1658     } else {
1659         format!("{}(\n{}{}\n{})",
1660                 callee_str,
1661                 nested_shape.indent.to_string(context.config),
1662                 list_str,
1663                 shape.block().indent.to_string(context.config))
1664     };
1665
1666     Ok(result)
1667 }
1668
1669 fn rewrite_call_args(context: &RewriteContext,
1670                      args: &[ptr::P<ast::Expr>],
1671                      span: Span,
1672                      shape: Shape,
1673                      one_line_width: usize)
1674                      -> Option<String> {
1675     let arg_count = args.len();
1676
1677     let items = itemize_list(context.codemap,
1678                              args.iter(),
1679                              ")",
1680                              |item| item.span.lo,
1681                              |item| item.span.hi,
1682                              |item| item.rewrite(context, shape),
1683                              span.lo,
1684                              span.hi);
1685     let mut item_vec: Vec<_> = items.collect();
1686
1687     // Try letting the last argument overflow to the next line with block
1688     // indentation. If its first line fits on one line with the other arguments,
1689     // we format the function arguments horizontally.
1690     let overflow_last = match args.last().map(|x| &x.node) {
1691         Some(&ast::ExprKind::Closure(..)) |
1692         Some(&ast::ExprKind::Block(..)) |
1693         Some(&ast::ExprKind::Match(..)) if arg_count > 1 => true,
1694         _ => false,
1695     };
1696
1697     let mut orig_last = None;
1698     let mut placeholder = None;
1699
1700     // Replace the last item with its first line to see if it fits with
1701     // first arguments.
1702     if overflow_last {
1703         let nested_shape = Shape {
1704             indent: shape.indent.block_only(),
1705             ..shape
1706         };
1707         let rewrite = args.last().unwrap().rewrite(context, nested_shape);
1708
1709         if let Some(rewrite) = rewrite {
1710             let rewrite_first_line = Some(rewrite[..first_line_width(&rewrite)].to_owned());
1711             placeholder = Some(rewrite);
1712
1713             swap(&mut item_vec[arg_count - 1].item, &mut orig_last);
1714             item_vec[arg_count - 1].item = rewrite_first_line;
1715         }
1716     }
1717
1718     let one_line_shape = Shape {
1719         width: one_line_width,
1720         ..shape
1721     };
1722
1723     let tactic =
1724         definitive_tactic(&item_vec,
1725                           ListTactic::LimitedHorizontalVertical(context.config.fn_call_width),
1726                           one_line_width);
1727
1728     // Replace the stub with the full overflowing last argument if the rewrite
1729     // succeeded and its first line fits with the other arguments.
1730     match (overflow_last, tactic, placeholder) {
1731         (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
1732             item_vec[arg_count - 1].item = placeholder;
1733         }
1734         (true, _, _) => {
1735             item_vec[arg_count - 1].item = orig_last;
1736         }
1737         (false, _, _) => {}
1738     }
1739
1740     let mut fmt = ListFormatting {
1741         tactic: tactic,
1742         separator: ",",
1743         trailing_separator: if context.inside_macro ||
1744                                context.config.fn_call_style == IndentStyle::Visual ||
1745                                arg_count <= 1 {
1746             SeparatorTactic::Never
1747         } else {
1748             context.config.trailing_comma
1749         },
1750         shape: one_line_shape,
1751         ends_with_newline: false,
1752         config: context.config,
1753     };
1754
1755     match write_list(&item_vec, &fmt) {
1756         // If arguments do not fit in a single line and do not contain newline,
1757         // try to put it on the next line. Try this only when we are in block mode
1758         // and not rewriting macro.
1759         Some(ref s) if context.config.fn_call_style == IndentStyle::Block &&
1760                        !context.inside_macro &&
1761                        (!s.contains('\n') &&
1762                         (s.len() > one_line_width || s.len() > context.config.fn_call_width)) => {
1763             fmt.trailing_separator = SeparatorTactic::Vertical;
1764             write_list(&item_vec, &fmt)
1765         }
1766         rewrite @ _ => rewrite,
1767     }
1768 }
1769
1770 fn rewrite_paren(context: &RewriteContext, subexpr: &ast::Expr, shape: Shape) -> Option<String> {
1771     debug!("rewrite_paren, shape: {:?}", shape);
1772     // 1 is for opening paren, 2 is for opening+closing, we want to keep the closing
1773     // paren on the same line as the subexpr.
