Detect recursion in aliases (#835)

pkg/parser/node/yaml.go

@@ -175,6 +175,14 @@ func convert(
 	case yaml.ScalarNode:
 		result.Value = &ScalarValue{Value: yamlNode.Value}
 	case yaml.AliasNode:
+		// test for recursion
+		for aParent := parent; aParent != nil; aParent = aParent.Parent {
+			// If we've found a parent with the same anchor, it means we have a recursion
+			if aParent.YAMLNode != nil && aParent.YAMLNode.Anchor == yamlNode.Value {
+				return nil, parsererror.NewRich(yamlNode.Line, yamlNode.Column, "recursive alias '%s'", yamlNode.Value)
+			}
+		}
+
 		// YAML aliases generally don't need line and column helper values
 		// since they are merged into some other data structure afterwards
 		// and this helps to find bugs easier in the future

pkg/parser/parser_test.go

@@ -618,6 +618,8 @@ func TestRichErrors(t *testing.T) {
 			"expected a scalar value or a list with scalar values")},
 		{"testdata/rich-errors-matrix.yml", parsererror.NewRich(3, 5,
 			"matrix can be defined only under a task, docker_builder or pipe")},
+		{"testdata/rich-errors-recursion.yml", parsererror.NewRich(6, 9,
+			"recursive alias 'RECURSION'")},
 	}
 
 	for _, testCase := range testCases {

pkg/parser/testdata/rich-errors-recursion.yml

@@ -0,0 +1,9 @@
+container:
+  image: debian:latest
+
+recursion: &RECURSION
+  env:
+    <<: *RECURSION
+
+task:
+  script: true