compiler/rustc_ast_lowering/src/expr.rs

   1 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
   2
   3 use rustc_ast::attr;
   4 use rustc_ast::ptr::P as AstP;
   5 use rustc_ast::*;
   6 use rustc_data_structures::fx::FxHashMap;
   7 use rustc_data_structures::stack::ensure_sufficient_stack;
   8 use rustc_data_structures::thin_vec::ThinVec;
   9 use rustc_errors::struct_span_err;
  10 use rustc_hir as hir;
  11 use rustc_hir::def::Res;
  12 use rustc_span::hygiene::ForLoopLoc;
  13 use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
  14 use rustc_span::symbol::{sym, Ident, Symbol};
  15 use rustc_target::asm;
  16 use std::collections::hash_map::Entry;
  17 use std::fmt::Write;
  18
  19 impl<'hir> LoweringContext<'_, 'hir> {
  20     fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
  21         self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
  22     }
  23
  24     pub(super) fn lower_expr(&mut self, e: &Expr) -> &'hir hir::Expr<'hir> {
  25         self.arena.alloc(self.lower_expr_mut(e))
  26     }
  27
  28     pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
  29         ensure_sufficient_stack(|| {
  30             let kind = match e.kind {
  31                 ExprKind::Box(ref inner) => hir::ExprKind::Box(self.lower_expr(inner)),
  32                 ExprKind::Array(ref exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
  33                 ExprKind::Repeat(ref expr, ref count) => {
  34                     let expr = self.lower_expr(expr);
  35                     let count = self.lower_anon_const(count);
  36                     hir::ExprKind::Repeat(expr, count)
  37                 }
  38                 ExprKind::Tup(ref elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
  39                 ExprKind::Call(ref f, ref args) => {
  40                     let f = self.lower_expr(f);
  41                     hir::ExprKind::Call(f, self.lower_exprs(args))
  42                 }
  43                 ExprKind::MethodCall(ref seg, ref args, span) => {
  44                     let hir_seg = self.arena.alloc(self.lower_path_segment(
  45                         e.span,
  46                         seg,
  47                         ParamMode::Optional,
  48                         0,
  49                         ParenthesizedGenericArgs::Err,
  50                         ImplTraitContext::disallowed(),
  51                         None,
  52                     ));
  53                     let args = self.lower_exprs(args);
  54                     hir::ExprKind::MethodCall(hir_seg, seg.ident.span, args, span)
  55                 }
  56                 ExprKind::Binary(binop, ref lhs, ref rhs) => {
  57                     let binop = self.lower_binop(binop);
  58                     let lhs = self.lower_expr(lhs);
  59                     let rhs = self.lower_expr(rhs);
  60                     hir::ExprKind::Binary(binop, lhs, rhs)
  61                 }
  62                 ExprKind::Unary(op, ref ohs) => {
  63                     let op = self.lower_unop(op);
  64                     let ohs = self.lower_expr(ohs);
  65                     hir::ExprKind::Unary(op, ohs)
  66                 }
  67                 ExprKind::Lit(ref l) => hir::ExprKind::Lit(respan(l.span, l.kind.clone())),
  68                 ExprKind::Cast(ref expr, ref ty) => {
  69                     let expr = self.lower_expr(expr);
  70                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
  71                     hir::ExprKind::Cast(expr, ty)
  72                 }
  73                 ExprKind::Type(ref expr, ref ty) => {
  74                     let expr = self.lower_expr(expr);
  75                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
  76                     hir::ExprKind::Type(expr, ty)
  77                 }
  78                 ExprKind::AddrOf(k, m, ref ohs) => {
  79                     let ohs = self.lower_expr(ohs);
  80                     hir::ExprKind::AddrOf(k, m, ohs)
  81                 }
  82                 ExprKind::Let(ref pat, ref scrutinee) => {
  83                     self.lower_expr_let(e.span, pat, scrutinee)
  84                 }
  85                 ExprKind::If(ref cond, ref then, ref else_opt) => {
  86                     self.lower_expr_if(e.span, cond, then, else_opt.as_deref())
  87                 }
  88                 ExprKind::While(ref cond, ref body, opt_label) => self
  89                     .with_loop_scope(e.id, |this| {
  90                         this.lower_expr_while_in_loop_scope(e.span, cond, body, opt_label)
  91                     }),
  92                 ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
  93                     hir::ExprKind::Loop(
  94                         this.lower_block(body, false),
  95                         opt_label,
  96                         hir::LoopSource::Loop,
  97                     )
  98                 }),
  99                 ExprKind::TryBlock(ref body) => self.lower_expr_try_block(body),
 100                 ExprKind::Match(ref expr, ref arms) => hir::ExprKind::Match(
 101                     self.lower_expr(expr),
 102                     self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
 103                     hir::MatchSource::Normal,
 104                 ),
 105                 ExprKind::Async(capture_clause, closure_node_id, ref block) => self
 106                     .make_async_expr(
 107                         capture_clause,
 108                         closure_node_id,
 109                         None,
 110                         block.span,
 111                         hir::AsyncGeneratorKind::Block,
 112                         |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
 113                     ),
 114                 ExprKind::Await(ref expr) => self.lower_expr_await(e.span, expr),
 115                 ExprKind::Closure(
 116                     capture_clause,
 117                     asyncness,
 118                     movability,
 119                     ref decl,
 120                     ref body,
 121                     fn_decl_span,
 122                 ) => {
 123                     if let Async::Yes { closure_id, .. } = asyncness {
 124                         self.lower_expr_async_closure(
 125                             capture_clause,
 126                             closure_id,
 127                             decl,
 128                             body,
 129                             fn_decl_span,
 130                         )
 131                     } else {
 132                         self.lower_expr_closure(
 133                             capture_clause,
 134                             movability,
 135                             decl,
 136                             body,
 137                             fn_decl_span,
 138                         )
 139                     }
 140                 }
 141                 ExprKind::Block(ref blk, opt_label) => {
 142                     hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
 143                 }
 144                 ExprKind::Assign(ref el, ref er, span) => {
 145                     hir::ExprKind::Assign(self.lower_expr(el), self.lower_expr(er), span)
 146                 }
 147                 ExprKind::AssignOp(op, ref el, ref er) => hir::ExprKind::AssignOp(
 148                     self.lower_binop(op),
 149                     self.lower_expr(el),
 150                     self.lower_expr(er),
 151                 ),
 152                 ExprKind::Field(ref el, ident) => hir::ExprKind::Field(self.lower_expr(el), ident),
 153                 ExprKind::Index(ref el, ref er) => {
 154                     hir::ExprKind::Index(self.lower_expr(el), self.lower_expr(er))
 155                 }
 156                 ExprKind::Range(Some(ref e1), Some(ref e2), RangeLimits::Closed) => {
 157                     self.lower_expr_range_closed(e.span, e1, e2)
 158                 }
 159                 ExprKind::Range(ref e1, ref e2, lims) => {
 160                     self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), lims)
 161                 }
 162                 ExprKind::Path(ref qself, ref path) => {
 163                     let qpath = self.lower_qpath(
 164                         e.id,
 165                         qself,
 166                         path,
 167                         ParamMode::Optional,
 168                         ImplTraitContext::disallowed(),
 169                     );
 170                     hir::ExprKind::Path(qpath)
 171                 }
 172                 ExprKind::Break(opt_label, ref opt_expr) => {
 173                     let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
 174                     hir::ExprKind::Break(self.lower_jump_destination(e.id, opt_label), opt_expr)
 175                 }
 176                 ExprKind::Continue(opt_label) => {
 177                     hir::ExprKind::Continue(self.lower_jump_destination(e.id, opt_label))
 178                 }
 179                 ExprKind::Ret(ref e) => {
 180                     let e = e.as_ref().map(|x| self.lower_expr(x));
 181                     hir::ExprKind::Ret(e)
 182                 }
 183                 ExprKind::InlineAsm(ref asm) => self.lower_expr_asm(e.span, asm),
 184                 ExprKind::LlvmInlineAsm(ref asm) => self.lower_expr_llvm_asm(asm),
 185                 ExprKind::Struct(ref path, ref fields, ref maybe_expr) => {
 186                     let maybe_expr = maybe_expr.as_ref().map(|x| self.lower_expr(x));
 187                     hir::ExprKind::Struct(
 188                         self.arena.alloc(self.lower_qpath(
 189                             e.id,
 190                             &None,
 191                             path,
 192                             ParamMode::Optional,
 193                             ImplTraitContext::disallowed(),
 194                         )),
 195                         self.arena.alloc_from_iter(fields.iter().map(|x| self.lower_field(x))),
 196                         maybe_expr,
 197                     )
 198                 }
 199                 ExprKind::Yield(ref opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
 200                 ExprKind::Err => hir::ExprKind::Err,
 201                 ExprKind::Try(ref sub_expr) => self.lower_expr_try(e.span, sub_expr),
 202                 ExprKind::Paren(ref ex) => {
 203                     let mut ex = self.lower_expr_mut(ex);
 204                     // Include parens in span, but only if it is a super-span.
