Merge branch 'ob/revert-of-revert-is-reapply'

The default log message created by "git revert", when reverting a
commit that records a revert, has been tweaked.

* ob/revert-of-revert-is-reapply:
  git-revert.txt: add discussion
  sequencer: beautify subject of reverts of reverts

3 files changed, 44 insertions, 0 deletions

diff --git a/Documentation/git-revert.txt b/Documentation/git-revert.txt
index d2e10d3dce..cbe0208834 100644
--- a/Documentation/git-revert.txt
+++ b/Documentation/git-revert.txt
@@ -142,6 +142,16 @@ EXAMPLES
 	changes. The revert only modifies the working tree and the
 	index.
 
+DISCUSSION
+----------
+
+While git creates a basic commit message automatically, it is
+_strongly_ recommended to explain why the original commit is being
+reverted.
+In addition, repeatedly reverting reverts will result in increasingly
+unwieldy subject lines, for example 'Reapply "Reapply "<original subject>""'.
+Please consider rewording these to be shorter and more unique.
+
 CONFIGURATION
 -------------
 
diff --git a/sequencer.c b/sequencer.c
index afebf7e37c..3c5fdd68f4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2257,6 +2257,8 @@ static int do_pick_commit(struct repository *r,
 	 */
 
 	if (command == TODO_REVERT) {
+		const char *orig_subject;
+
 		base = commit;
 		base_label = msg.label;
 		next = parent;
@@ -2264,6 +2266,15 @@ static int do_pick_commit(struct repository *r,
 		if (opts->commit_use_reference) {
 			strbuf_addstr(&msgbuf,
 				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
+		} else if (skip_prefix(msg.subject, "Revert \"", &orig_subject) &&
+			   /*
+			    * We don't touch pre-existing repeated reverts, because
+			    * theoretically these can be nested arbitrarily deeply,
+			    * thus requiring excessive complexity to deal with.
+			    */
+			   !starts_with(orig_subject, "Revert \"")) {
+			strbuf_addstr(&msgbuf, "Reapply \"");
+			strbuf_addstr(&msgbuf, orig_subject);
 		} else {
 			strbuf_addstr(&msgbuf, "Revert \"");
 			strbuf_addstr(&msgbuf, msg.subject);
diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
index e2ef619323..4158590322 100755
--- a/t/t3501-revert-cherry-pick.sh
+++ b/t/t3501-revert-cherry-pick.sh
@@ -176,6 +176,29 @@ test_expect_success 'advice from failed revert' '
 	test_cmp expected actual
 '
 
+test_expect_subject () {
+	echo "$1" >expect &&
+	git log -1 --pretty=%s >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'titles of fresh reverts' '
+	test_commit --no-tag A file1 &&
+	test_commit --no-tag B file1 &&
+	git revert --no-edit HEAD &&
+	test_expect_subject "Revert \"B\"" &&
+	git revert --no-edit HEAD &&
+	test_expect_subject "Reapply \"B\"" &&
+	git revert --no-edit HEAD &&
+	test_expect_subject "Revert \"Reapply \"B\"\""
+'
+
+test_expect_success 'title of legacy double revert' '
+	test_commit --no-tag "Revert \"Revert \"B\"\"" file1 &&
+	git revert --no-edit HEAD &&
+	test_expect_subject "Revert \"Revert \"Revert \"B\"\"\""
+'
+
 test_expect_success 'identification of reverted commit (default)' '
 	test_commit to-ident &&
 	test_when_finished "git reset --hard to-ident" &&