compilationclangabstract-syntax-tree

Synthesize a declaration from a Qualified type (QualType) in Clang

When using the Clang C++ API, assuming that I have a QualType, how would I synthesize a variable declaration of that particular QualType, this is just to interrogate properties of that declaration then, I don't plan to inject this anywhere.

Went through the particular hierarchy under clang::Decl but could not really find a clue there...

Solution

  • If you want to synthesize a variable declaration from a QualType, you can use ASTContext::getTrivialTypeSourceInfo to create a TypeSourceInfo for the QualType, then construct a VarDecl using VarDecl::Create with the TypeSourceInfo and the appropriate declaration context.

    One example fragment doing something like this in the Clang sources is in SemaTemplateDeductionGuide.cpp:

          auto *TSI = SemaRef.Context.getTrivialTypeSourceInfo(T, Loc);
      if (NestedPattern)
        TSI = SemaRef.SubstType(TSI, OuterInstantiationArgs, Loc,
                                DeclarationName());
      if (!TSI)
        return nullptr;

      ParmVarDecl *NewParam =
          ParmVarDecl::Create(SemaRef.Context, DC, Loc, Loc, nullptr,
                              TSI->getType(), TSI, SC_None, nullptr);