How to add better copy detection to gitk?

In command line Git, the show, diff and log commands have got an option to --find-copies-harder.

Is there a way I can tell (or patch) gitk to use this, too? I need this from time to time, and my projects are small enough such that I don't care about the reduced performance.

(I don't want to craft the history to force copy detection any more.)

I noticed that the --find-copies-harder appears within the gitk code, but I don't understand why. So I have tried the command line gitk --all --find-copies-harder, but it didn't work: In a commit with a new file copied from another versioned file, gitk still did not display the fact that this file was copied.

Update: Editing the view by entering --find-copies-harder into the field Additional arguments to git log: also has no effect: A copied (and slightly modified) file is still not shown as copied, while in the command line git show --find-copies-harder it is.

Solution

The necessary change is:

diff --git a/gitk-git/gitk b/gitk-git/gitk
index 23d9dd1fe0..a98a115080 100755
--- a/gitk-git/gitk
+++ b/gitk-git/gitk
@@ -7909,7 +7909,7 @@ proc diffcmd {ids flags} {
         if {$log_showroot} {
             lappend flags --root
         }
-        set cmd [concat | git diff-tree -r $flags $ids]
+        set cmd [concat | git diff-tree --find-copies-harder -r $flags $ids]
     }
     return $cmd
 }

With this, gitk displays the copy in the second commit of the following test repository

git init
echo "a file" > a
git add a
git commit -m "a file"
cp a b
git add b
git commit -m "a copy"

as desired:

-------------------------------------- b --------------------------------------
similarity index 100%
copy from a
copy to b

But note that there might be unintended side effects, since the modified procedure 'diffcmd' is called in several places. I did not systematically test all these code paths.

(I have also sent a generalized version of this patch to the Git mailing list.)