Scaffolder: Provide 'each' context when evaluating 'if' (#32546)

* Scaffolder: Evaluate 'if' conditions inside the context of 'each', if it exists

Signed-off-by: Jacob Raihle kdm951 <jacob.raihle@teliacompany.com>

* chore: small little cleanup
Signed-off-by: benjdlambert <ben@blam.sh>

* Reuse pre-iteration context instead of creating it twice

Signed-off-by: Jacob Raihle kdm951 <jacob.raihle@teliacompany.com>

---------

Signed-off-by: Jacob Raihle kdm951 <jacob.raihle@teliacompany.com>
Co-authored-by: benjdlambert <ben@blam.sh>

.changeset/lemon-things-cheat.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-scaffolder-backend': patch
+---
+
+Support `if` conditions inside `each` loops for scaffolder steps

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

@@ -1066,6 +1066,50 @@ describe('NunjucksWorkflowRunner', () => {
       }
     });
 
+    it('should run a step repeatedly - only iterations where the "if" condition is truthy', async () => {
+      const truthyConditions = [true, 1, 'a', {}];
+      const falsyConditions = [false, 0, null, ''];
+      const conditions = [...truthyConditions, ...falsyConditions];
+      const task = createMockTaskWithSpec({
+        steps: [
+          {
+            id: 'test',
+            name: 'name',
+            each: '${{parameters.conditions}}',
+            action: 'jest-mock-action',
+            input: { condition: '${{each.value}}' },
+            if: '${{each.value}}',
+          },
+        ],
+        parameters: {
+          conditions,
+        },
+      });
+      await runner.execute(task);
+
+      truthyConditions.forEach((condition, idx) => {
+        expectTaskLog(
+          `info: Running step each: {"key":"${idx}","value":"${condition}"}`,
+        );
+        expect(fakeActionHandler).toHaveBeenCalledWith(
+          expect.objectContaining({ input: { condition } }),
+        );
+      });
+
+      falsyConditions.forEach((condition, idx) => {
+        expectTaskLog(
+          `info: Skipping step each: {"key":"${
+            idx + truthyConditions.length
+          }","value":"${condition}"}`,
+        );
+        expect(fakeActionHandler).not.toHaveBeenCalledWith(
+          expect.objectContaining({ input: { condition } }),
+        );
+      });
+
+      expect(fakeActionHandler).toHaveBeenCalledTimes(truthyConditions.length);
+    });
+
     it('should run a step repeatedly with validation of single-expression value', async () => {
       const numbers = [5, 7, 9];
       const task = createMockTaskWithSpec({

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

@@ -270,6 +270,7 @@ export class NunjucksWorkflowRunner implements WorkflowRunner {
       if (
         step.if === false ||
         (typeof step.if === 'string' &&
+          step.each === undefined &&
           !isTruthy(this.render(step.if, context, renderTemplate)))
       ) {
         await stepTrack.skipFalsy();
@@ -340,20 +341,18 @@ export class NunjucksWorkflowRunner implements WorkflowRunner {
         }
       }
 
+      const preIterationContext = {
+        ...context,
+        environment: {
+          parameters: this.environment?.parameters ?? {},
+          secrets: this.environment?.secrets ?? {},
+        },
+        secrets: task.secrets ?? {},
+      };
+
       const resolvedEach =
         step.each &&
-        this.render(
-          step.each,
-          {
-            ...context,
-            environment: {
-              parameters: this.environment?.parameters || {},
-              secrets: this.environment?.secrets ?? {},
-            },
-            secrets: task?.secrets ?? {},
-          },
-          renderTemplate,
-        );
+        this.render(step.each, preIterationContext, renderTemplate);
 
       if (step.each && !resolvedEach) {
         throw new InputError(
@@ -367,26 +366,29 @@ export class NunjucksWorkflowRunner implements WorkflowRunner {
               each: { key, value },
             }))
           : [{}]
-      ).map(i => ({
-        ...i,
-        // Secrets are only passed when templating the input to actions for security reasons
-        input: step.input
-          ? this.render(
-              step.input,
-              {
-                ...context,
-                environment: {
-                  parameters: this.environment?.parameters ?? {},
-                  secrets: this.environment?.secrets ?? {},
-                },
-                secrets: task.secrets ?? {},
-                ...i,
-              },
-              renderTemplate,
-            )
-          : {},
-      }));
+      ).map(i => {
+        const fullContext = { ...preIterationContext, ...i };
+        // Evaluate if condition once per iteration, only when using 'each'
+        const shouldRun =
+          !('each' in i) ||
+          !step.if ||
+          isTruthy(this.render(step.if, fullContext, renderTemplate));
+
+        return {
+          ...i,
+          shouldRun,
+          // Secrets are only passed when templating the input to actions for security reasons
+          input: step.input
+            ? this.render(step.input, fullContext, renderTemplate)
+            : {},
+        };
+      });
       for (const iteration of iterations) {
+        if (!iteration.shouldRun) {
+          // No need to check schema or authorization for iterations that will not run
+          continue;
+        }
+
         const actionId = `${action.id}${
           iteration.each ? `[${iteration.each.key}]` : ''
         }`;
@@ -424,10 +426,20 @@ export class NunjucksWorkflowRunner implements WorkflowRunner {
 
       for (const iteration of iterations) {
         if (iteration.each) {
+          if (!iteration.shouldRun) {
+            taskLogger.info(
+              `Skipping step each: ${JSON.stringify(
+                iteration.each,
+                (k, v) => (k ? String(v) : v),
+                0,
+              )}`,
+            );
+            continue;
+          }
           taskLogger.info(
             `Running step each: ${JSON.stringify(
               iteration.each,
-              (k, v) => (k ? v.toString() : v),
+              (k, v) => (k ? String(v) : v),
               0,
             )}`,
           );