status: support --porcelain[=<version>]

Update --porcelain argument to take optional version parameter
to allow multiple porcelain formats to be supported in the future.

The token "v1" is the default value and indicates the traditional
porcelain format.  (The token "1" is an alias for that.)

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-status.txt

@@ -32,11 +32,14 @@ OPTIONS
 --branch::
 	Show the branch and tracking info even in short-format.
 
---porcelain::
+--porcelain[=<version>]::
 	Give the output in an easy-to-parse format for scripts.
 	This is similar to the short output, but will remain stable
 	across Git versions and regardless of user configuration. See
 	below for details.
++
+The version parameter is used to specify the format version.
+This is optional and defaults to the original version 'v1' format.
 
 --long::
 	Give the output in the long-format. This is the default.
@@ -96,7 +99,7 @@ configuration variable documented in linkgit:git-config[1].
 
 -z::
 	Terminate entries with NUL, instead of LF.  This implies
-	the `--porcelain` output format if no other format is given.
+	the `--porcelain=v1` output format if no other format is given.
 
 --column[=<options>]::
 --no-column::

builtin/commit.c

@@ -144,6 +144,21 @@ static struct strbuf message = STRBUF_INIT;
 
 static enum wt_status_format status_format = STATUS_FORMAT_UNSPECIFIED;
 
+static int opt_parse_porcelain(const struct option *opt, const char *arg, int unset)
+{
+	enum wt_status_format *value = (enum wt_status_format *)opt->value;
+	if (unset)
+		*value = STATUS_FORMAT_NONE;
+	else if (!arg)
+		*value = STATUS_FORMAT_PORCELAIN;
+	else if (!strcmp(arg, "v1") || !strcmp(arg, "1"))
+		*value = STATUS_FORMAT_PORCELAIN;
+	else
+		die("unsupported porcelain version '%s'", arg);
+
+	return 0;
+}
+
 static int opt_parse_m(const struct option *opt, const char *arg, int unset)
 {
 	struct strbuf *buf = opt->value;
@@ -1316,9 +1331,9 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 			    N_("show status concisely"), STATUS_FORMAT_SHORT),
 		OPT_BOOL('b', "branch", &s.show_branch,
 			 N_("show branch information")),
-		OPT_SET_INT(0, "porcelain", &status_format,
-			    N_("machine-readable output"),
-			    STATUS_FORMAT_PORCELAIN),
+		{ OPTION_CALLBACK, 0, "porcelain", &status_format,
+		  N_("version"), N_("machine-readable output"),
+		  PARSE_OPT_OPTARG, opt_parse_porcelain },
 		OPT_SET_INT(0, "long", &status_format,
 			    N_("show status in long format (default)"),
 			    STATUS_FORMAT_LONG),

t/t7060-wtstatus.sh

@@ -228,4 +228,25 @@ test_expect_success 'status --branch with detached HEAD' '
 	test_i18ncmp expected actual
 '
 
+## Duplicate the above test and verify --porcelain=v1 arg parsing.
+test_expect_success 'status --porcelain=v1 --branch with detached HEAD' '
+	git reset --hard &&
+	git checkout master^0 &&
+	git status --branch --porcelain=v1 >actual &&
+	cat >expected <<-EOF &&
+	## HEAD (no branch)
+	?? .gitconfig
+	?? actual
+	?? expect
+	?? expected
+	?? mdconflict/
+	EOF
+	test_i18ncmp expected actual
+'
+
+## Verify parser error on invalid --porcelain argument.
+test_expect_success 'status --porcelain=bogus' '
+	test_must_fail git status --porcelain=bogus
+'
+
 test_done