[release/9.0] Fix a case in MethodImpl overriding which wasn't handled as expected in ilc.exe for native aot#107409
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jeffschwMSFT merged 6 commits intorelease/9.0from Sep 5, 2024
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…in ilc.exe for native aot - This was causing real C# applications to fail to behave correctly on NativeAOT builds - Enable testing for covariant byref returns on nativeaot (split testing up so that the tests do not expect TypeLoadException, which NativeAOT doesn't reliably generate) - Fix implementation of SynthesizedPgoIncompatible project file flag for test script generation - Put copy of attributetesting.il test into the managed type system unit test suite - Add regression test of issue noted in #96175 into managed type system unit test suite - Update workflow documentation to include a better path to finding details on how to run CoreCLR and Libraries tests for Native AOT Fixes #96175
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approved. please get a code review. we can merge when ready
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Backport of #106716 to release/9.0
/cc @davidwrighton
Customer Impact
This bug was found when people internally and externally began using the covariant returns feature which makes use of MethodImpl metadata records for overrides on virtual methods in ways that are not done with the C# compiler under any other circumstance.
Regression
This is not a regression, but merely a newly important bug, which has become important as customers have started using covariant methods.
Testing
The existing testbed for covariant returns would have caught this issue, but it was not supported on NativeAOT, as it mingled tests which tested the
TypeLoadExceptionthrowing paths and the normal execution paths. This fix was tested by changing the splitting the tests into tests which throw and tests which test correct behavior. In addition, a unit test specific to this issue was added to the type system unit test suite, and the most critical of the newly enabled tests was added to the type system unit test suite.Risk
Medium. The virtual method resolution algorithm in the managed type system is notoriously complex, and used in crossgen2 as well as native aot. The fix taken was minimal, and did not attempt to address all possible issues in MethodImpl resolution, but instead was limited to ensuring that the code patterns generated by the C# compiler worked correctly. The medium level of risk is what caused the fairly extensive test effort put in as part of this change.