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expr.rs
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use std::assert_matches::assert_matches;
use rustc_ast::ptr::P as AstP;
use rustc_ast::*;
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::HirId;
use rustc_middle::span_bug;
use rustc_session::errors::report_lit_error;
use rustc_span::source_map::{respan, Spanned};
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{DesugaringKind, Span, DUMMY_SP};
use thin_vec::{thin_vec, ThinVec};
use super::errors::{
AsyncCoroutinesNotSupported, AwaitOnlyInAsyncFnAndBlocks, BaseExpressionDoubleDot,
ClosureCannotBeStatic, CoroutineTooManyParameters,
FunctionalRecordUpdateDestructuringAssignment, InclusiveRangeWithNoEnd, MatchArmWithNoBody,
NeverPatternWithBody, NeverPatternWithGuard, UnderscoreExprLhsAssign,
};
use super::{
ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs, ResolverAstLoweringExt,
};
use crate::errors::YieldInClosure;
use crate::{FnDeclKind, ImplTraitPosition};
impl<'hir> LoweringContext<'_, 'hir> {
fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
}
pub(super) fn lower_expr(&mut self, e: &Expr) -> &'hir hir::Expr<'hir> {
self.arena.alloc(self.lower_expr_mut(e))
}
pub(super) fn lower_expr_mut(&mut self, e: &Expr) -> hir::Expr<'hir> {
ensure_sufficient_stack(|| {
match &e.kind {
// Parenthesis expression does not have a HirId and is handled specially.
ExprKind::Paren(ex) => {
let mut ex = self.lower_expr_mut(ex);
// Include parens in span, but only if it is a super-span.
if e.span.contains(ex.span) {
ex.span = self.lower_span(e.span);
}
// Merge attributes into the inner expression.
if !e.attrs.is_empty() {
let old_attrs = self.attrs.get(&ex.hir_id.local_id).copied().unwrap_or(&[]);
self.attrs.insert(
ex.hir_id.local_id,
&*self.arena.alloc_from_iter(
e.attrs
.iter()
.map(|a| self.lower_attr(a))
.chain(old_attrs.iter().cloned()),
),
);
}
return ex;
}
// Desugar `ExprForLoop`
// from: `[opt_ident]: for await? <pat> in <iter> <body>`
//
// This also needs special handling because the HirId of the returned `hir::Expr` will not
// correspond to the `e.id`, so `lower_expr_for` handles attribute lowering itself.
ExprKind::ForLoop { pat, iter, body, label, kind } => {
return self.lower_expr_for(e, pat, iter, body, *label, *kind);
}
_ => (),
}
let hir_id = self.lower_node_id(e.id);
self.lower_attrs(hir_id, &e.attrs);
let kind = match &e.kind {
ExprKind::Array(exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
ExprKind::ConstBlock(c) => {
let c = self.with_new_scopes(c.value.span, |this| {
let def_id = this.local_def_id(c.id);
hir::ConstBlock {
def_id,
hir_id: this.lower_node_id(c.id),
body: this.with_def_id_parent(def_id, |this| {
this.lower_const_body(c.value.span, Some(&c.value))
}),
}
});
hir::ExprKind::ConstBlock(c)
}
ExprKind::Repeat(expr, count) => {
let expr = self.lower_expr(expr);
let count = self.lower_array_length(count);
hir::ExprKind::Repeat(expr, count)
}
ExprKind::Tup(elts) => hir::ExprKind::Tup(self.lower_exprs(elts)),
ExprKind::Call(f, args) => {
if let Some(legacy_args) = self.resolver.legacy_const_generic_args(f) {
self.lower_legacy_const_generics((**f).clone(), args.clone(), &legacy_args)
} else {
let f = self.lower_expr(f);
hir::ExprKind::Call(f, self.lower_exprs(args))
}
}
ExprKind::MethodCall(box MethodCall { seg, receiver, args, span }) => {
let hir_seg = self.arena.alloc(self.lower_path_segment(
e.span,
seg,
