git-commit: Allow to amend a merge commit that does not change the tree

Johannes Sixt · gitster · commit 13aba1e514c1 · 2007-12-03T00:25:26.000-08:00
Normally, it should not be allowed to generate an empty commit. A merge commit generated with git 'merge -s ours' does not change the tree (along the first parent), but merges are not "empty" even if they do not change the tree. Hence, commit 8588452 allowed to amend a merge commit that does not change the tree, but 4fb5fd5 disallowed it again in an attempt to avoid that an existing commit is amended such that it becomes empty. With this change, a commit can be edited (create a new one or amend an existing one) either if there are changes or if there are at least two parents. Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at> Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-commit.sh b/git-commit.sh
@@ -515,13 +515,16 @@ else
 	# we need to check if there is anything to commit
 	run_status >/dev/null
 fi
-if [ "$?" != "0" -a ! -f "$GIT_DIR/MERGE_HEAD" ]
-then
+case "$?,$PARENTS" in
+0,* | *,-p' '?*-p' '?*)
+	# a merge commit can record the same tree as its parent.
+	;;
+*)
 	rm -f "$GIT_DIR/COMMIT_EDITMSG" "$GIT_DIR/SQUASH_MSG"
 	use_status_color=t
 	run_status
 	exit 1
-fi
+esac
 
 case "$no_edit" in
 '')
diff --git a/t/t7501-commit.sh b/t/t7501-commit.sh
@@ -244,4 +244,36 @@ test_expect_success 'multiple -m' '
 
 '
 
+test_expect_success 'same tree (single parent)' '
+
+	if git commit -m empty
+	then
+		echo oops -- should have complained
+		false
+	else
+		: happy
+	fi
+
+'
+
+test_expect_success 'same tree (merge and amend merge)' '
+
+	git checkout -b side HEAD^ &&
+	echo zero >zero &&
+	git add zero &&
+	git commit -m "add zero" &&
+	git checkout master &&
+
+	git merge -s ours side -m "empty ok" &&
+	git diff HEAD^ HEAD >actual &&
+	: >expected &&
+	diff -u expected actual &&
+
+	git commit --amend -m "empty really ok" &&
+	git diff HEAD^ HEAD >actual &&
+	: >expected &&
+	diff -u expected actual
+
+'
+
 test_done
