src/tools/rustfmt/src/expr.rs

   1 use std::borrow::Cow;
   2 use std::cmp::min;
   3
   4 use itertools::Itertools;
   5 use rustc_ast::token::{DelimToken, LitKind};
   6 use rustc_ast::{ast, ptr};
   7 use rustc_span::{BytePos, Span};
   8
   9 use crate::chains::rewrite_chain;
  10 use crate::closures;
  11 use crate::comment::{
  12     combine_strs_with_missing_comments, contains_comment, recover_comment_removed, rewrite_comment,
  13     rewrite_missing_comment, CharClasses, FindUncommented,
  14 };
  15 use crate::config::lists::*;
  16 use crate::config::{Config, ControlBraceStyle, HexLiteralCase, IndentStyle, Version};
  17 use crate::lists::{
  18     definitive_tactic, itemize_list, shape_for_tactic, struct_lit_formatting, struct_lit_shape,
  19     struct_lit_tactic, write_list, ListFormatting, Separator,
  20 };
  21 use crate::macros::{rewrite_macro, MacroPosition};
  22 use crate::matches::rewrite_match;
  23 use crate::overflow::{self, IntoOverflowableItem, OverflowableItem};
  24 use crate::pairs::{rewrite_all_pairs, rewrite_pair, PairParts};
  25 use crate::rewrite::{Rewrite, RewriteContext};
  26 use crate::shape::{Indent, Shape};
  27 use crate::source_map::{LineRangeUtils, SpanUtils};
  28 use crate::spanned::Spanned;
  29 use crate::string::{rewrite_string, StringFormat};
  30 use crate::types::{rewrite_path, PathContext};
  31 use crate::utils::{
  32     colon_spaces, contains_skip, count_newlines, first_line_ends_with, inner_attributes,
  33     last_line_extendable, last_line_width, mk_sp, outer_attributes, semicolon_for_expr,
  34     unicode_str_width, wrap_str,
  35 };
  36 use crate::vertical::rewrite_with_alignment;
  37 use crate::visitor::FmtVisitor;
  38
  39 impl Rewrite for ast::Expr {
  40     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
  41         format_expr(self, ExprType::SubExpression, context, shape)
  42     }
  43 }
  44
  45 #[derive(Copy, Clone, PartialEq)]
  46 pub(crate) enum ExprType {
  47     Statement,
  48     SubExpression,
  49 }
  50
  51 pub(crate) fn format_expr(
  52     expr: &ast::Expr,
  53     expr_type: ExprType,
  54     context: &RewriteContext<'_>,
  55     shape: Shape,
  56 ) -> Option<String> {
  57     skip_out_of_file_lines_range!(context, expr.span);
  58
  59     if contains_skip(&*expr.attrs) {
  60         return Some(context.snippet(expr.span()).to_owned());
  61     }
  62     let shape = if expr_type == ExprType::Statement && semicolon_for_expr(context, expr) {
  63         shape.sub_width(1)?
  64     } else {
  65         shape
  66     };
  67
  68     let expr_rw = match expr.kind {
  69         ast::ExprKind::Array(ref expr_vec) => rewrite_array(
  70             "",
  71             expr_vec.iter(),
  72             expr.span,
  73             context,
  74             shape,
  75             choose_separator_tactic(context, expr.span),
  76             None,
  77         ),
  78         ast::ExprKind::Lit(ref l) => {
  79             if let Some(expr_rw) = rewrite_literal(context, l, shape) {
  80                 Some(expr_rw)
  81             } else {
  82                 if let LitKind::StrRaw(_) = l.token.kind {
  83                     Some(context.snippet(l.span).trim().into())
  84                 } else {
  85                     None
  86                 }
  87             }
  88         }
  89         ast::ExprKind::Call(ref callee, ref args) => {
  90             let inner_span = mk_sp(callee.span.hi(), expr.span.hi());
  91             let callee_str = callee.rewrite(context, shape)?;
  92             rewrite_call(context, &callee_str, args, inner_span, shape)
  93         }
  94         ast::ExprKind::Paren(ref subexpr) => rewrite_paren(context, subexpr, shape, expr.span),
  95         ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
  96             // FIXME: format comments between operands and operator
  97             rewrite_all_pairs(expr, shape, context).or_else(|| {
  98                 rewrite_pair(
  99                     &**lhs,
 100                     &**rhs,
 101                     PairParts::infix(&format!(" {} ", context.snippet(op.span))),
 102                     context,
 103                     shape,
 104                     context.config.binop_separator(),
 105                 )
 106             })
 107         }
 108         ast::ExprKind::Unary(op, ref subexpr) => rewrite_unary_op(context, op, subexpr, shape),
 109         ast::ExprKind::Struct(ref struct_expr) => {
 110             let ast::StructExpr {
 111                 fields, path, rest, ..
 112             } = &**struct_expr;
 113             rewrite_struct_lit(context, path, fields, rest, &expr.attrs, expr.span, shape)
 114         }
 115         ast::ExprKind::Tup(ref items) => {
 116             rewrite_tuple(context, items.iter(), expr.span, shape, items.len() == 1)
 117         }
 118         ast::ExprKind::Let(..) => None,
 119         ast::ExprKind::If(..)
 120         | ast::ExprKind::ForLoop(..)
 121         | ast::ExprKind::Loop(..)
 122         | ast::ExprKind::While(..) => to_control_flow(expr, expr_type)
 123             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 124         ast::ExprKind::ConstBlock(ref anon_const) => {
 125             Some(format!("const {}", anon_const.rewrite(context, shape)?))
 126         }
 127         ast::ExprKind::Block(ref block, opt_label) => {
 128             match expr_type {
 129                 ExprType::Statement => {
 130                     if is_unsafe_block(block) {
 131                         rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 132                     } else if let rw @ Some(_) =
 133                         rewrite_empty_block(context, block, Some(&expr.attrs), opt_label, "", shape)
 134                     {
 135                         // Rewrite block without trying to put it in a single line.
 136                         rw
 137                     } else {
 138                         let prefix = block_prefix(context, block, shape)?;
 139
 140                         rewrite_block_with_visitor(
 141                             context,
 142                             &prefix,
 143                             block,
 144                             Some(&expr.attrs),
 145                             opt_label,
 146                             shape,
 147                             true,
 148                         )
 149                     }
 150                 }
 151                 ExprType::SubExpression => {
 152                     rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 153                 }
 154             }
 155         }
 156         ast::ExprKind::Match(ref cond, ref arms) => {
 157             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 158         }
 159         ast::ExprKind::Path(ref qself, ref path) => {
 160             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 161         }
 162         ast::ExprKind::Assign(ref lhs, ref rhs, _) => {
 163             rewrite_assignment(context, lhs, rhs, None, shape)
 164         }
 165         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 166             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 167         }
 168         ast::ExprKind::Continue(ref opt_label) => {
 169             let id_str = match *opt_label {
 170                 Some(label) => format!(" {}", label.ident),
 171                 None => String::new(),
 172             };
 173             Some(format!("continue{}", id_str))
 174         }
 175         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 176             let id_str = match *opt_label {
 177                 Some(label) => format!(" {}", label.ident),
 178                 None => String::new(),
 179             };
 180
 181             if let Some(ref expr) = *opt_expr {
 182                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 183             } else {
 184                 Some(format!("break{}", id_str))
 185             }
 186         }
 187         ast::ExprKind::Yield(ref opt_expr) => {
 188             if let Some(ref expr) = *opt_expr {
 189                 rewrite_unary_prefix(context, "yield ", &**expr, shape)
 190             } else {
 191                 Some("yield".to_string())
 192             }
 193         }
 194         ast::ExprKind::Closure(capture, ref is_async, movability, ref fn_decl, ref body, _) => {
 195             closures::rewrite_closure(
 196                 capture, is_async, movability, fn_decl, body, expr.span, context, shape,
 197             )
 198         }
 199         ast::ExprKind::Try(..) | ast::ExprKind::Field(..) | ast::ExprKind::MethodCall(..) => {
 200             rewrite_chain(expr, context, shape)
 201         }
 202         ast::ExprKind::MacCall(ref mac) => {
 203             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 204                 wrap_str(
 205                     context.snippet(expr.span).to_owned(),
 206                     context.config.max_width(),
 207                     shape,
 208                 )
 209             })
 210         }
 211         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 212         ast::ExprKind::Ret(Some(ref expr)) => {
 213             rewrite_unary_prefix(context, "return ", &**expr, shape)
 214         }
 215         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 216         ast::ExprKind::AddrOf(borrow_kind, mutability, ref expr) => {
 217             rewrite_expr_addrof(context, borrow_kind, mutability, expr, shape)
 218         }
 219         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 220             &**expr,
 221             &**ty,
 222             PairParts::infix(" as "),
 223             context,
 224             shape,
 225             SeparatorPlace::Front,
 226         ),
 227         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 228             &**expr,
 229             &**ty,
 230             PairParts::infix(": "),
 231             context,
 232             shape,
 233             SeparatorPlace::Back,
 234         ),
 235         ast::ExprKind::Index(ref expr, ref index) => {
 236             rewrite_index(&**expr, &**index, context, shape)
 237         }
 238         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 239             &**expr,
 240             &*repeats.value,
 241             PairParts::new("[", "; ", "]"),
 242             context,
 243             shape,
 244             SeparatorPlace::Back,
 245         ),
 246         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 247             let delim = match limits {
 248                 ast::RangeLimits::HalfOpen => "..",
 249                 ast::RangeLimits::Closed => "..=",
 250             };
 251
 252             fn needs_space_before_range(context: &RewriteContext<'_>, lhs: &ast::Expr) -> bool {
 253                 match lhs.kind {
 254                     ast::ExprKind::Lit(ref lit) => match lit.kind {
 255                         ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) => {
 256                             context.snippet(lit.span).ends_with('.')
