[couchdb] 04/04: Improve GroupKey notification

[da...@apache.org]

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davisp pushed a commit to branch ebtree-fixes
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit 3fb53ec57d0a2345b89fae8237571627277b9909
Author: Paul J. Davis <pa...@gmail.com>
AuthorDate: Wed Aug 5 13:21:01 2020 -0500

    Improve GroupKey notification
    
    The default `<<0:1>>` NoGroupSet being passed to reduce functions is a
    bit awkward.
---
 src/ebtree/src/ebtree.erl | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/ebtree/src/ebtree.erl b/src/ebtree/src/ebtree.erl
index 5051d94..1cbc507 100644
--- a/src/ebtree/src/ebtree.erl
+++ b/src/ebtree/src/ebtree.erl
@@ -392,8 +392,12 @@ group_reduce(Db, #tree{} = Tree, StartKey, EndKey, GroupKeyFun, UserAccFun, User
     {CurrentGroup, UserAcc1, MapValues, ReduceValues} = fold(Db, Tree, Fun, {NoGroupYet, UserAcc0, [], []}, Options),
     if
         MapValues /= [] orelse ReduceValues /= [] ->
-            FinalGroup = do_reduce(Tree, MapValues, ReduceValues),
-            UserAccFun({CurrentGroup, FinalGroup}, UserAcc1);
+            FinalGroupKey = case CurrentGroup of
+                NoGroupYet -> undefined;
+                _ -> CurrentGroup
+            end,
+            FinalReduction = do_reduce(Tree, MapValues, ReduceValues),
+            UserAccFun({FinalGroupKey, FinalReduction}, UserAcc1);
         true ->
             UserAcc1
     end.