Refining add op

pkg/yqlib/operator_add.go

@@ -38,9 +38,9 @@ func toNodes(candidate *CandidateNode, lhs *CandidateNode) []*CandidateNode {
 
 func addOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("Add operator")
-	// if we don't have any matching nodes, but we were piped into (have a parent exp?) then we
-	// shouldn't calcWhenEmpt
-	calcWhenEmpty := expressionNode.Parent == nil
+	// only calculate when empty IF we are the root expression; OR
+	// calcWhenEmpty := expressionNode.Parent == nil || expressionNode.Parent.LHS == expressionNode
+	calcWhenEmpty := context.MatchingNodes.Len() > 0
 
 	return crossFunction(d, context.ReadOnlyClone(), expressionNode, add, calcWhenEmpty)
 }

pkg/yqlib/operator_add_test.go

@@ -50,6 +50,62 @@ var addOperatorScenarios = []expressionScenario{
 		expression: `select(.) | "cat" + .`,
 		expected:   []string{},
 	},
+	{
+		skipDoc:    true,
+		document:   `[]`,
+		expression: `.[] | (.a + "|" + .b)`,
+		expected:   []string{},
+	},
+	{
+		skipDoc:    true,
+		document:   `[]`,
+		expression: `.[] | (.a + "|")`,
+		expected:   []string{},
+	},
+	{
+		skipDoc:    true,
+		document:   `[]`,
+		expression: `.[] | ("|" + .a)`,
+		expected:   []string{},
+	},
+	{
+		skipDoc:    true,
+		document:   `resources: [foo, bar, baz]`,
+		expression: `.missing + .resources | .[]`,
+		expected: []string{
+			"D0, P[resources 0], (!!str)::foo\n",
+			"D0, P[resources 1], (!!str)::bar\n",
+			"D0, P[resources 2], (!!str)::baz\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `resources: [foo, bar, baz]`,
+		expression: `. | .missing + .resources | .[]`,
+		expected: []string{
+			"D0, P[resources 0], (!!str)::foo\n",
+			"D0, P[resources 1], (!!str)::bar\n",
+			"D0, P[resources 2], (!!str)::baz\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `resources: [foo, bar, baz]`,
+		expression: `. | .missing + .resources`,
+		expected: []string{
+			"D0, P[resources], (!!seq)::[foo, bar, baz]\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `resources: [foo, bar, baz]`,
+		expression: `. | .missing + .resources | .[]`,
+		expected: []string{
+			"D0, P[resources 0], (!!str)::foo\n",
+			"D0, P[resources 1], (!!str)::bar\n",
+			"D0, P[resources 2], (!!str)::baz\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   `[{a: foo, b: bar}, {a: 1, b: 2}]`,