feat(core)!: extract Flutter free types into firebase_core_common

packages/firebase_core/firebase_core/lib/firebase_core.dart

@@ -4,12 +4,16 @@
 // found in the LICENSE file.
 
 import 'package:firebase_core_platform_interface/firebase_core_platform_interface.dart'
-    hide MethodChannelFirebaseApp, MethodChannelFirebase;
+    hide MethodChannelFirebaseApp;
 import 'package:flutter/foundation.dart';
 
 export 'package:firebase_core_platform_interface/firebase_core_platform_interface.dart'
-    show FirebaseOptions, defaultFirebaseAppName, FirebaseException;
+    show
+        FirebaseApp,
+        FirebaseException,
+        FirebaseOptions,
+        FirebaseService,
+        defaultFirebaseAppName;
 
 part 'src/firebase.dart';
-part 'src/firebase_app.dart';
 part 'src/port_mapping.dart';

packages/firebase_core/firebase_core/lib/src/firebase.dart

@@ -20,12 +20,26 @@ class Firebase {
   static FirebasePlatform? delegatePackingProperty;
 
   static FirebasePlatform get _delegate {
-    return delegatePackingProperty ??= FirebasePlatform.instance;
+    final delegate = delegatePackingProperty;
+    if (delegate != null) {
+      return delegate;
+    }
+
+    // The platform interface cannot depend on the `MethodChannel`
+    // implementation (it has to stay usable without Flutter), which is why the
+    // default implementation is installed lazily here instead. Platform
+    // implementations register themselves, for example `FirebaseCoreWeb` does
+    // so from `registerWith`, in which case they are kept as is.
+    if (!FirebasePlatform.isRegistered) {
+      FirebasePlatform.instance = MethodChannelFirebase();
+    }
+
+    return delegatePackingProperty = FirebasePlatform.instance;
   }
 
   /// Returns a list of all [FirebaseApp] instances that have been created.
   static List<FirebaseApp> get apps {
-    return _delegate.apps.map(FirebaseApp._).toList(growable: false);
+    return _delegate.apps.map(FirebaseApp.fromPlatform).toList(growable: false);
   }
 
   /// Initializes a new [FirebaseApp] instance by [name] and [options] and
@@ -81,7 +95,7 @@ class Firebase {
       options: resolvedOptions,
     );
 
-    return FirebaseApp._(app);
+    return FirebaseApp.fromPlatform(app);
   }
 
   /// Returns a [FirebaseApp] instance.
@@ -91,7 +105,7 @@ class Firebase {
   static FirebaseApp app([String name = defaultFirebaseAppName]) {
     FirebaseAppPlatform app = _delegate.app(name);
 
-    return FirebaseApp._(app);
+    return FirebaseApp.fromPlatform(app);
   }
 
   // TODO(rrousselGit): remove ==/hashCode

packages/firebase_core/firebase_core_common/CHANGELOG.md

@@ -0,0 +1,12 @@
+## 0.1.0
+
+- Initial release.
+- Pure Dart types and platform interfaces extracted from
+  `firebase_core_platform_interface` (`FirebaseApp`, `FirebaseAppPlatform`,
+  `FirebaseOptions`, `FirebaseException`, `FirebasePlatform`, `FirebasePlugin`
+  and the shared exception helpers), so that Firebase Core platform
+  implementations can be consumed outside of Flutter.
+- `FirebasePlatform.instance` no longer defaults to the `MethodChannel`
+  implementation: implementations must register themselves (`FirebaseCoreWeb`
+  does so from `registerWith`) and `FirebasePlatform.isRegistered` allows
+  checking whether that happened.

packages/firebase_core/firebase_core_common/LICENSE

@@ -0,0 +1,27 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/firebase_core/firebase_core_common/README.md

@@ -0,0 +1,14 @@
+# firebase_core_common
+
+Pure Dart shared types and platform interfaces used by
+[`firebase_core`](https://pub.dev/packages/firebase_core) and its platform
+implementations.
+
+This package contains no Flutter dependency and never imports `package:flutter/*`
+(neither directly nor transitively). It exists so that platform implementations
+such as [`firebase_core_web`](https://pub.dev/packages/firebase_core_web) can be
+used outside of Flutter, for example in pure Dart web applications.
+
+It is not intended to be used directly by end users. The Flutter facing API is
+exposed by `firebase_core`, and `firebase_core_platform_interface` re-exports
+this package for backwards compatibility.

