Merge branch 'bf/set-head-symref'

When "git fetch $remote" notices that refs/remotes/$remote/HEAD is
missing and discovers what branch the other side points with its
HEAD, refs/remotes/$remote/HEAD is updated to point to it.

* bf/set-head-symref:
  fetch set_head: handle mirrored bare repositories
  fetch: set remote/HEAD if it does not exist
  refs: add create_only option to refs_update_symref_extended
  refs: add TRANSACTION_CREATE_EXISTS error
  remote set-head: better output for --auto
  remote set-head: refactor for readability
  refs: atomically record overwritten ref in update_symref
  refs: standardize output of refs_read_symbolic_ref
  t/t5505-remote: test failure of set-head
  t/t5505-remote: set default branch to main

1 files changed, 18 insertions, 1 deletions

diff --git a/refs.h b/refs.h
index e15a31ac80..09be47afbe 100644
--- a/refs.h
+++ b/refs.h
@@ -83,6 +83,17 @@ int refs_read_ref_full(struct ref_store *refs, const char *refname,
 
 int refs_read_ref(struct ref_store *refs, const char *refname, struct object_id *oid);
 
+#define NOT_A_SYMREF -2
+
+/*
+ * Read the symbolic ref named "refname" and write its immediate referent into
+ * the provided buffer. Referent is left empty if "refname" is not a symbolic
+ * ref. It does not resolve the symbolic reference recursively in case the
+ * target is also a symbolic ref.
+ *
+ * Returns 0 on success, -2 if the "refname" is not a symbolic ref,
+ * -1 otherwise.
+ */
 int refs_read_symbolic_ref(struct ref_store *ref_store, const char *refname,
 			   struct strbuf *referent);
 
@@ -604,6 +615,10 @@ int refs_copy_existing_ref(struct ref_store *refs, const char *oldref,
 int refs_update_symref(struct ref_store *refs, const char *refname,
 		       const char *target, const char *logmsg);
 
+int refs_update_symref_extended(struct ref_store *refs, const char *refname,
+		       const char *target, const char *logmsg,
+		       struct strbuf *referent, int create_only);
+
 enum action_on_err {
 	UPDATE_REFS_MSG_ON_ERR,
 	UPDATE_REFS_DIE_ON_ERR,
@@ -805,8 +820,10 @@ int ref_transaction_verify(struct ref_transaction *transaction,
 
 /* Naming conflict (for example, the ref names A and A/B conflict). */
 #define TRANSACTION_NAME_CONFLICT -1
+/* When only creation was requested, but the ref already exists. */
+#define TRANSACTION_CREATE_EXISTS -2
 /* All other errors. */
-#define TRANSACTION_GENERIC_ERROR -2
+#define TRANSACTION_GENERIC_ERROR -3
 
 /*
  * Perform the preparatory stages of committing `transaction`. Acquire