[Sema] Do not diagnose contextual type mismatches for malformed key path expressions

[LucianoPAlmeida]

This just skips contextual type diagnostic for malformed key path expressions, because this leads at the very least, extra not good diagnostics. What do you think?

[xedin]

If it's already determined and diagnosed that that key path expression is invalid why not just return Type() while generating constraints for it and avoid running solver for invalid AST?

[LucianoPAlmeida]

If it's already determined and diagnosed that that key path expression is invalid why not just return Type() while generating constraints for it and avoid running solver for invalid AST?

Humm, haven't thought about that ... makes sense, let's try that! Thanks, @xedin :)

[LucianoPAlmeida]

If it's already determined and diagnosed that that key path expression is invalid why not just return Type() while generating constraints for it and avoid running solver for invalid AST?

Seems like doing this, affects code completion in a way, I'm still looking into this and not familiar with code completion ... but seems like it needs to type check \Root to provide completion

[LucianoPAlmeida]

If it's already determined and diagnosed that that key path expression is invalid why not just return Type() while generating constraints for it and avoid running solver for invalid AST?

@xedin
Seems like it still needs to type check in order to provide code completion in situations like:
https://github.com/apple/swift/blob/e35d2d355f54052c75c98d03a0c038d4f576b9f9/test/IDE/complete_swift_key_path.swift#L47

So should we keep this approach, or maybe run the solver only if it is type checking for code completion using SuppressDiagnostics flag otherwise return Type() in CSGen? Not really sure about this last one ...

[xedin]

If code completion relies on this behavior then, LGTM! :) Let's name that method {is, has}SingleInvalidComponent though for clarify.

[xedin]

@LucianoPAlmeida before you merge please add one more test case like let _: KeyPath<A, C> = \A to make sure that contextual failure is still recorded.

[LucianoPAlmeida]

@xedin

@LucianoPAlmeida before you merge please add one more test case like let _: KeyPath<A, C> = \A to make sure that contextual failure is still recorded.

Just added, together with a minor adjustments

[LucianoPAlmeida]

@swift-ci please smoke test

[LucianoPAlmeida]

@swift-ci Please smoke test Windows platform

[xedin]

Looks good! Naming could use some more though.

[LucianoPAlmeida]

@swift-ci Please smoke test

[LucianoPAlmeida]

@xedin Naming and comments fixed :) Just making sure if there's anything else or we could land this?

[xedin]