[libc++] Fix eager generator expression in DefineLinkerScript
As explained in https://gitlab.kitware.com/cmake/cmake/-/issues/21045,
both branches of an $<IF> generator expression are evaluated eagerly
by CMake. As a result, if the non-selected branch contains an invalid
generator expression (such as getting the OUTPUT_NAME property of a
non-existent target), a hard error will occur.
This failed builds using the cxxrt ABI library, which doesn't create
a CMake target currently.
Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: d275da17e4f0a17615b24c352aab0d34f647bfa7
diff --git a/cmake/Modules/DefineLinkerScript.cmake b/cmake/Modules/DefineLinkerScript.cmake
index 41426bf..be7f026 100644
--- a/cmake/Modules/DefineLinkerScript.cmake
+++ b/cmake/Modules/DefineLinkerScript.cmake
@@ -34,7 +34,13 @@
if ("${lib}" STREQUAL "cxx-headers")
continue()
endif()
- set(libname "$<IF:$<TARGET_EXISTS:${lib}>,$<TARGET_PROPERTY:${lib},OUTPUT_NAME>,${lib}>")
+ # If ${lib} is not a target, we use a dummy target which we know will
+ # have an OUTPUT_NAME property so that CMake doesn't fail when evaluating
+ # the non-selected branch of the `IF`. It doesn't matter what it evaluates
+ # to because it's not selected, but it must not cause an error.
+ # See https://gitlab.kitware.com/cmake/cmake/-/issues/21045.
+ set(output_name_tgt "$<IF:$<TARGET_EXISTS:${lib}>,${lib},${target}>")
+ set(libname "$<IF:$<TARGET_EXISTS:${lib}>,$<TARGET_PROPERTY:${output_name_tgt},OUTPUT_NAME>,${lib}>")
list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}${libname}")
endforeach()
endif()