Role of prefix is unclear

### What package does this bug report belong to?

shared_preferences

### What target platforms are you seeing this bug on?

Web, Linux

### Have you already upgraded your packages?

Yes

### Dependency versions

<details><summary>pubspec.lock</summary>

```lock
# Generated by pub
# See https://dart.dev/tools/pub/glossary#lockfile
packages:
  async:
    dependency: transitive
    description:
      name: async
      sha256: "947bfcf187f74dbc5e146c9eb9c0f10c9f8b30743e341481c1e2ed3ecc18c20c"
      url: "https://pub.dev"
    source: hosted
    version: "2.11.0"
  boolean_selector:
    dependency: transitive
    description:
      name: boolean_selector
      sha256: "6cfb5af12253eaf2b368f07bacc5a80d1301a071c73360d746b7f2e32d762c66"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.1"
  characters:
    dependency: transitive
    description:
      name: characters
      sha256: "04a925763edad70e8443c99234dc3328f442e811f1d8fd1a72f1c8ad0f69a605"
      url: "https://pub.dev"
    source: hosted
    version: "1.3.0"
  clock:
    dependency: transitive
    description:
      name: clock
      sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
      url: "https://pub.dev"
    source: hosted
    version: "1.1.1"
  collection:
    dependency: transitive
    description:
      name: collection
      sha256: ee67cb0715911d28db6bf4af1026078bd6f0128b07a5f66fb2ed94ec6783c09a
      url: "https://pub.dev"
    source: hosted
    version: "1.18.0"
  fake_async:
    dependency: transitive
    description:
      name: fake_async
      sha256: "511392330127add0b769b75a987850d136345d9227c6b94c96a04cf4a391bf78"
      url: "https://pub.dev"
    source: hosted
    version: "1.3.1"
  ffi:
    dependency: transitive
    description:
      name: ffi
      sha256: "16ed7b077ef01ad6170a3d0c57caa4a112a38d7a2ed5602e0aca9ca6f3d98da6"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.3"
  file:
    dependency: transitive
    description:
      name: file
      sha256: a3b4f84adafef897088c160faf7dfffb7696046cb13ae90b508c2cbc95d3b8d4
      url: "https://pub.dev"
    source: hosted
    version: "7.0.1"
  flutter:
    dependency: "direct main"
    description: flutter
    source: sdk
    version: "0.0.0"
  flutter_lints:
    dependency: "direct dev"
    description:
      name: flutter_lints
      sha256: "3f41d009ba7172d5ff9be5f6e6e6abb4300e263aab8866d2a0842ed2a70f8f0c"
      url: "https://pub.dev"
    source: hosted
    version: "4.0.0"
  flutter_test:
    dependency: "direct dev"
    description: flutter
    source: sdk
    version: "0.0.0"
  flutter_web_plugins:
    dependency: transitive
    description: flutter
    source: sdk
    version: "0.0.0"
  leak_tracker:
    dependency: transitive
    description:
      name: leak_tracker
      sha256: "3f87a60e8c63aecc975dda1ceedbc8f24de75f09e4856ea27daf8958f2f0ce05"
      url: "https://pub.dev"
    source: hosted
    version: "10.0.5"
  leak_tracker_flutter_testing:
    dependency: transitive
    description:
      name: leak_tracker_flutter_testing
      sha256: "932549fb305594d82d7183ecd9fa93463e9914e1b67cacc34bc40906594a1806"
      url: "https://pub.dev"
    source: hosted
    version: "3.0.5"
  leak_tracker_testing:
    dependency: transitive
    description:
      name: leak_tracker_testing
      sha256: "6ba465d5d76e67ddf503e1161d1f4a6bc42306f9d66ca1e8f079a47290fb06d3"
