fix: resolve Self type references in delegate method assist

[rmehri01]

This PR makes the delegate method assist resolve any Self type references in the parameters or return type. It also works across macros such as the uint_impl! macro used for saturating_mul in the issue example.

Closes #14485

[Veykril]

Looking at the assist, I'm surprised we aren't using the PathTransform yet to fix up paths. We definitely should do that here instead (and then add support for substituting Self appropriately). Not sure how simple that is though.

[rmehri01]

Yeah that sounds like a good idea, I could give it a try! PathTransform expects a SemanticsScope for the target scope though, so is there a way to get that with a macro in the way? Like in this example, since ctx.sema.scope won't work:

macro_rules! test_method {
    () => {
        fn test(self) -> Self {
            self
        }
    };
}

struct Bar;

impl Bar {
    test_method!();
}

struct Foo {
    bar: $0Bar,
}

[Veykril]

Why wouldn't it work there? We can take a scope from a macro expansion's node just fine

[rmehri01]

Ah I was running into an issue where it said the lookup failed in this instance of Semantics but I added sema.parse_or_expand, which seems to update the cache and gets it to work!

I added the change to PathTransform to change Self now but I'm not sure if its the right way to do it, seems to at least pass the tests I had before.

[Veykril]

Suggested change

	let method_source = match method.source(ctx.db()) {
	let method_source = match ctx.sema.source(method) {

We can do this instead of the extra parse_or_expand, this will do the caching for us then

[Veykril]

Suggested change

	PathTransform::generic_transformation(
	&ctx.sema.scope(strukt.syntax()).unwrap(),
	&ctx.sema.scope(method_source.syntax()).unwrap(),
	)
	.apply(f.syntax());
	if let Some((target, source)) =
	ctx.sema.scope(strukt.syntax()).zip(ctx.sema.scope(method_source.syntax()))
	{
	PathTransform::generic_transformation(&target, &source).apply(f.syntax());
	}

The unwraps shouldn't really be possible to hit here, but we are trying to not use unwraps in assist code if possible.

[rmehri01]

Ah okay, sorry about that!

[Veykril]

We probably wanna prefer keeping Self if it does not need to be replaced. So a check if the source and target scopes have the same Self (and in that case, skip this transformation here entirely). We can give Ctx a new bool field for that and set it accordingly in build_ctx by giving SemanticsScope a function like fn has_same_self_type(&self, other: &SemanticsScope<'_>) -> bool which just checks if the top ImplDefScopes of each scope's resolver has the same def in them.

[rmehri01]

Oh yeah good catch, thanks :)

[Veykril]

Thanks!
@bors r+

[bors]

📌 Commit d8f0a9d has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit d8f0a9d with merge fbe39bb...

[bors]

💔 Test failed - checks-actions

[Veykril]

rebased
@bors r+

[bors]

📌 Commit 7e768cb has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7e768cb with merge 6bbb2ac...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing 6bbb2ac to master...