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::{Delimiter, 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                 qself,
 112                 fields,
 113                 path,
 114                 rest,
 115             } = &**struct_expr;
 116             rewrite_struct_lit(
 117                 context,
 118                 path,
 119                 qself.as_ref(),
 120                 fields,
 121                 rest,
 122                 &expr.attrs,
 123                 expr.span,
 124                 shape,
 125             )
 126         }
 127         ast::ExprKind::Tup(ref items) => {
 128             rewrite_tuple(context, items.iter(), expr.span, shape, items.len() == 1)
 129         }
 130         ast::ExprKind::Let(..) => None,
 131         ast::ExprKind::If(..)
 132         | ast::ExprKind::ForLoop(..)
 133         | ast::ExprKind::Loop(..)
 134         | ast::ExprKind::While(..) => to_control_flow(expr, expr_type)
 135             .and_then(|control_flow| control_flow.rewrite(context, shape)),
 136         ast::ExprKind::ConstBlock(ref anon_const) => {
 137             Some(format!("const {}", anon_const.rewrite(context, shape)?))
 138         }
 139         ast::ExprKind::Block(ref block, opt_label) => {
 140             match expr_type {
 141                 ExprType::Statement => {
 142                     if is_unsafe_block(block) {
 143                         rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 144                     } else if let rw @ Some(_) =
 145                         rewrite_empty_block(context, block, Some(&expr.attrs), opt_label, "", shape)
 146                     {
 147                         // Rewrite block without trying to put it in a single line.
 148                         rw
 149                     } else {
 150                         let prefix = block_prefix(context, block, shape)?;
 151
 152                         rewrite_block_with_visitor(
 153                             context,
 154                             &prefix,
 155                             block,
 156                             Some(&expr.attrs),
 157                             opt_label,
 158                             shape,
 159                             true,
 160                         )
 161                     }
 162                 }
 163                 ExprType::SubExpression => {
 164                     rewrite_block(block, Some(&expr.attrs), opt_label, context, shape)
 165                 }
 166             }
 167         }
 168         ast::ExprKind::Match(ref cond, ref arms) => {
 169             rewrite_match(context, cond, arms, shape, expr.span, &expr.attrs)
 170         }
 171         ast::ExprKind::Path(ref qself, ref path) => {
 172             rewrite_path(context, PathContext::Expr, qself.as_ref(), path, shape)
 173         }
 174         ast::ExprKind::Assign(ref lhs, ref rhs, _) => {
 175             rewrite_assignment(context, lhs, rhs, None, shape)
 176         }
 177         ast::ExprKind::AssignOp(ref op, ref lhs, ref rhs) => {
 178             rewrite_assignment(context, lhs, rhs, Some(op), shape)
 179         }
 180         ast::ExprKind::Continue(ref opt_label) => {
 181             let id_str = match *opt_label {
 182                 Some(label) => format!(" {}", label.ident),
 183                 None => String::new(),
 184             };
 185             Some(format!("continue{}", id_str))
 186         }
 187         ast::ExprKind::Break(ref opt_label, ref opt_expr) => {
 188             let id_str = match *opt_label {
 189                 Some(label) => format!(" {}", label.ident),
 190                 None => String::new(),
 191             };
 192
 193             if let Some(ref expr) = *opt_expr {
 194                 rewrite_unary_prefix(context, &format!("break{} ", id_str), &**expr, shape)
 195             } else {
 196                 Some(format!("break{}", id_str))
 197             }
 198         }
 199         ast::ExprKind::Yield(ref opt_expr) => {
 200             if let Some(ref expr) = *opt_expr {
 201                 rewrite_unary_prefix(context, "yield ", &**expr, shape)
 202             } else {
 203                 Some("yield".to_string())
 204             }
 205         }
 206         ast::ExprKind::Closure(capture, ref is_async, movability, ref fn_decl, ref body, _) => {
 207             closures::rewrite_closure(
 208                 capture, is_async, movability, fn_decl, body, expr.span, context, shape,
 209             )
 210         }
 211         ast::ExprKind::Try(..)
 212         | ast::ExprKind::Field(..)
 213         | ast::ExprKind::MethodCall(..)
 214         | ast::ExprKind::Await(_) => rewrite_chain(expr, context, shape),
 215         ast::ExprKind::MacCall(ref mac) => {
 216             rewrite_macro(mac, None, context, shape, MacroPosition::Expression).or_else(|| {
 217                 wrap_str(
 218                     context.snippet(expr.span).to_owned(),
 219                     context.config.max_width(),
 220                     shape,
 221                 )
 222             })
 223         }
 224         ast::ExprKind::Ret(None) => Some("return".to_owned()),
 225         ast::ExprKind::Ret(Some(ref expr)) => {
 226             rewrite_unary_prefix(context, "return ", &**expr, shape)
 227         }
 228         ast::ExprKind::Yeet(None) => Some("do yeet".to_owned()),
 229         ast::ExprKind::Yeet(Some(ref expr)) => {
 230             rewrite_unary_prefix(context, "do yeet ", &**expr, shape)
 231         }
 232         ast::ExprKind::Box(ref expr) => rewrite_unary_prefix(context, "box ", &**expr, shape),
 233         ast::ExprKind::AddrOf(borrow_kind, mutability, ref expr) => {
 234             rewrite_expr_addrof(context, borrow_kind, mutability, expr, shape)
 235         }
 236         ast::ExprKind::Cast(ref expr, ref ty) => rewrite_pair(
 237             &**expr,
 238             &**ty,
 239             PairParts::infix(" as "),
 240             context,
 241             shape,
 242             SeparatorPlace::Front,
 243         ),
 244         ast::ExprKind::Type(ref expr, ref ty) => rewrite_pair(
 245             &**expr,
 246             &**ty,
 247             PairParts::infix(": "),
 248             context,
 249             shape,
 250             SeparatorPlace::Back,
 251         ),
 252         ast::ExprKind::Index(ref expr, ref index) => {
 253             rewrite_index(&**expr, &**index, context, shape)
 254         }
 255         ast::ExprKind::Repeat(ref expr, ref repeats) => rewrite_pair(
 256             &**expr,
 257             &*repeats.value,
 258             PairParts::new("[", "; ", "]"),
 259             context,
 260             shape,
 261             SeparatorPlace::Back,
 262         ),
 263         ast::ExprKind::Range(ref lhs, ref rhs, limits) => {
 264             let delim = match limits {
 265                 ast::RangeLimits::HalfOpen => "..",
 266                 ast::RangeLimits::Closed => "..=",
 267             };
 268
 269             fn needs_space_before_range(context: &RewriteContext<'_>, lhs: &ast::Expr) -> bool {
 270                 match lhs.kind {
 271                     ast::ExprKind::Lit(ref lit) => match lit.kind {
 272                         ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) => {
 273                             context.snippet(lit.span).ends_with('.')
 274                         }
 275                         _ => false,
 276                     },
 277                     ast::ExprKind::Unary(_, ref expr) => needs_space_before_range(context, expr),
 278                     _ => false,
 279                 }
 280             }
 281
 282             fn needs_space_after_range(rhs: &ast::Expr) -> bool {
 283                 // Don't format `.. ..` into `....`, which is invalid.
 284                 //
 285                 // This check is unnecessary for `lhs`, because a range
 286                 // starting from another range needs parentheses as `(x ..) ..`
 287                 // (`x .. ..` is a range from `x` to `..`).
 288                 matches!(rhs.kind, ast::ExprKind::Range(None, _, _))
 289             }
 290
 291             let default_sp_delim = |lhs: Option<&ast::Expr>, rhs: Option<&ast::Expr>| {
 292                 let space_if = |b: bool| if b { " " } else { "" };
 293
 294                 format!(
 295                     "{}{}{}",
 296                     lhs.map_or("", |lhs| space_if(needs_space_before_range(context, lhs))),
 297                     delim,
 298                     rhs.map_or("", |rhs| space_if(needs_space_after_range(rhs))),
 299                 )
 300             };
 301
 302             match (lhs.as_ref().map(|x| &**x), rhs.as_ref().map(|x| &**x)) {
 303                 (Some(lhs), Some(rhs)) => {
 304                     let sp_delim = if context.config.spaces_around_ranges() {
 305                         format!(" {} ", delim)
 306                     } else {
 307                         default_sp_delim(Some(lhs), Some(rhs))
 308                     };
 309                     rewrite_pair(
 310                         &*lhs,
 311                         &*rhs,
 312                         PairParts::infix(&sp_delim),
 313                         context,
 314                         shape,
 315                         context.config.binop_separator(),
 316                     )
 317                 }
 318                 (None, Some(rhs)) => {
 319                     let sp_delim = if context.config.spaces_around_ranges() {
 320                         format!("{} ", delim)
 321                     } else {
 322                         default_sp_delim(None, Some(rhs))
 323                     };
 324                     rewrite_unary_prefix(context, &sp_delim, &*rhs, shape)
 325                 }
 326                 (Some(lhs), None) => {
 327                     let sp_delim = if context.config.spaces_around_ranges() {
 328                         format!(" {}", delim)
 329                     } else {
 330                         default_sp_delim(Some(lhs), None)
 331                     };
 332                     rewrite_unary_suffix(context, &sp_delim, &*lhs, shape)
 333                 }
 334                 (None, None) => Some(delim.to_owned()),
 335             }
 336         }
 337         // We do not format these expressions yet, but they should still
 338         // satisfy our width restrictions.
 339         // Style Guide RFC for InlineAsm variant pending
 340         // https://github.com/rust-dev-tools/fmt-rfcs/issues/152
 341         ast::ExprKind::InlineAsm(..) => Some(context.snippet(expr.span).to_owned()),
 342         ast::ExprKind::TryBlock(ref block) => {
 343             if let rw @ Some(_) =
 344                 rewrite_single_line_block(context, "try ", block, Some(&expr.attrs), None, shape)
 345             {
 346                 rw
 347             } else {
 348                 // 9 = `try `
 349                 let budget = shape.width.saturating_sub(9);
 350                 Some(format!(
 351                     "{}{}",
 352                     "try ",
 353                     rewrite_block(
 354                         block,
 355                         Some(&expr.attrs),
 356                         None,
 357                         context,
 358                         Shape::legacy(budget, shape.indent)
 359                     )?
