[libc++] Use generator expression in Linker script generation

[ldionne]

Summary

This is an alternative to the workaround in r374510.

[ldionne]

@phosek Can you please confirm this also fixes your issue in the Runtimes build?

[phosek]

In D68880#1706330, @ldionne wrote:

@phosek Can you please confirm this also fixes your issue in the Runtimes build?

I got the following error:

Error evaluating generator expression:

  $<TARGET_EXISTS:unwind_shared>

Expression did not evaluate to a known generator expression

[phosek]

In D68880#1706543, @phosek wrote:

In D68880#1706330, @ldionne wrote:

@phosek Can you please confirm this also fixes your issue in the Runtimes build?

I got the following error:

Error evaluating generator expression:

  $<TARGET_EXISTS:unwind_shared>

Expression did not evaluate to a known generator expression

It seems like TARGET_EXISTS was only introduced in CMake 3.12 but I have 3.10 on my workstation. I'll try to upgrade my CMake and try again, but this may prevent us from rolling this out to LLVM which is still requiring 3.4.

[phosek]

In D68880#1706558, @phosek wrote:

In D68880#1706543, @phosek wrote:

In D68880#1706330, @ldionne wrote:

@phosek Can you please confirm this also fixes your issue in the Runtimes build?

I got the following error:

Error evaluating generator expression:

  $<TARGET_EXISTS:unwind_shared>

Expression did not evaluate to a known generator expression

It seems like TARGET_EXISTS was only introduced in CMake 3.12 but I have 3.10 on my workstation. I'll try to upgrade my CMake and try again, but this may prevent us from rolling this out to LLVM which is still requiring 3.4.

With CMake 3.13 it works!

[ldionne]

Rebase onto master now that we're on CMake 3.13

[ldionne]

@phosek Can you make sure this works on Linux with the runtimes build?

[phosek]

In D68880#2167605, @ldionne wrote:

@phosek Can you make sure this works on Linux with the runtimes build?

LGTM this seems to be working with the runtimes build.

[ldionne]

In D68880#2170950, @phosek wrote:

In D68880#2167605, @ldionne wrote:

@phosek Can you make sure this works on Linux with the runtimes build?

LGTM this seems to be working with the runtimes build.

Thanks for checking!

libcxx/cmake/Modules/DefineLinkerScript.cmake

function(define_linker_script target)
   get_target_property(interface_libs "${target}" INTERFACE_LINK_LIBRARIES)
 
   set(link_libraries)
   if (interface_libs)
     foreach(lib IN LISTS interface_libs)
       if ("${lib}" STREQUAL "cxx-headers")
         continue()
       endif()
-      if (TARGET "${lib}" OR
-          (${lib} MATCHES "cxxabi(_static|_shared)?" AND HAVE_LIBCXXABI) OR
-          (${lib} MATCHES "unwind(_static|_shared)?" AND HAVE_LIBUNWIND))
-        list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}$<TARGET_PROPERTY:${lib},OUTPUT_NAME>")
-      else()
-        list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}${lib}")
-      endif()
+      set(libname "$<IF:$<TARGET_EXISTS:${lib}>,$<TARGET_PROPERTY:${lib},OUTPUT_NAME>,${lib}>")
+      list(APPEND link_libraries "${CMAKE_LINK_LIBRARY_FLAG}${libname}")
     endforeach()
   endif()
   string(REPLACE ";" " " link_libraries "${link_libraries}")
 
   set(linker_script "INPUT(${soname} ${link_libraries})")
   add_custom_command(TARGET "${target}" POST_BUILD
     COMMAND "${CMAKE_COMMAND}" -E remove "${symlink}"
     COMMAND "${CMAKE_COMMAND}" -E echo "${linker_script}" > "${symlink}"
     COMMENT "Generating linker script: '${linker_script}' as file ${symlink}"
     VERBATIM
   )
 endfunction()