2 AsyncGeneratorsNotSupported, AsyncNonMoveClosureNotSupported, AwaitOnlyInAsyncFnAndBlocks,
3 BaseExpressionDoubleDot, ClosureCannotBeStatic, FunctionalRecordUpdateDestructuringAssignemnt,
4 GeneratorTooManyParameters, InclusiveRangeWithNoEnd, NotSupportedForLifetimeBinderAsyncClosure,
5 RustcBoxAttributeError, UnderscoreExprLhsAssign,
7 use super::ResolverAstLoweringExt;
8 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
9 use crate::{FnDeclKind, ImplTraitPosition};
11 use rustc_ast::ptr::P as AstP;
13 use rustc_data_structures::stack::ensure_sufficient_stack;
15 use rustc_hir::def::Res;
16 use rustc_hir::definitions::DefPathData;
17 use rustc_session::errors::report_lit_error;
18 use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
19 use rustc_span::symbol::{sym, Ident};
20 use rustc_span::DUMMY_SP;
21 use thin_vec::thin_vec;
23 impl<'hir> LoweringContext<'_, 'hir> {
24 fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
25 self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
28 pub(super) fn lower_expr(&mut self, e: &Expr) -> &'hir hir::Expr<'hir> {
29 self.arena.alloc(self.lower_expr_mut(e))
32 pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
33 ensure_sufficient_stack(|| {
35 // Paranthesis expression does not have a HirId and is handled specially.
36 ExprKind::Paren(ex) => {
37 let mut ex = self.lower_expr_mut(ex);
38 // Include parens in span, but only if it is a super-span.
39 if e.span.contains(ex.span) {
40 ex.span = self.lower_span(e.span);
42 // Merge attributes into the inner expression.
43 if !e.attrs.is_empty() {
45 self.attrs.get(&ex.hir_id.local_id).map(|la| *la).unwrap_or(&[]);
48 &*self.arena.alloc_from_iter(
51 .map(|a| self.lower_attr(a))
52 .chain(old_attrs.iter().cloned()),
58 // Desugar `ExprForLoop`
59 // from: `[opt_ident]: for <pat> in <head> <body>`
61 // This also needs special handling because the HirId of the returned `hir::Expr` will not
62 // correspond to the `e.id`, so `lower_expr_for` handles attribute lowering itself.
63 ExprKind::ForLoop(pat, head, body, opt_label) => {
64 return self.lower_expr_for(e, pat, head, body, *opt_label);
69 let hir_id = self.lower_node_id(e.id);
70 self.lower_attrs(hir_id, &e.attrs);
72 let kind = match &e.kind {
73 ExprKind::Box(inner) => hir::ExprKind::Box(self.lower_expr(inner)),
74 ExprKind::Array(exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
75 ExprKind::ConstBlock(anon_const) => {
76 let anon_const = self.lower_anon_const(anon_const);
77 hir::ExprKind::ConstBlock(anon_const)
79 ExprKind::Repeat(expr, count) => {
80 let expr = self.lower_expr(expr);
81 let count = self.lower_array_length(count);
82 hir::ExprKind::Repeat(expr, count)
84 ExprKind::Tup(elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
85 ExprKind::Call(f, args) => {
86 if e.attrs.get(0).map_or(false, |a| a.has_name(sym::rustc_box)) {
87 if let [inner] = &args[..] && e.attrs.len() == 1 {
88 let kind = hir::ExprKind::Box(self.lower_expr(&inner));
89 return hir::Expr { hir_id, kind, span: self.lower_span(e.span) };
91 self.tcx.sess.emit_err(RustcBoxAttributeError { span: e.span });
94 } else if let Some(legacy_args) = self.resolver.legacy_const_generic_args(f) {
95 self.lower_legacy_const_generics((**f).clone(), args.clone(), &legacy_args)
97 let f = self.lower_expr(f);
98 hir::ExprKind::Call(f, self.lower_exprs(args))
101 ExprKind::MethodCall(box MethodCall { seg, receiver, args, span }) => {
102 let hir_seg = self.arena.alloc(self.lower_path_segment(
106 ParenthesizedGenericArgs::Err,
107 &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
109 let receiver = self.lower_expr(receiver);
111 self.arena.alloc_from_iter(args.iter().map(|x| self.lower_expr_mut(x)));
112 hir::ExprKind::MethodCall(hir_seg, receiver, args, self.lower_span(*span))
114 ExprKind::Binary(binop, lhs, rhs) => {
115 let binop = self.lower_binop(*binop);
116 let lhs = self.lower_expr(lhs);
117 let rhs = self.lower_expr(rhs);
118 hir::ExprKind::Binary(binop, lhs, rhs)
120 ExprKind::Unary(op, ohs) => {
121 let op = self.lower_unop(*op);
122 let ohs = self.lower_expr(ohs);
123 hir::ExprKind::Unary(op, ohs)
125 ExprKind::Lit(token_lit) => {
126 let lit_kind = match LitKind::from_token_lit(*token_lit) {
127 Ok(lit_kind) => lit_kind,
129 report_lit_error(&self.tcx.sess.parse_sess, err, *token_lit, e.span);
133 hir::ExprKind::Lit(respan(self.lower_span(e.span), lit_kind))
135 ExprKind::IncludedBytes(bytes) => hir::ExprKind::Lit(respan(
136 self.lower_span(e.span),
137 LitKind::ByteStr(bytes.clone(), StrStyle::Cooked),
139 ExprKind::Cast(expr, ty) => {
140 let expr = self.lower_expr(expr);
142 self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
143 hir::ExprKind::Cast(expr, ty)
145 ExprKind::Type(expr, ty) => {
146 let expr = self.lower_expr(expr);
148 self.lower_ty(ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
149 hir::ExprKind::Type(expr, ty)
151 ExprKind::AddrOf(k, m, ohs) => {
152 let ohs = self.lower_expr(ohs);
153 hir::ExprKind::AddrOf(*k, *m, ohs)
155 ExprKind::Let(pat, scrutinee, span) => {
156 hir::ExprKind::Let(self.arena.alloc(hir::Let {
157 hir_id: self.next_id(),
158 span: self.lower_span(*span),
159 pat: self.lower_pat(pat),
161 init: self.lower_expr(scrutinee),
164 ExprKind::If(cond, then, else_opt) => {
165 self.lower_expr_if(cond, then, else_opt.as_deref())
167 ExprKind::While(cond, body, opt_label) => self.with_loop_scope(e.id, |this| {
168 let span = this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
169 this.lower_expr_while_in_loop_scope(span, cond, body, *opt_label)
171 ExprKind::Loop(body, opt_label, span) => self.with_loop_scope(e.id, |this| {
173 this.lower_block(body, false),
174 this.lower_label(*opt_label),
175 hir::LoopSource::Loop,
176 this.lower_span(*span),
179 ExprKind::TryBlock(body) => self.lower_expr_try_block(body),
180 ExprKind::Match(expr, arms) => hir::ExprKind::Match(
181 self.lower_expr(expr),
182 self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
183 hir::MatchSource::Normal,
185 ExprKind::Async(capture_clause, closure_node_id, block) => self.make_async_expr(
191 hir::AsyncGeneratorKind::Block,