 257                         }
 258                         _ => false,
 259                     },
 260                     ast::ExprKind::Unary(_, ref expr) => needs_space_before_range(context, expr),
 261                     _ => false,
 262                 }
 263             }
 264
 265             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 266                 // Don't format `.. ..` into `....`, which is invalid.
 267                 //
 268                 // This check is unnecessary for `lhs`, because a range
 269                 // starting from another range needs parentheses as `(x ..) ..`
 270                 // (`x .. ..` is a range from `x` to `..`).
 271                 matches!(rhs.kind, ast::ExprKind::Range(None, _, _))
 272             }
 273
 274             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 275                 let space_if = |b: bool| if b { " " } else { "" };
 276
 277                 format!(
 278                     "{}{}{}",
 279                     lhs.map_or("", |lhs| space_if(needs_space_before_range(context, lhs))),
 280                     delim,
 281                     rhs.map_or("", |rhs| space_if(needs_space_after_range(rhs))),
 282                 )
 283             };
 284
 285             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 286                 (Some(lhs), Some(rhs)) => {
 287                     let sp_delim = if context.config.spaces_around_ranges() {
 288                         format!(" {} ", delim)
 289                     } else {
 290                         default_sp_delim(Some(lhs), Some(rhs))
 291                     };
 292                     rewrite_pair(
 293                         &*lhs,
 294                         &*rhs,
 295                         PairParts::infix(&sp_delim),
 296                         context,
 297                         shape,
 298                         context.config.binop_separator(),
 299                     )
 300                 }
 301                 (None, Some(rhs)) => {
 302                     let sp_delim = if context.config.spaces_around_ranges() {
 303                         format!("{} ", delim)
 304                     } else {
 305                         default_sp_delim(None, Some(rhs))
 306                     };
 307                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 308                 }
 309                 (Some(lhs), None) => {
 310                     let sp_delim = if context.config.spaces_around_ranges() {
 311                         format!(" {}", delim)
 312                     } else {
 313                         default_sp_delim(Some(lhs), None)
 314                     };
 315                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 316                 }
 317                 (None, None) => Some(delim.to_owned()),
 318             }
 319         }
 320         // We do not format these expressions yet, but they should still
 321         // satisfy our width restrictions.
 322         // Style Guide RFC for InlineAsm variant pending
 323         // https://github.com/rust-dev-tools/fmt-rfcs/issues/152
 324         ast::ExprKind::LlvmInlineAsm(..) | ast::ExprKind::InlineAsm(..) => {
 325             Some(context.snippet(expr.span).to_owned())
 326         }
 327         ast::ExprKind::TryBlock(ref block) => {
 328             if let rw @ Some(_) =
 329                 rewrite_single_line_block(context, "try ", block, Some(&expr.attrs), None, shape)
 330             {
 331                 rw
 332             } else {
 333                 // 9 = `try `
 334                 let budget = shape.width.saturating_sub(9);
 335                 Some(format!(
 336                     "{}{}",
 337                     "try ",
 338                     rewrite_block(
 339                         block,
 340                         Some(&expr.attrs),
 341                         None,
 342                         context,
 343                         Shape::legacy(budget, shape.indent)
 344                     )?
 345                 ))
 346             }
 347         }
 348         ast::ExprKind::Async(capture_by, _node_id, ref block) => {
 349             let mover = if capture_by == ast::CaptureBy::Value {
 350                 "move "
 351             } else {
 352                 ""
 353             };
 354             if let rw @ Some(_) = rewrite_single_line_block(
 355                 context,
 356                 format!("{}{}", "async ", mover).as_str(),
 357                 block,
 358                 Some(&expr.attrs),
 359                 None,
 360                 shape,
 361             ) {
 362                 rw
 363             } else {
 364                 // 6 = `async `
 365                 let budget = shape.width.saturating_sub(6);
 366                 Some(format!(
 367                     "{}{}{}",
 368                     "async ",
 369                     mover,
 370                     rewrite_block(
 371                         block,
 372                         Some(&expr.attrs),
 373                         None,
 374                         context,
 375                         Shape::legacy(budget, shape.indent)
 376                     )?
 377                 ))
 378             }
 379         }
 380         ast::ExprKind::Await(_) => rewrite_chain(expr, context, shape),
 381         ast::ExprKind::Underscore => Some("_".to_owned()),
 382         ast::ExprKind::Err => None,
 383     };
 384
 385     expr_rw
 386         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 387         .and_then(|expr_str| {
 388             let attrs = outer_attributes(&expr.attrs);
 389             let attrs_str = attrs.rewrite(context, shape)?;
 390             let span = mk_sp(
 391                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 392                 expr.span.lo(),
 393             );
 394             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 395         })
 396 }
 397
 398 pub(crate) fn rewrite_array<'a, T: 'a + IntoOverflowableItem<'a>>(
 399     name: &'a str,
 400     exprs: impl Iterator<Item = &'a T>,
 401     span: Span,
 402     context: &'a RewriteContext<'_>,
 403     shape: Shape,
 404     force_separator_tactic: Option<SeparatorTactic>,
 405     delim_token: Option<DelimToken>,
 406 ) -> Option<String> {
 407     overflow::rewrite_with_square_brackets(
 408         context,
 409         name,
 410         exprs,
 411         shape,
 412         span,
 413         force_separator_tactic,
 414         delim_token,
 415     )
 416 }
 417
 418 fn rewrite_empty_block(
 419     context: &RewriteContext<'_>,
 420     block: &ast::Block,
 421     attrs: Option<&[ast::Attribute]>,
 422     label: Option<ast::Label>,
 423     prefix: &str,
 424     shape: Shape,
 425 ) -> Option<String> {
 426     if block_has_statements(block) {
 427         return None;
 428     }
 429
 430     let label_str = rewrite_label(label);
 431     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 432         return None;
 433     }
 434
 435     if !block_contains_comment(context, block) && shape.width >= 2 {
 436         return Some(format!("{}{}{{}}", prefix, label_str));
 437     }
 438
 439     // If a block contains only a single-line comment, then leave it on one line.
 440     let user_str = context.snippet(block.span);
 441     let user_str = user_str.trim();
 442     if user_str.starts_with('{') && user_str.ends_with('}') {
 443         let comment_str = user_str[1..user_str.len() - 1].trim();
 444         if block.stmts.is_empty()
 445             && !comment_str.contains('\n')
 446             && !comment_str.starts_with("//")
 447             && comment_str.len() + 4 <= shape.width
 448         {
 449             return Some(format!("{}{}{{ {} }}", prefix, label_str, comment_str));
 450         }
 451     }
 452
 453     None
 454 }
 455
 456 fn block_prefix(context: &RewriteContext<'_>, block: &ast::Block, shape: Shape) -> Option<String> {
 457     Some(match block.rules {
 458         ast::BlockCheckMode::Unsafe(..) => {
 459             let snippet = context.snippet(block.span);
 460             let open_pos = snippet.find_uncommented("{")?;
 461             // Extract comment between unsafe and block start.
 462             let trimmed = &snippet[6..open_pos].trim();
 463
 464             if !trimmed.is_empty() {
 465                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 466                 let budget = shape.width.checked_sub(9)?;
 467                 format!(
 468                     "unsafe {} ",
 469                     rewrite_comment(
 470                         trimmed,
 471                         true,
 472                         Shape::legacy(budget, shape.indent + 7),
 473                         context.config,
 474                     )?
