Workaround for debug symbol error with auto member function?

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.