1 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
4 use rustc_data_structures::thin_vec::ThinVec;
5 use rustc_errors::struct_span_err;
7 use rustc_hir::def::Res;
8 use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
9 use rustc_span::symbol::{sym, Symbol};
12 use syntax::ptr::P as AstP;
14 impl<'hir> LoweringContext<'_, 'hir> {
15 fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
16 self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
19 pub(super) fn lower_expr(&mut self, e: &Expr) -> &'hir hir::Expr<'hir> {
20 self.arena.alloc(self.lower_expr_mut(e))
23 pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
24 let kind = match e.kind {
25 ExprKind::Box(ref inner) => hir::ExprKind::Box(self.lower_expr(inner)),
26 ExprKind::Array(ref exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
27 ExprKind::Repeat(ref expr, ref count) => {
28 let expr = self.lower_expr(expr);
29 let count = self.lower_anon_const(count);
30 hir::ExprKind::Repeat(expr, count)
32 ExprKind::Tup(ref elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
33 ExprKind::Call(ref f, ref args) => {
34 let f = self.lower_expr(f);
35 hir::ExprKind::Call(f, self.lower_exprs(args))
37 ExprKind::MethodCall(ref seg, ref args) => {
38 let hir_seg = self.arena.alloc(self.lower_path_segment(
43 ParenthesizedGenericArgs::Err,
44 ImplTraitContext::disallowed(),
47 let args = self.lower_exprs(args);
48 hir::ExprKind::MethodCall(hir_seg, seg.ident.span, args)
50 ExprKind::Binary(binop, ref lhs, ref rhs) => {
51 let binop = self.lower_binop(binop);
52 let lhs = self.lower_expr(lhs);
53 let rhs = self.lower_expr(rhs);
54 hir::ExprKind::Binary(binop, lhs, rhs)
56 ExprKind::Unary(op, ref ohs) => {
57 let op = self.lower_unop(op);
58 let ohs = self.lower_expr(ohs);
59 hir::ExprKind::Unary(op, ohs)
61 ExprKind::Lit(ref l) => hir::ExprKind::Lit(respan(l.span, l.kind.clone())),
62 ExprKind::Cast(ref expr, ref ty) => {
63 let expr = self.lower_expr(expr);
64 let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
65 hir::ExprKind::Cast(expr, ty)
67 ExprKind::Type(ref expr, ref ty) => {
68 let expr = self.lower_expr(expr);
69 let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
70 hir::ExprKind::Type(expr, ty)
72 ExprKind::AddrOf(k, m, ref ohs) => {
73 let ohs = self.lower_expr(ohs);
74 hir::ExprKind::AddrOf(k, m, ohs)
76 ExprKind::Let(ref pat, ref scrutinee) => self.lower_expr_let(e.span, pat, scrutinee),
77 ExprKind::If(ref cond, ref then, ref else_opt) => {
78 self.lower_expr_if(e.span, cond, then, else_opt.as_deref())
80 ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
81 this.lower_expr_while_in_loop_scope(e.span, cond, body, opt_label)
83 ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
84 hir::ExprKind::Loop(this.lower_block(body, false), opt_label, hir::LoopSource::Loop)
86 ExprKind::TryBlock(ref body) => self.lower_expr_try_block(body),
87 ExprKind::Match(ref expr, ref arms) => hir::ExprKind::Match(
88 self.lower_expr(expr),
89 self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
90 hir::MatchSource::Normal,
92 ExprKind::Async(capture_clause, closure_node_id, ref block) => self.make_async_expr(
97 hir::AsyncGeneratorKind::Block,
98 |this| this.with_new_scopes(|this| this.lower_block_expr(block)),
100 ExprKind::Await(ref expr) => self.lower_expr_await(e.span, expr),
109 if let IsAsync::Async { closure_id, .. } = asyncness {
110 self.lower_expr_async_closure(
118 self.lower_expr_closure(capture_clause, movability, decl, body, fn_decl_span)
121 ExprKind::Block(ref blk, opt_label) => {
122 hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
124 ExprKind::Assign(ref el, ref er, span) => {
125 hir::ExprKind::Assign(self.lower_expr(el), self.lower_expr(er), span)
127 ExprKind::AssignOp(op, ref el, ref er) => hir::ExprKind::AssignOp(
128 self.lower_binop(op),
132 ExprKind::Field(ref el, ident) => hir::ExprKind::Field(self.lower_expr(el), ident),
133 ExprKind::Index(ref el, ref er) => {
134 hir::ExprKind::Index(self.lower_expr(el), self.lower_expr(er))
136 ExprKind::Range(Some(ref e1), Some(ref e2), RangeLimits::Closed) => {
137 self.lower_expr_range_closed(e.span, e1, e2)
139 ExprKind::Range(ref e1, ref e2, lims) => {
140 self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), lims)
142 ExprKind::Path(ref qself, ref path) => {
143 let qpath = self.lower_qpath(
148 ImplTraitContext::disallowed(),
150 hir::ExprKind::Path(qpath)
152 ExprKind::Break(opt_label, ref opt_expr) => {
153 let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
154 hir::ExprKind::Break(self.lower_jump_destination(e.id, opt_label), opt_expr)
156 ExprKind::Continue(opt_label) => {
157 hir::ExprKind::Continue(self.lower_jump_destination(e.id, opt_label))
159 ExprKind::Ret(ref e) => {
160 let e = e.as_ref().map(|x| self.lower_expr(x));
161 hir::ExprKind::Ret(e)
163 ExprKind::InlineAsm(ref asm) => self.lower_expr_asm(asm),
164 ExprKind::Struct(ref path, ref fields, ref maybe_expr) => {
165 let maybe_expr = maybe_expr.as_ref().map(|x| self.lower_expr(x));
166 hir::ExprKind::Struct(
167 self.arena.alloc(self.lower_qpath(
172 ImplTraitContext::disallowed(),
174 self.arena.alloc_from_iter(fields.iter().map(|x| self.lower_field(x))),
178 ExprKind::Paren(ref ex) => {
179 let mut ex = self.lower_expr_mut(ex);
180 // Include parens in span, but only if it is a super-span.