 360                 ))
 361             }
 362         }
 363         ast::ExprKind::Async(capture_by, _node_id, ref block) => {
 364             let mover = if capture_by == ast::CaptureBy::Value {
 365                 "move "
 366             } else {
 367                 ""
 368             };
 369             if let rw @ Some(_) = rewrite_single_line_block(
 370                 context,
 371                 format!("{}{}", "async ", mover).as_str(),
 372                 block,
 373                 Some(&expr.attrs),
 374                 None,
 375                 shape,
 376             ) {
 377                 rw
 378             } else {
 379                 // 6 = `async `
 380                 let budget = shape.width.saturating_sub(6);
 381                 Some(format!(
 382                     "{}{}{}",
 383                     "async ",
 384                     mover,
 385                     rewrite_block(
 386                         block,
 387                         Some(&expr.attrs),
 388                         None,
 389                         context,
 390                         Shape::legacy(budget, shape.indent)
 391                     )?
 392                 ))
 393             }
 394         }
 395         ast::ExprKind::Underscore => Some("_".to_owned()),
 396         ast::ExprKind::Err => None,
 397     };
 398
 399     expr_rw
 400         .and_then(|expr_str| recover_comment_removed(expr_str, expr.span, context))
 401         .and_then(|expr_str| {
 402             let attrs = outer_attributes(&expr.attrs);
 403             let attrs_str = attrs.rewrite(context, shape)?;
 404             let span = mk_sp(
 405                 attrs.last().map_or(expr.span.lo(), |attr| attr.span.hi()),
 406                 expr.span.lo(),
 407             );
 408             combine_strs_with_missing_comments(context, &attrs_str, &expr_str, span, shape, false)
 409         })
 410 }
 411
 412 pub(crate) fn rewrite_array<'a, T: 'a + IntoOverflowableItem<'a>>(
 413     name: &'a str,
 414     exprs: impl Iterator<Item = &'a T>,
 415     span: Span,
 416     context: &'a RewriteContext<'_>,
 417     shape: Shape,
 418     force_separator_tactic: Option<SeparatorTactic>,
 419     delim_token: Option<Delimiter>,
 420 ) -> Option<String> {
 421     overflow::rewrite_with_square_brackets(
 422         context,
 423         name,
 424         exprs,
 425         shape,
 426         span,
 427         force_separator_tactic,
 428         delim_token,
 429     )
 430 }
 431
 432 fn rewrite_empty_block(
 433     context: &RewriteContext<'_>,
 434     block: &ast::Block,
 435     attrs: Option<&[ast::Attribute]>,
 436     label: Option<ast::Label>,
 437     prefix: &str,
 438     shape: Shape,
 439 ) -> Option<String> {
 440     if block_has_statements(block) {
 441         return None;
 442     }
 443
 444     let label_str = rewrite_label(label);
 445     if attrs.map_or(false, |a| !inner_attributes(a).is_empty()) {
 446         return None;
 447     }
 448
 449     if !block_contains_comment(context, block) && shape.width >= 2 {
 450         return Some(format!("{}{}{{}}", prefix, label_str));
 451     }
 452
 453     // If a block contains only a single-line comment, then leave it on one line.
 454     let user_str = context.snippet(block.span);
 455     let user_str = user_str.trim();
 456     if user_str.starts_with('{') && user_str.ends_with('}') {
 457         let comment_str = user_str[1..user_str.len() - 1].trim();
 458         if block.stmts.is_empty()
 459             && !comment_str.contains('\n')
 460             && !comment_str.starts_with("//")
 461             && comment_str.len() + 4 <= shape.width
 462         {
 463             return Some(format!("{}{}{{ {} }}", prefix, label_str, comment_str));
 464         }
 465     }
 466
 467     None
 468 }
 469
 470 fn block_prefix(context: &RewriteContext<'_>, block: &ast::Block, shape: Shape) -> Option<String> {
 471     Some(match block.rules {
 472         ast::BlockCheckMode::Unsafe(..) => {
 473             let snippet = context.snippet(block.span);
 474             let open_pos = snippet.find_uncommented("{")?;
 475             // Extract comment between unsafe and block start.
 476             let trimmed = &snippet[6..open_pos].trim();
 477
 478             if !trimmed.is_empty() {
 479                 // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
 480                 let budget = shape.width.checked_sub(9)?;
 481                 format!(
 482                     "unsafe {} ",
 483                     rewrite_comment(
 484                         trimmed,
 485                         true,
 486                         Shape::legacy(budget, shape.indent + 7),
 487                         context.config,
 488                     )?
 489                 )
 490             } else {
 491                 "unsafe ".to_owned()
 492             }
 493         }
 494         ast::BlockCheckMode::Default => String::new(),
 495     })
 496 }
 497
 498 fn rewrite_single_line_block(
 499     context: &RewriteContext<'_>,
 500     prefix: &str,
 501     block: &ast::Block,
 502     attrs: Option<&[ast::Attribute]>,
 503     label: Option<ast::Label>,
 504     shape: Shape,
 505 ) -> Option<String> {
 506     if is_simple_block(context, block, attrs) {
 507         let expr_shape = shape.offset_left(last_line_width(prefix))?;
 508         let expr_str = block.stmts[0].rewrite(context, expr_shape)?;
 509         let label_str = rewrite_label(label);
 510         let result = format!("{}{}{{ {} }}", prefix, label_str, expr_str);
 511         if result.len() <= shape.width && !result.contains('\n') {
 512             return Some(result);
 513         }
 514     }
 515     None
 516 }
 517
 518 pub(crate) fn rewrite_block_with_visitor(
 519     context: &RewriteContext<'_>,
 520     prefix: &str,
 521     block: &ast::Block,
 522     attrs: Option<&[ast::Attribute]>,
 523     label: Option<ast::Label>,
 524     shape: Shape,
 525     has_braces: bool,
 526 ) -> Option<String> {
 527     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, prefix, shape) {
 528         return rw;
 529     }
 530
 531     let mut visitor = FmtVisitor::from_context(context);
 532     visitor.block_indent = shape.indent;
 533     visitor.is_if_else_block = context.is_if_else_block();
 534     match (block.rules, label) {
 535         (ast::BlockCheckMode::Unsafe(..), _) | (ast::BlockCheckMode::Default, Some(_)) => {
 536             let snippet = context.snippet(block.span);
 537             let open_pos = snippet.find_uncommented("{")?;
 538             visitor.last_pos = block.span.lo() + BytePos(open_pos as u32)
 539         }
 540         (ast::BlockCheckMode::Default, None) => visitor.last_pos = block.span.lo(),
 541     }
 542
 543     let inner_attrs = attrs.map(inner_attributes);
 544     let label_str = rewrite_label(label);
 545     visitor.visit_block(block, inner_attrs.as_deref(), has_braces);
 546     let visitor_context = visitor.get_context();
 547     context
 548         .skipped_range
 549         .borrow_mut()
 550         .append(&mut visitor_context.skipped_range.borrow_mut());
 551     Some(format!("{}{}{}", prefix, label_str, visitor.buffer))
 552 }
 553
 554 impl Rewrite for ast::Block {
 555     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 556         rewrite_block(self, None, None, context, shape)
 557     }
 558 }
 559
 560 fn rewrite_block(
 561     block: &ast::Block,
 562     attrs: Option<&[ast::Attribute]>,
 563     label: Option<ast::Label>,
 564     context: &RewriteContext<'_>,
 565     shape: Shape,
 566 ) -> Option<String> {
 567     let prefix = block_prefix(context, block, shape)?;
 568
 569     // shape.width is used only for the single line case: either the empty block `{}`,
 570     // or an unsafe expression `unsafe { e }`.
 571     if let rw @ Some(_) = rewrite_empty_block(context, block, attrs, label, &prefix, shape) {
 572         return rw;
 573     }
 574
 575     let result = rewrite_block_with_visitor(context, &prefix, block, attrs, label, shape, true);
 576     if let Some(ref result_str) = result {
 577         if result_str.lines().count() <= 3 {
 578             if let rw @ Some(_) =
 579                 rewrite_single_line_block(context, &prefix, block, attrs, label, shape)
 580             {
 581                 return rw;
 582             }
 583         }
 584     }
 585
 586     result
 587 }
 588
 589 // Rewrite condition if the given expression has one.
 590 pub(crate) fn rewrite_cond(
 591     context: &RewriteContext<'_>,
 592     expr: &ast::Expr,
 593     shape: Shape,
 594 ) -> Option<String> {
 595     match expr.kind {
 596         ast::ExprKind::Match(ref cond, _) => {
 597             // `match `cond` {`
 598             let cond_shape = match context.config.indent_style() {
 599                 IndentStyle::Visual => shape.shrink_left(6).and_then(|s| s.sub_width(2))?,
 600                 IndentStyle::Block => shape.offset_left(8)?,
 601             };
 602             cond.rewrite(context, cond_shape)
 603         }
 604         _ => to_control_flow(expr, ExprType::SubExpression).and_then(|control_flow| {
 605             let alt_block_sep =
 606                 String::from("\n") + &shape.indent.block_only().to_string(context.config);
 607             control_flow
 608                 .rewrite_cond(context, shape, &alt_block_sep)
 609                 .map(|rw| rw.0)
 610         }),
 611     }
 612 }
 613
 614 // Abstraction over control flow expressions
 615 #[derive(Debug)]
 616 struct ControlFlow<'a> {
 617     cond: Option<&'a ast::Expr>,
 618     block: &'a ast::Block,
 619     else_block: Option<&'a ast::Expr>,
 620     label: Option<ast::Label>,
 621     pat: Option<&'a ast::Pat>,
 622     keyword: &'a str,
 623     matcher: &'a str,
 624     connector: &'a str,
 625     allow_single_line: bool,
 626     // HACK: `true` if this is an `if` expression in an `else if`.
