build: Add -Wreserved-identifier supported by clang #1206

1. 
   real-or-random commented at 2:17 pm on February 2, 2023: contributor

   This warns on certain identifiers reserved by the C standard, namely

   • identifiers that begin with an underscore followed by an uppercase letter, and
   • identifiers in the global namespace that begin with an underscore.

   We had used such identifiers in the past for macros in include guards, and we should make sure that we don’t reintroduce such identifiers going forward.

   Note that C reserves more identifiers for “future library directions”, e.g., identifiers that begin with “str” followed by a lowercase letter. But even the C standards committee has decided that this is somewhat silly and adopted a proposal [1] for C23 that removes the restriction that programs using these identifiers have UB. Instead, these identifiers are now “potentially reserved”, which is not a normative restriction but simply an informative warning that the identifiers may become fully reserved in the future.

   [1] https://www.open-std.org/jtc1/sc22/WG14/www/docs/n2625.pdf

2. build: Add -Wreserved-identifier supported by clang

   This warns on certain identifiers reserved by the C standard, namely
    * identifiers that begin with an underscore followed by an uppercase
      letter, and
    * identifiers in the global namespace that begin with an underscore.
   
   We had used such identifiers in the past for macros in include guards,
   and we should make sure that we don't reintroduce such identifiers
   going forward.
   
   Note that C reserves more identifiers for "future library directions",
   e.g., identifiers that begin with "str" followed by a lowercase letter.
   But even the C standards committee has decided that this is somewhat
   silly and adopted a proposal [1] for C23 that removes the restriction
   that programs using these identifiers have UB. Instead, these
   identifiers are now "potentially reserved", which is not a normative
   restriction but simply an informative warning that the identifiers
   may become fully reserved in the future.
   
   [1] https://www.open-std.org/jtc1/sc22/WG14/www/docs/n2625.pdf

   8c7e0fc1de
3. 
   jonasnick commented at 4:00 pm on February 2, 2023: contributor

   tested ACK 8c7e0fc1de048be98a1f1bc75557671afc14beaa
4. 
   sipa commented at 9:14 pm on February 2, 2023: contributor

   utACK 8c7e0fc1de048be98a1f1bc75557671afc14beaa
5. real-or-random merged this on Feb 3, 2023
6. real-or-random closed this on Feb 3, 2023

   ---

7. hebasto cross-referenced this on Feb 7, 2023 from issue build: Add CMake-based build system by hebasto
8. hebasto referenced this in commit 7c0cc5d976 on Mar 7, 2023
9. dhruv referenced this in commit a5df79db12 on Mar 7, 2023
10. dhruv referenced this in commit 77b510d84c on Mar 7, 2023
11. sipa referenced this in commit 763079a3f1 on Mar 8, 2023
12. div72 referenced this in commit 945b094575 on Mar 14, 2023
13. hebasto cross-referenced this on Apr 11, 2023 from issue test: Silent noisy clang warnings about Valgrind code on macOS x86_64 by hebasto
14. vmta referenced this in commit e1120c94a1 on Jun 4, 2023
15. vmta referenced this in commit 8f03457eed on Jul 1, 2023
16. jonasnick cross-referenced this on Jul 20, 2023 from issue Upstream PRs 1160, 1193, 1169, 1190, 1192, 1194, 1196, 1195, 1170, 1172, 1200, 1199, 1203, 1201, 1206, 1078, 1209, 979, 1212, 1218, 1217, 1221, 1222 by jonasnick

Contributors
real-or-random jonasnick sipa