 205                     if e.span.contains(ex.span) {
 206                         ex.span = e.span;
 207                     }
 208                     // Merge attributes into the inner expression.
 209                     let mut attrs = e.attrs.clone();
 210                     attrs.extend::<Vec<_>>(ex.attrs.into());
 211                     ex.attrs = attrs;
 212                     return ex;
 213                 }
 214
 215                 // Desugar `ExprForLoop`
 216                 // from: `[opt_ident]: for <pat> in <head> <body>`
 217                 ExprKind::ForLoop(ref pat, ref head, ref body, opt_label) => {
 218                     return self.lower_expr_for(e, pat, head, body, opt_label);
 219                 }
 220                 ExprKind::MacCall(_) => panic!("{:?} shouldn't exist here", e.span),
 221             };
 222
 223             hir::Expr {
 224                 hir_id: self.lower_node_id(e.id),
 225                 kind,
 226                 span: e.span,
 227                 attrs: e.attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into(),
 228             }
 229         })
 230     }
 231
 232     fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
 233         match u {
 234             UnOp::Deref => hir::UnOp::UnDeref,
 235             UnOp::Not => hir::UnOp::UnNot,
 236             UnOp::Neg => hir::UnOp::UnNeg,
 237         }
 238     }
 239
 240     fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
 241         Spanned {
 242             node: match b.node {
 243                 BinOpKind::Add => hir::BinOpKind::Add,
 244                 BinOpKind::Sub => hir::BinOpKind::Sub,
 245                 BinOpKind::Mul => hir::BinOpKind::Mul,
 246                 BinOpKind::Div => hir::BinOpKind::Div,
 247                 BinOpKind::Rem => hir::BinOpKind::Rem,
 248                 BinOpKind::And => hir::BinOpKind::And,
 249                 BinOpKind::Or => hir::BinOpKind::Or,
 250                 BinOpKind::BitXor => hir::BinOpKind::BitXor,
 251                 BinOpKind::BitAnd => hir::BinOpKind::BitAnd,
 252                 BinOpKind::BitOr => hir::BinOpKind::BitOr,
 253                 BinOpKind::Shl => hir::BinOpKind::Shl,
 254                 BinOpKind::Shr => hir::BinOpKind::Shr,
 255                 BinOpKind::Eq => hir::BinOpKind::Eq,
 256                 BinOpKind::Lt => hir::BinOpKind::Lt,
 257                 BinOpKind::Le => hir::BinOpKind::Le,
 258                 BinOpKind::Ne => hir::BinOpKind::Ne,
 259                 BinOpKind::Ge => hir::BinOpKind::Ge,
 260                 BinOpKind::Gt => hir::BinOpKind::Gt,
 261             },
 262             span: b.span,
 263         }
 264     }
 265
 266     /// Emit an error and lower `ast::ExprKind::Let(pat, scrutinee)` into:
 267     /// ```rust
 268     /// match scrutinee { pats => true, _ => false }
 269     /// ```
 270     fn lower_expr_let(&mut self, span: Span, pat: &Pat, scrutinee: &Expr) -> hir::ExprKind<'hir> {
 271         // If we got here, the `let` expression is not allowed.
 272
 273         if self.sess.opts.unstable_features.is_nightly_build() {
 274             self.sess
 275                 .struct_span_err(span, "`let` expressions are not supported here")
 276                 .note("only supported directly in conditions of `if`- and `while`-expressions")
 277                 .note("as well as when nested within `&&` and parenthesis in those conditions")
 278                 .emit();
 279         } else {
 280             self.sess
 281                 .struct_span_err(span, "expected expression, found statement (`let`)")
 282                 .note("variable declaration using `let` is a statement")
 283                 .emit();
 284         }
 285
 286         // For better recovery, we emit:
 287         // ```
 288         // match scrutinee { pat => true, _ => false }
 289         // ```
 290         // While this doesn't fully match the user's intent, it has key advantages:
 291         // 1. We can avoid using `abort_if_errors`.
 292         // 2. We can typeck both `pat` and `scrutinee`.
 293         // 3. `pat` is allowed to be refutable.
 294         // 4. The return type of the block is `bool` which seems like what the user wanted.
 295         let scrutinee = self.lower_expr(scrutinee);
 296         let then_arm = {
 297             let pat = self.lower_pat(pat);
 298             let expr = self.expr_bool(span, true);
 299             self.arm(pat, expr)
 300         };
 301         let else_arm = {
 302             let pat = self.pat_wild(span);
 303             let expr = self.expr_bool(span, false);
 304             self.arm(pat, expr)
 305         };
 306         hir::ExprKind::Match(
 307             scrutinee,
 308             arena_vec![self; then_arm, else_arm],
 309             hir::MatchSource::Normal,
 310         )
 311     }
 312
 313     fn lower_expr_if(
 314         &mut self,
 315         span: Span,
 316         cond: &Expr,
 317         then: &Block,
 318         else_opt: Option<&Expr>,
 319     ) -> hir::ExprKind<'hir> {
 320         // FIXME(#53667): handle lowering of && and parens.
 321
 322         // `_ => else_block` where `else_block` is `{}` if there's `None`:
 323         let else_pat = self.pat_wild(span);
 324         let (else_expr, contains_else_clause) = match else_opt {
 325             None => (self.expr_block_empty(span), false),
 326             Some(els) => (self.lower_expr(els), true),
 327         };
 328         let else_arm = self.arm(else_pat, else_expr);
 329
 330         // Handle then + scrutinee:
 331         let then_expr = self.lower_block_expr(then);
 332         let (then_pat, scrutinee, desugar) = match cond.kind {
 333             // `<pat> => <then>`:
 334             ExprKind::Let(ref pat, ref scrutinee) => {
 335                 let scrutinee = self.lower_expr(scrutinee);
 336                 let pat = self.lower_pat(pat);
 337                 (pat, scrutinee, hir::MatchSource::IfLetDesugar { contains_else_clause })
 338             }
 339             // `true => <then>`:
 340             _ => {
 341                 // Lower condition:
 342                 let cond = self.lower_expr(cond);
 343                 let span_block =
 344                     self.mark_span_with_reason(DesugaringKind::CondTemporary, cond.span, None);
 345                 // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
 346                 // to preserve drop semantics since `if cond { ... }` does not
 347                 // let temporaries live outside of `cond`.
 348                 let cond = self.expr_drop_temps(span_block, cond, ThinVec::new());
 349                 let pat = self.pat_bool(span, true);
 350                 (pat, cond, hir::MatchSource::IfDesugar { contains_else_clause })
 351             }
 352         };
 353         let then_arm = self.arm(then_pat, self.arena.alloc(then_expr));
 354
 355         hir::ExprKind::Match(scrutinee, arena_vec![self; then_arm, else_arm], desugar)
 356     }
 357
 358     fn lower_expr_while_in_loop_scope(
 359         &mut self,
 360         span: Span,
 361         cond: &Expr,
 362         body: &Block,
 363         opt_label: Option<Label>,
 364     ) -> hir::ExprKind<'hir> {
 365         // FIXME(#53667): handle lowering of && and parens.
 366
 367         // Note that the block AND the condition are evaluated in the loop scope.
 368         // This is done to allow `break` from inside the condition of the loop.
 369
 370         // `_ => break`:
 371         let else_arm = {
 372             let else_pat = self.pat_wild(span);
 373             let else_expr = self.expr_break(span, ThinVec::new());
 374             self.arm(else_pat, else_expr)
 375         };
 376
 377         // Handle then + scrutinee:
 378         let then_expr = self.lower_block_expr(body);
 379         let (then_pat, scrutinee, desugar, source) = match cond.kind {
 380             ExprKind::Let(ref pat, ref scrutinee) => {
 381                 // to:
 382                 //
 383                 //   [opt_ident]: loop {
 384                 //     match <sub_expr> {
 385                 //       <pat> => <body>,
 386                 //       _ => break
 387                 //     }
 388                 //   }
 389                 let scrutinee = self.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
 390                 let pat = self.lower_pat(pat);
 391                 (pat, scrutinee, hir::MatchSource::WhileLetDesugar, hir::LoopSource::WhileLet)
 392             }
 393             _ => {
 394                 // We desugar: `'label: while $cond $body` into:
 395                 //
 396                 // ```
 397                 // 'label: loop {
 398                 //     match drop-temps { $cond } {
 399                 //         true => $body,
 400                 //         _ => break,
 401                 //     }
 402                 // }
 403                 // ```
 404
 405                 // Lower condition:
 406                 let cond = self.with_loop_condition_scope(|this| this.lower_expr(cond));
 407                 let span_block =
 408                     self.mark_span_with_reason(DesugaringKind::CondTemporary, cond.span, None);
 409                 // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
 410                 // to preserve drop semantics since `while cond { ... }` does not
 411                 // let temporaries live outside of `cond`.
