[clangd] Add an option to disable special handling of standard library headers in include-cleaner

[philnik777]

While there are good reasons for adding some special magic for standard libraries, this really gets in the way when actually working on a standard library. For example, the include cleaner is completely broken, since it's always mapping public symbols to the public headers, even though library-internal headers should actually be used. It would be awesome if there was a flag for clangd to disable such special magic, allowing it to be used when working on a standard library without patching your own version together.

[llvmbot]

@llvm/issue-subscribers-clangd

Author: Nikolas Klauser (philnik777)

While there are good reasons for adding some special magic for standard libraries, this really gets in the way when actually working on a standard library. For example, the include cleaner is completely broken, since it's always mapping public symbols to the public headers, even though library-internal headers should actually be used. It would be awesome if there was a flag for clangd to disable such special magic, allowing it to be used when working on a standard library without patching your own version together.

[HighCommander4]

Are there other examples of special handling besides include-cleaner that you've come across?

[philnik777]

I'm pretty sure I've run into other stuff, but I can't remember right now. Could just be me misremembering as well. The two other things I've patched in are adding custom clang-tidy checks (which is really not standard-library specific) and the include inserter to always use angle brackets, but I can't remember why I did that.

[llvmbot]

@llvm/issue-subscribers-clang-include-cleaner

Author: Nikolas Klauser (philnik777)

While there are good reasons for adding some special magic for standard libraries, this really gets in the way when actually working on a standard library. For example, the include cleaner is completely broken, since it's always mapping public symbols to the public headers, even though library-internal headers should actually be used. It would be awesome if there was a flag for clangd to disable such special magic, allowing it to be used when working on a standard library without patching your own version together.

[HighCommander4]

Ok; I've tweaked the issue title to make it specific to include-cleaner for now. (Note that include-cleaner is a top-level "extra tool" living at clang-tools-extra/include-cleaner, so that may impact how such an option needs to be implemented.)

If you find other cases of special handling, we can track those in other issues.

[philnik777]

I mostly wanted to express that I don't think there should be an option per site, but a single flag to say "I don't want special handling" regardless where it is. Maybe I should have made that more clear. I don't really see a use-case to be more fine-grained other than people doing more weird stuff with their standard libraries.

[HighCommander4]

Understood.

I'm going to keep the issue title as is to keep the issue focused. ("Audit all codepaths used by clangd that might treat system headers differently" is a larger and fuzzier task that's not likely to be done all at once.)

I'm fine though with keeping the name of such an option general (i.e. not specific to include-cleaner), with a view to possibly having the option affect other features as well in the future.