[PATCH v2 1/4] refs: add function to translate errors to strings

[Karthik Nayak <karthik.188@gmail.com>]

The commit 76e760b999 (refs: introduce enum-based transaction error
types, 2025-04-08) introduced enum-based transaction error types. The
refs transaction logic was also modified to propagate these errors. For
clients of the ref transaction system, it would be beneficial to provide
human readable messages for these errors.

There is already an existing mapping in 'builtin/update-ref.c', move it
to 'refs.c' as `ref_transaction_error_msg()` and use the same within the
'builtin/update-ref.c'.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 builtin/update-ref.c | 26 ++------------------------
 refs.c               | 30 ++++++++++++++++++++++++++++++
 refs.h               |  5 +++++
 3 files changed, 37 insertions(+), 24 deletions(-)

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 2b1e336ba1..09b99143bf 100644
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -575,30 +575,7 @@ static void print_rejected_refs(const char *refname,
 				void *cb_data UNUSED)
 {
 	struct strbuf sb = STRBUF_INIT;
-	const char *reason = "";
-
-	switch (err) {
-	case REF_TRANSACTION_ERROR_NAME_CONFLICT:
-		reason = "refname conflict";
-		break;
-	case REF_TRANSACTION_ERROR_CREATE_EXISTS:
-		reason = "reference already exists";
-		break;
-	case REF_TRANSACTION_ERROR_NONEXISTENT_REF:
-		reason = "reference does not exist";
-		break;
-	case REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE:
-		reason = "incorrect old value provided";
-		break;
-	case REF_TRANSACTION_ERROR_INVALID_NEW_VALUE:
-		reason = "invalid new value provided";
-		break;
-	case REF_TRANSACTION_ERROR_EXPECTED_SYMREF:
-		reason = "expected symref but found regular ref";
-		break;
-	default:
-		reason = "unkown failure";
-	}
+	char *reason = ref_transaction_error_msg(err);
 
 	strbuf_addf(&sb, "rejected %s %s %s %s\n", refname,
 		    new_oid ? oid_to_hex(new_oid) : new_target,
@@ -606,6 +583,7 @@ static void print_rejected_refs(const char *refname,
 		    reason);
 
 	fwrite(sb.buf, sb.len, 1, stdout);
+	free(reason);
 	strbuf_release(&sb);
 }
 
diff --git a/refs.c b/refs.c
index 6559db3789..4548fd8fcf 100644
--- a/refs.c
+++ b/refs.c
@@ -3314,3 +3314,33 @@ int ref_update_expects_existing_old_ref(struct ref_update *update)
 	return (update->flags & REF_HAVE_OLD) &&
 		(!is_null_oid(&update->old_oid) || update->old_target);
 }
+
+char *ref_transaction_error_msg(enum ref_transaction_error err)
+{
+	const char *reason = "";
+
+	switch (err) {
+	case REF_TRANSACTION_ERROR_NAME_CONFLICT:
+		reason = "refname conflict";
+		break;
+	case REF_TRANSACTION_ERROR_CREATE_EXISTS:
+		reason = "reference already exists";
+		break;
+	case REF_TRANSACTION_ERROR_NONEXISTENT_REF:
+		reason = "reference does not exist";
+		break;
+	case REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE:
+		reason = "incorrect old value provided";
+		break;
+	case REF_TRANSACTION_ERROR_INVALID_NEW_VALUE:
+		reason = "invalid new value provided";
+		break;
+	case REF_TRANSACTION_ERROR_EXPECTED_SYMREF:
+		reason = "expected symref but found regular ref";
+		break;
+	default:
+		reason = "unkown failure";
+	}
+
+	return xstrdup(reason);
+}
diff --git a/refs.h b/refs.h
index 46a6008e07..a0b2e3c43d 100644
--- a/refs.h
+++ b/refs.h
@@ -907,6 +907,11 @@ void ref_transaction_for_each_rejected_update(struct ref_transaction *transactio
 					      ref_transaction_for_each_rejected_update_fn cb,
 					      void *cb_data);
 
+/*
+ * Translate errors to human readable error messages.
+ */
+char *ref_transaction_error_msg(enum ref_transaction_error err);
+
 /*
  * Free `*transaction` and all associated data.
  */

-- 
2.49.0