1774     let sub_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
1775     let subexpr_str = subexpr.rewrite(context, sub_shape);
1776     debug!("rewrite_paren, subexpr_str: `{:?}`", subexpr_str);
1777
1778     subexpr_str.map(|s| if context.config.spaces_within_parens && s.len() > 0 {
1779                         format!("( {} )", s)
1780                     } else {
1781                         format!("({})", s)
1782                     })
1783 }
1784
1785 fn rewrite_index(expr: &ast::Expr,
1786                  index: &ast::Expr,
1787                  context: &RewriteContext,
1788                  shape: Shape)
1789                  -> Option<String> {
1790     let expr_str = try_opt!(expr.rewrite(context, shape));
1791
1792     let (lbr, rbr) = if context.config.spaces_within_square_brackets {
1793         ("[ ", " ]")
1794     } else {
1795         ("[", "]")
1796     };
1797
1798     let budget = shape
1799         .width
1800         .checked_sub(expr_str.len() + lbr.len() + rbr.len())
1801         .unwrap_or(0);
1802     let index_str = index.rewrite(context, Shape::legacy(budget, shape.indent));
1803     if let Some(index_str) = index_str {
1804         return Some(format!("{}{}{}{}", expr_str, lbr, index_str, rbr));
1805     }
1806
1807     let indent = shape.indent.block_indent(&context.config);
1808     let indent = indent.to_string(&context.config);
1809     // FIXME this is not right, since we don't take into account that shape.width
1810     // might be reduced from max_width by something on the right.
1811     let budget = try_opt!(context
1812                               .config
1813                               .max_width
1814                               .checked_sub(indent.len() + lbr.len() + rbr.len()));
1815     let index_str = try_opt!(index.rewrite(context, Shape::legacy(budget, shape.indent)));
1816     Some(format!("{}\n{}{}{}{}", expr_str, indent, lbr, index_str, rbr))
1817 }
1818
1819 fn rewrite_struct_lit<'a>(context: &RewriteContext,
1820                           path: &ast::Path,
1821                           fields: &'a [ast::Field],
1822                           base: Option<&'a ast::Expr>,
1823                           span: Span,
1824                           shape: Shape)
1825                           -> Option<String> {
1826     debug!("rewrite_struct_lit: shape {:?}", shape);
1827
1828     enum StructLitField<'a> {
1829         Regular(&'a ast::Field),
1830         Base(&'a ast::Expr),
1831     }
1832
1833     // 2 = " {".len()
1834     let path_shape = try_opt!(shape.sub_width(2));
1835     let path_str = try_opt!(rewrite_path(context, PathContext::Expr, None, path, path_shape));
1836
1837     if fields.len() == 0 && base.is_none() {
1838         return Some(format!("{} {{}}", path_str));
1839     }
1840
1841     let field_iter = fields
1842         .into_iter()
1843         .map(StructLitField::Regular)
1844         .chain(base.into_iter().map(StructLitField::Base));
1845
1846     // Foo { a: Foo } - indent is +3, width is -5.
1847     let (h_shape, v_shape) = try_opt!(struct_lit_shape(shape, context, path_str.len() + 3, 2));
1848
1849     let span_lo = |item: &StructLitField| match *item {
1850         StructLitField::Regular(field) => field.span.lo,
1851         StructLitField::Base(expr) => {
1852             let last_field_hi = fields.last().map_or(span.lo, |field| field.span.hi);
1853             let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo));
1854             let pos = snippet.find_uncommented("..").unwrap();
1855             last_field_hi + BytePos(pos as u32)
1856         }
1857     };
1858     let span_hi = |item: &StructLitField| match *item {
1859         StructLitField::Regular(field) => field.span.hi,
1860         StructLitField::Base(expr) => expr.span.hi,
1861     };
1862     let rewrite = |item: &StructLitField| match *item {
1863         StructLitField::Regular(field) => {
1864             // The 1 taken from the v_budget is for the comma.
1865             rewrite_field(context, field, try_opt!(v_shape.sub_width(1)))
1866         }
1867         StructLitField::Base(expr) => {
1868             // 2 = ..
1869             expr.rewrite(context, try_opt!(v_shape.shrink_left(2)))
1870                 .map(|s| format!("..{}", s))
1871         }
1872     };
1873
1874     let items = itemize_list(context.codemap,
1875                              field_iter,
1876                              "}",
1877                              span_lo,
1878                              span_hi,
1879                              rewrite,
1880                              context.codemap.span_after(span, "{"),
1881                              span.hi);
1882     let item_vec = items.collect::<Vec<_>>();
1883
1884     let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1885     let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1886     let fmt = struct_lit_formatting(nested_shape, tactic, context, base.is_some());
1887
1888     let fields_str = try_opt!(write_list(&item_vec, &fmt));
1889     let fields_str = if context.config.struct_lit_style == IndentStyle::Block &&
1890                         (fields_str.contains('\n') ||
1891                          context.config.struct_lit_multiline_style == MultilineStyle::ForceMulti ||
1892                          fields_str.len() > h_shape.map(|s| s.width).unwrap_or(0)) {
1893         format!("\n{}{}\n{}",
1894                 v_shape.indent.to_string(context.config),
1895                 fields_str,
1896                 shape.indent.to_string(context.config))
1897     } else {
1898         // One liner or visual indent.