 627     nested_if: bool,
 628     span: Span,
 629 }
 630
 631 fn extract_pats_and_cond(expr: &ast::Expr) -> (Option<&ast::Pat>, &ast::Expr) {
 632     match expr.kind {
 633         ast::ExprKind::Let(ref pat, ref cond, _) => (Some(pat), cond),
 634         _ => (None, expr),
 635     }
 636 }
 637
 638 // FIXME: Refactor this.
 639 fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow<'_>> {
 640     match expr.kind {
 641         ast::ExprKind::If(ref cond, ref if_block, ref else_block) => {
 642             let (pat, cond) = extract_pats_and_cond(cond);
 643             Some(ControlFlow::new_if(
 644                 cond,
 645                 pat,
 646                 if_block,
 647                 else_block.as_ref().map(|e| &**e),
 648                 expr_type == ExprType::SubExpression,
 649                 false,
 650                 expr.span,
 651             ))
 652         }
 653         ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
 654             Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
 655         }
 656         ast::ExprKind::Loop(ref block, label) => {
 657             Some(ControlFlow::new_loop(block, label, expr.span))
 658         }
 659         ast::ExprKind::While(ref cond, ref block, label) => {
 660             let (pat, cond) = extract_pats_and_cond(cond);
 661             Some(ControlFlow::new_while(pat, cond, block, label, expr.span))
 662         }
 663         _ => None,
 664     }
 665 }
 666
 667 fn choose_matcher(pat: Option<&ast::Pat>) -> &'static str {
 668     pat.map_or("", |_| "let")
 669 }
 670
 671 impl<'a> ControlFlow<'a> {
 672     fn new_if(
 673         cond: &'a ast::Expr,
 674         pat: Option<&'a ast::Pat>,
 675         block: &'a ast::Block,
 676         else_block: Option<&'a ast::Expr>,
 677         allow_single_line: bool,
 678         nested_if: bool,
 679         span: Span,
 680     ) -> ControlFlow<'a> {
 681         let matcher = choose_matcher(pat);
 682         ControlFlow {
 683             cond: Some(cond),
 684             block,
 685             else_block,
 686             label: None,
 687             pat,
 688             keyword: "if",
 689             matcher,
 690             connector: " =",
 691             allow_single_line,
 692             nested_if,
 693             span,
 694         }
 695     }
 696
 697     fn new_loop(block: &'a ast::Block, label: Option<ast::Label>, span: Span) -> ControlFlow<'a> {
 698         ControlFlow {
 699             cond: None,
 700             block,
 701             else_block: None,
 702             label,
 703             pat: None,
 704             keyword: "loop",
 705             matcher: "",
 706             connector: "",
 707             allow_single_line: false,
 708             nested_if: false,
 709             span,
 710         }
 711     }
 712
 713     fn new_while(
 714         pat: Option<&'a ast::Pat>,
 715         cond: &'a ast::Expr,
 716         block: &'a ast::Block,
 717         label: Option<ast::Label>,
 718         span: Span,
 719     ) -> ControlFlow<'a> {
 720         let matcher = choose_matcher(pat);
 721         ControlFlow {
 722             cond: Some(cond),
 723             block,
 724             else_block: None,
 725             label,
 726             pat,
 727             keyword: "while",
 728             matcher,
 729             connector: " =",
 730             allow_single_line: false,
 731             nested_if: false,
 732             span,
 733         }
 734     }
 735
 736     fn new_for(
 737         pat: &'a ast::Pat,
 738         cond: &'a ast::Expr,
 739         block: &'a ast::Block,
 740         label: Option<ast::Label>,
 741         span: Span,
 742     ) -> ControlFlow<'a> {
 743         ControlFlow {
 744             cond: Some(cond),
 745             block,
 746             else_block: None,
 747             label,
 748             pat: Some(pat),
 749             keyword: "for",
 750             matcher: "",
 751             connector: " in",
 752             allow_single_line: false,
 753             nested_if: false,
 754             span,
 755         }
 756     }
 757
 758     fn rewrite_single_line(
 759         &self,
 760         pat_expr_str: &str,
 761         context: &RewriteContext<'_>,
 762         width: usize,
 763     ) -> Option<String> {
 764         assert!(self.allow_single_line);
 765         let else_block = self.else_block?;
 766         let fixed_cost = self.keyword.len() + "  {  } else {  }".len();
 767
 768         if let ast::ExprKind::Block(ref else_node, _) = else_block.kind {
 769             if !is_simple_block(context, self.block, None)
 770                 || !is_simple_block(context, else_node, None)
 771                 || pat_expr_str.contains('\n')
 772             {
 773                 return None;
 774             }
 775
 776             let new_width = width.checked_sub(pat_expr_str.len() + fixed_cost)?;
 777             let expr = &self.block.stmts[0];
 778             let if_str = expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 779
 780             let new_width = new_width.checked_sub(if_str.len())?;
 781             let else_expr = &else_node.stmts[0];
 782             let else_str = else_expr.rewrite(context, Shape::legacy(new_width, Indent::empty()))?;
 783
 784             if if_str.contains('\n') || else_str.contains('\n') {
 785                 return None;
 786             }
 787
 788             let result = format!(
 789                 "{} {} {{ {} }} else {{ {} }}",
 790                 self.keyword, pat_expr_str, if_str, else_str
 791             );
 792
 793             if result.len() <= width {
 794                 return Some(result);
 795             }
 796         }
 797
 798         None
 799     }
 800 }
 801
 802 /// Returns `true` if the last line of pat_str has leading whitespace and it is wider than the
 803 /// shape's indent.
 804 fn last_line_offsetted(start_column: usize, pat_str: &str) -> bool {
 805     let mut leading_whitespaces = 0;
 806     for c in pat_str.chars().rev() {
 807         match c {
 808             '\n' => break,
 809             _ if c.is_whitespace() => leading_whitespaces += 1,
 810             _ => leading_whitespaces = 0,
 811         }
 812     }
 813     leading_whitespaces > start_column
 814 }
 815
 816 impl<'a> ControlFlow<'a> {
 817     fn rewrite_pat_expr(
 818         &self,
 819         context: &RewriteContext<'_>,
 820         expr: &ast::Expr,
 821         shape: Shape,
 822         offset: usize,
 823     ) -> Option<String> {
 824         debug!("rewrite_pat_expr {:?} {:?} {:?}", shape, self.pat, expr);
 825
 826         let cond_shape = shape.offset_left(offset)?;
 827         if let Some(pat) = self.pat {
 828             let matcher = if self.matcher.is_empty() {
 829                 self.matcher.to_owned()
 830             } else {
 831                 format!("{} ", self.matcher)
 832             };
 833             let pat_shape = cond_shape
 834                 .offset_left(matcher.len())?
 835                 .sub_width(self.connector.len())?;
 836             let pat_string = pat.rewrite(context, pat_shape)?;
 837             let comments_lo = context
 838                 .snippet_provider
 839                 .span_after(self.span.with_lo(pat.span.hi()), self.connector.trim());
 840             let comments_span = mk_sp(comments_lo, expr.span.lo());
 841             return rewrite_assign_rhs_with_comments(
 842                 context,
 843                 &format!("{}{}{}", matcher, pat_string, self.connector),
 844                 expr,
 845                 cond_shape,
 846                 &RhsAssignKind::Expr(&expr.kind, expr.span),
 847                 RhsTactics::Default,
 848                 comments_span,
 849                 true,
 850             );
 851         }
 852
 853         let expr_rw = expr.rewrite(context, cond_shape);
 854         // The expression may (partially) fit on the current line.
 855         // We do not allow splitting between `if` and condition.
 856         if self.keyword == "if" || expr_rw.is_some() {
 857             return expr_rw;
 858         }
 859
 860         // The expression won't fit on the current line, jump to next.
 861         let nested_shape = shape
 862             .block_indent(context.config.tab_spaces())
 863             .with_max_width(context.config);
 864         let nested_indent_str = nested_shape.indent.to_string_with_newline(context.config);
 865         expr.rewrite(context, nested_shape)
 866             .map(|expr_rw| format!("{}{}", nested_indent_str, expr_rw))
 867     }
 868
 869     fn rewrite_cond(
 870         &self,
 871         context: &RewriteContext<'_>,
 872         shape: Shape,
 873         alt_block_sep: &str,
 874     ) -> Option<(String, usize)> {
 875         // Do not take the rhs overhead from the upper expressions into account
 876         // when rewriting pattern.
 877         let new_width = context.budget(shape.used_width());
 878         let fresh_shape = Shape {
 879             width: new_width,
 880             ..shape
 881         };
 882         let constr_shape = if self.nested_if {
 883             // We are part of an if-elseif-else chain. Our constraints are tightened.
 884             // 7 = "} else " .len()
 885             fresh_shape.offset_left(7)?
 886         } else {
 887             fresh_shape
 888         };
 889
 890         let label_string = rewrite_label(self.label);
 891         // 1 = space after keyword.
 892         let offset = self.keyword.len() + label_string.len() + 1;
 893
 894         let pat_expr_string = match self.cond {
 895             Some(cond) => self.rewrite_pat_expr(context, cond, constr_shape, offset)?,
 896             None => String::new(),
 897         };
 898
 899         let brace_overhead =
 900             if context.config.control_brace_style() != ControlBraceStyle::AlwaysNextLine {
 901                 // 2 = ` {`
 902                 2
 903             } else {
 904                 0
 905             };
 906         let one_line_budget = context
 907             .config
 908             .max_width()
 909             .saturating_sub(constr_shape.used_width() + offset + brace_overhead);
 910         let force_newline_brace = (pat_expr_string.contains('\n')
 911             || pat_expr_string.len() > one_line_budget)
 912             && (!last_line_extendable(&pat_expr_string)
 913                 || last_line_offsetted(shape.used_width(), &pat_expr_string));
 914
 915         // Try to format if-else on single line.
