Pass trailingSlash from Next.js config to firebase.json (#5445)

* Don't use internal redirects for the backend test
* pass trailingSlash from next config to firebase.json

Co-authored-by: James Daniels <jamesdaniels@google.com>

CHANGELOG.md

@@ -1,3 +1,5 @@
 - Refactors Functions Emulator. (#5422)
 - Fixes race condition when discovering functions. (#5444)
 - Fixes issue where `init firestore` was unecessarilly checking for default resource location. (#5230 and #5452)
+- Pass `trailingSlash` from Next.js config to `firebase.json` (#5445)
+- Don't use Next.js internal redirects for the backend test (#5445)

src/frameworks/index.ts

@@ -41,6 +41,7 @@ export interface BuildResult {
   redirects?: any[];
   headers?: any[];
   wantsBackend?: boolean;
+  trailingSlash?: boolean;
 }
 
 export interface Framework {
@@ -405,10 +406,12 @@ export async function prepareFrameworks(
         rewrites = [],
         redirects = [],
         headers = [],
+        trailingSlash,
       } = (await build(getProjectPath())) || {};
       config.rewrites.push(...rewrites);
       config.redirects.push(...redirects);
       config.headers.push(...headers);
+      config.trailingSlash ??= trailingSlash;
       if (await pathExists(hostingDist)) await rm(hostingDist, { recursive: true });
       await mkdirp(hostingDist);
       await ɵcodegenPublicDirectory(getProjectPath(), hostingDist);

src/frameworks/next/index.ts

@@ -95,7 +95,7 @@ export async function build(dir: string): Promise<BuildResult> {
   });
 
   const reasonsForBackend = [];
-  const { distDir } = await getConfig(dir);
+  const { distDir, trailingSlash } = await getConfig(dir);
 
   if (await isUsingMiddleware(join(dir, distDir), false)) {
     reasonsForBackend.push("middleware");
@@ -171,7 +171,9 @@ export async function build(dir: string): Promise<BuildResult> {
     headers,
   }));
 
-  const isEveryRedirectSupported = nextJsRedirects.every(isRedirectSupportedByHosting);
+  const isEveryRedirectSupported = nextJsRedirects
+    .filter((it) => !it.internal)
+    .every(isRedirectSupportedByHosting);
   if (!isEveryRedirectSupported) {
     reasonsForBackend.push("advanced redirects");
   }
@@ -227,7 +229,7 @@ export async function build(dir: string): Promise<BuildResult> {
     console.log("");
   }
 
-  return { wantsBackend, headers, redirects, rewrites };
+  return { wantsBackend, headers, redirects, rewrites, trailingSlash };
 }
 
 /**
@@ -442,5 +444,10 @@ async function getConfig(dir: string): Promise<NextConfig & { distDir: string }>
       }
     }
   }
-  return { distDir: ".next", ...config };
+  return {
+    distDir: ".next",
+    // trailingSlash defaults to false in Next.js: https://nextjs.org/docs/api-reference/next.config.js/trailing-slash
+    trailingSlash: false,
+    ...config,
+  };
 }