https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89947
Bug ID: 89947
Summary: Resolution of base classes fail for some automatic
types in template struct functions
Product: gcc
Version: 8.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: paolo at luccalug dot it
Target Milestone: ---
Created attachment 46081
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46081&action=edit
A minimal testcase
I'm using G++ 8.2.1 installed with the Arch Linux package `gcc
8.2.1+20181127-1`.
```
$ g++ -v
g++ (GCC) 8.2.1 20181127
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
```
A minimal source file that triggers the problem is the following:
```
namespace ns {
struct A { void f(){} };
}
template<typename C> struct B { void f(){} };
struct C : public ns::A, B<C> {};
template<typename T> struct X { // NOTE: no error if X were not a template
C getC() { return C(); } // NOTE: no error if `getC` were outside of
this class
void f() {
// NOTE: no error if we're running this code from outside of
this class: `x.getC().A...`
getC().A::f(); // ‘A’ has not been declared
auto c4 = getC(); c4.A::f(); // ‘A’ has not been declared
decltype(getC()) c5 = getC(); c5.A::f(); // ‘A’ has not been
declared
C c6 = getC(); c6.A::f(); // this one works
getC().B::f(); // ‘template<class C> struct B’ used without
template parameters
auto c1 = getC(); c1.B::f(); // ‘template<class C> struct B’
used without template parameters
decltype(getC()) c2 = getC(); c1.B::f(); // ‘template<class C>
struct B’ used without template parameters
C c3 = getC(); c3.B::f(); // this one works
}
};
int main() {
X<void> x;
x.f();
return 0;
}
```
G++ fails to build it with default options (and any options I tried):
```
$ g++ test.cpp
test.cpp: In member function ‘void X<T>::f()’:
test.cpp:14:10: error: ‘A’ has not been declared
getC().A::f(); // ‘A’ has not been declared
^
test.cpp:15:24: error: ‘A’ has not been declared
auto c4 = getC(); c4.A::f(); // ‘A’ has not been declared
^
test.cpp:16:36: error: ‘A’ has not been declared
decltype(getC()) c5 = getC(); c5.A::f(); // ‘A’ has not been declared
^
test.cpp:19:10: error: ‘template<class C> struct B’ used without template
parameters
getC().B::f(); // ‘template<class C> struct B’ used without template
parameters
^
test.cpp:20:24: error: ‘template<class C> struct B’ used without template
parameters
auto c1 = getC(); c1.B::f(); // ‘template<class C> struct B’ used without
template parameters
^
test.cpp:21:36: error: ‘template<class C> struct B’ used without template
parameters
decltype(getC()) c2 = getC(); c1.B::f(); // ‘template<class C> struct B’
used without template parameters
```
Clang (8.0.0) gives no error, and I believe that's the expected behavior.
