Create overridable constants file

packages/telemetry/package.json

@@ -112,6 +112,7 @@
     "@firebase/app": "0.14.6",
     "@opentelemetry/sdk-trace-web": "2.1.0",
     "@rollup/plugin-json": "6.1.0",
+    "@rollup/plugin-replace": "6.0.2",
     "@testing-library/dom": "10.4.1",
     "@testing-library/react": "16.3.0",
     "@types/react": "19.1.13",

packages/telemetry/rollup.config.js

@@ -17,14 +17,25 @@
 
 import json from '@rollup/plugin-json';
 import copy from 'rollup-plugin-copy';
+import replacePlugin from '@rollup/plugin-replace';
 import typescriptPlugin from 'rollup-plugin-typescript2';
 import typescript from 'typescript';
 import pkg from './package.json';
 import { emitModulePackageFile } from '../../scripts/build/rollup_emit_module_package_file';
 
-const deps = Object.keys(
-  Object.assign({}, pkg.peerDependencies, pkg.dependencies)
-);
+const deps = [
+  ...Object.keys(Object.assign({}, pkg.peerDependencies, pkg.dependencies)),
+  './auto-constants'
+];
+
+function replaceSource(path) {
+  return replacePlugin({
+    './src/auto-constants': `'${path}'`,
+    '../auto-constants': `'${path}'`,
+    delimiters: ["'", "'"],
+    preventAssignment: true
+  });
+}
 
 const buildPlugins = [typescriptPlugin({ typescript }), json()];
 
@@ -36,7 +47,7 @@ const browserBuilds = [
       format: 'es',
       sourcemap: true
     },
-    plugins: buildPlugins,
+    plugins: [...buildPlugins, replaceSource('./auto-constants.mjs')],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   },
   {
@@ -46,7 +57,7 @@ const browserBuilds = [
       format: 'cjs',
       sourcemap: true
     },
-    plugins: buildPlugins,
+    plugins: [...buildPlugins, replaceSource('./auto-constants.js')],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   }
 ];
@@ -59,7 +70,7 @@ const nodeBuilds = [
       format: 'cjs',
       sourcemap: true
     },
-    plugins: buildPlugins,
+    plugins: [...buildPlugins, replaceSource('./auto-constants.js')],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   },
   {
@@ -69,7 +80,11 @@ const nodeBuilds = [
       format: 'es',
       sourcemap: true
     },
-    plugins: [...buildPlugins, emitModulePackageFile()],
+    plugins: [
+      ...buildPlugins,
+      emitModulePackageFile(),
+      replaceSource('../auto-constants.mjs')
+    ],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   }
 ];
@@ -100,7 +115,8 @@ const reactBuilds = [
             dest: 'dist'
           }
         ]
-      })
+      }),
+      replaceSource('../auto-constants.mjs')
     ],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   },
@@ -117,7 +133,8 @@ const reactBuilds = [
         typescript,
         tsconfig: 'tsconfig.react.json'
       }),
-      json()
+      json(),
+      replaceSource('../auto-constants.js')
     ],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   }
@@ -148,7 +165,8 @@ const angularBuilds = [
             dest: 'dist'
           }
         ]
-      })
+      }),
+      replaceSource('../auto-constants.mjs')
     ],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   },
@@ -164,15 +182,36 @@ const angularBuilds = [
         typescript,
         tsconfig: 'tsconfig.angular.json'
       }),
-      json()
+      json(),
+      replaceSource('../auto-constants.js')
     ],
     external: id => deps.some(dep => id === dep || id.startsWith(`${dep}/`))
   }
 ];
 
+const autoinitBuild = [
+  {
+    input: './src/auto-constants.ts',
+    output: {
+      file: './dist/auto-constants.js',
+      format: 'cjs'
+    },
+    plugins: buildPlugins
+  },
+  {
+    input: './src/auto-constants.ts',
+    output: {
+      file: './dist/auto-constants.mjs',
+      format: 'es'
+    },
+    plugins: buildPlugins
+  }
+];
+
 export default [
   ...browserBuilds,
   ...nodeBuilds,
   ...reactBuilds,
-  ...angularBuilds
+  ...angularBuilds,
+  ...autoinitBuild
 ];

packages/telemetry/src/api.test.ts

@@ -42,6 +42,7 @@ import {
 import { TelemetryService } from './service';
 import { registerTelemetry } from './register';
 import { _FirebaseInstallationsInternal } from '@firebase/installations';
+import { AUTO_CONSTANTS } from './auto-constants';
 
 const PROJECT_ID = 'my-project';
 const APP_ID = 'my-appid';
@@ -278,6 +279,7 @@ describe('Top level API', () => {
     });
 
     it('should use explicit app version when provided', () => {
+      AUTO_CONSTANTS.appVersion = '1.2.3'; // Unused
       const telemetry = new TelemetryService(
         fakeTelemetry.app,
         fakeTelemetry.loggerProvider
@@ -296,6 +298,19 @@ describe('Top level API', () => {
       });
     });
 
