[PATCH] 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 <redacted>
---
 * And then finally the error message one.  I didn't change
   the message itself to spell out the rules here, though.

 attr.c | 39 +++++++++++++++++++++++++--------------
 attr.h |  3 +++
 2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/attr.c b/attr.c
index 7f20e21..8f54871 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);
 }

 struct git_attr *git_attr_counted(const char *name, size_t len)

@@ -90,7 +105,7 @@ struct git_attr *git_attr_counted(const char *name, size_t 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);
                        return NULL;
                }
        }

diff --git a/attr.h b/attr.h
index 78d6d5a..fc72030 100644
--- a/attr.h
+++ b/attr.h

@@ -13,6 +13,9 @@ extern struct git_attr *git_attr(const char *);
 /* The same, but with counted string */
 extern struct git_attr *git_attr_counted(const char *, size_t);

+extern int attr_name_valid(const char *name, size_t namelen);