enhance(yaml): silent fix anchor merges in YAML maps

compiler/native/compile_test.go

@@ -2162,19 +2162,21 @@ func TestNative_Compile_LegacyMergeAnchor(t *testing.T) {
 		t.Errorf("Compile() mismatch (-want +got):\n%s", diff)
 	}
 
-	// run test on current version (should fail)
-	yaml, err = os.ReadFile("../types/yaml/buildkite/testdata/merge_anchor.yml") // has `version: "1"` instead of `version: "legacy"`
+	// run test on current version
+	yaml, err = os.ReadFile("testdata/steps_merge_anchor_1.yml") // has `version: "1"` instead of `version: "legacy"`
 	if err != nil {
 		t.Errorf("Reading yaml file return err: %v", err)
 	}
 
 	got, _, err = compiler.Compile(context.Background(), yaml)
-	if err == nil {
-		t.Errorf("Compile should have returned err")
+	if err != nil {
+		t.Errorf("Compile returned err: %v", err)
 	}
 
-	if got != nil {
-		t.Errorf("Compile is %v, want %v", got, nil)
+	want.Version = "1"
+
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Errorf("Compile() mismatch (-want +got):\n%s", diff)
 	}
 }
 

compiler/native/testdata/steps_merge_anchor_1.yml

@@ -0,0 +1,46 @@
+# test file that uses the non-standard multiple anchor keys in one step to test custom step unmarshaler
+
+version: "1"
+
+aliases:
+  images:
+    alpine: &alpine-image
+      image: alpine:latest
+    postgres: &pg-image
+      image: postgres
+
+  events:
+    push: &event-push
+      ruleset:
+        event:
+          - push
+  env:
+    dev-env: &dev-environment
+      environment:
+        REGION: dev 
+
+services:
+  - name: service-a
+    <<: *pg-image
+    <<: *dev-environment
+    ports:
+      - "5432:5432"
+
+steps:
+  - name: alpha
+    <<: *alpine-image
+    <<: *event-push
+    commands:
+      - echo alpha
+
+  - name: beta
+    <<: [ *alpine-image, *event-push ]
+    commands:
+      - echo beta
+
+  - name: gamma
+    <<: *alpine-image
+    <<: *event-push
+    <<: *dev-environment
+    commands:
+      - echo gamma

internal/testdata/buildkite_new_version.yml

@@ -0,0 +1,18 @@
+version: "1"
+
+aliases:
+  images:
+    alpine: &alpine-image
+      image: alpine:latest
+
+  env:
+    dev-env: &dev-environment
+      environment:
+        REGION: dev 
+
+steps:
+  - name: example
+    <<: *alpine-image
+    <<: *dev-environment
+    commands:
+      - echo $REGION

internal/yaml.go

@@ -4,6 +4,7 @@ package internal
 
 import (
 	"fmt"
+	"strings"
 
 	bkYaml "github.com/buildkite/yaml"
 	yaml "gopkg.in/yaml.v3"
@@ -55,9 +56,90 @@ func ParseYAML(data []byte) (*types.Build, error) {
 		// unmarshal the bytes into the yaml configuration
 		err := yaml.Unmarshal(data, config)
 		if err != nil {
-			return nil, fmt.Errorf("unable to unmarshal yaml: %w", err)
+			// if error is related to duplicate `<<` keys, attempt to fix
+			if strings.Contains(err.Error(), "mapping key \"<<\" already defined") {
+				root := new(yaml.Node)
+
+				if err := yaml.Unmarshal(data, root); err != nil {
+					fmt.Println("error unmarshalling YAML:", err)
+
+					return nil, err
+				}
+
+				collapseMergeAnchors(root.Content[0])
+
+				newData, err := yaml.Marshal(root)
+				if err != nil {
+					return nil, err
+				}
+
+				err = yaml.Unmarshal(newData, config)
+				if err != nil {
+					return nil, fmt.Errorf("unable to unmarshal yaml: %w", err)
+				}
+			} else {
+				return nil, fmt.Errorf("unable to unmarshal yaml: %w", err)
+			}
 		}
 	}
 
 	return config, nil
 }
+
+// collapseMergeAnchors traverses the entire pipeline and replaces duplicate `<<` keys with a single key->sequence.
+func collapseMergeAnchors(node *yaml.Node) {
+	// only replace on maps
+	if node.Kind == yaml.MappingNode {
+		var (
+			anchors      []*yaml.Node
+			keysToRemove []int
+			firstIndex   int
+			firstFound   bool
+		)
+
+		// traverse mapping node content
+		for i := 0; i < len(node.Content); i += 2 {
+			keyNode := node.Content[i]
+
+			// anchor found
+			if keyNode.Value == "<<" {
+				if (i+1) < len(node.Content) && node.Content[i+1].Kind == yaml.AliasNode {
+					anchors = append(anchors, node.Content[i+1])
+				}
+
+				if !firstFound {
+					firstIndex = i
+					firstFound = true
+				} else {
+					keysToRemove = append(keysToRemove, i)
+				}
+			}
+		}
+
+		// only replace if there were duplicates
+		if len(anchors) > 1 && firstFound {
+			seqNode := &yaml.Node{
+				Kind:    yaml.SequenceNode,
+				Content: anchors,
+			}
+
+			node.Content[firstIndex] = &yaml.Node{Kind: yaml.ScalarNode, Value: "<<"}
+			node.Content[firstIndex+1] = seqNode
+
+			for i := len(keysToRemove) - 1; i >= 0; i-- {
+				index := keysToRemove[i]
+
+				node.Content = append(node.Content[:index], node.Content[index+2:]...)
+			}
+		}
+
+		// go to next level
+		for _, content := range node.Content {
+			collapseMergeAnchors(content)
+		}
+	} else if node.Kind == yaml.SequenceNode {
+		for _, item := range node.Content {
+			collapseMergeAnchors(item)
+		}
+	}
+}

internal/yaml_test.go

@@ -47,6 +47,10 @@ func TestInternal_ParseYAML(t *testing.T) {
 			file: "testdata/buildkite.yml",
 			want: wantBuild,
 		},
+		{
+			file: "testdata/buildkite_new_version.yml",
+			want: wantBuild,
+		},
 		{
 			file: "testdata/no_version.yml",
 			want: wantBuild,