refs: implement removal of ref storages

We're about to introduce logic to migrate ref storages. One part of the
migration will be to delete the files that are part of the old ref
storage format. We don't yet have a way to delete such data generically
across ref backends though.

Implement a new `delete` callback and expose it via a new
`ref_storage_delete()` function.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -1861,6 +1861,11 @@ int ref_store_create_on_disk(struct ref_store *refs, int flags, struct strbuf *e
 	return refs->be->create_on_disk(refs, flags, err);
 }
 
+int ref_store_remove_on_disk(struct ref_store *refs, struct strbuf *err)
+{
+	return refs->be->remove_on_disk(refs, err);
+}
+
 int repo_resolve_gitlink_ref(struct repository *r,
 			     const char *submodule, const char *refname,
 			     struct object_id *oid)

refs.h

@@ -129,6 +129,11 @@ int ref_store_create_on_disk(struct ref_store *refs, int flags, struct strbuf *e
  */
 void ref_store_release(struct ref_store *ref_store);
 
+/*
+ * Remove the ref store from disk. This deletes all associated data.
+ */
+int ref_store_remove_on_disk(struct ref_store *refs, struct strbuf *err);
+
 /*
  * Return the peeled value of the oid currently being iterated via
  * for_each_ref(), etc. This is equivalent to calling:

refs/files-backend.c

@@ -3342,11 +3342,73 @@ static int files_ref_store_create_on_disk(struct ref_store *ref_store,
 	return 0;
 }
 
+struct remove_one_root_ref_data {
+	const char *gitdir;
+	struct strbuf *err;
+};
+
+static int remove_one_root_ref(const char *refname,
+			       void *cb_data)
+{
+	struct remove_one_root_ref_data *data = cb_data;
+	struct strbuf buf = STRBUF_INIT;
+	int ret = 0;
+
+	strbuf_addf(&buf, "%s/%s", data->gitdir, refname);
+
+	ret = unlink(buf.buf);
+	if (ret < 0)
+		strbuf_addf(data->err, "could not delete %s: %s\n",
+			    refname, strerror(errno));
+
+	strbuf_release(&buf);
+	return ret;
+}
+
+static int files_ref_store_remove_on_disk(struct ref_store *ref_store,
+					  struct strbuf *err)
+{
+	struct files_ref_store *refs =
+		files_downcast(ref_store, REF_STORE_WRITE, "remove");
+	struct remove_one_root_ref_data data = {
+		.gitdir = refs->base.gitdir,
+		.err = err,
+	};
+	struct strbuf sb = STRBUF_INIT;
+	int ret = 0;
+
+	strbuf_addf(&sb, "%s/refs", refs->base.gitdir);
+	if (remove_dir_recursively(&sb, 0) < 0) {
+		strbuf_addf(err, "could not delete refs: %s",
+			    strerror(errno));
+		ret = -1;
+	}
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/logs", refs->base.gitdir);
+	if (remove_dir_recursively(&sb, 0) < 0) {
+		strbuf_addf(err, "could not delete logs: %s",
+			    strerror(errno));
+		ret = -1;
+	}
+	strbuf_reset(&sb);
+
+	if (for_each_root_ref(refs, remove_one_root_ref, &data) < 0)
+		ret = -1;
+
+	if (ref_store_remove_on_disk(refs->packed_ref_store, err) < 0)
+		ret = -1;
+
+	strbuf_release(&sb);
+	return ret;
+}
+
 struct ref_storage_be refs_be_files = {
 	.name = "files",
 	.init = files_ref_store_init,
 	.release = files_ref_store_release,
 	.create_on_disk = files_ref_store_create_on_disk,
+	.remove_on_disk = files_ref_store_remove_on_disk,
 
 	.transaction_prepare = files_transaction_prepare,
 	.transaction_finish = files_transaction_finish,

refs/packed-backend.c

@@ -1,5 +1,6 @@
 #include "../git-compat-util.h"
 #include "../config.h"
+#include "../dir.h"
 #include "../gettext.h"
 #include "../hash.h"
 #include "../hex.h"
@@ -1266,6 +1267,19 @@ static int packed_ref_store_create_on_disk(struct ref_store *ref_store UNUSED,
 	return 0;
 }
 
