update-ref: implement --initial

Signed-off-by: Vicent Marti <vmg@strn.cat>

Author: vmg

Documentation/git-update-ref.adoc

@@ -10,7 +10,7 @@ SYNOPSIS
 [synopsis]
 git update-ref [-m <reason>] [--no-deref] -d <ref> [<old-oid>]
 git update-ref [-m <reason>] [--no-deref] [--create-reflog] <ref> <new-oid> [<old-oid>]
-git update-ref [-m <reason>] [--no-deref] --stdin [-z] [--batch-updates]
+git update-ref [-m <reason>] [--no-deref] --stdin [-z] [--initial] [--batch-updates]
 
 DESCRIPTION
 -----------
@@ -59,6 +59,13 @@ performs all modifications together.  Specify commands of the form:
 With `--create-reflog`, update-ref will create a reflog for each ref
 even if one would not ordinarily be created.
 
+With `--initial`, update-ref assumes the ref store is empty and skips the
+checks that detect conflicts with existing references, writing the queued
+updates as an initial bulk load.  This is only valid when no references
+exist yet (for example, immediately after `git init`); using it against a
+populated ref store is unsupported.  It can only be used together with
+`--stdin`.
+
 With `--batch-updates`, update-ref executes the updates in a batch but allows
 individual updates to fail due to invalid or incorrect user input, applying only
 the successful updates. However, system-related errors—such as I/O failures or

builtin/update-ref.c

@@ -15,7 +15,7 @@
 static const char * const git_update_ref_usage[] = {
 	N_("git update-ref [<options>] -d <refname> [<old-oid>]"),
 	N_("git update-ref [<options>]    <refname> <new-oid> [<old-oid>]"),
-	N_("git update-ref [<options>] --stdin [-z] [--batch-updates]"),
+	N_("git update-ref [<options>] --stdin [-z] [--initial] [--batch-updates]"),
 	NULL
 };
 
@@ -842,6 +842,9 @@ int cmd_update_ref(int argc,
 		OPT_BOOL( 0 , "create-reflog", &create_reflog, N_("create a reflog")),
 		OPT_BIT('0', "batch-updates", &flags, N_("batch reference updates"),
 			REF_TRANSACTION_ALLOW_FAILURE),
+		OPT_BIT(0, "initial", &flags,
+			N_("assume the ref store is empty and skip checks"),
+			REF_TRANSACTION_FLAG_INITIAL),
 		OPT_HIDDEN_BOOL(0, "batch-report-early",
 				&report_rejections_on_prepare,
 				N_("report batch-update rejections during prepare")),
@@ -873,6 +876,8 @@ int cmd_update_ref(int argc,
 		return 0;
 	} else if (flags & REF_TRANSACTION_ALLOW_FAILURE) {
 		die("--batch-updates can only be used with --stdin");
+	} else if (flags & REF_TRANSACTION_FLAG_INITIAL) {
+		die("--initial can only be used with --stdin");
 	} else if (report_rejections_on_prepare) {
 		die("--batch-report-early can only be used with --stdin");
 	}