 475                 )
 476             } else {
 477                 "unsafe ".to_owned()
 478             }
 479         }
 480         ast::BlockCheckMode::Default => String::new(),
 481     })
 482 }
 483
 484 fn rewrite_single_line_block(
 485     context: &RewriteContext<'_>,
 486     prefix: &str,
 487     block: &ast::Block,
 488     attrs: Option<&[ast::Attribute]>,
 489     label: Option<ast::Label>,
 490     shape: Shape,
 491 ) -> Option<String> {
 492     if is_simple_block(context, block, attrs) {
 493         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 494         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 495         let label_str = rewrite_label(label);
 496         let result = format!("{}{}{{ {} }}", prefix, label_str, expr_str);
 497         if result.len() <= shape.width && !result.contains('\n') {
 498             return Some(result);
 499         }
 500     }
 501     None
 502 }
 503
 504 pub(crate) fn rewrite_block_with_visitor(
 505     context: &RewriteContext<'_>,
 506     prefix: &str,
 507     block: &ast::Block,
 508     attrs: Option<&[ast::Attribute]>,
 509     label: Option<ast::Label>,
 510     shape: Shape,
 511     has_braces: bool,
 512 ) -> Option<String> {
 513     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, prefix, shape) {
 514         return rw;
 515     }
 516
 517     let mut visitor = FmtVisitor::from_context(context);
 518     visitor.block_indent = shape.indent;
 519     visitor.is_if_else_block = context.is_if_else_block();
 520     match (block.rules, label) {
 521         (ast::BlockCheckMode::Unsafe(..), _) | (ast::BlockCheckMode::Default, Some(_)) => {
 522             let snippet = context.snippet(block.span);
 523             let open_pos = snippet.find_uncommented("{")?;
 524             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 525         }
 526         (ast::BlockCheckMode::Default, None) => visitor.last_pos = block.span.lo(),
 527     }
 528
 529     let inner_attrs = attrs.map(inner_attributes);
 530     let label_str = rewrite_label(label);
 531     visitor.visit_block(block, inner_attrs.as_deref(), has_braces);
 532     let visitor_context = visitor.get_context();
 533     context
 534         .skipped_range
 535         .borrow_mut()
 536         .append(&mut visitor_context.skipped_range.borrow_mut());
 537     Some(format!("{}{}{}", prefix, label_str, visitor.buffer))
 538 }
 539
 540 impl Rewrite for ast::Block {
 541     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 542         rewrite_block(self, None, None, context, shape)
 543     }
 544 }
 545
 546 fn rewrite_block(
 547     block: &ast::Block,
 548     attrs: Option<&[ast::Attribute]>,
 549     label: Option<ast::Label>,
 550     context: &RewriteContext<'_>,
 551     shape: Shape,
 552 ) -> Option<String> {
 553     let prefix = block_prefix(context, block, shape)?;
 554
 555     // shape.width is used only for the single line case: either the empty block `{}`,
 556     // or an unsafe expression `unsafe { e }`.
 557     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, &prefix, shape) {
 558         return rw;
 559     }
 560
 561     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, label, shape, true);
 562     if let Some(ref result_str) = result {
 563         if result_str.lines().count() <= 3 {
 564             if let rw @ Some(_) =
 565                 rewrite_single_line_block(context, &prefix, block, attrs, label, shape)
 566             {
 567                 return rw;
 568             }
 569         }
 570     }
 571
 572     result
 573 }
 574
 575 // Rewrite condition if the given expression has one.
 576 pub(crate) fn rewrite_cond(
 577     context: &RewriteContext<'_>,
 578     expr: &ast::Expr,
 579     shape: Shape,
 580 ) -> Option<String> {
 581     match expr.kind {
 582         ast::ExprKind::Match(ref cond, _) => {
 583             // `match `cond` {`
 584             let cond_shape = match context.config.indent_style() {
 585                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 586                 IndentStyle::Block => shape.offset_left(8)?,
 587             };
 588             cond.rewrite(context, cond_shape)
 589         }
 590         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 591             let alt_block_sep =
 592                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 593             control_flow
 594                 .rewrite_cond(context, shape, &alt_block_sep)
 595                 .map(|rw| rw.0)
 596         }),
 597     }
 598 }
 599
 600 // Abstraction over control flow expressions
 601 #[derive(Debug)]
 602 struct ControlFlow<'a> {
 603     cond: Option<&'a ast::Expr>,
 604     block: &'a ast::Block,
 605     else_block: Option<&'a ast::Expr>,
 606     label: Option<ast::Label>,
 607     pat: Option<&'a ast::Pat>,
 608     keyword: &'a str,
 609     matcher: &'a str,
 610     connector: &'a str,
 611     allow_single_line: bool,
 612     // HACK: `true` if this is an `if` expression in an `else if`.
 613     nested_if: bool,
 614     span: Span,
 615 }
 616
 617 fn extract_pats_and_cond(expr: &ast::Expr) -> (Option<&ast::Pat>, &ast::Expr) {
 618     match expr.kind {
 619         ast::ExprKind::Let(ref pat, ref cond, _) => (Some(pat), cond),
 620         _ => (None, expr),
 621     }
 622 }
 623
 624 // FIXME: Refactor this.
 625 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'_>> {
 626     match expr.kind {
 627         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => {
 628             let (pat, cond) = extract_pats_and_cond(cond);
 629             Some(ControlFlow::new_if(
 630                 cond,
 631                 pat,
 632                 if_block,
 633                 else_block.as_ref().map(|e| &**e),
 634                 expr_type == ExprType::SubExpression,
 635                 false,
 636                 expr.span,
 637             ))
 638         }
 639         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 640             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 641         }
 642         ast::ExprKind::Loop(ref block, label) => {
 643             Some(ControlFlow::new_loop(block, label, expr.span))
 644         }
 645         ast::ExprKind::While(ref cond, ref block, label) => {
 646             let (pat, cond) = extract_pats_and_cond(cond);
 647             Some(ControlFlow::new_while(pat, cond, block, label, expr.span))
 648         }
 649         _ => None,
 650     }
 651 }
 652
 653 fn choose_matcher(pat: Option<&ast::Pat>) -> &'static str {
 654     pat.map_or("", |_| "let")
 655 }
 656
 657 impl<'a> ControlFlow<'a> {
 658     fn new_if(
 659         cond: &'a ast::Expr,
 660         pat: Option<&'a ast::Pat>,
 661         block: &'a ast::Block,
 662         else_block: Option<&'a ast::Expr>,
 663         allow_single_line: bool,
 664         nested_if: bool,
 665         span: Span,
 666     ) -> ControlFlow<'a> {
 667         let matcher = choose_matcher(pat);
 668         ControlFlow {
 669             cond: Some(cond),
 670             block,
 671             else_block,
 672             label: None,
 673             pat,
 674             keyword: "if",
 675             matcher,
 676             connector: " =",
 677             allow_single_line,
 678             nested_if,
 679             span,
 680         }
 681     }
 682
 683     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 684         ControlFlow {
 685             cond: None,
 686             block,
 687             else_block: None,
 688             label,
 689             pat: None,
 690             keyword: "loop",
 691             matcher: "",
 692             connector: "",
 693             allow_single_line: false,
 694             nested_if: false,
 695             span,
 696         }
 697     }
 698
 699     fn new_while(
 700         pat: Option<&'a ast::Pat>,
 701         cond: &'a ast::Expr,
 702         block: &'a ast::Block,
 703         label: Option<ast::Label>,
 704         span: Span,
 705     ) -> ControlFlow<'a> {
 706         let matcher = choose_matcher(pat);
 707         ControlFlow {
 708             cond: Some(cond),
 709             block,
 710             else_block: None,
 711             label,
 712             pat,
 713             keyword: "while",
 714             matcher,
 715             connector: " =",
 716             allow_single_line: false,
 717             nested_if: false,
 718             span,
 719         }
 720     }
 721
 722     fn new_for(
 723         pat: &'a ast::Pat,
 724         cond: &'a ast::Expr,
 725         block: &'a ast::Block,
 726         label: Option<ast::Label>,
 727         span: Span,
 728     ) -> ControlFlow<'a> {
 729         ControlFlow {
 730             cond: Some(cond),
 731             block,
 732             else_block: None,
 733             label,
 734             pat: Some(pat),
 735             keyword: "for",
 736             matcher: "",
 737             connector: " in",
 738             allow_single_line: false,
 739             nested_if: false,
 740             span,
 741         }
 742     }
 743
 744     fn rewrite_single_line(
 745         &self,
 746         pat_expr_str: &str,
 747         context: &RewriteContext<'_>,
 748         width: usize,
 749     ) -> Option<String> {
 750         assert!(self.allow_single_line);
 751         let else_block = self.else_block?;
 752         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 753
 754         if let ast::ExprKind::Block(ref else_node, _) = else_block.kind {
 755             if !is_simple_block(context, self.block, None)
 756                 || !is_simple_block(context, else_node, None)
 757                 || pat_expr_str.contains('\n')
 758             {
 759                 return None;
 760             }
 761
 762             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 763             let expr = &self.block.stmts[0];
 764             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 765
 766             let new_width = new_width.checked_sub(if_str.len())?;
 767             let else_expr = &else_node.stmts[0];
 768             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 769
 770             if if_str.contains('\n') || else_str.contains('\n') {
 771                 return None;
 772             }
 773
 774             let result = format!(
 775                 "{} {} {{ {} }} else {{ {} }}",
 776                 self.keyword, pat_expr_str, if_str, else_str
 777             );
 778
 779             if result.len() <= width {
 780                 return Some(result);
 781             }
 782         }
 783
 784         None
 785     }
 786 }
 787
 788 /// Returns `true` if the last line of pat_str has leading whitespace and it is wider than the
 789 /// shape's indent.
