Create an InternalExpression type which allows precanned access to env.FIREBASE_CONFIG

spec/fixtures/sources/commonjs-params/index.js

@@ -21,18 +21,20 @@ params.defineInt("ANOTHER_INT", {
 
 params.defineSecret("SUPER_SECRET_FLAG");
 
+// N.B: invocation of the precanned internal params should not affect the manifest
+
 exports.v1http = functions.https.onRequest((req, resp) => {
-  resp.status(200).send("PASS");
+  resp.status(200).send(params.projectID);
 });
 
 exports.v1callable = functions.https.onCall(() => {
-  return "PASS";
+  return params.databaseURL;
 });
 
 exports.v2http = functionsv2.https.onRequest((req, resp) => {
-  resp.status(200).send("PASS");
+  resp.status(200).send(params.gcloudProject);
 });
 
 exports.v2callable = functionsv2.https.onCall(() => {
-  return "PASS";
+  return params.databaseURL;
 });

src/params/index.ts

@@ -35,6 +35,7 @@ import {
   StringParam,
   SecretParam,
   Expression,
+  InternalExpression,
 } from "./types";
 
 export { ParamOptions, Expression };
@@ -64,6 +65,39 @@ export function clearParams() {
   declaredParams.splice(0, declaredParams.length);
 }
 
+/**
+ * A builtin param that resolves to the default RTDB database URL associated
+ * with the project, without prompting the deployer. Empty string if none exists.
+ */
+export const databaseURL = new InternalExpression(
+  "DATABASE_URL",
+  (env: NodeJS.ProcessEnv) => JSON.parse(env.FIREBASE_CONFIG)?.databaseURL
+);
+/**
+ * A builtin param that resolves to the Cloud project ID associated with
+ * the project, without prompting the deployer.
+ */
+export const projectID = new InternalExpression(
+  "PROJECT_ID",
+  (env: NodeJS.ProcessEnv) => JSON.parse(env.FIREBASE_CONFIG)?.projectId
+);
+/**
+ * A builtin param that resolves to the Cloud project ID, without prompting
+ * the deployer.
+ */
+export const gcloudProject = new InternalExpression(
+  "GCLOUD_PROJECT",
+  (env: NodeJS.ProcessEnv) => JSON.parse(env.FIREBASE_CONFIG)?.projectId
+);
+/**
+ * A builtin param that resolves to the Cloud storage bucket associated
+ * with the function, without prompting the deployer.
+ */
+export const storageBucket = new InternalExpression(
+  "STORAGE_BUCKET",
+  (env: NodeJS.ProcessEnv) => JSON.parse(env.FIREBASE_CONFIG)?.storageBucket
+);
+
 /**
  * Declares a secret param, that will persist values only in Cloud Secret Manager.
  * Secrets are stored interally as bytestrings. Use ParamOptions.`as` to provide type

src/params/types.ts

@@ -41,6 +41,33 @@ export abstract class Expression<T extends string | number | boolean | string[]>
   }
 }
 
+/**
+ * A CEL expression which represents an internal Firebase variable. This class
+ * cannot be instantiated by developers, but we provide several canned instances
+ * of it to make available params that will never have to be defined at
+ * deployment time, and can always be read from process.env.
+ */
+export class InternalExpression extends Expression<string> {
+  constructor(
+    private readonly name: string,
+    private readonly getter: (env: NodeJS.ProcessEnv) => string
+  ) {
+    super();
+  }
+
+  value(): string {
+    return this.getter(process.env) || "";
+  }
+
+  toString(): string {
+    return `params.${this.name}`;
+  }
+
+  toCEL(): string {
+    throw new Error("An InternalExpression should never be marshalled for wire transmission.");
+  }
+}
+
 function quoteIfString<T extends string | number | boolean | string[]>(literal: T): T {
   // TODO(vsfan@): CEL's string escape semantics are slightly different than Javascript's, what do we do here?
   return typeof literal === "string" ? (`"${literal}"` as T) : literal;