feat: add kernel mode with isolation by default (microsoft#6520)

* feat: add kernel mode with isolation by default

* Change files

* chore: fix change file

* chore: slight kernel mode valid value change

Co-authored-by: EisenbergEffect <roeisenb@microsoft.com>

change/@microsoft-fast-element-1ac61e2b-196f-4ad4-98de-72cbadfe2a55.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "feat: add kernel mode with isolation by default",
+  "packageName": "@microsoft/fast-element",
+  "email": "roeisenb@microsoft.com",
+  "dependentChangeType": "prerelease"
+}

packages/web-components/fast-element/src/interfaces.ts

@@ -90,17 +90,65 @@ export interface FASTGlobal {
     addMessages(messages: Record<number, string>): void;
 }
 
+let kernelMode;
+const kernelAttr = "fast-kernel";
+
+try {
+    if (document.currentScript) {
+        kernelMode = document.currentScript.getAttribute(kernelAttr);
+    } else {
+        const scripts = document.getElementsByTagName("script");
+        const currentScript = scripts[scripts.length - 1];
+        kernelMode = currentScript.getAttribute(kernelAttr);
+    }
+} catch (e) {
+    kernelMode = "isolate";
+}
+
 /**
- * Core services shared across FAST instances.
+ * Core services that can be shared across FAST instances.
  * @internal
  */
-export const enum KernelServiceId {
-    updateQueue = 1,
-    observable = 2,
-    contextEvent = 3,
-    elementRegistry = 4,
+type KernelServiceId = {
+    readonly updateQueue: string | number;
+    readonly observable: string | number;
+    readonly contextEvent: string | number;
+    readonly elementRegistry: string | number;
+};
+
+let KernelServiceId: KernelServiceId;
+
+switch (kernelMode) {
+    case "share": // share the kernel across major versions
+        KernelServiceId = Object.freeze({
+            updateQueue: 1,
+            observable: 2,
+            contextEvent: 3,
+            elementRegistry: 4,
+        });
+        break;
+    case "share-v2": // only share the kernel with other v2 instances
+        KernelServiceId = Object.freeze({
+            updateQueue: 1.2,
+            observable: 2.2,
+            contextEvent: 3.2,
+            elementRegistry: 4.2,
+        });
+        break;
+    default:
+        // fully isolate the kernel from all other FAST instances
+        const postfix = `-${Math.random().toString(36).substring(2, 8)}`;
+        KernelServiceId = Object.freeze({
+            updateQueue: `1.2${postfix}`,
+            observable: `2.2${postfix}`,
+            contextEvent: `3.2${postfix}`,
+            elementRegistry: `4.2${postfix}`,
+        });
+        break;
 }
 
+export { KernelServiceId };
+
 /**
  * A node that can be targeted by styles.
  * @public