Workaround for debug symbol error with auto member function? - c++

Question

There seems to be an issue with debug symbols and auto.
I have an auto function in a class:
#include <cstddef>
template <typename T>
struct binary_expr {
auto operator()(std::size_t i){
return 1;
}
};
int main(){
binary_expr<double> b;
return 0;
}
When I compile with G++ (4.8.2) and -g, I have this error:
g++ -g -std=c++1y auto.cpp
auto.cpp: In instantiation of ‘struct binary_expr<double>’:
auto.cpp:11:25: required from here
auto.cpp:4:8: internal compiler error: in gen_type_die_with_usage, at dwarf2out.c:19484
struct binary_expr {
^
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://bugs.gentoo.org/> for instructions.
With clang++ (3.4) and -g, I have this:
clang++ -g -std=c++1y auto.cpp
error: debug information for auto is not yet supported
1 error generated.
If I remove the -g or set the type explicitly, it works perfectly.
Isn't clang++ supposed to be C++14 feature complete ?
Is there a workaround for these limitations or I'm screwed ?

Answer 1

This now seems to works on Clang 3.5 SVN. Live Example. It seems that the culprit was a commit from May 2013, see this message on the Clang mailing list.
PR16091: Error when attempting to emit debug info for undeduced auto
return types
Perhaps we should just suppress this, rather than erroring, but since
we have the infrastructure for it I figured I'd use it - if this is
determined to be not the right thing we should probably remove that
infrastructure entirely. I guess it's lying around from the early days
of implementing debug info support.
// RUN: %clang_cc1 -emit-llvm-only -std=c++1y -g %s 2>&1 | FileCheck %s
2
3 struct foo {
4 auto func(); // CHECK: error: debug information for auto is not yet supported
5 };
6
7 foo f;
However, I cannot find the commit that removed this info, perhaps there was an improvement that now prevents that this behavior is being triggered.

Answer 2

Even after some time, the only workaround I have found is to make the function template, pretty stupid workaround... Apparently, clang has no problem with auto functions that are template. I don't know if this works in every case, but until now it had worked for me.
#include <cstddef>
template <typename T>
struct binary_expr {
template<typename E = void>
auto operator()(std::size_t i){
return 1;
}
};
int main(){
binary_expr<double> b;
return 0;
}