Bug shown by out-of-line definition of template method.

Clang Frontend
#1

Hello.

The following C++ code triggers a bug in clang:

#2

Hello.

The following C++ code triggers a bug in clang:

===================================================
template <typename T>
struct Outer {
  template <typename U>
  struct Inner {};

  template <typename U>
  typename Outer<T>::template Inner<U>
  foo(typename Outer<T>::template Inner<U>);
};

template <typename T>
template <typename U>
typename Outer<T>::template Inner<U>
Outer<T>::foo(typename Outer<T>::template Inner<U>) {
  return Inner<U>();
}

# llvm/Debug/bin/clang++ -fsyntax-only bug.cc
bug.cc:14:11: error: out-of-line definition of 'foo' does not match any
      declaration in 'struct Outer'
Outer<T>::foo(typename Outer<T>::template Inner<U>) {
~~~~~~~~~~^
1 diagnostic generated.

I tried to trace it to its origin: the wrong error message is generated
in a call to method

  bool Sema::IsOverload(FunctionDecl *New, FunctionDecl *Old);

namely, in the very last of the following tests:

  if (NewTemplate &&
(!TemplateParameterListsAreEqual(NewTemplate->getTemplateParameters(),
                                 OldTemplate->getTemplateParameters(),
                                 false, TPL_TemplateMatch) ||
      OldType->getResultType() != NewType->getResultType()))
    return true;

The result types of the out-of-line method definition type (NewType) and
the method declaration type (OldType) do not match:

declaration result type: TemplateSpecializationType
Inner<type-parameter-1-0>

definition result type: TypenameType
typename Outer<type-parameter-0-0>::Inner<type-parameter-1-0>

In contrast, parameter types do match, as they are both normalized to
Inner<type-parameter-1-0>.

This instance of the bug will disappear if the result type of the method
definition is normalized before comparision ... but honestly I am not
sure at all regarding how to perform such a normalization (is it enough
to query TemplateType::getTemplateId() ?) and whether or not this is the
right place to do it.

Sema::RebuildTypeInCurrentInstantiation is supposed to perform this normalization, because we can't actually get the types right until we know that we're in the scope of Outer<T> (which happens after we've parsed the return type). Since this is probably a bug in that normalization, it's best if I address it, because it requires fairly deep knowledge of the type and template systems to get right.

Anyway, I hope that the observations above are useful for clang experts.

Very useful, thank you! I've filed this bug here:

  http://llvm.org/bugs/show_bug.cgi?id=6268

and will address it when I can.

  - Doug