Teach llvm_add_library() to search arbitrary directories for includes.

[zturner]

Summary

Since header files are not compilation units, CMake does not require
you to specify them in the CMakeLists.txt file.  As a result, unless
a header file is explicitly added, CMake won't know about it, and
when generating IDE-based projects, CMake won't put the header files
into the IDE project.  LLVM currently tries to deal with this in two
ways:

  1) It looks for all .h files that are in the project directory,
     and adds those.
  2) llvm_add_library() understands the ADDITIONAL_HEADERS argument,
     which allows one to list an arbitrary list of headers.

This patch takes things one step further.  It adds the ability for
llvm_add_library() to take an ADDITIONAL_HEADER_DIRS argument,
which will specify a list of folders which CMake will glob for
header files.  Furthermore, it will glob not only for .h files, but
also for .inc files.

Included in this CL is an update to one of the existing users of
ADDITIONAL_HEADERS to use this new argument instead, to serve as an
illustration of how this cleans up the CMake.

The big advantage of this new approach is that until now, there was
no way for the IDE projects to locate the header files that are in
the include tree.  In other words, if you are in, for example,
lib/DebugInfo/DWARF, the corresponding includes for this project
will be located under include/DebugInfo/DWARF.  Now, in the
CMakeLists.txt for lib/DebugInfo/DWARF, you can simply write:

  ADDITIONAL_HEADER_DIRS
  ../../include/DebugInfo/DWARF

as an argument to llvm_add_library(), and all header files will get 
added to the IDE project.

[zturner]

friendly ping to bring this to the top of your inbox

[beanz]

LGTM. This seems like general goodness that reduces the complexity of our CMake files, and I verified it works as expected for Xcode.

Can you please cleanup any uses of ADDITIONAL_HEADERS that make sense?

[zturner]

Yes, will probably do that as a followup, and simultaneously deprecate the
use of ADDITIONAL_HEADERS.

If someone really wanted to get clever, they could also update
llvm_add_library to translate the source directory to a corresponding
include directory and automatically append it to ADDITIONAL_HEADER_DIRS.
This would make all IDE projects way better in my opinion.

cmake/modules/LLVMProcessSources.cmake

   endif()
 endmacro(add_td_sources)
 
+function(add_header_files_for_glob hdrs_out glob)
+  file(GLOB hds ${glob})
+  set(${hdrs_out} ${hds} PARENT_SCOPE)
+endfunction(add_header_files_for_glob)
 
-macro(add_header_files srcs)
-  file(GLOB hds *.h)
-  if( hds )
-    set_source_files_properties(${hds} PROPERTIES HEADER_FILE_ONLY ON)
-    list(APPEND ${srcs} ${hds})
-  endif()
-endmacro(add_header_files)
+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")
+    list(APPEND all_headers ${hds})
+    add_header_files_for_glob(hds "${additional_dir}/*.inc")
+    list(APPEND all_headers ${hds})
+  endforeach(additional_dir)
+
+  set( ${hdrs_out} ${all_headers} PARENT_SCOPE )
+endfunction(find_all_header_files)
 
 
 function(llvm_process_sources OUT_VAR)
-  cmake_parse_arguments(ARG "" "" "ADDITIONAL_HEADERS" ${ARGN})
+  cmake_parse_arguments(ARG "" "" "ADDITIONAL_HEADERS;ADDITIONAL_HEADER_DIRS" ${ARGN})
   set(sources ${ARG_UNPARSED_ARGUMENTS})
   llvm_check_source_file_list( ${sources} )
   if( MSVC_IDE OR XCODE )
     # This adds .td and .h files to the Visual Studio solution:
     add_td_sources(sources)
-    add_header_files(sources)
+    find_all_header_files(hdrs "${ARG_ADDITIONAL_HEADER_DIRS}")
+    if (hdrs)
+      set_source_files_properties(${hdrs} PROPERTIES HEADER_FILE_ONLY ON)
+    endif()
     set_source_files_properties(${ARG_ADDITIONAL_HEADERS} PROPERTIES HEADER_FILE_ONLY ON)
-    list(APPEND sources ${ARG_ADDITIONAL_HEADERS})
+    list(APPEND sources ${ARG_ADDITIONAL_HEADERS} ${hdrs})
   endif()
 
   set( ${OUT_VAR} ${sources} PARENT_SCOPE )

lib/Support/CMakeLists.txt

   Valgrind.cpp
   Watchdog.cpp
 
-  ADDITIONAL_HEADERS
-  Unix/Host.inc
-  Unix/Memory.inc
-  Unix/Mutex.inc
-  Unix/Path.inc
-  Unix/Process.inc
-  Unix/Program.inc
-  Unix/RWMutex.inc
-  Unix/Signals.inc
-  Unix/ThreadLocal.inc
-  Unix/TimeValue.inc
-  Unix/Watchdog.inc
-  Windows/DynamicLibrary.inc
-  Windows/Host.inc
-  Windows/Memory.inc
-  Windows/Mutex.inc
-  Windows/Path.inc
-  Windows/Process.inc
-  Windows/Program.inc
-  Windows/RWMutex.inc
-  Windows/Signals.inc
-  Windows/ThreadLocal.inc
-  Windows/TimeValue.inc
-  Windows/Watchdog.inc
+  ADDITIONAL_HEADER_DIRS
+  Unix
+  Windows
 
   LINK_LIBS ${system_libs}
   )