git: support separate arg for `--config-env`'s value

While not documented as such, many of the top-level options like
`--git-dir` and `--work-tree` support two syntaxes: they accept both an
equals sign between option and its value, and they do support option and
value as two separate arguments. The recently added `--config-env`
option only supports the syntax with an equals sign.

Mitigate this inconsistency by accepting both syntaxes and add tests to
verify both work.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -255,6 +255,14 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			git_config_push_parameter((*argv)[1]);
 			(*argv)++;
 			(*argc)--;
+		} else if (!strcmp(cmd, "--config-env")) {
+			if (*argc < 2) {
+				fprintf(stderr, _("no config key given for --config-env\n" ));
+				usage(git_usage_string);
+			}
+			git_config_push_env((*argv)[1]);
+			(*argv)++;
+			(*argc)--;
 		} else if (skip_prefix(cmd, "--config-env=", &cmd)) {
 			git_config_push_env(cmd);
 		} else if (!strcmp(cmd, "--literal-pathspecs")) {

t/t1300-config.sh

@@ -1372,16 +1372,29 @@ test_expect_success 'git --config-env=key=envvar support' '
 	cat >expect <<-\EOF &&
 	value
 	value
+	value
+	value
+	false
 	false
 	EOF
 	{
 		ENVVAR=value git --config-env=core.name=ENVVAR config core.name &&
+		ENVVAR=value git --config-env core.name=ENVVAR config core.name &&
 		ENVVAR=value git --config-env=foo.CamelCase=ENVVAR config foo.camelcase &&
-		ENVVAR= git --config-env=foo.flag=ENVVAR config --bool foo.flag
+		ENVVAR=value git --config-env foo.CamelCase=ENVVAR config foo.camelcase &&
+		ENVVAR= git --config-env=foo.flag=ENVVAR config --bool foo.flag &&
+		ENVVAR= git --config-env foo.flag=ENVVAR config --bool foo.flag
 	} >actual &&
 	test_cmp expect actual
 '
 
+test_expect_success 'git --config-env with missing value' '
+	test_must_fail env ENVVAR=value git --config-env 2>error &&
+	grep "no config key given for --config-env" error &&
+	test_must_fail env ENVVAR=value git --config-env config core.name 2>error &&
+	grep "invalid config format: config" error
+'
+
 test_expect_success 'git --config-env fails with invalid parameters' '
 	test_must_fail git --config-env=foo.flag config --bool foo.flag 2>error &&
 	test_i18ngrep "invalid config format: foo.flag" error &&