packages/firebase_core/firebase_core_common/lib/firebase_core_common.dart

@@ -0,0 +1,24 @@
+// Copyright 2026, the Chromium project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Pure Dart shared types and platform interfaces for Firebase Core.
+///
+/// This library must never import `package:flutter/*` or any library which
+/// does, so that Firebase Core platform implementations (such as
+/// `firebase_core_web`) can be used outside of Flutter, for example in
+/// pure Dart web applications.
+///
+/// `firebase_core_platform_interface` re-exports this library, so importing
+/// that package (directly or through `firebase_core`) keeps giving access to
+/// exactly the same types.
+library;
+
+export 'src/default_firebase_app_name.dart';
+export 'src/firebase_app.dart';
+export 'src/firebase_core_exceptions.dart';
+export 'src/firebase_exception.dart';
+export 'src/firebase_options.dart';
+export 'src/platform_interface/platform_interface_firebase.dart';
+export 'src/platform_interface/platform_interface_firebase_app.dart';
+export 'src/platform_interface/platform_interface_firebase_plugin.dart';

packages/firebase_core/firebase_core_common/lib/src/default_firebase_app_name.dart

@@ -0,0 +1,6 @@
+// Copyright 2026, the Chromium project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// The default Firebase application name.
+const String defaultFirebaseAppName = '[DEFAULT]';

packages/firebase_core/firebase_core/lib/src/firebase_app.dart → packages/firebase_core/firebase_core_common/lib/src/firebase_app.dart

@@ -3,12 +3,22 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-part of '../firebase_core.dart';
+import 'firebase_options.dart';
+import 'platform_interface/platform_interface_firebase_app.dart';
 
 /// Represents a single Firebase app instance.
 ///
 /// You can get an instance by calling [Firebase.app()].
 class FirebaseApp {
+  /// Creates a [FirebaseApp] from a [FirebaseAppPlatform] delegate.
+  ///
+  /// This is not intended to be used directly. On Flutter, use
+  /// `Firebase.initializeApp()` or `Firebase.app()` instead. When using the
+  /// platform interfaces directly, for example outside of Flutter, wrap the
+  /// result of [FirebasePlatform.initializeApp] with this constructor.
+  factory FirebaseApp.fromPlatform(FirebaseAppPlatform delegate) =>
+      FirebaseApp._(delegate);
+
   /// A [FirebaseApp] instance can only be accessed from a call to `app()` on
   /// [FirebaseCore].
   ///

packages/firebase_core/firebase_core_platform_interface/lib/src/firebase_core_exceptions.dart → packages/firebase_core/firebase_core_common/lib/src/firebase_core_exceptions.dart

@@ -3,7 +3,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-part of '../firebase_core_platform_interface.dart';
+import 'default_firebase_app_name.dart';
+import 'firebase_exception.dart';
 
 /// Throws a consistent cross-platform error message when usage of an app occurs but
 /// no app has been created.

packages/firebase_core/firebase_core_platform_interface/lib/src/firebase_exception.dart → packages/firebase_core/firebase_core_common/lib/src/firebase_exception.dart

@@ -3,7 +3,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-part of '../firebase_core_platform_interface.dart';
+import 'package:meta/meta.dart';
 
 /// A generic class which provides exceptions in a Firebase-friendly format
 /// to users.

packages/firebase_core/firebase_core_platform_interface/lib/src/firebase_options.dart → packages/firebase_core/firebase_core_common/lib/src/firebase_options.dart

@@ -3,8 +3,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// ignore_for_file: deprecated_member_use_from_same_package
-part of '../firebase_core_platform_interface.dart';
+import 'package:collection/collection.dart';
+import 'package:meta/meta.dart';
 
 /// The options used to configure a Firebase app.
 ///
@@ -53,29 +53,6 @@ class FirebaseOptions {
     this.appGroupId,
   });
 
-  /// Named constructor to create [FirebaseOptions] from a the response of Pigeon channel.
-  ///
-  /// This constructor is used when platforms cannot directly return a
-  /// [FirebaseOptions] instance, for example when data is sent back from a
-  /// [MethodChannel].
-  FirebaseOptions.fromPigeon(CoreFirebaseOptions options)
-      : apiKey = options.apiKey,
-        appId = options.appId,
-        messagingSenderId = options.messagingSenderId,
-        projectId = options.projectId,
-        authDomain = options.authDomain,
-        databaseURL = options.databaseURL,
-        storageBucket = options.storageBucket,
-        measurementId = options.measurementId,
-        trackingId = options.trackingId,
-        deepLinkURLScheme = options.deepLinkURLScheme,
-        androidClientId = options.androidClientId,
-        iosClientId = options.iosClientId,
-        iosBundleId = options.iosBundleId,
-        appGroupId = options.appGroupId,
-        recaptchaSiteKey =
-            ''; // Placeholder to coordinate with fluttefire cli current operation.
-
   /// Returns a copy of this FirebaseOptions with the given fields replaced with
   /// the new values.
   FirebaseOptions copyWith({

packages/firebase_core/firebase_core_platform_interface/lib/src/platform_interface/platform_interface_firebase.dart → packages/firebase_core/firebase_core_common/lib/src/platform_interface/platform_interface_firebase.dart

@@ -3,7 +3,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-part of '../../firebase_core_platform_interface.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+import '../default_firebase_app_name.dart';
+import '../firebase_exception.dart';
+import '../firebase_options.dart';
+import 'platform_interface_firebase_app.dart';
 
