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Auto merge of #17174 - Kohei316:fix-infer-async-block-with-tail-retur…
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…n-expr, r=Veykril

Fix: infer type of async block with tail return expr

Fixes #17106
The `infer_async_block` method calls the `infer_block` method internally, which returns the never type without coercion when `tail_expr` is `None` and `ctx.diverges` is `Diverges::Always`.This is the reason for the bug in this issue.
https://github.com/rust-lang/rust-analyzer/blob/cfce2bb46da62950a8b70ddb0b2a12332da1b1e1/crates/hir-ty/src/infer/expr.rs#L1411-L1413

This PR solves the bug by adding a process to coerce after calling `infer_block` method.

This code passes all the tests, including tests I added for this isuue, however, I am not sure if this solution is right. I think that this solution is an ad hoc solution. So, I would appreciate to have your review.
I apologize if I'm off the mark, but `infer_async_block` method should be rewritten to share code with the process of infering type of `expr::Closure` instead of the `infer_block` method. That way it will be closer to the infer process of rustc.
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bors committed May 23, 2024
2 parents 68fe34a + 425ed6a commit 6e8646d
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18 changes: 17 additions & 1 deletion src/tools/rust-analyzer/crates/hir-ty/src/infer/expr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -933,8 +933,24 @@ impl InferenceContext<'_> {
let prev_ret_coercion =
mem::replace(&mut self.return_coercion, Some(CoerceMany::new(ret_ty.clone())));

// FIXME: We should handle async blocks like we handle closures
let expected = &Expectation::has_type(ret_ty);
let (_, inner_ty) = self.with_breakable_ctx(BreakableKind::Border, None, None, |this| {
this.infer_block(tgt_expr, *id, statements, *tail, None, &Expectation::has_type(ret_ty))
let ty = this.infer_block(tgt_expr, *id, statements, *tail, None, expected);
if let Some(target) = expected.only_has_type(&mut this.table) {
match this.coerce(Some(tgt_expr), &ty, &target) {
Ok(res) => res,
Err(_) => {
this.result.type_mismatches.insert(
tgt_expr.into(),
TypeMismatch { expected: target.clone(), actual: ty.clone() },
);
target
}
}
} else {
ty
}
});

self.diverges = prev_diverges;
Expand Down
26 changes: 26 additions & 0 deletions src/tools/rust-analyzer/crates/ide/src/inlay_hints/bind_pat.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1120,4 +1120,30 @@ fn test() {
"#,
);
}

#[test]
fn type_hints_async_block() {
check_types(
r#"
//- minicore: future
async fn main() {
let _x = async { 8_i32 };
//^^ impl Future<Output = i32>
}"#,
);
}

#[test]
fn type_hints_async_block_with_tail_return_exp() {
check_types(
r#"
//- minicore: future
async fn main() {
let _x = async {
//^^ impl Future<Output = i32>
return 8_i32;
};
}"#,
);
}
}

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