parse: add git_parse_maybe_pathname()

This extraction of logic from config.c's git_config_pathname() allows
for parsing a fully-qualified path from a relative path along with
validation of the existence of the path without failing with a die().

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: derrickstolee

config.c

@@ -1278,24 +1278,12 @@ int git_config_string(char **dest, const char *var, const char *value)
 
 int git_config_pathname(char **dest, const char *var, const char *value)
 {
-	bool is_optional;
-	char *path;
-
 	if (!value)
 		return config_error_nonbool(var);
 
-	is_optional = skip_prefix(value, ":(optional)", &value);
-	path = interpolate_path(value, 0);
-	if (!path)
+	if (git_parse_maybe_pathname(value, dest) < 0)
 		die(_("failed to expand user dir in: '%s'"), value);
 
-	if (is_optional && is_missing_file(path)) {
-		free(path);
-		*dest = NULL;
-		return 0;
-	}
-
-	*dest = path;
 	return 0;
 }
 

parse.c

@@ -1,6 +1,7 @@
 #include "git-compat-util.h"
 #include "gettext.h"
 #include "parse.h"
+#include "path.h"
 
 static uintmax_t get_unit_factor(const char *end)
 {
@@ -209,3 +210,26 @@ unsigned long git_env_ulong(const char *k, unsigned long val)
 		die(_("failed to parse %s"), k);
 	return val;
 }
+
+int git_parse_maybe_pathname(const char *value, char **dest)
+{
+	bool is_optional;
+	char *path;
+
+	if (!value)
+		return -1;
+
+	is_optional = skip_prefix(value, ":(optional)", &value);
+	path = interpolate_path(value, 0);
+	if (!path)
+		return -1;
+
+	if (is_optional && is_missing_file(path)) {
+		free(path);
+		*dest = NULL;
+		return 0;
+	}
+
+	*dest = path;
+	return 0;
+}

parse.h

@@ -19,4 +19,6 @@ int git_parse_maybe_bool_text(const char *value);
 int git_env_bool(const char *, int);
 unsigned long git_env_ulong(const char *, unsigned long);
 
+int git_parse_maybe_pathname(const char *value, char **dest);
+
 #endif /* PARSE_H */