192 |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
194 ExprKind::Await(expr) => {
195 let dot_await_span = if expr.span.hi() < e.span.hi() {
196 let span_with_whitespace = self
200 .span_extend_while(expr.span, char::is_whitespace)
201 .unwrap_or(expr.span);
202 span_with_whitespace.shrink_to_hi().with_hi(e.span.hi())
204 // this is a recovered `await expr`
207 self.lower_expr_await(dot_await_span, expr)
209 ExprKind::Closure(box Closure {
220 if let Async::Yes { closure_id, .. } = asyncness {
221 self.lower_expr_async_closure(
233 self.lower_expr_closure(
246 ExprKind::Block(blk, opt_label) => {
247 let opt_label = self.lower_label(*opt_label);
248 hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
250 ExprKind::Assign(el, er, span) => self.lower_expr_assign(el, er, *span, e.span),
251 ExprKind::AssignOp(op, el, er) => hir::ExprKind::AssignOp(
252 self.lower_binop(*op),
256 ExprKind::Field(el, ident) => {
257 hir::ExprKind::Field(self.lower_expr(el), self.lower_ident(*ident))
259 ExprKind::Index(el, er) => {
260 hir::ExprKind::Index(self.lower_expr(el), self.lower_expr(er))
262 ExprKind::Range(Some(e1), Some(e2), RangeLimits::Closed) => {
263 self.lower_expr_range_closed(e.span, e1, e2)
265 ExprKind::Range(e1, e2, lims) => {
266 self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), *lims)
268 ExprKind::Underscore => {
269 self.tcx.sess.emit_err(UnderscoreExprLhsAssign { span: e.span });
272 ExprKind::Path(qself, path) => {
273 let qpath = self.lower_qpath(
278 &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
280 hir::ExprKind::Path(qpath)
282 ExprKind::Break(opt_label, opt_expr) => {
283 let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
284 hir::ExprKind::Break(self.lower_jump_destination(e.id, *opt_label), opt_expr)
286 ExprKind::Continue(opt_label) => {
287 hir::ExprKind::Continue(self.lower_jump_destination(e.id, *opt_label))
289 ExprKind::Ret(e) => {
290 let e = e.as_ref().map(|x| self.lower_expr(x));
291 hir::ExprKind::Ret(e)
293 ExprKind::Yeet(sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
294 ExprKind::InlineAsm(asm) => {
295 hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
297 ExprKind::Struct(se) => {
298 let rest = match &se.rest {
299 StructRest::Base(e) => Some(self.lower_expr(e)),
300 StructRest::Rest(sp) => {
301 self.tcx.sess.emit_err(BaseExpressionDoubleDot { span: *sp });
302 Some(&*self.arena.alloc(self.expr_err(*sp)))
304 StructRest::None => None,
306 hir::ExprKind::Struct(
307 self.arena.alloc(self.lower_qpath(
312 &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
315 .alloc_from_iter(se.fields.iter().map(|x| self.lower_expr_field(x))),
319 ExprKind::Yield(opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
320 ExprKind::Err => hir::ExprKind::Err,
321 ExprKind::Try(sub_expr) => self.lower_expr_try(e.span, sub_expr),
323 ExprKind::Paren(_) | ExprKind::ForLoop(..) => unreachable!("already handled"),
325 ExprKind::MacCall(_) => panic!("{:?} shouldn't exist here", e.span),
328 hir::Expr { hir_id, kind, span: self.lower_span(e.span) }
332 fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
334 UnOp::Deref => hir::UnOp::Deref,
335 UnOp::Not => hir::UnOp::Not,
336 UnOp::Neg => hir::UnOp::Neg,
340 fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
343 BinOpKind::Add => hir::BinOpKind::Add,
344 BinOpKind::Sub => hir::BinOpKind::Sub,
345 BinOpKind::Mul => hir::BinOpKind::Mul,
346 BinOpKind::Div => hir::BinOpKind::Div,
347 BinOpKind::Rem => hir::BinOpKind::Rem,
348 BinOpKind::And => hir::BinOpKind::And,
349 BinOpKind::Or => hir::BinOpKind::Or,
350 BinOpKind::BitXor => hir::BinOpKind::BitXor,
351 BinOpKind::BitAnd => hir::BinOpKind::BitAnd,
352 BinOpKind::BitOr => hir::BinOpKind::BitOr,
353 BinOpKind::Shl => hir::BinOpKind::Shl,
354 BinOpKind::Shr => hir::BinOpKind::Shr,
355 BinOpKind::Eq => hir::BinOpKind::Eq,
356 BinOpKind::Lt => hir::BinOpKind::Lt,
357 BinOpKind::Le => hir::BinOpKind::Le,
358 BinOpKind::Ne => hir::BinOpKind::Ne,
359 BinOpKind::Ge => hir::BinOpKind::Ge,
360 BinOpKind::Gt => hir::BinOpKind::Gt,
362 span: self.lower_span(b.span),
366 fn lower_legacy_const_generics(
369 args: Vec<AstP<Expr>>,
370 legacy_args_idx: &[usize],
371 ) -> hir::ExprKind<'hir> {
372 let ExprKind::Path(None, path) = &mut f.kind else {
376 // Split the arguments into const generics and normal arguments
377 let mut real_args = vec![];
378 let mut generic_args = vec![];
379 for (idx, arg) in args.into_iter().enumerate() {
380 if legacy_args_idx.contains(&idx) {
381 let parent_def_id = self.current_hir_id_owner;
382 let node_id = self.next_node_id();
384 // Add a definition for the in-band const def.
385 self.create_def(parent_def_id.def_id, node_id, DefPathData::AnonConst, f.span);
387 let anon_const = AnonConst { id: node_id, value: arg };
388 generic_args.push(AngleBracketedArg::Arg(GenericArg::Const(anon_const)));
394 // Add generic args to the last element of the path.
395 let last_segment = path.segments.last_mut().unwrap();
396 assert!(last_segment.args.is_none());
397 last_segment.args = Some(AstP(GenericArgs::AngleBracketed(AngleBracketedArgs {
402 // Now lower everything as normal.
403 let f = self.lower_expr(&f);
404 hir::ExprKind::Call(f, self.lower_exprs(&real_args))
411 else_opt: Option<&Expr>,
412 ) -> hir::ExprKind<'hir> {
413 let lowered_cond = self.lower_cond(cond);
414 let then_expr = self.lower_block_expr(then);
415 if let Some(rslt) = else_opt {
418 self.arena.alloc(then_expr),
419 Some(self.lower_expr(rslt)),
422 hir::ExprKind::If(lowered_cond, self.arena.alloc(then_expr), None)
426 // Lowers a condition (i.e. `cond` in `if cond` or `while cond`), wrapping it in a terminating scope
427 // so that temporaries created in the condition don't live beyond it.
428 fn lower_cond(&mut self, cond: &Expr) -> &'hir hir::Expr<'hir> {
429 fn has_let_expr(expr: &Expr) -> bool {
431 ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs),
432 ExprKind::Let(..) => true,
437 // We have to take special care for `let` exprs in the condition, e.g. in
438 // `if let pat = val` or `if foo && let pat = val`, as we _do_ want `val` to live beyond the
439 // condition in this case.
