[ASTImporter] Set the described template if not set

[martong]

Summary

During the addition of an injected class type to a record it may happen
that a CXXRecordDecl in the redecl chain does not have a described
template set and this caused an assert in LLDB.

[shafik]

Can you add a test?

[a_sidorin]

Hello Gabor,

This looks good, but as Shafik mentioned, adding a test would be nice.

[shafik]

@martong Unfortunately this causes a regression on one of the lldb tests TestDataFormatterLibcxxVector.py e.g.

lldb-dotest -p TestDataFormatterLibcxxVector.py -t -G gmodules --no-multiprocess

So this is specific to modules. If you can't reproduce this I can provide a back-trace.

[martong]

@shafik Ok, I'll take a look into the regression soon. What are exactly gmodules? Is it macOS only? Do you have a description or some docs about it?

[shafik]

I don't believe it is directly related to modules but that it just triggers the issue because it may be bringing in more. You can find a description here https://clang.llvm.org/docs/CommandGuide/clang.html#cmdoption-g and @aprantl pointed me to this talk if you want to even more http://llvm.org/devmtg/2015-10/#talk19

[shafik]

@martong have you had a chance to look at this some more? We ran into another problem that this fixes partially. Can I help in any way?

[martong]

@martong have you had a chance to look at this some more? We ran into another problem that this fixes partially.

I didn't have time to deal with this yet (these days we are preparing an internal release and that took away my time).

Can I help in any way?

I think the only thing missing is to have a test. You mentioned previously that you could help with that and I would appreciate all your help. I think a test with clang-import-test would be just great.

lib/AST/ASTImporter.cpp

if (ClassTemplateDecl *FromDescribed =
             break;
           }
         }
         // Create an injected type for the whole redecl chain.
         SmallVector<Decl *, 2> Redecls =
             getCanonicalForwardRedeclChain(D2CXX);
         for (auto *R : Redecls) {
           auto *RI = cast<CXXRecordDecl>(R);
+          // Existing Decl in the chain might not have the described
+          // template set, so we set it now.
+          RI->setDescribedClassTemplate(ToDescribed);
           RI->setTypeForDecl(nullptr);
           // Below we create a new injected type and assign that to the
           // canonical decl, subsequent declarations in the chain will reuse
           // that type.
           Importer.getToContext().getInjectedClassNameType(
               RI, ToDescribed->getInjectedClassNameSpecialization());
         }
         // Set the new type for the previous injected decl too.