 916         if self.allow_single_line && context.config.single_line_if_else_max_width() > 0 {
 917             let trial = self.rewrite_single_line(&pat_expr_string, context, shape.width);
 918
 919             if let Some(cond_str) = trial {
 920                 if cond_str.len() <= context.config.single_line_if_else_max_width() {
 921                     return Some((cond_str, 0));
 922                 }
 923             }
 924         }
 925
 926         let cond_span = if let Some(cond) = self.cond {
 927             cond.span
 928         } else {
 929             mk_sp(self.block.span.lo(), self.block.span.lo())
 930         };
 931
 932         // `for event in event`
 933         // Do not include label in the span.
 934         let lo = self
 935             .label
 936             .map_or(self.span.lo(), |label| label.ident.span.hi());
 937         let between_kwd_cond = mk_sp(
 938             context
 939                 .snippet_provider
 940                 .span_after(mk_sp(lo, self.span.hi()), self.keyword.trim()),
 941             if self.pat.is_none() {
 942                 cond_span.lo()
 943             } else if self.matcher.is_empty() {
 944                 self.pat.unwrap().span.lo()
 945             } else {
 946                 context
 947                     .snippet_provider
 948                     .span_before(self.span, self.matcher.trim())
 949             },
 950         );
 951
 952         let between_kwd_cond_comment = extract_comment(between_kwd_cond, context, shape);
 953
 954         let after_cond_comment =
 955             extract_comment(mk_sp(cond_span.hi(), self.block.span.lo()), context, shape);
 956
 957         let block_sep = if self.cond.is_none() && between_kwd_cond_comment.is_some() {
 958             ""
 959         } else if context.config.control_brace_style() == ControlBraceStyle::AlwaysNextLine
 960             || force_newline_brace
 961         {
 962             alt_block_sep
 963         } else {
 964             " "
 965         };
 966
 967         let used_width = if pat_expr_string.contains('\n') {
 968             last_line_width(&pat_expr_string)
 969         } else {
 970             // 2 = spaces after keyword and condition.
 971             label_string.len() + self.keyword.len() + pat_expr_string.len() + 2
 972         };
 973
 974         Some((
 975             format!(
 976                 "{}{}{}{}{}",
 977                 label_string,
 978                 self.keyword,
 979                 between_kwd_cond_comment.as_ref().map_or(
 980                     if pat_expr_string.is_empty() || pat_expr_string.starts_with('\n') {
 981                         ""
 982                     } else {
 983                         " "
 984                     },
 985                     |s| &**s,
 986                 ),
 987                 pat_expr_string,
 988                 after_cond_comment.as_ref().map_or(block_sep, |s| &**s)
 989             ),
 990             used_width,
 991         ))
 992     }
 993 }
 994
 995 impl<'a> Rewrite for ControlFlow<'a> {
 996     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 997         debug!("ControlFlow::rewrite {:?} {:?}", self, shape);
 998
 999         let alt_block_sep = &shape.indent.to_string_with_newline(context.config);
1000         let (cond_str, used_width) = self.rewrite_cond(context, shape, alt_block_sep)?;
1001         // If `used_width` is 0, it indicates that whole control flow is written in a single line.
1002         if used_width == 0 {
1003             return Some(cond_str);
1004         }
1005
1006         let block_width = shape.width.saturating_sub(used_width);
1007         // This is used only for the empty block case: `{}`. So, we use 1 if we know
1008         // we should avoid the single line case.
1009         let block_width = if self.else_block.is_some() || self.nested_if {
1010             min(1, block_width)
1011         } else {
1012             block_width
1013         };
1014         let block_shape = Shape {
1015             width: block_width,
1016             ..shape
1017         };
1018         let block_str = {
1019             let old_val = context.is_if_else_block.replace(self.else_block.is_some());
1020             let result =
1021                 rewrite_block_with_visitor(context, "", self.block, None, None, block_shape, true);
1022             context.is_if_else_block.replace(old_val);
1023             result?
1024         };
1025
1026         let mut result = format!("{}{}", cond_str, block_str);
1027
1028         if let Some(else_block) = self.else_block {
1029             let shape = Shape::indented(shape.indent, context.config);
1030             let mut last_in_chain = false;
1031             let rewrite = match else_block.kind {
1032                 // If the else expression is another if-else expression, prevent it
1033                 // from being formatted on a single line.
1034                 // Note how we're passing the original shape, as the
1035                 // cost of "else" should not cascade.
1036                 ast::ExprKind::If(ref cond, ref if_block, ref next_else_block) => {
1037                     let (pats, cond) = extract_pats_and_cond(cond);
1038                     ControlFlow::new_if(
1039                         cond,
1040                         pats,
1041                         if_block,
1042                         next_else_block.as_ref().map(|e| &**e),
1043                         false,
1044                         true,
1045                         mk_sp(else_block.span.lo(), self.span.hi()),
1046                     )
1047                     .rewrite(context, shape)
1048                 }
1049                 _ => {
1050                     last_in_chain = true;
1051                     // When rewriting a block, the width is only used for single line
1052                     // blocks, passing 1 lets us avoid that.
1053                     let else_shape = Shape {
1054                         width: min(1, shape.width),
1055                         ..shape
1056                     };
1057                     format_expr(else_block, ExprType::Statement, context, else_shape)
1058                 }
1059             };
1060
1061             let between_kwd_else_block = mk_sp(
1062                 self.block.span.hi(),
1063                 context
1064                     .snippet_provider
1065                     .span_before(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1066             );
1067             let between_kwd_else_block_comment =
1068                 extract_comment(between_kwd_else_block, context, shape);
1069
1070             let after_else = mk_sp(
1071                 context
1072                     .snippet_provider
1073                     .span_after(mk_sp(self.block.span.hi(), else_block.span.lo()), "else"),
1074                 else_block.span.lo(),
1075             );
1076             let after_else_comment = extract_comment(after_else, context, shape);
1077
1078             let between_sep = match context.config.control_brace_style() {
1079                 ControlBraceStyle::AlwaysNextLine | ControlBraceStyle::ClosingNextLine => {
1080                     &*alt_block_sep
1081                 }
1082                 ControlBraceStyle::AlwaysSameLine => " ",
1083             };
1084             let after_sep = match context.config.control_brace_style() {
1085                 ControlBraceStyle::AlwaysNextLine if last_in_chain => &*alt_block_sep,
1086                 _ => " ",
1087             };
1088
1089             result.push_str(&format!(
1090                 "{}else{}",
1091                 between_kwd_else_block_comment
1092                     .as_ref()
1093                     .map_or(between_sep, |s| &**s),
1094                 after_else_comment.as_ref().map_or(after_sep, |s| &**s),
1095             ));
1096             result.push_str(&rewrite?);
1097         }
1098
1099         Some(result)
1100     }
1101 }
1102
1103 fn rewrite_label(opt_label: Option<ast::Label>) -> Cow<'static, str> {
1104     match opt_label {
1105         Some(label) => Cow::from(format!("{}: ", label.ident)),
1106         None => Cow::from(""),
1107     }
1108 }
1109
1110 fn extract_comment(span: Span, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1111     match rewrite_missing_comment(span, shape, context) {
1112         Some(ref comment) if !comment.is_empty() => Some(format!(
1113             "{indent}{}{indent}",
1114             comment,
1115             indent = shape.indent.to_string_with_newline(context.config)
1116         )),
1117         _ => None,
1118     }
1119 }
1120
1121 pub(crate) fn block_contains_comment(context: &RewriteContext<'_>, block: &ast::Block) -> bool {
1122     contains_comment(context.snippet(block.span))
1123 }
1124
1125 // Checks that a block contains no statements, an expression and no comments or
1126 // attributes.
1127 // FIXME: incorrectly returns false when comment is contained completely within
1128 // the expression.
1129 pub(crate) fn is_simple_block(
1130     context: &RewriteContext<'_>,
1131     block: &ast::Block,
1132     attrs: Option<&[ast::Attribute]>,
1133 ) -> bool {
1134     block.stmts.len() == 1
1135         && stmt_is_expr(&block.stmts[0])
1136         && !block_contains_comment(context, block)
1137         && attrs.map_or(true, |a| a.is_empty())
1138 }
1139
1140 /// Checks whether a block contains at most one statement or expression, and no
1141 /// comments or attributes.
1142 pub(crate) fn is_simple_block_stmt(
1143     context: &RewriteContext<'_>,
1144     block: &ast::Block,
1145     attrs: Option<&[ast::Attribute]>,
1146 ) -> bool {
1147     block.stmts.len() <= 1
1148         && !block_contains_comment(context, block)
1149         && attrs.map_or(true, |a| a.is_empty())
1150 }
1151
1152 fn block_has_statements(block: &ast::Block) -> bool {
1153     block
1154         .stmts
1155         .iter()
1156         .any(|stmt| !matches!(stmt.kind, ast::StmtKind::Empty))
1157 }
1158
1159 /// Checks whether a block contains no statements, expressions, comments, or
1160 /// inner attributes.
1161 pub(crate) fn is_empty_block(
1162     context: &RewriteContext<'_>,
1163     block: &ast::Block,
1164     attrs: Option<&[ast::Attribute]>,
1165 ) -> bool {
1166     !block_has_statements(block)
1167         && !block_contains_comment(context, block)
1168         && attrs.map_or(true, |a| inner_attributes(a).is_empty())
1169 }
1170
1171 pub(crate) fn stmt_is_expr(stmt: &ast::Stmt) -> bool {
1172     matches!(stmt.kind, ast::StmtKind::Expr(..))
