Re: [PATCH 09/16] prune: factor out loose-object directory traversal

  2. The original code had strange behavior when it found a
     file of the form "[0-9a-f]{2}/.{38}" that did _not_
     contain all hex digits. It executed a "break" from the
     loop, meaning that we stopped pruning in that directory
     (but still pruned other directories!). This was
     probably a bug; we do not want to process the file as
     an object, but we should keep going otherwise.

Signed-off-by: Jeff King <redacted>
---
I admit the speedup in (1) almost certainly doesn't matter. It is real,
and I found out about it while writing a different program that was
basically "count-objects" across a large number of repositories. However
for a single repo it's probably not big enough to matter (calling
count-objects in a loop while get dominated by the startup costs). The
end result is a little more obvious IMHO, but that's subjective.

 builtin/prune.c | 87 ++++++++++++++++------------------------------------
 cache.h         | 31 +++++++++++++++++++
 sha1_file.c     | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 152 insertions(+), 61 deletions(-)

[...]

diff --git a/cache.h b/cache.h
index cd16e25..7abe7f6 100644
--- a/cache.h
+++ b/cache.h

@@ -1239,6 +1239,37 @@ extern unsigned long unpack_object_header_buffer(const unsigned char *buf, unsig
 extern unsigned long get_size_from_delta(struct packed_git *, struct pack_window **, off_t);
 extern int unpack_object_header(struct packed_git *, struct pack_window **, off_t *, unsigned long *);
 
+/*
+ * Iterate over the files in the loose-object parts of the object
+ * directory "path", triggering the following callbacks:
+ *
+ *  - loose_object is called for each loose object we find.
+ *
+ *  - loose_cruft is called for any files that do not appear to be
+ *    loose objects.
+ *
+ *  - loose_subdir is called for each top-level hashed subdirectory
+ *    of the object directory (e.g., "$OBJDIR/f0"). It is called
+ *    after the objects in the directory are processed.
+ *
+ * Any callback that is NULL will be ignored. Callbacks returning non-zero
+ * will end the iteration.
+ */
+typedef int each_loose_object_fn(const unsigned char *sha1,
+				 const char *path,
+				 void *data);
+typedef int each_loose_cruft_fn(const char *basename,
+				const char *path,
+				void *data);
+typedef int each_loose_subdir_fn(const char *basename,
+				 const char *path,
+				 void *data);
+int for_each_loose_file_in_objdir(const char *path,
+				  each_loose_object_fn obj_cb,
+				  each_loose_cruft_fn cruft_cb,
+				  each_loose_subdir_fn subdir_cb,
+				  void *data);
+
 struct object_info {
 	/* Request */
 	enum object_type *typep;

diff --git a/sha1_file.c b/sha1_file.c
index bae1c15..9fdad47 100644
--- a/sha1_file.c
+++ b/sha1_file.c

@@ -3218,3 +3218,98 @@ void assert_sha1_type(const unsigned char *sha1, enum object_type expect)
 		die("%s is not a valid '%s' object", sha1_to_hex(sha1),
 		    typename(expect));
 }
+
+static int opendir_error(const char *path)
+{
+	if (errno == ENOENT)
+		return 0;
+	return error("unable to open %s: %s", path, strerror(errno));
+}
+
+static int for_each_file_in_obj_subdir(struct strbuf *path,
+				       const char *prefix,
+				       each_loose_object_fn obj_cb,
+				       each_loose_cruft_fn cruft_cb,
+				       each_loose_subdir_fn subdir_cb,
+				       void *data)
+{
+	size_t baselen = path->len;
+	DIR *dir = opendir(path->buf);
+	struct dirent *de;
+	int r = 0;
+
+	if (!dir)
+		return opendir_error(path->buf);