Enumerations with a fixed underlying type documentation issue

[pinskia]

The current documentation (https://clang.llvm.org/docs/LanguageExtensions.html) has:
"Clang provides support for C++11 enumerations with a fixed underlying type within Objective-C. For example, one can write an enumeration type as:"

But it is actually allowed in C and not just Objective-C. In fact it is no longer an extension for C23.
Also the documentation mentions __has_feature(objc_fixed_enum) being true if the extension exists but it is false for C even though it is there for C too.

Otherwise the extension for the C case is not documented at all.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
2. In the comments of this issue, request for it to be assigned to you, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Andrew Pinski (pinskia)

The current documentation (https://clang.llvm.org/docs/LanguageExtensions.html) has: "Clang provides support for C++11 enumerations with a fixed underlying type within Objective-C. For example, one can write an enumeration type as:"

But it is actually allowed in C and not just Objective-C. In fact it is no longer an extension for C23.
Also the documentation mentions __has_feature(objc_fixed_enum) being true if the extension exists but it is false for C even though it is there for C too.

Otherwise the extension for the C case is not documented at all.

[AaronBallman]

This strikes me as a good first issue as it mostly involves updating the existing LanguageExtensions documentation for terminology; there is some effort involved in seeing where Clang extends C and C++ and making sure the details are correct.

The __has_feature(objc_fixed_enum) is correct for Objective-C but would be a very odd name for a feature test macro in C. We may want to consider using __has_extension(c_fixed_enum) to complement __has_extension(cxx_fixed_enum). This aspect of the issue is also in good first issue territory.

[AidanGoldfarb]

I think this would be a good first issue for me to tackle, can this be assigned to me?

[erichkeane]

Fixed in #117507