181 if e.span.contains(ex.span) {
184 // Merge attributes into the inner expression.
185 let mut attrs = e.attrs.clone();
186 attrs.extend::<Vec<_>>(ex.attrs.into());
191 ExprKind::Yield(ref opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
193 ExprKind::Err => hir::ExprKind::Err,
195 // Desugar `ExprForLoop`
196 // from: `[opt_ident]: for <pat> in <head> <body>`
197 ExprKind::ForLoop(ref pat, ref head, ref body, opt_label) => {
198 return self.lower_expr_for(e, pat, head, body, opt_label);
200 ExprKind::Try(ref sub_expr) => self.lower_expr_try(e.span, sub_expr),
201 ExprKind::Mac(_) => panic!("Shouldn't exist here"),
205 hir_id: self.lower_node_id(e.id),
208 attrs: e.attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into(),
212 fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
214 UnOp::Deref => hir::UnOp::UnDeref,
215 UnOp::Not => hir::UnOp::UnNot,
216 UnOp::Neg => hir::UnOp::UnNeg,
220 fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
223 BinOpKind::Add => hir::BinOpKind::Add,
224 BinOpKind::Sub => hir::BinOpKind::Sub,
225 BinOpKind::Mul => hir::BinOpKind::Mul,
226 BinOpKind::Div => hir::BinOpKind::Div,
227 BinOpKind::Rem => hir::BinOpKind::Rem,
228 BinOpKind::And => hir::BinOpKind::And,
229 BinOpKind::Or => hir::BinOpKind::Or,
230 BinOpKind::BitXor => hir::BinOpKind::BitXor,
231 BinOpKind::BitAnd => hir::BinOpKind::BitAnd,
232 BinOpKind::BitOr => hir::BinOpKind::BitOr,
233 BinOpKind::Shl => hir::BinOpKind::Shl,
234 BinOpKind::Shr => hir::BinOpKind::Shr,
235 BinOpKind::Eq => hir::BinOpKind::Eq,
236 BinOpKind::Lt => hir::BinOpKind::Lt,
237 BinOpKind::Le => hir::BinOpKind::Le,
238 BinOpKind::Ne => hir::BinOpKind::Ne,
239 BinOpKind::Ge => hir::BinOpKind::Ge,
240 BinOpKind::Gt => hir::BinOpKind::Gt,
246 /// Emit an error and lower `ast::ExprKind::Let(pat, scrutinee)` into:
248 /// match scrutinee { pats => true, _ => false }
250 fn lower_expr_let(&mut self, span: Span, pat: &Pat, scrutinee: &Expr) -> hir::ExprKind<'hir> {
251 // If we got here, the `let` expression is not allowed.
253 if self.sess.opts.unstable_features.is_nightly_build() {
255 .struct_span_err(span, "`let` expressions are not supported here")
256 .note("only supported directly in conditions of `if`- and `while`-expressions")
257 .note("as well as when nested within `&&` and parenthesis in those conditions")
261 .struct_span_err(span, "expected expression, found statement (`let`)")
262 .note("variable declaration using `let` is a statement")
266 // For better recovery, we emit:
268 // match scrutinee { pat => true, _ => false }
270 // While this doesn't fully match the user's intent, it has key advantages:
271 // 1. We can avoid using `abort_if_errors`.
272 // 2. We can typeck both `pat` and `scrutinee`.
273 // 3. `pat` is allowed to be refutable.
274 // 4. The return type of the block is `bool` which seems like what the user wanted.
275 let scrutinee = self.lower_expr(scrutinee);
277 let pat = self.lower_pat(pat);
278 let expr = self.expr_bool(span, true);
282 let pat = self.pat_wild(span);
283 let expr = self.expr_bool(span, false);
286 hir::ExprKind::Match(
288 arena_vec![self; then_arm, else_arm],
289 hir::MatchSource::Normal,
298 else_opt: Option<&Expr>,
299 ) -> hir::ExprKind<'hir> {
300 // FIXME(#53667): handle lowering of && and parens.
302 // `_ => else_block` where `else_block` is `{}` if there's `None`:
303 let else_pat = self.pat_wild(span);
304 let (else_expr, contains_else_clause) = match else_opt {
305 None => (self.expr_block_empty(span), false),
306 Some(els) => (self.lower_expr(els), true),
308 let else_arm = self.arm(else_pat, else_expr);
310 // Handle then + scrutinee:
311 let then_expr = self.lower_block_expr(then);
312 let (then_pat, scrutinee, desugar) = match cond.kind {
313 // `<pat> => <then>`:
314 ExprKind::Let(ref pat, ref scrutinee) => {
315 let scrutinee = self.lower_expr(scrutinee);
316 let pat = self.lower_pat(pat);
317 (pat, scrutinee, hir::MatchSource::IfLetDesugar { contains_else_clause })
322 let cond = self.lower_expr(cond);
324 self.mark_span_with_reason(DesugaringKind::CondTemporary, cond.span, None);
325 // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
326 // to preserve drop semantics since `if cond { ... }` does not
327 // let temporaries live outside of `cond`.