 412                 let cond = self.expr_drop_temps(span_block, cond, ThinVec::new());
 413                 // `true => <then>`:
 414                 let pat = self.pat_bool(span, true);
 415                 (pat, cond, hir::MatchSource::WhileDesugar, hir::LoopSource::While)
 416             }
 417         };
 418         let then_arm = self.arm(then_pat, self.arena.alloc(then_expr));
 419
 420         // `match <scrutinee> { ... }`
 421         let match_expr =
 422             self.expr_match(span, scrutinee, arena_vec![self; then_arm, else_arm], desugar);
 423
 424         // `[opt_ident]: loop { ... }`
 425         hir::ExprKind::Loop(self.block_expr(self.arena.alloc(match_expr)), opt_label, source)
 426     }
 427
 428     /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_ok(<expr>) }`,
 429     /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_ok(()) }`
 430     /// and save the block id to use it as a break target for desugaring of the `?` operator.
 431     fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind<'hir> {
 432         self.with_catch_scope(body.id, |this| {
 433             let mut block = this.lower_block_noalloc(body, true);
 434
 435             // Final expression of the block (if present) or `()` with span at the end of block
 436             let (try_span, tail_expr) = if let Some(expr) = block.expr.take() {
 437                 (
 438                     this.mark_span_with_reason(
 439                         DesugaringKind::TryBlock,
 440                         expr.span,
 441                         this.allow_try_trait.clone(),
 442                     ),
 443                     expr,
 444                 )
 445             } else {
 446                 let try_span = this.mark_span_with_reason(
 447                     DesugaringKind::TryBlock,
 448                     this.sess.source_map().end_point(body.span),
 449                     this.allow_try_trait.clone(),
 450                 );
 451
 452                 (try_span, this.expr_unit(try_span))
 453             };
 454
 455             let ok_wrapped_span =
 456                 this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
 457
 458             // `::std::ops::Try::from_ok($tail_expr)`
 459             block.expr = Some(this.wrap_in_try_constructor(
 460                 hir::LangItem::TryFromOk,
 461                 try_span,
 462                 tail_expr,
 463                 ok_wrapped_span,
 464             ));
 465
 466             hir::ExprKind::Block(this.arena.alloc(block), None)
 467         })
 468     }
 469
 470     fn wrap_in_try_constructor(
 471         &mut self,
 472         lang_item: hir::LangItem,
 473         method_span: Span,
 474         expr: &'hir hir::Expr<'hir>,
 475         overall_span: Span,
 476     ) -> &'hir hir::Expr<'hir> {
 477         let constructor =
 478             self.arena.alloc(self.expr_lang_item_path(method_span, lang_item, ThinVec::new()));
 479         self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
 480     }
 481
 482     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
 483         hir::Arm {
 484             hir_id: self.next_id(),
 485             attrs: self.lower_attrs(&arm.attrs),
 486             pat: self.lower_pat(&arm.pat),
 487             guard: match arm.guard {
 488                 Some(ref x) => Some(hir::Guard::If(self.lower_expr(x))),
 489                 _ => None,
 490             },
 491             body: self.lower_expr(&arm.body),
 492             span: arm.span,
 493         }
 494     }
 495
 496     /// Lower an `async` construct to a generator that is then wrapped so it implements `Future`.
 497     ///
 498     /// This results in:
 499     ///
 500     /// ```text
 501     /// std::future::from_generator(static move? |_task_context| -> <ret_ty> {
 502     ///     <body>
 503     /// })
 504     /// ```
 505     pub(super) fn make_async_expr(
 506         &mut self,
 507         capture_clause: CaptureBy,
 508         closure_node_id: NodeId,
 509         ret_ty: Option<AstP<Ty>>,
 510         span: Span,
 511         async_gen_kind: hir::AsyncGeneratorKind,
 512         body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
 513     ) -> hir::ExprKind<'hir> {
 514         let output = match ret_ty {
 515             Some(ty) => hir::FnRetTy::Return(self.lower_ty(&ty, ImplTraitContext::disallowed())),
 516             None => hir::FnRetTy::DefaultReturn(span),
 517         };
 518
 519         // Resume argument type. We let the compiler infer this to simplify the lowering. It is
 520         // fully constrained by `future::from_generator`.
 521         let input_ty = hir::Ty { hir_id: self.next_id(), kind: hir::TyKind::Infer, span };
 522
 523         // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
 524         let decl = self.arena.alloc(hir::FnDecl {
 525             inputs: arena_vec![self; input_ty],
 526             output,
 527             c_variadic: false,
 528             implicit_self: hir::ImplicitSelfKind::None,
 529         });
 530
 531         // Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
 532         let (pat, task_context_hid) = self.pat_ident_binding_mode(
 533             span,
 534             Ident::with_dummy_span(sym::_task_context),
 535             hir::BindingAnnotation::Mutable,
 536         );
 537         let param = hir::Param { attrs: &[], hir_id: self.next_id(), pat, ty_span: span, span };
 538         let params = arena_vec![self; param];
 539
 540         let body_id = self.lower_body(move |this| {
 541             this.generator_kind = Some(hir::GeneratorKind::Async(async_gen_kind));
 542
 543             let old_ctx = this.task_context;
 544             this.task_context = Some(task_context_hid);
 545             let res = body(this);
 546             this.task_context = old_ctx;
 547             (params, res)
 548         });
 549
 550         // `static |_task_context| -> <ret_ty> { body }`:
 551         let generator_kind = hir::ExprKind::Closure(
 552             capture_clause,
 553             decl,
 554             body_id,
 555             span,
 556             Some(hir::Movability::Static),
 557         );
 558         let generator = hir::Expr {
 559             hir_id: self.lower_node_id(closure_node_id),
 560             kind: generator_kind,
 561             span,
 562             attrs: ThinVec::new(),
 563         };
 564
 565         // `future::from_generator`:
 566         let unstable_span =
 567             self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
 568         let gen_future =
 569             self.expr_lang_item_path(unstable_span, hir::LangItem::FromGenerator, ThinVec::new());
 570
 571         // `future::from_generator(generator)`:
 572         hir::ExprKind::Call(self.arena.alloc(gen_future), arena_vec![self; generator])
 573     }
 574
 575     /// Desugar `<expr>.await` into:
 576     /// ```rust
 577     /// match <expr> {
 578     ///     mut pinned => loop {
 579     ///         match unsafe { ::std::future::Future::poll(
 580     ///             <::std::pin::Pin>::new_unchecked(&mut pinned),
 581     ///             ::std::future::get_context(task_context),
 582     ///         ) } {
 583     ///             ::std::task::Poll::Ready(result) => break result,
 584     ///             ::std::task::Poll::Pending => {}
 585     ///         }
 586     ///         task_context = yield ();
 587     ///     }
 588     /// }
 589     /// ```
 590     fn lower_expr_await(&mut self, await_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
 591         match self.generator_kind {
 592             Some(hir::GeneratorKind::Async(_)) => {}
 593             Some(hir::GeneratorKind::Gen) | None => {
 594                 let mut err = struct_span_err!(
 595                     self.sess,
 596                     await_span,
 597                     E0728,
 598                     "`await` is only allowed inside `async` functions and blocks"
 599                 );
 600                 err.span_label(await_span, "only allowed inside `async` functions and blocks");
 601                 if let Some(item_sp) = self.current_item {
 602                     err.span_label(item_sp, "this is not `async`");
 603                 }
 604                 err.emit();
 605             }
 606         }
 607         let span = self.mark_span_with_reason(DesugaringKind::Await, await_span, None);
 608         let gen_future_span = self.mark_span_with_reason(
 609             DesugaringKind::Await,
 610             await_span,
 611             self.allow_gen_future.clone(),
 612         );
 613         let expr = self.lower_expr(expr);
 614
 615         let pinned_ident = Ident::with_dummy_span(sym::pinned);
 616         let (pinned_pat, pinned_pat_hid) =
 617             self.pat_ident_binding_mode(span, pinned_ident, hir::BindingAnnotation::Mutable);
 618
 619         let task_context_ident = Ident::with_dummy_span(sym::_task_context);
 620
 621         // unsafe {
 622         //     ::std::future::Future::poll(
 623         //         ::std::pin::Pin::new_unchecked(&mut pinned),
 624         //         ::std::future::get_context(task_context),
 625         //     )
 626         // }
 627         let poll_expr = {
 628             let pinned = self.expr_ident(span, pinned_ident, pinned_pat_hid);
 629             let ref_mut_pinned = self.expr_mut_addr_of(span, pinned);
 630             let task_context = if let Some(task_context_hid) = self.task_context {
 631                 self.expr_ident_mut(span, task_context_ident, task_context_hid)
 632             } else {
 633                 // Use of `await` outside of an async context, we cannot use `task_context` here.
