Merge branch 'maint-1.7.6' into maint-1.7.7

* maint-1.7.6:
  Update draft release notes to 1.7.6.6
  thin-pack: try harder to use preferred base objects as base

Author: gitster

Documentation/RelNotes/1.7.6.6.txt

@@ -8,4 +8,9 @@ Fixes since v1.7.6.5
    directory when two paths in question are in adjacent directories and
    the name of the one directory is a prefix of the other.
 
+ * When producing a "thin pack" (primarily used in bundles and smart
+   HTTP transfers) out of a fully packed repository, we unnecessarily
+   avoided sending recent objects as a delta against objects we know
+   the other side has.
+
 Also contains minor fixes and documentation updates.

builtin/pack-objects.c

@@ -1421,11 +1421,16 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		return -1;
 
 	/*
-	 * We do not bother to try a delta that we discarded
-	 * on an earlier try, but only when reusing delta data.
+	 * We do not bother to try a delta that we discarded on an
+	 * earlier try, but only when reusing delta data.  Note that
+	 * src_entry that is marked as the preferred_base should always
+	 * be considered, as even if we produce a suboptimal delta against
+	 * it, we will still save the transfer cost, as we already know
+	 * the other side has it and we won't send src_entry at all.
 	 */
 	if (reuse_delta && trg_entry->in_pack &&
 	    trg_entry->in_pack == src_entry->in_pack &&
+	    !src_entry->preferred_base &&
 	    trg_entry->in_pack_type != OBJ_REF_DELTA &&
 	    trg_entry->in_pack_type != OBJ_OFS_DELTA)
 		return 0;