style: minor tweaks to ScaleError

Some small tweaks to the style of `ScaleError`, while we're working on
it.

`message` doesn't need to be a public property. `Error` already has it.
Likewise with `stack` - we can use the parent's implementation.

Instead of `getDetailedMessage` we can have a property getter which is
very slightly nicer to read at callsites (`e.detailedMessage` vs.
`e.getDetailedMessage()`).

Author: iainlane

lambdas/functions/control-plane/src/lambda.ts

@@ -67,10 +67,7 @@ export async function scaleUpHandler(event: SQSEvent, context: Context): Promise
           itemIdentifier: sqsMessages[i].messageId,
         });
       }
-      logger.warn(
-        `ScaleError detected, ${e.failedInstanceCount} could not be created. A retry will be attempted via SQS.`,
-        { error: e },
-      );
+      logger.warn(`${e.detailedMessage} A retry will be attempted via SQS.`, { error: e });
     } else {
       logger.error(`Error processing batch (size: ${sqsMessages.length}): ${(e as Error).message}, ignoring batch`, {
         error: e,

lambdas/functions/control-plane/src/scale-runners/ScaleError.ts

@@ -1,19 +1,18 @@
 class ScaleError extends Error {
   constructor(
-    public message: string,
-    public failedInstanceCount: number = 1,
+    message: string,
+    public readonly failedInstanceCount: number = 1,
   ) {
     super(message);
     this.name = 'ScaleError';
-    this.stack = new Error().stack;
   }
 
   /**
    * Gets a formatted error message including the failed instance count
    */
-  public getDetailedMessage(): string {
+  public get detailedMessage(): string {
     return `${this.message} (Failed to create ${this.failedInstanceCount} instance${this.failedInstanceCount !== 1 ? 's' : ''})`;
   }
 }
 
-export default ScaleError;
+export default ScaleError;