 790 fn last_line_offsetted(start_column: usize, pat_str: &str) -> bool {
 791     let mut leading_whitespaces = 0;
 792     for c in pat_str.chars().rev() {
 793         match c {
 794             '\n' => break,
 795             _ if c.is_whitespace() => leading_whitespaces += 1,
 796             _ => leading_whitespaces = 0,
 797         }
 798     }
 799     leading_whitespaces > start_column
 800 }
 801
 802 impl<'a> ControlFlow<'a> {
 803     fn rewrite_pat_expr(
 804         &self,
 805         context: &RewriteContext<'_>,
 806         expr: &ast::Expr,
 807         shape: Shape,
 808         offset: usize,
 809     ) -> Option<String> {
 810         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pat, expr);
 811
 812         let cond_shape = shape.offset_left(offset)?;
 813         if let Some(pat) = self.pat {
 814             let matcher = if self.matcher.is_empty() {
 815                 self.matcher.to_owned()
 816             } else {
 817                 format!("{} ", self.matcher)
 818             };
 819             let pat_shape = cond_shape
 820                 .offset_left(matcher.len())?
 821                 .sub_width(self.connector.len())?;
 822             let pat_string = pat.rewrite(context, pat_shape)?;
 823             let comments_lo = context
 824                 .snippet_provider
 825                 .span_after(self.span.with_lo(pat.span.hi()), self.connector.trim());
 826             let comments_span = mk_sp(comments_lo, expr.span.lo());
 827             return rewrite_assign_rhs_with_comments(
 828                 context,
 829                 &format!("{}{}{}", matcher, pat_string, self.connector),
 830                 expr,
 831                 cond_shape,
 832                 RhsTactics::Default,
 833                 comments_span,
 834                 true,
 835             );
 836         }
 837
 838         let expr_rw = expr.rewrite(context, cond_shape);
 839         // The expression may (partially) fit on the current line.
 840         // We do not allow splitting between `if` and condition.
 841         if self.keyword == "if" || expr_rw.is_some() {
 842             return expr_rw;
 843         }
 844
 845         // The expression won't fit on the current line, jump to next.
 846         let nested_shape = shape
 847             .block_indent(context.config.tab_spaces())
 848             .with_max_width(context.config);
 849         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 850         expr.rewrite(context, nested_shape)
 851             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 852     }
 853
 854     fn rewrite_cond(
 855         &self,
 856         context: &RewriteContext<'_>,
 857         shape: Shape,
 858         alt_block_sep: &str,
 859     ) -> Option<(String, usize)> {
 860         // Do not take the rhs overhead from the upper expressions into account
 861         // when rewriting pattern.
 862         let new_width = context.budget(shape.used_width());
 863         let fresh_shape = Shape {
 864             width: new_width,
 865             ..shape
 866         };
 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             fresh_shape.offset_left(7)?
 871         } else {
 872             fresh_shape
 873         };
 874
 875         let label_string = rewrite_label(self.label);
 876         // 1 = space after keyword.
 877         let offset = self.keyword.len() + label_string.len() + 1;
 878
 879         let pat_expr_string = match self.cond {
 880             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 881             None => String::new(),
 882         };
 883
 884         let brace_overhead =
 885             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 886                 // 2 = ` {`
 887                 2
 888             } else {
 889                 0
 890             };
 891         let one_line_budget = context
 892             .config
 893             .max_width()
 894             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
 895         let force_newline_brace = (pat_expr_string.contains('\n')
 896             || pat_expr_string.len() > one_line_budget)
 897             && (!last_line_extendable(&pat_expr_string)
 898                 || last_line_offsetted(shape.used_width(), &pat_expr_string));
 899
 900         // Try to format if-else on single line.
 901         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
 902             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
 903
 904             if let Some(cond_str) = trial {
 905                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
 906                     return Some((cond_str, 0));
 907                 }
 908             }
 909         }
 910
 911         let cond_span = if let Some(cond) = self.cond {
 912             cond.span
 913         } else {
 914             mk_sp(self.block.span.lo(), self.block.span.lo())
 915         };
 916
 917         // `for event in event`
 918         // Do not include label in the span.
 919         let lo = self
 920             .label
 921             .map_or(self.span.lo(), |label| label.ident.span.hi());
 922         let between_kwd_cond = mk_sp(
 923             context
 924                 .snippet_provider
 925                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
 926             if self.pat.is_none() {
 927                 cond_span.lo()
 928             } else if self.matcher.is_empty() {
 929                 self.pat.unwrap().span.lo()
 930             } else {
 931                 context
 932                     .snippet_provider
 933                     .span_before(self.span, self.matcher.trim())
 934             },
 935         );
 936
 937         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
 938
 939         let after_cond_comment =
 940             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
 941
 942         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
 943             ""
 944         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
 945             || force_newline_brace
 946         {
 947             alt_block_sep
 948         } else {
 949             " "
 950         };
 951
 952         let used_width = if pat_expr_string.contains('\n') {
 953             last_line_width(&pat_expr_string)
 954         } else {
 955             // 2 = spaces after keyword and condition.
 956             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
 957         };
 958
 959         Some((
 960             format!(
 961                 "{}{}{}{}{}",
 962                 label_string,
 963                 self.keyword,
 964                 between_kwd_cond_comment.as_ref().map_or(
 965                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
 966                         ""
 967                     } else {
 968                         " "
 969                     },
 970                     |s| &**s,
 971                 ),
 972                 pat_expr_string,
 973                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
 974             ),
 975             used_width,
 976         ))
 977     }
 978 }
 979
 980 impl<'a> Rewrite for ControlFlow<'a> {
 981     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 982         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
 983
 984         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
 985         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
 986         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
 987         if used_width == 0 {
 988             return Some(cond_str);
 989         }
 990
 991         let block_width = shape.width.saturating_sub(used_width);
 992         // This is used only for the empty block case: `{}`. So, we use 1 if we know
 993         // we should avoid the single line case.
 994         let block_width = if self.else_block.is_some() || self.nested_if {
 995             min(1, block_width)
 996         } else {
 997             block_width
 998         };
 999         let block_shape = Shape {
1000             width: block_width,
1001             ..shape
1002         };
1003         let block_str = {
1004             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1005             let result =
1006                 rewrite_block_with_visitor(context, "", self.block, None, None, block_shape, true);
1007             context.is_if_else_block.replace(old_val);
1008             result?
1009         };
1010
1011         let mut result = format!("{}{}", cond_str, block_str);
1012
1013         if let Some(else_block) = self.else_block {
1014             let shape = Shape::indented(shape.indent, context.config);
1015             let mut last_in_chain = false;
1016             let rewrite = match else_block.kind {
1017                 // If the else expression is another if-else expression, prevent it
1018                 // from being formatted on a single line.
1019                 // Note how we're passing the original shape, as the
1020                 // cost of "else" should not cascade.
1021                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1022                     let (pats, cond) = extract_pats_and_cond(cond);
1023                     ControlFlow::new_if(
1024                         cond,
1025                         pats,
1026                         if_block,
1027                         next_else_block.as_ref().map(|e| &**e),
1028                         false,
1029                         true,
1030                         mk_sp(else_block.span.lo(), self.span.hi()),
1031                     )
1032                     .rewrite(context, shape)
1033                 }
1034                 _ => {
1035                     last_in_chain = true;
1036                     // When rewriting a block, the width is only used for single line
1037                     // blocks, passing 1 lets us avoid that.
1038                     let else_shape = Shape {
1039                         width: min(1, shape.width),
1040                         ..shape
1041                     };
1042                     format_expr(else_block, ExprType::Statement, context, else_shape)
1043                 }
1044             };
1045
1046             let between_kwd_else_block = mk_sp(
1047                 self.block.span.hi(),
1048                 context
1049                     .snippet_provider
1050                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1051             );
1052             let between_kwd_else_block_comment =
1053                 extract_comment(between_kwd_else_block, context, shape);
1054
1055             let after_else = mk_sp(
1056                 context
1057                     .snippet_provider
1058                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1059                 else_block.span.lo(),
1060             );
1061             let after_else_comment = extract_comment(after_else, context, shape);
1062
1063             let between_sep = match context.config.control_brace_style() {
1064                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1065                     &*alt_block_sep
1066                 }
1067                 ControlBraceStyle::AlwaysSameLine => " ",
1068             };
1069             let after_sep = match context.config.control_brace_style() {
1070                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1071                 _ => " ",
1072             };
1073
1074             result.push_str(&format!(
1075                 "{}else{}",
1076                 between_kwd_else_block_comment
1077                     .as_ref()
1078                     .map_or(between_sep, |s| &**s),
1079                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1080             ));
1081             result.push_str(&rewrite?);
1082         }
1083
1084         Some(result)
1085     }
1086 }
1087
1088 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1089     match opt_label {
1090         Some(label) => Cow::from(format!("{}: ", label.ident)),
1091         None => Cow::from(""),
1092     }
1093 }
1094
1095 fn extract_comment(span: Span, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1096     match rewrite_missing_comment(span, shape, context) {
1097         Some(ref comment) if !comment.is_empty() => Some(format!(
1098             "{indent}{}{indent}",
1099             comment,
1100             indent = shape.indent.to_string_with_newline(context.config)
1101         )),
1102         _ => None,
1103     }
1104 }
1105
1106 pub(crate) fn block_contains_comment(context: &RewriteContext<'_>, block: &ast::Block) -> bool {
1107     contains_comment(context.snippet(block.span))
1108 }
1109
1110 // Checks that a block contains no statements, an expression and no comments or
1111 // attributes.