 634                 self.expr_err(span)
 635             };
 636             let new_unchecked = self.expr_call_lang_item_fn_mut(
 637                 span,
 638                 hir::LangItem::PinNewUnchecked,
 639                 arena_vec![self; ref_mut_pinned],
 640             );
 641             let get_context = self.expr_call_lang_item_fn_mut(
 642                 gen_future_span,
 643                 hir::LangItem::GetContext,
 644                 arena_vec![self; task_context],
 645             );
 646             let call = self.expr_call_lang_item_fn(
 647                 span,
 648                 hir::LangItem::FuturePoll,
 649                 arena_vec![self; new_unchecked, get_context],
 650             );
 651             self.arena.alloc(self.expr_unsafe(call))
 652         };
 653
 654         // `::std::task::Poll::Ready(result) => break result`
 655         let loop_node_id = self.resolver.next_node_id();
 656         let loop_hir_id = self.lower_node_id(loop_node_id);
 657         let ready_arm = {
 658             let x_ident = Ident::with_dummy_span(sym::result);
 659             let (x_pat, x_pat_hid) = self.pat_ident(span, x_ident);
 660             let x_expr = self.expr_ident(span, x_ident, x_pat_hid);
 661             let ready_field = self.single_pat_field(span, x_pat);
 662             let ready_pat = self.pat_lang_item_variant(span, hir::LangItem::PollReady, ready_field);
 663             let break_x = self.with_loop_scope(loop_node_id, move |this| {
 664                 let expr_break =
 665                     hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
 666                 this.arena.alloc(this.expr(await_span, expr_break, ThinVec::new()))
 667             });
 668             self.arm(ready_pat, break_x)
 669         };
 670
 671         // `::std::task::Poll::Pending => {}`
 672         let pending_arm = {
 673             let pending_pat = self.pat_lang_item_variant(span, hir::LangItem::PollPending, &[]);
 674             let empty_block = self.expr_block_empty(span);
 675             self.arm(pending_pat, empty_block)
 676         };
 677
 678         let inner_match_stmt = {
 679             let match_expr = self.expr_match(
 680                 span,
 681                 poll_expr,
 682                 arena_vec![self; ready_arm, pending_arm],
 683                 hir::MatchSource::AwaitDesugar,
 684             );
 685             self.stmt_expr(span, match_expr)
 686         };
 687
 688         // task_context = yield ();
 689         let yield_stmt = {
 690             let unit = self.expr_unit(span);
 691             let yield_expr = self.expr(
 692                 span,
 693                 hir::ExprKind::Yield(unit, hir::YieldSource::Await { expr: Some(expr.hir_id) }),
 694                 ThinVec::new(),
 695             );
 696             let yield_expr = self.arena.alloc(yield_expr);
 697
 698             if let Some(task_context_hid) = self.task_context {
 699                 let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
 700                 let assign =
 701                     self.expr(span, hir::ExprKind::Assign(lhs, yield_expr, span), AttrVec::new());
 702                 self.stmt_expr(span, assign)
 703             } else {
 704                 // Use of `await` outside of an async context. Return `yield_expr` so that we can
 705                 // proceed with type checking.
 706                 self.stmt(span, hir::StmtKind::Semi(yield_expr))
 707             }
 708         };
 709
 710         let loop_block = self.block_all(span, arena_vec![self; inner_match_stmt, yield_stmt], None);
 711
 712         // loop { .. }
 713         let loop_expr = self.arena.alloc(hir::Expr {
 714             hir_id: loop_hir_id,
 715             kind: hir::ExprKind::Loop(loop_block, None, hir::LoopSource::Loop),
 716             span,
 717             attrs: ThinVec::new(),
 718         });
 719
 720         // mut pinned => loop { ... }
 721         let pinned_arm = self.arm(pinned_pat, loop_expr);
 722
 723         // match <expr> {
 724         //     mut pinned => loop { .. }
 725         // }
 726         hir::ExprKind::Match(expr, arena_vec![self; pinned_arm], hir::MatchSource::AwaitDesugar)
 727     }
 728
 729     fn lower_expr_closure(
 730         &mut self,
 731         capture_clause: CaptureBy,
 732         movability: Movability,
 733         decl: &FnDecl,
 734         body: &Expr,
 735         fn_decl_span: Span,
 736     ) -> hir::ExprKind<'hir> {
 737         // Lower outside new scope to preserve `is_in_loop_condition`.
 738         let fn_decl = self.lower_fn_decl(decl, None, false, None);
 739
 740         self.with_new_scopes(move |this| {
 741             let prev = this.current_item;
 742             this.current_item = Some(fn_decl_span);
 743             let mut generator_kind = None;
 744             let body_id = this.lower_fn_body(decl, |this| {
 745                 let e = this.lower_expr_mut(body);
 746                 generator_kind = this.generator_kind;
 747                 e
 748             });
 749             let generator_option =
 750                 this.generator_movability_for_fn(&decl, fn_decl_span, generator_kind, movability);
 751             this.current_item = prev;
 752             hir::ExprKind::Closure(capture_clause, fn_decl, body_id, fn_decl_span, generator_option)
 753         })
 754     }
 755
 756     fn generator_movability_for_fn(
 757         &mut self,
 758         decl: &FnDecl,
 759         fn_decl_span: Span,
 760         generator_kind: Option<hir::GeneratorKind>,
 761         movability: Movability,
 762     ) -> Option<hir::Movability> {
 763         match generator_kind {
 764             Some(hir::GeneratorKind::Gen) => {
 765                 if decl.inputs.len() > 1 {
 766                     struct_span_err!(
 767                         self.sess,
 768                         fn_decl_span,
 769                         E0628,
 770                         "too many parameters for a generator (expected 0 or 1 parameters)"
 771                     )
 772                     .emit();
 773                 }
 774                 Some(movability)
 775             }
 776             Some(hir::GeneratorKind::Async(_)) => {
 777                 panic!("non-`async` closure body turned `async` during lowering");
 778             }
 779             None => {
 780                 if movability == Movability::Static {
 781                     struct_span_err!(self.sess, fn_decl_span, E0697, "closures cannot be static")
 782                         .emit();
 783                 }
 784                 None
 785             }
 786         }
 787     }
 788
 789     fn lower_expr_async_closure(
 790         &mut self,
 791         capture_clause: CaptureBy,
 792         closure_id: NodeId,
 793         decl: &FnDecl,
 794         body: &Expr,
 795         fn_decl_span: Span,
 796     ) -> hir::ExprKind<'hir> {
 797         let outer_decl =
 798             FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
 799         // We need to lower the declaration outside the new scope, because we
 800         // have to conserve the state of being inside a loop condition for the
 801         // closure argument types.
 802         let fn_decl = self.lower_fn_decl(&outer_decl, None, false, None);
 803
 804         self.with_new_scopes(move |this| {
 805             // FIXME(cramertj): allow `async` non-`move` closures with arguments.
 806             if capture_clause == CaptureBy::Ref && !decl.inputs.is_empty() {
 807                 struct_span_err!(
 808                     this.sess,
 809                     fn_decl_span,
 810                     E0708,
 811                     "`async` non-`move` closures with parameters are not currently supported",
 812                 )
 813                 .help(
 814                     "consider using `let` statements to manually capture \
 815                     variables by reference before entering an `async move` closure",
 816                 )
 817                 .emit();
 818             }
 819
 820             // Transform `async |x: u8| -> X { ... }` into
 821             // `|x: u8| future_from_generator(|| -> X { ... })`.
