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Auto merge of #119061 - compiler-errors:async-gen-abi, r=wesleywiser

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Desugar `yield` in `async gen` correctly, ensure `gen` always returns unit

1. Ensure `async gen` blocks desugar `yield $expr` to `task_context = yield async_gen_ready($expr)`. Previously we were not assigning the `task_context` correctly, meaning that `yield` expressions in async generators returned type `ResumeTy` instead of `()`, and that we were not storing the `task_context`  (which is probably unsound if we were reading the old task-context which has an invalidated borrow or something...)
2. Ensure that all `(async?) gen` blocks and `(async?) gen` fns return unit. Previously we were only checking this for `gen fn`, meaning that `gen {}` and `async gen {}` and `async gen fn` were allowed to return values that weren't unit. This is why #119058 was an ICE rather than an E0308.

Fixes #119058.
This commit is contained in:
bors 2023-12-19 00:42:50 +00:00
commit 59096cdad0
6 changed files with 125 additions and 23 deletions
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52
compiler/rustc_ast_lowering/src/expr.rs
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@ -917,12 +917,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
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 task_context = if let Some(task_context_hid) = self.task_context {
self.expr_ident_mut(span, task_context_ident, task_context_hid)
} else {
// Use of `await` outside of an async context, we cannot use `task_context` here.
self.expr_err(span, self.tcx.sess.span_delayed_bug(span, "no task_context hir id"))
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,
@ -991,16 +992,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
);
let yield_expr = self.arena.alloc(yield_expr);
if let Some(task_context_hid) = self.task_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)
} else {
// Use of `await` outside of an async context. Return `yield_expr` so that we can
// proceed with type checking.
self.stmt(span, hir::StmtKind::Semi(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);
@ -1635,19 +1634,32 @@ impl<'hir> LoweringContext<'_, 'hir> {
}
};
let mut yielded =
let yielded =
opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
if is_async_gen {
// yield async_gen_ready($expr);
yielded = self.expr_call_lang_item_fn(
// `yield $expr` is transformed into `task_context = yield async_gen_ready($expr)`.
// This ensures that we store our resumed `ResumeContext` correctly, and also that
// the apparent value of the `yield` expression is `()`.
let wrapped_yielded = self.expr_call_lang_item_fn(
span,
hir::LangItem::AsyncGenReady,
std::slice::from_ref(yielded),
);
}
let yield_expr = self.arena.alloc(
self.expr(span, hir::ExprKind::Yield(wrapped_yielded, hir::YieldSource::Yield)),
);
hir::ExprKind::Yield(yielded, hir::YieldSource::Yield)
let Some(task_context_hid) = self.task_context else {
unreachable!("use of `await` outside of an async context.");
};
let task_context_ident = Ident::with_dummy_span(sym::_task_context);
let lhs = self.expr_ident(span, task_context_ident, task_context_hid);
hir::ExprKind::Assign(lhs, yield_expr, self.lower_span(span))
} else {
hir::ExprKind::Yield(yielded, hir::YieldSource::Yield)
}
}
/// Desugar `ExprForLoop` from: `[opt_ident]: for <pat> in <head> <body>` into: