rerere: check dirname format while iterating rr_cache directory

In rerere_gc(), we walk over the .git/rr_cache directory and create a
struct for each entry we find. We feed any name we get from readdir() to
find_rerere_dir(), which then calls get_sha1_hex() on it (since we use
the binary hash as a lookup key). If that fails (i.e., the directory
name is not what we expected), it returns NULL. But the comment in
find_rerere_dir() says "BUG".

It _would_ be a bug for the call from new_rerere_id_hex(), the only
other code path, to fail here; it's generating the hex internally. But
the call in rerere_gc() is using it say "is this a plausible directory
name".

Let's instead have rerere_gc() do its own "is this plausible" check.
That has two benefits:

  - we can now reliably BUG() inside find_rerere_dir(), which would
    catch bugs in the other code path (and we now will never return NULL
    from the function, which makes it easier to see that a rerere_id
    struct will always have a non-NULL "collection" field).

  - it makes the use of the binary hash an implementation detail of
    find_rerere_dir(), not known by callers. That will free us up to
    change it in a future patch.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/rerere.c b/rerere.c
index d6928c1b5c1a84980e403c805d2e5fcd072e40aa..7b0c262ac65efaa8d0b5fa64a0e2c50b9da518c0 100644 (file)
--- a/rerere.c
+++ b/rerere.c
@@ -146,7 +146,7 @@ static struct rerere_dir *find_rerere_dir(const char *hex)
        int pos;
 
        if (get_sha1_hex(hex, hash))
-               return NULL; /* BUG */
+               BUG("cannot parse rerere dir hex?");
        pos = hash_pos(hash, rerere_dir, rerere_dir_nr, rerere_dir_hash);
        if (pos < 0) {
                rr_dir = xmalloc(sizeof(*rr_dir));
@@ -1178,6 +1178,13 @@ static void prune_one(struct rerere_id *id,
                unlink_rr_item(id);
 }
 
+/* Does the basename in "path" look plausibly like an rr-cache entry? */
+static int is_rr_cache_dirname(const char *path)
+{
+       unsigned char hash[GIT_MAX_RAWSZ];
+       return !get_sha1_hex(path, hash);
+}
+
 void rerere_gc(struct repository *r, struct string_list *rr)
 {
        struct string_list to_remove = STRING_LIST_INIT_DUP;
@@ -1205,10 +1212,11 @@ void rerere_gc(struct repository *r, struct string_list *rr)
 
                if (is_dot_or_dotdot(e->d_name))
                        continue;
-               rr_dir = find_rerere_dir(e->d_name);
-               if (!rr_dir)
+               if (!is_rr_cache_dirname(e->d_name))
                        continue; /* or should we remove e->d_name? */
 
+               rr_dir = find_rerere_dir(e->d_name);
+
                now_empty = 1;
                for (id.variant = 0, id.collection = rr_dir;
                     id.variant < id.collection->status_nr;