+static int packed_ref_store_remove_on_disk(struct ref_store *ref_store,
+					   struct strbuf *err)
+{
+	struct packed_ref_store *refs = packed_downcast(ref_store, 0, "remove");
+
+	if (remove_path(refs->path) < 0) {
+		strbuf_addstr(err, "could not delete packed-refs");
+		return -1;
+	}
+
+	return 0;
+}
+
 /*
  * Write the packed refs from the current snapshot to the packed-refs
  * tempfile, incorporating any changes from `updates`. `updates` must
@@ -1724,6 +1738,7 @@ struct ref_storage_be refs_be_packed = {
 	.init = packed_ref_store_init,
 	.release = packed_ref_store_release,
 	.create_on_disk = packed_ref_store_create_on_disk,
+	.remove_on_disk = packed_ref_store_remove_on_disk,
 
 	.transaction_prepare = packed_transaction_prepare,
 	.transaction_finish = packed_transaction_finish,

refs/refs-internal.h

@@ -517,6 +517,12 @@ typedef int ref_store_create_on_disk_fn(struct ref_store *refs,
 					int flags,
 					struct strbuf *err);
 
+/*
+ * Remove the reference store from disk.
+ */
+typedef int ref_store_remove_on_disk_fn(struct ref_store *refs,
+					struct strbuf *err);
+
 typedef int ref_transaction_prepare_fn(struct ref_store *refs,
 				       struct ref_transaction *transaction,
 				       struct strbuf *err);
@@ -649,6 +655,7 @@ struct ref_storage_be {
 	ref_store_init_fn *init;
 	ref_store_release_fn *release;
 	ref_store_create_on_disk_fn *create_on_disk;
+	ref_store_remove_on_disk_fn *remove_on_disk;
 
 	ref_transaction_prepare_fn *transaction_prepare;
 	ref_transaction_finish_fn *transaction_finish;

refs/reftable-backend.c

@@ -1,6 +1,7 @@
 #include "../git-compat-util.h"
 #include "../abspath.h"
 #include "../chdir-notify.h"
+#include "../dir.h"
 #include "../environment.h"
 #include "../gettext.h"
 #include "../hash.h"
@@ -343,6 +344,56 @@ static int reftable_be_create_on_disk(struct ref_store *ref_store,
 	return 0;
 }
 
+static int reftable_be_remove_on_disk(struct ref_store *ref_store,
+				      struct strbuf *err)
+{
+	struct reftable_ref_store *refs =
+		reftable_be_downcast(ref_store, REF_STORE_WRITE, "remove");
+	struct strbuf sb = STRBUF_INIT;
+	int ret = 0;
+
+	/*
+	 * Release the ref store such that all stacks are closed. This is
+	 * required so that the "tables.list" file is not open anymore, which
+	 * would otherwise make it impossible to remove the file on Windows.
+	 */
+	reftable_be_release(ref_store);
+
+	strbuf_addf(&sb, "%s/reftable", refs->base.gitdir);
+	if (remove_dir_recursively(&sb, 0) < 0) {
+		strbuf_addf(err, "could not delete reftables: %s",
+			    strerror(errno));
+		ret = -1;
+	}
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/HEAD", refs->base.gitdir);
+	if (unlink(sb.buf) < 0) {
+		strbuf_addf(err, "could not delete stub HEAD: %s",
+			    strerror(errno));
+		ret = -1;
+	}
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/refs/heads", refs->base.gitdir);
+	if (unlink(sb.buf) < 0) {
+		strbuf_addf(err, "could not delete stub heads: %s",
+			    strerror(errno));
+		ret = -1;
+	}
+	strbuf_reset(&sb);
+
+	strbuf_addf(&sb, "%s/refs", refs->base.gitdir);
+	if (rmdir(sb.buf) < 0) {
+		strbuf_addf(err, "could not delete refs directory: %s",
+			    strerror(errno));
+		ret = -1;
+	}
+
+	strbuf_release(&sb);
+	return ret;
+}
+
 struct reftable_ref_iterator {
 	struct ref_iterator base;
 	struct reftable_ref_store *refs;
@@ -2196,6 +2247,7 @@ struct ref_storage_be refs_be_reftable = {
 	.init = reftable_be_init,
 	.release = reftable_be_release,
 	.create_on_disk = reftable_be_create_on_disk,
+	.remove_on_disk = reftable_be_remove_on_disk,
 
 	.transaction_prepare = reftable_be_transaction_prepare,
 	.transaction_finish = reftable_be_transaction_finish,