alias: treat empty subsection [alias ""] as plain [alias]

When git-config stores a key of the form alias..name, it records
it under an empty subsection ([alias ""]). The new subsection-aware
alias lookup would see a non-NULL but zero-length subsection and
fall into the subsection code path, where it required a "command"
key and thus silently ignored the entry.

Normalize an empty subsection to NULL before any further processing
so that entries stored this way continue to work as plain
case-insensitive aliases, matching the pre-subsection behaviour.

Users who relied on alias..name to create an alias literally named
".name" may want to migrate to subsection syntax, which looks less confusing:

    [alias ".name"]
        command = <value>

Add tests covering both the empty-subsection compatibility case and
the leading-dot alias via the new syntax.

Signed-off-by: Jonatan Holmgren <jonatan@jontes.page>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: jonatan-holmgren

alias.c

@@ -30,6 +30,10 @@ static int config_alias_cb(const char *var, const char *value,
 	 * - [alias "name"]
 	 *       command = value  (with subsection, case-sensitive)
 	 */
+	/* Treat [alias ""] (empty subsection) the same as plain [alias]. */
+	if (subsection && !subsection_len)
+		subsection = NULL;
+
 	if (subsection && strcmp(key, "command"))
 		return 0;
 

t/t0014-alias.sh

@@ -183,4 +183,18 @@ test_expect_success 'subsection aliases listed in help -a' '
 	test_grep "förgrena" output
 '
 
+test_expect_success 'empty subsection treated as no subsection' '
+	test_config "alias..something" "!echo foobar" &&
+	git something >actual &&
+	echo foobar >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'alias with leading dot via subsection syntax' '
+	test_config alias.".something".command "!echo foobar" &&
+	git .something >actual &&
+	echo foobar >expect &&
+	test_cmp expect actual
+'
+
 test_done