pull --rebase=<type>: allow single-letter abbreviations for the type

Git for Windows' original 4aa8b8c828 (Teach 'git pull' to handle
--rebase=interactive, 2011-10-21) had support for the very convenient
abbreviation

	git pull --rebase=i

which was later lost when it was ported to the builtin `git pull`, and
it was not introduced before the patch eventually made it into Git as
f5eb87b98d (pull: allow interactive rebase with --rebase=interactive,
2016-01-13).

However, it is *really* a useful short hand for the occasional rebasing
pull on branches that do not usually want to be rebased.

So let's reintroduce this convenience, at long last.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pull.c

@@ -48,11 +48,11 @@ static enum rebase_type parse_config_rebase(const char *key, const char *value,
 		return REBASE_FALSE;
 	else if (v > 0)
 		return REBASE_TRUE;
-	else if (!strcmp(value, "preserve"))
+	else if (!strcmp(value, "preserve") || !strcmp(value, "p"))
 		return REBASE_PRESERVE;
-	else if (!strcmp(value, "merges"))
+	else if (!strcmp(value, "merges") || !strcmp(value, "m"))
 		return REBASE_MERGES;
-	else if (!strcmp(value, "interactive"))
+	else if (!strcmp(value, "interactive") || !strcmp(value, "i"))
 		return REBASE_INTERACTIVE;
 
 	if (fatal)

t/t5520-pull.sh

@@ -475,10 +475,22 @@ test_expect_success 'pull.rebase=interactive' '
 	false
 	EOF
 	test_set_editor "$TRASH_DIRECTORY/fake-editor" &&
+	test_when_finished "test_might_fail git rebase --abort" &&
 	test_must_fail git pull --rebase=interactive . copy &&
 	test "I was here" = "$(cat fake.out)"
 '
 
+test_expect_success 'pull --rebase=i' '
+	write_script "$TRASH_DIRECTORY/fake-editor" <<-\EOF &&
+	echo I was here, too >fake.out &&
+	false
+	EOF
+	test_set_editor "$TRASH_DIRECTORY/fake-editor" &&
+	test_when_finished "test_might_fail git rebase --abort" &&
+	test_must_fail git pull --rebase=i . copy &&
+	test "I was here, too" = "$(cat fake.out)"
+'
+
 test_expect_success 'pull.rebase=invalid fails' '
 	git reset --hard before-preserve-rebase &&
 	test_config pull.rebase invalid &&