1112 // FIXME: incorrectly returns false when comment is contained completely within
1113 // the expression.
1114 pub(crate) fn is_simple_block(
1115     context: &RewriteContext<'_>,
1116     block: &ast::Block,
1117     attrs: Option<&[ast::Attribute]>,
1118 ) -> bool {
1119     block.stmts.len() == 1
1120         && stmt_is_expr(&block.stmts[0])
1121         && !block_contains_comment(context, block)
1122         && attrs.map_or(true, |a| a.is_empty())
1123 }
1124
1125 /// Checks whether a block contains at most one statement or expression, and no
1126 /// comments or attributes.
1127 pub(crate) fn is_simple_block_stmt(
1128     context: &RewriteContext<'_>,
1129     block: &ast::Block,
1130     attrs: Option<&[ast::Attribute]>,
1131 ) -> bool {
1132     block.stmts.len() <= 1
1133         && !block_contains_comment(context, block)
1134         && attrs.map_or(true, |a| a.is_empty())
1135 }
1136
1137 fn block_has_statements(block: &ast::Block) -> bool {
1138     block
1139         .stmts
1140         .iter()
1141         .any(|stmt| !matches!(stmt.kind, ast::StmtKind::Empty))
1142 }
1143
1144 /// Checks whether a block contains no statements, expressions, comments, or
1145 /// inner attributes.
1146 pub(crate) fn is_empty_block(
1147     context: &RewriteContext<'_>,
1148     block: &ast::Block,
1149     attrs: Option<&[ast::Attribute]>,
1150 ) -> bool {
1151     !block_has_statements(block)
1152         && !block_contains_comment(context, block)
1153         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1154 }
1155
1156 pub(crate) fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1157     matches!(stmt.kind, ast::StmtKind::Expr(..))
1158 }
1159
1160 pub(crate) fn is_unsafe_block(block: &ast::Block) -> bool {
1161     matches!(block.rules, ast::BlockCheckMode::Unsafe(..))
1162 }
1163
1164 pub(crate) fn rewrite_literal(
1165     context: &RewriteContext<'_>,
1166     l: &ast::Lit,
1167     shape: Shape,
1168 ) -> Option<String> {
1169     match l.kind {
1170         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1171         ast::LitKind::Int(..) => rewrite_int_lit(context, l, shape),
1172         _ => wrap_str(
1173             context.snippet(l.span).to_owned(),
1174             context.config.max_width(),
1175             shape,
1176         ),
1177     }
1178 }
1179
1180 fn rewrite_string_lit(context: &RewriteContext<'_>, span: Span, shape: Shape) -> Option<String> {
1181     let string_lit = context.snippet(span);
1182
1183     if !context.config.format_strings() {
1184         if string_lit
1185             .lines()
1186             .dropping_back(1)
1187             .all(|line| line.ends_with('\\'))
1188             && context.config.version() == Version::Two
1189         {
1190             return Some(string_lit.to_owned());
1191         } else {
1192             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1193         }
1194     }
1195
1196     // Remove the quote characters.
1197     let str_lit = &string_lit[1..string_lit.len() - 1];
1198
1199     rewrite_string(
1200         str_lit,
1201         &StringFormat::new(shape.visual_indent(0), context.config),
1202         shape.width.saturating_sub(2),
1203     )
1204 }
1205
1206 fn rewrite_int_lit(context: &RewriteContext<'_>, lit: &ast::Lit, shape: Shape) -> Option<String> {
1207     let span = lit.span;
1208     let symbol = lit.token.symbol.as_str();
1209
1210     if let Some(symbol_stripped) = symbol.strip_prefix("0x") {
1211         let hex_lit = match context.config.hex_literal_case() {
1212             HexLiteralCase::Preserve => None,
1213             HexLiteralCase::Upper => Some(symbol_stripped.to_ascii_uppercase()),
1214             HexLiteralCase::Lower => Some(symbol_stripped.to_ascii_lowercase()),
1215         };
1216         if let Some(hex_lit) = hex_lit {
1217             return wrap_str(
1218                 format!(
1219                     "0x{}{}",
1220                     hex_lit,
1221                     lit.token.suffix.map_or(String::new(), |s| s.to_string())
1222                 ),
1223                 context.config.max_width(),
1224                 shape,
1225             );
1226         }
1227     }
1228
1229     wrap_str(
1230         context.snippet(span).to_owned(),
1231         context.config.max_width(),
1232         shape,
1233     )
1234 }
1235
1236 fn choose_separator_tactic(context: &RewriteContext<'_>, span: Span) -> Option<SeparatorTactic> {
1237     if context.inside_macro() {
1238         if span_ends_with_comma(context, span) {
1239             Some(SeparatorTactic::Always)
1240         } else {
1241             Some(SeparatorTactic::Never)
1242         }
1243     } else {
1244         None
1245     }
1246 }
1247
1248 pub(crate) fn rewrite_call(
1249     context: &RewriteContext<'_>,
1250     callee: &str,
1251     args: &[ptr::P<ast::Expr>],
1252     span: Span,
1253     shape: Shape,
1254 ) -> Option<String> {
1255     overflow::rewrite_with_parens(
1256         context,
1257         callee,
1258         args.iter(),
1259         shape,
1260         span,
1261         context.config.fn_call_width(),
1262         choose_separator_tactic(context, span),
1263     )
1264 }
1265
1266 pub(crate) fn is_simple_expr(expr: &ast::Expr) -> bool {
1267     match expr.kind {
1268         ast::ExprKind::Lit(..) => true,
1269         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1270         ast::ExprKind::AddrOf(_, _, ref expr)
1271         | ast::ExprKind::Box(ref expr)
1272         | ast::ExprKind::Cast(ref expr, _)
1273         | ast::ExprKind::Field(ref expr, _)
1274         | ast::ExprKind::Try(ref expr)
1275         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1276         ast::ExprKind::Index(ref lhs, ref rhs) => is_simple_expr(lhs) && is_simple_expr(rhs),
1277         ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1278             is_simple_expr(lhs) && is_simple_expr(&*rhs.value)
1279         }
1280         _ => false,
1281     }
1282 }
1283
1284 pub(crate) fn is_every_expr_simple(lists: &[OverflowableItem<'_>]) -> bool {
1285     lists.iter().all(OverflowableItem::is_simple)
1286 }
1287
1288 pub(crate) fn can_be_overflowed_expr(
1289     context: &RewriteContext<'_>,
1290     expr: &ast::Expr,
1291     args_len: usize,
1292 ) -> bool {
1293     match expr.kind {
1294         _ if !expr.attrs.is_empty() => false,
1295         ast::ExprKind::Match(..) => {
1296             (context.use_block_indent() && args_len == 1)
1297                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1298                 || context.config.overflow_delimited_expr()
1299         }
1300         ast::ExprKind::If(..)
1301         | ast::ExprKind::ForLoop(..)
1302         | ast::ExprKind::Loop(..)
1303         | ast::ExprKind::While(..) => {
1304             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1305         }
1306
1307         // Handle always block-like expressions
1308         ast::ExprKind::Async(..) | ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => true,
1309
1310         // Handle `[]` and `{}`-like expressions
1311         ast::ExprKind::Array(..) | ast::ExprKind::Struct(..) => {
1312             context.config.overflow_delimited_expr()
1313                 || (context.use_block_indent() && args_len == 1)
1314         }
1315         ast::ExprKind::MacCall(ref mac) => {
1316             match (
1317                 rustc_ast::ast::MacDelimiter::from_token(mac.args.delim()),
1318                 context.config.overflow_delimited_expr(),
1319             ) {
1320                 (Some(ast::MacDelimiter::Bracket), true)
1321                 | (Some(ast::MacDelimiter::Brace), true) => true,
1322                 _ => context.use_block_indent() && args_len == 1,
1323             }
1324         }
1325
1326         // Handle parenthetical expressions
1327         ast::ExprKind::Call(..) | ast::ExprKind::MethodCall(..) | ast::ExprKind::Tup(..) => {
1328             context.use_block_indent() && args_len == 1
1329         }
1330
1331         // Handle unary-like expressions
1332         ast::ExprKind::AddrOf(_, _, ref expr)
1333         | ast::ExprKind::Box(ref expr)
1334         | ast::ExprKind::Try(ref expr)
1335         | ast::ExprKind::Unary(_, ref expr)
1336         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1337         _ => false,
1338     }
1339 }
1340
1341 pub(crate) fn is_nested_call(expr: &ast::Expr) -> bool {
1342     match expr.kind {
1343         ast::ExprKind::Call(..) | ast::ExprKind::MacCall(..) => true,
1344         ast::ExprKind::AddrOf(_, _, ref expr)
1345         | ast::ExprKind::Box(ref expr)
1346         | ast::ExprKind::Try(ref expr)
1347         | ast::ExprKind::Unary(_, ref expr)
1348         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1349         _ => false,
1350     }
1351 }
1352
1353 /// Returns `true` if a function call or a method call represented by the given span ends with a
1354 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1355 /// comma from macro can potentially break the code.
