Fixed select bug (#958)

pkg/yqlib/operator_select.go

@@ -17,22 +17,25 @@ func selectOperator(d *dataTreeNavigator, context Context, expressionNode *Expre
 			return Context{}, err
 		}
 
-		// grab the first value
-		first := rhs.MatchingNodes.Front()
+		// find any truthy node
+		var errDecoding error
+		includeResult := false
 
-		if first != nil {
-			result := first.Value.(*CandidateNode)
-			log.Debugf("result %v", NodeToString(result))
-			includeResult, errDecoding := isTruthy(result)
+		for resultEl := rhs.MatchingNodes.Front(); resultEl != nil; resultEl = resultEl.Next() {
+			result := resultEl.Value.(*CandidateNode)
+			includeResult, errDecoding = isTruthy(result)
 			log.Debugf("isTruthy %v", includeResult)
 			if errDecoding != nil {
 				return Context{}, errDecoding
 			}
+			if includeResult {
+				break
+			}
+		}
 
 		if includeResult {
 			results.PushBack(candidate)
 		}
 	}
-	}
 	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_select_test.go

@@ -5,6 +5,28 @@ import (
 )
 
 var selectOperatorScenarios = []expressionScenario{
+	{
+		skipDoc:    true,
+		document:   `cat`,
+		expression: `select(false, true)`,
+		expected: []string{
+			"D0, P[], (doc)::cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `cat`,
+		expression: `select(true, false)`,
+		expected: []string{
+			"D0, P[], (doc)::cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `cat`,
+		expression: `select(false)`,
+		expected:   []string{},
+	},
 	{
 		description: "Select elements from array",
 		document:    `[cat,goat,dog]`,