From c7b089a5aeb2817e91543dee1db571fe7e66d7d3 Mon Sep 17 00:00:00 2001
From: blam <ben@blam.sh>
Date: Tue, 28 Sep 2021 04:10:33 +0200
Subject: [PATCH] chore: adding the new if syntax and using the power of
 nunjucks

Signed-off-by: blam <ben@blam.sh
Signed-off-by: blam <ben@blam.sh>
---
 .../tasks/DefaultWorkflowRunner.test.ts       | 72 ++++++++++++++++++-
 .../scaffolder/tasks/DefaultWorkflowRunner.ts | 15 ++++
 2 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.test.ts b/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.test.ts
index dea94e9b52..c249606658 100644
--- a/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.test.ts
+++ b/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.test.ts
@@ -60,6 +60,7 @@ describe('DefaultWorkflowRunner', () => {
       description: 'Mock action for testing',
       handler: async ctx => {
         ctx.output('mock', 'backstage');
+        ctx.output('shouldRun', true);
       },
     });
 
@@ -85,7 +86,76 @@ describe('DefaultWorkflowRunner', () => {
   });
 
   describe('validation', () => {});
-  describe('running', () => {});
+  describe('conditionals', () => {
+    it('should execute steps conditionally', async () => {
+      const task = createMockTaskWithSpec({
+        apiVersion: 'backstage.io/v1beta3',
+        steps: [
+          { id: 'test', name: 'test', action: 'output-action' },
+          {
+            id: 'conditional',
+            name: 'conditional',
+            action: 'output-action',
+            if: '${{ steps.test.output.shouldRun }}',
+          },
+        ],
+        output: {
+          result: '${{ steps.conditional.output.mock }}',
+        },
+        parameters: {},
+      });
+
+      const { output } = await runner.execute(task);
+
+      expect(output.result).toBe('backstage');
+    });
+
+    it('should skips steps conditionally', async () => {
+      const task = createMockTaskWithSpec({
+        apiVersion: 'backstage.io/v1beta3',
+        steps: [
+          { id: 'test', name: 'test', action: 'output-action' },
+          {
+            id: 'conditional',
+            name: 'conditional',
+            action: 'output-action',
+            if: '${{ not steps.test.output.shouldRun}}',
+          },
+        ],
+        output: {
+          result: '${{ steps.conditional.output.mock }}',
+        },
+        parameters: {},
+      });
+
+      const { output } = await runner.execute(task);
+
+      expect(output.result).toBeUndefined();
+    });
+
+    it('should skips steps using the negating equals operator', async () => {
+      const task = createMockTaskWithSpec({
+        apiVersion: 'backstage.io/v1beta3',
+        steps: [
+          { id: 'test', name: 'test', action: 'output-action' },
+          {
+            id: 'conditional',
+            name: 'conditional',
+            action: 'output-action',
+            if: '${{ steps.test.output.mock !== "backstage"}}',
+          },
+        ],
+        output: {
+          result: '${{ steps.conditional.output.mock }}',
+        },
+        parameters: {},
+      });
+
+      const { output } = await runner.execute(task);
+
+      expect(output.result).toBeUndefined();
+    });
+  });
 
   describe('templating', () => {
     it('should template the input to an action', async () => {
diff --git a/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.ts b/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.ts
index c8f77f066a..889048d04a 100644
--- a/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.ts
+++ b/plugins/scaffolder-backend/src/scaffolder/tasks/DefaultWorkflowRunner.ts
@@ -30,6 +30,7 @@ import path from 'path';
 import { JsonObject, JsonValue } from '@backstage/config';
 import { InputError } from '@backstage/errors';
 import { PassThrough } from 'stream';
+import { isTruthy } from './helper';
 
 type Options = {
   workingDirectory: string;
@@ -92,6 +93,9 @@ export class DefaultWorkflowRunner implements WorkflowRunner {
       try {
         if (typeof value === 'string') {
           const templated = this.nunjucks.renderString(value, context);
+          if (templated === '') {
+            return undefined;
+          }
           try {
             return JSON.parse(templated);
           } catch {
@@ -147,6 +151,16 @@ export class DefaultWorkflowRunner implements WorkflowRunner {
 
       for (const step of task.spec.steps) {
         try {
+          if (step.if) {
+            const ifResult = await this.render(step.if, context);
+            if (!isTruthy(ifResult)) {
+              await task.emitLog(
+                `Skipping step ${step.id} because it's if condition was false`,
+              );
+              continue;
+            }
+          }
+
           const action = this.options.actionRegistry.get(step.action);
           const { taskLogger, streamLogger } = createStepLogger({ task, step });
 
@@ -189,6 +203,7 @@ export class DefaultWorkflowRunner implements WorkflowRunner {
             stepId: step.id,
             status: 'failed',
           });
+          throw err;
         }
       }