 /// The interface that implementations of `firebase_core` must extend.
 ///
@@ -19,15 +24,43 @@ abstract class FirebasePlatform extends PlatformInterface {
 
   static final Object _token = Object();
 
+  /// Whether a [FirebasePlatform] implementation has been registered.
+  ///
+  /// Implementations register themselves by setting [FirebasePlatform.instance],
+  /// usually from their `registerWith` method which is called by the Flutter
+  /// plugin registrant (or manually when running outside of Flutter).
+  static bool get isRegistered => _instance != null;
+
   /// The default instance of [FirebasePlatform] to use.
   ///
-  /// Platform-specific plugins should override this with their own class
+  /// Platform-specific plugins should set this with their own class
   /// that extends [FirebasePlatform] when they register themselves.
   ///
-  /// Defaults to [MethodChannelFirebase].
-  static FirebasePlatform get instance => _instance;
+  /// Throws a [FirebaseException] if no implementation has been registered yet.
+  /// On Flutter, `firebase_core` registers its `MethodChannel` implementation
+  /// before the first usage of the `Firebase` API. Other platforms must call
+  /// the `registerWith` method of their implementation, for example
+  /// `FirebaseCoreWeb.registerWith(null)` on web.
+  static FirebasePlatform get instance {
+    final FirebasePlatform? instance = _instance;
+
+    if (instance == null) {
+      throw FirebaseException(
+        plugin: 'core',
+        code: 'no-platform-implementation',
+        message: 'No Firebase Core platform implementation has been '
+            'registered.\n\nIf you are using Flutter, this usually means that '
+            'the platform you are running on is not supported, or that '
+            '`Firebase.initializeApp()` has not been called yet.\n\nIf you are '
+            'not using Flutter, register your implementation manually, for '
+            'example by calling `FirebaseCoreWeb.registerWith(null)` on web.',
+      );
+    }
+
+    return instance;
+  }
 
-  static FirebasePlatform _instance = MethodChannelFirebase();
+  static FirebasePlatform? _instance;
 
   static set instance(FirebasePlatform instance) {
     PlatformInterface.verify(instance, _token);

packages/firebase_core/firebase_core_platform_interface/lib/src/platform_interface/platform_interface_firebase_app.dart → packages/firebase_core/firebase_core_common/lib/src/platform_interface/platform_interface_firebase_app.dart

@@ -3,7 +3,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-part of '../../firebase_core_platform_interface.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+import '../default_firebase_app_name.dart';
+import '../firebase_options.dart';
 
 /// A class storing the name and options of a Firebase app.
 ///
@@ -26,7 +29,7 @@ class FirebaseAppPlatform extends PlatformInterface {
   final FirebaseOptions options;
 
   /// Returns whether this instance is the default Firebase app.
-  bool get _isDefault => name == defaultFirebaseAppName;
+  bool get isDefault => name == defaultFirebaseAppName;
 
   /// Returns true if automatic data collection is enabled for this app.
   bool get isAutomaticDataCollectionEnabled {

packages/firebase_core/firebase_core_platform_interface/lib/src/platform_interface/platform_interface_firebase_plugin.dart → packages/firebase_core/firebase_core_common/lib/src/platform_interface/platform_interface_firebase_plugin.dart

@@ -3,8 +3,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-part of '../../firebase_core_platform_interface.dart';
-
 /// The base class that other FlutterFire plugins must extend.
 ///
 /// This class provides access to common plugin properties and constants which
@@ -21,6 +19,24 @@ abstract class FirebasePlugin {
   /// requires that the value is synchronously available for use after initialization.
   static Map<dynamic, dynamic> _constantsForPluginApps = {};
 
+  /// Registers the plugin [constants] of [appName].
+  ///
+  /// Platform implementations call this once core has been initialized, so
+  /// that the constants are synchronously available to plugins afterwards.
+  static void registerConstantsForApp(
+    String appName,
+    Map<dynamic, dynamic>? constants,
+  ) {
+    if (constants != null) {
+      _constantsForPluginApps[appName] = constants;
+    }
+  }
+
+  /// Removes the constants registered for the plugins of [appName].
+  static void removeConstantsForApp(String appName) {
+    _constantsForPluginApps.remove(appName);
+  }
+
   final String _appName;
 
   final String _methodChannelName;

packages/firebase_core/firebase_core_common/pubspec.yaml

@@ -0,0 +1,21 @@
+name: firebase_core_common
+description: Pure Dart shared types and platform interfaces used by firebase_core
+  and its platform implementations.
+homepage: https://firebase.google.com/docs/flutter/setup
+repository: https://github.com/firebase/flutterfire/tree/main/packages/firebase_core/firebase_core_common
+version: 0.1.0
+resolution: workspace
+topics:
+  - firebase
+  - core
+
+environment:
+  sdk: '^3.6.0'
+
+dependencies:
+  collection: ^1.0.0
+  meta: ^1.8.0
+  plugin_platform_interface: ^2.1.3
+
+dev_dependencies:
+  test: ^1.25.0