lib-storage: Fix sort index writing to not leave sort_id=0 gaps

This fixes errors like:
Error: INBOX: Broken sort-f indexes, resetting

diff --git a/src/lib-storage/index/index-sort-string.c b/src/lib-storage/index/index-sort-string.c
index 8e8ee1d8f9630be4f57760f67496d71c7901470a..2779e92701190a09f4b9b5da9edd611781db1576 100644 (file)
--- a/src/lib-storage/index/index-sort-string.c
+++ b/src/lib-storage/index/index-sort-string.c
@@ -739,6 +739,7 @@ static void index_sort_write_changed_sort_ids(struct sort_string_context *ctx)
        uint32_t ext_id = ctx->ext_id;
        const struct mail_sort_node *nodes;
        unsigned int i, count;
+       uint32_t lowest_failed_seq;
 
        if (ctx->no_writing) {
                /* our reset_id is already stale - don't even bother
@@ -749,11 +750,30 @@ static void index_sort_write_changed_sort_ids(struct sort_string_context *ctx)
        mail_index_ext_reset_inc(itrans, ext_id,
                                 ctx->highest_reset_id, FALSE);
 
-       /* add the missing sort IDs to index */
+       /* We require that there aren't sort_id=0 gaps in the middle of the
+          mails. At this point they could exist though, because some of the
+          mail lookups may have failed. Failures due to expunges don't matter,
+          because on the next lookup those mails will be lost anyway.
+          Otherwise, make sure we don't write those gaps out
+
+          First find the lowest non-expunged mail that has no_update set. */
+       nodes = array_get_modifiable(&ctx->sorted_nodes, &count);
+       lowest_failed_seq = (uint32_t)-1;
+       for (i = 0; i < count; i++) {
+               uint32_t seq = nodes[i].seq;
+
+               if (nodes[i].no_update && lowest_failed_seq > seq &&
+                   !mail_index_is_expunged(ctx->program->t->view, seq))
+                       lowest_failed_seq = seq;
+       }
+
+       /* add the missing sort IDs to index, but only for those sequences
+          that are below lowest_failed_seq */
        nodes = array_get_modifiable(&ctx->sorted_nodes, &count);
        for (i = 0; i < count; i++) {
                i_assert(nodes[i].sort_id != 0);
-               if (!nodes[i].sort_id_changed || nodes[i].no_update)
+               if (!nodes[i].sort_id_changed || nodes[i].no_update ||
+                   nodes[i].seq >= lowest_failed_seq)
                        continue;
 
                mail_index_update_ext(itrans, nodes[i].seq, ext_id,