1173 }
1174
1175 pub(crate) fn is_unsafe_block(block: &ast::Block) -> bool {
1176     matches!(block.rules, ast::BlockCheckMode::Unsafe(..))
1177 }
1178
1179 pub(crate) fn rewrite_literal(
1180     context: &RewriteContext<'_>,
1181     l: &ast::Lit,
1182     shape: Shape,
1183 ) -> Option<String> {
1184     match l.kind {
1185         ast::LitKind::Str(_, ast::StrStyle::Cooked) => rewrite_string_lit(context, l.span, shape),
1186         ast::LitKind::Int(..) => rewrite_int_lit(context, l, shape),
1187         _ => wrap_str(
1188             context.snippet(l.span).to_owned(),
1189             context.config.max_width(),
1190             shape,
1191         ),
1192     }
1193 }
1194
1195 fn rewrite_string_lit(context: &RewriteContext<'_>, span: Span, shape: Shape) -> Option<String> {
1196     let string_lit = context.snippet(span);
1197
1198     if !context.config.format_strings() {
1199         if string_lit
1200             .lines()
1201             .dropping_back(1)
1202             .all(|line| line.ends_with('\\'))
1203             && context.config.version() == Version::Two
1204         {
1205             return Some(string_lit.to_owned());
1206         } else {
1207             return wrap_str(string_lit.to_owned(), context.config.max_width(), shape);
1208         }
1209     }
1210
1211     // Remove the quote characters.
1212     let str_lit = &string_lit[1..string_lit.len() - 1];
1213
1214     rewrite_string(
1215         str_lit,
1216         &StringFormat::new(shape.visual_indent(0), context.config),
1217         shape.width.saturating_sub(2),
1218     )
1219 }
1220
1221 fn rewrite_int_lit(context: &RewriteContext<'_>, lit: &ast::Lit, shape: Shape) -> Option<String> {
1222     let span = lit.span;
1223     let symbol = lit.token.symbol.as_str();
1224
1225     if let Some(symbol_stripped) = symbol.strip_prefix("0x") {
1226         let hex_lit = match context.config.hex_literal_case() {
1227             HexLiteralCase::Preserve => None,
1228             HexLiteralCase::Upper => Some(symbol_stripped.to_ascii_uppercase()),
1229             HexLiteralCase::Lower => Some(symbol_stripped.to_ascii_lowercase()),
1230         };
1231         if let Some(hex_lit) = hex_lit {
1232             return wrap_str(
1233                 format!(
1234                     "0x{}{}",
1235                     hex_lit,
1236                     lit.token.suffix.map_or(String::new(), |s| s.to_string())
1237                 ),
1238                 context.config.max_width(),
1239                 shape,
1240             );
1241         }
1242     }
1243
1244     wrap_str(
1245         context.snippet(span).to_owned(),
1246         context.config.max_width(),
1247         shape,
1248     )
1249 }
1250
1251 fn choose_separator_tactic(context: &RewriteContext<'_>, span: Span) -> Option<SeparatorTactic> {
1252     if context.inside_macro() {
1253         if span_ends_with_comma(context, span) {
1254             Some(SeparatorTactic::Always)
1255         } else {
1256             Some(SeparatorTactic::Never)
1257         }
1258     } else {
1259         None
1260     }
1261 }
1262
1263 pub(crate) fn rewrite_call(
1264     context: &RewriteContext<'_>,
1265     callee: &str,
1266     args: &[ptr::P<ast::Expr>],
1267     span: Span,
1268     shape: Shape,
1269 ) -> Option<String> {
1270     overflow::rewrite_with_parens(
1271         context,
1272         callee,
1273         args.iter(),
1274         shape,
1275         span,
1276         context.config.fn_call_width(),
1277         choose_separator_tactic(context, span),
1278     )
1279 }
1280
1281 pub(crate) fn is_simple_expr(expr: &ast::Expr) -> bool {
1282     match expr.kind {
1283         ast::ExprKind::Lit(..) => true,
1284         ast::ExprKind::Path(ref qself, ref path) => qself.is_none() && path.segments.len() <= 1,
1285         ast::ExprKind::AddrOf(_, _, ref expr)
1286         | ast::ExprKind::Box(ref expr)
1287         | ast::ExprKind::Cast(ref expr, _)
1288         | ast::ExprKind::Field(ref expr, _)
1289         | ast::ExprKind::Try(ref expr)
1290         | ast::ExprKind::Unary(_, ref expr) => is_simple_expr(expr),
1291         ast::ExprKind::Index(ref lhs, ref rhs) => is_simple_expr(lhs) && is_simple_expr(rhs),
1292         ast::ExprKind::Repeat(ref lhs, ref rhs) => {
1293             is_simple_expr(lhs) && is_simple_expr(&*rhs.value)
1294         }
1295         _ => false,
1296     }
1297 }
1298
1299 pub(crate) fn is_every_expr_simple(lists: &[OverflowableItem<'_>]) -> bool {
1300     lists.iter().all(OverflowableItem::is_simple)
1301 }
1302
1303 pub(crate) fn can_be_overflowed_expr(
1304     context: &RewriteContext<'_>,
1305     expr: &ast::Expr,
1306     args_len: usize,
1307 ) -> bool {
1308     match expr.kind {
1309         _ if !expr.attrs.is_empty() => false,
1310         ast::ExprKind::Match(..) => {
1311             (context.use_block_indent() && args_len == 1)
1312                 || (context.config.indent_style() == IndentStyle::Visual && args_len > 1)
1313                 || context.config.overflow_delimited_expr()
1314         }
1315         ast::ExprKind::If(..)
1316         | ast::ExprKind::ForLoop(..)
1317         | ast::ExprKind::Loop(..)
1318         | ast::ExprKind::While(..) => {
1319             context.config.combine_control_expr() && context.use_block_indent() && args_len == 1
1320         }
1321
1322         // Handle always block-like expressions
1323         ast::ExprKind::Async(..) | ast::ExprKind::Block(..) | ast::ExprKind::Closure(..) => true,
1324
1325         // Handle `[]` and `{}`-like expressions
1326         ast::ExprKind::Array(..) | ast::ExprKind::Struct(..) => {
1327             context.config.overflow_delimited_expr()
1328                 || (context.use_block_indent() && args_len == 1)
1329         }
1330         ast::ExprKind::MacCall(ref mac) => {
1331             match (
1332                 rustc_ast::ast::MacDelimiter::from_token(mac.args.delim().unwrap()),
1333                 context.config.overflow_delimited_expr(),
1334             ) {
1335                 (Some(ast::MacDelimiter::Bracket), true)
1336                 | (Some(ast::MacDelimiter::Brace), true) => true,
1337                 _ => context.use_block_indent() && args_len == 1,
1338             }
1339         }
1340
1341         // Handle parenthetical expressions
1342         ast::ExprKind::Call(..) | ast::ExprKind::MethodCall(..) | ast::ExprKind::Tup(..) => {
1343             context.use_block_indent() && args_len == 1
1344         }
1345
1346         // Handle unary-like expressions
1347         ast::ExprKind::AddrOf(_, _, ref expr)
1348         | ast::ExprKind::Box(ref expr)
1349         | ast::ExprKind::Try(ref expr)
1350         | ast::ExprKind::Unary(_, ref expr)
1351         | ast::ExprKind::Cast(ref expr, _) => can_be_overflowed_expr(context, expr, args_len),
1352         _ => false,
1353     }
1354 }
1355
1356 pub(crate) fn is_nested_call(expr: &ast::Expr) -> bool {
1357     match expr.kind {
1358         ast::ExprKind::Call(..) | ast::ExprKind::MacCall(..) => true,
1359         ast::ExprKind::AddrOf(_, _, ref expr)
1360         | ast::ExprKind::Box(ref expr)
1361         | ast::ExprKind::Try(ref expr)
1362         | ast::ExprKind::Unary(_, ref expr)
1363         | ast::ExprKind::Cast(ref expr, _) => is_nested_call(expr),
1364         _ => false,
1365     }
1366 }
1367
1368 /// Returns `true` if a function call or a method call represented by the given span ends with a
1369 /// trailing comma. This function is used when rewriting macro, as adding or removing a trailing
1370 /// comma from macro can potentially break the code.
1371 pub(crate) fn span_ends_with_comma(context: &RewriteContext<'_>, span: Span) -> bool {
1372     let mut result: bool = Default::default();
1373     let mut prev_char: char = Default::default();
1374     let closing_delimiters = &[')', '}', ']'];
1375
1376     for (kind, c) in CharClasses::new(context.snippet(span).chars()) {
1377         match c {
1378             _ if kind.is_comment() || c.is_whitespace() => continue,
1379             c if closing_delimiters.contains(&c) => {
1380                 result &= !closing_delimiters.contains(&prev_char);
1381             }
1382             ',' => result = true,
1383             _ => result = false,
1384         }
1385         prev_char = c;
1386     }
1387
1388     result
1389 }
1390
1391 fn rewrite_paren(
1392     context: &RewriteContext<'_>,
1393     mut subexpr: &ast::Expr,
1394     shape: Shape,
1395     mut span: Span,
1396 ) -> Option<String> {
1397     debug!("rewrite_paren, shape: {:?}", shape);
1398
1399     // Extract comments within parens.
1400     let mut pre_span;
1401     let mut post_span;
1402     let mut pre_comment;
1403     let mut post_comment;
1404     let remove_nested_parens = context.config.remove_nested_parens();
1405     loop {
1406         // 1 = "(" or ")"
1407         pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
1408         post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
1409         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
1410         post_comment = rewrite_missing_comment(post_span, shape, context)?;
1411
1412         // Remove nested parens if there are no comments.
