Generate clauses for placeholder associated types

[lowr]

Currently, we don't generate clauses for placeholder associated types (TyKind::AssociatedType) except for some FromEnvs. This leads to NoSolution for goals like (IntoIterator::IntoIter)<Opaque>: Iterator where Opaque = impl IntoIterator.

For every associated type in a trait definition

trait Foo {
    type Assoc<'a, T>: Bar<U = Ty> where WC;
}

chalk with this patch generates

forall<Self, 'a, T> {
    Implemented((Foo::Assoc<'a, T>)<Self>: Bar) :- WC.
    AliasEq(<<(Foo::Assoc<'a, T>)<Self>> as Bar>::U = Ty) :- WC.
}

To be honest, I'm not entirely sure if AssociatedTyDatum::to_program_clauses() is the best place to generate those clauses in, but analogous clauses for placeholder opaque types are generated in OpaqueTyDatum::to_program_clauses(), which I modeled after.

Spotted in rust-lang/rust-analyzer#14680.

[jackh726]

@bors r+

[bors]

📌 Commit 5ffee10 has been approved by jackh726

It is now in the queue for this repository.

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout fix/clauses-for-assoc-placeholders (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self fix/clauses-for-assoc-placeholders --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging tests/test/projection.rs
CONFLICT (content): Merge conflict in tests/test/projection.rs
Auto-merging chalk-solve/src/clauses.rs
Automatic merge failed; fix conflicts and then commit the result.

[bors]

☔ The latest upstream changes (presumably #780) made this pull request unmergeable. Please resolve the merge conflicts.

[lowr]

I'll rebase this one after #792 lands as it's likely to cause another conflict.

[jackh726]

@bors r+

[bors]

📌 Commit 52b52cf has been approved by jackh726

It is now in the queue for this repository.

[bors]

⌛ Testing commit 52b52cf with merge e856e21...

[bors]

☀️ Test successful - checks-actions
Approved by: jackh726
Pushing e856e21 to master...