328 let cond = self.expr_drop_temps(span_block, cond, ThinVec::new());
329 let pat = self.pat_bool(span, true);
330 (pat, cond, hir::MatchSource::IfDesugar { contains_else_clause })
333 let then_arm = self.arm(then_pat, self.arena.alloc(then_expr));
335 hir::ExprKind::Match(scrutinee, arena_vec![self; then_arm, else_arm], desugar)
338 fn lower_expr_while_in_loop_scope(
343 opt_label: Option<Label>,
344 ) -> hir::ExprKind<'hir> {
345 // FIXME(#53667): handle lowering of && and parens.
347 // Note that the block AND the condition are evaluated in the loop scope.
348 // This is done to allow `break` from inside the condition of the loop.
352 let else_pat = self.pat_wild(span);
353 let else_expr = self.expr_break(span, ThinVec::new());
354 self.arm(else_pat, else_expr)
357 // Handle then + scrutinee:
358 let then_expr = self.lower_block_expr(body);
359 let (then_pat, scrutinee, desugar, source) = match cond.kind {
360 ExprKind::Let(ref pat, ref scrutinee) => {
363 // [opt_ident]: loop {
364 // match <sub_expr> {
369 let scrutinee = self.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
370 let pat = self.lower_pat(pat);
371 (pat, scrutinee, hir::MatchSource::WhileLetDesugar, hir::LoopSource::WhileLet)
374 // We desugar: `'label: while $cond $body` into:
378 // match drop-temps { $cond } {
386 let cond = self.with_loop_condition_scope(|this| this.lower_expr(cond));
388 self.mark_span_with_reason(DesugaringKind::CondTemporary, cond.span, None);
389 // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
390 // to preserve drop semantics since `while cond { ... }` does not
391 // let temporaries live outside of `cond`.
392 let cond = self.expr_drop_temps(span_block, cond, ThinVec::new());
394 let pat = self.pat_bool(span, true);
395 (pat, cond, hir::MatchSource::WhileDesugar, hir::LoopSource::While)
398 let then_arm = self.arm(then_pat, self.arena.alloc(then_expr));
400 // `match <scrutinee> { ... }`
401 let match_expr = self.expr_match(
404 arena_vec![self; then_arm, else_arm],
408 // `[opt_ident]: loop { ... }`
409 hir::ExprKind::Loop(self.block_expr(self.arena.alloc(match_expr)), opt_label, source)
412 /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_ok(<expr>) }`,
413 /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_ok(()) }`
414 /// and save the block id to use it as a break target for desugaring of the `?` operator.
415 fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind<'hir> {
416 self.with_catch_scope(body.id, |this| {
417 let mut block = this.lower_block_noalloc(body, true);
419 let try_span = this.mark_span_with_reason(
420 DesugaringKind::TryBlock,
422 this.allow_try_trait.clone(),
425 // Final expression of the block (if present) or `()` with span at the end of block
426 let tail_expr = block
429 .unwrap_or_else(|| this.expr_unit(this.sess.source_map().end_point(try_span)));
431 let ok_wrapped_span =
432 this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
434 // `::std::ops::Try::from_ok($tail_expr)`
435 block.expr = Some(this.wrap_in_try_constructor(
442 hir::ExprKind::Block(this.arena.alloc(block), None)
446 fn wrap_in_try_constructor(
450 expr: &'hir hir::Expr<'hir>,
452 ) -> &'hir hir::Expr<'hir> {
453 let path = &[sym::ops, sym::Try, method];
455 self.arena.alloc(self.expr_std_path(method_span, path, None, ThinVec::new()));
456 self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
459 fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
461 hir_id: self.next_id(),
462 attrs: self.lower_attrs(&arm.attrs),
463 pat: self.lower_pat(&arm.pat),
464 guard: match arm.guard {
465 Some(ref x) => Some(hir::Guard::If(self.lower_expr(x))),
468 body: self.lower_expr(&arm.body),
473 pub(super) fn make_async_expr(
475 capture_clause: CaptureBy,
476 closure_node_id: NodeId,
477 ret_ty: Option<AstP<Ty>>,
479 async_gen_kind: hir::AsyncGeneratorKind,
480 body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
481 ) -> hir::ExprKind<'hir> {
482 let output = match ret_ty {
483 Some(ty) => FunctionRetTy::Ty(ty),
484 None => FunctionRetTy::Default(span),
486 let ast_decl = FnDecl { inputs: vec![], output };
487 let decl = self.lower_fn_decl(&ast_decl, None, /* impl trait allowed */ false, None);
488 let body_id = self.lower_fn_body(&ast_decl, |this| {
489 this.generator_kind = Some(hir::GeneratorKind::Async(async_gen_kind));
493 // `static || -> <ret_ty> { body }`:
494 let generator_kind = hir::ExprKind::Closure(
499 Some(hir::Movability::Static),
501 let generator = hir::Expr {
502 hir_id: self.lower_node_id(closure_node_id),
503 kind: generator_kind,
505 attrs: ThinVec::new(),
508 // `future::from_generator`:
510 self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone());
511 let gen_future = self.expr_std_path(
513 &[sym::future, sym::from_generator],
518 // `future::from_generator(generator)`:
519 hir::ExprKind::Call(self.arena.alloc(gen_future), arena_vec![self; generator])
522 /// Desugar `<expr>.await` into:
525 /// mut pinned => loop {
526 /// match ::std::future::poll_with_tls_context(unsafe {
527 /// <::std::pin::Pin>::new_unchecked(&mut pinned)
