packfile, git-zlib: widen `use_pack()` and zstream avail fields to `size_t`

Bundling the two widenings: four call sites pass `&stream.avail_in`
directly to `use_pack()`, and widening either type fencepost alone would
force a bridge variable at each. Doing both together is the simpler end
state and is the prerequisite for the `do_compress()` widening in the
next commit, which is what lets `write_no_reuse_object()` lose its last
`cast_size_t_to_ulong()` shim.

The unsigned-long locals widened at the other `use_pack()` callers
(avail / remaining / left) hold pack-window sizes bounded by
`core.packedGitWindowSize`, so the change is type consistency rather
than a new >4GB capability. `git_zstream.avail_in`/`avail_out` likewise
reach zlib's `uInt` fields only after `zlib_buf_cap()`'s 1 GiB cap, so
the wrapper already accepted `size_t`-shaped inputs in practice.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -488,7 +488,7 @@ static void copy_pack_data(struct hashfile *f,
 		off_t len)
 {
 	unsigned char *in;
-	unsigned long avail;
+	size_t avail;
 
 	while (len) {
 		in = use_pack(p, w_curs, offset, &avail);
@@ -2260,7 +2260,7 @@ static void check_object(struct object_entry *entry, uint32_t object_index)
 		struct object_id base_ref;
 		struct object_entry *base_entry;
 		unsigned long used, used_0;
-		unsigned long avail;
+		size_t avail;
 		off_t ofs;
 		unsigned char *buf, c;
 		enum object_type type;
@@ -2756,8 +2756,8 @@ size_t oe_get_size_slow(struct packing_data *pack,
 	struct pack_window *w_curs;
 	unsigned char *buf;
 	enum object_type type;
-	unsigned long used, avail;
-	size_t size;
+	unsigned long used;
+	size_t avail, size;
 
 	if (e->type_ != OBJ_OFS_DELTA && e->type_ != OBJ_REF_DELTA) {
 		size_t sz;

git-zlib.h

@@ -5,8 +5,8 @@
 
 typedef struct git_zstream {
 	struct z_stream_s z;
-	unsigned long avail_in;
-	unsigned long avail_out;
+	size_t avail_in;
+	size_t avail_out;
 	size_t total_in;
 	size_t total_out;
 	unsigned char *next_in;

pack-check.c

@@ -34,7 +34,7 @@ int check_pack_crc(struct packed_git *p, struct pack_window **w_curs,
 	uint32_t data_crc = crc32(0, NULL, 0);
 
 	do {
-		unsigned long avail;
+		size_t avail;
 		void *data = use_pack(p, w_curs, offset, &avail);
 		if (avail > len)
 			avail = len;
@@ -71,7 +71,7 @@ static int verify_packfile(struct repository *r,
 
 	r->hash_algo->init_fn(&ctx);
 	do {
-		unsigned long remaining;
+		size_t remaining;
 		unsigned char *in = use_pack(p, w_curs, offset, &remaining);
 		offset += remaining;
 		if (!pack_sig_ofs)

packfile.c

@@ -704,7 +704,7 @@ static int in_window(struct repository *r, struct pack_window *win,
 unsigned char *use_pack(struct packed_git *p,
 		struct pack_window **w_cursor,
 		off_t offset,
-		unsigned long *left)
+		size_t *left)
 {
 	struct pack_window *win = *w_cursor;
 
@@ -1228,7 +1228,7 @@ int unpack_object_header(struct packed_git *p,
 			 size_t *sizep)
 {
 	unsigned char *base;
-	unsigned long left;
+	size_t left;
 	unsigned long used;
 	enum object_type type;
 

packfile.h

@@ -402,7 +402,8 @@ uint32_t get_pack_fanout(struct packed_git *p, uint32_t value);
 
 struct object_database;
 
-unsigned char *use_pack(struct packed_git *, struct pack_window **, off_t, unsigned long *);
+unsigned char *use_pack(struct packed_git *, struct pack_window **, off_t,
+			size_t *);
 void close_pack_windows(struct packed_git *);
 void close_pack(struct packed_git *);
 void unuse_pack(struct pack_window **);