[libc++] change the visibility of libc++ header to public in libcxx module

[RichardLuo0]

This PR addresses a problem that headers may not be able to be found if #include is used with std modules.

Consider the following file:

#include <boost/json.hpp>
import std;

int main(int, const char **) { }

boost will include something from libc++, but we are using -nostdinc++, so the compiler can not find any default std header.
Therefore the locally built header needs to be public.

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[llvmbot]

@llvm/pr-subscribers-libcxx

Author: RichardLuo (RichardLuo0)

Changes

Same as #91182

---

Full diff: https://github.com/llvm/llvm-project/pull/91240.diff

1 Files Affected:

• (modified) libcxx/modules/CMakeLists.txt.in (+1-1)

diff --git a/libcxx/modules/CMakeLists.txt.in b/libcxx/modules/CMakeLists.txt.in
index c35f6fecb1fd76..9fef16e9cefde9 100644
--- a/libcxx/modules/CMakeLists.txt.in
+++ b/libcxx/modules/CMakeLists.txt.in
@@ -41,7 +41,7 @@ target_sources(std
     std.cppm
 )
 
-target_include_directories(std SYSTEM PRIVATE @LIBCXX_CONFIGURED_INCLUDE_DIRS@)
+target_include_directories(std SYSTEM PUBLIC @LIBCXX_CONFIGURED_INCLUDE_DIRS@)
 
 if (NOT @LIBCXX_ENABLE_EXCEPTIONS@)
   target_compile_options(std PUBLIC -fno-exceptions)

[mordante]

Can you add a description why this change would be beneficial?

[RichardLuo0]

Can you add a description why this change would be beneficial?

It is for the same reason as #91182

Consider the following file:

#include <boost/json.hpp>
import std;

int main(int, const char **) { }

boost will include something from libc++, but we are using -nostdinc++, so the compiler can not find any default std header.
Therefore the locally built header needs to be public.

Besides, if we are using assert, the <cassert> has to be found because assert is a macro so it can not be exported.

[mordante]

I see. Typically we first land a commit in main and then backport it to the release branch.

I've updated the commit message to the text of the other PR. Typically when we merge the commit message will be the message stored in git. It's good practice to have a good commit message.

I just started the CI and want to look whether it's happy. (I expect it will be.)

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[RichardLuo0]

⚠️ We detected that you are using a GitHub private e-mail address to contribute to the repo. Please turn off Keep my email addresses private setting in your account. See LLVM Discourse for more information.

I have set it to non-private now.

@mordante I don't understand why the checks failed on Fetch LLVM sources.

[mordante]

⚠️ We detected that you are using a GitHub private e-mail address to contribute to the repo. Please turn off Keep my email addresses private setting in your account. See LLVM Discourse for more information.

I have set it to non-private now.

@mordante I don't understand why the checks failed on Fetch LLVM sources.

Can you rebase the patch, I expect that fixes the CI issue.

[RichardLuo0]

I rebased the PR, can you try the CI again?

[ldionne]

I suspect the Windows CI is failing because a newer LLVM was somehow installed on the machines, which could be due to #95228 being tested. If that's the case, then I think we just learned that the state of CI machines on Windows is shared across all PRs, which is a bit concerning.

For the scope of this change I think we can just ignore the failures on Windows.

[ldionne]

Also rebasing onto main again should solve this issue.

[mordante]

There were other CI jobs failing too, our "typical cancellation issue".

[mstorsjo]

I suspect the Windows CI is failing because a newer LLVM was somehow installed on the machines, which could be due to #95228 being tested. If that's the case, then I think we just learned that the state of CI machines on Windows is shared across all PRs, which is a bit concerning.

For the scope of this change I think we can just ignore the failures on Windows.

It’s not that the other jobs caused a new version to be installed; the jobs don’t cross contaminate the environment (that’d be concerning).

The base images used for the runners are continuously updated. Today, it seems like they’ve rolled out a new image that contained a newer version of LLVM out of the box. The command we used for installing the version of LLVM we wanted failed, when the installation turned out to be a downgrade.

As part of #95228 I added a flag to tell it that we’re ok with downgrading - to prevent this from becoming an issue in the future, when a newer version appears in the base image again.

[RichardLuo0]

@mordante Should I rebase again?
In fact, can you just merge this? This PR doesn't change anything that may break CI, to be honest.

[ldionne]

Merging since the CI issues are unrelated.

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