[llvm] [cmake] Add additional headers only if they exist

[mgorny]

Summary

Modify the add_header_files_for_glob() function to only add files
that do exist, rather than all matches of the glob. This fixes CMake
error when one of the include directories (which happen to include
/usr/include) contain broken symlinks.

[mgorny]

Ping.

[smeenai]

llvm/cmake/modules/LLVMProcessSources.cmake

35 ↗

(On Diff #191637)

I'd add a comment explaining this is for broken symlinks, otherwise I'd be wondering why you were checking for the existence of a file you just globbed...

Actually, is EXISTS resolving symlinks documented anywhere? It's unclear if it would return the existence of the symlink itself or the target of the symlink.

[mgorny]

llvm/cmake/modules/LLVMProcessSources.cmake

35 ↗

(On Diff #191637)

I'd add a comment explaining this is for broken symlinks, otherwise I'd be wondering why you were checking for the existence of a file you just globbed...

Good idea.

Actually, is EXISTS resolving symlinks documented anywhere? It's unclear if it would return the existence of the symlink itself or the target of the symlink.

To be honest, I don't see it in CMake docs. I think I presumed that behavior from shell's -f operator but there's indeed some potential ambiguity here.

[smeenai]

LGTM with the comment added.

llvm/cmake/modules/LLVMProcessSources.cmake

35 ↗

(On Diff #191637)

Looks like it just calls access, which should resolve symlinks.

[smeenai]

llvm/cmake/modules/LLVMProcessSources.cmake

35 ↗

(On Diff #191637)

I submitted https://gitlab.kitware.com/cmake/cmake/merge_requests/3189 to CMake to clarify this.

[mgorny]

llvm/cmake/modules/LLVMProcessSources.cmake

35 ↗

(On Diff #191637)

Thank you. I'll add the comment later today and push it.

llvm/trunk/cmake/modules/LLVMProcessSources.cmake

if( tds )
     source_group("TableGen descriptions" FILES ${tds})
     set_source_files_properties(${tds} PROPERTIES HEADER_FILE_ONLY ON)
     list(APPEND ${srcs} ${tds})
   endif()
 endmacro(add_td_sources)
 
 function(add_header_files_for_glob hdrs_out glob)
   file(GLOB hds ${glob})
-  set(${hdrs_out} ${hds} PARENT_SCOPE)
+  set(filtered)
+  foreach(file ${hds})
+    # Explicit existence check is necessary to filter dangling symlinks
+    # out.  See https://bugs.gentoo.org/674662.
+    if(EXISTS ${file})
+      list(APPEND filtered ${file})
+    endif()
+  endforeach()
+  set(${hdrs_out} ${filtered} PARENT_SCOPE)
 endfunction(add_header_files_for_glob)
 
 function(find_all_header_files hdrs_out additional_headerdirs)
   add_header_files_for_glob(hds *.h)
   list(APPEND all_headers ${hds})
 
   foreach(additional_dir ${additional_headerdirs})
     add_header_files_for_glob(hds "${additional_dir}/*.h")