config: teach "git config --file -" to read from the standard input

The patch extends git config --file interface to allow read config from
stdin.

Editing stdin or setting value in stdin is an error.

Include by absolute path is allowed in stdin config, but not by relative
path.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/config.c

@@ -360,6 +360,9 @@ static int get_colorbool(int print)
 
 static void check_write(void)
 {
+	if (given_config_source.use_stdin)
+		die("writing to stdin is not supported");
+
 	if (given_config_source.blob)
 		die("writing config blobs is not supported");
 }
@@ -472,6 +475,12 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_config_usage, builtin_config_options);
 	}
 
+	if (given_config_source.file &&
+			!strcmp(given_config_source.file, "-")) {
+		given_config_source.file = NULL;
+		given_config_source.use_stdin = 1;
+	}
+
 	if (use_global_config) {
 		char *user_config = NULL;
 		char *xdg_config = NULL;
@@ -558,6 +567,8 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		check_argc(argc, 0, 0);
 		if (!given_config_source.file && nongit)
 			die("not in a git directory");
+		if (given_config_source.use_stdin)
+			die("editing stdin is not supported");
 		if (given_config_source.blob)
 			die("editing blobs is not supported");
 		git_config(git_default_config, NULL);

cache.h

@@ -1147,6 +1147,7 @@ extern int update_server_info(int);
 #define CONFIG_GENERIC_ERROR 7
 
 struct git_config_source {
+	unsigned int use_stdin:1;
 	const char *file;
 	const char *blob;
 };

config.c

@@ -1031,24 +1031,35 @@ static int do_config_from(struct config_source *top, config_fn_t fn, void *data)
 	return ret;
 }
 
+static int do_config_from_file(config_fn_t fn,
+		const char *name, const char *path, FILE *f, void *data)
+{
+	struct config_source top;
+
+	top.u.file = f;
+	top.name = name;
+	top.path = path;
+	top.die_on_error = 1;
+	top.do_fgetc = config_file_fgetc;
+	top.do_ungetc = config_file_ungetc;
+	top.do_ftell = config_file_ftell;
+
+	return do_config_from(&top, fn, data);
+}
+
+static int git_config_from_stdin(config_fn_t fn, void *data)
+{
+	return do_config_from_file(fn, "<stdin>", NULL, stdin, data);
+}
+
 int git_config_from_file(config_fn_t fn, const char *filename, void *data)
 {
-	int ret;
-	FILE *f = fopen(filename, "r");
+	int ret = -1;
+	FILE *f;
 
-	ret = -1;
+	f = fopen(filename, "r");
 	if (f) {
-		struct config_source top;
-
-		top.u.file = f;
-		top.name = top.path = filename;
-		top.die_on_error = 1;
-		top.do_fgetc = config_file_fgetc;
-		top.do_ungetc = config_file_ungetc;
-		top.do_ftell = config_file_ftell;
-
-		ret = do_config_from(&top, fn, data);
-
+		ret = do_config_from_file(fn, filename, filename, f, data);
 		fclose(f);
 	}
 	return ret;
@@ -1190,7 +1201,9 @@ int git_config_with_options(config_fn_t fn, void *data,
 	 * If we have a specific filename, use it. Otherwise, follow the
 	 * regular lookup sequence.
 	 */
-	if (config_source && config_source->file)
+	if (config_source && config_source->use_stdin)
+		return git_config_from_stdin(fn, data);
+	else if (config_source && config_source->file)
 		return git_config_from_file(fn, config_source->file, data);
 	else if (config_source && config_source->blob)
 		return git_config_from_blob_ref(fn, config_source->blob, data);

t/t1300-repo-config.sh

@@ -475,15 +475,28 @@ ein.bahn=strasse
 EOF
 
 test_expect_success 'alternative GIT_CONFIG' '
-	GIT_CONFIG=other-config git config -l >output &&
+	GIT_CONFIG=other-config git config --list >output &&
 	test_cmp expect output
 '
 
 test_expect_success 'alternative GIT_CONFIG (--file)' '
-	git config --file other-config -l > output &&
+	git config --file other-config --list >output &&
 	test_cmp expect output
 '
 
+test_expect_success 'alternative GIT_CONFIG (--file=-)' '
+	git config --file - --list <other-config >output &&
+	test_cmp expect output
+'
+
+test_expect_success 'setting a value in stdin is an error' '
+	test_must_fail git config --file - some.value foo
+'
+
+test_expect_success 'editing stdin is an error' '
+	test_must_fail git config --file - --edit
+'
+
 test_expect_success 'refer config from subdirectory' '
 	mkdir x &&
 	(

t/t1305-config-include.sh

@@ -113,7 +113,7 @@ test_expect_success 'missing include files are ignored' '
 test_expect_success 'absolute includes from command line work' '
 	echo "[test]one = 1" >one &&
 	echo 1 >expect &&
-	git -c include.path="$PWD/one" config test.one >actual &&
+	git -c include.path="$(pwd)/one" config test.one >actual &&
 	test_cmp expect actual
 '
 
@@ -138,6 +138,20 @@ test_expect_success 'relative includes from blobs fail' '
 	test_must_fail git config --blob=$blob test.one
 '
 
+test_expect_success 'absolute includes from stdin work' '
+	echo "[test]one = 1" >one &&
+	echo 1 >expect &&
+	echo "[include]path=\"$(pwd)/one\"" |
+	git config --file - test.one >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'relative includes from stdin line fail' '
+	echo "[test]one = 1" >one &&
+	echo "[include]path=one" |
+	test_must_fail git config --file - test.one
+'
+
 test_expect_success 'include cycles are detected' '
 	cat >.gitconfig <<-\EOF &&
 	[test]value = gitconfig