Always handle non-normal (per-worktree or pseudo) refs in the files
backend instead of alternate backends.

Sometimes a ref transaction will update both a per-worktree ref and a
normal ref.  For instance, an ordinary commit might update
refs/heads/master and HEAD (or at least HEAD's reflog).

Updates to normal refs continue to go through the chosen backend.

Updates to non-normal refs are moved to a separate files backend
transaction.

Signed-off-by: David Turner <dtur...@twopensource.com>
---
 refs.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 79 insertions(+), 2 deletions(-)

diff --git a/refs.c b/refs.c
index 227c018..18ba356 100644
--- a/refs.c
+++ b/refs.c
@@ -9,6 +9,11 @@
 #include "object.h"
 #include "tag.h"
 
+static const char split_transaction_fail_warning[] = N_(
+       "A ref transaction was split across two refs backends.  Part of the "
+       "transaction succeeded, but then the update to the per-worktree refs "
+       "failed.  Your repository may be in an inconsistent state.");
+
 /*
  * We always have a files backend and it is the default.
  */
@@ -791,6 +796,13 @@ void ref_transaction_free(struct ref_transaction 
*transaction)
        free(transaction);
 }
 
+static void add_update_obj(struct ref_transaction *transaction,
+                          struct ref_update *update)
+{
+       ALLOC_GROW(transaction->updates, transaction->nr + 1, 
transaction->alloc);
+       transaction->updates[transaction->nr++] = update;
+}
+
 static struct ref_update *add_update(struct ref_transaction *transaction,
                                     const char *refname)
 {
@@ -798,8 +810,7 @@ static struct ref_update *add_update(struct ref_transaction 
*transaction,
        struct ref_update *update = xcalloc(1, sizeof(*update) + len);
 
        memcpy((char *)update->refname, refname, len); /* includes NUL */
-       ALLOC_GROW(transaction->updates, transaction->nr + 1, 
transaction->alloc);
-       transaction->updates[transaction->nr++] = update;
+       add_update_obj(transaction, update);
        return update;
 }
 
@@ -1217,11 +1228,38 @@ static int dereference_symrefs(struct ref_transaction 
*transaction,
        return 0;
 }
 
+/*
+ * Move all non-normal ref updates into a specially-created
+ * files-backend transaction
+ */
+static int move_abnormal_ref_updates(struct ref_transaction *transaction,
+                                    struct ref_transaction *files_transaction,
+                                    struct strbuf *err)
+{
+       int i;
+
+       for (i = 0; i < transaction->nr; i++) {
+               int last;
+               struct ref_update *update = transaction->updates[i];
+
+               if (ref_type(update->refname) == REF_TYPE_NORMAL)
+                       continue;
+
+               last = --transaction->nr;
+               transaction->updates[i] = transaction->updates[last];
+               add_update_obj(files_transaction, update);
+       }
+
+       return 0;
+}
+
 int ref_transaction_commit(struct ref_transaction *transaction,
                           struct strbuf *err)
 {
        int ret = -1;
        struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+       struct string_list files_affected_refnames = STRING_LIST_INIT_NODUP;
+       struct ref_transaction *files_transaction = NULL;
 
        assert(err);
 
@@ -1237,6 +1275,26 @@ int ref_transaction_commit(struct ref_transaction 
*transaction,
        if (ret)
                goto done;
 
+       if (the_refs_backend != &refs_be_files) {
+               files_transaction = ref_transaction_begin(err);
+               if (!files_transaction)
+                       goto done;
+
+               ret = move_abnormal_ref_updates(transaction, files_transaction,
+                                               err);
+               if (ret)
+                       goto done;
+
+               /* files backend commit */
+               if (get_affected_refnames(files_transaction,
+                                                &files_affected_refnames,
+                                                err)) {
+                       ret = TRANSACTION_GENERIC_ERROR;
+                       goto done;
+               }
+       }
+
+       /* main backend commit */
        if (get_affected_refnames(transaction, &affected_refnames, err)) {
                ret = TRANSACTION_GENERIC_ERROR;
                goto done;
@@ -1244,8 +1302,24 @@ int ref_transaction_commit(struct ref_transaction 
*transaction,
 
        ret = the_refs_backend->transaction_commit(transaction,
                                                   &affected_refnames, err);
+       if (ret)
+               goto done;
+
+       if (files_transaction) {
+               ret = refs_be_files.transaction_commit(files_transaction,
+                                                      &files_affected_refnames,
+                                                      err);
+               if (ret) {
+                       warning(split_transaction_fail_warning);
+                       goto done;
+               }
+       }
+
 done:
        string_list_clear(&affected_refnames, 0);
+       string_list_clear(&files_affected_refnames, 0);
+       if (files_transaction)
+               ref_transaction_free(files_transaction);
        return ret;
 }
 
@@ -1285,6 +1359,9 @@ int peel_ref(const char *refname, unsigned char *sha1)
 int create_symref(const char *ref_target, const char *refs_heads_master,
                  const char *logmsg)
 {
+       if (ref_type(ref_target) != REF_TYPE_NORMAL)
+               return refs_be_files.create_symref(ref_target, 
refs_heads_master,
+                                                  logmsg);
        return the_refs_backend->create_symref(ref_target, refs_heads_master,
                                               logmsg);
 }
-- 
2.4.2.749.g730654d-twtrsrc

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