441 // In order to mantain the drop behavior for the non `let` parts of the condition,
442 // we still wrap them in terminating scopes, e.g. `if foo && let pat = val` essentially
443 // gets transformed into `if { let _t = foo; _t } && let pat = val`
445 ExprKind::Binary(op @ Spanned { node: ast::BinOpKind::And, .. }, lhs, rhs)
446 if has_let_expr(cond) =>
448 let op = self.lower_binop(*op);
449 let lhs = self.lower_cond(lhs);
450 let rhs = self.lower_cond(rhs);
452 self.arena.alloc(self.expr(cond.span, hir::ExprKind::Binary(op, lhs, rhs)))
454 ExprKind::Let(..) => self.lower_expr(cond),
456 let cond = self.lower_expr(cond);
457 let reason = DesugaringKind::CondTemporary;
458 let span_block = self.mark_span_with_reason(reason, cond.span, None);
459 self.expr_drop_temps(span_block, cond)
464 // We desugar: `'label: while $cond $body` into:
468 // if { let _t = $cond; _t } {
477 // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
478 // to preserve drop semantics since `while $cond { ... }` does not
479 // let temporaries live outside of `cond`.
480 fn lower_expr_while_in_loop_scope(
485 opt_label: Option<Label>,
486 ) -> hir::ExprKind<'hir> {
487 let lowered_cond = self.with_loop_condition_scope(|t| t.lower_cond(cond));
488 let then = self.lower_block_expr(body);
489 let expr_break = self.expr_break(span);
490 let stmt_break = self.stmt_expr(span, expr_break);
491 let else_blk = self.block_all(span, arena_vec![self; stmt_break], None);
492 let else_expr = self.arena.alloc(self.expr_block(else_blk));
493 let if_kind = hir::ExprKind::If(lowered_cond, self.arena.alloc(then), Some(else_expr));
494 let if_expr = self.expr(span, if_kind);
495 let block = self.block_expr(self.arena.alloc(if_expr));
496 let span = self.lower_span(span.with_hi(cond.span.hi()));
497 let opt_label = self.lower_label(opt_label);
498 hir::ExprKind::Loop(block, opt_label, hir::LoopSource::While, span)
501 /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_output(<expr>) }`,
502 /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_output(()) }`
503 /// and save the block id to use it as a break target for desugaring of the `?` operator.
504 fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind<'hir> {
505 self.with_catch_scope(body.id, |this| {
506 let mut block = this.lower_block_noalloc(body, true);
508 // Final expression of the block (if present) or `()` with span at the end of block
509 let (try_span, tail_expr) = if let Some(expr) = block.expr.take() {
511 this.mark_span_with_reason(
512 DesugaringKind::TryBlock,
514 this.allow_try_trait.clone(),
519 let try_span = this.mark_span_with_reason(
520 DesugaringKind::TryBlock,
521 this.tcx.sess.source_map().end_point(body.span),
522 this.allow_try_trait.clone(),
525 (try_span, this.expr_unit(try_span))
528 let ok_wrapped_span =
529 this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
531 // `::std::ops::Try::from_output($tail_expr)`
532 block.expr = Some(this.wrap_in_try_constructor(
533 hir::LangItem::TryTraitFromOutput,
539 hir::ExprKind::Block(this.arena.alloc(block), None)
543 fn wrap_in_try_constructor(
545 lang_item: hir::LangItem,
547 expr: &'hir hir::Expr<'hir>,
549 ) -> &'hir hir::Expr<'hir> {
550 let constructor = self.arena.alloc(self.expr_lang_item_path(method_span, lang_item, None));
551 self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
554 fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
555 let pat = self.lower_pat(&arm.pat);
556 let guard = arm.guard.as_ref().map(|cond| {
557 if let ExprKind::Let(pat, scrutinee, span) = &cond.kind {
558 hir::Guard::IfLet(self.arena.alloc(hir::Let {
559 hir_id: self.next_id(),
560 span: self.lower_span(*span),
561 pat: self.lower_pat(pat),
563 init: self.lower_expr(scrutinee),
566 hir::Guard::If(self.lower_expr(cond))
569 let hir_id = self.next_id();
570 self.lower_attrs(hir_id, &arm.attrs);
575 body: self.lower_expr(&arm.body),
576 span: self.lower_span(arm.span),
580 /// Lower an `async` construct to a generator that implements `Future`.
585 /// std::future::identity_future(static move? |_task_context| -> <ret_ty> {
589 pub(super) fn make_async_expr(
591 capture_clause: CaptureBy,
592 outer_hir_id: hir::HirId,
593 closure_node_id: NodeId,
594 ret_ty: Option<hir::FnRetTy<'hir>>,
596 async_gen_kind: hir::AsyncGeneratorKind,
597 body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
598 ) -> hir::ExprKind<'hir> {
599 let output = ret_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span)));
601 // Resume argument type: `ResumeTy`
603 self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
604 let resume_ty = hir::QPath::LangItem(hir::LangItem::ResumeTy, unstable_span, None);
605 let input_ty = hir::Ty {
606 hir_id: self.next_id(),
607 kind: hir::TyKind::Path(resume_ty),
611 // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
612 let fn_decl = self.arena.alloc(hir::FnDecl {
613 inputs: arena_vec![self; input_ty],
616 implicit_self: hir::ImplicitSelfKind::None,
617 lifetime_elision_allowed: false,
620 // Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
621 let (pat, task_context_hid) = self.pat_ident_binding_mode(
623 Ident::with_dummy_span(sym::_task_context),
624 hir::BindingAnnotation::MUT,
626 let param = hir::Param {
627 hir_id: self.next_id(),
629 ty_span: self.lower_span(span),
630 span: self.lower_span(span),
632 let params = arena_vec![self; param];
634 let body = self.lower_body(move |this| {
635 this.generator_kind = Some(hir::GeneratorKind::Async(async_gen_kind));
637 let old_ctx = this.task_context;
638 this.task_context = Some(task_context_hid);
639 let res = body(this);
640 this.task_context = old_ctx;
644 // `static |_task_context| -> <ret_ty> { body }`:
645 let generator_kind = {
646 let c = self.arena.alloc(hir::Closure {
647 def_id: self.local_def_id(closure_node_id),
648 binder: hir::ClosureBinder::Default,
650 bound_generic_params: &[],
653 fn_decl_span: self.lower_span(span),
655 movability: Some(hir::Movability::Static),
656 constness: hir::Constness::NotConst,
659 hir::ExprKind::Closure(c)
662 let hir_id = self.lower_node_id(closure_node_id);
664 self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
666 if self.tcx.features().closure_track_caller
667 && let Some(attrs) = self.attrs.get(&outer_hir_id.local_id)
668 && attrs.into_iter().any(|attr| attr.has_name(sym::track_caller))
673 kind: AttrKind::Normal(ptr::P(NormalAttr {
675 path: Path::from_ident(Ident::new(sym::track_caller, span)),
676 args: AttrArgs::Empty,
681 id: self.tcx.sess.parse_sess.attr_id_generator.mk_attr_id(),
682 style: AttrStyle::Outer,
688 let generator = hir::Expr { hir_id, kind: generator_kind, span: self.lower_span(span) };
691 // For some reason, the async block needs to flow through *any*
692 // call (like the identity function), as otherwise type and lifetime
693 // inference have a hard time figuring things out.