      url: "https://pub.dev"
    source: hosted
    version: "3.0.1"
  lints:
    dependency: transitive
    description:
      name: lints
      sha256: "976c774dd944a42e83e2467f4cc670daef7eed6295b10b36ae8c85bcbf828235"
      url: "https://pub.dev"
    source: hosted
    version: "4.0.0"
  matcher:
    dependency: transitive
    description:
      name: matcher
      sha256: d2323aa2060500f906aa31a895b4030b6da3ebdcc5619d14ce1aada65cd161cb
      url: "https://pub.dev"
    source: hosted
    version: "0.12.16+1"
  material_color_utilities:
    dependency: transitive
    description:
      name: material_color_utilities
      sha256: f7142bb1154231d7ea5f96bc7bde4bda2a0945d2806bb11670e30b850d56bdec
      url: "https://pub.dev"
    source: hosted
    version: "0.11.1"
  meta:
    dependency: transitive
    description:
      name: meta
      sha256: bdb68674043280c3428e9ec998512fb681678676b3c54e773629ffe74419f8c7
      url: "https://pub.dev"
    source: hosted
    version: "1.15.0"
  path:
    dependency: transitive
    description:
      name: path
      sha256: "087ce49c3f0dc39180befefc60fdb4acd8f8620e5682fe2476afd0b3688bb4af"
      url: "https://pub.dev"
    source: hosted
    version: "1.9.0"
  path_provider_linux:
    dependency: transitive
    description:
      name: path_provider_linux
      sha256: f7a1fe3a634fe7734c8d3f2766ad746ae2a2884abe22e241a8b301bf5cac3279
      url: "https://pub.dev"
    source: hosted
    version: "2.2.1"
  path_provider_platform_interface:
    dependency: transitive
    description:
      name: path_provider_platform_interface
      sha256: "88f5779f72ba699763fa3a3b06aa4bf6de76c8e5de842cf6f29e2e06476c2334"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.2"
  path_provider_windows:
    dependency: transitive
    description:
      name: path_provider_windows
      sha256: bd6f00dbd873bfb70d0761682da2b3a2c2fccc2b9e84c495821639601d81afe7
      url: "https://pub.dev"
    source: hosted
    version: "2.3.0"
  platform:
    dependency: transitive
    description:
      name: platform
      sha256: "5d6b1b0036a5f331ebc77c850ebc8506cbc1e9416c27e59b439f917a902a4984"
      url: "https://pub.dev"
    source: hosted
    version: "3.1.6"
  plugin_platform_interface:
    dependency: transitive
    description:
      name: plugin_platform_interface
      sha256: "4820fbfdb9478b1ebae27888254d445073732dae3d6ea81f0b7e06d5dedc3f02"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.8"
  shared_preferences:
    dependency: "direct main"
    description:
      name: shared_preferences
      sha256: "746e5369a43170c25816cc472ee016d3a66bc13fcf430c0bc41ad7b4b2922051"
      url: "https://pub.dev"
    source: hosted
    version: "2.3.2"
  shared_preferences_android:
    dependency: transitive
    description:
      name: shared_preferences_android
      sha256: "3b9febd815c9ca29c9e3520d50ec32f49157711e143b7a4ca039eb87e8ade5ab"
      url: "https://pub.dev"
    source: hosted
    version: "2.3.3"
  shared_preferences_foundation:
    dependency: transitive
    description:
      name: shared_preferences_foundation
      sha256: "07e050c7cd39bad516f8d64c455f04508d09df104be326d8c02551590a0d513d"
      url: "https://pub.dev"
    source: hosted
    version: "2.5.3"
  shared_preferences_linux:
    dependency: transitive
    description:
      name: shared_preferences_linux
      sha256: "580abfd40f415611503cae30adf626e6656dfb2f0cee8f465ece7b6defb40f2f"
