NFC: Make clang resource headers an interface library

[etcwilde]

Making the clang resource headers into an interface library instead of a custom target means that we can attach the header search paths to the library. Targets that "link" against this library will automatically have the appropriate paths added to their header search paths to find them. Then downstream projects that embed a copy of clang can query the generated ClangTargets.cmake file for the header location instead of attempting to compute them.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-backend-x86

Author: Evan Wilde (etcwilde)

Changes

Making the clang resource headers into an interface library instead of a custom target means that we can attach the header search paths to the library. Targets that "link" against this library will automatically have the appropriate paths added to their header search paths to find them. Then downstream projects that embed a copy of clang can query the generated ClangTargets.cmake file for the header location instead of attempting to compute them.

---

Full diff: https://github.com/llvm/llvm-project/pull/88317.diff

1 Files Affected:

• (modified) clang/lib/Headers/CMakeLists.txt (+6-2)

diff --git a/clang/lib/Headers/CMakeLists.txt b/clang/lib/Headers/CMakeLists.txt
index 97104ccd8db59c..0367f611526f41 100644
--- a/clang/lib/Headers/CMakeLists.txt
+++ b/clang/lib/Headers/CMakeLists.txt
@@ -437,14 +437,14 @@ foreach( f ${generated_files} )
 endforeach( f )
 
 function(add_header_target target_name file_list)
-  add_custom_target(${target_name} DEPENDS ${file_list})
+  add_library(${target_name} INTERFACE ${file_list})
   set_target_properties(${target_name} PROPERTIES
     FOLDER "Misc"
     RUNTIME_OUTPUT_DIRECTORY "${output_dir}")
 endfunction()
 
 # The catch-all clang-resource-headers target
-add_custom_target("clang-resource-headers" ALL DEPENDS ${out_files})
+add_library(clang-resource-headers INTERFACE ${out_files})
 set_target_properties("clang-resource-headers" PROPERTIES
   FOLDER "Misc"
   RUNTIME_OUTPUT_DIRECTORY "${output_dir}")
@@ -501,6 +501,10 @@ add_header_target("windows-resource-headers" ${windows_only_files})
 add_header_target("utility-resource-headers" ${utility_files})
 
 get_clang_resource_dir(header_install_dir SUBDIR include)
+target_include_directories(clang-resource-headers INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+  $<INSTALL_INTERFACE:${header_install_dir}>)
+set_property(GLOBAL APPEND PROPERTY CLANG_EXPORTS clang-resource-headers)
 
 #############################################################
 # Install rules for the catch-all clang-resource-headers target

[compnerd]

This seems like a step in the right direction - avoiding custom targets is generally better.

[compnerd]

Thanks, this seems good!

[JDevlieghere]

Hey @etcwilde, this breaks the Xcode standalone build for lldb: https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/lldb-cmake-standalone/121/

The failing command in the generated script phase is:

cmake -E copy_directory  /Users/jonas/llvm/xcode-build/Debug/bin/LLDB.framework/Versions/A/Resources/Clang/include

It looks like it's missing the source directly. Mind taking a look?

[ayermolo]

I am seeing a cmake error in one of the build steps in our enviroment:

CMake Error at CMakeLists.txt:86 (get_property):
  get_property could not find TARGET clang-resource-headers.  Perhaps it has
  not yet been created.

Reverting this diff internally made build pass.
I'll try to create small repro, but in meantime can you revert?