694 // Without this, we would get:
695 // E0720 in tests/ui/impl-trait/in-trait/default-body-with-rpit.rs
696 // E0700 in tests/ui/self/self_lifetime-async.rs
698 // `future::identity_future`:
699 let identity_future =
700 self.expr_lang_item_path(unstable_span, hir::LangItem::IdentityFuture, None);
702 // `future::identity_future(generator)`:
703 hir::ExprKind::Call(self.arena.alloc(identity_future), arena_vec![self; generator])
706 /// Desugar `<expr>.await` into:
707 /// ```ignore (pseudo-rust)
708 /// match ::std::future::IntoFuture::into_future(<expr>) {
709 /// mut __awaitee => loop {
710 /// match unsafe { ::std::future::Future::poll(
711 /// <::std::pin::Pin>::new_unchecked(&mut __awaitee),
712 /// ::std::future::get_context(task_context),
714 /// ::std::task::Poll::Ready(result) => break result,
715 /// ::std::task::Poll::Pending => {}
717 /// task_context = yield ();
721 fn lower_expr_await(&mut self, dot_await_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
722 let full_span = expr.span.to(dot_await_span);
723 match self.generator_kind {
724 Some(hir::GeneratorKind::Async(_)) => {}
725 Some(hir::GeneratorKind::Gen) | None => {
726 self.tcx.sess.emit_err(AwaitOnlyInAsyncFnAndBlocks {
728 item_span: self.current_item,
732 let span = self.mark_span_with_reason(DesugaringKind::Await, dot_await_span, None);
733 let gen_future_span = self.mark_span_with_reason(
734 DesugaringKind::Await,
736 self.allow_gen_future.clone(),
738 let expr = self.lower_expr_mut(expr);
739 let expr_hir_id = expr.hir_id;
741 // Note that the name of this binding must not be changed to something else because
742 // debuggers and debugger extensions expect it to be called `__awaitee`. They use
743 // this name to identify what is being awaited by a suspended async functions.
744 let awaitee_ident = Ident::with_dummy_span(sym::__awaitee);
745 let (awaitee_pat, awaitee_pat_hid) =
746 self.pat_ident_binding_mode(span, awaitee_ident, hir::BindingAnnotation::MUT);
748 let task_context_ident = Ident::with_dummy_span(sym::_task_context);
751 // ::std::future::Future::poll(
752 // ::std::pin::Pin::new_unchecked(&mut __awaitee),
753 // ::std::future::get_context(task_context),
757 let awaitee = self.expr_ident(span, awaitee_ident, awaitee_pat_hid);
758 let ref_mut_awaitee = self.expr_mut_addr_of(span, awaitee);
759 let task_context = if let Some(task_context_hid) = self.task_context {
760 self.expr_ident_mut(span, task_context_ident, task_context_hid)
762 // Use of `await` outside of an async context, we cannot use `task_context` here.
765 let new_unchecked = self.expr_call_lang_item_fn_mut(
767 hir::LangItem::PinNewUnchecked,
768 arena_vec![self; ref_mut_awaitee],
771 let get_context = self.expr_call_lang_item_fn_mut(
773 hir::LangItem::GetContext,
774 arena_vec![self; task_context],
777 let call = self.expr_call_lang_item_fn(
779 hir::LangItem::FuturePoll,
780 arena_vec![self; new_unchecked, get_context],
783 self.arena.alloc(self.expr_unsafe(call))
786 // `::std::task::Poll::Ready(result) => break result`
787 let loop_node_id = self.next_node_id();
788 let loop_hir_id = self.lower_node_id(loop_node_id);
790 let x_ident = Ident::with_dummy_span(sym::result);
791 let (x_pat, x_pat_hid) = self.pat_ident(gen_future_span, x_ident);
792 let x_expr = self.expr_ident(gen_future_span, x_ident, x_pat_hid);
793 let ready_field = self.single_pat_field(gen_future_span, x_pat);
794 let ready_pat = self.pat_lang_item_variant(
796 hir::LangItem::PollReady,
800 let break_x = self.with_loop_scope(loop_node_id, move |this| {
802 hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
803 this.arena.alloc(this.expr(gen_future_span, expr_break))
805 self.arm(ready_pat, break_x)
808 // `::std::task::Poll::Pending => {}`
810 let pending_pat = self.pat_lang_item_variant(
812 hir::LangItem::PollPending,
816 let empty_block = self.expr_block_empty(span);
817 self.arm(pending_pat, empty_block)
820 let inner_match_stmt = {
821 let match_expr = self.expr_match(
824 arena_vec![self; ready_arm, pending_arm],
825 hir::MatchSource::AwaitDesugar,
827 self.stmt_expr(span, match_expr)
830 // task_context = yield ();
832 let unit = self.expr_unit(span);
833 let yield_expr = self.expr(
835 hir::ExprKind::Yield(unit, hir::YieldSource::Await { expr: Some(expr_hir_id) }),
837 let yield_expr = self.arena.alloc(yield_expr);
839 if let Some(task_context_hid) = self.task_context {
840 let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
842 self.expr(span, hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span)));
843 self.stmt_expr(span, assign)
845 // Use of `await` outside of an async context. Return `yield_expr` so that we can
846 // proceed with type checking.
847 self.stmt(span, hir::StmtKind::Semi(yield_expr))
851 let loop_block = self.block_all(span, arena_vec![self; inner_match_stmt, yield_stmt], None);
854 let loop_expr = self.arena.alloc(hir::Expr {
856 kind: hir::ExprKind::Loop(
859 hir::LoopSource::Loop,
860 self.lower_span(span),
862 span: self.lower_span(span),
865 // mut __awaitee => loop { ... }
866 let awaitee_arm = self.arm(awaitee_pat, loop_expr);
868 // `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
869 let into_future_span = self.mark_span_with_reason(
870 DesugaringKind::Await,
872 self.allow_into_future.clone(),
874 let into_future_expr = self.expr_call_lang_item_fn(
876 hir::LangItem::IntoFutureIntoFuture,
877 arena_vec![self; expr],
881 // match <into_future_expr> {
882 // mut __awaitee => loop { .. }
884 hir::ExprKind::Match(
886 arena_vec![self; awaitee_arm],
887 hir::MatchSource::AwaitDesugar,
891 fn lower_expr_closure(
893 binder: &ClosureBinder,
894 capture_clause: CaptureBy,
897 movability: Movability,
902 ) -> hir::ExprKind<'hir> {
903 let (binder_clause, generic_params) = self.lower_closure_binder(binder);
905 let (body_id, generator_option) = self.with_new_scopes(move |this| {
906 let prev = this.current_item;
907 this.current_item = Some(fn_decl_span);
908 let mut generator_kind = None;
909 let body_id = this.lower_fn_body(decl, |this| {
910 let e = this.lower_expr_mut(body);
911 generator_kind = this.generator_kind;
914 let generator_option =
915 this.generator_movability_for_fn(&decl, fn_decl_span, generator_kind, movability);
916 this.current_item = prev;
917 (body_id, generator_option)
920 let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
921 // Lower outside new scope to preserve `is_in_loop_condition`.
