feat: accept Expression for v2 RTDB instance option

spec/v2/providers/database.spec.ts

@@ -26,6 +26,7 @@ import * as database from "../../../src/v2/providers/database";
 import { expectType } from "../../common/metaprogramming";
 import { MINIMAL_V2_ENDPOINT } from "../../fixtures";
 import { CloudEvent, onInit } from "../../../src/v2/core";
+import * as params from "../../../src/params";
 
 const RAW_RTDB_EVENT: database.RawRTDBCloudEvent = {
   data: {
@@ -46,6 +47,9 @@ const RAW_RTDB_EVENT: database.RawRTDBCloudEvent = {
   authtype: "unauthenticated",
 };
 
+const TEST_RTDB_INSTANCE_ENV_VAR = "TEST_RTDB_INSTANCE_FOR_GETOPTS";
+const RESOLVED_RTDB_INSTANCE = "resolved-instance";
+
 describe("database", () => {
   describe("makeParams", () => {
     it("should make params with basic path", () => {
@@ -146,6 +150,21 @@ describe("database", () => {
         },
       });
     });
+
+    it("should resolve instance Expression to runtime string", () => {
+      const prev = process.env[TEST_RTDB_INSTANCE_ENV_VAR];
+      process.env[TEST_RTDB_INSTANCE_ENV_VAR] = RESOLVED_RTDB_INSTANCE;
+      try {
+        const p = params.defineString(TEST_RTDB_INSTANCE_ENV_VAR);
+        expect(database.getOpts({ ref: "/foo", instance: p })).to.deep.include({
+          path: "foo",
+          instance: RESOLVED_RTDB_INSTANCE,
+        });
+      } finally {
+        if (prev === undefined) delete process.env[TEST_RTDB_INSTANCE_ENV_VAR];
+        else process.env[TEST_RTDB_INSTANCE_ENV_VAR] = prev;
+      }
+    });
   });
 
   describe("makeEndpoint", () => {

src/v2/providers/database.ts

@@ -117,7 +117,7 @@ export interface ReferenceOptions<Ref extends string = string> extends options.E
    * Examples: 'my-instance-1', 'my-instance-*'
    * Note: The capture syntax cannot be used for 'instance'.
    */
-  instance?: string;
+  instance?: string | Expression<string>;
 
   /**
    * If true, do not deploy or emulate this function.
@@ -488,7 +488,10 @@ export function getOpts(referenceOrOpts: string | ReferenceOptions) {
     opts = {};
   } else {
     path = normalizePath(referenceOrOpts.ref);
-    instance = referenceOrOpts.instance || "*";
+    instance =
+      referenceOrOpts.instance instanceof Expression
+        ? referenceOrOpts.instance.value()
+        : referenceOrOpts.instance || "*";
     opts = { ...referenceOrOpts };
     delete (opts as any).ref;
     delete (opts as any).instance;