ParamMode::Optional,
ParenthesizedGenericArgs::Err,
ImplTraitContext::Disallowed(ImplTraitPosition::Path),
// Method calls can't have bound modifiers
None,
));
let receiver = self.lower_expr(receiver);
let args =
self.arena.alloc_from_iter(args.iter().map(|x| self.lower_expr_mut(x)));
hir::ExprKind::MethodCall(hir_seg, receiver, args, self.lower_span(*span))
}
ExprKind::Binary(binop, lhs, rhs) => {
let binop = self.lower_binop(*binop);
let lhs = self.lower_expr(lhs);
let rhs = self.lower_expr(rhs);
hir::ExprKind::Binary(binop, lhs, rhs)
}
ExprKind::Unary(op, ohs) => {
let op = self.lower_unop(*op);
let ohs = self.lower_expr(ohs);
hir::ExprKind::Unary(op, ohs)
}
ExprKind::Lit(token_lit) => {
let lit_kind = match LitKind::from_token_lit(*token_lit) {
Ok(lit_kind) => lit_kind,
Err(err) => {
let guar =
report_lit_error(&self.tcx.sess.psess, err, *token_lit, e.span);
LitKind::Err(guar)
}
};
let lit = self.arena.alloc(respan(self.lower_span(e.span), lit_kind));
hir::ExprKind::Lit(lit)
}
ExprKind::IncludedBytes(bytes) => {
let lit = self.arena.alloc(respan(
self.lower_span(e.span),
LitKind::ByteStr(bytes.clone(), StrStyle::Cooked),
));
hir::ExprKind::Lit(lit)
}
ExprKind::Cast(expr, ty) => {
let expr = self.lower_expr(expr);
let ty =
self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Cast));
hir::ExprKind::Cast(expr, ty)
}
ExprKind::Type(expr, ty) => {
let expr = self.lower_expr(expr);
let ty =
self.lower_ty(ty, ImplTraitContext::Disallowed(ImplTraitPosition::Cast));
hir::ExprKind::Type(expr, ty)
}
ExprKind::AddrOf(k, m, ohs) => {
let ohs = self.lower_expr(ohs);
hir::ExprKind::AddrOf(*k, *m, ohs)
}
ExprKind::Let(pat, scrutinee, span, recovered) => {
hir::ExprKind::Let(self.arena.alloc(hir::LetExpr {
span: self.lower_span(*span),
pat: self.lower_pat(pat),
ty: None,
init: self.lower_expr(scrutinee),
recovered: *recovered,
}))
}
ExprKind::If(cond, then, else_opt) => {
self.lower_expr_if(cond, then, else_opt.as_deref())
}
ExprKind::While(cond, body, opt_label) => self.with_loop_scope(e.id, |this| {
let span = this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
this.lower_expr_while_in_loop_scope(span, cond, body, *opt_label)
}),
ExprKind::Loop(body, opt_label, span) => self.with_loop_scope(e.id, |this| {
hir::ExprKind::Loop(
this.lower_block(body, false),
this.lower_label(*opt_label),
hir::LoopSource::Loop,
this.lower_span(*span),
)
}),
ExprKind::TryBlock(body) => self.lower_expr_try_block(body),
ExprKind::Match(expr, arms, kind) => hir::ExprKind::Match(
self.lower_expr(expr),
self.arena.alloc_from_iter(arms.iter().map(|x| self.lower_arm(x))),
match kind {
MatchKind::Prefix => hir::MatchSource::Normal,
MatchKind::Postfix => hir::MatchSource::Postfix,
},
),
ExprKind::Await(expr, await_kw_span) => self.lower_expr_await(*await_kw_span, expr),
ExprKind::Closure(box Closure {
binder,
capture_clause,
constness,
coroutine_kind,
movability,
fn_decl,
body,
fn_decl_span,
fn_arg_span,
}) => match coroutine_kind {
Some(coroutine_kind) => self.lower_expr_coroutine_closure(
binder,
*capture_clause,
e.id,
hir_id,
*coroutine_kind,
fn_decl,
body,
*fn_decl_span,
*fn_arg_span,
),
None => {
let peeled = body.peel_uwu();
if let ast::ExprKind::Gen(
_,
block,
gen_kind @ ast::GenBlockKind::Async,
span,
) = &peeled.kind
{
let coroutine_kind = match gen_kind {
GenBlockKind::Async => CoroutineKind::Async {
span: *span,
closure_id: peeled.node_id(),
return_impl_trait_id: self.next_node_id(),
