Possible gcc bug with C++14 polymorphic lambdas? - c++

Question

I've found a strange behavior using polymorphic C++14 lambdas (lambdas with auto in their parameters):
Snippet 0:
#include <iostream>
template<typename T> void doLambda(T&& mFn)
{
std::forward<T>(mFn)(int{0});
}
template<typename T> void test(T&& mV)
{
doLambda([&mV](auto mE)
{
std::forward<decltype(mV)>(mV);
});
}
int main() { test(int{0}); return 0; }
clang++ 3.5.1: the snippet compiles and runs successfully.
g++ 4.9.2: the snippet fails to compile:
example.cpp: In instantiation of 'test(T&&)::<lambda(auto:1)> [with auto:1 = int; T = int]':
5 : required from 'void doLambda(T&&) [with T = test(T&&) [with T = int]::]'
13 : required from 'void test(T&&) [with T = int]'
18 : required from here
12 : error: 'mV' was not declared in this scope
std::forward<decltype(mV)>(mV);
^
Compilation failed
Snippet 1:
The only difference from snippet 0 is that the auto inside the lambda was replaced to int.
#include <iostream>
template<typename T> void doLambda(T&& mFn)
{
std::forward<T>(mFn)(int{0});
}
template<typename T> void test(T&& mV)
{
doLambda([&mV](int mE)
{
std::forward<decltype(mV)>(mV);
});
}
int main() { test(int{0}); return 0; }
clang++ 3.5.1: the snippet compiles and runs successfully.
g++ 4.9.2: the snippet compiles and runs successfully.
Snippet 3:
The lambda is now called in-place. auto is still used.
#include <iostream>
template<typename T> void test(T&& mV)
{
[&mV](auto mE)
{
std::forward<decltype(mV)>(mV);
}(int{0});
}
int main() { test(int{0}); return 0; }
clang++ 3.5.1: the snippet compiles and runs successfully.
g++ 4.9.2: the snippet compiles and runs successfully.
Why is g++ complaining about snippet 0? Is there anything wrong in my code? Is this a known bug or should I submit this?

Answer 1

As stated in the comments, this behavior is indeed a gcc bug.