Make InProgressMethods immutable so it's safer to use as react state

extensions/ql-vscode/src/data-extensions-editor/shared/in-progress-methods.ts

@@ -1,16 +1,30 @@
 /**
  * A class that keeps track of which methods are in progress for each package.
+ *
+ * This class is immutable and therefore is safe to be used in a react useState hook.
  */
 export class InProgressMethods {
   // A map of in-progress method signatures for each package.
-  private readonly methodMap: Map<string, Set<string>>;
+  private readonly methodMap: ReadonlyMap<string, Set<string>>;
 
-  constructor() {
-    this.methodMap = new Map<string, Set<string>>();
+  constructor(methodMap?: ReadonlyMap<string, Set<string>>) {
+    this.methodMap = methodMap ?? new Map<string, Set<string>>();
   }
 
-  public setPackageMethods(packageName: string, methods: Set<string>): void {
-    this.methodMap.set(packageName, methods);
+  /**
+   * Sets the in-progress methods for the given package.
+   * Returns a new InProgressMethods instance.
+   */
+  public setPackageMethods(
+    packageName: string,
+    methods: Set<string>,
+  ): InProgressMethods {
+    const newMethodMap = new Map<string, Set<string>>();
+    this.methodMap.forEach((value, key) => {
+      newMethodMap.set(key, new Set<string>(value));
+    });
+    newMethodMap.set(packageName, methods);
+    return new InProgressMethods(newMethodMap);
   }
 
   public hasMethod(packageName: string, method: string): boolean {
@@ -20,12 +34,4 @@ export class InProgressMethods {
     }
     return false;
   }
-
-  public static fromExisting(methods: InProgressMethods): InProgressMethods {
-    const newInProgressMethods = new InProgressMethods();
-    methods.methodMap.forEach((value, key) => {
-      newInProgressMethods.methodMap.set(key, new Set<string>(value));
-    });
-    return newInProgressMethods;
-  }
 }

extensions/ql-vscode/src/view/data-extensions-editor/DataExtensionsEditor.tsx

@@ -141,15 +141,12 @@ export function DataExtensionsEditor({
             );
             break;
           case "setInProgressMethods":
-            setInProgressMethods((oldInProgressMethods) => {
-              const methods =
-                InProgressMethods.fromExisting(oldInProgressMethods);
-              methods.setPackageMethods(
+            setInProgressMethods((oldInProgressMethods) =>
+              oldInProgressMethods.setPackageMethods(
                 msg.packageName,
                 new Set(msg.inProgressMethods),
-              );
-              return methods;
-            });
+              ),
+            );
             break;
           default:
             assertNever(msg);