[clang-tidy] Don't try to build CTTestTidyModule for Windows with dylibs

[mstorsjo]

Summary

In MinGW mode, it's possible to build LLVM/Clang with
LLVM_LINK_LLVM_DYLIB (which implicitly enables plugins too). Other
existing ways of building plugins on Windows is to build with
LLVM_EXPORT_SYMBOLS_FOR_PLUGINS, where each executable exports its
symbols.

With LLVM_LINK_LLVM_DYLIB, we can't generally skip building plugins
even if they are set up with PLUGIN_TOOL, as some plugins (e.g.
under clang/examples) set up that way do build properly (as
they manually call clang_target_link_libraries, which links in the
libclang-cpp.dll dylib).

For CTTestTidyModule, there's no corresponding dylib that would
provide the same exports.

Alternatively, we could make the condition
if (NOT WIN32 OR LLVM_EXPORT_SYMBOLS_FOR_PLUGINS), as that's the
only way this plugin would be possible to link on Windows.

(Currently, building this plugin with LLVM_EXPORT_SYMBOLS_FOR_PLUGINS
fails to link one symbol though, but in principle, it could
work.)

[mstorsjo]

@rnk Can you have a look at this?

[rnk]

lgtm

[jeremyd2019]

clang-tools-extra/test/CMakeLists.txt

84

I only just noticed this patch, but it feels to me like this was intended to be OR here, because the condition to be avoided seems to be WIN32 AND LLVM_LINK_LLVM_DYLIB, which inverted is NOT WIN32 OR NOT LLVM_LINK_LLVM_DYLIB

[mstorsjo]

clang-tools-extra/test/CMakeLists.txt

84

Oh indeed, thanks, good catch! I'll push a patch fixing that.

clang-tools-extra/test/CMakeLists.txt

 )
 foreach(dep ${LLVM_UTILS_DEPS})
   if(TARGET ${dep})
     list(APPEND CLANG_TOOLS_TEST_DEPS ${dep})
   endif()
 endforeach()
 
 if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
+  if (NOT WIN32 AND NOT LLVM_LINK_LLVM_DYLIB)
     llvm_add_library(
         CTTestTidyModule
         MODULE clang-tidy/CTTestTidyModule.cpp
         PLUGIN_TOOL clang-tidy
         DEPENDS clang-tidy-headers)
+  endif()
 
   if(CLANG_BUILT_STANDALONE)
     # LLVMHello library is needed below
     if (EXISTS ${LLVM_MAIN_SRC_DIR}/lib/Transforms/Hello
        AND NOT TARGET LLVMHello)
       add_subdirectory(${LLVM_MAIN_SRC_DIR}/lib/Transforms/Hello
         lib/Transforms/Hello)
     endif()