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To: gcc@gcc.gnu.org
From: Markus Faehling <markus@faehling.com>
Subject: GCC/clang warning incompatibility with unused private member variables
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Date: Fri, 11 Jun 2021 21:37:04 +0200
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Hello,

I'm currently facing a problem where I cannot get both gcc and clang 
warning-free simultaneously in my project. My code looks somewhat like this:

class Test {
     int a_;
     void b() {};
};

This code gives me the(usually very useful) "-Wunused-private-field" 
warning on clang. But because I have the unused member on purpose, I 
would like to add the [[maybe_unused]] attribute to it:

class Test {
     [[maybe_unused]] int a_;
     void b() {};
};

While this version is warning-free in clang, gcc has a "-Wattributes" 
warning because it ignores the [[maybe_unused]] warning. But I do not 
want to disable either of these warnings because they are still very 
useful in other situations.

Would it be possible to ignore the "-Wattributes" warning for 
[[maybe_unused]] in places where other compilers might use the attribute?

Demonstration on godbolt.org: https://godbolt.org/z/8oT4Kr5eM

Regards,

Markus Faehling