      url: "https://pub.dev"
    source: hosted
    version: "2.4.1"
  shared_preferences_platform_interface:
    dependency: transitive
    description:
      name: shared_preferences_platform_interface
      sha256: "57cbf196c486bc2cf1f02b85784932c6094376284b3ad5779d1b1c6c6a816b80"
      url: "https://pub.dev"
    source: hosted
    version: "2.4.1"
  shared_preferences_web:
    dependency: transitive
    description:
      name: shared_preferences_web
      sha256: d2ca4132d3946fec2184261726b355836a82c33d7d5b67af32692aff18a4684e
      url: "https://pub.dev"
    source: hosted
    version: "2.4.2"
  shared_preferences_windows:
    dependency: transitive
    description:
      name: shared_preferences_windows
      sha256: "94ef0f72b2d71bc3e700e025db3710911bd51a71cefb65cc609dd0d9a982e3c1"
      url: "https://pub.dev"
    source: hosted
    version: "2.4.1"
  sky_engine:
    dependency: transitive
    description: flutter
    source: sdk
    version: "0.0.99"
  source_span:
    dependency: transitive
    description:
      name: source_span
      sha256: "53e943d4206a5e30df338fd4c6e7a077e02254531b138a15aec3bd143c1a8b3c"
      url: "https://pub.dev"
    source: hosted
    version: "1.10.0"
  stack_trace:
    dependency: transitive
    description:
      name: stack_trace
      sha256: "73713990125a6d93122541237550ee3352a2d84baad52d375a4cad2eb9b7ce0b"
      url: "https://pub.dev"
    source: hosted
    version: "1.11.1"
  stream_channel:
    dependency: transitive
    description:
      name: stream_channel
      sha256: ba2aa5d8cc609d96bbb2899c28934f9e1af5cddbd60a827822ea467161eb54e7
      url: "https://pub.dev"
    source: hosted
    version: "2.1.2"
  string_scanner:
    dependency: transitive
    description:
      name: string_scanner
      sha256: "556692adab6cfa87322a115640c11f13cb77b3f076ddcc5d6ae3c20242bedcde"
      url: "https://pub.dev"
    source: hosted
    version: "1.2.0"
  term_glyph:
    dependency: transitive
    description:
      name: term_glyph
      sha256: a29248a84fbb7c79282b40b8c72a1209db169a2e0542bce341da992fe1bc7e84
      url: "https://pub.dev"
    source: hosted
    version: "1.2.1"
  test_api:
    dependency: transitive
    description:
      name: test_api
      sha256: "5b8a98dafc4d5c4c9c72d8b31ab2b23fc13422348d2997120294d3bac86b4ddb"
      url: "https://pub.dev"
    source: hosted
    version: "0.7.2"
  vector_math:
    dependency: transitive
    description:
      name: vector_math
      sha256: "80b3257d1492ce4d091729e3a67a60407d227c27241d6927be0130c98e741803"
      url: "https://pub.dev"
    source: hosted
    version: "2.1.4"
  vm_service:
    dependency: transitive
    description:
      name: vm_service
      sha256: "5c5f338a667b4c644744b661f309fb8080bb94b18a7e91ef1dbd343bed00ed6d"
      url: "https://pub.dev"
    source: hosted
    version: "14.2.5"
  web:
    dependency: transitive
    description:
      name: web
      sha256: cd3543bd5798f6ad290ea73d210f423502e71900302dde696f8bff84bf89a1cb
      url: "https://pub.dev"
    source: hosted
    version: "1.1.0"
  xdg_directories:
    dependency: transitive
    description:
      name: xdg_directories
      sha256: "7a3f37b05d989967cdddcbb571f1ea834867ae2faa29725fd085180e0883aa15"
      url: "https://pub.dev"
    source: hosted
    version: "1.1.0"
sdks:
  dart: ">=3.5.4 <4.0.0"
  flutter: ">=3.24.0"
```

