log: if --decorate is not given, default to --decorate=auto

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -52,6 +52,11 @@ struct line_opt_callback_data {
 	struct string_list args;
 };
 
+static int auto_decoration_style(void)
+{
+	return (isatty(1) || pager_in_use()) ? DECORATE_SHORT_REFS : 0;
+}
+
 static int parse_decoration_style(const char *var, const char *value)
 {
 	switch (git_config_maybe_bool(var, value)) {
@@ -67,7 +72,7 @@ static int parse_decoration_style(const char *var, const char *value)
 	else if (!strcmp(value, "short"))
 		return DECORATE_SHORT_REFS;
 	else if (!strcmp(value, "auto"))
-		return (isatty(1) || pager_in_use()) ? DECORATE_SHORT_REFS : 0;
+		return auto_decoration_style();
 	return -1;
 }
 
@@ -405,6 +410,8 @@ static int git_log_config(const char *var, const char *value, void *cb)
 		if (decoration_style < 0)
 			decoration_style = 0; /* maybe warn? */
 		return 0;
+	} else {
+		decoration_style = auto_decoration_style();
 	}
 	if (!strcmp(var, "log.showroot")) {
 		default_show_root = git_config_bool(var, value);

t/t4202-log.sh

@@ -4,6 +4,7 @@ test_description='git log'
 
 . ./test-lib.sh
 . "$TEST_DIRECTORY/lib-gpg.sh"
+. "$TEST_DIRECTORY/lib-terminal.sh"
 
 test_expect_success setup '
 
@@ -520,7 +521,7 @@ test_expect_success 'log --graph with merge' '
 '
 
 test_expect_success 'log.decorate configuration' '
-	git log --oneline >expect.none &&
+	git log --oneline --no-decorate >expect.none &&
 	git log --oneline --decorate >expect.short &&
 	git log --oneline --decorate=full >expect.full &&
 
@@ -576,6 +577,13 @@ test_expect_success 'log.decorate configuration' '
 
 '
 
+test_expect_success TTY 'log output on a TTY' '
+	git log --oneline --decorate >expect.short &&
+
+	test_terminal git log --oneline >actual &&
+	test_cmp expect.short actual
+'
+
 test_expect_success 'reflog is expected format' '
 	git log -g --abbrev-commit --pretty=oneline >expect &&
 	git reflog >actual &&