Refactor type_from_string() to allow continuing after detecting an error

In the next commits, we will enhance the fsck_tag() function to check
tag objects more thoroughly. To this end, we need a function to verify
that a given string is a valid object type, but that does not die() in
the negative case.

While at it, prepare type_from_string() for counted strings, i.e. strings
with an explicitly specified length rather than a NUL termination.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object.c

@@ -33,13 +33,20 @@ const char *typename(unsigned int type)
 	return object_type_strings[type];
 }
 
-int type_from_string(const char *str)
+int type_from_string_gently(const char *str, ssize_t len, int gentle)
 {
 	int i;
 
+	if (len < 0)
+		len = strlen(str);
+
 	for (i = 1; i < ARRAY_SIZE(object_type_strings); i++)
-		if (!strcmp(str, object_type_strings[i]))
+		if (!strncmp(str, object_type_strings[i], len))
 			return i;
+
+	if (gentle)
+		return -1;
+
 	die("invalid object type \"%s\"", str);
 }
 

object.h

@@ -53,7 +53,8 @@ struct object {
 };
 
 extern const char *typename(unsigned int type);
-extern int type_from_string(const char *str);
+extern int type_from_string_gently(const char *str, ssize_t, int gentle);
+#define type_from_string(str) type_from_string_gently(str, -1, 0)
 
 /*
  * Return the current number of buckets in the object hashmap.