CMake: Clean up VersionFromVCS.cmake

[tstellar]

Summary

Fix a few problems in VersionFromVCS.cmake to make it more reliable:

• Stop using git svn info to retrieve the svn revision. I am unable to determine what the svn revision returned by this command means. During my testing this command returned a revision from a month ago which was not the HEAD of any of my local branches.
  
  Also, this revision was never actually added to the version string due to a typo in the script. All it was used for was to reject the revision number returned by git svn find-rev HEAD when the revision numbers didn't match.

• Populate LLVM_REPOSITORY variable using git svn info --url. This lets avoid having to do a search and replace on the output of git svn info

• Populate GIT_COMMIT even when we detect a git repo without any svn information.

[mgorny]

cmake/modules/VersionFromVCS.cmake

39

Sorry for a bit offtopic but any idea why are we having a timeout for git commands? AFAICS they do not involve any network activity, so I don't see a good reason to timeout here. Furthermore, git can be a bit slow which makes 5 seconds kinda dangerous.

[tstellar]

cmake/modules/VersionFromVCS.cmake

39

I think it was probably just a copy and paste from the svn commands. I can fix this in a follow up commit.

[beanz]

Mostly looks good, a few inline comments below.

cmake/modules/VersionFromVCS.cmake

37

If the git svn information hasn't been updated recently the output of this command will also contain the log of rebuilding the git-svn data. Maybe run git svn fetch first to rebuild. Then when you run git svn info --url the only output should be the url.

46–47

Instead of doing this strip you could add OUTPUT_STRIP_TRAILING_WHITESPACE to the execute_process call. The same applies to the other places we call string(STRIP...)

[tstellar]

Use OUTPUT_STRIP_TRAILING_WHITESPACE for some of the git commands.

Also, revert the changes made to the git svn info invocation. What
we have now works, and I think trying to use --url and add the additional
git svn fetch will complicate the patch too much. I really just want
to get the vcs revision parsing working.

[beanz]

LGTM!

cmake/modules/VersionFromVCS.cmake

if( Subversion_FOUND )
       endif()
       if( Project_WC_URL )
         set(LLVM_REPOSITORY ${Project_WC_URL} PARENT_SCOPE)
       endif()
     endif()
   elseif( EXISTS ${SOURCE_DIR}/.git )
     set(result "${result}git")
     # Try to get a ref-id
-    if( EXISTS ${SOURCE_DIR}/.git/svn )
-      find_program(git_executable NAMES git git.exe git.cmd)
-      if( git_executable )
-        set(is_git_svn_rev_exact false)
+
+      if( EXISTS ${SOURCE_DIR}/.git/svn )
+        # Get the repository URL
         execute_process(COMMAND
           ${git_executable} svn info
           WORKING_DIRECTORY ${SOURCE_DIR}
           TIMEOUT 5
           RESULT_VARIABLE git_result
           OUTPUT_VARIABLE git_output)
         if( git_result EQUAL 0 )
           string(REGEX MATCH "URL: ([^ \n]*)" svn_url ${git_output})
           if(svn_url)
             set(LLVM_REPOSITORY ${CMAKE_MATCH_1} PARENT_SCOPE)
           endif()
+        endif()
 
-          string(REGEX REPLACE "^(.*\n)?Revision: ([^\n]+).*"
-            "\\2" git_svn_rev_number "${git_output}")
-          set(SVN_REVISION ${git_svn_rev_number} PARENT_SCOPE)
-          set(git_svn_rev "-svn-${git_svn_rev}")
-
-          # Determine if the HEAD points directly at a subversion revision.
-          execute_process(COMMAND ${git_executable} svn find-rev HEAD
-            WORKING_DIRECTORY ${SOURCE_DIR}
-            TIMEOUT 5
-            RESULT_VARIABLE git_result
-            OUTPUT_VARIABLE git_output)
-          if( git_result EQUAL 0 )
-            string(STRIP "${git_output}" git_head_svn_rev_number)
-            if( git_head_svn_rev_number EQUAL git_svn_rev_number )
-              set(is_git_svn_rev_exact true)
-            endif()
-          endif()
+        # Get the svn revision number for this git commit if one exists.
+          OUTPUT_VARIABLE git_head_svn_rev_number
+          OUTPUT_STRIP_TRAILING_WHITESPACE)
+        if( git_result EQUAL 0 AND git_output)
+          set(SVN_REVISION ${git_head_svn_rev_number} PARENT_SCOPE)
+          set(git_svn_rev "-svn-${git_head_svn_rev_number}")
         else()
           set(git_svn_rev "")
         endif()
-        execute_process(COMMAND
-          ${git_executable} rev-parse --short HEAD
-          WORKING_DIRECTORY ${SOURCE_DIR}
-          TIMEOUT 5
-          RESULT_VARIABLE git_result
-          OUTPUT_VARIABLE git_output)
+      endif()
+
+      # Get the git ref id
+        OUTPUT_VARIABLE git_ref_id
+        OUTPUT_STRIP_TRAILING_WHITESPACE)
 
-        if( git_result EQUAL 0 AND NOT is_git_svn_rev_exact )
-          string(STRIP "${git_output}" git_ref_id)
-          set(GIT_COMMIT ${git_ref_id} PARENT_SCOPE)
-          set(result "${result}${git_svn_rev}-${git_ref_id}")
-        else()
-          set(result "${result}${git_svn_rev}")
-        endif()
-
-      endif()
+      if( git_result EQUAL 0 )
     endif()
   endif()
   set(${VERS} ${result} PARENT_SCOPE)
 endfunction(add_version_info_from_vcs)