[PATCH 18/18] completion: support branch-diff

Tab completion of `branch-diff` is very convenient, especially given
that the revision arguments that need to be passed to `git branch-diff`
are typically more complex than, say, your grandfather's `git log`
arguments.

Without this patch, we would only complete the `branch-diff` part but
not the options and other arguments.

This of itself may already be slightly disruptive for well-trained
fingers that assume that `git bra<TAB>ori<TAB>mas<TAB>` would expand to
`git branch origin/master`, as we now no longer automatically append a
space after completing `git branch`: this is now ambiguous.

Signed-off-by: Johannes Schindelin <redacted>
---
 contrib/completion/git-completion.bash | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 01dd9ff07a2..45addd525ac 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash

@@ -1496,6 +1496,24 @@ _git_format_patch ()
 	__git_complete_revlist
 }
 
+__git_branch_diff_options="
+	--no-patches --creation-weight= --dual-color
+"
+
+_git_branch_diff ()
+{
+	case "$cur" in
+	--*)
+		__gitcomp "
+			$__git_branch_diff_options
+			$__git_diff_common_options
+			"
+		return
+		;;
+	esac
+	__git_complete_revlist
+}
+
 _git_fsck ()
 {
 	case "$cur" in

-- 
2.17.0.395.g6a618d6010f.dirty