fix: export Netlify config separately from the serverless function (sveltejs#15335)

This PR ensures the Netlify `config `export can be detected by exporting
it directly from the instrumented file. Previously, it was not exported
at all. I've also tried adding it as an export to `builder.instrument`
but the Netlify dev server could not read the `config` export when it's
dynamically imported and awaited alongside the serverless function.

---

### Please don't delete this checklist! Before submitting the PR, please
make sure you do the following:
- [ ] It's really useful if your PR references an issue where it is
discussed ahead of time. In many cases, features are absent for a
reason. For large changes, please create an RFC:
https://github.com/sveltejs/rfcs
- [x] This message body should clearly illustrate what problems it
solves.
- [x] Ideally, include a test that fails without this PR but passes with
it.

### Tests
- [x] Run the tests with `pnpm test` and lint the project with `pnpm
lint` and `pnpm check`

### Changesets
- [x] If your PR makes a change that should be noted in one or more
packages' changelogs, generate a changeset by running `pnpm changeset`
and following the prompts. Changesets that add features should be
`minor` and those that fix bugs should be `patch`. Please prefix
changeset messages with `feat:`, `fix:`, or `chore:`.

### Edits

- [x] Please ensure that 'Allow edits from maintainers' is checked. PRs
without this option may be closed.

Author: teemingc

.changeset/four-cougars-own.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-netlify': patch
+---
+
+fix: export Netlify config directly from the instrumented serverless function

packages/adapter-netlify/index.js

@@ -191,16 +191,16 @@ async function generate_edge_functions({ builder }) {
 			outfile: '.netlify/edge-functions/render.js',
 			...esbuild_config
 		}),
-		builder.hasServerInstrumentationFile?.() &&
+		builder.hasServerInstrumentationFile() &&
 			esbuild.build({
 				entryPoints: [`${builder.getServerDirectory()}/instrumentation.server.js`],
 				outfile: '.netlify/edge/instrumentation.server.js',
 				...esbuild_config
 			})
 	]);
 
-	if (builder.hasServerInstrumentationFile?.()) {
-		builder.instrument?.({
+	if (builder.hasServerInstrumentationFile()) {
+		builder.instrument({
 			entrypoint: '.netlify/edge-functions/render.js',
 			instrumentation: '.netlify/edge/instrumentation.server.js',
 			start: '.netlify/edge/start.js'
@@ -274,37 +274,43 @@ function generate_lambda_functions({ builder, publish, split }) {
 				routes
 			});
 
-			const fn = `import { init } from '../serverless.js';\n\nexport default init(${manifest});\n\nexport const config = {\n\tpath: "${pattern}",\n\texcludedPath: "/.netlify/*",\n\tpreferStatic: true\n};\n`;
+			const fn = generate_serverless_function_module(manifest);
+			const config = generate_config_export(pattern);
 
-			writeFileSync(`.netlify/functions-internal/${name}.mjs`, fn);
-			if (builder.hasServerInstrumentationFile?.()) {
-				builder.instrument?.({
+			if (builder.hasServerInstrumentationFile()) {
+				writeFileSync(`.netlify/functions-internal/${name}.mjs`, fn);
+				builder.instrument({
 					entrypoint: `.netlify/functions-internal/${name}.mjs`,
 					instrumentation: '.netlify/server/instrumentation.server.js',
 					start: `.netlify/functions-start/${name}.start.mjs`,
 					module: {
-						exports: ['default']
+						generateText: generate_traced_module(config)
 					}
 				});
+			} else {
+				writeFileSync(`.netlify/functions-internal/${name}.mjs`, `${fn}\n${config}`);
 			}
 		}
 	} else {
 		const manifest = builder.generateManifest({
 			relativePath: '../server'
 		});
 
-		const fn = `import { init } from '../serverless.js';\n\nexport default init(${manifest});\n\nexport const config = {\n\tpath: "/*",\n\texcludedPath: "/.netlify/*",\n\tpreferStatic: true\n};\n`;
+		const fn = generate_serverless_function_module(manifest);
+		const config = generate_config_export('/*');
 
-		writeFileSync(`.netlify/functions-internal/${FUNCTION_PREFIX}render.mjs`, fn);
-		if (builder.hasServerInstrumentationFile?.()) {
-			builder.instrument?.({
+		if (builder.hasServerInstrumentationFile()) {
+			writeFileSync(`.netlify/functions-internal/${FUNCTION_PREFIX}render.mjs`, fn);
+			builder.instrument({
 				entrypoint: `.netlify/functions-internal/${FUNCTION_PREFIX}render.mjs`,
 				instrumentation: '.netlify/server/instrumentation.server.js',
 				start: `.netlify/functions-start/${FUNCTION_PREFIX}render.start.mjs`,
 				module: {
-					exports: ['default']
+					generateText: generate_traced_module(config)
 				}
 			});
+		} else {
+			writeFileSync(`.netlify/functions-internal/${FUNCTION_PREFIX}render.mjs`, `${fn}\n${config}`);
 		}
 	}
 
@@ -386,3 +392,44 @@ function matches(a, b) {
 		return b.length === 1 && b[0].rest;
 	}
 }
+
+/**
+ * @param {string} manifest
+ * @returns {string}
+ */
+function generate_serverless_function_module(manifest) {
+	return `\
+import { init } from '../serverless.js';
+
+export default init(${manifest});
+`;
+}
+
+/**
+ * @param {string} pattern
+ * @returns {string}
+ */
+function generate_config_export(pattern) {
+	return `\
+export const config = {
+	path: "${pattern}",
+	excludedPath: "/.netlify/*",
+	preferStatic: true
+};
+`;
+}
+
+/**
+ * @param {string} config
+ * @returns {(opts: { instrumentation: string; start: string }) => string}
+ */
+function generate_traced_module(config) {
+	return ({ instrumentation, start }) => {
+		return `\
+import './${instrumentation}';
+const { default: _0 } = await import('./${start}');
+export { _0 as default };
+
+${config}`;
+	};
+}

packages/adapter-netlify/test/apps/basic/netlify.toml

@@ -1,2 +1,9 @@
 [build]
 publish = "build"
+
+# TODO: remove this after we refactor to the Netlify frameworks API
+# we are purposely misusing the user functions config to discover our framework
+# build output because our adapter still outputs using an older API but the new
+# Netlify dev server adheres to the new API
+[functions]
+directory = ".netlify/functions-internal"