529 /// ::std::task::Poll::Ready(result) => break result,
530 /// ::std::task::Poll::Pending => {}
536 fn lower_expr_await(&mut self, await_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
537 match self.generator_kind {
538 Some(hir::GeneratorKind::Async(_)) => {}
539 Some(hir::GeneratorKind::Gen) | None => {
540 let mut err = struct_span_err!(
544 "`await` is only allowed inside `async` functions and blocks"
546 err.span_label(await_span, "only allowed inside `async` functions and blocks");
547 if let Some(item_sp) = self.current_item {
548 err.span_label(item_sp, "this is not `async`");
553 let span = self.mark_span_with_reason(DesugaringKind::Await, await_span, None);
554 let gen_future_span = self.mark_span_with_reason(
555 DesugaringKind::Await,
557 self.allow_gen_future.clone(),
560 let pinned_ident = Ident::with_dummy_span(sym::pinned);
561 let (pinned_pat, pinned_pat_hid) =
562 self.pat_ident_binding_mode(span, pinned_ident, hir::BindingAnnotation::Mutable);
564 // ::std::future::poll_with_tls_context(unsafe {
565 // ::std::pin::Pin::new_unchecked(&mut pinned)
568 let pinned = self.expr_ident(span, pinned_ident, pinned_pat_hid);
569 let ref_mut_pinned = self.expr_mut_addr_of(span, pinned);
570 let pin_ty_id = self.next_id();
571 let new_unchecked_expr_kind = self.expr_call_std_assoc_fn(
574 &[sym::pin, sym::Pin],
576 arena_vec![self; ref_mut_pinned],
579 self.arena.alloc(self.expr(span, new_unchecked_expr_kind, ThinVec::new()));
580 let unsafe_expr = self.expr_unsafe(new_unchecked);
581 self.expr_call_std_path(
583 &[sym::future, sym::poll_with_tls_context],
584 arena_vec![self; unsafe_expr],
588 // `::std::task::Poll::Ready(result) => break result`
589 let loop_node_id = self.resolver.next_node_id();
590 let loop_hir_id = self.lower_node_id(loop_node_id);
592 let x_ident = Ident::with_dummy_span(sym::result);
593 let (x_pat, x_pat_hid) = self.pat_ident(span, x_ident);
594 let x_expr = self.expr_ident(span, x_ident, x_pat_hid);
595 let ready_pat = self.pat_std_enum(
597 &[sym::task, sym::Poll, sym::Ready],
598 arena_vec![self; x_pat],
600 let break_x = self.with_loop_scope(loop_node_id, move |this| {
602 hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
603 this.arena.alloc(this.expr(await_span, expr_break, ThinVec::new()))
605 self.arm(ready_pat, break_x)
608 // `::std::task::Poll::Pending => {}`
610 let pending_pat = self.pat_std_enum(span, &[sym::task, sym::Poll, sym::Pending], &[]);
611 let empty_block = self.expr_block_empty(span);
612 self.arm(pending_pat, empty_block)
615 let inner_match_stmt = {
616 let match_expr = self.expr_match(
619 arena_vec![self; ready_arm, pending_arm],
620 hir::MatchSource::AwaitDesugar,
622 self.stmt_expr(span, match_expr)
626 let unit = self.expr_unit(span);
627 let yield_expr = self.expr(
629 hir::ExprKind::Yield(unit, hir::YieldSource::Await),
632 self.stmt_expr(span, yield_expr)
635 let loop_block = self.block_all(span, arena_vec![self; inner_match_stmt, yield_stmt], None);
638 let loop_expr = self.arena.alloc(hir::Expr {
640 kind: hir::ExprKind::Loop(loop_block, None, hir::LoopSource::Loop),
642 attrs: ThinVec::new(),
645 // mut pinned => loop { ... }
646 let pinned_arm = self.arm(pinned_pat, loop_expr);
649 // mut pinned => loop { .. }
651 let expr = self.lower_expr(expr);
652 hir::ExprKind::Match(expr, arena_vec![self; pinned_arm], hir::MatchSource::AwaitDesugar)
655 fn lower_expr_closure(
657 capture_clause: CaptureBy,
658 movability: Movability,
662 ) -> hir::ExprKind<'hir> {
663 // Lower outside new scope to preserve `is_in_loop_condition`.
664 let fn_decl = self.lower_fn_decl(decl, None, false, None);
666 self.with_new_scopes(move |this| {
667 let prev = this.current_item;
668 this.current_item = Some(fn_decl_span);
669 let mut generator_kind = None;
670 let body_id = this.lower_fn_body(decl, |this| {
671 let e = this.lower_expr_mut(body);
672 generator_kind = this.generator_kind;
675 let generator_option =
676 this.generator_movability_for_fn(&decl, fn_decl_span, generator_kind, movability);
677 this.current_item = prev;
678 hir::ExprKind::Closure(capture_clause, fn_decl, body_id, fn_decl_span, generator_option)
682 fn generator_movability_for_fn(
686 generator_kind: Option<hir::GeneratorKind>,
687 movability: Movability,
688 ) -> Option<hir::Movability> {
689 match generator_kind {
690 Some(hir::GeneratorKind::Gen) => {
691 if !decl.inputs.is_empty() {
696 "generators cannot have explicit parameters"
702 Some(hir::GeneratorKind::Async(_)) => {
703 bug!("non-`async` closure body turned `async` during lowering");
706 if movability == Movability::Static {
707 struct_span_err!(self.sess, fn_decl_span, E0697, "closures cannot be static")
715 fn lower_expr_async_closure(
717 capture_clause: CaptureBy,
722 ) -> hir::ExprKind<'hir> {
724 FnDecl { inputs: decl.inputs.clone(), output: FunctionRetTy::Default(fn_decl_span) };
725 // We need to lower the declaration outside the new scope, because we
726 // have to conserve the state of being inside a loop condition for the
727 // closure argument types.
