[clang-doc] Use ExitOnError over manually handling exit conditions

[ilovepi]

clang-doc uses a lot of manual error checks, most of which exit the program, particularly when opening or manipulating files. We should prefer automated facilities, like llvm:: ExitOnError to do this in a consistent manner, and improve maintainability.

[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: Paul Kirth (ilovepi)

clang-doc uses a lot of manual error checks, most of which exit the program, particularly when opening or manipulating files. We should prefer automated facilities, like `llvm:: ExitOnError` to do this in a consistent manner, and improve maintainability.

[yashnator]

Hi, can I work on this?

[snarang181]

Hello @ilovepi, I am trying to make a first-time contribution and picked this issue as the entry-point. I have a PR up for this, looking forward to some feedback and I can work around any suggestions you might have. Link to the PR: #141699.
Thanks!

[ilovepi]

sorry for missing your replies @yashnator and @snarang181. Contributions are always welcome. I know @snarang181 already has a PR up that looks promising, so @yashnator you may want to look for another issue. Clang-doc still lacks significant test coverage, so improving that would be extremely helpful. Basically, any C or C++ construct should have a proper set of tests for it. That includes things like templates, different instantiations, constexpr, consteval, concepts, different exception types, etc. Test coverage is very sparse, so adding coverage for any of those would be welcome.