Re: [boost] Bug report rejected as conformant

Subject: Re: [boost] Bug report rejected as conformant
From: Edward Diener (eldiener_at_[hidden])
Date: 2018-01-13 21:43:29

On 1/13/2018 4:08 PM, Marc Glisse via Boost wrote:
> On Sat, 13 Jan 2018, Edward Diener via Boost wrote:
> 
>> On 1/13/2018 1:55 PM, Marc Glisse via Boost wrote:
>>> On Sat, 13 Jan 2018, Edward Diener via Boost wrote:
>>>
>>>> I recently reported a preprocessor bug in Oracle C++ 12.6 on their 
>>>> online forum when compiling a C program example. I even cited the 
>>>> C11 standard in showing that Oracle C++ 12.6's actions were 
>>>> non-conformant. The answer I was given, from an Oracle C++ developer 
>>>> who said he was a member of the C++ standard committee, is that 
>>>> since Oracle C++ 12.6 gives a warning message rather than a compiler 
>>>> error the compiler was compliant with the C standard, since the 
>>>> standard only requires a diagnostic message to be considered 
>>>> standard compliant when it does not implement the compiler according 
>>>> to the standard, and that a warning was a diagnostic message. 
>>>> Furthermore since there was a way to force the particular warning to 
>>>> be considered an error, Oracle was not going to change their 
>>>> compiler. At that point I "lost it" so to speak.
>>>>
>>>> I cannot conceive that any C/C++ standard would specify that giving 
>>>> a warning rather than an error, when not complying with the C/C++ 
>>>> standard, would then make the compiler compliant. Comments ?
>>>
>>> Uh, that's what all compilers do all the time when they implement 
>>> extensions to the standard. With gcc, you even need to specify 
>>> -Wpedantic to get those required diagnostics. I am really surprised 
>>> that this is the first compiler for which you notice this...
>>
>> So a compiler is allowed to implement an extension to the standard 
>> which is non-compliant with the standard,
> 
> "non-compliant" is your judgement.

"Non-compliant" simply means that the compiler does not follow the C++ 
standard. What is judgmental about that ? Or do you believe there is no 
such thing as following the C++ standard so whatever a compiler does it 
is perfectly OK to call itself compliant ?

> 
>> and then claim compliance to the standard by outputting a warning 
>> message instead ?
> 
> That's always been all the standards require. Picking a random sentence 
> from the C++ standard: "if [...], a conforming implementation shall 
> issue at least one diagnostic message". Seems pretty clear to me that 
> warnings satisfy this requirement. And from discussions in the C++ 
> committee, it is definitely interpreted that way.

Please quote an actual place rather than a random sentence.

> 
>> In that case what hope is there for the programmer to write C/C++ 
>> standard compliant code using such a compiler,
> 
> Note that this is not a priority for compiler vendors. Accepting legacy 
> programs comes before rejecting invalid ones.
> 
> If the compiler is giving you a warning, read it? How is prefixing the 
> message with "error:" clearer than with "warning:"?

An error stops the compilation, a warning does not unless you tell the 
compiler to treat warnings as errors. Good luck using the typical 
compiler if you do the latter.

> 
>> since the compiler is "inventing" a standard which does not exist ?
>>
>> Note that the error I reported was not when using any 
>> -std=some_compilers_extension mode ( as in gcc's -std=gnu++nn mode as 
>> opposed to -std=c++nn mode) but with -std=c11 mode, which is explained 
>> as being an implementation of the c11 standard. In other words if I 
>> were using an Oracle c11 mode, as in a hypothetical -std=oracle++c11, 
>> I would not have complained about their extension to the standard or 
>> their cavalier treatment of a bug as not being a bug because they 
>> produced a warning. But that was not the case and the mode being used 
>> was the -std=c11 mode, which evidently means to Oracle C++ whatever 
>> they feel like defining as the c11 standard even if it does not follow 
>> the actual c11 standard.
> 
> Again, this is in no way specific to Oracle's compiler.

I do not care if it is Podunk C++. The principal that a compiler says it 
is standard conforming because it issues a warning rather than an error 
when it does not conform to the standard is what bothers me. If such 
behavior is actually part of the C or C++ standard then there is never 
any point at reporting bugs to any C++ implementation because their 
answer to any valid bug can be "we issue a warning but we are not going 
to bother to fix the bug because the warning makes us compliant".

> 
> I am still trying to figure out why you are getting so angry about it. 
> If the extension was breaking some subtle sfinae detection code, I could 
> understand, but the preprocessor cannot be involved there. Does it break 
> some feature detection in a configuration script? That's one case where 
> indeed warnings can be much less helpful than errors, but I would still 
> be surprised if that is the case you are in.
> 
> (maybe I should read your bug report before posting anything else...)

My anger is wrong. But my point of view is I believe valid. Why waste 
time trying to test a compiler when the result is that the compiler 
developers do not care if they have a bug in their implementation 
because all they have to do is tell you that their warning satisfies the 
standard and therefore there is no point of fixing their bug. I don't 
care what the bug actually is in this case, it's the attitude of the 
compiler implementor that irks me.