refs: add a optimize_required field to struct ref_storage_be

To allow users of the refs namespace to check if the reference backend
requires optimization, add a new field `optimize_required` field to
`struct ref_storage_be`. This field is of type `optimize_required_fn`
which is also introduced in this commit.

Modify the debug, files, packed and reftable backend to implement this
field. A following commit will expose this via 'git pack-refs' and 'git
refs optimize'.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Acked-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -2318,6 +2318,13 @@ int refs_optimize(struct ref_store *refs, struct refs_optimize_opts *opts)
 	return refs->be->optimize(refs, opts);
 }
 
+int refs_optimize_required(struct ref_store *refs,
+			   struct refs_optimize_opts *opts,
+			   bool *required)
+{
+	return refs->be->optimize_required(refs, opts, required);
+}
+
 int reference_get_peeled_oid(struct repository *repo,
 			     const struct reference *ref,
 			     struct object_id *peeled_oid)

refs.h

@@ -520,6 +520,13 @@ struct refs_optimize_opts {
  */
 int refs_optimize(struct ref_store *refs, struct refs_optimize_opts *opts);
 
+/*
+ * Check if refs backend can be optimized by calling 'refs_optimize'.
+ */
+int refs_optimize_required(struct ref_store *ref_store,
+			   struct refs_optimize_opts *opts,
+			   bool *required);
+
 /*
  * Setup reflog before using. Fill in err and return -1 on failure.
  */

refs/debug.c

@@ -124,6 +124,17 @@ static int debug_optimize(struct ref_store *ref_store, struct refs_optimize_opts
 	return res;
 }
 
+static int debug_optimize_required(struct ref_store *ref_store,
+				   struct refs_optimize_opts *opts,
+				   bool *required)
+{
+	struct debug_ref_store *drefs = (struct debug_ref_store *)ref_store;
+	int res = drefs->refs->be->optimize_required(drefs->refs, opts, required);
+	trace_printf_key(&trace_refs, "optimize_required: %s, res: %d\n",
+			 required ? "yes" : "no", res);
+	return res;
+}
+
 static int debug_rename_ref(struct ref_store *ref_store, const char *oldref,
 			    const char *newref, const char *logmsg)
 {
@@ -431,6 +442,8 @@ struct ref_storage_be refs_be_debug = {
 	.transaction_abort = debug_transaction_abort,
 
 	.optimize = debug_optimize,
+	.optimize_required = debug_optimize_required,
+
 	.rename_ref = debug_rename_ref,
 	.copy_ref = debug_copy_ref,
 

refs/files-backend.c

@@ -1512,6 +1512,16 @@ static int files_optimize(struct ref_store *ref_store,
 	return 0;
 }
 
+static int files_optimize_required(struct ref_store *ref_store,
+				   struct refs_optimize_opts *opts,
+				   bool *required)
+{
+	struct files_ref_store *refs = files_downcast(ref_store, REF_STORE_READ,
+						      "optimize_required");
+	*required = should_pack_refs(refs, opts);
+	return 0;
+}
+
 /*
  * People using contrib's git-new-workdir have .git/logs/refs ->
  * /some/other/path/.git/logs/refs, and that may live on another device.
@@ -3982,6 +3992,7 @@ struct ref_storage_be refs_be_files = {
 	.transaction_abort = files_transaction_abort,
 
 	.optimize = files_optimize,
+	.optimize_required = files_optimize_required,
 	.rename_ref = files_rename_ref,
 	.copy_ref = files_copy_ref,
 

refs/packed-backend.c

@@ -1784,6 +1784,17 @@ static int packed_optimize(struct ref_store *ref_store UNUSED,
 	return 0;
 }
 
+static int packed_optimize_required(struct ref_store *ref_store UNUSED,
+				    struct refs_optimize_opts *opts UNUSED,
+				    bool *required)
+{
+	/*
+	 * Packed refs are already optimized.
+	 */
+	*required = false;
+	return 0;
+}
+
 static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_store UNUSED)
 {
 	return empty_ref_iterator_begin();
@@ -2130,6 +2141,8 @@ struct ref_storage_be refs_be_packed = {
 	.transaction_abort = packed_transaction_abort,
 
 	.optimize = packed_optimize,
+	.optimize_required = packed_optimize_required,
+
 	.rename_ref = NULL,
 	.copy_ref = NULL,
 

refs/refs-internal.h

@@ -424,6 +424,11 @@ typedef int ref_transaction_commit_fn(struct ref_store *refs,
 
 typedef int optimize_fn(struct ref_store *ref_store,
 			struct refs_optimize_opts *opts);
+
+typedef int optimize_required_fn(struct ref_store *ref_store,
+				 struct refs_optimize_opts *opts,
+				 bool *required);
+
 typedef int rename_ref_fn(struct ref_store *ref_store,
 			  const char *oldref, const char *newref,
 			  const char *logmsg);
@@ -549,6 +554,7 @@ struct ref_storage_be {
 	ref_transaction_abort_fn *transaction_abort;
 
 	optimize_fn *optimize;
+	optimize_required_fn *optimize_required;
 	rename_ref_fn *rename_ref;
 	copy_ref_fn *copy_ref;
 

refs/reftable-backend.c

@@ -1733,6 +1733,29 @@ out:
 	return ret;
 }
 
+static int reftable_be_optimize_required(struct ref_store *ref_store,
+					 struct refs_optimize_opts *opts,
+					 bool *required)
+{
+	struct reftable_ref_store *refs = reftable_be_downcast(ref_store, REF_STORE_READ,
+							       "optimize_refs_required");
+	struct reftable_stack *stack;
+	bool use_heuristics = false;
+
+	if (refs->err)
+		return refs->err;
+
+	stack = refs->worktree_backend.stack;
+	if (!stack)
+		stack = refs->main_backend.stack;
+
+	if (opts->flags & REFS_OPTIMIZE_AUTO)
+		use_heuristics = true;
+
+	return reftable_stack_compaction_required(stack, use_heuristics,
+						  required);
+}
+
 struct write_create_symref_arg {
 	struct reftable_ref_store *refs;
 	struct reftable_stack *stack;
@@ -2756,6 +2779,8 @@ struct ref_storage_be refs_be_reftable = {
 	.transaction_abort = reftable_be_transaction_abort,
 
 	.optimize = reftable_be_optimize,
+	.optimize_required = reftable_be_optimize_required,
+
 	.rename_ref = reftable_be_rename_ref,
 	.copy_ref = reftable_be_copy_ref,