1413         if let ast::ExprKind::Paren(ref subsubexpr) = subexpr.kind {
1414             if remove_nested_parens && pre_comment.is_empty() && post_comment.is_empty() {
1415                 span = subexpr.span;
1416                 subexpr = subsubexpr;
1417                 continue;
1418             }
1419         }
1420
1421         break;
1422     }
1423
1424     // 1 = `(` and `)`
1425     let sub_shape = shape.offset_left(1)?.sub_width(1)?;
1426     let subexpr_str = subexpr.rewrite(context, sub_shape)?;
1427     let fits_single_line = !pre_comment.contains("//") && !post_comment.contains("//");
1428     if fits_single_line {
1429         Some(format!("({}{}{})", pre_comment, subexpr_str, post_comment))
1430     } else {
1431         rewrite_paren_in_multi_line(context, subexpr, shape, pre_span, post_span)
1432     }
1433 }
1434
1435 fn rewrite_paren_in_multi_line(
1436     context: &RewriteContext<'_>,
1437     subexpr: &ast::Expr,
1438     shape: Shape,
1439     pre_span: Span,
1440     post_span: Span,
1441 ) -> Option<String> {
1442     let nested_indent = shape.indent.block_indent(context.config);
1443     let nested_shape = Shape::indented(nested_indent, context.config);
1444     let pre_comment = rewrite_missing_comment(pre_span, nested_shape, context)?;
1445     let post_comment = rewrite_missing_comment(post_span, nested_shape, context)?;
1446     let subexpr_str = subexpr.rewrite(context, nested_shape)?;
1447
1448     let mut result = String::with_capacity(subexpr_str.len() * 2);
1449     result.push('(');
1450     if !pre_comment.is_empty() {
1451         result.push_str(&nested_indent.to_string_with_newline(context.config));
1452         result.push_str(&pre_comment);
1453     }
1454     result.push_str(&nested_indent.to_string_with_newline(context.config));
1455     result.push_str(&subexpr_str);
1456     if !post_comment.is_empty() {
1457         result.push_str(&nested_indent.to_string_with_newline(context.config));
1458         result.push_str(&post_comment);
1459     }
1460     result.push_str(&shape.indent.to_string_with_newline(context.config));
1461     result.push(')');
1462
1463     Some(result)
1464 }
1465
1466 fn rewrite_index(
1467     expr: &ast::Expr,
1468     index: &ast::Expr,
1469     context: &RewriteContext<'_>,
1470     shape: Shape,
1471 ) -> Option<String> {
1472     let expr_str = expr.rewrite(context, shape)?;
1473
1474     let offset = last_line_width(&expr_str) + 1;
1475     let rhs_overhead = shape.rhs_overhead(context.config);
1476     let index_shape = if expr_str.contains('\n') {
1477         Shape::legacy(context.config.max_width(), shape.indent)
1478             .offset_left(offset)
1479             .and_then(|shape| shape.sub_width(1 + rhs_overhead))
1480     } else {
1481         match context.config.indent_style() {
1482             IndentStyle::Block => shape
1483                 .offset_left(offset)
1484                 .and_then(|shape| shape.sub_width(1)),
1485             IndentStyle::Visual => shape.visual_indent(offset).sub_width(offset + 1),
1486         }
1487     };
1488     let orig_index_rw = index_shape.and_then(|s| index.rewrite(context, s));
1489
1490     // Return if index fits in a single line.
1491     match orig_index_rw {
1492         Some(ref index_str) if !index_str.contains('\n') => {
1493             return Some(format!("{}[{}]", expr_str, index_str));
1494         }
1495         _ => (),
1496     }
1497
1498     // Try putting index on the next line and see if it fits in a single line.
1499     let indent = shape.indent.block_indent(context.config);
1500     let index_shape = Shape::indented(indent, context.config).offset_left(1)?;
1501     let index_shape = index_shape.sub_width(1 + rhs_overhead)?;
1502     let new_index_rw = index.rewrite(context, index_shape);
1503     match (orig_index_rw, new_index_rw) {
1504         (_, Some(ref new_index_str)) if !new_index_str.contains('\n') => Some(format!(
1505             "{}{}[{}]",
1506             expr_str,
1507             indent.to_string_with_newline(context.config),
1508             new_index_str,
1509         )),
1510         (None, Some(ref new_index_str)) => Some(format!(
1511             "{}{}[{}]",
1512             expr_str,
1513             indent.to_string_with_newline(context.config),
1514             new_index_str,
1515         )),
1516         (Some(ref index_str), _) => Some(format!("{}[{}]", expr_str, index_str)),
1517         _ => None,
1518     }
1519 }
1520
1521 fn struct_lit_can_be_aligned(fields: &[ast::ExprField], has_base: bool) -> bool {
1522     !has_base && fields.iter().all(|field| !field.is_shorthand)
1523 }
1524
1525 fn rewrite_struct_lit<'a>(
1526     context: &RewriteContext<'_>,
1527     path: &ast::Path,
1528     qself: Option<&ast::QSelf>,
1529     fields: &'a [ast::ExprField],
1530     struct_rest: &ast::StructRest,
1531     attrs: &[ast::Attribute],
1532     span: Span,
1533     shape: Shape,
1534 ) -> Option<String> {
1535     debug!("rewrite_struct_lit: shape {:?}", shape);
1536
1537     enum StructLitField<'a> {
1538         Regular(&'a ast::ExprField),
1539         Base(&'a ast::Expr),
1540         Rest(Span),
1541     }
1542
1543     // 2 = " {".len()
1544     let path_shape = shape.sub_width(2)?;
1545     let path_str = rewrite_path(context, PathContext::Expr, qself, path, path_shape)?;
1546
1547     let has_base_or_rest = match struct_rest {
1548         ast::StructRest::None if fields.is_empty() => return Some(format!("{} {{}}", path_str)),
1549         ast::StructRest::Rest(_) if fields.is_empty() => {
1550             return Some(format!("{} {{ .. }}", path_str));
1551         }
1552         ast::StructRest::Rest(_) | ast::StructRest::Base(_) => true,
1553         _ => false,
1554     };
1555
1556     // Foo { a: Foo } - indent is +3, width is -5.
1557     let (h_shape, v_shape) = struct_lit_shape(shape, context, path_str.len() + 3, 2)?;
1558
1559     let one_line_width = h_shape.map_or(0, |shape| shape.width);
1560     let body_lo = context.snippet_provider.span_after(span, "{");
1561     let fields_str = if struct_lit_can_be_aligned(fields, has_base_or_rest)
1562         && context.config.struct_field_align_threshold() > 0
1563     {
1564         rewrite_with_alignment(
1565             fields,
1566             context,
1567             v_shape,
1568             mk_sp(body_lo, span.hi()),
1569             one_line_width,
1570         )?
1571     } else {
1572         let field_iter = fields.iter().map(StructLitField::Regular).chain(
1573             match struct_rest {
1574                 ast::StructRest::Base(expr) => Some(StructLitField::Base(&**expr)),
1575                 ast::StructRest::Rest(span) => Some(StructLitField::Rest(*span)),
1576                 ast::StructRest::None => None,
1577             }
1578             .into_iter(),
1579         );
1580
1581         let span_lo = |item: &StructLitField<'_>| match *item {
1582             StructLitField::Regular(field) => field.span().lo(),
1583             StructLitField::Base(expr) => {
1584                 let last_field_hi = fields.last().map_or(span.lo(), |field| field.span.hi());
1585                 let snippet = context.snippet(mk_sp(last_field_hi, expr.span.lo()));
1586                 let pos = snippet.find_uncommented("..").unwrap();
1587                 last_field_hi + BytePos(pos as u32)
1588             }
1589             StructLitField::Rest(span) => span.lo(),
1590         };
1591         let span_hi = |item: &StructLitField<'_>| match *item {
1592             StructLitField::Regular(field) => field.span().hi(),
1593             StructLitField::Base(expr) => expr.span.hi(),
1594             StructLitField::Rest(span) => span.hi(),
1595         };
1596         let rewrite = |item: &StructLitField<'_>| match *item {
1597             StructLitField::Regular(field) => {
1598                 // The 1 taken from the v_budget is for the comma.
1599                 rewrite_field(context, field, v_shape.sub_width(1)?, 0)
1600             }
1601             StructLitField::Base(expr) => {
1602                 // 2 = ..
1603                 expr.rewrite(context, v_shape.offset_left(2)?)
1604                     .map(|s| format!("..{}", s))
1605             }
1606             StructLitField::Rest(_) => Some("..".to_owned()),
1607         };
1608
1609         let items = itemize_list(
1610             context.snippet_provider,
1611             field_iter,
1612             "}",
1613             ",",
1614             span_lo,
1615             span_hi,
1616             rewrite,
1617             body_lo,
1618             span.hi(),
1619             false,
1620         );
1621         let item_vec = items.collect::<Vec<_>>();
1622
1623         let tactic = struct_lit_tactic(h_shape, context, &item_vec);
1624         let nested_shape = shape_for_tactic(tactic, h_shape, v_shape);
1625
1626         let ends_with_comma = span_ends_with_comma(context, span);
1627         let force_no_trailing_comma = context.inside_macro() && !ends_with_comma;
1628
1629         let fmt = struct_lit_formatting(
1630             nested_shape,
1631             tactic,
1632             context,
1633             force_no_trailing_comma || has_base_or_rest || !context.use_block_indent(),
1634         );
1635
1636         write_list(&item_vec, &fmt)?
1637     };
1638
1639     let fields_str =
1640         wrap_struct_field(context, attrs, &fields_str, shape, v_shape, one_line_width)?;
1641     Some(format!("{} {{{}}}", path_str, fields_str))
1642
1643     // FIXME if context.config.indent_style() == Visual, but we run out
1644     // of space, we should fall back to BlockIndent.
