scaffolder-backend: add dry-run support for actions and runner

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

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

@@ -39,12 +39,19 @@ export type ActionContext<Input extends JsonObject> = {
   createTemporaryDirectory(): Promise<string>;
 
   templateInfo?: TemplateInfo;
+
+  /**
+   * Whether this action invocation is a dry-run or not.
+   * This will only ever be true if the actions as marked as supporting dry-runs.
+   */
+  isDryRun?: boolean;
 };
 
 /** @public */
 export type TemplateAction<Input extends JsonObject> = {
   id: string;
   description?: string;
+  supportsDryRun?: boolean;
   schema?: {
     input?: Schema;
     output?: Schema;

plugins/scaffolder-backend/src/scaffolder/tasks/NunjucksWorkflowRunner.ts

@@ -23,7 +23,7 @@ import nunjucks from 'nunjucks';
 import { JsonObject, JsonValue } from '@backstage/types';
 import { InputError } from '@backstage/errors';
 import { PassThrough } from 'stream';
-import { isTruthy } from './helper';
+import { generateExampleOutput, isTruthy } from './helper';
 import { validate as validateJsonSchema } from 'jsonschema';
 import { parseRepoUrl } from '../actions/builtin/publish/util';
 import { TemplateActionRegistry } from '../actions';
@@ -236,6 +236,23 @@ export class NunjucksWorkflowRunner implements WorkflowRunner {
           const action = this.options.actionRegistry.get(step.action);
           const { taskLogger, streamLogger } = createStepLogger({ task, step });
 
+          if (task.isDryRun && !action.supportsDryRun) {
+            task.emitLog(
+              `Skipping because ${action.id} does not support dry-run`,
+            );
+            const outputSchema = action.schema?.output;
+            if (outputSchema) {
+              context.steps[step.id] = {
+                output: generateExampleOutput(outputSchema) as {
+                  [name in string]: JsonValue;
+                },
+              };
+            } else {
+              context.steps[step.id] = { output: {} };
+            }
+            continue;
+          }
+
           // Secrets are only passed when templating the input to actions for security reasons
           const input =
             (step.input &&

plugins/scaffolder-backend/src/scaffolder/tasks/helper.ts

@@ -15,6 +15,7 @@
  */
 
 import { isArray } from 'lodash';
+import { Schema } from 'jsonschema';
 
 /**
  * Returns true if the input is not `false`, `undefined`, `null`, `""`, `0`, or
@@ -24,3 +25,31 @@ import { isArray } from 'lodash';
 export function isTruthy(value: any): boolean {
   return isArray(value) ? value.length > 0 : !!value;
 }
+
+export function generateExampleOutput(schema: Schema): unknown {
+  const { examples } = schema as { examples?: unknown };
+  if (examples && Array.isArray(examples)) {
+    return examples[0];
+  }
+  if (schema.type === 'object') {
+    return Object.fromEntries(
+      Object.entries(schema.properties ?? {}).map(([key, value]) => [
+        key,
+        generateExampleOutput(value),
+      ]),
+    );
+  } else if (schema.type === 'array') {
+    const [firstSchema] = [schema.items]?.flat();
+    if (firstSchema) {
+      return [generateExampleOutput(firstSchema)];
+    }
+    return [];
+  } else if (schema.type === 'string') {
+    return '<example>';
+  } else if (schema.type === 'number') {
+    return 0;
+  } else if (schema.type === 'boolean') {
+    return false;
+  }
+  return '<unknown>';
+}

plugins/scaffolder-backend/src/scaffolder/tasks/types.ts

@@ -111,6 +111,7 @@ export interface TaskContext {
   secrets?: TaskSecrets;
   createdBy?: string;
   done: boolean;
+  isDryRun?: boolean;
   emitLog(message: string, logMetadata?: JsonObject): Promise<void>;
   complete(result: TaskCompletionState, metadata?: JsonObject): Promise<void>;
   getWorkspaceName(): Promise<string>;