config: store "git -c" variables using more robust format

The previous commit added a new format for $GIT_CONFIG_PARAMETERS which
is able to robustly handle subsections with "=" in them. Let's start
writing the new format. Unfortunately, this does much less than you'd
hope, because "git -c" itself has the same ambiguity problem! But it's
still worth doing:

  - we've now pushed the problem from the inter-process communication
    into the "-c" command-line parser. This would free us up to later
    add an unambiguous format there (e.g., separate arguments like "git
    --config key value", etc).

  - for --config-env, the parser already disallows "=" in the
    environment variable name. So:

      git --config-env section.with=equals.key=ENVVAR

    will robustly set section.with=equals.key to the contents of
    $ENVVAR.

The new test shows the improvement for --config-env.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -332,7 +332,7 @@ int git_config_include(const char *var, const char *value, void *data)
 	return ret;
 }
 
-void git_config_push_parameter(const char *text)
+static void git_config_push_split_parameter(const char *key, const char *value)
 {
 	struct strbuf env = STRBUF_INIT;
 	const char *old = getenv(CONFIG_DATA_ENVIRONMENT);
@@ -340,20 +340,60 @@ void git_config_push_parameter(const char *text)
 		strbuf_addstr(&env, old);
 		strbuf_addch(&env, ' ');
 	}
-	sq_quote_buf(&env, text);
+	sq_quote_buf(&env, key);
+	strbuf_addch(&env, '=');
+	if (value)
+		sq_quote_buf(&env, value);
 	setenv(CONFIG_DATA_ENVIRONMENT, env.buf, 1);
 	strbuf_release(&env);
 }
 
+void git_config_push_parameter(const char *text)
+{
+	const char *value;
+
+	/*
+	 * When we see:
+	 *
+	 *   section.subsection=with=equals.key=value
+	 *
+	 * we cannot tell if it means:
+	 *
+	 *   [section "subsection=with=equals"]
+	 *   key = value
+	 *
+	 * or:
+	 *
+	 *   [section]
+	 *   subsection = with=equals.key=value
+	 *
+	 * We parse left-to-right for the first "=", meaning we'll prefer to
+	 * keep the value intact over the subsection. This is historical, but
+	 * also sensible since values are more likely to contain odd or
+	 * untrusted input than a section name.
+	 *
+	 * A missing equals is explicitly allowed (as a bool-only entry).
+	 */
+	value = strchr(text, '=');
+	if (value) {
+		char *key = xmemdupz(text, value - text);
+		git_config_push_split_parameter(key, value + 1);
+		free(key);
+	} else {
+		git_config_push_split_parameter(text, NULL);
+	}
+}
+
 void git_config_push_env(const char *spec)
 {
-	struct strbuf buf = STRBUF_INIT;
+	char *key;
 	const char *env_name;
 	const char *env_value;
 
 	env_name = strrchr(spec, '=');
 	if (!env_name)
 		die(_("invalid config format: %s"), spec);
+	key = xmemdupz(spec, env_name - spec);
 	env_name++;
 	if (!*env_name)
 		die(_("missing environment variable name for configuration '%.*s'"),
@@ -364,10 +404,8 @@ void git_config_push_env(const char *spec)
 		die(_("missing environment variable '%s' for configuration '%.*s'"),
 		    env_name, (int)(env_name - spec - 1), spec);
 
-	strbuf_add(&buf, spec, env_name - spec);
-	strbuf_addstr(&buf, env_value);
-	git_config_push_parameter(buf.buf);
-	strbuf_release(&buf);
+	git_config_push_split_parameter(key, env_value);
+	free(key);
 }
 
 static inline int iskeychar(int c)

t/t1300-config.sh

@@ -1416,6 +1416,14 @@ test_expect_success 'git -c and --config-env override each other' '
 	test_cmp expect actual
 '
 
+test_expect_success '--config-env handles keys with equals' '
+	echo value=with=equals >expect &&
+	ENVVAR=value=with=equals git \
+		--config-env=section.subsection=with=equals.key=ENVVAR \
+		config section.subsection=with=equals.key >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'git config --edit works' '
 	git config -f tmp test.value no &&
 	echo test.value=yes >expect &&