},
GenBlockKind::Gen => CoroutineKind::Gen {
span: *span,
closure_id: peeled.node_id(),
return_impl_trait_id: self.next_node_id(),
},
GenBlockKind::AsyncGen => CoroutineKind::AsyncGen {
span: *span,
closure_id: peeled.node_id(),
return_impl_trait_id: self.next_node_id(),
},
};
let id = self.next_node_id();
self.lower_expr_coroutine_closure(
binder,
*capture_clause,
e.id,
hir_id,
coroutine_kind,
fn_decl,
&ast::Expr {
id,
span: *span,
kind: ExprKind::Block(block.clone(), None),
attrs: thin_vec![],
tokens: None,
},
*fn_decl_span,
*fn_arg_span,
)
} else {
self.lower_expr_closure(
binder,
*capture_clause,
e.id,
hir_id,
*constness,
*movability,
fn_decl,
body,
*fn_decl_span,
*fn_arg_span,
)
}
}
},
ExprKind::Gen(capture_clause, block, genblock_kind, decl_span) => {
let desugaring_kind = match genblock_kind {
GenBlockKind::Async => hir::CoroutineDesugaring::Async,
GenBlockKind::Gen => hir::CoroutineDesugaring::Gen,
GenBlockKind::AsyncGen => hir::CoroutineDesugaring::AsyncGen,
};
self.make_desugared_coroutine_expr(
*capture_clause,
e.id,
None,
*decl_span,
e.span,
desugaring_kind,
hir::CoroutineSource::Block,
|this| this.with_new_scopes(e.span, |this| this.lower_block_expr(block)),
)
}
ExprKind::Block(blk, opt_label) => {
let opt_label = self.lower_label(*opt_label);
hir::ExprKind::Block(self.lower_block(blk, opt_label.is_some()), opt_label)
}
ExprKind::Assign(el, er, span) => self.lower_expr_assign(el, er, *span, e.span),
ExprKind::AssignOp(op, el, er) => hir::ExprKind::AssignOp(
self.lower_binop(*op),
self.lower_expr(el),
self.lower_expr(er),
),
ExprKind::Field(el, ident) => {
hir::ExprKind::Field(self.lower_expr(el), self.lower_ident(*ident))
}
ExprKind::Index(el, er, brackets_span) => {
hir::ExprKind::Index(self.lower_expr(el), self.lower_expr(er), *brackets_span)
}
ExprKind::Range(Some(e1), Some(e2), RangeLimits::Closed) => {
self.lower_expr_range_closed(e.span, e1, e2)
}
ExprKind::Range(e1, e2, lims) => {
self.lower_expr_range(e.span, e1.as_deref(), e2.as_deref(), *lims)
}
ExprKind::Underscore => {
let guar = self.dcx().emit_err(UnderscoreExprLhsAssign { span: e.span });
hir::ExprKind::Err(guar)
}
ExprKind::Path(qself, path) => {
let qpath = self.lower_qpath(
e.id,
qself,
path,
ParamMode::Optional,
ImplTraitContext::Disallowed(ImplTraitPosition::Path),
None,
);
hir::ExprKind::Path(qpath)
}
ExprKind::Break(opt_label, opt_expr) => {
let opt_expr = opt_expr.as_ref().map(|x| self.lower_expr(x));
hir::ExprKind::Break(self.lower_jump_destination(e.id, *opt_label), opt_expr)
}
ExprKind::Continue(opt_label) => {
hir::ExprKind::Continue(self.lower_jump_destination(e.id, *opt_label))
}
ExprKind::Ret(e) => {
let e = e.as_ref().map(|x| self.lower_expr(x));
hir::ExprKind::Ret(e)
}
ExprKind::Yeet(sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
ExprKind::Become(sub_expr) => {
let sub_expr = self.lower_expr(sub_expr);
hir::ExprKind::Become(sub_expr)
}
ExprKind::InlineAsm(asm) => {
hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
}
ExprKind::FormatArgs(fmt) => self.lower_format_args(e.span, fmt),
ExprKind::OffsetOf(container, fields) => hir::ExprKind::OffsetOf(
self.lower_ty(
container,
ImplTraitContext::Disallowed(ImplTraitPosition::OffsetOf),
),
self.arena.alloc_from_iter(fields.iter().map(|&ident| self.lower_ident(ident))),
),
ExprKind::Struct(se) => {
let rest = match &se.rest {
StructRest::Base(e) => Some(self.lower_expr(e)),
StructRest::Rest(sp) => {