+    it('should use auto constants if available', () => {
+      AUTO_CONSTANTS.appVersion = '1.2.3';
+
+      captureError(fakeTelemetry, 'a string error');
+
+      expect(emittedLogs.length).to.equal(1);
+      const log = emittedLogs[0];
+      expect(log.attributes).to.deep.equal({
+        [LOG_ENTRY_ATTRIBUTE_KEYS.APP_VERSION]: '1.2.3',
+        [LOG_ENTRY_ATTRIBUTE_KEYS.SESSION_ID]: MOCK_SESSION_ID
+      });
+    });
+
     describe('Session Metadata', () => {
       it('should generate and store a new session ID if none exists', () => {
         captureError(fakeTelemetry, 'error');

packages/telemetry/src/api.ts

@@ -16,16 +16,13 @@
  */
 
 import { _getProvider, FirebaseApp, getApp } from '@firebase/app';
-import {
-  LOG_ENTRY_ATTRIBUTE_KEYS,
-  TELEMETRY_SESSION_ID_KEY,
-  TELEMETRY_TYPE
-} from './constants';
+import { LOG_ENTRY_ATTRIBUTE_KEYS, TELEMETRY_TYPE } from './constants';
 import { Telemetry, TelemetryOptions } from './public-types';
 import { Provider } from '@firebase/component';
 import { AnyValueMap, SeverityNumber } from '@opentelemetry/api-logs';
 import { trace } from '@opentelemetry/api';
 import { TelemetryService } from './service';
+import { getAppVersion, getSessionId } from './helpers';
 
 declare module '@firebase/component' {
   interface NameServiceMapping {
@@ -97,28 +94,12 @@ export function captureError(
   }
 
   // Add app version metadata
-  let appVersion = 'unset';
-  // TODO: implement app version fallback logic
-  if ((telemetry as TelemetryService).options?.appVersion) {
-    appVersion = (telemetry as TelemetryService).options!.appVersion!;
-  }
-  customAttributes[LOG_ENTRY_ATTRIBUTE_KEYS.APP_VERSION] = appVersion;
+  customAttributes['app.version'] = getAppVersion(telemetry);
 
   // Add session ID metadata
-  if (
-    typeof sessionStorage !== 'undefined' &&
-    typeof crypto?.randomUUID === 'function'
-  ) {
-    try {
-      let sessionId = sessionStorage.getItem(TELEMETRY_SESSION_ID_KEY);
-      if (!sessionId) {
-        sessionId = crypto.randomUUID();
-        sessionStorage.setItem(TELEMETRY_SESSION_ID_KEY, sessionId);
-      }
-      customAttributes[LOG_ENTRY_ATTRIBUTE_KEYS.SESSION_ID] = sessionId;
-    } catch (e) {
-      // Ignore errors accessing sessionStorage (e.g. security restrictions)
-    }
+  const sessionId = getSessionId();
+  if (sessionId) {
+    customAttributes[LOG_ENTRY_ATTRIBUTE_KEYS.SESSION_ID] = sessionId;
   }
 
   if (error instanceof Error) {

packages/telemetry/src/auto-constants.ts

@@ -0,0 +1,24 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * A map of constants intended to be optionally overwritten during the application build process.
+ * The supported keys are:
+ * - appVersion: string indicating the version of source code being deployed (eg. git commit hash)
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export const AUTO_CONSTANTS: any = {};

packages/telemetry/src/helpers.ts

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as constants from './auto-constants';
+import { TELEMETRY_SESSION_ID_KEY } from './constants';
+import { Telemetry } from './public-types';
+import { TelemetryService } from './service';
+
+export function getAppVersion(telemetry: Telemetry): string {
+  if ((telemetry as TelemetryService).options?.appVersion) {
+    return (telemetry as TelemetryService).options!.appVersion!;
+  } else if (constants.AUTO_CONSTANTS?.appVersion) {
+    return constants.AUTO_CONSTANTS.appVersion;
+  }
+  return 'unset';
+}
+
+export function getSessionId(): string | undefined {
+  if (
+    typeof sessionStorage !== 'undefined' &&
+    typeof crypto?.randomUUID === 'function'
+  ) {
+    try {
+      let sessionId = sessionStorage.getItem(TELEMETRY_SESSION_ID_KEY);
+      if (!sessionId) {
+        sessionId = crypto.randomUUID();
+        sessionStorage.setItem(TELEMETRY_SESSION_ID_KEY, sessionId);
+      }
+      return sessionId;
+    } catch (e) {
+      // Ignore errors accessing sessionStorage (e.g. security restrictions)
+    }
+  }
+}