728 let fn_decl = self.lower_fn_decl(&outer_decl, None, false, None);
730 self.with_new_scopes(move |this| {
731 // FIXME(cramertj): allow `async` non-`move` closures with arguments.
732 if capture_clause == CaptureBy::Ref && !decl.inputs.is_empty() {
737 "`async` non-`move` closures with parameters are not currently supported",
740 "consider using `let` statements to manually capture \
741 variables by reference before entering an `async move` closure",
746 // Transform `async |x: u8| -> X { ... }` into
747 // `|x: u8| future_from_generator(|| -> X { ... })`.
748 let body_id = this.lower_fn_body(&outer_decl, |this| {
750 if let FunctionRetTy::Ty(ty) = &decl.output { Some(ty.clone()) } else { None };
751 let async_body = this.make_async_expr(
756 hir::AsyncGeneratorKind::Closure,
757 |this| this.with_new_scopes(|this| this.lower_expr_mut(body)),
759 this.expr(fn_decl_span, async_body, ThinVec::new())
761 hir::ExprKind::Closure(capture_clause, fn_decl, body_id, fn_decl_span, None)
765 /// Desugar `<start>..=<end>` into `std::ops::RangeInclusive::new(<start>, <end>)`.
766 fn lower_expr_range_closed(&mut self, span: Span, e1: &Expr, e2: &Expr) -> hir::ExprKind<'hir> {
767 let id = self.next_id();
768 let e1 = self.lower_expr_mut(e1);
769 let e2 = self.lower_expr_mut(e2);
770 self.expr_call_std_assoc_fn(
773 &[sym::ops, sym::RangeInclusive],
775 arena_vec![self; e1, e2],
785 ) -> hir::ExprKind<'hir> {
786 use syntax::ast::RangeLimits::*;
788 let path = match (e1, e2, lims) {
789 (None, None, HalfOpen) => sym::RangeFull,
790 (Some(..), None, HalfOpen) => sym::RangeFrom,
791 (None, Some(..), HalfOpen) => sym::RangeTo,
792 (Some(..), Some(..), HalfOpen) => sym::Range,
793 (None, Some(..), Closed) => sym::RangeToInclusive,
794 (Some(..), Some(..), Closed) => unreachable!(),
795 (_, None, Closed) => {
796 self.diagnostic().span_fatal(span, "inclusive range with no end").raise()
800 let fields = self.arena.alloc_from_iter(
801 e1.iter().map(|e| ("start", e)).chain(e2.iter().map(|e| ("end", e))).map(|(s, e)| {
802 let expr = self.lower_expr(&e);
803 let ident = Ident::new(Symbol::intern(s), e.span);
804 self.field(ident, expr, e.span)
808 let is_unit = fields.is_empty();
809 let struct_path = [sym::ops, path];
810 let struct_path = self.std_path(span, &struct_path, None, is_unit);
811 let struct_path = hir::QPath::Resolved(None, struct_path);
814 hir::ExprKind::Path(struct_path)
816 hir::ExprKind::Struct(self.arena.alloc(struct_path), fields, None)
820 fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
821 let target_id = match destination {
823 if let Some(loop_id) = self.resolver.get_label_res(id) {
824 Ok(self.lower_node_id(loop_id))
826 Err(hir::LoopIdError::UnresolvedLabel)
833 .map(|id| Ok(self.lower_node_id(id)))
834 .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope))
837 hir::Destination { label: destination.map(|(_, label)| label), target_id }
840 fn lower_jump_destination(&mut self, id: NodeId, opt_label: Option<Label>) -> hir::Destination {
841 if self.is_in_loop_condition && opt_label.is_none() {
844 target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
847 self.lower_loop_destination(opt_label.map(|label| (id, label)))
851 fn with_catch_scope<T>(&mut self, catch_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
852 let len = self.catch_scopes.len();
853 self.catch_scopes.push(catch_id);
855 let result = f(self);
858 self.catch_scopes.len(),
859 "catch scopes should be added and removed in stack order"
862 self.catch_scopes.pop().unwrap();
867 fn with_loop_scope<T>(&mut self, loop_id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
868 // We're no longer in the base loop's condition; we're in another loop.