let guar = self.dcx().emit_err(BaseExpressionDoubleDot { span: *sp });
Some(&*self.arena.alloc(self.expr_err(*sp, guar)))
}
StructRest::None => None,
};
hir::ExprKind::Struct(
self.arena.alloc(self.lower_qpath(
e.id,
&se.qself,
&se.path,
ParamMode::Optional,
ImplTraitContext::Disallowed(ImplTraitPosition::Path),
None,
)),
self.arena
.alloc_from_iter(se.fields.iter().map(|x| self.lower_expr_field(x))),
rest,
)
}
ExprKind::Yield(opt_expr) => self.lower_expr_yield(e.span, opt_expr.as_deref()),
ExprKind::Err(guar) => hir::ExprKind::Err(*guar),
ExprKind::Dummy => {
span_bug!(e.span, "lowered ExprKind::Dummy")
}
ExprKind::Try(sub_expr) => self.lower_expr_try(e.span, sub_expr),
ExprKind::Paren(_) | ExprKind::ForLoop { .. } => {
unreachable!("already handled")
}
ExprKind::MacCall(_) => panic!("{:?} shouldn't exist here", e.span),
};
hir::Expr { hir_id, kind, span: self.lower_span(e.span) }
})
}
fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
match u {
UnOp::Deref => hir::UnOp::Deref,
UnOp::Not => hir::UnOp::Not,
UnOp::Neg => hir::UnOp::Neg,
}
}
fn lower_binop(&mut self, b: BinOp) -> BinOp {
Spanned { node: b.node, span: self.lower_span(b.span) }
}
fn lower_legacy_const_generics(
&mut self,
mut f: Expr,
args: ThinVec<AstP<Expr>>,
legacy_args_idx: &[usize],
) -> hir::ExprKind<'hir> {
let ExprKind::Path(None, path) = &mut f.kind else {
unreachable!();
};
// Split the arguments into const generics and normal arguments
let mut real_args = vec![];
let mut generic_args = ThinVec::new();
for (idx, arg) in args.into_iter().enumerate() {
if legacy_args_idx.contains(&idx) {
let parent_def_id = self.current_def_id_parent;
let node_id = self.next_node_id();
// HACK(min_generic_const_args): see lower_anon_const
if !arg.is_potential_trivial_const_arg() {
// Add a definition for the in-band const def.
self.create_def(parent_def_id, node_id, kw::Empty, DefKind::AnonConst, f.span);
}
let anon_const = AnonConst { id: node_id, value: arg };
generic_args.push(AngleBracketedArg::Arg(GenericArg::Const(anon_const)));
} else {
real_args.push(arg);
}
}
// Add generic args to the last element of the path.
let last_segment = path.segments.last_mut().unwrap();
assert!(last_segment.args.is_none());
last_segment.args = Some(AstP(GenericArgs::AngleBracketed(AngleBracketedArgs {
span: DUMMY_SP,
args: generic_args,
})));
// Now lower everything as normal.
let f = self.lower_expr(&f);
hir::ExprKind::Call(f, self.lower_exprs(&real_args))
}
fn lower_expr_if(
&mut self,
cond: &Expr,
then: &Block,
else_opt: Option<&Expr>,
) -> hir::ExprKind<'hir> {
let lowered_cond = self.lower_cond(cond);
let then_expr = self.lower_block_expr(then);
if let Some(rslt) = else_opt {
hir::ExprKind::If(
lowered_cond,
self.arena.alloc(then_expr),
Some(self.lower_expr(rslt)),
)
} else {
hir::ExprKind::If(lowered_cond, self.arena.alloc(then_expr), None)
}
}
// Lowers a condition (i.e. `cond` in `if cond` or `while cond`), wrapping it in a terminating scope
// so that temporaries created in the condition don't live beyond it.
fn lower_cond(&mut self, cond: &Expr) -> &'hir hir::Expr<'hir> {
fn has_let_expr(expr: &Expr) -> bool {
match &expr.kind {
ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs),
ExprKind::Let(..) => true,
_ => false,
}
}
// We have to take special care for `let` exprs in the condition, e.g. in
// `if let pat = val` or `if foo && let pat = val`, as we _do_ want `val` to live beyond the
// condition in this case.
