RFR: 8325163: Enable -Wpedantic on clang [v2]

[Magnus Ihse Bursie]

On Mon, 5 Feb 2024 10:58:17 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> Inspired by (the later backed-out) [JDK-8296115](https://bugs.openjdk.org/browse/JDK-8296115), I propose to enable `-Wpedantic` for clang. This has already found some irregularities in the code, like mistakenly using `#import` instead of `#include`. In this patch, I disable warnings for these individual buggy or badly written files, but I intend to post follow-up issues on the respective teams to have them properly fixed.
>> 
>> Unfortunately, it is not possible to enable `-Wpedantic` on gcc, since individual warnings in `-Wpedantic` cannot be disabled. This means that code like this:
>> 
>> 
>> #define DEBUG_ONLY(code) code;
>> 
>> DEBUG_ONLY(foo());
>> 
>> 
>> will result in a `; ;`. This breaks the C standard, but is benign, and we use it all over the place. On clang, we can ignore this by `-Wno-extra-semi`, but this is not available on gcc.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   FIx dtrace build

The split in different categories of flags is perhaps not perfect, and more a heuristic to help us manage them. However, I think we are talking about two different categories here. The `/Z` flags change the behavior of the compiler to be more standards compliant (similar to `-std=c++1` on gcc/clang). The `-Wpedantic" flag enables a batch of additional warnings on top of `-Wall` and `-Wextra`. The only way this makes it more "standards compliant" is that the standard requires the compiler to produce a warning in these situations. But that is not really why we want to turn it on; we want it to be able to catch bad or suboptimal code.

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PR Comment: https://git.openjdk.org/jdk/pull/17687#issuecomment-1927025804