Improve type-check for scaffolder output parameters

If an action uses zod to define the actions output schema, it is now ensured that `ctx.output` is using only the defined properties

Signed-off-by: Andreas Berger <andreas@berger-ecommerce.com>

plugins/scaffolder-node/src/actions/createTemplateAction.ts

@@ -33,7 +33,14 @@ export type TemplateActionOptions<
     input?: TInputSchema;
     output?: TOutputSchema;
   };
-  handler: (ctx: ActionContext<TActionInput>) => Promise<void>;
+  handler: (
+    ctx: ActionContext<
+      TActionInput,
+      TOutputSchema extends z.ZodType<any, any, infer IReturn>
+        ? IReturn
+        : undefined
+    >,
+  ) => Promise<void>;
 };
 
 /**
@@ -48,9 +55,12 @@ export const createTemplateAction = <
   TActionInput = TInputSchema extends z.ZodType<any, any, infer IReturn>
     ? IReturn
     : TParams,
+  TActionOutput = TOutputSchema extends z.ZodType<any, any, infer IReturn>
+    ? IReturn
+    : undefined,
 >(
   action: TemplateActionOptions<TActionInput, TInputSchema, TOutputSchema>,
-): TemplateAction<TActionInput> => {
+): TemplateAction<TActionInput, TActionOutput> => {
   const inputSchema =
     action.schema?.input && 'safeParseAsync' in action.schema.input
       ? zodToJsonSchema(action.schema.input)
@@ -61,7 +71,7 @@ export const createTemplateAction = <
       ? zodToJsonSchema(action.schema.output)
       : action.schema?.output;
 
-  const templateAction = {
+  return {
     ...action,
     schema: {
       ...action.schema,
@@ -69,6 +79,4 @@ export const createTemplateAction = <
       output: outputSchema,
     },
   };
-
-  return templateAction;
 };

plugins/scaffolder-node/src/actions/types.ts

@@ -17,7 +17,7 @@
 import { Logger } from 'winston';
 import { Writable } from 'stream';
 import { JsonObject, JsonValue } from '@backstage/types';
-import { TaskSecrets } from '../tasks/types';
+import { TaskSecrets } from '../tasks';
 import { TemplateInfo } from '@backstage/plugin-scaffolder-common';
 import { UserEntity } from '@backstage/catalog-model';
 import { Schema } from 'jsonschema';
@@ -26,13 +26,19 @@ import { Schema } from 'jsonschema';
  * ActionContext is passed into scaffolder actions.
  * @public
  */
-export type ActionContext<TActionInput extends JsonObject> = {
+export type ActionContext<
+  TActionInput extends JsonObject,
+  TActionOutput extends JsonObject | undefined = undefined,
+> = {
   logger: Logger;
   logStream: Writable;
   secrets?: TaskSecrets;
   workspacePath: string;
   input: TActionInput;
-  output(name: string, value: JsonValue): void;
+  output<KEY extends keyof TActionOutput>(
+    name: TActionOutput extends undefined ? string : KEY,
+    value: TActionOutput extends undefined ? JsonValue : TActionOutput[KEY],
+  ): void;
 
   /**
    * Creates a temporary directory for use by the action, which is then cleaned up automatically.
@@ -68,7 +74,10 @@ export type ActionContext<TActionInput extends JsonObject> = {
 };
 
 /** @public */
-export type TemplateAction<TActionInput = unknown> = {
+export type TemplateAction<
+  TActionInput = unknown,
+  TActionOutput = undefined,
+> = {
   id: string;
   description?: string;
   examples?: { description: string; example: string }[];
@@ -77,5 +86,5 @@ export type TemplateAction<TActionInput = unknown> = {
     input?: Schema;
     output?: Schema;
   };
-  handler: (ctx: ActionContext<TActionInput>) => Promise<void>;
+  handler: (ctx: ActionContext<TActionInput, TActionOutput>) => Promise<void>;
 };