//
// In order to maintain the drop behavior for the non `let` parts of the condition,
// we still wrap them in terminating scopes, e.g. `if foo && let pat = val` essentially
// gets transformed into `if { let _t = foo; _t } && let pat = val`
match &cond.kind {
ExprKind::Binary(op @ Spanned { node: ast::BinOpKind::And, .. }, lhs, rhs)
if has_let_expr(cond) =>
{
let op = self.lower_binop(*op);
let lhs = self.lower_cond(lhs);
let rhs = self.lower_cond(rhs);
self.arena.alloc(self.expr(cond.span, hir::ExprKind::Binary(op, lhs, rhs)))
}
ExprKind::Let(..) => self.lower_expr(cond),
_ => {
let cond = self.lower_expr(cond);
let reason = DesugaringKind::CondTemporary;
let span_block = self.mark_span_with_reason(reason, cond.span, None);
self.expr_drop_temps(span_block, cond)
}
}
}
// We desugar: `'label: while $cond $body` into:
//
// ```
// 'label: loop {
// if { let _t = $cond; _t } {
// $body
// }
// else {
// break;
// }
// }
// ```
//
// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
// to preserve drop semantics since `while $cond { ... }` does not
// let temporaries live outside of `cond`.
fn lower_expr_while_in_loop_scope(
&mut self,
span: Span,
cond: &Expr,
body: &Block,
opt_label: Option<Label>,
) -> hir::ExprKind<'hir> {
let lowered_cond = self.with_loop_condition_scope(|t| t.lower_cond(cond));
let then = self.lower_block_expr(body);
let expr_break = self.expr_break(span);
let stmt_break = self.stmt_expr(span, expr_break);
let else_blk = self.block_all(span, arena_vec![self; stmt_break], None);
let else_expr = self.arena.alloc(self.expr_block(else_blk));
let if_kind = hir::ExprKind::If(lowered_cond, self.arena.alloc(then), Some(else_expr));
let if_expr = self.expr(span, if_kind);
let block = self.block_expr(self.arena.alloc(if_expr));
let span = self.lower_span(span.with_hi(cond.span.hi()));
let opt_label = self.lower_label(opt_label);
hir::ExprKind::Loop(block, opt_label, hir::LoopSource::While, span)
}
/// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_output(<expr>) }`,
/// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_output(()) }`
/// and save the block id to use it as a break target for desugaring of the `?` operator.
fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind<'hir> {
self.with_catch_scope(body.id, |this| {
let mut block = this.lower_block_noalloc(body, true);
// Final expression of the block (if present) or `()` with span at the end of block
let (try_span, tail_expr) = if let Some(expr) = block.expr.take() {
(
this.mark_span_with_reason(
DesugaringKind::TryBlock,
expr.span,
Some(this.allow_try_trait.clone()),
),
expr,
)
} else {
let try_span = this.mark_span_with_reason(
DesugaringKind::TryBlock,
this.tcx.sess.source_map().end_point(body.span),
Some(this.allow_try_trait.clone()),
);
(try_span, this.expr_unit(try_span))
};
let ok_wrapped_span =
this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
// `::std::ops::Try::from_output($tail_expr)`
block.expr = Some(this.wrap_in_try_constructor(
hir::LangItem::TryTraitFromOutput,
try_span,
tail_expr,
ok_wrapped_span,
));
hir::ExprKind::Block(this.arena.alloc(block), None)
})
}
fn wrap_in_try_constructor(
&mut self,
lang_item: hir::LangItem,
method_span: Span,
expr: &'hir hir::Expr<'hir>,
overall_span: Span,
) -> &'hir hir::Expr<'hir> {
let constructor = self.arena.alloc(self.expr_lang_item_path(method_span, lang_item));
self.expr_call(overall_span, constructor, std::slice::from_ref(expr))
}
fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
let pat = self.lower_pat(&arm.pat);
let guard = arm.guard.as_ref().map(|cond| self.lower_expr(cond));
let hir_id = self.next_id();
let span = self.lower_span(arm.span);
self.lower_attrs(hir_id, &arm.attrs);
let is_never_pattern = pat.is_never_pattern();
let body = if let Some(body) = &arm.body
&& !is_never_pattern
{
self.lower_expr(body)
} else {
// Either `body.is_none()` or `is_never_pattern` here.
