There's been a lot of changing of the hardcoded "40" values to
the_hash_algo->hexsz, but we've so far missed this one where we
hardcoded 38 for the loose object file length.

This is because a SHA-1 like abcde[...] gets turned into
objects/ab/cde[...]. There's no reason to suppose the same won't be
the case for SHA-256, and reading between the lines in
hash-function-transition.txt the format is planned to be the same.

However, we may want to modify this code for the hash function
transition. There's a potential pathological case here where we'll
only consider the loose objects for the currently active hash, but
objects for that hash will share a directory storage with the other
hash.

Thus we could theoretically have 1k SHA-1 loose objects, and say 1
million SHA-256 objects, and not notice because we're currently using
SHA-1.

Signed-off-by: Ævar Arnfjörð Bjarmason <ava...@gmail.com>
---
 builtin/gc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 8c2312681c..9c2c63276d 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -156,6 +156,8 @@ static int too_many_loose_objects(void)
        int auto_threshold;
        int num_loose = 0;
        int needed = 0;
+       const unsigned hexsz = the_hash_algo->hexsz;
+       const unsigned hexsz_loose = hexsz - 2;
 
        dir = opendir(git_path("objects/17"));
        if (!dir)
@@ -163,8 +165,8 @@ static int too_many_loose_objects(void)
 
        auto_threshold = DIV_ROUND_UP(gc_auto_threshold, 256);
        while ((ent = readdir(dir)) != NULL) {
-               if (strspn(ent->d_name, "0123456789abcdef") != 38 ||
-                   ent->d_name[38] != '\0')
+               if (strspn(ent->d_name, "0123456789abcdef") != hexsz_loose ||
+                   ent->d_name[hexsz_loose] != '\0')
                        continue;
                if (++num_loose > auto_threshold) {
                        needed = 1;
-- 
2.21.0.360.g471c308f928

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