 822             let body_id = this.lower_fn_body(&outer_decl, |this| {
 823                 let async_ret_ty =
 824                     if let FnRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
 825                 let async_body = this.make_async_expr(
 826                     capture_clause,
 827                     closure_id,
 828                     async_ret_ty,
 829                     body.span,
 830                     hir::AsyncGeneratorKind::Closure,
 831                     |this| this.with_new_scopes(|this| this.lower_expr_mut(body)),
 832                 );
 833                 this.expr(fn_decl_span, async_body, ThinVec::new())
 834             });
 835             hir::ExprKind::Closure(capture_clause, fn_decl, body_id, fn_decl_span, None)
 836         })
 837     }
 838
 839     /// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
 840     fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
 841         let e1 = self.lower_expr_mut(e1);
 842         let e2 = self.lower_expr_mut(e2);
 843         let fn_path = hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, span);
 844         let fn_expr =
 845             self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), ThinVec::new()));
 846         hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
 847     }
 848
 849     fn lower_expr_range(
 850         &mut self,
 851         span: Span,
 852         e1: Option<&Expr>,
 853         e2: Option<&Expr>,
 854         lims: RangeLimits,
 855     ) -> hir::ExprKind<'hir> {
 856         use rustc_ast::RangeLimits::*;
 857
 858         let lang_item = match (e1, e2, lims) {
 859             (None, None, HalfOpen) => hir::LangItem::RangeFull,
 860             (Some(..), None, HalfOpen) => hir::LangItem::RangeFrom,
 861             (None, Some(..), HalfOpen) => hir::LangItem::RangeTo,
 862             (Some(..), Some(..), HalfOpen) => hir::LangItem::Range,
 863             (None, Some(..), Closed) => hir::LangItem::RangeToInclusive,
 864             (Some(..), Some(..), Closed) => unreachable!(),
 865             (_, None, Closed) => {
 866                 self.diagnostic().span_fatal(span, "inclusive range with no end").raise()
 867             }
 868         };
 869
 870         let fields = self.arena.alloc_from_iter(
 871             e1.iter().map(|e| ("start", e)).chain(e2.iter().map(|e| ("end", e))).map(|(s, e)| {
 872                 let expr = self.lower_expr(&e);
 873                 let ident = Ident::new(Symbol::intern(s), e.span);
 874                 self.field(ident, expr, e.span)
 875             }),
 876         );
 877
 878         hir::ExprKind::Struct(self.arena.alloc(hir::QPath::LangItem(lang_item, span)), fields, None)
 879     }
 880
 881     fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
 882         let target_id = match destination {
 883             Some((id, _)) => {
 884                 if let Some(loop_id) = self.resolver.get_label_res(id) {
 885                     Ok(self.lower_node_id(loop_id))
 886                 } else {
 887                     Err(hir::LoopIdError::UnresolvedLabel)
 888                 }
 889             }
 890             None => self
 891                 .loop_scopes
 892                 .last()
 893                 .cloned()
 894                 .map(|id| Ok(self.lower_node_id(id)))
 895                 .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope)),
 896         };
 897         hir::Destination { label: destination.map(|(_, label)| label), target_id }
 898     }
 899
 900     fn lower_jump_destination(&mut self, id: NodeId, opt_label: Option<Label>) -> hir::Destination {
 901         if self.is_in_loop_condition && opt_label.is_none() {
 902             hir::Destination {
 903                 label: None,
 904                 target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition),
 905             }
 906         } else {
 907             self.lower_loop_destination(opt_label.map(|label| (id, label)))
 908         }
 909     }
 910
 911     fn with_catch_scope<T>(&mut self, catch_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
 912         let len = self.catch_scopes.len();
 913         self.catch_scopes.push(catch_id);
 914
 915         let result = f(self);
 916         assert_eq!(
 917             len + 1,
 918             self.catch_scopes.len(),
 919             "catch scopes should be added and removed in stack order"
 920         );
 921
 922         self.catch_scopes.pop().unwrap();
 923
 924         result
 925     }
 926
 927     fn with_loop_scope<T>(&mut self, loop_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
 928         // We're no longer in the base loop's condition; we're in another loop.
 929         let was_in_loop_condition = self.is_in_loop_condition;
 930         self.is_in_loop_condition = false;
 931
 932         let len = self.loop_scopes.len();
 933         self.loop_scopes.push(loop_id);
 934
 935         let result = f(self);
 936         assert_eq!(
 937             len + 1,
 938             self.loop_scopes.len(),
 939             "loop scopes should be added and removed in stack order"
 940         );
 941
 942         self.loop_scopes.pop().unwrap();
 943
 944         self.is_in_loop_condition = was_in_loop_condition;
 945
 946         result
 947     }
 948
 949     fn with_loop_condition_scope<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
 950         let was_in_loop_condition = self.is_in_loop_condition;
 951         self.is_in_loop_condition = true;
 952
 953         let result = f(self);
 954
 955         self.is_in_loop_condition = was_in_loop_condition;
 956
 957         result
 958     }
 959
 960     fn lower_expr_asm(&mut self, sp: Span, asm: &InlineAsm) -> hir::ExprKind<'hir> {
 961         if self.sess.asm_arch.is_none() {
 962             struct_span_err!(self.sess, sp, E0472, "asm! is unsupported on this target").emit();
 963         }
 964         if asm.options.contains(InlineAsmOptions::ATT_SYNTAX)
 965             && !matches!(
 966                 self.sess.asm_arch,
 967                 Some(asm::InlineAsmArch::X86 | asm::InlineAsmArch::X86_64)
 968             )
 969         {
 970             self.sess
 971                 .struct_span_err(sp, "the `att_syntax` option is only supported on x86")
 972                 .emit();
 973         }
 974
 975         // Lower operands to HIR, filter_map skips any operands with invalid
 976         // register classes.
 977         let sess = self.sess;
 978         let operands: Vec<_> = asm
 979             .operands
 980             .iter()
 981             .filter_map(|(op, op_sp)| {
 982                 let lower_reg = |reg| {
 983                     Some(match reg {
 984                         InlineAsmRegOrRegClass::Reg(s) => asm::InlineAsmRegOrRegClass::Reg(
 985                             asm::InlineAsmReg::parse(
 986                                 sess.asm_arch?,
 987                                 |feature| sess.target_features.contains(&Symbol::intern(feature)),
 988                                 &sess.target.target,
 989                                 s,
 990                             )
 991                             .map_err(|e| {
 992                                 let msg = format!("invalid register `{}`: {}", s.as_str(), e);
 993                                 sess.struct_span_err(*op_sp, &msg).emit();
 994                             })
 995                             .ok()?,
 996                         ),
 997                         InlineAsmRegOrRegClass::RegClass(s) => {
 998                             asm::InlineAsmRegOrRegClass::RegClass(
 999                                 asm::InlineAsmRegClass::parse(sess.asm_arch?, s)
1000                                     .map_err(|e| {
1001                                         let msg = format!(
1002                                             "invalid register class `{}`: {}",
1003                                             s.as_str(),
1004                                             e
1005                                         );
1006                                         sess.struct_span_err(*op_sp, &msg).emit();
1007                                     })
1008                                     .ok()?,
1009                             )
1010                         }
1011                     })
1012                 };
1013
1014                 // lower_reg is executed last because we need to lower all
1015                 // sub-expressions even if we throw them away later.
1016                 let op = match *op {
1017                     InlineAsmOperand::In { reg, ref expr } => hir::InlineAsmOperand::In {
1018                         expr: self.lower_expr_mut(expr),
1019                         reg: lower_reg(reg)?,
1020                     },
1021                     InlineAsmOperand::Out { reg, late, ref expr } => hir::InlineAsmOperand::Out {
1022                         late,
1023                         expr: expr.as_ref().map(|expr| self.lower_expr_mut(expr)),
1024                         reg: lower_reg(reg)?,
1025                     },
1026                     InlineAsmOperand::InOut { reg, late, ref expr } => {
1027                         hir::InlineAsmOperand::InOut {
1028                             late,
1029                             expr: self.lower_expr_mut(expr),
1030                             reg: lower_reg(reg)?,
1031                         }
1032                     }
1033                     InlineAsmOperand::SplitInOut { reg, late, ref in_expr, ref out_expr } => {
1034                         hir::InlineAsmOperand::SplitInOut {
1035                             late,
1036                             in_expr: self.lower_expr_mut(in_expr),
1037                             out_expr: out_expr.as_ref().map(|expr| self.lower_expr_mut(expr)),
1038                             reg: lower_reg(reg)?,
1039                         }
1040                     }
1041                     InlineAsmOperand::Const { ref expr } => {
1042                         hir::InlineAsmOperand::Const { expr: self.lower_expr_mut(expr) }
1043                     }
1044                     InlineAsmOperand::Sym { ref expr } => {
1045                         hir::InlineAsmOperand::Sym { expr: self.lower_expr_mut(expr) }
1046                     }
1047                 };
1048                 Some(op)
1049             })
1050             .collect();
1051
1052         // Stop if there were any errors when lowering the register classes
1053         if operands.len() != asm.operands.len() || sess.asm_arch.is_none() {
1054             return hir::ExprKind::Err;
1055         }
1056
1057         // Validate template modifiers against the register classes for the operands
1058         let asm_arch = sess.asm_arch.unwrap();
1059         for p in &asm.template {
1060             if let InlineAsmTemplatePiece::Placeholder {
1061                 operand_idx,
1062                 modifier: Some(modifier),
1063                 span: placeholder_span,
1064             } = *p
1065             {
1066                 let op_sp = asm.operands[operand_idx].1;
1067                 match &operands[operand_idx] {
1068                     hir::InlineAsmOperand::In { reg, .. }
1069                     | hir::InlineAsmOperand::Out { reg, .. }
1070                     | hir::InlineAsmOperand::InOut { reg, .. }
1071                     | hir::InlineAsmOperand::SplitInOut { reg, .. } => {
1072                         let class = reg.reg_class();
1073                         let valid_modifiers = class.valid_modifiers(asm_arch);
1074                         if !valid_modifiers.contains(&modifier) {
1075                             let mut err = sess.struct_span_err(
1076                                 placeholder_span,
1077                                 "invalid asm template modifier for this register class",
1078                             );
1079                             err.span_label(placeholder_span, "template modifier");
1080                             err.span_label(op_sp, "argument");
1081                             if !valid_modifiers.is_empty() {
1082                                 let mut mods = format!("`{}`", valid_modifiers[0]);
1083                                 for m in &valid_modifiers[1..] {
1084                                     let _ = write!(mods, ", `{}`", m);
1085                                 }
1086                                 err.note(&format!(
1087                                     "the `{}` register class supports \
1088                                      the following template modifiers: {}",
1089                                     class.name(),
1090                                     mods
1091                                 ));
1092                             } else {
1093                                 err.note(&format!(
1094                                     "the `{}` register class does not support template modifiers",
1095                                     class.name()
1096                                 ));
1097                             }
1098                             err.emit();
1099                         }
1100                     }
1101                     hir::InlineAsmOperand::Const { .. } => {
1102                         let mut err = sess.struct_span_err(
1103                             placeholder_span,
1104                             "asm template modifiers are not allowed for `const` arguments",
1105                         );
1106                         err.span_label(placeholder_span, "template modifier");
1107                         err.span_label(op_sp, "argument");
1108                         err.emit();
1109                     }
1110                     hir::InlineAsmOperand::Sym { .. } => {
1111                         let mut err = sess.struct_span_err(
1112                             placeholder_span,
1113                             "asm template modifiers are not allowed for `sym` arguments",
1114                         );
1115                         err.span_label(placeholder_span, "template modifier");
1116                         err.span_label(op_sp, "argument");
1117                         err.emit();
1118                     }
1119                 }
1120             }
1121         }
1122
1123         let mut used_input_regs = FxHashMap::default();
1124         let mut used_output_regs = FxHashMap::default();
1125         for (idx, op) in operands.iter().enumerate() {
1126             let op_sp = asm.operands[idx].1;
1127             if let Some(reg) = op.reg() {
1128                 // Validate register classes against currently enabled target
1129                 // features. We check that at least one type is available for
1130                 // the current target.