1356 pub(crate) fn span_ends_with_comma(context: &RewriteContext<'_>, span: Span) -> bool {
1357     let mut result: bool = Default::default();
1358     let mut prev_char: char = Default::default();
1359     let closing_delimiters = &[')', '}', ']'];
1360
1361     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1362         match c {
1363             _ if kind.is_comment() || c.is_whitespace() => continue,
1364             c if closing_delimiters.contains(&c) => {
1365                 result &= !closing_delimiters.contains(&prev_char);
1366             }
1367             ',' => result = true,
1368             _ => result = false,
1369         }
1370         prev_char = c;
1371     }
1372
1373     result
1374 }
1375
1376 fn rewrite_paren(
1377     context: &RewriteContext<'_>,
1378     mut subexpr: &ast::Expr,
1379     shape: Shape,
1380     mut span: Span,
1381 ) -> Option<String> {
1382     debug!("rewrite_paren, shape: {:?}", shape);
1383
1384     // Extract comments within parens.
1385     let mut pre_span;
1386     let mut post_span;
1387     let mut pre_comment;
1388     let mut post_comment;
1389     let remove_nested_parens = context.config.remove_nested_parens();
1390     loop {
1391         // 1 = "(" or ")"
1392         pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1393         post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1394         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1395         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1396
1397         // Remove nested parens if there are no comments.
1398         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.kind {
1399             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1400                 span = subexpr.span;
1401                 subexpr = subsubexpr;
1402                 continue;
1403             }
1404         }
1405
1406         break;
1407     }
1408
1409     // 1 = `(` and `)`
1410     let sub_shape = shape.offset_left(1)?.sub_width(1)?;
1411     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1412     let fits_single_line = !pre_comment.contains("//") && !post_comment.contains("//");
1413     if fits_single_line {
1414         Some(format!("({}{}{})", pre_comment, subexpr_str, post_comment))
1415     } else {
1416         rewrite_paren_in_multi_line(context, subexpr, shape, pre_span, post_span)
1417     }
1418 }
1419
1420 fn rewrite_paren_in_multi_line(
1421     context: &RewriteContext<'_>,
1422     subexpr: &ast::Expr,
1423     shape: Shape,
1424     pre_span: Span,
1425     post_span: Span,
1426 ) -> Option<String> {
1427     let nested_indent = shape.indent.block_indent(context.config);
1428     let nested_shape = Shape::indented(nested_indent, context.config);
1429     let pre_comment = rewrite_missing_comment(pre_span, nested_shape, context)?;
1430     let post_comment = rewrite_missing_comment(post_span, nested_shape, context)?;
1431     let subexpr_str = subexpr.rewrite(context, nested_shape)?;
1432
1433     let mut result = String::with_capacity(subexpr_str.len() * 2);
1434     result.push('(');
1435     if !pre_comment.is_empty() {
1436         result.push_str(&nested_indent.to_string_with_newline(context.config));
1437         result.push_str(&pre_comment);
1438     }
1439     result.push_str(&nested_indent.to_string_with_newline(context.config));
1440     result.push_str(&subexpr_str);
1441     if !post_comment.is_empty() {
1442         result.push_str(&nested_indent.to_string_with_newline(context.config));
1443         result.push_str(&post_comment);
1444     }
1445     result.push_str(&shape.indent.to_string_with_newline(context.config));
1446     result.push(')');
1447
1448     Some(result)
1449 }
1450
1451 fn rewrite_index(
1452     expr: &ast::Expr,
1453     index: &ast::Expr,
1454     context: &RewriteContext<'_>,
1455     shape: Shape,
1456 ) -> Option<String> {
1457     let expr_str = expr.rewrite(context, shape)?;
1458
1459     let offset = last_line_width(&expr_str) + 1;
1460     let rhs_overhead = shape.rhs_overhead(context.config);
1461     let index_shape = if expr_str.contains('\n') {
1462         Shape::legacy(context.config.max_width(), shape.indent)
1463             .offset_left(offset)
1464             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1465     } else {
1466         match context.config.indent_style() {
1467             IndentStyle::Block => shape
1468                 .offset_left(offset)
1469                 .and_then(|shape| shape.sub_width(1)),
1470             IndentStyle::Visual => shape.visual_indent(offset).sub_width(offset + 1),
1471         }
1472     };
1473     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1474
1475     // Return if index fits in a single line.
1476     match orig_index_rw {
1477         Some(ref index_str) if !index_str.contains('\n') => {
1478             return Some(format!("{}[{}]", expr_str, index_str));
1479         }
1480         _ => (),
1481     }
1482
1483     // Try putting index on the next line and see if it fits in a single line.
1484     let indent = shape.indent.block_indent(context.config);
1485     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1486     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1487     let new_index_rw = index.rewrite(context, index_shape);
1488     match (orig_index_rw, new_index_rw) {
1489         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1490             "{}{}[{}]",
1491             expr_str,
1492             indent.to_string_with_newline(context.config),
1493             new_index_str,
1494         )),
1495         (None, Some(ref new_index_str)) => Some(format!(
1496             "{}{}[{}]",
1497             expr_str,
1498             indent.to_string_with_newline(context.config),
1499             new_index_str,
1500         )),
1501         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1502         _ => None,
1503     }
1504 }
1505
1506 fn struct_lit_can_be_aligned(fields: &[ast::ExprField], has_base: bool) -> bool {
1507     !has_base && fields.iter().all(|field| !field.is_shorthand)
1508 }
1509
1510 fn rewrite_struct_lit<'a>(
1511     context: &RewriteContext<'_>,
1512     path: &ast::Path,
1513     fields: &'a [ast::ExprField],
1514     struct_rest: &ast::StructRest,
1515     attrs: &[ast::Attribute],
1516     span: Span,
1517     shape: Shape,
1518 ) -> Option<String> {
1519     debug!("rewrite_struct_lit: shape {:?}", shape);
1520
1521     enum StructLitField<'a> {
1522         Regular(&'a ast::ExprField),
1523         Base(&'a ast::Expr),
1524         Rest(&'a Span),
1525     }
1526
1527     // 2 = " {".len()
1528     let path_shape = shape.sub_width(2)?;
1529     let path_str = rewrite_path(context, PathContext::Expr, None, path, path_shape)?;
1530
1531     let has_base_or_rest = match struct_rest {
1532         ast::StructRest::None if fields.is_empty() => return Some(format!("{} {{}}", path_str)),
1533         ast::StructRest::Rest(_) if fields.is_empty() => {
1534             return Some(format!("{} {{ .. }}", path_str));
1535         }
1536         ast::StructRest::Rest(_) | ast::StructRest::Base(_) => true,
1537         _ => false,
1538     };
1539
1540     // Foo { a: Foo } - indent is +3, width is -5.
1541     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1542
1543     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1544     let body_lo = context.snippet_provider.span_after(span, "{");
1545     let fields_str = if struct_lit_can_be_aligned(fields, has_base_or_rest)
1546         && context.config.struct_field_align_threshold() > 0
1547     {
1548         rewrite_with_alignment(
1549             fields,
1550             context,
1551             v_shape,
1552             mk_sp(body_lo, span.hi()),
1553             one_line_width,
1554         )?
1555     } else {
1556         let field_iter = fields.iter().map(StructLitField::Regular).chain(
1557             match struct_rest {
1558                 ast::StructRest::Base(expr) => Some(StructLitField::Base(&**expr)),
1559                 ast::StructRest::Rest(span) => Some(StructLitField::Rest(span)),
1560                 ast::StructRest::None => None,
1561             }
1562             .into_iter(),
1563         );
1564
1565         let span_lo = |item: &StructLitField<'_>| match *item {
1566             StructLitField::Regular(field) => field.span().lo(),
1567             StructLitField::Base(expr) => {
1568                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1569                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1570                 let pos = snippet.find_uncommented("..").unwrap();
1571                 last_field_hi + BytePos(pos as u32)
1572             }
1573             StructLitField::Rest(span) => span.lo(),
1574         };
1575         let span_hi = |item: &StructLitField<'_>| match *item {
1576             StructLitField::Regular(field) => field.span().hi(),
1577             StructLitField::Base(expr) => expr.span.hi(),
1578             StructLitField::Rest(span) => span.hi(),
1579         };
1580         let rewrite = |item: &StructLitField<'_>| match *item {
1581             StructLitField::Regular(field) => {
1582                 // The 1 taken from the v_budget is for the comma.
1583                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1584             }
1585             StructLitField::Base(expr) => {
1586                 // 2 = ..
1587                 expr.rewrite(context, v_shape.offset_left(2)?)