if !is_never_pattern {
if self.tcx.features().never_patterns {
// If the feature is off we already emitted the error after parsing.
let suggestion = span.shrink_to_hi();
self.dcx().emit_err(MatchArmWithNoBody { span, suggestion });
}
} else if let Some(body) = &arm.body {
self.dcx().emit_err(NeverPatternWithBody { span: body.span });
} else if let Some(g) = &arm.guard {
self.dcx().emit_err(NeverPatternWithGuard { span: g.span });
}
// We add a fake `loop {}` arm body so that it typecks to `!`. The mir lowering of never
// patterns ensures this loop is not reachable.
let block = self.arena.alloc(hir::Block {
stmts: &[],
expr: None,
hir_id: self.next_id(),
rules: hir::BlockCheckMode::DefaultBlock,
span,
targeted_by_break: false,
});
self.arena.alloc(hir::Expr {
hir_id: self.next_id(),
kind: hir::ExprKind::Loop(block, None, hir::LoopSource::Loop, span),
span,
})
};
hir::Arm { hir_id, pat, guard, body, span }
}
/// Lower/desugar a coroutine construct.
///
/// In particular, this creates the correct async resume argument and `_task_context`.
///
/// This results in:
///
/// ```text
/// static move? |<_task_context?>| -> <return_ty> {
/// <body>
/// }
/// ```
pub(super) fn make_desugared_coroutine_expr(
&mut self,
capture_clause: CaptureBy,
closure_node_id: NodeId,
return_ty: Option<hir::FnRetTy<'hir>>,
fn_decl_span: Span,
span: Span,
desugaring_kind: hir::CoroutineDesugaring,
coroutine_source: hir::CoroutineSource,
body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
) -> hir::ExprKind<'hir> {
let closure_def_id = self.local_def_id(closure_node_id);
let coroutine_kind = hir::CoroutineKind::Desugared(desugaring_kind, coroutine_source);
// The `async` desugaring takes a resume argument and maintains a `task_context`,
// whereas a generator does not.
let (inputs, params, task_context): (&[_], &[_], _) = match desugaring_kind {
hir::CoroutineDesugaring::Async | hir::CoroutineDesugaring::AsyncGen => {
// Resume argument type: `ResumeTy`
let unstable_span = self.mark_span_with_reason(
DesugaringKind::Async,
self.lower_span(span),
Some(self.allow_gen_future.clone()),
);
let resume_ty = self.make_lang_item_qpath(hir::LangItem::ResumeTy, unstable_span);
let input_ty = hir::Ty {
hir_id: self.next_id(),
kind: hir::TyKind::Path(resume_ty),
span: unstable_span,
};
let inputs = arena_vec![self; input_ty];
// Lower the argument pattern/ident. The ident is used again in the `.await` lowering.
let (pat, task_context_hid) = self.pat_ident_binding_mode(
span,
Ident::with_dummy_span(sym::_task_context),
hir::BindingMode::MUT,
);
let param = hir::Param {
hir_id: self.next_id(),
pat,
ty_span: self.lower_span(span),
span: self.lower_span(span),
};
let params = arena_vec![self; param];
(inputs, params, Some(task_context_hid))
}
hir::CoroutineDesugaring::Gen => (&[], &[], None),
};
let output =
return_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span)));
let fn_decl = self.arena.alloc(hir::FnDecl {
inputs,
output,
c_variadic: false,
implicit_self: hir::ImplicitSelfKind::None,
lifetime_elision_allowed: false,
});
let body = self.with_def_id_parent(closure_def_id, move |this| {
this.lower_body(move |this| {
this.coroutine_kind = Some(coroutine_kind);
let old_ctx = this.task_context;
if task_context.is_some() {
this.task_context = task_context;
}
let res = body(this);
this.task_context = old_ctx;
(params, res)
})
});
// `static |<_task_context?>| -> <return_ty> { <body> }`:
hir::ExprKind::Closure(self.arena.alloc(hir::Closure {
def_id: closure_def_id,
binder: hir::ClosureBinder::Default,
capture_clause,
bound_generic_params: &[],
fn_decl,
body,
fn_decl_span: self.lower_span(fn_decl_span),
fn_arg_span: None,
kind: hir::ClosureKind::Coroutine(coroutine_kind),
constness: hir::Constness::NotConst,
}))
}
/// Forwards a possible `#[track_caller]` annotation from `outer_hir_id` to
/// `inner_hir_id` in case the `async_fn_track_caller` feature is enabled.
