[cfe-dev] [PATCH] Warn when an anonymous warning group is used more than once

[Douglas Gregor]

Sent from my iPhone

On Jan 9, 2013, at 5:19 PM, Jordan Rose <jordan_rose at apple.com> wrote:

> [+cfe-dev, -cfe-commits for the new "coding" convention]
> 
>> Hi, everyone. One thing that's bothered me about our diagnostic TableGen files is the anonymous use of warning groups:
>> 
>> def warn_foo : Warning<"foo is bad">, InGroup<DiagGroup<"foo">>;
>> def warn_foo_cxx : Warning<"foo is even worse in C++">, InGroup<DiagGroup<"foo">>;
>> 
>> If we ever want to put the warning groups in a hierarchy, or change the name, there's a big chance we'll miss one.
>> 
>> So, I wrote a new warning for clang-tblgen, which even has a fixit if the group already has a name:
>> 
>> warning: group 'foo' is referred to anonymously
>> def warn_foo : Warning<"foo is bad">, InGroup<DiagGroup<"foo">>;
>>                                       ~~~~~~~~^~~~~~~~~~~~~~~~~
>>                                       InGroup<Foo>
>> 
>> And then fixed all the warnings, with the intent that we make this a new style requirement going forwards: groups that cover more than one diagnostic must be named.
> 
> 
> Sean has suggested making this an error instead of a warning, since we go for a warning-free build anyway. I'm not sure why I thought a warning was preferable; we'd obviously make anyone fix their code before committing if they triggered the warning. The only thing I can think of is that it might be better for quick testing when transitioning from one diagnostic to another, or when trying out a new diagnostic under an existing flag.
> 
> Opinions? I'm fine either way.

I'd prefer an error. 

> Jordan
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