1131                 let reg_class = reg.reg_class();
1132                 let mut required_features: Vec<&str> = vec![];
1133                 for &(_, feature) in reg_class.supported_types(asm_arch) {
1134                     if let Some(feature) = feature {
1135                         if self.sess.target_features.contains(&Symbol::intern(feature)) {
1136                             required_features.clear();
1137                             break;
1138                         } else {
1139                             required_features.push(feature);
1140                         }
1141                     } else {
1142                         required_features.clear();
1143                         break;
1144                     }
1145                 }
1146                 // We are sorting primitive strs here and can use unstable sort here
1147                 required_features.sort_unstable();
1148                 required_features.dedup();
1149                 match &required_features[..] {
1150                     [] => {}
1151                     [feature] => {
1152                         let msg = format!(
1153                             "register class `{}` requires the `{}` target feature",
1154                             reg_class.name(),
1155                             feature
1156                         );
1157                         sess.struct_span_err(op_sp, &msg).emit();
1158                     }
1159                     features => {
1160                         let msg = format!(
1161                             "register class `{}` requires at least one target feature: {}",
1162                             reg_class.name(),
1163                             features.join(", ")
1164                         );
1165                         sess.struct_span_err(op_sp, &msg).emit();
1166                     }
1167                 }
1168
1169                 // Check for conflicts between explicit register operands.
1170                 if let asm::InlineAsmRegOrRegClass::Reg(reg) = reg {
1171                     let (input, output) = match op {
1172                         hir::InlineAsmOperand::In { .. } => (true, false),
1173                         // Late output do not conflict with inputs, but normal outputs do
1174                         hir::InlineAsmOperand::Out { late, .. } => (!late, true),
1175                         hir::InlineAsmOperand::InOut { .. }
1176                         | hir::InlineAsmOperand::SplitInOut { .. } => (true, true),
1177                         hir::InlineAsmOperand::Const { .. } | hir::InlineAsmOperand::Sym { .. } => {
1178                             unreachable!()
1179                         }
1180                     };
1181
1182                     // Flag to output the error only once per operand
1183                     let mut skip = false;
1184                     reg.overlapping_regs(|r| {
1185                         let mut check = |used_regs: &mut FxHashMap<asm::InlineAsmReg, usize>,
1186                                          input| {
1187                             match used_regs.entry(r) {
1188                                 Entry::Occupied(o) => {
1189                                     if !skip {
1190                                         skip = true;
1191
1192                                         let idx2 = *o.get();
1193                                         let op2 = &operands[idx2];
1194                                         let op_sp2 = asm.operands[idx2].1;
1195                                         let reg2 = match op2.reg() {
1196                                             Some(asm::InlineAsmRegOrRegClass::Reg(r)) => r,
1197                                             _ => unreachable!(),
1198                                         };
1199
1200                                         let msg = format!(
1201                                             "register `{}` conflicts with register `{}`",
1202                                             reg.name(),
1203                                             reg2.name()
1204                                         );
1205                                         let mut err = sess.struct_span_err(op_sp, &msg);
1206                                         err.span_label(
1207                                             op_sp,
1208                                             &format!("register `{}`", reg.name()),
1209                                         );
1210                                         err.span_label(
1211                                             op_sp2,
1212                                             &format!("register `{}`", reg2.name()),
1213                                         );
1214
1215                                         match (op, op2) {
1216                                             (
1217                                                 hir::InlineAsmOperand::In { .. },
1218                                                 hir::InlineAsmOperand::Out { late, .. },
1219                                             )
1220                                             | (
1221                                                 hir::InlineAsmOperand::Out { late, .. },
1222                                                 hir::InlineAsmOperand::In { .. },
1223                                             ) => {
1224                                                 assert!(!*late);
1225                                                 let out_op_sp = if input { op_sp2 } else { op_sp };
1226                                                 let msg = "use `lateout` instead of \
1227                                                      `out` to avoid conflict";
1228                                                 err.span_help(out_op_sp, msg);
1229                                             }
1230                                             _ => {}
1231                                         }
1232
1233                                         err.emit();
1234                                     }
1235                                 }
1236                                 Entry::Vacant(v) => {
1237                                     v.insert(idx);
1238                                 }
1239                             }
1240                         };
1241                         if input {
1242                             check(&mut used_input_regs, true);
1243                         }
1244                         if output {
1245                             check(&mut used_output_regs, false);
1246                         }
1247                     });
1248                 }
1249             }
1250         }
1251
1252         let operands = self.arena.alloc_from_iter(operands);
1253         let template = self.arena.alloc_from_iter(asm.template.iter().cloned());
1254         let line_spans = self.arena.alloc_slice(&asm.line_spans[..]);
1255         let hir_asm = hir::InlineAsm { template, operands, options: asm.options, line_spans };
1256         hir::ExprKind::InlineAsm(self.arena.alloc(hir_asm))
1257     }
1258
1259     fn lower_expr_llvm_asm(&mut self, asm: &LlvmInlineAsm) -> hir::ExprKind<'hir> {
1260         let inner = hir::LlvmInlineAsmInner {
1261             inputs: asm.inputs.iter().map(|&(c, _)| c).collect(),
1262             outputs: asm
1263                 .outputs
1264                 .iter()
1265                 .map(|out| hir::LlvmInlineAsmOutput {
1266                     constraint: out.constraint,
1267                     is_rw: out.is_rw,
1268                     is_indirect: out.is_indirect,
1269                     span: out.expr.span,
1270                 })
1271                 .collect(),
1272             asm: asm.asm,
1273             asm_str_style: asm.asm_str_style,
1274             clobbers: asm.clobbers.clone(),
1275             volatile: asm.volatile,
1276             alignstack: asm.alignstack,
1277             dialect: asm.dialect,
1278         };
1279         let hir_asm = hir::LlvmInlineAsm {
1280             inner,
1281             inputs_exprs: self.arena.alloc_from_iter(
1282                 asm.inputs.iter().map(|&(_, ref input)| self.lower_expr_mut(input)),
1283             ),
1284             outputs_exprs: self
1285                 .arena
1286                 .alloc_from_iter(asm.outputs.iter().map(|out| self.lower_expr_mut(&out.expr))),
1287         };
1288         hir::ExprKind::LlvmInlineAsm(self.arena.alloc(hir_asm))
1289     }
1290
1291     fn lower_field(&mut self, f: &Field) -> hir::Field<'hir> {
1292         hir::Field {
1293             hir_id: self.next_id(),
1294             ident: f.ident,
1295             expr: self.lower_expr(&f.expr),
1296             span: f.span,
1297             is_shorthand: f.is_shorthand,
1298         }
1299     }
1300
1301     fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
1302         match self.generator_kind {
1303             Some(hir::GeneratorKind::Gen) => {}
1304             Some(hir::GeneratorKind::Async(_)) => {
1305                 struct_span_err!(
1306                     self.sess,
1307                     span,
1308                     E0727,
1309                     "`async` generators are not yet supported"
1310                 )
1311                 .emit();
1312             }
1313             None => self.generator_kind = Some(hir::GeneratorKind::Gen),
1314         }
1315
1316         let expr =
1317             opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
1318
1319         hir::ExprKind::Yield(expr, hir::YieldSource::Yield)
1320     }
1321
1322     /// Desugar `ExprForLoop` from: `[opt_ident]: for <pat> in <head> <body>` into:
1323     /// ```rust
1324     /// {
1325     ///     let result = match ::std::iter::IntoIterator::into_iter(<head>) {
1326     ///         mut iter => {
1327     ///             [opt_ident]: loop {
1328     ///                 let mut __next;
1329     ///                 match ::std::iter::Iterator::next(&mut iter) {
1330     ///                     ::std::option::Option::Some(val) => __next = val,
1331     ///                     ::std::option::Option::None => break
1332     ///                 };
1333     ///                 let <pat> = __next;
1334     ///                 StmtKind::Expr(<body>);
1335     ///             }
1336     ///         }
1337     ///     };
1338     ///     result
1339     /// }
1340     /// ```
1341     fn lower_expr_for(
1342         &mut self,
1343         e: &Expr,
1344         pat: &Pat,
1345         head: &Expr,
1346         body: &Block,
