Backport "Properly handle SAM types with wildcards" to LTS #19112
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Previously there were two separate checks for contextual function types as result types: one in SAMType for non-PartialFunctions and one in ExpandSAM for PartialFunctions. This is replaced by a single check (with a detailed error message like we already had for PartialFunctions). [Cherry-picked 18f90d9][modified]
[Cherry-picked 89735d0][modified] When typing a closure with an expected type containing a wildcard, the closure type itself should not contain wildcards, because it might be expanded to an anonymous class extending the closure type (this happens on non-JVM backends as well as on the JVM itself in situations where a SAM trait does not compile down to a SAM interface). We were already approximating wildcards in the method type returned by the SAMType extractor, but to fix this issue we had to change the extractor to perform the approximation on the expected type itself to generate a valid parent type. The SAMType extractor now returns both the approximated parent type and the type of the method itself. The wildcard approximation analysis relies on a new `VarianceMap` opaque type extracted from Inferencing#variances. Fixes #16065. Fixes #18096.
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No regressions detected in the community build up to lts-16941. |
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Backports #18201 to the LTS branch.
PR submitted by the release tooling.