fix: preserve ./netlify/functions-internal (#8899)

Closes #8903

.changeset/famous-llamas-play.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-netlify': patch
+---
+
+fix: preserve functions-internal folder so that auto-generated functions are not removed when ntl build is run

packages/adapter-netlify/index.js

@@ -1,8 +1,16 @@
-import { appendFileSync, existsSync, readFileSync, writeFileSync } from 'fs';
+import {
+	appendFileSync,
+	existsSync,
+	readFileSync,
+	writeFileSync,
+	unlinkSync,
+	createReadStream
+} from 'fs';
 import { dirname, join, resolve, posix } from 'path';
 import { fileURLToPath } from 'url';
 import esbuild from 'esbuild';
 import toml from '@iarna/toml';
+import { createInterface } from 'readline';
 
 /**
  * @typedef {{
@@ -51,10 +59,43 @@ export default function ({ split = false, edge = edge_set_in_env_var } = {}) {
 			// "build" is the default publish directory when Netlify detects SvelteKit
 			const publish = get_publish_directory(netlify_config, builder) || 'build';
 
+			const redirects_file_path = join(publish, '_redirects');
+
+			// If redirects file exists - empty any netlify generated files in functions-internal
+			// Without removing other files that may have been auto generated by integrations
+			if (existsSync(redirects_file_path)) {
+				// Read each line of the file
+				const fileStream = createReadStream(redirects_file_path);
+				const rl = createInterface({
+					input: fileStream,
+					crlfDelay: Infinity
+				});
+
+				// Create an array of lines
+				const lines = [];
+				for await (const line of rl) {
+					lines.push(line);
+				}
+
+				const functions_internal = join('.netlify', 'functions-internal');
+
+				// Loop through redirects, and delete corresponding functions-internal files
+				lines.forEach((line) => {
+					if (line) {
+						// example line /.netlify/functions/{function_name} 200
+						const path = line.split(' ')[1];
+						const function_name = path.split('/').pop();
+						const mjsFile = join(functions_internal, `${function_name}.mjs`);
+						const jsonFile = join(functions_internal, `${function_name}.json`);
+						if (existsSync(mjsFile)) unlinkSync(mjsFile);
+						if (existsSync(jsonFile)) unlinkSync(jsonFile);
+					}
+				});
+			}
+
 			// empty out existing build directories
 			builder.rimraf(publish);
 			builder.rimraf('.netlify/edge-functions');
-			builder.rimraf('.netlify/functions-internal');
 			builder.rimraf('.netlify/server');
 			builder.rimraf('.netlify/package.json');
 			builder.rimraf('.netlify/serverless.js');