869 let was_in_loop_condition = self.is_in_loop_condition;
870 self.is_in_loop_condition = false;
872 let len = self.loop_scopes.len();
873 self.loop_scopes.push(loop_id);
875 let result = f(self);
878 self.loop_scopes.len(),
879 "loop scopes should be added and removed in stack order"
882 self.loop_scopes.pop().unwrap();
884 self.is_in_loop_condition = was_in_loop_condition;
889 fn with_loop_condition_scope<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
890 let was_in_loop_condition = self.is_in_loop_condition;
891 self.is_in_loop_condition = true;
893 let result = f(self);
895 self.is_in_loop_condition = was_in_loop_condition;
900 fn lower_expr_asm(&mut self, asm: &InlineAsm) -> hir::ExprKind<'hir> {
901 let inner = hir::InlineAsmInner {
902 inputs: asm.inputs.iter().map(|&(c, _)| c).collect(),
906 .map(|out| hir::InlineAsmOutput {
907 constraint: out.constraint,
909 is_indirect: out.is_indirect,
914 asm_str_style: asm.asm_str_style,
915 clobbers: asm.clobbers.clone().into(),
916 volatile: asm.volatile,
917 alignstack: asm.alignstack,
918 dialect: asm.dialect,
920 let hir_asm = hir::InlineAsm {
922 inputs_exprs: self.arena.alloc_from_iter(
923 asm.inputs.iter().map(|&(_, ref input)| self.lower_expr_mut(input)),
927 .alloc_from_iter(asm.outputs.iter().map(|out| self.lower_expr_mut(&out.expr))),
929 hir::ExprKind::InlineAsm(self.arena.alloc(hir_asm))
932 fn lower_field(&mut self, f: &Field) -> hir::Field<'hir> {
934 hir_id: self.next_id(),
936 expr: self.lower_expr(&f.expr),
938 is_shorthand: f.is_shorthand,
942 fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
943 match self.generator_kind {
944 Some(hir::GeneratorKind::Gen) => {}
945 Some(hir::GeneratorKind::Async(_)) => {
950 "`async` generators are not yet supported"
953 return hir::ExprKind::Err;
955 None => self.generator_kind = Some(hir::GeneratorKind::Gen),
959 opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
961 hir::ExprKind::Yield(expr, hir::YieldSource::Yield)
964 /// Desugar `ExprForLoop` from: `[opt_ident]: for <pat> in <head> <body>` into:
967 /// let result = match ::std::iter::IntoIterator::into_iter(<head>) {
969 /// [opt_ident]: loop {
971 /// match ::std::iter::Iterator::next(&mut iter) {
972 /// ::std::option::Option::Some(val) => __next = val,
973 /// ::std::option::Option::None => break
975 /// let <pat> = __next;
976 /// StmtKind::Expr(<body>);
989 opt_label: Option<Label>,
990 ) -> hir::Expr<'hir> {
992 let mut head = self.lower_expr_mut(head);
993 let desugared_span = self.mark_span_with_reason(DesugaringKind::ForLoop, head.span, None);
994 head.span = desugared_span;
996 let iter = Ident::with_dummy_span(sym::iter);
998 let next_ident = Ident::with_dummy_span(sym::__next);
999 let (next_pat, next_pat_hid) = self.pat_ident_binding_mode(
1002 hir::BindingAnnotation::Mutable,
1005 // `::std::option::Option::Some(val) => __next = val`
1007 let val_ident = Ident::with_dummy_span(sym::val);
1008 let (val_pat, val_pat_hid) = self.pat_ident(pat.span, val_ident);
1009 let val_expr = self.expr_ident(pat.span, val_ident, val_pat_hid);
1010 let next_expr = self.expr_ident(pat.span, next_ident, next_pat_hid);
1011 let assign = self.arena.alloc(self.expr(
1013 hir::ExprKind::Assign(next_expr, val_expr, pat.span),
1016 let some_pat = self.pat_some(pat.span, val_pat);
1017 self.arm(some_pat, assign)
1020 // `::std::option::Option::None => break`
1023 self.with_loop_scope(e.id, |this| this.expr_break(e.span, ThinVec::new()));
1024 let pat = self.pat_none(e.span);
1025 self.arm(pat, break_expr)
1029 let (iter_pat, iter_pat_nid) =
1030 self.pat_ident_binding_mode(desugared_span, iter, hir::BindingAnnotation::Mutable);
1032 // `match ::std::iter::Iterator::next(&mut iter) { ... }`
1034 let iter = self.expr_ident(desugared_span, iter, iter_pat_nid);
1035 let ref_mut_iter = self.expr_mut_addr_of(desugared_span, iter);
1036 let next_path = &[sym::iter, sym::Iterator, sym::next];
1038 self.expr_call_std_path(desugared_span, next_path, arena_vec![self; ref_mut_iter]);
1039 let arms = arena_vec![self; pat_arm, break_arm];
1041 self.expr_match(desugared_span, next_expr, arms, hir::MatchSource::ForLoopDesugar)
1043 let match_stmt = self.stmt_expr(desugared_span, match_expr);
1045 let next_expr = self.expr_ident(desugared_span, next_ident, next_pat_hid);
1048 let next_let = self.stmt_let_pat(
1053 hir::LocalSource::ForLoopDesugar,
1056 // `let <pat> = __next`
1057 let pat = self.lower_pat(pat);
1058 let pat_let = self.stmt_let_pat(
1063 hir::LocalSource::ForLoopDesugar,
1066 let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
1067 let body_expr = self.expr_block(body_block, ThinVec::new());
1068 let body_stmt = self.stmt_expr(body.span, body_expr);
1070 let loop_block = self.block_all(
1072 arena_vec![self; next_let, match_stmt, pat_let, body_stmt],
1076 // `[opt_ident]: loop { ... }`
1077 let kind = hir::ExprKind::Loop(loop_block, opt_label, hir::LoopSource::ForLoop);
1078 let loop_expr = self.arena.alloc(hir::Expr {
1079 hir_id: self.lower_node_id(e.id),
1082 attrs: ThinVec::new(),
1085 // `mut iter => { ... }`
1086 let iter_arm = self.arm(iter_pat, loop_expr);
1088 // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
1089 let into_iter_expr = {
1090 let into_iter_path = &[sym::iter, sym::IntoIterator, sym::into_iter];
1091 self.expr_call_std_path(desugared_span, into_iter_path, arena_vec![self; head])
1094 let match_expr = self.arena.alloc(self.expr_match(
1097 arena_vec![self; iter_arm],
1098 hir::MatchSource::ForLoopDesugar,
1101 // This is effectively `{ let _result = ...; _result }`.