1347         opt_label: Option<Label>,
1348     ) -> hir::Expr<'hir> {
1349         let orig_head_span = head.span;
1350         // expand <head>
1351         let mut head = self.lower_expr_mut(head);
1352         let desugared_span = self.mark_span_with_reason(
1353             DesugaringKind::ForLoop(ForLoopLoc::Head),
1354             orig_head_span,
1355             None,
1356         );
1357         head.span = desugared_span;
1358
1359         let iter = Ident::with_dummy_span(sym::iter);
1360
1361         let next_ident = Ident::with_dummy_span(sym::__next);
1362         let (next_pat, next_pat_hid) = self.pat_ident_binding_mode(
1363             desugared_span,
1364             next_ident,
1365             hir::BindingAnnotation::Mutable,
1366         );
1367
1368         // `::std::option::Option::Some(val) => __next = val`
1369         let pat_arm = {
1370             let val_ident = Ident::with_dummy_span(sym::val);
1371             let (val_pat, val_pat_hid) = self.pat_ident(pat.span, val_ident);
1372             let val_expr = self.expr_ident(pat.span, val_ident, val_pat_hid);
1373             let next_expr = self.expr_ident(pat.span, next_ident, next_pat_hid);
1374             let assign = self.arena.alloc(self.expr(
1375                 pat.span,
1376                 hir::ExprKind::Assign(next_expr, val_expr, pat.span),
1377                 ThinVec::new(),
1378             ));
1379             let some_pat = self.pat_some(pat.span, val_pat);
1380             self.arm(some_pat, assign)
1381         };
1382
1383         // `::std::option::Option::None => break`
1384         let break_arm = {
1385             let break_expr =
1386                 self.with_loop_scope(e.id, |this| this.expr_break(e.span, ThinVec::new()));
1387             let pat = self.pat_none(e.span);
1388             self.arm(pat, break_expr)
1389         };
1390
1391         // `mut iter`
1392         let (iter_pat, iter_pat_nid) =
1393             self.pat_ident_binding_mode(desugared_span, iter, hir::BindingAnnotation::Mutable);
1394
1395         // `match ::std::iter::Iterator::next(&mut iter) { ... }`
1396         let match_expr = {
1397             let iter = self.expr_ident(desugared_span, iter, iter_pat_nid);
1398             let ref_mut_iter = self.expr_mut_addr_of(desugared_span, iter);
1399             let next_expr = self.expr_call_lang_item_fn(
1400                 desugared_span,
1401                 hir::LangItem::IteratorNext,
1402                 arena_vec![self; ref_mut_iter],
1403             );
1404             let arms = arena_vec![self; pat_arm, break_arm];
1405
1406             self.expr_match(desugared_span, next_expr, arms, hir::MatchSource::ForLoopDesugar)
1407         };
1408         let match_stmt = self.stmt_expr(desugared_span, match_expr);
1409
1410         let next_expr = self.expr_ident(desugared_span, next_ident, next_pat_hid);
1411
1412         // `let mut __next`
1413         let next_let = self.stmt_let_pat(
1414             ThinVec::new(),
1415             desugared_span,
1416             None,
1417             next_pat,
1418             hir::LocalSource::ForLoopDesugar,
1419         );
1420
1421         // `let <pat> = __next`
1422         let pat = self.lower_pat(pat);
1423         let pat_let = self.stmt_let_pat(
1424             ThinVec::new(),
1425             desugared_span,
1426             Some(next_expr),
1427             pat,
1428             hir::LocalSource::ForLoopDesugar,
1429         );
1430
1431         let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
1432         let body_expr = self.expr_block(body_block, ThinVec::new());
1433         let body_stmt = self.stmt_expr(body.span, body_expr);
1434
1435         let loop_block = self.block_all(
1436             e.span,
1437             arena_vec![self; next_let, match_stmt, pat_let, body_stmt],
1438             None,
1439         );
1440
1441         // `[opt_ident]: loop { ... }`
1442         let kind = hir::ExprKind::Loop(loop_block, opt_label, hir::LoopSource::ForLoop);
1443         let loop_expr = self.arena.alloc(hir::Expr {
1444             hir_id: self.lower_node_id(e.id),
1445             kind,
1446             span: e.span,
1447             attrs: ThinVec::new(),
1448         });
1449
1450         // `mut iter => { ... }`
1451         let iter_arm = self.arm(iter_pat, loop_expr);
1452
1453         let into_iter_span = self.mark_span_with_reason(
1454             DesugaringKind::ForLoop(ForLoopLoc::IntoIter),
1455             orig_head_span,
1456             None,
1457         );
1458
1459         // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
1460         let into_iter_expr = {
1461             self.expr_call_lang_item_fn(
1462                 into_iter_span,
1463                 hir::LangItem::IntoIterIntoIter,
1464                 arena_vec![self; head],
1465             )
1466         };
1467
1468         let match_expr = self.arena.alloc(self.expr_match(
1469             desugared_span,
1470             into_iter_expr,
1471             arena_vec![self; iter_arm],
1472             hir::MatchSource::ForLoopDesugar,
1473         ));
1474
1475         // This is effectively `{ let _result = ...; _result }`.
1476         // The construct was introduced in #21984 and is necessary to make sure that
1477         // temporaries in the `head` expression are dropped and do not leak to the
1478         // surrounding scope of the `match` since the `match` is not a terminating scope.
1479         //
1480         // Also, add the attributes to the outer returned expr node.
1481         self.expr_drop_temps_mut(desugared_span, match_expr, e.attrs.clone())
1482     }
1483
1484     /// Desugar `ExprKind::Try` from: `<expr>?` into:
1485     /// ```rust
1486     /// match Try::into_result(<expr>) {
1487     ///     Ok(val) => #[allow(unreachable_code)] val,
1488     ///     Err(err) => #[allow(unreachable_code)]
1489     ///                 // If there is an enclosing `try {...}`:
1490     ///                 break 'catch_target Try::from_error(From::from(err)),
1491     ///                 // Otherwise:
1492     ///                 return Try::from_error(From::from(err)),
1493     /// }
1494     /// ```
1495     fn lower_expr_try(&mut self, span: Span, sub_expr: &Expr) -> hir::ExprKind<'hir> {
1496         let unstable_span = self.mark_span_with_reason(
1497             DesugaringKind::QuestionMark,
1498             span,
1499             self.allow_try_trait.clone(),
1500         );
1501         let try_span = self.sess.source_map().end_point(span);
1502         let try_span = self.mark_span_with_reason(
1503             DesugaringKind::QuestionMark,
1504             try_span,
1505             self.allow_try_trait.clone(),
1506         );
1507
1508         // `Try::into_result(<expr>)`
1509         let scrutinee = {
1510             // expand <expr>
1511             let sub_expr = self.lower_expr_mut(sub_expr);
1512
1513             self.expr_call_lang_item_fn(
1514                 unstable_span,
1515                 hir::LangItem::TryIntoResult,
1516                 arena_vec![self; sub_expr],
1517             )
1518         };
1519
1520         // `#[allow(unreachable_code)]`
1521         let attr = {
1522             // `allow(unreachable_code)`
1523             let allow = {
1524                 let allow_ident = Ident::new(sym::allow, span);
1525                 let uc_ident = Ident::new(sym::unreachable_code, span);
1526                 let uc_nested = attr::mk_nested_word_item(uc_ident);
1527                 attr::mk_list_item(allow_ident, vec![uc_nested])
1528             };
1529             attr::mk_attr_outer(allow)
1530         };
1531         let attrs = vec![attr];
1532
1533         // `Ok(val) => #[allow(unreachable_code)] val,`
1534         let ok_arm = {
1535             let val_ident = Ident::with_dummy_span(sym::val);
1536             let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
1537             let val_expr = self.arena.alloc(self.expr_ident_with_attrs(
1538                 span,
1539                 val_ident,
1540                 val_pat_nid,
1541                 ThinVec::from(attrs.clone()),
1542             ));
1543             let ok_pat = self.pat_ok(span, val_pat);
1544             self.arm(ok_pat, val_expr)
1545         };
1546
1547         // `Err(err) => #[allow(unreachable_code)]
1548         //              return Try::from_error(From::from(err)),`
1549         let err_arm = {
1550             let err_ident = Ident::with_dummy_span(sym::err);
1551             let (err_local, err_local_nid) = self.pat_ident(try_span, err_ident);
1552             let from_expr = {
1553                 let err_expr = self.expr_ident_mut(try_span, err_ident, err_local_nid);
1554                 self.expr_call_lang_item_fn(
1555                     try_span,
1556                     hir::LangItem::FromFrom,
1557                     arena_vec![self; err_expr],
1558                 )
1559             };
1560             let from_err_expr = self.wrap_in_try_constructor(
1561                 hir::LangItem::TryFromError,
1562                 unstable_span,
1563                 from_expr,
1564                 unstable_span,
1565             );
1566             let thin_attrs = ThinVec::from(attrs);
1567             let catch_scope = self.catch_scopes.last().copied();
1568             let ret_expr = if let Some(catch_node) = catch_scope {
1569                 let target_id = Ok(self.lower_node_id(catch_node));
1570                 self.arena.alloc(self.expr(
1571                     try_span,
1572                     hir::ExprKind::Break(
1573                         hir::Destination { label: None, target_id },
1574                         Some(from_err_expr),
1575                     ),
1576                     thin_attrs,
1577                 ))
1578             } else {
1579                 self.arena.alloc(self.expr(
1580                     try_span,
1581                     hir::ExprKind::Ret(Some(from_err_expr)),
1582                     thin_attrs,
1583                 ))
1584             };
1585
1586             let err_pat = self.pat_err(try_span, err_local);
1587             self.arm(err_pat, ret_expr)
1588         };
1589
1590         hir::ExprKind::Match(
1591             scrutinee,
1592             arena_vec![self; err_arm, ok_arm],
1593             hir::MatchSource::TryDesugar,
1594         )
1595     }
1596
1597     // =========================================================================
1598     // Helper methods for building HIR.
