[llvm-branch-commits] [libcxx] release/18.x: Reapply [libcxx] [modules] Fix relative paths with absolute LIBCXX_INSTALL_MODULES_DIR (#86020) (PR #86197)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport 50801f1095d33e712c3a51fdeef82569bd09007f

Requested by: @<!-- -->mstorsjo

---
Full diff: https://github.com/llvm/llvm-project/pull/86197.diff


1 Files Affected:

- (modified) libcxx/modules/CMakeLists.txt (+13-2) 


``````````diff
diff --git a/libcxx/modules/CMakeLists.txt b/libcxx/modules/CMakeLists.txt
index 0dea8cfca94ac3..d47d19a4755317 100644
--- a/libcxx/modules/CMakeLists.txt
+++ b/libcxx/modules/CMakeLists.txt
@@ -206,9 +206,20 @@ add_custom_target(generate-cxx-modules
 # Configure the modules manifest.
 # Use the relative path between the installation and the module in the json
 # file. This allows moving the entire installation to a different location.
+if("${CMAKE_INSTALL_PREFIX}" STREQUAL "")
+  set(BASE_DIRECTORY "/")
+else()
+  set(BASE_DIRECTORY ${CMAKE_INSTALL_PREFIX})
+endif()
+cmake_path(ABSOLUTE_PATH LIBCXX_INSTALL_LIBRARY_DIR
+  BASE_DIRECTORY ${BASE_DIRECTORY}
+  OUTPUT_VARIABLE ABS_LIBRARY_DIR)
+cmake_path(ABSOLUTE_PATH LIBCXX_INSTALL_MODULES_DIR
+  BASE_DIRECTORY ${BASE_DIRECTORY}
+  OUTPUT_VARIABLE ABS_MODULES_DIR)
 file(RELATIVE_PATH LIBCXX_MODULE_RELATIVE_PATH
-  ${CMAKE_INSTALL_PREFIX}/${LIBCXX_INSTALL_LIBRARY_DIR}
-  ${CMAKE_INSTALL_PREFIX}/${LIBCXX_INSTALL_MODULES_DIR})
+  ${ABS_LIBRARY_DIR}
+  ${ABS_MODULES_DIR})
 configure_file(
   "modules.json.in"
   "${LIBCXX_LIBRARY_DIR}/libc++.modules.json"

``````````

</details>


https://github.com/llvm/llvm-project/pull/86197