sha1-file: remove OBJECT_INFO_SKIP_CACHED

In a partial clone, if a user provides the hash of the empty tree ("git
mktree </dev/null" - for SHA-1, this is 4b825d...) to a command which
requires that that object be parsed, for example:

  git diff-tree 4b825d <a non-empty tree>

then Git will lazily fetch the empty tree, unnecessarily, because
parsing of that object invokes repo_has_object_file(), which does not
special-case the empty tree.

Instead, teach repo_has_object_file() to consult find_cached_object()
(which handles the empty tree), thus bringing it in line with the rest
of the object-store-accessing functions. A cost is that
repo_has_object_file() will now need to oideq upon each invocation, but
that is trivial compared to the filesystem lookup or the pack index
search required anyway. (And if find_cached_object() needs to do more
because of previous invocations to pretend_object_file(), all the more
reason to be consistent in whether we present cached objects.)

As a historical note, the function now known as repo_read_object_file()
was taught the empty tree in 346245a1bb ("hard-code the empty tree
object", 2008-02-13), and the function now known as oid_object_info()
was taught the empty tree in c4d9986f5f ("sha1_object_info: examine
cached_object store too", 2011-02-07). repo_has_object_file() was never
updated, perhaps due to oversight. The flag OBJECT_INFO_SKIP_CACHED,
introduced later in dfdd4afcf9 ("sha1_file: teach
sha1_object_info_extended more flags", 2017-06-26) and used in
e83e71c5e1 ("sha1_file: refactor has_sha1_file_with_flags", 2017-06-26),
was introduced to preserve this difference in empty-tree handling, but
now it can be removed.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object-store.h

@@ -271,8 +271,6 @@ struct object_info {
 #define OBJECT_INFO_LOOKUP_REPLACE 1
 /* Allow reading from a loose object file of unknown/bogus type */
 #define OBJECT_INFO_ALLOW_UNKNOWN_TYPE 2
-/* Do not check cached storage */
-#define OBJECT_INFO_SKIP_CACHED 4
 /* Do not retry packed storage after checking packed and loose storage */
 #define OBJECT_INFO_QUICK 8
 /* Do not check loose object */

sha1-file.c

@@ -1417,6 +1417,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 			     struct object_info *oi, unsigned flags)
 {
 	static struct object_info blank_oi = OBJECT_INFO_INIT;
+	struct cached_object *co;
 	struct pack_entry e;
 	int rtype;
 	const struct object_id *real = oid;
@@ -1431,24 +1432,22 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 	if (!oi)
 		oi = &blank_oi;
 
-	if (!(flags & OBJECT_INFO_SKIP_CACHED)) {
-		struct cached_object *co = find_cached_object(real);
-		if (co) {
-			if (oi->typep)
-				*(oi->typep) = co->type;
-			if (oi->sizep)
-				*(oi->sizep) = co->size;
-			if (oi->disk_sizep)
-				*(oi->disk_sizep) = 0;
-			if (oi->delta_base_sha1)
-				hashclr(oi->delta_base_sha1);
-			if (oi->type_name)
-				strbuf_addstr(oi->type_name, type_name(co->type));
-			if (oi->contentp)
-				*oi->contentp = xmemdupz(co->buf, co->size);
-			oi->whence = OI_CACHED;
-			return 0;
-		}
+	co = find_cached_object(real);
+	if (co) {
+		if (oi->typep)
+			*(oi->typep) = co->type;
+		if (oi->sizep)
+			*(oi->sizep) = co->size;
+		if (oi->disk_sizep)
+			*(oi->disk_sizep) = 0;
+		if (oi->delta_base_sha1)
+			hashclr(oi->delta_base_sha1);
+		if (oi->type_name)
+			strbuf_addstr(oi->type_name, type_name(co->type));
+		if (oi->contentp)
+			*oi->contentp = xmemdupz(co->buf, co->size);
+		oi->whence = OI_CACHED;
+		return 0;
 	}
 
 	while (1) {
@@ -1932,8 +1931,7 @@ int repo_has_object_file_with_flags(struct repository *r,
 {
 	if (!startup_info->have_repository)
 		return 0;
-	return oid_object_info_extended(r, oid, NULL,
-					flags | OBJECT_INFO_SKIP_CACHED) >= 0;
+	return oid_object_info_extended(r, oid, NULL, flags) >= 0;
 }
 
 int repo_has_object_file(struct repository *r,