pub(super) fn maybe_forward_track_caller(
&mut self,
span: Span,
outer_hir_id: HirId,
inner_hir_id: HirId,
) {
if self.tcx.features().async_fn_track_caller
&& let Some(attrs) = self.attrs.get(&outer_hir_id.local_id)
&& attrs.into_iter().any(|attr| attr.has_name(sym::track_caller))
{
let unstable_span = self.mark_span_with_reason(
DesugaringKind::Async,
span,
Some(self.allow_gen_future.clone()),
);
self.lower_attrs(
inner_hir_id,
&[Attribute {
kind: AttrKind::Normal(ptr::P(NormalAttr::from_ident(Ident::new(
sym::track_caller,
span,
)))),
id: self.tcx.sess.psess.attr_id_generator.mk_attr_id(),
style: AttrStyle::Outer,
span: unstable_span,
}],
);
}
}
/// Desugar `<expr>.await` into:
/// ```ignore (pseudo-rust)
/// match ::std::future::IntoFuture::into_future(<expr>) {
/// mut __awaitee => loop {
/// match unsafe { ::std::future::Future::poll(
/// <::std::pin::Pin>::new_unchecked(&mut __awaitee),
/// ::std::future::get_context(task_context),
/// ) } {
/// ::std::task::Poll::Ready(result) => break result,
/// ::std::task::Poll::Pending => {}
/// }
/// task_context = yield ();
/// }
/// }
/// ```
fn lower_expr_await(&mut self, await_kw_span: Span, expr: &Expr) -> hir::ExprKind<'hir> {
let expr = self.arena.alloc(self.lower_expr_mut(expr));
self.make_lowered_await(await_kw_span, expr, FutureKind::Future)
}
/// Takes an expr that has already been lowered and generates a desugared await loop around it
fn make_lowered_await(
&mut self,
await_kw_span: Span,
expr: &'hir hir::Expr<'hir>,
await_kind: FutureKind,
) -> hir::ExprKind<'hir> {
let full_span = expr.span.to(await_kw_span);
let is_async_gen = match self.coroutine_kind {
Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)) => false,
Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::AsyncGen, _)) => true,
Some(hir::CoroutineKind::Coroutine(_))
| Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Gen, _))
| None => {
// Lower to a block `{ EXPR; <error> }` so that the awaited expr
// is not accidentally orphaned.
let stmt_id = self.next_id();
let expr_err = self.expr(
expr.span,
hir::ExprKind::Err(self.dcx().emit_err(AwaitOnlyInAsyncFnAndBlocks {
await_kw_span,
item_span: self.current_item,
})),
);
return hir::ExprKind::Block(
self.block_all(
expr.span,
arena_vec![self; hir::Stmt {
hir_id: stmt_id,
kind: hir::StmtKind::Semi(expr),
span: expr.span,
}],
Some(self.arena.alloc(expr_err)),
),
None,
);
}
};
let features = match await_kind {
FutureKind::Future => None,
FutureKind::AsyncIterator => Some(self.allow_for_await.clone()),
};
let span = self.mark_span_with_reason(DesugaringKind::Await, await_kw_span, features);
let gen_future_span = self.mark_span_with_reason(
DesugaringKind::Await,
full_span,
Some(self.allow_gen_future.clone()),
);
let expr_hir_id = expr.hir_id;
// Note that the name of this binding must not be changed to something else because
// debuggers and debugger extensions expect it to be called `__awaitee`. They use
// this name to identify what is being awaited by a suspended async functions.