1599     // =========================================================================
1600
1601     /// Constructs a `true` or `false` literal expression.
1602     pub(super) fn expr_bool(&mut self, span: Span, val: bool) -> &'hir hir::Expr<'hir> {
1603         let lit = Spanned { span, node: LitKind::Bool(val) };
1604         self.arena.alloc(self.expr(span, hir::ExprKind::Lit(lit), ThinVec::new()))
1605     }
1606
1607     /// Wrap the given `expr` in a terminating scope using `hir::ExprKind::DropTemps`.
1608     ///
1609     /// In terms of drop order, it has the same effect as wrapping `expr` in
1610     /// `{ let _t = $expr; _t }` but should provide better compile-time performance.
1611     ///
1612     /// The drop order can be important in e.g. `if expr { .. }`.
1613     pub(super) fn expr_drop_temps(
1614         &mut self,
1615         span: Span,
1616         expr: &'hir hir::Expr<'hir>,
1617         attrs: AttrVec,
1618     ) -> &'hir hir::Expr<'hir> {
1619         self.arena.alloc(self.expr_drop_temps_mut(span, expr, attrs))
1620     }
1621
1622     pub(super) fn expr_drop_temps_mut(
1623         &mut self,
1624         span: Span,
1625         expr: &'hir hir::Expr<'hir>,
1626         attrs: AttrVec,
1627     ) -> hir::Expr<'hir> {
1628         self.expr(span, hir::ExprKind::DropTemps(expr), attrs)
1629     }
1630
1631     fn expr_match(
1632         &mut self,
1633         span: Span,
1634         arg: &'hir hir::Expr<'hir>,
1635         arms: &'hir [hir::Arm<'hir>],
1636         source: hir::MatchSource,
1637     ) -> hir::Expr<'hir> {
1638         self.expr(span, hir::ExprKind::Match(arg, arms, source), ThinVec::new())
1639     }
1640
1641     fn expr_break(&mut self, span: Span, attrs: AttrVec) -> &'hir hir::Expr<'hir> {
1642         let expr_break = hir::ExprKind::Break(self.lower_loop_destination(None), None);
1643         self.arena.alloc(self.expr(span, expr_break, attrs))
1644     }
1645
1646     fn expr_mut_addr_of(&mut self, span: Span, e: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
1647         self.expr(
1648             span,
1649             hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e),
1650             ThinVec::new(),
1651         )
1652     }
1653
1654     fn expr_unit(&mut self, sp: Span) -> &'hir hir::Expr<'hir> {
1655         self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[]), ThinVec::new()))
1656     }
1657
1658     fn expr_call_mut(
1659         &mut self,
1660         span: Span,
1661         e: &'hir hir::Expr<'hir>,
1662         args: &'hir [hir::Expr<'hir>],
1663     ) -> hir::Expr<'hir> {
1664         self.expr(span, hir::ExprKind::Call(e, args), ThinVec::new())
1665     }
1666
1667     fn expr_call(
1668         &mut self,
1669         span: Span,
1670         e: &'hir hir::Expr<'hir>,
1671         args: &'hir [hir::Expr<'hir>],
1672     ) -> &'hir hir::Expr<'hir> {
1673         self.arena.alloc(self.expr_call_mut(span, e, args))
1674     }
1675
1676     fn expr_call_lang_item_fn_mut(
1677         &mut self,
1678         span: Span,
1679         lang_item: hir::LangItem,
1680         args: &'hir [hir::Expr<'hir>],
1681     ) -> hir::Expr<'hir> {
1682         let path = self.arena.alloc(self.expr_lang_item_path(span, lang_item, ThinVec::new()));
1683         self.expr_call_mut(span, path, args)
1684     }
1685
1686     fn expr_call_lang_item_fn(
1687         &mut self,
1688         span: Span,
1689         lang_item: hir::LangItem,
1690         args: &'hir [hir::Expr<'hir>],
1691     ) -> &'hir hir::Expr<'hir> {
1692         self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args))
1693     }
1694
1695     fn expr_lang_item_path(
1696         &mut self,
1697         span: Span,
1698         lang_item: hir::LangItem,
1699         attrs: AttrVec,
1700     ) -> hir::Expr<'hir> {
1701         self.expr(span, hir::ExprKind::Path(hir::QPath::LangItem(lang_item, span)), attrs)
1702     }
1703
1704     pub(super) fn expr_ident(
1705         &mut self,
1706         sp: Span,
1707         ident: Ident,
1708         binding: hir::HirId,
1709     ) -> &'hir hir::Expr<'hir> {
1710         self.arena.alloc(self.expr_ident_mut(sp, ident, binding))
1711     }
1712
1713     pub(super) fn expr_ident_mut(
1714         &mut self,
1715         sp: Span,
1716         ident: Ident,
1717         binding: hir::HirId,
1718     ) -> hir::Expr<'hir> {
1719         self.expr_ident_with_attrs(sp, ident, binding, ThinVec::new())
1720     }
1721
1722     fn expr_ident_with_attrs(
1723         &mut self,
1724         span: Span,
1725         ident: Ident,
1726         binding: hir::HirId,
1727         attrs: AttrVec,
1728     ) -> hir::Expr<'hir> {
1729         let expr_path = hir::ExprKind::Path(hir::QPath::Resolved(
1730             None,
1731             self.arena.alloc(hir::Path {
1732                 span,
1733                 res: Res::Local(binding),
1734                 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1735             }),
1736         ));
1737
1738         self.expr(span, expr_path, attrs)
1739     }
1740
1741     fn expr_unsafe(&mut self, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
1742         let hir_id = self.next_id();
1743         let span = expr.span;
1744         self.expr(
1745             span,
1746             hir::ExprKind::Block(
1747                 self.arena.alloc(hir::Block {
1748                     stmts: &[],
1749                     expr: Some(expr),
1750                     hir_id,
1751                     rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
1752                     span,
1753                     targeted_by_break: false,
1754                 }),
1755                 None,
1756             ),
1757             ThinVec::new(),
1758         )
1759     }
1760
1761     fn expr_block_empty(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
1762         let blk = self.block_all(span, &[], None);
1763         let expr = self.expr_block(blk, ThinVec::new());
1764         self.arena.alloc(expr)
1765     }
1766
1767     pub(super) fn expr_block(
1768         &mut self,
1769         b: &'hir hir::Block<'hir>,
1770         attrs: AttrVec,
1771     ) -> hir::Expr<'hir> {
1772         self.expr(b.span, hir::ExprKind::Block(b, None), attrs)
1773     }
1774
1775     pub(super) fn expr(
1776         &mut self,
1777         span: Span,
1778         kind: hir::ExprKind<'hir>,
1779         attrs: AttrVec,
1780     ) -> hir::Expr<'hir> {
1781         hir::Expr { hir_id: self.next_id(), kind, span, attrs }
1782     }
1783
1784     fn field(&mut self, ident: Ident, expr: &'hir hir::Expr<'hir>, span: Span) -> hir::Field<'hir> {
1785         hir::Field { hir_id: self.next_id(), ident, span, expr, is_shorthand: false }
1786     }
1787
1788     fn arm(&mut self, pat: &'hir hir::Pat<'hir>, expr: &'hir hir::Expr<'hir>) -> hir::Arm<'hir> {
1789         hir::Arm {
1790             hir_id: self.next_id(),
1791             attrs: &[],
1792             pat,
1793             guard: None,
1794             span: expr.span,
1795             body: expr,
1796         }
1797     }
1798 }