922 let fn_decl = self.lower_fn_decl(decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
924 let c = self.arena.alloc(hir::Closure {
925 def_id: self.local_def_id(closure_id),
926 binder: binder_clause,
928 bound_generic_params,
931 fn_decl_span: self.lower_span(fn_decl_span),
932 fn_arg_span: Some(self.lower_span(fn_arg_span)),
933 movability: generator_option,
934 constness: self.lower_constness(constness),
937 hir::ExprKind::Closure(c)
940 fn generator_movability_for_fn(
944 generator_kind: Option<hir::GeneratorKind>,
945 movability: Movability,
946 ) -> Option<hir::Movability> {
947 match generator_kind {
948 Some(hir::GeneratorKind::Gen) => {
949 if decl.inputs.len() > 1 {
950 self.tcx.sess.emit_err(GeneratorTooManyParameters { fn_decl_span });
954 Some(hir::GeneratorKind::Async(_)) => {
955 panic!("non-`async` closure body turned `async` during lowering");
958 if movability == Movability::Static {
959 self.tcx.sess.emit_err(ClosureCannotBeStatic { fn_decl_span });
966 fn lower_closure_binder<'c>(
968 binder: &'c ClosureBinder,
969 ) -> (hir::ClosureBinder, &'c [GenericParam]) {
970 let (binder, params) = match binder {
971 ClosureBinder::NotPresent => (hir::ClosureBinder::Default, &[][..]),
972 ClosureBinder::For { span, generic_params } => {
973 let span = self.lower_span(*span);
974 (hir::ClosureBinder::For { span }, &**generic_params)
981 fn lower_expr_async_closure(
983 binder: &ClosureBinder,
984 capture_clause: CaptureBy,
986 closure_hir_id: hir::HirId,
987 inner_closure_id: NodeId,
992 ) -> hir::ExprKind<'hir> {
993 if let &ClosureBinder::For { span, .. } = binder {
994 self.tcx.sess.emit_err(NotSupportedForLifetimeBinderAsyncClosure { span });
997 let (binder_clause, generic_params) = self.lower_closure_binder(binder);
1000 FnDecl { inputs: decl.inputs.clone(), output: FnRetTy::Default(fn_decl_span) };
1002 let body = self.with_new_scopes(|this| {
1003 // FIXME(cramertj): allow `async` non-`move` closures with arguments.
1004 if capture_clause == CaptureBy::Ref && !decl.inputs.is_empty() {
1005 this.tcx.sess.emit_err(AsyncNonMoveClosureNotSupported { fn_decl_span });
1008 // Transform `async |x: u8| -> X { ... }` into
1009 // `|x: u8| identity_future(|| -> X { ... })`.
1010 let body_id = this.lower_fn_body(&outer_decl, |this| {
1011 let async_ret_ty = if let FnRetTy::Ty(ty) = &decl.output {
1012 let itctx = ImplTraitContext::Disallowed(ImplTraitPosition::AsyncBlock);
1013 Some(hir::FnRetTy::Return(this.lower_ty(&ty, &itctx)))
1018 let async_body = this.make_async_expr(
1024 hir::AsyncGeneratorKind::Closure,
1025 |this| this.with_new_scopes(|this| this.lower_expr_mut(body)),
1027 this.expr(fn_decl_span, async_body)
1032 let bound_generic_params = self.lower_lifetime_binder(closure_id, generic_params);
1033 // We need to lower the declaration outside the new scope, because we
1034 // have to conserve the state of being inside a loop condition for the
1035 // closure argument types.
1037 self.lower_fn_decl(&outer_decl, closure_id, fn_decl_span, FnDeclKind::Closure, None);
1039 let c = self.arena.alloc(hir::Closure {
1040 def_id: self.local_def_id(closure_id),
1041 binder: binder_clause,
1043 bound_generic_params,
1046 fn_decl_span: self.lower_span(fn_decl_span),
1047 fn_arg_span: Some(self.lower_span(fn_arg_span)),
1049 constness: hir::Constness::NotConst,
1051 hir::ExprKind::Closure(c)
1054 /// Destructure the LHS of complex assignments.
1055 /// For instance, lower `(a, b) = t` to `{ let (lhs1, lhs2) = t; a = lhs1; b = lhs2; }`.
1056 fn lower_expr_assign(
1062 ) -> hir::ExprKind<'hir> {
1063 // Return early in case of an ordinary assignment.
1064 fn is_ordinary(lower_ctx: &mut LoweringContext<'_, '_>, lhs: &Expr) -> bool {
1067 | ExprKind::Struct(..)
1069 | ExprKind::Underscore => false,
1070 // Check for tuple struct constructor.
1071 ExprKind::Call(callee, ..) => lower_ctx.extract_tuple_struct_path(callee).is_none(),
1072 ExprKind::Paren(e) => {
1074 // We special-case `(..)` for consistency with patterns.
1075 ExprKind::Range(None, None, RangeLimits::HalfOpen) => false,
1076 _ => is_ordinary(lower_ctx, e),
1082 if is_ordinary(self, lhs) {
1083 return hir::ExprKind::Assign(
1084 self.lower_expr(lhs),
1085 self.lower_expr(rhs),
1086 self.lower_span(eq_sign_span),
1090 let mut assignments = vec![];
1092 // The LHS becomes a pattern: `(lhs1, lhs2)`.
1093 let pat = self.destructure_assign(lhs, eq_sign_span, &mut assignments);
1094 let rhs = self.lower_expr(rhs);
1096 // Introduce a `let` for destructuring: `let (lhs1, lhs2) = t`.
1097 let destructure_let = self.stmt_let_pat(
1102 hir::LocalSource::AssignDesugar(self.lower_span(eq_sign_span)),
1105 // `a = lhs1; b = lhs2;`.
1108 .alloc_from_iter(std::iter::once(destructure_let).chain(assignments.into_iter()));
1110 // Wrap everything in a block.
1111 hir::ExprKind::Block(&self.block_all(whole_span, stmts, None), None)
1114 /// If the given expression is a path to a tuple struct, returns that path.
1115 /// It is not a complete check, but just tries to reject most paths early
1116 /// if they are not tuple structs.
1117 /// Type checking will take care of the full validation later.
1118 fn extract_tuple_struct_path<'a>(
1121 ) -> Option<(&'a Option<AstP<QSelf>>, &'a Path)> {
1122 if let ExprKind::Path(qself, path) = &expr.kind {
1123 // Does the path resolve to something disallowed in a tuple struct/variant pattern?
1124 if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
1125 if let Some(res) = partial_res.full_res() && !res.expected_in_tuple_struct_pat() {
1129 return Some((qself, path));
1134 /// If the given expression is a path to a unit struct, returns that path.
1135 /// It is not a complete check, but just tries to reject most paths early
1136 /// if they are not unit structs.
1137 /// Type checking will take care of the full validation later.
1138 fn extract_unit_struct_path<'a>(
1141 ) -> Option<(&'a Option<AstP<QSelf>>, &'a Path)> {
1142 if let ExprKind::Path(qself, path) = &expr.kind {
1143 // Does the path resolve to something disallowed in a unit struct/variant pattern?
1144 if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
1145 if let Some(res) = partial_res.full_res() && !res.expected_in_unit_struct_pat() {
1149 return Some((qself, path));
1154 /// Convert the LHS of a destructuring assignment to a pattern.
1155 /// Each sub-assignment is recorded in `assignments`.
1156 fn destructure_assign(
1160 assignments: &mut Vec<hir::Stmt<'hir>>,
1161 ) -> &'hir hir::Pat<'hir> {
1162 self.arena.alloc(self.destructure_assign_mut(lhs, eq_sign_span, assignments))
1165 fn destructure_assign_mut(
1169 assignments: &mut Vec<hir::Stmt<'hir>>,
1170 ) -> hir::Pat<'hir> {
1172 // Underscore pattern.
1173 ExprKind::Underscore => {
1174 return self.pat_without_dbm(lhs.span, hir::PatKind::Wild);
1177 ExprKind::Array(elements) => {
1179 self.destructure_sequence(elements, "slice", eq_sign_span, assignments);
1180 let slice_pat = if let Some((i, span)) = rest {
1181 let (before, after) = pats.split_at(i);
1182 hir::PatKind::Slice(
1184 Some(self.arena.alloc(self.pat_without_dbm(span, hir::PatKind::Wild))),
1188 hir::PatKind::Slice(pats, None, &[])
1190 return self.pat_without_dbm(lhs.span, slice_pat);
1193 ExprKind::Call(callee, args) => {
1194 if let Some((qself, path)) = self.extract_tuple_struct_path(callee) {
1195 let (pats, rest) = self.destructure_sequence(
1197 "tuple struct or variant",
1201 let qpath = self.lower_qpath(
1205 ParamMode::Optional,
1206 &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
1208 // Destructure like a tuple struct.