1899         format!(" {} ", fields_str)
1900     };
1901
1902     Some(format!("{} {{{}}}", path_str, fields_str))
1903
1904     // FIXME if context.config.struct_lit_style == Visual, but we run out
1905     // of space, we should fall back to BlockIndent.
1906 }
1907
1908 pub fn type_annotation_separator(config: &Config) -> &str {
1909     colon_spaces(config.space_before_type_annotation,
1910                  config.space_after_type_annotation_colon)
1911 }
1912
1913 fn rewrite_field(context: &RewriteContext, field: &ast::Field, shape: Shape) -> Option<String> {
1914     let name = &field.ident.node.to_string();
1915     if field.is_shorthand {
1916         Some(name.to_string())
1917     } else {
1918         let separator = type_annotation_separator(context.config);
1919         let overhead = name.len() + separator.len();
1920         let mut expr_shape = try_opt!(shape.sub_width(overhead));
1921         expr_shape.offset += overhead;
1922         let expr = field.expr.rewrite(context, expr_shape);
1923
1924         let mut attrs_str = try_opt!((*field.attrs).rewrite(context, shape));
1925         if !attrs_str.is_empty() {
1926             attrs_str.push_str(&format!("\n{}", shape.indent.to_string(context.config)));
1927         };
1928
1929         match expr {
1930             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1931             None => {
1932                 let expr_offset = shape.indent.block_indent(context.config);
1933                 let expr = field
1934                     .expr
1935                     .rewrite(context, Shape::indented(expr_offset, context.config));
1936                 expr.map(|s| {
1937                              format!("{}{}:\n{}{}",
1938                                      attrs_str,
1939                                      name,
1940                                      expr_offset.to_string(&context.config),
1941                                      s)
1942                          })
1943             }
1944         }
1945     }
1946 }
1947
1948 pub fn rewrite_tuple<'a, I>(context: &RewriteContext,
1949                             mut items: I,
1950                             span: Span,
1951                             shape: Shape)
1952                             -> Option<String>
1953     where I: ExactSizeIterator,
1954           <I as Iterator>::Item: Deref,
1955           <I::Item as Deref>::Target: Rewrite + Spanned + 'a
1956 {
1957     debug!("rewrite_tuple {:?}", shape);
1958     // In case of length 1, need a trailing comma
1959     if items.len() == 1 {
1960         // 3 = "(" + ",)"
1961         let nested_shape = try_opt!(shape.sub_width(3)).visual_indent(1);
1962         return items
1963             .next()
1964             .unwrap()
1965             .rewrite(context, nested_shape)
1966             .map(|s| if context.config.spaces_within_parens {
1967                      format!("( {}, )", s)
1968                  } else {
1969                      format!("({},)", s)
1970                  });
1971     }
1972
1973     let list_lo = context.codemap.span_after(span, "(");
1974     let nested_shape = try_opt!(shape.sub_width(2)).visual_indent(1);
1975     let items = itemize_list(context.codemap,
1976                              items,
1977                              ")",
1978                              |item| item.span().lo,
1979                              |item| item.span().hi,
1980                              |item| item.rewrite(context, nested_shape),
1981                              list_lo,
1982                              span.hi - BytePos(1));
1983     let list_str = try_opt!(format_item_list(items, nested_shape, context.config));
1984
1985     if context.config.spaces_within_parens && list_str.len() > 0 {
1986         Some(format!("( {} )", list_str))
1987     } else {
1988         Some(format!("({})", list_str))
1989     }
1990 }
1991
1992 pub fn rewrite_unary_prefix<R: Rewrite>(context: &RewriteContext,
1993                                         prefix: &str,
1994                                         rewrite: &R,
1995                                         shape: Shape)
1996                                         -> Option<String> {
1997     rewrite
1998         .rewrite(context, try_opt!(shape.offset_left(prefix.len())))
1999         .map(|r| format!("{}{}", prefix, r))
2000 }
2001
2002 // FIXME: this is probably not correct for multi-line Rewrites. we should
2003 // subtract suffix.len() from the last line budget, not the first!
