Fix Issue 20692 - Nested alias declarations and getMember trait can c…

[BorisCarvajal]

…rash dmd

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20692	normal	Nested alias declarations and getMember trait can crash dmd

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#10952"

[RazvanN7]

Can you please offer an explanation describing the problem and explaining the fix? Honestly, I would expect that the provided test case fails with a "forward reference" error, since dmd isn't able to partially analyze structs

[BorisCarvajal]

Indeed that could be a possible outcome of compilation if dmd were not able to resolve the symbol, and maybe dmd should give up on the first analyzing pass on the function.
But in this case dmd can really resolve the alias in the second recursive try on the function gun.

Let me remember the changes:

• In the first inspection of gun(), the symbol can't be resolved in the first part of aliasSemantic() code and then lies the first problem, it calls to toDsymbol but it's not defined for TypeTraits so it returns null for everything, given the fact that TypeTraits can contain types or symbols I naturally put one definition there.
• Now comes a TypeTraits typeSemantic call with the second triggered bug, there was a scope flag manipulation code in aliasSemantic that removed SCOPE.alias_ from the input scope on exit not taking care if it already had that flag set, somehow this function is called with the same previous scope but without the alias_ flag and if the trait resolves to a symbol not within an alias scope it will fail with an error.

Edit: I've forgotten if the point one (the problematic toDsymbol call) strictly happens in AliasDeclaration.toAlias or aliasSemantic.