[PATCH 17/30] packed-backend: create shell of v2 writes

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 Makefile                |  1 +
 refs/packed-backend.c   | 75 +++++++++++++++++++++++++++++++++++------
 refs/packed-backend.h   |  7 ++++
 refs/packed-format-v2.c | 38 +++++++++++++++++++++
 4 files changed, 110 insertions(+), 11 deletions(-)
 create mode 100644 refs/packed-format-v2.c

diff --git a/Makefile b/Makefile
index 3dc887941d4..16cd245e0ad 100644
--- a/Makefile
+++ b/Makefile
@@ -1058,6 +1058,7 @@ LIB_OBJS += refs/files-backend.o
 LIB_OBJS += refs/iterator.o
 LIB_OBJS += refs/packed-backend.o
 LIB_OBJS += refs/packed-format-v1.o
+LIB_OBJS += refs/packed-format-v2.o
 LIB_OBJS += refs/ref-cache.o
 LIB_OBJS += refspec.o
 LIB_OBJS += remote.o
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 655aab939be..09f7b74584f 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -692,6 +692,45 @@ error:
 	return ok;
 }
 
+static int write_with_updates_v1(struct packed_ref_store *refs,
+				 struct string_list *updates,
+				 struct strbuf *err)
+{
+	FILE *out;
+
+	out = fdopen_tempfile(refs->tempfile, "w");
+	if (!out) {
+		strbuf_addf(err, "unable to fdopen packed-refs tempfile: %s",
+			    strerror(errno));
+		goto error;
+	}
+
+	if (write_packed_file_header_v1(out) < 0) {
+		add_write_error(refs, err);
+		goto error;
+	}
+
+	return merge_iterator_and_updates(refs, updates, err,
+					  write_packed_entry_v1, out);
+
+error:
+	return -1;
+}
+
+static int write_with_updates_v2(struct packed_ref_store *refs,
+				 struct string_list *updates,
+				 struct strbuf *err)
+{
+	struct write_packed_refs_v2_context *ctx = create_v2_context(refs, updates, err);
+	int ok = -1;
+
+	if ((ok = write_packed_refs_v2(ctx)) < 0)
+		add_write_error(refs, err);
+
+	free_v2_context(ctx);
+	return ok;
+}
+
 /*
  * Write the packed refs from the current snapshot to the packed-refs
  * tempfile, incorporating any changes from `updates`. `updates` must
@@ -707,9 +746,9 @@ static int write_with_updates(struct packed_ref_store *refs,
 			      struct strbuf *err)
 {
 	int ok;
-	FILE *out;
 	struct strbuf sb = STRBUF_INIT;
 	char *packed_refs_path;
+	int version;
 
 	if (!is_lock_file_locked(&refs->lock))
 		BUG("write_with_updates() called while unlocked");
@@ -731,21 +770,35 @@ static int write_with_updates(struct packed_ref_store *refs,
 	}
 	strbuf_release(&sb);
 
-	out = fdopen_tempfile(refs->tempfile, "w");
-	if (!out) {
-		strbuf_addf(err, "unable to fdopen packed-refs tempfile: %s",
-			    strerror(errno));
-		goto error;
+	if (git_config_get_int("refs.packedrefsversion", &version)) {
+		/*
+		 * Set the default depending on the current extension
+		 * list. Default to version 1 if available, but allow a
+		 * default of 2 if only "packed-v2" exists.
+		 */
+		if (refs->store_flags & REF_STORE_FORMAT_PACKED)
+			version = 1;
+		else if (refs->store_flags & REF_STORE_FORMAT_PACKED_V2)
+			version = 2;
+		else
+			BUG("writing a packed-refs file without an extension");
 	}
 
-	if (write_packed_file_header_v1(out) < 0) {
-		add_write_error(refs, err);
+	switch (version) {
+	case 1:
+		ok = write_with_updates_v1(refs, updates, err);
+		break;
+
+	case 2:
+		ok = write_with_updates_v2(refs, updates, err);
+		break;
+
+	default:
+		strbuf_addf(err, "unknown packed-refs version: %d",
+			    version);
 		goto error;
 	}
 
-	ok = merge_iterator_and_updates(refs, updates, err,
-					write_packed_entry_v1, out);
-
 	if (ok != ITER_DONE) {
 		strbuf_addstr(err, "unable to write packed-refs file: "
 			      "error iterating over old contents");
diff --git a/refs/packed-backend.h b/refs/packed-backend.h
index b6908bb002c..e76f26bfc46 100644
--- a/refs/packed-backend.h
+++ b/refs/packed-backend.h
@@ -243,4 +243,11 @@ int write_packed_entry_v1(const char *refname,
 			  const struct object_id *peeled,
 			  void *write_data);
 
+struct write_packed_refs_v2_context;
+struct write_packed_refs_v2_context *create_v2_context(struct packed_ref_store *refs,
+						       struct string_list *updates,
+						       struct strbuf *err);
+int write_packed_refs_v2(struct write_packed_refs_v2_context *ctx);
+void free_v2_context(struct write_packed_refs_v2_context *ctx);
+
 #endif /* REFS_PACKED_BACKEND_H */
diff --git a/refs/packed-format-v2.c b/refs/packed-format-v2.c
new file mode 100644
index 00000000000..ecf3cc93694
--- /dev/null
+++ b/refs/packed-format-v2.c
@@ -0,0 +1,38 @@
+#include "../cache.h"
+#include "../config.h"
+#include "../refs.h"
+#include "refs-internal.h"
+#include "packed-backend.h"
+#include "../iterator.h"
+#include "../lockfile.h"
+#include "../chdir-notify.h"
+
+struct write_packed_refs_v2_context {
+	struct packed_ref_store *refs;
+	struct string_list *updates;
+	struct strbuf *err;
+};
+
+struct write_packed_refs_v2_context *create_v2_context(struct packed_ref_store *refs,
+						       struct string_list *updates,
+						       struct strbuf *err)
+{
+	struct write_packed_refs_v2_context *ctx;
+	CALLOC_ARRAY(ctx, 1);
+
+	ctx->refs = refs;
+	ctx->updates = updates;
+	ctx->err = err;
+
+	return ctx;
+}
+
+int write_packed_refs_v2(struct write_packed_refs_v2_context *ctx)
+{
+	return 0;
+}
+
+void free_v2_context(struct write_packed_refs_v2_context *ctx)
+{
+	free(ctx);
+}
-- 
gitgitgadget