1209 let tuple_struct_pat = hir::PatKind::TupleStruct(
1212 hir::DotDotPos::new(rest.map(|r| r.0)),
1214 return self.pat_without_dbm(lhs.span, tuple_struct_pat);
1217 // Unit structs and enum variants.
1218 ExprKind::Path(..) => {
1219 if let Some((qself, path)) = self.extract_unit_struct_path(lhs) {
1220 let qpath = self.lower_qpath(
1224 ParamMode::Optional,
1225 &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
1227 // Destructure like a unit struct.
1228 let unit_struct_pat = hir::PatKind::Path(qpath);
1229 return self.pat_without_dbm(lhs.span, unit_struct_pat);
1233 ExprKind::Struct(se) => {
1234 let field_pats = self.arena.alloc_from_iter(se.fields.iter().map(|f| {
1235 let pat = self.destructure_assign(&f.expr, eq_sign_span, assignments);
1237 hir_id: self.next_id(),
1238 ident: self.lower_ident(f.ident),
1240 is_shorthand: f.is_shorthand,
1241 span: self.lower_span(f.span),
1244 let qpath = self.lower_qpath(
1248 ParamMode::Optional,
1249 &ImplTraitContext::Disallowed(ImplTraitPosition::Path),
1251 let fields_omitted = match &se.rest {
1252 StructRest::Base(e) => {
1253 self.tcx.sess.emit_err(FunctionalRecordUpdateDestructuringAssignemnt {
1258 StructRest::Rest(_) => true,
1259 StructRest::None => false,
1261 let struct_pat = hir::PatKind::Struct(qpath, field_pats, fields_omitted);
1262 return self.pat_without_dbm(lhs.span, struct_pat);
1265 ExprKind::Tup(elements) => {
1267 self.destructure_sequence(elements, "tuple", eq_sign_span, assignments);
1268 let tuple_pat = hir::PatKind::Tuple(pats, hir::DotDotPos::new(rest.map(|r| r.0)));
1269 return self.pat_without_dbm(lhs.span, tuple_pat);
1271 ExprKind::Paren(e) => {
1272 // We special-case `(..)` for consistency with patterns.
1273 if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
1274 let tuple_pat = hir::PatKind::Tuple(&[], hir::DotDotPos::new(Some(0)));
1275 return self.pat_without_dbm(lhs.span, tuple_pat);
1277 return self.destructure_assign_mut(e, eq_sign_span, assignments);
1282 // Treat all other cases as normal lvalue.
1283 let ident = Ident::new(sym::lhs, self.lower_span(lhs.span));
1284 let (pat, binding) = self.pat_ident_mut(lhs.span, ident);
1285 let ident = self.expr_ident(lhs.span, ident, binding);
1287 hir::ExprKind::Assign(self.lower_expr(lhs), ident, self.lower_span(eq_sign_span));
1288 let expr = self.expr(lhs.span, assign);
1289 assignments.push(self.stmt_expr(lhs.span, expr));
1293 /// Destructure a sequence of expressions occurring on the LHS of an assignment.
1294 /// Such a sequence occurs in a tuple (struct)/slice.
1295 /// Return a sequence of corresponding patterns, and the index and the span of `..` if it
1297 /// Each sub-assignment is recorded in `assignments`.
1298 fn destructure_sequence(
1300 elements: &[AstP<Expr>],
1303 assignments: &mut Vec<hir::Stmt<'hir>>,
1304 ) -> (&'hir [hir::Pat<'hir>], Option<(usize, Span)>) {
1305 let mut rest = None;
1307 self.arena.alloc_from_iter(elements.iter().enumerate().filter_map(|(i, e)| {
1308 // Check for `..` pattern.
1309 if let ExprKind::Range(None, None, RangeLimits::HalfOpen) = e.kind {
1310 if let Some((_, prev_span)) = rest {
1311 self.ban_extra_rest_pat(e.span, prev_span, ctx);
1313 rest = Some((i, e.span));
1317 Some(self.destructure_assign_mut(e, eq_sign_span, assignments))
1323 /// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
1324 fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
1325 let e1 = self.lower_expr_mut(e1);
1326 let e2 = self.lower_expr_mut(e2);
1328 hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, self.lower_span(span), None);
1329 let fn_expr = self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path)));
1330 hir::ExprKind::Call(fn_expr, arena_vec![self; e1, e2])
1333 fn lower_expr_range(
1339 ) -> hir::ExprKind<'hir> {
1340 use rustc_ast::RangeLimits::*;
1342 let lang_item = match (e1, e2, lims) {
1343 (None, None, HalfOpen) => hir::LangItem::RangeFull,
1344 (Some(..), None, HalfOpen) => hir::LangItem::RangeFrom,
1345 (None, Some(..), HalfOpen) => hir::LangItem::RangeTo,
1346 (Some(..), Some(..), HalfOpen) => hir::LangItem::Range,
1347 (None, Some(..), Closed) => hir::LangItem::RangeToInclusive,
1348 (Some(..), Some(..), Closed) => unreachable!(),
1349 (start, None, Closed) => {
1350 self.tcx.sess.emit_err(InclusiveRangeWithNoEnd { span });
1352 Some(..) => hir::LangItem::RangeFrom,
1353 None => hir::LangItem::RangeFull,
1358 let fields = self.arena.alloc_from_iter(
1359 e1.iter().map(|e| (sym::start, e)).chain(e2.iter().map(|e| (sym::end, e))).map(
1361 let expr = self.lower_expr(&e);
1362 let ident = Ident::new(s, self.lower_span(e.span));
1363 self.expr_field(ident, expr, e.span)
1368 hir::ExprKind::Struct(
1369 self.arena.alloc(hir::QPath::LangItem(lang_item, self.lower_span(span), None)),
1375 fn lower_label(&self, opt_label: Option<Label>) -> Option<Label> {
1376 let label = opt_label?;
1377 Some(Label { ident: self.lower_ident(label.ident) })
1380 fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
1381 let target_id = match destination {
1383 if let Some(loop_id) = self.resolver.get_label_res(id) {
1384 Ok(self.lower_node_id(loop_id))
1386 Err(hir::LoopIdError::UnresolvedLabel)
1391 .map(|id| Ok(self.lower_node_id(id)))
1392 .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope)),
1394 let label = self.lower_label(destination.map(|(_, label)| label));
1395 hir::Destination { label, target_id }
1398 fn lower_jump_destination(&mut self, id: NodeId, opt_label: Option<Label>) -> hir::Destination {
1399 if self.is_in_loop_condition && opt_label.is_none() {
1402 target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition),
1405 self.lower_loop_destination(opt_label.map(|label| (id, label)))
1409 fn with_catch_scope<T>(&mut self, catch_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
1410 let old_scope = self.catch_scope.replace(catch_id);
1411 let result = f(self);
1412 self.catch_scope = old_scope;
1416 fn with_loop_scope<T>(&mut self, loop_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
1417 // We're no longer in the base loop's condition; we're in another loop.
