attr: expose validity check for attribute names

Export attr_name_valid() function, and a helper function that
returns the message to be given when a given <name, len> pair
is not a good name for an attribute.

We could later update the message to exactly spell out what the
rules for a good attribute name are, etc.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 35 insertions, 14 deletions

diff --git a/attr.c b/attr.c
index 9bec24352f..14bbfd4245 100644
--- a/attr.c
+++ b/attr.c
@@ -59,23 +59,38 @@ static unsigned hash_name(const char *name, int namelen)
 	return val;
 }
 
-static int invalid_attr_name(const char *name, int namelen)
+int attr_name_valid(const char *name, size_t namelen)
 {
 	/*
 	 * Attribute name cannot begin with '-' and must consist of
 	 * characters from [-A-Za-z0-9_.].
 	 */
 	if (namelen <= 0 || *name == '-')
-		return -1;
+		return 0;
 	while (namelen--) {
 		char ch = *name++;
 		if (! (ch == '-' || ch == '.' || ch == '_' ||
 		       ('0' <= ch && ch <= '9') ||
 		       ('a' <= ch && ch <= 'z') ||
 		       ('A' <= ch && ch <= 'Z')) )
-			return -1;
+			return 0;
 	}
-	return 0;
+	return 1;
+}
+
+void invalid_attr_name_message(struct strbuf *err, const char *name, int len)
+{
+	strbuf_addf(err, _("%.*s is not a valid attribute name"),
+		    len, name);
+}
+
+static void report_invalid_attr(const char *name, size_t len,
+				const char *src, int lineno)
+{
+	struct strbuf err = STRBUF_INIT;
+	invalid_attr_name_message(&err, name, len);
+	fprintf(stderr, "%s: %s:%d\n", err.buf, src, lineno);
+	strbuf_release(&err);
 }
 
 static struct git_attr *git_attr_internal(const char *name, int len)
@@ -90,7 +105,7 @@ static struct git_attr *git_attr_internal(const char *name, int len)
 			return a;
 	}
 
-	if (invalid_attr_name(name, len))
+	if (!attr_name_valid(name, len))
 		return NULL;
 
 	FLEX_ALLOC_MEM(a, name, name, len);
@@ -176,17 +191,15 @@ static const char *parse_attr(const char *src, int lineno, const char *cp,
 			cp++;
 			len--;
 		}
-		if (invalid_attr_name(cp, len)) {
-			fprintf(stderr,
-				"%.*s is not a valid attribute name: %s:%d\n",
-				len, cp, src, lineno);
+		if (!attr_name_valid(cp, len)) {
+			report_invalid_attr(cp, len, src, lineno);
 			return NULL;
 		}
 	} else {
 		/*
 		 * As this function is always called twice, once with
 		 * e == NULL in the first pass and then e != NULL in
-		 * the second pass, no need for invalid_attr_name()
+		 * the second pass, no need for attr_name_valid()
 		 * check here.
 		 */
 		if (*cp == '-' || *cp == '!') {
@@ -229,10 +242,8 @@ static struct match_attr *parse_attr_line(const char *line, const char *src,
 		name += strlen(ATTRIBUTE_MACRO_PREFIX);
 		name += strspn(name, blank);
 		namelen = strcspn(name, blank);
-		if (invalid_attr_name(name, namelen)) {
-			fprintf(stderr,
-				"%.*s is not a valid attribute name: %s:%d\n",
-				namelen, name, src, lineno);
+		if (!attr_name_valid(name, namelen)) {
+			report_invalid_attr(name, namelen, src, lineno);
 			goto fail_return;
 		}
 	}
diff --git a/attr.h b/attr.h
index c84f164b8e..1c6a6d865b 100644
--- a/attr.h
+++ b/attr.h
@@ -10,6 +10,16 @@ struct git_attr;
  */
 struct git_attr *git_attr(const char *);
 
+/*
+ * Return the name of the attribute represented by the argument.  The
+ * return value is a pointer to a null-delimited string that is part
+ * of the internal data structure; it should not be modified or freed.
+ */
+extern const char *git_attr_name(const struct git_attr *);
+
+extern int attr_name_valid(const char *name, size_t namelen);
+extern void invalid_attr_name_message(struct strbuf *, const char *, int);
+
 /* Internal use */
 extern const char git_attr__true[];
 extern const char git_attr__false[];