1645 }
1646
1647 pub(crate) fn wrap_struct_field(
1648     context: &RewriteContext<'_>,
1649     attrs: &[ast::Attribute],
1650     fields_str: &str,
1651     shape: Shape,
1652     nested_shape: Shape,
1653     one_line_width: usize,
1654 ) -> Option<String> {
1655     let should_vertical = context.config.indent_style() == IndentStyle::Block
1656         && (fields_str.contains('\n')
1657             || !context.config.struct_lit_single_line()
1658             || fields_str.len() > one_line_width);
1659
1660     let inner_attrs = &inner_attributes(attrs);
1661     if inner_attrs.is_empty() {
1662         if should_vertical {
1663             Some(format!(
1664                 "{}{}{}",
1665                 nested_shape.indent.to_string_with_newline(context.config),
1666                 fields_str,
1667                 shape.indent.to_string_with_newline(context.config)
1668             ))
1669         } else {
1670             // One liner or visual indent.
1671             Some(format!(" {} ", fields_str))
1672         }
1673     } else {
1674         Some(format!(
1675             "{}{}{}{}{}",
1676             nested_shape.indent.to_string_with_newline(context.config),
1677             inner_attrs.rewrite(context, shape)?,
1678             nested_shape.indent.to_string_with_newline(context.config),
1679             fields_str,
1680             shape.indent.to_string_with_newline(context.config)
1681         ))
1682     }
1683 }
1684
1685 pub(crate) fn struct_lit_field_separator(config: &Config) -> &str {
1686     colon_spaces(config)
1687 }
1688
1689 pub(crate) fn rewrite_field(
1690     context: &RewriteContext<'_>,
1691     field: &ast::ExprField,
1692     shape: Shape,
1693     prefix_max_width: usize,
1694 ) -> Option<String> {
1695     if contains_skip(&field.attrs) {
1696         return Some(context.snippet(field.span()).to_owned());
1697     }
1698     let mut attrs_str = field.attrs.rewrite(context, shape)?;
1699     if !attrs_str.is_empty() {
1700         attrs_str.push_str(&shape.indent.to_string_with_newline(context.config));
1701     };
1702     let name = context.snippet(field.ident.span);
1703     if field.is_shorthand {
1704         Some(attrs_str + name)
1705     } else {
1706         let mut separator = String::from(struct_lit_field_separator(context.config));
1707         for _ in 0..prefix_max_width.saturating_sub(name.len()) {
1708             separator.push(' ');
1709         }
1710         let overhead = name.len() + separator.len();
1711         let expr_shape = shape.offset_left(overhead)?;
1712         let expr = field.expr.rewrite(context, expr_shape);
1713
1714         match expr {
1715             Some(ref e) if e.as_str() == name && context.config.use_field_init_shorthand() => {
1716                 Some(attrs_str + name)
1717             }
1718             Some(e) => Some(format!("{}{}{}{}", attrs_str, name, separator, e)),
1719             None => {
1720                 let expr_offset = shape.indent.block_indent(context.config);
1721                 let expr = field
1722                     .expr
1723                     .rewrite(context, Shape::indented(expr_offset, context.config));
1724                 expr.map(|s| {
1725                     format!(
1726                         "{}{}:\n{}{}",
1727                         attrs_str,
1728                         name,
1729                         expr_offset.to_string(context.config),
1730                         s
1731                     )
1732                 })
1733             }
1734         }
1735     }
1736 }
1737
1738 fn rewrite_tuple_in_visual_indent_style<'a, T: 'a + IntoOverflowableItem<'a>>(
1739     context: &RewriteContext<'_>,
1740     mut items: impl Iterator<Item = &'a T>,
1741     span: Span,
1742     shape: Shape,
1743     is_singleton_tuple: bool,
1744 ) -> Option<String> {
1745     // In case of length 1, need a trailing comma
1746     debug!("rewrite_tuple_in_visual_indent_style {:?}", shape);
1747     if is_singleton_tuple {
1748         // 3 = "(" + ",)"
1749         let nested_shape = shape.sub_width(3)?.visual_indent(1);
1750         return items
1751             .next()
1752             .unwrap()
1753             .rewrite(context, nested_shape)
1754             .map(|s| format!("({},)", s));
1755     }
1756
1757     let list_lo = context.snippet_provider.span_after(span, "(");
1758     let nested_shape = shape.sub_width(2)?.visual_indent(1);
1759     let items = itemize_list(
1760         context.snippet_provider,
1761         items,
1762         ")",
1763         ",",
1764         |item| item.span().lo(),
1765         |item| item.span().hi(),
1766         |item| item.rewrite(context, nested_shape),
1767         list_lo,
1768         span.hi() - BytePos(1),
1769         false,
1770     );
1771     let item_vec: Vec<_> = items.collect();
1772     let tactic = definitive_tactic(
1773         &item_vec,
1774         ListTactic::HorizontalVertical,
1775         Separator::Comma,
1776         nested_shape.width,
1777     );
1778     let fmt = ListFormatting::new(nested_shape, context.config)
1779         .tactic(tactic)
1780         .ends_with_newline(false);
1781     let list_str = write_list(&item_vec, &fmt)?;
1782
1783     Some(format!("({})", list_str))
1784 }
1785
1786 pub(crate) fn rewrite_tuple<'a, T: 'a + IntoOverflowableItem<'a>>(
1787     context: &'a RewriteContext<'_>,
1788     items: impl Iterator<Item = &'a T>,
1789     span: Span,
1790     shape: Shape,
1791     is_singleton_tuple: bool,
1792 ) -> Option<String> {
1793     debug!("rewrite_tuple {:?}", shape);
1794     if context.use_block_indent() {
1795         // We use the same rule as function calls for rewriting tuples.
1796         let force_tactic = if context.inside_macro() {
1797             if span_ends_with_comma(context, span) {
1798                 Some(SeparatorTactic::Always)
1799             } else {
1800                 Some(SeparatorTactic::Never)
1801             }
1802         } else if is_singleton_tuple {
1803             Some(SeparatorTactic::Always)
1804         } else {
1805             None
1806         };
1807         overflow::rewrite_with_parens(
1808             context,
1809             "",
1810             items,
1811             shape,
1812             span,
1813             context.config.fn_call_width(),
1814             force_tactic,
1815         )
1816     } else {
1817         rewrite_tuple_in_visual_indent_style(context, items, span, shape, is_singleton_tuple)
1818     }
1819 }
1820
1821 pub(crate) fn rewrite_unary_prefix<R: Rewrite>(
1822     context: &RewriteContext<'_>,
1823     prefix: &str,
1824     rewrite: &R,
1825     shape: Shape,
1826 ) -> Option<String> {
1827     rewrite
1828         .rewrite(context, shape.offset_left(prefix.len())?)
1829         .map(|r| format!("{}{}", prefix, r))
1830 }
1831
1832 // FIXME: this is probably not correct for multi-line Rewrites. we should
1833 // subtract suffix.len() from the last line budget, not the first!
1834 pub(crate) fn rewrite_unary_suffix<R: Rewrite>(
1835     context: &RewriteContext<'_>,
1836     suffix: &str,
1837     rewrite: &R,
1838     shape: Shape,
1839 ) -> Option<String> {
1840     rewrite
1841         .rewrite(context, shape.sub_width(suffix.len())?)
1842         .map(|mut r| {
1843             r.push_str(suffix);
1844             r
1845         })
1846 }
1847
1848 fn rewrite_unary_op(
1849     context: &RewriteContext<'_>,
1850     op: ast::UnOp,
1851     expr: &ast::Expr,
1852     shape: Shape,
1853 ) -> Option<String> {
1854     // For some reason, an UnOp is not spanned like BinOp!
1855     rewrite_unary_prefix(context, ast::UnOp::to_string(op), expr, shape)
1856 }
1857
1858 pub(crate) enum RhsAssignKind<'ast> {
1859     Expr(&'ast ast::ExprKind, Span),
1860     Bounds,
1861     Ty,
1862 }
1863
1864 impl<'ast> RhsAssignKind<'ast> {
1865     // TODO(calebcartwright)
1866     // Preemptive addition for handling RHS with chains, not yet utilized.
1867     // It may make more sense to construct the chain first and then check
1868     // whether there are actually chain elements.
1869     #[allow(dead_code)]
1870     fn is_chain(&self) -> bool {
1871         match self {
1872             RhsAssignKind::Expr(kind, _) => {
1873                 matches!(
1874                     kind,
1875                     ast::ExprKind::Try(..)
1876                         | ast::ExprKind::Field(..)
1877                         | ast::ExprKind::MethodCall(..)
1878                         | ast::ExprKind::Await(_)
1879                 )
1880             }
1881             _ => false,
1882         }
1883     }
1884 }
1885
1886 fn rewrite_assignment(
1887     context: &RewriteContext<'_>,
1888     lhs: &ast::Expr,
1889     rhs: &ast::Expr,
1890     op: Option<&ast::BinOp>,
1891     shape: Shape,
1892 ) -> Option<String> {
1893     let operator_str = match op {
1894         Some(op) => context.snippet(op.span),
1895         None => "=",
1896     };
1897
1898     // 1 = space between lhs and operator.
1899     let lhs_shape = shape.sub_width(operator_str.len() + 1)?;
1900     let lhs_str = format!("{} {}", lhs.rewrite(context, lhs_shape)?, operator_str);
1901
1902     rewrite_assign_rhs(
1903         context,
1904         lhs_str,
1905         rhs,
1906         &RhsAssignKind::Expr(&rhs.kind, rhs.span),
1907         shape,
1908     )
1909 }
1910
1911 /// Controls where to put the rhs.
1912 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
1913 pub(crate) enum RhsTactics {
1914     /// Use heuristics.
1915     Default,
1916     /// Put the rhs on the next line if it uses multiple line, without extra indentation.
1917     ForceNextLineWithoutIndent,
1918     /// Allow overflowing max width if neither `Default` nor `ForceNextLineWithoutIndent`
1919     /// did not work.
1920     AllowOverflow,
1921 }
1922
1923 // The left hand side must contain everything up to, and including, the
1924 // assignment operator.