1588                     .map(|s| format!("..{}", s))
1589             }
1590             StructLitField::Rest(_) => Some("..".to_owned()),
1591         };
1592
1593         let items = itemize_list(
1594             context.snippet_provider,
1595             field_iter,
1596             "}",
1597             ",",
1598             span_lo,
1599             span_hi,
1600             rewrite,
1601             body_lo,
1602             span.hi(),
1603             false,
1604         );
1605         let item_vec = items.collect::<Vec<_>>();
1606
1607         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1608         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1609
1610         let ends_with_comma = span_ends_with_comma(context, span);
1611         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1612
1613         let fmt = struct_lit_formatting(
1614             nested_shape,
1615             tactic,
1616             context,
1617             force_no_trailing_comma || has_base_or_rest || !context.use_block_indent(),
1618         );
1619
1620         write_list(&item_vec, &fmt)?
1621     };
1622
1623     let fields_str =
1624         wrap_struct_field(context, attrs, &fields_str, shape, v_shape, one_line_width)?;
1625     Some(format!("{} {{{}}}", path_str, fields_str))
1626
1627     // FIXME if context.config.indent_style() == Visual, but we run out
1628     // of space, we should fall back to BlockIndent.
1629 }
1630
1631 pub(crate) fn wrap_struct_field(
1632     context: &RewriteContext<'_>,
1633     attrs: &[ast::Attribute],
1634     fields_str: &str,
1635     shape: Shape,
1636     nested_shape: Shape,
1637     one_line_width: usize,
1638 ) -> Option<String> {
1639     let should_vertical = context.config.indent_style() == IndentStyle::Block
1640         && (fields_str.contains('\n')
1641             || !context.config.struct_lit_single_line()
1642             || fields_str.len() > one_line_width);
1643
1644     let inner_attrs = &inner_attributes(attrs);
1645     if inner_attrs.is_empty() {
1646         if should_vertical {
1647             Some(format!(
1648                 "{}{}{}",
1649                 nested_shape.indent.to_string_with_newline(context.config),
1650                 fields_str,
1651                 shape.indent.to_string_with_newline(context.config)
1652             ))
1653         } else {
1654             // One liner or visual indent.
1655             Some(format!(" {} ", fields_str))
1656         }
1657     } else {
1658         Some(format!(
1659             "{}{}{}{}{}",
1660             nested_shape.indent.to_string_with_newline(context.config),
1661             inner_attrs.rewrite(context, shape)?,
1662             nested_shape.indent.to_string_with_newline(context.config),
1663             fields_str,
1664             shape.indent.to_string_with_newline(context.config)
1665         ))
1666     }
1667 }
1668
1669 pub(crate) fn struct_lit_field_separator(config: &Config) -> &str {
1670     colon_spaces(config)
1671 }
1672
1673 pub(crate) fn rewrite_field(
1674     context: &RewriteContext<'_>,
1675     field: &ast::ExprField,
1676     shape: Shape,
1677     prefix_max_width: usize,
1678 ) -> Option<String> {
1679     if contains_skip(&field.attrs) {
1680         return Some(context.snippet(field.span()).to_owned());
1681     }
1682     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1683     if !attrs_str.is_empty() {
1684         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1685     };
1686     let name = context.snippet(field.ident.span);
1687     if field.is_shorthand {
1688         Some(attrs_str + name)
1689     } else {
1690         let mut separator = String::from(struct_lit_field_separator(context.config));
1691         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1692             separator.push(' ');
1693         }
1694         let overhead = name.len() + separator.len();
1695         let expr_shape = shape.offset_left(overhead)?;
1696         let expr = field.expr.rewrite(context, expr_shape);
1697
1698         match expr {
1699             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1700                 Some(attrs_str + name)
1701             }
1702             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1703             None => {
1704                 let expr_offset = shape.indent.block_indent(context.config);
1705                 let expr = field
1706                     .expr
1707                     .rewrite(context, Shape::indented(expr_offset, context.config));
1708                 expr.map(|s| {
1709                     format!(
1710                         "{}{}:\n{}{}",
1711                         attrs_str,
1712                         name,
1713                         expr_offset.to_string(context.config),
1714                         s
1715                     )
1716                 })
1717             }
1718         }
1719     }
1720 }
1721
1722 fn rewrite_tuple_in_visual_indent_style<'a, T: 'a + IntoOverflowableItem<'a>>(
1723     context: &RewriteContext<'_>,
1724     mut items: impl Iterator<Item = &'a T>,
1725     span: Span,
1726     shape: Shape,
1727     is_singleton_tuple: bool,
1728 ) -> Option<String> {
1729     // In case of length 1, need a trailing comma
1730     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1731     if is_singleton_tuple {
1732         // 3 = "(" + ",)"
1733         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1734         return items
1735             .next()
1736             .unwrap()
1737             .rewrite(context, nested_shape)
1738             .map(|s| format!("({},)", s));
1739     }
1740
1741     let list_lo = context.snippet_provider.span_after(span, "(");
1742     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1743     let items = itemize_list(
1744         context.snippet_provider,
1745         items,
1746         ")",
1747         ",",
1748         |item| item.span().lo(),
1749         |item| item.span().hi(),
1750         |item| item.rewrite(context, nested_shape),
1751         list_lo,
1752         span.hi() - BytePos(1),
1753         false,
1754     );
1755     let item_vec: Vec<_> = items.collect();
1756     let tactic = definitive_tactic(
1757         &item_vec,
1758         ListTactic::HorizontalVertical,
1759         Separator::Comma,
1760         nested_shape.width,
1761     );
1762     let fmt = ListFormatting::new(nested_shape, context.config)
1763         .tactic(tactic)
1764         .ends_with_newline(false);
1765     let list_str = write_list(&item_vec, &fmt)?;
1766
1767     Some(format!("({})", list_str))
1768 }
1769
1770 pub(crate) fn rewrite_tuple<'a, T: 'a + IntoOverflowableItem<'a>>(
1771     context: &'a RewriteContext<'_>,
1772     items: impl Iterator<Item = &'a T>,
1773     span: Span,
1774     shape: Shape,
1775     is_singleton_tuple: bool,
1776 ) -> Option<String> {
1777     debug!("rewrite_tuple {:?}", shape);
1778     if context.use_block_indent() {
1779         // We use the same rule as function calls for rewriting tuples.
1780         let force_tactic = if context.inside_macro() {
1781             if span_ends_with_comma(context, span) {
1782                 Some(SeparatorTactic::Always)
1783             } else {
1784                 Some(SeparatorTactic::Never)
1785             }
1786         } else if is_singleton_tuple {
1787             Some(SeparatorTactic::Always)
1788         } else {
1789             None
1790         };
1791         overflow::rewrite_with_parens(
1792             context,
1793             "",
1794             items,
1795             shape,
1796             span,
1797             context.config.fn_call_width(),
1798             force_tactic,
1799         )
1800     } else {
1801         rewrite_tuple_in_visual_indent_style(context, items, span, shape, is_singleton_tuple)
1802     }
1803 }
1804
1805 pub(crate) fn rewrite_unary_prefix<R: Rewrite>(
1806     context: &RewriteContext<'_>,
1807     prefix: &str,
1808     rewrite: &R,
1809     shape: Shape,
1810 ) -> Option<String> {
1811     rewrite
1812         .rewrite(context, shape.offset_left(prefix.len())?)
1813         .map(|r| format!("{}{}", prefix, r))
1814 }
1815
1816 // FIXME: this is probably not correct for multi-line Rewrites. we should
1817 // subtract suffix.len() from the last line budget, not the first!
1818 pub(crate) fn rewrite_unary_suffix<R: Rewrite>(
1819     context: &RewriteContext<'_>,
1820     suffix: &str,
1821     rewrite: &R,
1822     shape: Shape,
1823 ) -> Option<String> {
1824     rewrite
1825         .rewrite(context, shape.sub_width(suffix.len())?)
1826         .map(|mut r| {
1827             r.push_str(suffix);
1828             r
1829         })
1830 }
1831
1832 fn rewrite_unary_op(
1833     context: &RewriteContext<'_>,
1834     op: ast::UnOp,
1835     expr: &ast::Expr,
1836     shape: Shape,
1837 ) -> Option<String> {
1838     // For some reason, an UnOp is not spanned like BinOp!
1839     rewrite_unary_prefix(context, ast::UnOp::to_string(op), expr, shape)
1840 }
1841
1842 fn rewrite_assignment(
1843     context: &RewriteContext<'_>,
1844     lhs: &ast::Expr,
1845     rhs: &ast::Expr,
1846     op: Option<&ast::BinOp>,
1847     shape: Shape,
1848 ) -> Option<String> {
1849     let operator_str = match op {
1850         Some(op) => context.snippet(op.span),
1851         None => "=",
1852     };
1853
1854     // 1 = space between lhs and operator.
1855     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
1856     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
1857
1858     rewrite_assign_rhs(context, lhs_str, rhs, shape)
1859 }
1860
1861 /// Controls where to put the rhs.
1862 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1863 pub(crate) enum RhsTactics {
1864     /// Use heuristics.
1865     Default,
1866     /// Put the rhs on the next line if it uses multiple line, without extra indentation.
1867     ForceNextLineWithoutIndent,
1868     /// Allow overflowing max width if neither `Default` nor `ForceNextLineWithoutIndent`
1869     /// did not work.