let awaitee_ident = Ident::with_dummy_span(sym::__awaitee);
let (awaitee_pat, awaitee_pat_hid) =
self.pat_ident_binding_mode(gen_future_span, awaitee_ident, hir::BindingMode::MUT);
let task_context_ident = Ident::with_dummy_span(sym::_task_context);
// unsafe {
// ::std::future::Future::poll(
// ::std::pin::Pin::new_unchecked(&mut __awaitee),
// ::std::future::get_context(task_context),
// )
// }
let poll_expr = {
let awaitee = self.expr_ident(span, awaitee_ident, awaitee_pat_hid);
let ref_mut_awaitee = self.expr_mut_addr_of(span, awaitee);
let Some(task_context_hid) = self.task_context else {
unreachable!("use of `await` outside of an async context.");
};
let task_context = self.expr_ident_mut(span, task_context_ident, task_context_hid);
let new_unchecked = self.expr_call_lang_item_fn_mut(
span,
hir::LangItem::PinNewUnchecked,
arena_vec![self; ref_mut_awaitee],
);
let get_context = self.expr_call_lang_item_fn_mut(
gen_future_span,
hir::LangItem::GetContext,
arena_vec![self; task_context],
);
let call = match await_kind {
FutureKind::Future => self.expr_call_lang_item_fn(
span,
hir::LangItem::FuturePoll,
arena_vec![self; new_unchecked, get_context],
),
FutureKind::AsyncIterator => self.expr_call_lang_item_fn(
span,
hir::LangItem::AsyncIteratorPollNext,
arena_vec![self; new_unchecked, get_context],
),
};
self.arena.alloc(self.expr_unsafe(call))
};
// `::std::task::Poll::Ready(result) => break result`
let loop_node_id = self.next_node_id();
let loop_hir_id = self.lower_node_id(loop_node_id);
let ready_arm = {
let x_ident = Ident::with_dummy_span(sym::result);
let (x_pat, x_pat_hid) = self.pat_ident(gen_future_span, x_ident);
let x_expr = self.expr_ident(gen_future_span, x_ident, x_pat_hid);
let ready_field = self.single_pat_field(gen_future_span, x_pat);
let ready_pat = self.pat_lang_item_variant(span, hir::LangItem::PollReady, ready_field);
let break_x = self.with_loop_scope(loop_node_id, move |this| {
let expr_break =
hir::ExprKind::Break(this.lower_loop_destination(None), Some(x_expr));
this.arena.alloc(this.expr(gen_future_span, expr_break))
});
self.arm(ready_pat, break_x)
};
// `::std::task::Poll::Pending => {}`
let pending_arm = {
let pending_pat = self.pat_lang_item_variant(span, hir::LangItem::PollPending, &[]);
let empty_block = self.expr_block_empty(span);
self.arm(pending_pat, empty_block)
};
let inner_match_stmt = {
let match_expr = self.expr_match(
span,
poll_expr,
arena_vec![self; ready_arm, pending_arm],
hir::MatchSource::AwaitDesugar,
);
self.stmt_expr(span, match_expr)
};
// Depending on `async` of `async gen`:
// async - task_context = yield ();
// async gen - task_context = yield ASYNC_GEN_PENDING;
let yield_stmt = {
let yielded = if is_async_gen {
self.arena.alloc(self.expr_lang_item_path(span, hir::LangItem::AsyncGenPending))
} else {
self.expr_unit(span)
};
let yield_expr = self.expr(
span,
hir::ExprKind::Yield(yielded, hir::YieldSource::Await { expr: Some(expr_hir_id) }),
);
let yield_expr = self.arena.alloc(yield_expr);
let Some(task_context_hid) = self.task_context else {
unreachable!("use of `await` outside of an async context.");
};
let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
let assign =
self.expr(span, hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span)));
self.stmt_expr(span, assign)
};
let loop_block = self.block_all(span, arena_vec![self; inner_match_stmt, yield_stmt], None);
// loop { .. }
let loop_expr = self.arena.alloc(hir::Expr {
hir_id: loop_hir_id,
kind: hir::ExprKind::Loop(
loop_block,
None,
hir::LoopSource::Loop,
self.lower_span(span),
),
span: self.lower_span(span),
});
// mut __awaitee => loop { ... }
let awaitee_arm = self.arm(awaitee_pat, loop_expr);
// `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
let into_future_expr = match await_kind {
FutureKind::Future => self.expr_call_lang_item_fn(
span,
hir::LangItem::IntoFutureIntoFuture,
arena_vec![self; *expr],
),
// Not needed for `for await` because we expect to have already called
// `IntoAsyncIterator::into_async_iter` on it.
FutureKind::AsyncIterator => expr,
};
// match <into_future_expr> {
// mut __awaitee => loop { .. }