DllImportGenerator.UnitTests failure: The type or namespace name 'DllImportAttribute' could not be found

[sbomer]

Rolling build failure, logs on net7.0-OSX-Release-x64-CoreCLR_release-OSX.1014.Amd64.Open.

DllImportGenerator.UnitTests.Diagnostics.TargetFrameworkNotSupported_NoGeneratedDllImport_NoDiagnostic(targetFramework: Core) [FAIL]
      Assert.Empty() Failure
      Expected: <empty>
      Actual:   [(5,6): error CS0246: The type or namespace name 'DllImportAttribute' could not be found (are you missing a using directive or an assembly reference?), (5,6): error CS0246: The type or namespace name 'DllImport' could not be found (are you missing a using directive or an assembly reference?), (2,1): hidden CS8019: Unnecessary using directive.]
      Stack Trace:
        /_/src/libraries/System.Runtime.InteropServices/tests/DllImportGenerator.UnitTests/Diagnostics.cs(67,0): at DllImportGenerator.UnitTests.Diagnostics.TargetFrameworkNotSupported_NoGeneratedDllImport_NoDiagnostic(TestTargetFramework targetFramework)
        --- End of stack trace from previous location ---

This failure shows up in:

• DllImportGenerator.UnitTests.Diagnostics.TargetFrameworkNotSupported_NoDiagnostic
• DllImportGenerator.UnitTests.Diagnostics.TargetFrameworkNotSupported_NoGeneratedDllImport_NoDiagnostic
• DllImportGenerator.UnitTests.Compiles.ValidateSnippetsFallbackForwarder

The failure only shows up on OSX so far. This appears to be a new failure mode - I am seeing the first occurrence in the above pipeline run which has these new commits: bc6d349...4a19a49. But none of those commits look related to me so it may just be nondeterministic. One of these tests previously had similar unusual failures on OSX: #62467 (error CS0518: Predefined type 'System.Object' is not defined or imported, etc.).

/cc @AaronRobinsonMSFT

Build	Kind	Start Time
1582910	Rolling	2022-31-01

[AaronRobinsonMSFT]

@elinor-fung or @jkoritzinsky Did we change any failure cases where we would not find a type?

[jkoritzinsky]

No, we didn't. I think this is another sign of the GC Hole that we've been seeing pop up here and there. I think this has the same root issue as #62467.

[AaronRobinsonMSFT]

I believe this was fixed in #69106.