When geolocation api is disabled, app fails to load in Firefox

[jake-johnson-disney]

There's already an issue here: #30313 that was closed a long time ago, but the issue still exists.

In Firefox, it is possible for the user to completely disable the Geolocation API in about:config by toggling geo.enabled. In this case, window.navigator.geolocation will be undefined.

The application fails to fully load if trying to use geolocation anywhere with something like Uncaught : Null check operator used on a null value

Here's a simple example that reproduces the issue:

import 'dart:html' as html;

import 'package:flutter/material.dart';

void main() => runApp(
      MaterialApp(
        home: Material(
          child: Center(
            child: FutureBuilder<html.Geoposition?>(
              future: HtmlGeolocationManager().getCurrentPosition(),
              builder: (BuildContext context,
                  AsyncSnapshot<html.Geoposition?> snapshot) {
                if (snapshot.hasData) {
                  return Text(snapshot.data?.coords?.latitude.toString() ?? '');
                } else {
                  return const Text('getting location...');
                }
              },
            ),
          ),
        ),
      ),
    );

class HtmlGeolocationManager {
  final html.Geolocation? _geolocation;

  HtmlGeolocationManager() : _geolocation = html.window.navigator.geolocation;

  Future<html.Geoposition?> getCurrentPosition({
    bool? enableHighAccuracy,
    Duration? timeout,
  }) async {
    try {
      html.Geoposition? geoPosition;
      if (_geolocation != null) {
        geoPosition = await _geolocation.getCurrentPosition(
          enableHighAccuracy: enableHighAccuracy,
          timeout: timeout,
        );
      }

      return geoPosition;
    } on html.PositionError catch (e) {
      throw e;
    }
  }
}

I'd be happy to contribute a fix, if someone can help point me in the right direction

[jake-johnson-disney]

dart info:

❯ dart info      

If providing this information as part of reporting a bug, please review the information
below to ensure it only contains things you're comfortable posting publicly.

#### General info

- Dart 3.2.6 (stable) (Wed Jan 24 13:41:58 2024 +0000) on "macos_arm64"
- on macos / Version 14.2.1 (Build 23C71)
- locale is en-US

#### Project info

- sdk constraint: '>=3.2.6 <4.0.0'
- dependencies: cupertino_icons, flutter
- dev_dependencies: flutter_lints, flutter_test

#### Process info

| Memory |  CPU | Elapsed time | Command line                                                                               |
| -----: | ---: | -----------: | ------------------------------------------------------------------------------------------ |
|   4 MB | 0.0% |     18:24:25 | dart devtools --machine --allow-embedding                                                  |
|   8 MB | 0.0% |  07-00:09:27 | dart language-server --client-id=IntelliJ-IDEA --client-version=IU-223.8836.41 --protocol=analyzer |
| 670 MB | 0.0% |        46:29 | dart language-server --client-id=IntelliJ-IDEA --client-version=IU-223.8836.41 --protocol=analyzer |
|  13 MB | 0.0% |     18:24:25 | dart language-server --protocol=lsp --client-id=VS-Code --client-version=3.82.0            |
|  17 MB | 0.0% |  07-00:09:27 | flutter_tools.snapshot daemon                                                              |
|  27 MB | 0.4% |        46:30 | flutter_tools.snapshot daemon                                                              |
|  20 MB | 0.0% |     18:24:25 | flutter_tools.snapshot daemon                                                              |

[srujzs]

Thanks for filing and the repro!

I can't seem to quite reproduce the same issue with Firefox (I come across the rethrow instead even with the about:config changes, but it may be a user error), but I'm guessing that the culprit is the getting of geolocation. With Dart 3, native APIs are null-checked if their return type is non-nullable. This was not always the case in Dart 2.

An alternative is declaring a nullable version of geolocation using JS interop since it's a native API:

extension on Navigator {
  // Rename so you don't come across collisions with `Navigator.geolocation`.
  @JS('geolocation')
  external Geolocation? get geolocation_;
}

and using geolocation_ instead. Let me know if this works as a workaround.

There's a general theme of how to support compatibility with dart:html. In the past, we've tried to incorporate all the possible instances where an API might not exist, but this led to many nullable APIs even when they're not null in most cases. It also was not exhaustive (as you can see), and so may miss instances when an API could be unavailable.

As an aside, we're move to package:web going forward and investing effort there to move away from some of the complications of dart:html to something that is leaner and maps directly to the web. If you find that it's easier to use for your project, consider trying it out.