</details>


### Steps to reproduce

1. Store a key-value pair using shared_preferences on Linux or web, using `SharedPreferenceAsync` or `SharedPreferencesWithCache` (e.g. using the example that comes with the package, or otherwise).
2. Inspect the stored key in Chrome devtools or in the filesystem: it does not have any prefix attached to it.

### Expected results

From the shared_preferences documentation, I expect keys to have "flutter." (or another prefix) prepended to them:

> https://pub.dev/packages/shared_preferences
> By default, the SharedPreferences plugin will only read (and write) preferences that begin with the prefix flutter.. This is all handled internally by the plugin and does not require manually adding this prefix.
> 
> Alternatively, SharedPreferences can be configured to use any prefix by adding a call to setPrefix before any instances of SharedPreferences are instantiated.

and

> https://pub.dev/documentation/shared_preferences/latest/shared_preferences/SharedPreferences/setPrefix.html
> Sets the prefix that is attached to all keys for all shared preferences.

But on Linux and web, the stored keys don't have "flutter." or anything attached to them, even if `setPrefix` has been called with something non-empty.


### Actual results

The keys are stored exactly as passed in to e.g. `setInt`, with no prefix.

### Code sample

<details open><summary>Code sample</summary>

```dart
// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// ignore_for_file: public_member_api_docs

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'SharedPreferencesWithCache Demo',
      home: SharedPreferencesDemo(),
    );
  }
}

class SharedPreferencesDemo extends StatefulWidget {
  const SharedPreferencesDemo({super.key});

  @override
  SharedPreferencesDemoState createState() => SharedPreferencesDemoState();
}

class SharedPreferencesDemoState extends State<SharedPreferencesDemo> {
  final Future<SharedPreferencesWithCache> _prefs =
      SharedPreferencesWithCache.create(
          cacheOptions: const SharedPreferencesWithCacheOptions(
              // This cache will only accept the key 'counter'.
              allowList: <String>{'counter'}));
  late Future<int> _counter;
  int _externalCounter = 0;

  Future<void> _incrementCounter() async {
    final SharedPreferencesWithCache prefs = await _prefs;
    final int counter = (prefs.getInt('counter') ?? 0) + 1;

    setState(() {
      _counter = prefs.setInt('counter', counter).then((_) {
        return counter;
      });
    });
  }

  /// Gets external button presses that could occur in another instance, thread,
  /// or via some native system.
  Future<void> _getExternalCounter() async {
    final SharedPreferencesAsync prefs = SharedPreferencesAsync();
    setState(() async {
      _externalCounter = (await prefs.getInt('externalCounter')) ?? 0;
    });
  }

  @override
  void initState() {
    super.initState();
    _counter = _prefs.then((SharedPreferencesWithCache prefs) {
      return prefs.getInt('counter') ?? 0;
    });

    _getExternalCounter();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('SharedPreferencesWithCache Demo'),
      ),
      body: Center(
          child: FutureBuilder<int>(
              future: _counter,
              builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                switch (snapshot.connectionState) {
                  case ConnectionState.none:
                  case ConnectionState.waiting:
                    return const CircularProgressIndicator();
                  case ConnectionState.active:
                  case ConnectionState.done:
                    if (snapshot.hasError) {
                      return Text('Error: ${snapshot.error}');
                    } else {
                      return Text(
                        'Button tapped ${snapshot.data ?? 0 + _externalCounter} time${(snapshot.data ?? 0 + _externalCounter) == 1 ? '' : 's'}.\n\n'
                        'This should persist across restarts.',
                      );
                    }
                }
              })),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}
```

</details>


### Screenshots or Videos

<details open>
<summary>Screenshots / Video demonstration</summary>

![image](https://github.com/user-attachments/assets/a34e3d96-3bc8-4ea3-90a4-d3056a1b10de)


</details>


### Logs

_No response_

### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
[✓] Flutter (Channel stable, 3.24.4, on Ubuntu 24.04.1 LTS 6.8.0-48-generic, locale en_US.UTF-8)
    • Flutter version 3.24.4 on channel stable at /home/abc/code/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 603104015d (2 weeks ago), 2024-10-24 08:01:25 -0700
    • Engine revision db49896cf2
    • Dart version 3.5.4
    • DevTools version 2.37.3

[!] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /home/abc/Android/Sdk
    • Platform android-34, build-tools 34.0.0
    • Java binary at: /snap/android-studio/161/jbr/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.10+0-17.0.10b1087.21-11609105)
    ! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses

[✓] Chrome - develop for the web
    • Chrome at google-chrome

[✓] Linux toolchain - develop for Linux desktop
    • Ubuntu clang version 18.1.3 (1ubuntu1)
    • cmake version 3.28.3
    • ninja version 1.11.1
    • pkg-config version 1.8.1

[✓] Android Studio (version 2024.1)
    • Android Studio at /snap/android-studio/161
    • Flutter plugin version 81.0.2
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.10+0-17.0.10b1087.21-11609105)

[✓] VS Code (version 1.95.1)
    • VS Code at /snap/code/current/usr/share/code
    • Flutter extension version 3.100.0

[✓] Connected device (2 available)
    • Linux (desktop) • linux  • linux-x64      • Ubuntu 24.04.1 LTS 6.8.0-48-generic
    • Chrome (web)    • chrome • web-javascript • Google Chrome 130.0.6723.91

[✓] Network resources
    • All expected network resources are available.

! Doctor found issues in 1 category.
```

</details>


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Role of prefix is unclear #158404

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Role of prefix is unclear #158404

Description

What package does this bug report belong to?

What target platforms are you seeing this bug on?

Have you already upgraded your packages?

Dependency versions

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Videos

Logs

Flutter Doctor output

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions