docs: address inaccurate --empty default with --exec

The documentation for git-rebase(1) indicates that using the `--exec`
option will use `--empty=drop`. This is inaccurate: when `--interactive`
is not explicitly provided, `--exec` results in `--empty=keep`
behaviors.

Correctly indicate the behavior of `--exec` using `--empty=keep` when
`--interactive` is not specified.

Reported-by: Phillip Wood <[email protected]>
Signed-off-by: Brian Lyles <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: zivarah

Documentation/git-rebase.txt

@@ -295,11 +295,11 @@ See also INCOMPATIBLE OPTIONS below.
 	empty after rebasing (because they contain a subset of already
 	upstream changes).  With drop (the default), commits that
 	become empty are dropped.  With keep, such commits are kept.
-	With ask (implied by `--interactive`), the rebase will halt when
-	an empty commit is applied allowing you to choose whether to
-	drop it, edit files more, or just commit the empty changes.
-	Other options, like `--exec`, will use the default of drop unless
-	`-i`/`--interactive` is explicitly specified.
+	With ask, the rebase will halt when an empty commit is applied
+	allowing you to choose whether to drop it, edit files more, or just
+	commit the empty changes.
+	When the `-i`/`--interactive` option is used, the default becomes ask.
+	Otherwise, when the `--exec` option is used, the default becomes keep.
 +
 Note that commits which start empty are kept (unless `--no-keep-empty`
 is specified), and commits which are clean cherry-picks (as determined

t/t3424-rebase-empty.sh

@@ -167,4 +167,42 @@ test_expect_success 'rebase --merge does not leave state laying around' '
 	test_path_is_missing .git/MERGE_MSG
 '
 
+test_expect_success 'rebase --exec --empty=drop' '
+	git checkout -B testing localmods &&
+	git rebase --exec "true" --empty=drop upstream &&
+
+	test_write_lines D C B A >expect &&
+	git log --format=%s >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --exec --empty=keep' '
+	git checkout -B testing localmods &&
+	git rebase --exec "true" --empty=keep upstream &&
+
+	test_write_lines D C2 C B A >expect &&
+	git log --format=%s >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --exec uses default of --empty=keep' '
+	git checkout -B testing localmods &&
+	git rebase --exec "true" upstream &&
+
+	test_write_lines D C2 C B A >expect &&
+	git log --format=%s >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'rebase --exec --empty=ask' '
+	git checkout -B testing localmods &&
+	test_must_fail git rebase --exec "true" --empty=ask upstream &&
+
+	git rebase --skip &&
+
+	test_write_lines D C B A >expect &&
+	git log --format=%s >actual &&
+	test_cmp expect actual
+'
+
 test_done