Support integrations added in updateConfig() in astro:config:setup (#8672)

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

3 files changed, 95 insertions, 2 deletions

diff --git a/.changeset/cold-schools-yell.md b/.changeset/cold-schools-yell.md
new file mode 100644
index 000000000..7d6b4f381
--- /dev/null
+++ b/.changeset/cold-schools-yell.md
@@ -0,0 +1,34 @@
+---
+'astro': minor
+---
+
+Support adding integrations dynamically
+
+Astro integrations can now themselves dynamically add and configure additional integrations during set-up. This makes it possible for integration authors to bundle integrations more intelligently for their users.
+
+In the following example, a custom integration checks whether `@astrojs/sitemap` is already configured. If not, the integration adds Astro’s sitemap integration, passing any desired configuration options:
+
+```ts
+import sitemap from '@astrojs/sitemap';
+import type { AstroIntegration } from 'astro';
+
+const MyIntegration = (): AstroIntegration => {
+  return {
+    name: 'my-integration',
+
+    'astro:config:setup': ({ config, updateConfig }) => {
+      // Look for sitemap in user-configured integrations.
+      const userSitemap = config.integrations.find(
+        ({ name }) => name === '@astrojs/sitemap'
+      );
+
+      if (!userSitemap) {
+        // If sitemap wasn’t found, add it.
+        updateConfig({
+          integrations: [sitemap({ /* opts */ }],
+        });
+      }
+    },
+  };
+};
+```
diff --git a/packages/astro/src/integrations/index.ts b/packages/astro/src/integrations/index.ts
index c5c92a4e4..8d557cae7 100644
--- a/packages/astro/src/integrations/index.ts
+++ b/packages/astro/src/integrations/index.ts
@@ -75,7 +75,10 @@ export async function runHookConfigSetup({
 	let addedClientDirectives = new Map<string, Promise<string>>();
 	let astroJSXRenderer: AstroRenderer | null = null;
 
-	for (const integration of settings.config.integrations) {
+	// eslint-disable-next-line @typescript-eslint/prefer-for-of -- We need a for loop to be able to read integrations pushed while the loop is running.
+	for (let i = 0; i < updatedConfig.integrations.length; i++) {
+		const integration = updatedConfig.integrations[i];
+		
 		/**
 		 * By making integration hooks optional, Astro can now ignore null or undefined Integrations
 		 * instead of giving an internal error most people can't read
diff --git a/packages/astro/test/units/integrations/api.test.js b/packages/astro/test/units/integrations/api.test.js
index 0a7d57929..0940a78f7 100644
--- a/packages/astro/test/units/integrations/api.test.js
+++ b/packages/astro/test/units/integrations/api.test.js
@@ -1,5 +1,5 @@
 import { expect } from 'chai';
-import { runHookBuildSetup } from '../../../dist/integrations/index.js';
+import { runHookBuildSetup, runHookConfigSetup } from '../../../dist/integrations/index.js';
 import { validateSupportedFeatures } from '../../../dist/integrations/astroFeaturesValidation.js';
 import { defaultLogger } from '../test-utils.js';
 
@@ -29,6 +29,62 @@ describe('Integration API', () => {
 		});
 		expect(updatedViteConfig).to.haveOwnProperty('define');
 	});
+
+	it('runHookConfigSetup can update Astro config', async () => {
+		const site = 'https://test.com/';
+		const updatedSettings = await runHookConfigSetup({
+			logger: defaultLogger,
+			settings: {
+				config: {
+					integrations: [
+						{
+							name: 'test',
+							hooks: {
+								"astro:config:setup": ({ updateConfig }) => {
+									updateConfig({ site });
+								}
+							},
+						},
+					],
+				},
+			},
+		});
+		expect(updatedSettings.config.site).to.equal(site);
+	});
+	
+	it('runHookConfigSetup runs integrations added by another integration', async () => {
+		const site = 'https://test.com/';
+		const updatedSettings = await runHookConfigSetup({
+			logger: defaultLogger,
+			settings: {
+				config: {
+					integrations: [
+						{
+							name: 'test',
+							hooks: {
+								"astro:config:setup": ({ updateConfig }) => {
+									updateConfig({
+										integrations: [{
+											name: 'dynamically-added',
+											hooks: {
+												// eslint-disable-next-line @typescript-eslint/no-shadow
+												"astro:config:setup": ({ updateConfig }) => {
+													updateConfig({ site });
+												}
+											},
+										}],
+									});
+								}
+							},
+						},
+					],
+				},
+			},
+		});
+		expect(updatedSettings.config.site).to.equal(site);
+		expect(updatedSettings.config.integrations.length).to.equal(2);
+	});
+
 });
 
 describe('Astro feature map', function () {