1102 // The construct was introduced in #21984 and is necessary to make sure that
1103 // temporaries in the `head` expression are dropped and do not leak to the
1104 // surrounding scope of the `match` since the `match` is not a terminating scope.
1106 // Also, add the attributes to the outer returned expr node.
1107 self.expr_drop_temps_mut(desugared_span, match_expr, e.attrs.clone())
1110 /// Desugar `ExprKind::Try` from: `<expr>?` into:
1112 /// match Try::into_result(<expr>) {
1113 /// Ok(val) => #[allow(unreachable_code)] val,
1114 /// Err(err) => #[allow(unreachable_code)]
1115 /// // If there is an enclosing `try {...}`:
1116 /// break 'catch_target Try::from_error(From::from(err)),
1118 /// return Try::from_error(From::from(err)),
1121 fn lower_expr_try(&mut self, span: Span, sub_expr: &Expr) -> hir::ExprKind<'hir> {
1122 let unstable_span = self.mark_span_with_reason(
1123 DesugaringKind::QuestionMark,
1125 self.allow_try_trait.clone(),
1127 let try_span = self.sess.source_map().end_point(span);
1128 let try_span = self.mark_span_with_reason(
1129 DesugaringKind::QuestionMark,
1131 self.allow_try_trait.clone(),
1134 // `Try::into_result(<expr>)`
1137 let sub_expr = self.lower_expr_mut(sub_expr);
1139 let path = &[sym::ops, sym::Try, sym::into_result];
1140 self.expr_call_std_path(unstable_span, path, arena_vec![self; sub_expr])
1143 // `#[allow(unreachable_code)]`
1145 // `allow(unreachable_code)`
1147 let allow_ident = Ident::new(sym::allow, span);
1148 let uc_ident = Ident::new(sym::unreachable_code, span);
1149 let uc_nested = attr::mk_nested_word_item(uc_ident);
1150 attr::mk_list_item(allow_ident, vec![uc_nested])
1152 attr::mk_attr_outer(allow)
1154 let attrs = vec![attr];
1156 // `Ok(val) => #[allow(unreachable_code)] val,`
1158 let val_ident = Ident::with_dummy_span(sym::val);
1159 let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
1160 let val_expr = self.arena.alloc(self.expr_ident_with_attrs(
1164 ThinVec::from(attrs.clone()),
1166 let ok_pat = self.pat_ok(span, val_pat);
1167 self.arm(ok_pat, val_expr)
1170 // `Err(err) => #[allow(unreachable_code)]
1171 // return Try::from_error(From::from(err)),`
1173 let err_ident = Ident::with_dummy_span(sym::err);
1174 let (err_local, err_local_nid) = self.pat_ident(try_span, err_ident);
1176 let from_path = &[sym::convert, sym::From, sym::from];
1177 let err_expr = self.expr_ident_mut(try_span, err_ident, err_local_nid);
1178 self.expr_call_std_path(try_span, from_path, arena_vec![self; err_expr])
1181 self.wrap_in_try_constructor(sym::from_error, unstable_span, from_expr, try_span);
1182 let thin_attrs = ThinVec::from(attrs);
1183 let catch_scope = self.catch_scopes.last().map(|x| *x);
1184 let ret_expr = if let Some(catch_node) = catch_scope {
1185 let target_id = Ok(self.lower_node_id(catch_node));
1186 self.arena.alloc(self.expr(
1188 hir::ExprKind::Break(
1189 hir::Destination { label: None, target_id },
1190 Some(from_err_expr),
1195 self.arena.alloc(self.expr(
1197 hir::ExprKind::Ret(Some(from_err_expr)),
1202 let err_pat = self.pat_err(try_span, err_local);
1203 self.arm(err_pat, ret_expr)
1206 hir::ExprKind::Match(
1208 arena_vec![self; err_arm, ok_arm],
1209 hir::MatchSource::TryDesugar,
1213 // =========================================================================
1214 // Helper methods for building HIR.
1215 // =========================================================================
1217 /// Constructs a `true` or `false` literal expression.
1218 pub(super) fn expr_bool(&mut self, span: Span, val: bool) -> &'hir hir::Expr<'hir> {
1219 let lit = Spanned { span, node: LitKind::Bool(val) };
1220 self.arena.alloc(self.expr(span, hir::ExprKind::Lit(lit), ThinVec::new()))
1223 /// Wrap the given `expr` in a terminating scope using `hir::ExprKind::DropTemps`.
1225 /// In terms of drop order, it has the same effect as wrapping `expr` in
1226 /// `{ let _t = $expr; _t }` but should provide better compile-time performance.
1228 /// The drop order can be important in e.g. `if expr { .. }`.
