From 29616c48cd6b667366789372e120126a8c0bc5ed Mon Sep 17 00:00:00 2001
From: Tony Sun <tony.sun427@gmail.com>
Date: Tue, 21 Apr 2020 14:44:23 -0700
Subject: fix operator issue with empty arrays (#2805)

Previously, in https://github.com/apache/couchdb/pull/1783, the logic
was wrong in relation to how certain operators interacted with empty
arrays. We modify this logic to make it such that:

{"foo":"bar", "bar":{"$in":[]}}
and
{"foo":"bar", "bar":{"$all":[]}}

should return 0 results.
---
 src/mango/src/mango_selector.erl          |  4 ++--
 src/mango/test/21-empty-selector-tests.py | 24 +++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/mango/src/mango_selector.erl b/src/mango/src/mango_selector.erl
index 3ea83c220..e884dc55c 100644
--- a/src/mango/src/mango_selector.erl
+++ b/src/mango/src/mango_selector.erl
@@ -421,7 +421,7 @@ match({[{<<"$not">>, Arg}]}, Value, Cmp) ->
     not match(Arg, Value, Cmp);
 
 match({[{<<"$all">>, []}]}, _, _) ->
-    true;
+    false;
 % All of the values in Args must exist in Values or
 % Values == hd(Args) if Args is a single element list
 % that contains a list.
@@ -506,7 +506,7 @@ match({[{<<"$gt">>, Arg}]}, Value, Cmp) ->
     Cmp(Value, Arg) > 0;
 
 match({[{<<"$in">>, []}]}, _, _) ->
-    true;
+    false;
 match({[{<<"$in">>, Args}]}, Values, Cmp) when is_list(Values)->
     Pred = fun(Arg) ->
         lists:foldl(fun(Value,Match) ->
diff --git a/src/mango/test/21-empty-selector-tests.py b/src/mango/test/21-empty-selector-tests.py
index beb222c85..31ad8e645 100644
--- a/src/mango/test/21-empty-selector-tests.py
+++ b/src/mango/test/21-empty-selector-tests.py
@@ -35,14 +35,36 @@ def make_empty_selector_suite(klass):
             docs = self.db.find({"age": 22, "$or": []})
             assert len(docs) == 1
 
+        def test_empty_array_in_with_age(self):
+            resp = self.db.find({"age": 22, "company": {"$in": []}}, explain=True)
+            self.assertEqual(resp["index"]["type"], klass.INDEX_TYPE)
+            docs = self.db.find({"age": 22, "company": {"$in": []}})
+            assert len(docs) == 0
+
         def test_empty_array_and_with_age(self):
             resp = self.db.find(
-                {"age": 22, "$and": [{"b": {"$all": []}}]}, explain=True
+                {"age": 22, "$and": []}, explain=True
             )
             self.assertEqual(resp["index"]["type"], klass.INDEX_TYPE)
             docs = self.db.find({"age": 22, "$and": []})
             assert len(docs) == 1
 
+        def test_empty_array_all_age(self):
+            resp = self.db.find(
+                {"age": 22, "company": {"$all": []}}, explain=True
+            )
+            self.assertEqual(resp["index"]["type"], klass.INDEX_TYPE)
+            docs = self.db.find({"age": 22, "company": {"$all": []}})
+            assert len(docs) == 0
+
+        def test_empty_array_nested_all_with_age(self):
+            resp = self.db.find(
+                {"age": 22, "$and": [{"company": {"$all": []}}]}, explain=True
+            )
+            self.assertEqual(resp["index"]["type"], klass.INDEX_TYPE)
+            docs = self.db.find( {"age": 22, "$and": [{"company": {"$all": []}}]})
+            assert len(docs) == 0
+
         def test_empty_arrays_complex(self):
             resp = self.db.find({"$or": [], "a": {"$in": []}}, explain=True)
             self.assertEqual(resp["index"]["type"], klass.INDEX_TYPE)
-- 
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