[clang] [Clang] Fix name lookup for dependent bases (PR #114978)

[Matheus Izvekov via cfe-commits]

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@@ -169,14 +169,18 @@ bool CXXBasePaths::lookupInBases(ASTContext &Context,
     // Find the record of the base class subobjects for this type.
     QualType BaseType =
         Context.getCanonicalType(BaseSpec.getType()).getUnqualifiedType();
+    bool isCurrentInstantiation = false;
+    if (auto *TST = BaseSpec.getType()->getAs<TemplateSpecializationType>())
+      isCurrentInstantiation = TST->isCurrentInstantiation();
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mizvekov wrote:

This relies on a TemplateSpecializationType which is a type sugar to make this determination, and type sugar could be lost, for example with template instantiation.

Might be worth double checking and adding a test case where the base type is formed from instantiation.

This test would be equivalent to checking if the type is canonically an InjectedClassNameType:
```suggestion
    bool isCurrentInstantiation = isa<InjectedClassNameType>(BaseType);
```
This is reliable as it only depends on the canonical type.

https://github.com/llvm/llvm-project/pull/114978