Seal internal private types analyzer

[NewellClark]

Fix #49944.
As per the design meeting, this analyzer ignores InternalsVisibleToAttributes.
I've implemented a fixer, but due to this issue the code fixer won't show up in the IDE because it is reported at the end of compilation.

I've also found violations in dotnet/runtime (violations in src/tasks, violations in libs).

[codecov]

Codecov Report

Merging #5594 (afccbbc) into main (334bb06) will decrease coverage by 0.00%.
The diff coverage is 91.68%.

@@            Coverage Diff             @@
##             main    #5594      +/-   ##
==========================================
- Coverage   96.04%   96.03%   -0.01%     
==========================================
  Files        1323     1326       +3     
  Lines      305370   305731     +361     
  Branches     9687     9693       +6     
==========================================
+ Hits       293294   293621     +327     
- Misses       9739     9774      +35     
+ Partials     2337     2336       -1     

[mavasani]

As per the design meeting, this analyzer ignores InternalsVisibleToAttributes.

This means the logic will differ from CA1812 analyzer, which skips compilations which have IVT. I presume this was considered in the design meeting though.

roslyn-analyzers/src/NetAnalyzers/Core/Microsoft.CodeQuality.Analyzers/Maintainability/AvoidUninstantiatedInternalClasses.cs

Lines 53 to 65 in e52a3f1

	// If the assembly being built by this compilation exposes its internals to
	// any other assembly, don't report any "uninstantiated internal class" errors.
	// If we were to report an error for an internal type that is not instantiated
	// by this assembly, and then it turned out that the friend assembly did
	// instantiate the type, that would be a false positive. We've decided it's
	// better to have false negatives (which would happen if the type were *not*
	// instantiated by any friend assembly, but we didn't report the issue) than
	// to have false positives.
	var internalsVisibleToAttributeSymbol = wellKnownTypeProvider.GetOrCreateTypeByMetadataName(WellKnownTypeNames.SystemRuntimeCompilerServicesInternalsVisibleToAttribute);
	if (compilation.Assembly.HasAttribute(internalsVisibleToAttributeSymbol))
	{
	return;
	}

[mavasani]

Overall LGTM.

Note that the code fixer is never going to show up in VS as this is a compilation end diagnostic. It is still useful to retain it so a fix all can be applied from command line tooling, such as AnalyzerRunner or dotnet-format. In future, if we add some incremental analysis API such that compilation end analyzers and their code fixes can be enabled in the IDE, hopefully we will get the code fix to show up in VS.

Also calling out that compilation end diagnostics are essentially build-only diagnostics, which will only show up on build if the user bumps the severity to a warning or sets AnalysisMode to AllEnabledByDefault. They will only show up in live/intellisense diagnostics if full solution analysis mode is enabled. So basically, this will be disabled by default analyzer.

[mavasani]

@NewellClark Can you please resolve the merge conflicts?

[pranavkm]

@mavasani is this good to merge?

[Evangelink]

It would be nice to add the test @Youssef1313 was mentioning regarding partial classes with some part auto-generated.

[mavasani]

@pranavkm We need to resolve merge conflicts and respond to review feedback from @Youssef1313 and @Evangelink. This should be very close to merge.

[meziantou]

@ericstj ask me to post my remark here

I think the analyzer should exclude classes declared as [ComImport]/[CoClass] from the analysis as the fix may break the compilation:

using System.Runtime.InteropServices;

_ = (IFileSaveDialog)new FileSaveDialogRCW(); // If FileSaveDialogRCW is sealed: error CS0030: Cannot convert type 'FileSaveDialogRCW' to 'IFileSaveDialog'

[ComImport]
[Guid("C0B4E2F3-BA21-4773-8DBA-335EC946EB8B")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
[CoClass(typeof(FileSaveDialogRCW))]
internal interface IFileSaveDialog
{
}

[ComImport]
[ClassInterface(ClassInterfaceType.None)]
[Guid("C0B4E2F3-BA21-4773-8DBA-335EC946EB8B")]
class FileSaveDialogRCW // 👈 sealed is not valid here because of `(IFileSaveDialog)new NativeFileSaveDialog()`
{
}

[stephentoub]

@NewellClark, I'd like to see this merged. Are you still able to work on it? If not, I'll take it over. Thanks for your work on it!