Attempt to normalize `FnDef` signature in `InferCtxt::cmp` by compiler-errors ·...
source link: https://github.com/rust-lang/rust/pull/100473
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Stashes a normalization callback in InferCtxt so that the signature we get from tcx.fn_sig(..).subst(..) in InferCtxt::cmp can be properly normalized, since we cannot expect for it to have normalized types since it comes straight from astconv.
This is kind of a hack, but I will say that @jyn514 found the fact that we present unnormalized types to be very confusing in real life code, and I agree with that feeling. Though altogether I am still a bit unsure about whether this PR is worth the effort, so I'm open to alternatives and/or just closing it outright.
On the other hand, this isn't a ridiculously heavy implementation anyways -- it's less than a hundred lines of changes, and half of that is just miscellaneous cleanup.
This is stacked onto #100471 which is basically unrelated, and it can be rebased off of that when that lands or if needed.
The code:
trait Foo { type Bar; }
impl<T> Foo for T {
type Bar = i32;
}
fn foo<T>(_: <T as Foo>::Bar) {}
fn needs_i32_ref_fn(f: fn(&'static i32)) {}
fn main() {
needs_i32_ref_fn(foo::<()>);
}Before:
= note: expected fn pointer `fn(&'static i32)`
found fn item `fn(<() as Foo>::Bar) {foo::<()>}`
After:
= note: expected fn pointer `fn(&'static i32)`
found fn item `fn(i32) {foo::<()>}`
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