[5.1] [ConstraintSystem] Fix crash on function conversion reliant on conditional conformance

[theblixguy]

This PR fixes a compiler crasher related to a function conversion reliant on conditional conformance. Example:

protocol P {}
struct S<T> {}
extension S : P where T : P {}

func foo(_ fn: (S<String>) -> Void) {}
func bar(_ fn: (P) -> Void) {
  foo(fn)
}

Resolves SR-10992.

---

Cherry pick of #25721.

[theblixguy]

cc @xedin

[xedin]

@theblixguy Could you please squash everything into a single commit?

[theblixguy]

@xedin Done!

[xedin]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - f71921c295a585ef26c93ad0ce5b7d31d84343d7

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f71921c295a585ef26c93ad0ce5b7d31d84343d7

[xedin]

@theblixguy Looks like there are 2 tests which trigger exactly the same assert now this is trying to fix, bad squash? :)

[theblixguy]

Oh no! I’ll fix this in a moment.

[theblixguy]

Wait this has the same changes as the other PR 🤔

[xedin]

Maybe the difference is that 5.1 doesn't have all of the changes that master has.

[xedin]

But it kind of seems unlikely in this case, because assert in old getConstraintLocator should effectively be noop now for the case when summary flags is pre-computed, maybe something else is going on here.

[theblixguy]

It seems like there are still some uses of summaryFlags=0 left on this branch.

[theblixguy]

@xedin should be fixed now.

[xedin]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f76db4b

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - f76db4b

[theblixguy]

Hmm getting an unrelated assertion now:

18:57:41 swift: /home/buildnode/jenkins/workspace/swift-PR-Linux/branch-swift-5.1-branch/swift/lib/Sema/CSDiagnostics.cpp:220: swift::ValueDecl *swift::constraints::RequirementFailure::getDeclRef() const: Assertion `isa(AE->getFn()) || isa(AE->getFn())' failed.

[theblixguy]

@hamishknight seems like you were the last person who touched getDeclRef in commit 894a1e5 (PR #24826) and got rid of that assertion. I think we need your PR changes in the 5.1 branch as well.

I can either cherry-pick your commit into this branch or you can open a new PR and once your changes have been merged, we can re-run the CI to verify if this issue is fixed.

[xedin]

@theblixguy We need to figure out how to reduce the scope of the changes required, otherwise it wouldn't be able to land in 5.1

[theblixguy]

Hmm Hamish’s PR is pretty small and fixes two bugs in the process. Let me try adjusting getDeclRef only and see if the tests pass locally on my machine.

[xedin]

Alright, I'll try to look at his PR again tonight and get it in to 5.1

[theblixguy]

Sounds good!

[xedin]

@theblixguy looks like you'd have to resolve merge conflict because I can re-run CI.

[xedin]

@swift-ci please test

[theblixguy]

Sorry I messed up when fixing the merge conflict! Could you re run the CI? Thank you!

[xedin]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - e45732fd66ea65e2dedebae9213e97c88f8716e1

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - e45732fd66ea65e2dedebae9213e97c88f8716e1

[theblixguy]

Nice it seems like @hamishknight’s PR solved the problem 🎉