1229 pub(super) fn expr_drop_temps(
1232 expr: &'hir hir::Expr<'hir>,
1234 ) -> &'hir hir::Expr<'hir> {
1235 self.arena.alloc(self.expr_drop_temps_mut(span, expr, attrs))
1238 pub(super) fn expr_drop_temps_mut(
1241 expr: &'hir hir::Expr<'hir>,
1243 ) -> hir::Expr<'hir> {
1244 self.expr(span, hir::ExprKind::DropTemps(expr), attrs)
1250 arg: &'hir hir::Expr<'hir>,
1251 arms: &'hir [hir::Arm<'hir>],
1252 source: hir::MatchSource,
1253 ) -> hir::Expr<'hir> {
1254 self.expr(span, hir::ExprKind::Match(arg, arms, source), ThinVec::new())
1257 fn expr_break(&mut self, span: Span, attrs: AttrVec) -> &'hir hir::Expr<'hir> {
1258 let expr_break = hir::ExprKind::Break(self.lower_loop_destination(None), None);
1259 self.arena.alloc(self.expr(span, expr_break, attrs))
1262 fn expr_mut_addr_of(&mut self, span: Span, e: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
1265 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e),
1270 fn expr_unit(&mut self, sp: Span) -> &'hir hir::Expr<'hir> {
1271 self.arena.alloc(self.expr(sp, hir::ExprKind::Tup(&[]), ThinVec::new()))
1277 e: &'hir hir::Expr<'hir>,
1278 args: &'hir [hir::Expr<'hir>],
1279 ) -> &'hir hir::Expr<'hir> {
1280 self.arena.alloc(self.expr(span, hir::ExprKind::Call(e, args), ThinVec::new()))
1283 // Note: associated functions must use `expr_call_std_path`.
1284 fn expr_call_std_path(
1287 path_components: &[Symbol],
1288 args: &'hir [hir::Expr<'hir>],
1289 ) -> &'hir hir::Expr<'hir> {
1291 self.arena.alloc(self.expr_std_path(span, path_components, None, ThinVec::new()));
1292 self.expr_call(span, path, args)
1295 // Create an expression calling an associated function of an std type.
1297 // Associated functions cannot be resolved through the normal `std_path` function,
1298 // as they are resolved differently and so cannot use `expr_call_std_path`.
1300 // This function accepts the path component (`ty_path_components`) separately from
1301 // the name of the associated function (`assoc_fn_name`) in order to facilitate
1302 // separate resolution of the type and creation of a path referring to its associated
1304 fn expr_call_std_assoc_fn(
1306 ty_path_id: hir::HirId,
1308 ty_path_components: &[Symbol],
1309 assoc_fn_name: &str,
1310 args: &'hir [hir::Expr<'hir>],
1311 ) -> hir::ExprKind<'hir> {
1312 let ty_path = self.std_path(span, ty_path_components, None, false);
1314 self.arena.alloc(self.ty_path(ty_path_id, span, hir::QPath::Resolved(None, ty_path)));
1315 let fn_seg = self.arena.alloc(hir::PathSegment::from_ident(Ident::from_str(assoc_fn_name)));
1316 let fn_path = hir::QPath::TypeRelative(ty, fn_seg);
1318 self.arena.alloc(self.expr(span, hir::ExprKind::Path(fn_path), ThinVec::new()));
1319 hir::ExprKind::Call(fn_expr, args)
1325 components: &[Symbol],
1326 params: Option<&'hir hir::GenericArgs<'hir>>,
1328 ) -> hir::Expr<'hir> {
1329 let path = self.std_path(span, components, params, true);
1330 self.expr(span, hir::ExprKind::Path(hir::QPath::Resolved(None, path)), attrs)
1333 pub(super) fn expr_ident(
1337 binding: hir::HirId,
1338 ) -> &'hir hir::Expr<'hir> {
1339 self.arena.alloc(self.expr_ident_mut(sp, ident, binding))
1342 pub(super) fn expr_ident_mut(
1346 binding: hir::HirId,
1347 ) -> hir::Expr<'hir> {
1348 self.expr_ident_with_attrs(sp, ident, binding, ThinVec::new())
1351 fn expr_ident_with_attrs(
1355 binding: hir::HirId,
1357 ) -> hir::Expr<'hir> {
1358 let expr_path = hir::ExprKind::Path(hir::QPath::Resolved(
1360 self.arena.alloc(hir::Path {
1362 res: Res::Local(binding),
1363 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1367 self.expr(span, expr_path, attrs)
1370 fn expr_unsafe(&mut self, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
1371 let hir_id = self.next_id();
1372 let span = expr.span;
1375 hir::ExprKind::Block(
1376 self.arena.alloc(hir::Block {
1380 rules: hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::CompilerGenerated),
1382 targeted_by_break: false,
1390 fn expr_block_empty(&mut self, span: Span) -> &'hir hir::Expr<'hir> {
1391 let blk = self.block_all(span, &[], None);
1392 let expr = self.expr_block(blk, ThinVec::new());
1393 self.arena.alloc(expr)
1396 pub(super) fn expr_block(
1398 b: &'hir hir::Block<'hir>,
1400 ) -> hir::Expr<'hir> {
1401 self.expr(b.span, hir::ExprKind::Block(b, None), attrs)
1407 kind: hir::ExprKind<'hir>,
1409 ) -> hir::Expr<'hir> {
1410 hir::Expr { hir_id: self.next_id(), kind, span, attrs }
1413 fn field(&mut self, ident: Ident, expr: &'hir hir::Expr<'hir>, span: Span) -> hir::Field<'hir> {
1414 hir::Field { hir_id: self.next_id(), ident, span, expr, is_shorthand: false }
1417 fn arm(&mut self, pat: &'hir hir::Pat<'hir>, expr: &'hir hir::Expr<'hir>) -> hir::Arm<'hir> {
1419 hir_id: self.next_id(),