1925 pub(crate) fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
1926     context: &RewriteContext<'_>,
1927     lhs: S,
1928     ex: &R,
1929     rhs_kind: &RhsAssignKind<'_>,
1930     shape: Shape,
1931 ) -> Option<String> {
1932     rewrite_assign_rhs_with(context, lhs, ex, shape, rhs_kind, RhsTactics::Default)
1933 }
1934
1935 pub(crate) fn rewrite_assign_rhs_expr<R: Rewrite>(
1936     context: &RewriteContext<'_>,
1937     lhs: &str,
1938     ex: &R,
1939     shape: Shape,
1940     rhs_kind: &RhsAssignKind<'_>,
1941     rhs_tactics: RhsTactics,
1942 ) -> Option<String> {
1943     let last_line_width = last_line_width(lhs).saturating_sub(if lhs.contains('\n') {
1944         shape.indent.width()
1945     } else {
1946         0
1947     });
1948     // 1 = space between operator and rhs.
1949     let orig_shape = shape.offset_left(last_line_width + 1).unwrap_or(Shape {
1950         width: 0,
1951         offset: shape.offset + last_line_width + 1,
1952         ..shape
1953     });
1954     let has_rhs_comment = if let Some(offset) = lhs.find_last_uncommented("=") {
1955         lhs.trim_end().len() > offset + 1
1956     } else {
1957         false
1958     };
1959
1960     choose_rhs(
1961         context,
1962         ex,
1963         orig_shape,
1964         ex.rewrite(context, orig_shape),
1965         rhs_kind,
1966         rhs_tactics,
1967         has_rhs_comment,
1968     )
1969 }
1970
1971 pub(crate) fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
1972     context: &RewriteContext<'_>,
1973     lhs: S,
1974     ex: &R,
1975     shape: Shape,
1976     rhs_kind: &RhsAssignKind<'_>,
1977     rhs_tactics: RhsTactics,
1978 ) -> Option<String> {
1979     let lhs = lhs.into();
1980     let rhs = rewrite_assign_rhs_expr(context, &lhs, ex, shape, rhs_kind, rhs_tactics)?;
1981     Some(lhs + &rhs)
1982 }
1983
1984 pub(crate) fn rewrite_assign_rhs_with_comments<S: Into<String>, R: Rewrite>(
1985     context: &RewriteContext<'_>,
1986     lhs: S,
1987     ex: &R,
1988     shape: Shape,
1989     rhs_kind: &RhsAssignKind<'_>,
1990     rhs_tactics: RhsTactics,
1991     between_span: Span,
1992     allow_extend: bool,
1993 ) -> Option<String> {
1994     let lhs = lhs.into();
1995     let contains_comment = contains_comment(context.snippet(between_span));
1996     let shape = if contains_comment {
1997         shape.block_left(context.config.tab_spaces())?
1998     } else {
1999         shape
2000     };
2001     let rhs = rewrite_assign_rhs_expr(context, &lhs, ex, shape, rhs_kind, rhs_tactics)?;
2002
2003     if contains_comment {
2004         let rhs = rhs.trim_start();
2005         combine_strs_with_missing_comments(context, &lhs, rhs, between_span, shape, allow_extend)
2006     } else {
2007         Some(lhs + &rhs)
2008     }
2009 }
2010
2011 fn choose_rhs<R: Rewrite>(
2012     context: &RewriteContext<'_>,
2013     expr: &R,
2014     shape: Shape,
2015     orig_rhs: Option<String>,
2016     _rhs_kind: &RhsAssignKind<'_>,
2017     rhs_tactics: RhsTactics,
2018     has_rhs_comment: bool,
2019 ) -> Option<String> {
2020     match orig_rhs {
2021         Some(ref new_str) if new_str.is_empty() => Some(String::new()),
2022         Some(ref new_str)
2023             if !new_str.contains('\n') && unicode_str_width(new_str) <= shape.width =>
2024         {
2025             Some(format!(" {}", new_str))
2026         }
2027         _ => {
2028             // Expression did not fit on the same line as the identifier.
2029             // Try splitting the line and see if that works better.
2030             let new_shape = shape_from_rhs_tactic(context, shape, rhs_tactics)?;
2031             let new_rhs = expr.rewrite(context, new_shape);
2032             let new_indent_str = &shape
2033                 .indent
2034                 .block_indent(context.config)
2035                 .to_string_with_newline(context.config);
2036             let before_space_str = if has_rhs_comment { "" } else { " " };
2037
2038             match (orig_rhs, new_rhs) {
2039                 (Some(ref orig_rhs), Some(ref new_rhs))
2040                     if wrap_str(new_rhs.clone(), context.config.max_width(), new_shape)
2041                         .is_none() =>
2042                 {
2043                     Some(format!("{}{}", before_space_str, orig_rhs))
2044                 }
2045                 (Some(ref orig_rhs), Some(ref new_rhs))
2046                     if prefer_next_line(orig_rhs, new_rhs, rhs_tactics) =>
2047                 {
2048                     Some(format!("{}{}", new_indent_str, new_rhs))
2049                 }
2050                 (None, Some(ref new_rhs)) => Some(format!("{}{}", new_indent_str, new_rhs)),
2051                 (None, None) if rhs_tactics == RhsTactics::AllowOverflow => {
2052                     let shape = shape.infinite_width();
2053                     expr.rewrite(context, shape)
2054                         .map(|s| format!("{}{}", before_space_str, s))
2055                 }
2056                 (None, None) => None,
2057                 (Some(orig_rhs), _) => Some(format!("{}{}", before_space_str, orig_rhs)),
2058             }
2059         }
2060     }
2061 }
2062
2063 fn shape_from_rhs_tactic(
2064     context: &RewriteContext<'_>,
2065     shape: Shape,
2066     rhs_tactic: RhsTactics,
2067 ) -> Option<Shape> {
2068     match rhs_tactic {
2069         RhsTactics::ForceNextLineWithoutIndent => shape
2070             .with_max_width(context.config)
2071             .sub_width(shape.indent.width()),
2072         RhsTactics::Default | RhsTactics::AllowOverflow => {
2073             Shape::indented(shape.indent.block_indent(context.config), context.config)
2074                 .sub_width(shape.rhs_overhead(context.config))
2075         }
2076     }
2077 }
2078
2079 /// Returns true if formatting next_line_rhs is better on a new line when compared to the
2080 /// original's line formatting.
2081 ///
2082 /// It is considered better if:
2083 /// 1. the tactic is ForceNextLineWithoutIndent
2084 /// 2. next_line_rhs doesn't have newlines
2085 /// 3. the original line has more newlines than next_line_rhs
2086 /// 4. the original formatting of the first line ends with `(`, `{`, or `[` and next_line_rhs
2087 ///    doesn't
2088 pub(crate) fn prefer_next_line(
2089     orig_rhs: &str,
2090     next_line_rhs: &str,
2091     rhs_tactics: RhsTactics,
2092 ) -> bool {
2093     rhs_tactics == RhsTactics::ForceNextLineWithoutIndent
2094         || !next_line_rhs.contains('\n')
2095         || count_newlines(orig_rhs) > count_newlines(next_line_rhs) + 1
2096         || first_line_ends_with(orig_rhs, '(') && !first_line_ends_with(next_line_rhs, '(')
2097         || first_line_ends_with(orig_rhs, '{') && !first_line_ends_with(next_line_rhs, '{')
2098         || first_line_ends_with(orig_rhs, '[') && !first_line_ends_with(next_line_rhs, '[')
2099 }
2100
2101 fn rewrite_expr_addrof(
2102     context: &RewriteContext<'_>,
2103     borrow_kind: ast::BorrowKind,
2104     mutability: ast::Mutability,
2105     expr: &ast::Expr,
2106     shape: Shape,
2107 ) -> Option<String> {
2108     let operator_str = match (mutability, borrow_kind) {
2109         (ast::Mutability::Not, ast::BorrowKind::Ref) => "&",
2110         (ast::Mutability::Not, ast::BorrowKind::Raw) => "&raw const ",
2111         (ast::Mutability::Mut, ast::BorrowKind::Ref) => "&mut ",
2112         (ast::Mutability::Mut, ast::BorrowKind::Raw) => "&raw mut ",
2113     };
2114     rewrite_unary_prefix(context, operator_str, expr, shape)
2115 }
2116
2117 pub(crate) fn is_method_call(expr: &ast::Expr) -> bool {
2118     match expr.kind {
2119         ast::ExprKind::MethodCall(..) => true,
2120         ast::ExprKind::AddrOf(_, _, ref expr)
2121         | ast::ExprKind::Box(ref expr)
2122         | ast::ExprKind::Cast(ref expr, _)
2123         | ast::ExprKind::Try(ref expr)
2124         | ast::ExprKind::Unary(_, ref expr) => is_method_call(expr),
2125         _ => false,
2126     }
2127 }
2128
2129 #[cfg(test)]
2130 mod test {
2131     use super::last_line_offsetted;
2132
2133     #[test]
2134     fn test_last_line_offsetted() {
2135         let lines = "one\n    two";
2136         assert_eq!(last_line_offsetted(2, lines), true);
2137         assert_eq!(last_line_offsetted(4, lines), false);
2138         assert_eq!(last_line_offsetted(6, lines), false);
2139
2140         let lines = "one    two";
2141         assert_eq!(last_line_offsetted(2, lines), false);
2142         assert_eq!(last_line_offsetted(0, lines), false);
2143
2144         let lines = "\ntwo";
2145         assert_eq!(last_line_offsetted(2, lines), false);
2146         assert_eq!(last_line_offsetted(0, lines), false);
2147
2148         let lines = "one\n    two      three";
2149         assert_eq!(last_line_offsetted(2, lines), true);
2150         let lines = "one\n two      three";
2151         assert_eq!(last_line_offsetted(2, lines), false);
2152     }
2153 }