perf(netlify-legacy): exclude static paths from SSR function

Backporting #2822 to the netlify-legacy preset.

Since it's using "v1" Netlify Functions
(https://docs.netlify.com/functions/lambda-compatibility), it doesn't have access to
`excludedPath` and `preferStatic`, so we implement this with redirects.

src/presets/netlify/legacy/preset.ts

@@ -1,4 +1,4 @@
-import { existsSync, promises as fsp } from "node:fs";
+import { promises as fsp } from "node:fs";
 import { defineNitroPreset } from "nitropack/kit";
 import type { Nitro } from "nitropack/types";
 import { dirname, join } from "pathe";
@@ -24,7 +24,7 @@ const netlify = defineNitroPreset(
       },
       async compiled(nitro: Nitro) {
         await writeHeaders(nitro);
-        await writeRedirects(nitro);
+        await writeRedirects(nitro, "/.netlify/functions/server");
 
         if (nitro.options.netlify) {
           const configPath = join(

src/presets/netlify/legacy/utils.ts

@@ -1,8 +1,27 @@
 import { existsSync, promises as fsp } from "node:fs";
-import type { Nitro } from "nitropack/types";
+import type { Nitro, PublicAssetDir } from "nitropack/types";
 import { join } from "pathe";
+import { joinURL } from "ufo";
 
-export async function writeRedirects(nitro: Nitro) {
+export function generateCatchAllRedirects(
+  publicAssets: PublicAssetDir[],
+  catchAllPath?: string
+): string {
+  if (!catchAllPath) return "";
+
+  return [
+    // e.g.: /_nuxt/* /_nuxt/:splat 200
+    // Because of Netlify CDN shadowing
+    // (https://docs.netlify.com/routing/redirects/rewrites-proxies/#shadowing),
+    // this config avoids function invocations for all static paths, even 404s.
+    ...getStaticPaths(publicAssets).map(
+      (path) => `${path} ${path.replace("/*", "/:splat")} 200`
+    ),
+    `/* ${catchAllPath} 200`,
+  ].join("\n");
+}
+
+export async function writeRedirects(nitro: Nitro, catchAllPath?: string) {
   const redirectsPath = join(nitro.options.output.publicDir, "_redirects");
   const staticFallback = existsSync(
     join(nitro.options.output.publicDir, "404.html")
@@ -11,7 +30,7 @@ export async function writeRedirects(nitro: Nitro) {
     : "";
   let contents = nitro.options.static
     ? staticFallback
-    : "/* /.netlify/functions/server 200";
+    : generateCatchAllRedirects(nitro.options.publicAssets, catchAllPath);
 
   const rules = Object.entries(nitro.options.routeRules).sort(
     (a, b) => a[0].split(/\/(?!\*)/).length - b[0].split(/\/(?!\*)/).length
@@ -103,12 +122,20 @@ export async function writeHeaders(nitro: Nitro) {
   await fsp.writeFile(headersPath, contents);
 }
 
+export function getStaticPaths(publicAssets: PublicAssetDir[]): string[] {
+  return publicAssets
+    .filter(
+      (dir) => dir.fallthrough !== true && dir.baseURL && dir.baseURL !== "/"
+    )
+    .map((dir) => joinURL("/", dir.baseURL!, "*"));
+}
+
 export function deprecateSWR(nitro: Nitro) {
   if (nitro.options.future.nativeSWR) {
     return;
   }
   let hasLegacyOptions = false;
-  for (const [key, value] of Object.entries(nitro.options.routeRules)) {
+  for (const [_key, value] of Object.entries(nitro.options.routeRules)) {
     if (_hasProp(value, "isr")) {
       continue;
     }

test/presets/netlify-legacy.test.ts

@@ -9,6 +9,12 @@ describe("nitro:preset:netlify-legacy", async () => {
   const ctx = await setupTest("netlify-legacy", {
     compatibilityDate: "2024-01-01",
     config: {
+      publicAssets: [
+        {
+          dir: "dist/_nuxt",
+          baseURL: "_nuxt",
+        },
+      ],
       output: {
         publicDir: resolve(getPresetTmpDir("netlify-legacy"), "dist"),
       },
@@ -70,6 +76,8 @@ describe("nitro:preset:netlify-legacy", async () => {
         /rules/isr-ttl/*	/.netlify/builders/server 200
         /rules/isr/*	/.netlify/builders/server 200
         /rules/dynamic	/.netlify/functions/server 200
+        /_nuxt/* /_nuxt/:splat 200
+        /build/* /build/:splat 200
         /* /.netlify/functions/server 200"
       `);
       });

test/unit/netlify-legacy.utils.test.ts

@@ -0,0 +1,61 @@
+import { describe, expect, it } from "vitest";
+import { generateCatchAllRedirects } from "../../src/presets/netlify/legacy/utils";
+
+describe("generateCatchAllRedirects", () => {
+  it("returns empty string if `catchAllPath` is not defined", () => {
+    expect(generateCatchAllRedirects([], undefined)).toEqual("");
+  });
+
+  it("includes a redirect from `/*` to `catchAllPath` if defined", () => {
+    expect(generateCatchAllRedirects([], "/catch-all")).toEqual(
+      "/* /catch-all 200"
+    );
+  });
+
+  it("includes a splat redirect for each non-fallthrough non-root public asset path, BEFORE the catch-all", () => {
+    const publicAssets = [
+      {
+        fallthrough: true,
+        baseURL: "with-fallthrough",
+        dir: "with-fallthrough-dir",
+        maxAge: 0,
+      },
+      {
+        fallthrough: true,
+        dir: "with-fallthrough-no-baseURL-dir",
+        maxAge: 0,
+      },
+      {
+        fallthrough: false,
+        dir: "no-fallthrough-no-baseURL-dir",
+        maxAge: 0,
+      },
+      {
+        fallthrough: false,
+        dir: "no-fallthrough-root-baseURL-dir",
+        baseURL: "/",
+        maxAge: 0,
+      },
+      {
+        baseURL: "with-default-fallthrough",
+        dir: "with-default-fallthrough-dir",
+        maxAge: 0,
+      },
+      {
+        fallthrough: false,
+        baseURL: "nested/no-fallthrough",
+        dir: "nested/no-fallthrough-dir",
+        maxAge: 0,
+      },
+    ];
+    expect(
+      generateCatchAllRedirects(publicAssets, "/catch-all")
+    ).toMatchInlineSnapshot(
+      `
+"/with-default-fallthrough/* /with-default-fallthrough/:splat 200
+/nested/no-fallthrough/* /nested/no-fallthrough/:splat 200
+/* /catch-all 200"
+    `.trim()
+    );
+  });
+});