config: preserve <subsection> case for one-shot config on the command line

The "git -c <var>=<val> cmd" mechanism is to pretend that a
configuration variable <var> is set to <val> while the cmd is
running.  The code to do so however downcased <var> in its entirety,
which is wrong for a three-level <section>.<subsection>.<variable>.

The <subsection> part needs to stay as-is.

Reported-by: Lars Schneider <larsxschneider@gmail.com>
Diagnosed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 75 insertions, 1 deletions

diff --git a/config.c b/config.c
index 0dfed682b8..4128debc71 100644
--- a/config.c
+++ b/config.c
@@ -199,6 +199,34 @@ void git_config_push_parameter(const char *text)
 	strbuf_release(&env);
 }
 
+/*
+ * downcase the <section> and <variable> in <section>.<variable> or
+ * <section>.<subsection>.<variable> and do so in place.  <subsection>
+ * is left intact.
+ */
+static void canonicalize_config_variable_name(char *varname)
+{
+	char *cp, *last_dot;
+
+	/* downcase the first segment */
+	for (cp = varname; *cp; cp++) {
+		if (*cp == '.')
+			break;
+		*cp = tolower(*cp);
+	}
+	if (!*cp)
+		return;
+
+	/* find the last dot (we start from the first dot we just found) */
+	for (last_dot = cp; *cp; cp++)
+		if (*cp == '.')
+			last_dot = cp;
+
+	/* downcase the last segment */
+	for (cp = last_dot; *cp; cp++)
+		*cp = tolower(*cp);
+}
+
 int git_config_parse_parameter(const char *text,
 			       config_fn_t fn, void *data)
 {
@@ -221,7 +249,7 @@ int git_config_parse_parameter(const char *text,
 		strbuf_list_free(pair);
 		return error("bogus config parameter: %s", text);
 	}
-	strbuf_tolower(pair[0]);
+	canonicalize_config_variable_name(pair[0]->buf);
 	if (fn(pair[0]->buf, value, data) < 0) {
 		strbuf_list_free(pair);
 		return -1;
diff --git a/t/t1300-repo-config.sh b/t/t1300-repo-config.sh
index 923bfc5a26..7a16f66a9d 100755
--- a/t/t1300-repo-config.sh
+++ b/t/t1300-repo-config.sh
@@ -1097,6 +1097,52 @@ test_expect_success 'multiple git -c appends config' '
 	test_cmp expect actual
 '
 
+test_expect_success 'last one wins: two level vars' '
+
+	# sec.var and sec.VAR are the same variable, as the first
+	# and the last level of a configuration variable name is
+	# case insensitive.
+
+	echo VAL >expect &&
+
+	git -c sec.var=val -c sec.VAR=VAL config --get sec.var >actual &&
+	test_cmp expect actual &&
+	git -c SEC.var=val -c sec.var=VAL config --get sec.var >actual &&
+	test_cmp expect actual &&
+
+	git -c sec.var=val -c sec.VAR=VAL config --get SEC.var >actual &&
+	test_cmp expect actual &&
+	git -c SEC.var=val -c sec.var=VAL config --get sec.VAR >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'last one wins: three level vars' '
+
+	# v.a.r and v.A.r are not the same variable, as the middle
+	# level of a three-level configuration variable name is
+	# case sensitive.
+
+	echo val >expect &&
+	git -c v.a.r=val -c v.A.r=VAL config --get v.a.r >actual &&
+	test_cmp expect actual &&
+	git -c v.a.r=val -c v.A.r=VAL config --get V.a.R >actual &&
+	test_cmp expect actual &&
+
+	# v.a.r and V.a.R are the same variable, as the first
+	# and the last level of a configuration variable name is
+	# case insensitive.
+
+	echo VAL >expect &&
+	git -c v.a.r=val -c v.a.R=VAL config --get v.a.r >actual &&
+	test_cmp expect actual &&
+	git -c v.a.r=val -c V.a.r=VAL config --get v.a.r >actual &&
+	test_cmp expect actual &&
+	git -c v.a.r=val -c v.a.R=VAL config --get V.a.R >actual &&
+	test_cmp expect actual &&
+	git -c v.a.r=val -c V.a.r=VAL config --get V.a.R >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'git -c is not confused by empty environment' '
 	GIT_CONFIG_PARAMETERS="" git -c x.one=1 config --list
 '