1418 let was_in_loop_condition = self.is_in_loop_condition;
1419 self.is_in_loop_condition = false;
1421 let old_scope = self.loop_scope.replace(loop_id);
1422 let result = f(self);
1423 self.loop_scope = old_scope;
1425 self.is_in_loop_condition = was_in_loop_condition;
1430 fn with_loop_condition_scope<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
1431 let was_in_loop_condition = self.is_in_loop_condition;
1432 self.is_in_loop_condition = true;
1434 let result = f(self);
1436 self.is_in_loop_condition = was_in_loop_condition;
1441 fn lower_expr_field(&mut self, f: &ExprField) -> hir::ExprField<'hir> {
1442 let hir_id = self.lower_node_id(f.id);
1443 self.lower_attrs(hir_id, &f.attrs);
1446 ident: self.lower_ident(f.ident),
1447 expr: self.lower_expr(&f.expr),
1448 span: self.lower_span(f.span),
1449 is_shorthand: f.is_shorthand,
1453 fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
1454 match self.generator_kind {
1455 Some(hir::GeneratorKind::Gen) => {}
1456 Some(hir::GeneratorKind::Async(_)) => {
1457 self.tcx.sess.emit_err(AsyncGeneratorsNotSupported { span });
1459 None => self.generator_kind = Some(hir::GeneratorKind::Gen),
1463 opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
1465 hir::ExprKind::Yield(expr, hir::YieldSource::Yield)
1468 /// Desugar `ExprForLoop` from: `[opt_ident]: for <pat> in <head> <body>` into:
1469 /// ```ignore (pseudo-rust)
1471 /// let result = match IntoIterator::into_iter(<head>) {
1473 /// [opt_ident]: loop {
1474 /// match Iterator::next(&mut iter) {
1476 /// Some(<pat>) => <body>,
1490 opt_label: Option<Label>,
1491 ) -> hir::Expr<'hir> {
1492 let head = self.lower_expr_mut(head);
1493 let pat = self.lower_pat(pat);
1495 self.mark_span_with_reason(DesugaringKind::ForLoop, self.lower_span(e.span), None);
1496 let head_span = self.mark_span_with_reason(DesugaringKind::ForLoop, head.span, None);
1497 let pat_span = self.mark_span_with_reason(DesugaringKind::ForLoop, pat.span, None);
1501 let break_expr = self.with_loop_scope(e.id, |this| this.expr_break_alloc(for_span));
1502 let pat = self.pat_none(for_span);
1503 self.arm(pat, break_expr)
1506 // Some(<pat>) => <body>,
1508 let some_pat = self.pat_some(pat_span, pat);
1509 let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
1510 let body_expr = self.arena.alloc(self.expr_block(body_block));
1511 self.arm(some_pat, body_expr)
1515 let iter = Ident::with_dummy_span(sym::iter);
1516 let (iter_pat, iter_pat_nid) =
1517 self.pat_ident_binding_mode(head_span, iter, hir::BindingAnnotation::MUT);
1519 // `match Iterator::next(&mut iter) { ... }`
1521 let iter = self.expr_ident(head_span, iter, iter_pat_nid);
1522 let ref_mut_iter = self.expr_mut_addr_of(head_span, iter);
1523 let next_expr = self.expr_call_lang_item_fn(
1525 hir::LangItem::IteratorNext,
1526 arena_vec![self; ref_mut_iter],
1529 let arms = arena_vec![self; none_arm, some_arm];
1531 self.expr_match(head_span, next_expr, arms, hir::MatchSource::ForLoopDesugar)
1533 let match_stmt = self.stmt_expr(for_span, match_expr);
1535 let loop_block = self.block_all(for_span, arena_vec![self; match_stmt], None);
1537 // `[opt_ident]: loop { ... }`
1538 let kind = hir::ExprKind::Loop(
1540 self.lower_label(opt_label),
1541 hir::LoopSource::ForLoop,
1542 self.lower_span(for_span.with_hi(head.span.hi())),
1545 self.arena.alloc(hir::Expr { hir_id: self.lower_node_id(e.id), kind, span: for_span });
1547 // `mut iter => { ... }`
1548 let iter_arm = self.arm(iter_pat, loop_expr);
1550 // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
1551 let into_iter_expr = {
1552 self.expr_call_lang_item_fn(
1554 hir::LangItem::IntoIterIntoIter,
1555 arena_vec![self; head],
1560 let match_expr = self.arena.alloc(self.expr_match(
1563 arena_vec![self; iter_arm],
1564 hir::MatchSource::ForLoopDesugar,
1567 // This is effectively `{ let _result = ...; _result }`.
1568 // The construct was introduced in #21984 and is necessary to make sure that
1569 // temporaries in the `head` expression are dropped and do not leak to the
1570 // surrounding scope of the `match` since the `match` is not a terminating scope.
1572 // Also, add the attributes to the outer returned expr node.
1573 let expr = self.expr_drop_temps_mut(for_span, match_expr);
1574 self.lower_attrs(expr.hir_id, &e.attrs);
1578 /// Desugar `ExprKind::Try` from: `<expr>?` into:
1579 /// ```ignore (pseudo-rust)
1580 /// match Try::branch(<expr>) {
1581 /// ControlFlow::Continue(val) => #[allow(unreachable_code)] val,,
1582 /// ControlFlow::Break(residual) =>
1583 /// #[allow(unreachable_code)]
1584 /// // If there is an enclosing `try {...}`:
1585 /// break 'catch_target Try::from_residual(residual),
1587 /// return Try::from_residual(residual),
1590 fn lower_expr_try(&mut self, span: Span, sub_expr: &Expr) -> hir::ExprKind<'hir> {
1591 let unstable_span = self.mark_span_with_reason(
1592 DesugaringKind::QuestionMark,
1594 self.allow_try_trait.clone(),
1596 let try_span = self.tcx.sess.source_map().end_point(span);
1597 let try_span = self.mark_span_with_reason(
1598 DesugaringKind::QuestionMark,
1600 self.allow_try_trait.clone(),
1603 // `Try::branch(<expr>)`
1606 let sub_expr = self.lower_expr_mut(sub_expr);
1608 self.expr_call_lang_item_fn(
1610 hir::LangItem::TryTraitBranch,
1611 arena_vec![self; sub_expr],
1616 // `#[allow(unreachable_code)]`
1617 let attr = attr::mk_attr_nested_word(
1618 &self.tcx.sess.parse_sess.attr_id_generator,
1621 sym::unreachable_code,
1622 self.lower_span(span),
1624 let attrs: AttrVec = thin_vec![attr];
1626 // `ControlFlow::Continue(val) => #[allow(unreachable_code)] val,`
1627 let continue_arm = {
1628 let val_ident = Ident::with_dummy_span(sym::val);
1629 let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
1630 let val_expr = self.expr_ident(span, val_ident, val_pat_nid);
1631 self.lower_attrs(val_expr.hir_id, &attrs);
1632 let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
1633 self.arm(continue_pat, val_expr)
1636 // `ControlFlow::Break(residual) =>
1637 // #[allow(unreachable_code)]
1638 // return Try::from_residual(residual),`
1640 let residual_ident = Ident::with_dummy_span(sym::residual);
1641 let (residual_local, residual_local_nid) = self.pat_ident(try_span, residual_ident);
1642 let residual_expr = self.expr_ident_mut(try_span, residual_ident, residual_local_nid);
1643 let from_residual_expr = self.wrap_in_try_constructor(
1644 hir::LangItem::TryTraitFromResidual,
1646 self.arena.alloc(residual_expr),
1649 let ret_expr = if let Some(catch_node) = self.catch_scope {
1650 let target_id = Ok(self.lower_node_id(catch_node));
1651 self.arena.alloc(self.expr(
1653 hir::ExprKind::Break(
1654 hir::Destination { label: None, target_id },
1655 Some(from_residual_expr),
1659 self.arena.alloc(self.expr(try_span, hir::ExprKind::Ret(Some(from_residual_expr))))
1661 self.lower_attrs(ret_expr.hir_id, &attrs);
1663 let break_pat = self.pat_cf_break(try_span, residual_local);
1664 self.arm(break_pat, ret_expr)
1667 hir::ExprKind::Match(
1669 arena_vec![self; break_arm, continue_arm],
1670 hir::MatchSource::TryDesugar,
1674 /// Desugar `ExprKind::Yeet` from: `do yeet <expr>` into:
1675 /// ```ignore(illustrative)
1676 /// // If there is an enclosing `try {...}`:
1677 /// break 'catch_target FromResidual::from_residual(Yeet(residual));
1679 /// return FromResidual::from_residual(Yeet(residual));
1681 /// But to simplify this, there's a `from_yeet` lang item function which
1682 /// handles the combined `FromResidual::from_residual(Yeet(residual))`.
