fix(first): return the first value, not key, for a map

The no-filter branch returned Content[0]; for a map that is the first key. Splat to get the first value with its correct path (matches the filtered path and first.md).

pkg/yqlib/operator_first.go

@@ -8,9 +8,20 @@ func firstOperator(d *dataTreeNavigator, context Context, expressionNode *Expres
 	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		// If no RHS expression is provided, simply return the first entry in candidate.Content
+		// If no RHS expression is provided, simply return the first entry
 		if expressionNode == nil || expressionNode.RHS == nil {
-			if len(candidate.Content) > 0 {
+			if candidate.Kind == MappingNode {
+				// candidate.Content is [key0, value0, ...]; the first entry of a
+				// map is its first VALUE, not the key (first.md: "first matching
+				// value in a map"). Splat to get map values with correct paths.
+				splatted, err := splat(context.SingleChildContext(candidate), traversePreferences{})
+				if err != nil {
+					return Context{}, err
+				}
+				if splatted.MatchingNodes.Front() != nil {
+					results.PushBack(splatted.MatchingNodes.Front().Value.(*CandidateNode))
+				}
+			} else if len(candidate.Content) > 0 {
 				results.PushBack(candidate.Content[0])
 			}
 			continue

pkg/yqlib/operator_first_test.go

@@ -176,6 +176,15 @@ var firstOperatorScenarios = []expressionScenario{
 		expression:  `first`,
 		expected:    []string{},
 	},
+	{
+		description: "First value with no filter from a map",
+		skipDoc:     true,
+		document:    "{x: {a: banana}, y: {a: cat}}",
+		expression:  `first`,
+		expected: []string{
+			"D0, P[x], (!!map)::{a: banana}\n",
+		},
+	},
 }
 
 func TestFirstOperatorScenarios(t *testing.T) {