[clang] Fix missing installed header

[danielotero]

Since commit 8d468c1, the header openmp_wrappers/complex is hidden behind openmp_wrappers/complex.h due to a bug in CMake¹, so is not actually installed.

To test the issue, you can ask ninja to generate the file on your build:

$ ninja lib/clang/19/include/openmp_wrappers/complex.h
[199/199] Copying clang's openmp_wrappers/complex.h...
$ ninja lib/clang/19/include/openmp_wrappers/complex
ninja: error: unknown target 'lib/clang/19/include/openmp_wrappers/complex', did you mean 'lib/clang/19/include/openmp_wrappers/complex.h'? 

Re-ordering the entries workarounds the issue. The other option is to revert the cited commit, but I'm not sure which approach is preferred.

CC @etcwilde @jdoerfert

Footnotes

1. Here is the CMake report on the issue. ↩

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[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-backend-x86

Author: Daniel Otero (danielotero)

Changes

Since commit 8d468c1, the header openmp_wrappers/complex is hidden behind openmp_wrappers/complex.h due to a bug in CMake¹, so is not actually installed.

To test the issue, you can ask ninja to generate the file on your build:

$ ninja lib/clang/19/include/openmp_wrappers/complex.h
[199/199] Copying clang's openmp_wrappers/complex.h...
$ ninja lib/clang/19/include/openmp_wrappers/complex
ninja: error: unknown target 'lib/clang/19/include/openmp_wrappers/complex', did you mean 'lib/clang/19/include/openmp_wrappers/complex.h'? 

Re-ordering the entries workarounds the issue. The other option is to revert the cited commit, but I'm not sure which approach is preferred.

CC @etcwilde @jdoerfert

---

Full diff: https://github.com/llvm/llvm-project/pull/95979.diff

1 Files Affected:

• (modified) clang/lib/Headers/CMakeLists.txt (+3-1)

diff --git a/clang/lib/Headers/CMakeLists.txt b/clang/lib/Headers/CMakeLists.txt
index d3090e488306f..89fa0ecd45eb4 100644
--- a/clang/lib/Headers/CMakeLists.txt
+++ b/clang/lib/Headers/CMakeLists.txt
@@ -318,8 +318,10 @@ set(ppc_wrapper_files
 set(openmp_wrapper_files
   openmp_wrappers/math.h
   openmp_wrappers/cmath
-  openmp_wrappers/complex.h
+  # Due to a bug in CMake, `complex` must be before `complex.h`
+  # See: https://gitlab.kitware.com/cmake/cmake/-/issues/26058
   openmp_wrappers/complex
+  openmp_wrappers/complex.h
   openmp_wrappers/__clang_openmp_device_functions.h
   openmp_wrappers/complex_cmath.h
   openmp_wrappers/new

Footnotes

1. Here is the CMake report on the issue. ↩

[etcwilde]

Nice find. That's kind of horrifying. I'm fine with flipping the file order to avoid the source file caching bug in CMake.
CC @compnerd since he also knows CMake and may have opinions.

[mathstuf]

Nice find. That's kind of horrifying.

Indeed. CMake's old "guess the extension" behavior was always a…fun thing to deal with. Alas, this emergent behavior was unknown at the time and a straight fix is likely to break other projects :( . Plus it's not likely we'll get patched releases for the past 18 releases. Luckily, there is a fix here. We'll get this in the test suite and properly nailed down though; hopefully we can detect this behavior so that other projects can discover such instances as well.

[danielotero]

I forgot to say I don't have commit access, so feel free to merge this.

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[etcwilde]

@danielotero Thank you for your contribution.

[etcwilde]

For folks landing here, this should be fixed in CMake 4.1 by policy CMP0187.