1870     AllowOverflow,
1871 }
1872
1873 // The left hand side must contain everything up to, and including, the
1874 // assignment operator.
1875 pub(crate) fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
1876     context: &RewriteContext<'_>,
1877     lhs: S,
1878     ex: &R,
1879     shape: Shape,
1880 ) -> Option<String> {
1881     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
1882 }
1883
1884 pub(crate) fn rewrite_assign_rhs_expr<R: Rewrite>(
1885     context: &RewriteContext<'_>,
1886     lhs: &str,
1887     ex: &R,
1888     shape: Shape,
1889     rhs_tactics: RhsTactics,
1890 ) -> Option<String> {
1891     let last_line_width = last_line_width(lhs).saturating_sub(if lhs.contains('\n') {
1892         shape.indent.width()
1893     } else {
1894         0
1895     });
1896     // 1 = space between operator and rhs.
1897     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
1898         width: 0,
1899         offset: shape.offset + last_line_width + 1,
1900         ..shape
1901     });
1902     let has_rhs_comment = if let Some(offset) = lhs.find_last_uncommented("=") {
1903         lhs.trim_end().len() > offset + 1
1904     } else {
1905         false
1906     };
1907
1908     choose_rhs(
1909         context,
1910         ex,
1911         orig_shape,
1912         ex.rewrite(context, orig_shape),
1913         rhs_tactics,
1914         has_rhs_comment,
1915     )
1916 }
1917
1918 pub(crate) fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
1919     context: &RewriteContext<'_>,
1920     lhs: S,
1921     ex: &R,
1922     shape: Shape,
1923     rhs_tactics: RhsTactics,
1924 ) -> Option<String> {
1925     let lhs = lhs.into();
1926     let rhs = rewrite_assign_rhs_expr(context, &lhs, ex, shape, rhs_tactics)?;
1927     Some(lhs + &rhs)
1928 }
1929
1930 pub(crate) fn rewrite_assign_rhs_with_comments<S: Into<String>, R: Rewrite>(
1931     context: &RewriteContext<'_>,
1932     lhs: S,
1933     ex: &R,
1934     shape: Shape,
1935     rhs_tactics: RhsTactics,
1936     between_span: Span,
1937     allow_extend: bool,
1938 ) -> Option<String> {
1939     let lhs = lhs.into();
1940     let contains_comment = contains_comment(context.snippet(between_span));
1941     let shape = if contains_comment {
1942         shape.block_left(context.config.tab_spaces())?
1943     } else {
1944         shape
1945     };
1946     let rhs = rewrite_assign_rhs_expr(context, &lhs, ex, shape, rhs_tactics)?;
1947
1948     if contains_comment {
1949         let rhs = rhs.trim_start();
1950         combine_strs_with_missing_comments(context, &lhs, rhs, between_span, shape, allow_extend)
1951     } else {
1952         Some(lhs + &rhs)
1953     }
1954 }
1955
1956 fn choose_rhs<R: Rewrite>(
1957     context: &RewriteContext<'_>,
1958     expr: &R,
1959     shape: Shape,
1960     orig_rhs: Option<String>,
1961     rhs_tactics: RhsTactics,
1962     has_rhs_comment: bool,
1963 ) -> Option<String> {
1964     match orig_rhs {
1965         Some(ref new_str) if new_str.is_empty() => {
1966             return Some(String::new());
1967         }
1968         Some(ref new_str)
1969             if !new_str.contains('\n') && unicode_str_width(new_str) <= shape.width =>
1970         {
1971             Some(format!(" {}", new_str))
1972         }
1973         _ => {
1974             // Expression did not fit on the same line as the identifier.
1975             // Try splitting the line and see if that works better.
1976             let new_shape = shape_from_rhs_tactic(context, shape, rhs_tactics)?;
1977             let new_rhs = expr.rewrite(context, new_shape);
1978             let new_indent_str = &shape
1979                 .indent
1980                 .block_indent(context.config)
1981                 .to_string_with_newline(context.config);
1982             let before_space_str = if has_rhs_comment { "" } else { " " };
1983
1984             match (orig_rhs, new_rhs) {
1985                 (Some(ref orig_rhs), Some(ref new_rhs))
1986                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
1987                         .is_none() =>
1988                 {
1989                     Some(format!("{}{}", before_space_str, orig_rhs))
1990                 }
1991                 (Some(ref orig_rhs), Some(ref new_rhs))
1992                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
1993                 {
1994                     Some(format!("{}{}", new_indent_str, new_rhs))
1995                 }
1996                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
1997                 (None, None) if rhs_tactics == RhsTactics::AllowOverflow => {
1998                     let shape = shape.infinite_width();
1999                     expr.rewrite(context, shape)
2000                         .map(|s| format!("{}{}", before_space_str, s))
2001                 }
2002                 (None, None) => None,
2003                 (Some(orig_rhs), _) => Some(format!("{}{}", before_space_str, orig_rhs)),
2004             }
2005         }
2006     }
2007 }
2008
2009 fn shape_from_rhs_tactic(
2010     context: &RewriteContext<'_>,
2011     shape: Shape,
2012     rhs_tactic: RhsTactics,
2013 ) -> Option<Shape> {
2014     match rhs_tactic {
2015         RhsTactics::ForceNextLineWithoutIndent => shape
2016             .with_max_width(context.config)
2017             .sub_width(shape.indent.width()),
2018         RhsTactics::Default | RhsTactics::AllowOverflow => {
2019             Shape::indented(shape.indent.block_indent(context.config), context.config)
2020                 .sub_width(shape.rhs_overhead(context.config))
2021         }
2022     }
2023 }
2024
2025 /// Returns true if formatting next_line_rhs is better on a new line when compared to the
2026 /// original's line formatting.
2027 ///
2028 /// It is considered better if:
2029 /// 1. the tactic is ForceNextLineWithoutIndent
2030 /// 2. next_line_rhs doesn't have newlines
2031 /// 3. the original line has more newlines than next_line_rhs
2032 /// 4. the original formatting of the first line ends with `(`, `{`, or `[` and next_line_rhs
2033 ///    doesn't
2034 pub(crate) fn prefer_next_line(
2035     orig_rhs: &str,
2036     next_line_rhs: &str,
2037     rhs_tactics: RhsTactics,
2038 ) -> bool {
2039     rhs_tactics == RhsTactics::ForceNextLineWithoutIndent
2040         || !next_line_rhs.contains('\n')
2041         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2042         || first_line_ends_with(orig_rhs, '(') && !first_line_ends_with(next_line_rhs, '(')
2043         || first_line_ends_with(orig_rhs, '{') && !first_line_ends_with(next_line_rhs, '{')
2044         || first_line_ends_with(orig_rhs, '[') && !first_line_ends_with(next_line_rhs, '[')
2045 }
2046
2047 fn rewrite_expr_addrof(
2048     context: &RewriteContext<'_>,
2049     borrow_kind: ast::BorrowKind,
2050     mutability: ast::Mutability,
2051     expr: &ast::Expr,
2052     shape: Shape,
2053 ) -> Option<String> {
2054     let operator_str = match (mutability, borrow_kind) {
2055         (ast::Mutability::Not, ast::BorrowKind::Ref) => "&",
2056         (ast::Mutability::Not, ast::BorrowKind::Raw) => "&raw const ",
2057         (ast::Mutability::Mut, ast::BorrowKind::Ref) => "&mut ",
2058         (ast::Mutability::Mut, ast::BorrowKind::Raw) => "&raw mut ",
2059     };
2060     rewrite_unary_prefix(context, operator_str, expr, shape)
2061 }
2062
2063 pub(crate) fn is_method_call(expr: &ast::Expr) -> bool {
2064     match expr.kind {
2065         ast::ExprKind::MethodCall(..) => true,
2066         ast::ExprKind::AddrOf(_, _, ref expr)
2067         | ast::ExprKind::Box(ref expr)
2068         | ast::ExprKind::Cast(ref expr, _)
2069         | ast::ExprKind::Try(ref expr)
2070         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),
2071         _ => false,
2072     }
2073 }
2074
2075 #[cfg(test)]
2076 mod test {
2077     use super::last_line_offsetted;
2078
2079     #[test]
2080     fn test_last_line_offsetted() {
2081         let lines = "one\n    two";
2082         assert_eq!(last_line_offsetted(2, lines), true);
2083         assert_eq!(last_line_offsetted(4, lines), false);
2084         assert_eq!(last_line_offsetted(6, lines), false);
2085
2086         let lines = "one    two";
2087         assert_eq!(last_line_offsetted(2, lines), false);
2088         assert_eq!(last_line_offsetted(0, lines), false);
2089
2090         let lines = "\ntwo";
2091         assert_eq!(last_line_offsetted(2, lines), false);
2092         assert_eq!(last_line_offsetted(0, lines), false);
2093
2094         let lines = "one\n    two      three";
2095         assert_eq!(last_line_offsetted(2, lines), true);
2096         let lines = "one\n two      three";
2097         assert_eq!(last_line_offsetted(2, lines), false);
2098     }
2099 }