2004 pub fn rewrite_unary_suffix<R: Rewrite>(context: &RewriteContext,
2005                                         suffix: &str,
2006                                         rewrite: &R,
2007                                         shape: Shape)
2008                                         -> Option<String> {
2009     rewrite
2010         .rewrite(context, try_opt!(shape.sub_width(suffix.len())))
2011         .map(|mut r| {
2012                  r.push_str(suffix);
2013                  r
2014              })
2015 }
2016
2017 fn rewrite_unary_op(context: &RewriteContext,
2018                     op: &ast::UnOp,
2019                     expr: &ast::Expr,
2020                     shape: Shape)
2021                     -> Option<String> {
2022     // For some reason, an UnOp is not spanned like BinOp!
2023     let operator_str = match *op {
2024         ast::UnOp::Deref => "*",
2025         ast::UnOp::Not => "!",
2026         ast::UnOp::Neg => "-",
2027     };
2028     rewrite_unary_prefix(context, operator_str, expr, shape)
2029 }
2030
2031 fn rewrite_assignment(context: &RewriteContext,
2032                       lhs: &ast::Expr,
2033                       rhs: &ast::Expr,
2034                       op: Option<&ast::BinOp>,
2035                       shape: Shape)
2036                       -> Option<String> {
2037     let operator_str = match op {
2038         Some(op) => context.snippet(op.span),
2039         None => "=".to_owned(),
2040     };
2041
2042     // 1 = space between lhs and operator.
2043     let lhs_shape = try_opt!(shape.sub_width(operator_str.len() + 1));
2044     let lhs_str = format!("{} {}",
2045                           try_opt!(lhs.rewrite(context, lhs_shape)),
2046                           operator_str);
2047
2048     rewrite_assign_rhs(context, lhs_str, rhs, shape)
2049 }
2050
2051 // The left hand side must contain everything up to, and including, the
2052 // assignment operator.
2053 pub fn rewrite_assign_rhs<S: Into<String>>(context: &RewriteContext,
2054                                            lhs: S,
2055                                            ex: &ast::Expr,
2056                                            shape: Shape)
2057                                            -> Option<String> {
2058     let mut result = lhs.into();
2059     let last_line_width = last_line_width(&result) -
2060                           if result.contains('\n') {
2061                               shape.indent.width()
2062                           } else {
2063                               0
2064                           };
2065     // 1 = space between operator and rhs.
2066     let max_width = try_opt!(shape.width.checked_sub(last_line_width + 1));
2067     let rhs = ex.rewrite(context,
2068                          Shape::offset(max_width,
2069                                        shape.indent,
2070                                        shape.indent.alignment + last_line_width + 1));
2071
2072     fn count_line_breaks(src: &str) -> usize {
2073         src.chars().filter(|&x| x == '\n').count()
2074     }
2075
2076     match rhs {
2077         Some(ref new_str) if count_line_breaks(new_str) < 2 => {
2078             result.push(' ');
2079             result.push_str(new_str);
2080         }
2081         _ => {
2082             // Expression did not fit on the same line as the identifier or is
2083             // at least three lines big. Try splitting the line and see
2084             // if that works better.
2085             let new_offset = shape.indent.block_indent(context.config);
2086             let max_width = try_opt!((shape.width + shape.indent.width())
2087                                          .checked_sub(new_offset.width()));
2088             let new_shape = Shape::legacy(max_width, new_offset);
2089             let new_rhs = ex.rewrite(context, new_shape);
2090
2091             // FIXME: DRY!
2092             match (rhs, new_rhs) {
2093                 (Some(ref orig_rhs), Some(ref replacement_rhs))
2094                     if count_line_breaks(orig_rhs) > count_line_breaks(replacement_rhs) + 1 ||
2095                        (orig_rhs.rewrite(context, shape).is_none() &&
2096                         replacement_rhs.rewrite(context, new_shape).is_some()) => {
2097                     result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
2098                     result.push_str(replacement_rhs);
2099                 }
2100                 (None, Some(ref final_rhs)) => {
2101                     result.push_str(&format!("\n{}", new_offset.to_string(context.config)));
2102                     result.push_str(final_rhs);
2103                 }
2104                 (None, None) => return None,
2105                 (Some(ref orig_rhs), _) => {
2106                     result.push(' ');
2107                     result.push_str(orig_rhs);
2108                 }
2109             }
2110         }
2111     }
2112
2113     Some(result)
2114 }
2115
2116 fn rewrite_expr_addrof(context: &RewriteContext,
2117                        mutability: ast::Mutability,
2118                        expr: &ast::Expr,
2119                        shape: Shape)
2120                        -> Option<String> {
2121     let operator_str = match mutability {
2122         ast::Mutability::Immutable => "&",
2123         ast::Mutability::Mutable => "&mut ",
2124     };
2125     rewrite_unary_prefix(context, operator_str, expr, shape)
2126 }