[llvm] [libcxx] [ci] Make the CI find the right version of Clang-cl (PR #161736)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-github-workflow

Author: Martin Storsjö (mstorsjo)

<details>
<summary>Changes</summary>

We install a (or in practice, update a preexisting) copy of Clang, in order to get a specific version that we want. At that point in the procedure, this is the only version of Clang in the PATH.

However, the step of adding the MSVC build tools to the environment also ends up adding another copy of Clang, bundled with MSVC, into the PATH.

Due to this, CMake ends up finding and preferring the older version of Clang bundled with MSVC, rather than the one we intend to be used.

Manually add the directory of the version of Clang we want to use at the head of the search path, after initializing the MSVC build tool environment.

The directory name we add is a hardcoded guess of where it is installed - this is not ideal, but seems like the most straightforward solution for now.

---
Full diff: https://github.com/llvm/llvm-project/pull/161736.diff


1 Files Affected:

- (modified) .github/workflows/libcxx-build-and-test.yaml (+4) 


``````````diff
diff --git a/.github/workflows/libcxx-build-and-test.yaml b/.github/workflows/libcxx-build-and-test.yaml
index 1c07a0adc6e99..77f79a85a0a2f 100644
--- a/.github/workflows/libcxx-build-and-test.yaml
+++ b/.github/workflows/libcxx-build-and-test.yaml
@@ -281,6 +281,10 @@ jobs:
       - name: Set up the MSVC dev environment
         if: ${{ matrix.mingw != true }}
         uses: ilammy/msvc-dev-cmd at 0b201ec74fa43914dc39ae48a89fd1d8cb592756 # v1.13.0
+      - name: Add the installed Clang at the start of the path
+        if: ${{ matrix.mingw != true }}
+        run: |
+          echo "c:\Program Files\LLVM\bin" | Out-File -FilePath $Env:GITHUB_PATH -Encoding utf8 -Append
       - name: Build and test
         run: |
           bash libcxx/utils/ci/run-buildbot ${{ matrix.config }}

``````````

</details>


https://github.com/llvm/llvm-project/pull/161736