1683 fn lower_expr_yeet(&mut self, span: Span, sub_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
1684 // The expression (if present) or `()` otherwise.
1685 let (yeeted_span, yeeted_expr) = if let Some(sub_expr) = sub_expr {
1686 (sub_expr.span, self.lower_expr(sub_expr))
1688 (self.mark_span_with_reason(DesugaringKind::YeetExpr, span, None), self.expr_unit(span))
1691 let unstable_span = self.mark_span_with_reason(
1692 DesugaringKind::YeetExpr,
1694 self.allow_try_trait.clone(),
1697 let from_yeet_expr = self.wrap_in_try_constructor(
1698 hir::LangItem::TryTraitFromYeet,
1704 if let Some(catch_node) = self.catch_scope {
1705 let target_id = Ok(self.lower_node_id(catch_node));
1706 hir::ExprKind::Break(hir::Destination { label: None, target_id }, Some(from_yeet_expr))
1708 hir::ExprKind::Ret(Some(from_yeet_expr))
1712 // =========================================================================
1713 // Helper methods for building HIR.
1714 // =========================================================================
1716 /// Wrap the given `expr` in a terminating scope using `hir::ExprKind::DropTemps`.
1718 /// In terms of drop order, it has the same effect as wrapping `expr` in
1719 /// `{ let _t = $expr; _t }` but should provide better compile-time performance.
1721 /// The drop order can be important in e.g. `if expr { .. }`.
1722 pub(super) fn expr_drop_temps(
1725 expr: &'hir hir::Expr<'hir>,
1726 ) -> &'hir hir::Expr<'hir> {
1727 self.arena.alloc(self.expr_drop_temps_mut(span, expr))
1730 pub(super) fn expr_drop_temps_mut(
1733 expr: &'hir hir::Expr<'hir>,
1734 ) -> hir::Expr<'hir> {
1735 self.expr(span, hir::ExprKind::DropTemps(expr))
1741 arg: &'hir hir::Expr<'hir>,
1742 arms: &'hir [hir::Arm<'hir>],
1743 source: hir::MatchSource,
1744 ) -> hir::Expr<'hir> {
1745 self.expr(span, hir::ExprKind::Match(arg, arms, source))
1748 fn expr_break(&mut self, span: Span) -> hir::Expr<'hir> {
1749 let expr_break = hir::ExprKind::Break(self.lower_loop_destination(None), None);
1750 self.expr(span, expr_break)
1753 fn expr_break_alloc(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
1754 let expr_break = self.expr_break(span);
1755 self.arena.alloc(expr_break)
1758 fn expr_mut_addr_of(&mut self, span: Span, e: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
1759 self.expr(span, hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e))
1762 fn expr_unit(&mut self, sp: Span) -> &'hir hir::Expr<'hir> {
1763 self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[])))
1769 e: &'hir hir::Expr<'hir>,
1770 args: &'hir [hir::Expr<'hir>],
1771 ) -> hir::Expr<'hir> {
1772 self.expr(span, hir::ExprKind::Call(e, args))
1778 e: &'hir hir::Expr<'hir>,
1779 args: &'hir [hir::Expr<'hir>],
1780 ) -> &'hir hir::Expr<'hir> {
1781 self.arena.alloc(self.expr_call_mut(span, e, args))
1784 fn expr_call_lang_item_fn_mut(
1787 lang_item: hir::LangItem,
1788 args: &'hir [hir::Expr<'hir>],
1789 hir_id: Option<hir::HirId>,
1790 ) -> hir::Expr<'hir> {
1791 let path = self.arena.alloc(self.expr_lang_item_path(span, lang_item, hir_id));
1792 self.expr_call_mut(span, path, args)
1795 fn expr_call_lang_item_fn(
1798 lang_item: hir::LangItem,
1799 args: &'hir [hir::Expr<'hir>],
1800 hir_id: Option<hir::HirId>,
1801 ) -> &'hir hir::Expr<'hir> {
1802 self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args, hir_id))
1805 fn expr_lang_item_path(
1808 lang_item: hir::LangItem,
1809 hir_id: Option<hir::HirId>,
1810 ) -> hir::Expr<'hir> {
1813 hir::ExprKind::Path(hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id)),
1817 pub(super) fn expr_ident(
1821 binding: hir::HirId,
1822 ) -> &'hir hir::Expr<'hir> {
1823 self.arena.alloc(self.expr_ident_mut(sp, ident, binding))
1826 pub(super) fn expr_ident_mut(
1830 binding: hir::HirId,
1831 ) -> hir::Expr<'hir> {
1832 let hir_id = self.next_id();
1833 let res = Res::Local(binding);
1834 let expr_path = hir::ExprKind::Path(hir::QPath::Resolved(
1836 self.arena.alloc(hir::Path {
1837 span: self.lower_span(span),
1839 segments: arena_vec![self; hir::PathSegment::new(ident, hir_id, res)],
1843 self.expr(span, expr_path)
1846 fn expr_unsafe(&mut self, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
1847 let hir_id = self.next_id();
1848 let span = expr.span;
1851 hir::ExprKind::Block(
1852 self.arena.alloc(hir::Block {
1856 rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
1857 span: self.lower_span(span),
1858 targeted_by_break: false,
1865 fn expr_block_empty(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
1866 let blk = self.block_all(span, &[], None);
1867 let expr = self.expr_block(blk);
1868 self.arena.alloc(expr)
1871 pub(super) fn expr_block(&mut self, b: &'hir hir::Block<'hir>) -> hir::Expr<'hir> {
1872 self.expr(b.span, hir::ExprKind::Block(b, None))
1875 pub(super) fn expr(&mut self, span: Span, kind: hir::ExprKind<'hir>) -> hir::Expr<'hir> {
1876 let hir_id = self.next_id();
1877 hir::Expr { hir_id, kind, span: self.lower_span(span) }
1883 expr: &'hir hir::Expr<'hir>,
1885 ) -> hir::ExprField<'hir> {
1887 hir_id: self.next_id(),
1889 span: self.lower_span(span),
1891 is_shorthand: false,
1895 fn arm(&mut self, pat: &'hir hir::Pat<'hir>, expr: &'hir hir::Expr<'hir>) -> hir::Arm<'hir> {
1897 hir_id: self.next_id(),
1900 span: self.lower_span(expr.span),