fix(overlays): copy update object to avoid applying to references

test/overlay-previous-overlay/input.yaml

@@ -0,0 +1,17 @@
+type: object
+properties:
+  parent:
+    type: object
+    properties:
+      one:
+        type: object
+        properties:
+          child: {}
+      two:
+        type: object
+        properties:
+          child: {}
+      three:
+        type: object
+        properties:
+          child: {}

test/overlay-previous-overlay/options.yaml

@@ -0,0 +1,2 @@
+output: output.yaml
+overlayFile: overlay.yaml

test/overlay-previous-overlay/output.yaml

@@ -0,0 +1,77 @@
+type: object
+properties:
+  parent:
+    type: object
+    properties:
+      one:
+        type: object
+        properties:
+          child:
+            oneOf:
+              - type: object
+                properties:
+                  type:
+                    const: a
+                  a:
+                    type: object
+                    oneOf:
+                      - type: object
+                        properties:
+                          type:
+                            const: c
+                          c:
+                            type: object
+              - type: object
+                properties:
+                  type:
+                    const: b
+                  b:
+                    type: object
+      two:
+        type: object
+        properties:
+          child:
+            oneOf:
+              - type: object
+                properties:
+                  type:
+                    const: a
+                  a:
+                    type: object
+                    oneOf:
+                      - type: object
+                        properties:
+                          type:
+                            const: c
+                          c:
+                            type: object
+              - type: object
+                properties:
+                  type:
+                    const: b
+                  b:
+                    type: object
+      three:
+        type: object
+        properties:
+          child:
+            oneOf:
+              - type: object
+                properties:
+                  type:
+                    const: a
+                  a:
+                    type: object
+                    oneOf:
+                      - type: object
+                        properties:
+                          type:
+                            const: c
+                          c:
+                            type: object
+              - type: object
+                properties:
+                  type:
+                    const: b
+                  b:
+                    type: object

test/overlay-previous-overlay/overlay.yaml

@@ -0,0 +1,32 @@
+actions:
+
+# apply an overlay to add an object from this overlay into the original OpenAPI schema
+# this should be applied as a copy to each target, not a reference
+  - target: $..child
+    update:
+      oneOf:
+        - type: object
+          properties:
+            type:
+              const: a
+            a:
+              type: object
+        - type: object
+          properties:
+            type:
+              const: b
+            b:
+              type: object
+
+# apply a further overlay to the above overlaid object
+# as the above overlaid object should be a copy, we shouldn't keep
+# adding the overlay multiple times to the same referenced object
+  - target: $..child.oneOf[0].properties.a
+    update:
+      oneOf:
+        - type: object
+          properties:
+            type:
+              const: c
+            c:
+              type: object

utils/overlay.js

@@ -60,7 +60,9 @@ async function openapiOverlay(oaObj, options) {
       // Handle update actions
       targets.forEach(node => {
         if (node.parent && node.key !== undefined) {
-          node.parent[node.key] = deepMerge(node.value, update);
+          // make a copy of the update object any further updates aren't applied
+          // multiple times to the same object
+          node.parent[node.key] = deepMerge(node.value, structuredClone(update));
         }
       });
     }