I think it'd be better to add an `IsExplicit` to the AST. We can get this info directly from Clang which should be more reliable, see: http://clang.llvm.org/doxygen/classclang_1_1CXXConstructorDecl.html#a953d7d78b3eb58de1938396c52989806

If you're not sure how to do this I can help you.