[clang] Do not override libclang.so's SOVERSION if CLANG_FORCE_MATCHING_LIBCLANG_SOVERSION

[mgorny]

Summary

Instead of setting libclang.so's SOVERSION to CLANG_MAJOR_VERSION
when CLANG_FORCE_MATCHING_LIBCLANG_SOVERSION is enabled, do not override
it and let LLVM set the correct SOVERSION. This fixes libclang.so
missing LLVM_VERSION_SUFFIX, and harmonizes the SOVERSION with other
shared libraries.

[thesamesam]

It fixes a real-life issue I hit with Doxygen, as you know, so I'm happy with this - and I don't see a reason to treat libclang specially. I'll wait to see what any other reviewers say first though.

[MaskRay]

I don't understand this well, though. Is CLANG_VERSION_MAJOR wrong or not defined in some cases?

[mgorny]

In D135701#3850251, @MaskRay wrote:

I don't understand this well, though. Is CLANG_VERSION_MAJOR wrong or not defined in some cases?

It's about LLVM_VERSION_SUFFIX. Normally, SOVERSION for all libraries is ${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}.

clang/tools/libclang/CMakeLists.txt

 # The SOVERSION should be updated only if a change is made to the libclang
 # ABI, and when it is updated, it should be updated to the current
 # LLVM_VERSION_MAJOR.
 # Please also see clang/tools/libclang/libclang.map
 
 # This option defaults to CLANG_FORCE_MATCHING_LIBCLANG_SOVERSION
 # to ON - which means that it by default matches CLANG_VERSION_MAJOR
 #
 # TODO: This should probably not be a option going forward but we
 # we should commit to a way to do it. But due to getting this out
 # in LLVM 15.x we opted for a option.
+set(LIBCLANG_SOVERSION_ARG)
 if(NOT CLANG_FORCE_MATCHING_LIBCLANG_SOVERSION)
-  set(LIBCLANG_SOVERSION 13)
-else()
-  set(LIBCLANG_SOVERSION ${CLANG_VERSION_MAJOR})
+  set(LIBCLANG_SOVERSION_ARG SOVERSION 13)
 endif()
 
 # TODO: harmonize usage of LIBCLANG_SOVERSION / LIBCLANG_LIBARY_VERSION
 #       below; this was added under time-pressure to avoid reverting the
 #       better default from LLVM 14 for LLVM 15.0.0-rc3, hence no time
 #       to clean up previous inconsistencies.
 
 set(SOURCES
if (${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
       target_link_options(libclang PRIVATE "-Wl,-z,gnu-version-script-compat")
     endif()
     # Ensure that libclang.so gets rebuilt when the linker script changes.
     set_property(SOURCE ARCMigrate.cpp APPEND PROPERTY
                  OBJECT_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/libclang.map)
 
     set_target_properties(libclang PROPERTIES
                           VERSION ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}${LLVM_VERSION_SUFFIX}
-                          SOVERSION ${LIBCLANG_SOVERSION})
+                          ${LIBCLANG_SOVERSION_ARG})
   endif()
 endif()
 
 if(INTERNAL_INSTALL_PREFIX)
   set(LIBCLANG_HEADERS_INSTALL_DESTINATION "${INTERNAL_INSTALL_PREFIX}/include")
 else()
   set(LIBCLANG_HEADERS_INSTALL_DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}")
 endif()