From 5340ed0ad3e3332138e1726a000d218ae3af4959 Mon Sep 17 00:00:00 2001
From: Mike Farah <mikefarah@gmail.com>
Date: Sun, 16 May 2021 12:16:10 +1000
Subject: [PATCH] Fixed handling of null expressions in equals op

---
 pkg/yqlib/operator_equals.go      | 20 ++++++++++++++++----
 pkg/yqlib/operator_equals_test.go | 22 ++++++++++++++++++++++
 pkg/yqlib/operator_select.go      |  2 ++
 pkg/yqlib/operators.go            | 23 +++++++++++++----------
 4 files changed, 53 insertions(+), 14 deletions(-)

diff --git a/pkg/yqlib/operator_equals.go b/pkg/yqlib/operator_equals.go
index fe465eaf..157baf4d 100644
--- a/pkg/yqlib/operator_equals.go
+++ b/pkg/yqlib/operator_equals.go
@@ -10,14 +10,26 @@ func equalsOperator(d *dataTreeNavigator, context Context, expressionNode *Expre
 func isEquals(flip bool) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
 	return func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
 		value := false
-
+		log.Debugf("-- isEquals cross function")
 		if lhs == nil && rhs == nil {
 			owner := &CandidateNode{}
 			return createBooleanCandidate(owner, !flip), nil
 		} else if lhs == nil {
-			return createBooleanCandidate(rhs, flip), nil
+			log.Debugf("lhs nil, but rhs is not")
+			rhsNode := unwrapDoc(rhs.Node)
+			value := rhsNode.Tag == "!!null"
+			if flip {
+				value = !value
+			}
+			return createBooleanCandidate(rhs, value), nil
 		} else if rhs == nil {
-			return createBooleanCandidate(lhs, flip), nil
+			log.Debugf("lhs not nil, but rhs is")
+			lhsNode := unwrapDoc(lhs.Node)
+			value := lhsNode.Tag == "!!null"
+			if flip {
+				value = !value
+			}
+			return createBooleanCandidate(lhs, value), nil
 		}
 
 		lhsNode := unwrapDoc(lhs.Node)
@@ -37,6 +49,6 @@ func isEquals(flip bool) func(d *dataTreeNavigator, context Context, lhs *Candid
 }
 
 func notEqualsOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
-	log.Debugf("-- equalsOperation")
+	log.Debugf("-- notEqualsOperator")
 	return crossFunction(d, context, expressionNode, isEquals(true), true)
 }
diff --git a/pkg/yqlib/operator_equals_test.go b/pkg/yqlib/operator_equals_test.go
index 734f0872..2741fdfc 100644
--- a/pkg/yqlib/operator_equals_test.go
+++ b/pkg/yqlib/operator_equals_test.go
@@ -14,6 +14,28 @@ var equalsOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!bool)::false\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   "{a: {b: 10}}",
+		expression: "select(.c != null)",
+		expected:   []string{},
+	},
+	{
+		skipDoc:    true,
+		document:   "{a: {b: 10}}",
+		expression: "select(.d == .c)",
+		expected: []string{
+			"D0, P[], (doc)::{a: {b: 10}}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   "{a: {b: 10}}",
+		expression: "select(null == .c)",
+		expected: []string{
+			"D0, P[], (doc)::{a: {b: 10}}\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   "{a: { b: {things: \"\"}, f: [1], g: [] }}",
diff --git a/pkg/yqlib/operator_select.go b/pkg/yqlib/operator_select.go
index 5c659e8f..c89cbf4d 100644
--- a/pkg/yqlib/operator_select.go
+++ b/pkg/yqlib/operator_select.go
@@ -24,7 +24,9 @@ func selectOperator(d *dataTreeNavigator, context Context, expressionNode *Expre
 
 		if first != nil {
 			result := first.Value.(*CandidateNode)
+			log.Debugf("result %v", NodeToString(result))
 			includeResult, errDecoding := isTruthy(result)
+			log.Debugf("isTruthy %v", includeResult)
 			if errDecoding != nil {
 				return Context{}, errDecoding
 			}
diff --git a/pkg/yqlib/operators.go b/pkg/yqlib/operators.go
index 0a0e25dc..1242b6f4 100644
--- a/pkg/yqlib/operators.go
+++ b/pkg/yqlib/operators.go
@@ -24,7 +24,17 @@ func emptyOperator(d *dataTreeNavigator, context Context, expressionNode *Expres
 
 type crossFunctionCalculation func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error)
 
-func resultsForRhs(d *dataTreeNavigator, context Context, lhsCandidate *CandidateNode, rhs Context, calculation crossFunctionCalculation, results *list.List) error {
+func resultsForRhs(d *dataTreeNavigator, context Context, lhsCandidate *CandidateNode, rhs Context, calculation crossFunctionCalculation, results *list.List, calcWhenEmpty bool) error {
+
+	if calcWhenEmpty && rhs.MatchingNodes.Len() == 0 {
+		resultCandidate, err := calculation(d, context, lhsCandidate, nil)
+		if err != nil {
+			return err
+		}
+		results.PushBack(resultCandidate)
+		return nil
+	}
+
 	for rightEl := rhs.MatchingNodes.Front(); rightEl != nil; rightEl = rightEl.Next() {
 		log.Debugf("Applying calc")
 		rhsCandidate := rightEl.Value.(*CandidateNode)
@@ -52,14 +62,7 @@ func doCrossFunc(d *dataTreeNavigator, context Context, expressionNode *Expressi
 	}
 
 	if calcWhenEmpty && lhs.MatchingNodes.Len() == 0 {
-		if rhs.MatchingNodes.Len() == 0 {
-			resultCandidate, err := calculation(d, context, nil, nil)
-			if err != nil {
-				return Context{}, err
-			}
-			results.PushBack(resultCandidate)
-		}
-		err := resultsForRhs(d, context, nil, rhs, calculation, results)
+		err := resultsForRhs(d, context, nil, rhs, calculation, results, calcWhenEmpty)
 		if err != nil {
 			return Context{}, err
 		}
@@ -68,7 +71,7 @@ func doCrossFunc(d *dataTreeNavigator, context Context, expressionNode *Expressi
 	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		lhsCandidate := el.Value.(*CandidateNode)
 
-		err := resultsForRhs(d, context, lhsCandidate, rhs, calculation, results)
+		err := resultsForRhs(d, context, lhsCandidate, rhs, calculation, results, calcWhenEmpty)
 		if err != nil {
 			return Context{}, err
 		}