Packages cannot declare which platforms they support

[timsneath]

With the advent of FFI, there are an increasing number of packages (not platform plugins) that contain only Dart code, but which are designed to work on only certain platforms. This will increase as we add more platforms and transition more code to adopt FFI, since it will be increasingly infeasible for a platform integration package to support the wide range of platforms that Dart itself supports.

As an obvious example, the win32 package by design only supports Windows, but it doesn't have any means to enumerate that.

This leads to customer confusion. For example:
halildurmus/filepicker_windows#9 (comment)
halildurmus/win32#166

One potential solution would be to have an entry in pubspec.yaml for supported_platforms which would override the detection logic built into pana and allow plugin authors to explicitly declare which platforms they choose to support.

[alann-maulana]

Finally found this issue. It happen when publishing a package meant for all Flutter platforms.

Using native package flutter_image_compress for both Android and iOS, otherwise (Web, MacOS, Windows & Linux) is using pure Dart package image_compression.

So when image_compression_flutter published it only detects Android, iOS and Web platforms only.

Result of pana check

~!$ pana -s path . --no-warning
## ✓ Follow Dart file conventions (20 / 20)
### [*] 10/10 points: Provide a valid `pubspec.yaml`


### [*] 5/5 points: Provide a valid `README.md`


### [*] 5/5 points: Provide a valid `CHANGELOG.md`


## ✓ Provide documentation (10 / 10)
### [*] 10/10 points: Package has an example

* Found example at: `example/lib/main.dart`

## ✓ Support multiple platforms (20 / 20)
### [*] 20/20 points: Supports 3 of 3 possible platforms (**iOS**, **Android**, **Web**)

Found 4 issues. Showing the first 2:


These issues are present but do not affect the score, because they may not originate in your package:

<details>
<summary>
Package does not support Flutter platform Windows
</summary>

Because:
* `package:image_compression_flutter/image_compression_flutter.dart` that imports:
* `package:image_compression_flutter/src/compressor_io.dart` that imports:
* `package:image_compression_flutter/src/flutter_compressor.dart` that imports:
* `package:flutter_image_compress/flutter_image_compress.dart` that declares support for platforms: Android, iOS
</details>

## ✓ Pass static analysis (30 / 30)
### [*] 30/30 points: code has no errors, warnings, lints, or formatting issues


## ✓ Support up-to-date dependencies (20 / 20)
### [*] 10/10 points: All of the package dependencies are supported in the latest version

|Package|Constraint|Compatible|Latest|
|:-|:-|:-|:-|
|[`flutter`]|`flutter`|0.0.0|0.0.0|
|[`flutter_image_compress`]|`^1.0.0`|1.0.0|1.0.0|
|[`image_compression`]|`^1.0.3`|1.0.3|1.0.3|

<details><summary>Transitive dependencies</summary>

|Package|Constraint|Compatible|Latest|
|:-|:-|:-|:-|
|[`archive`]|-|3.1.2|3.1.2|
|[`characters`]|-|1.1.0|1.1.0|
|[`collection`]|-|1.15.0|1.15.0|
|[`crypto`]|-|3.0.1|3.0.1|
|[`image`]|-|3.0.2|3.0.2|
|[`meta`]|-|1.3.0|1.7.0|
|[`mime`]|-|1.0.0|1.0.0|
|[`path`]|-|1.8.0|1.8.0|
|[`petitparser`]|-|4.1.0|4.2.0|
|[`sky_engine`]|-|0.0.99|0.0.99|
|[`typed_data`]|-|1.3.0|1.3.0|
|[`vector_math`]|-|2.1.0|2.1.0|
|[`xml`]|-|5.1.2|5.1.2|
</details>

To reproduce run `dart pub outdated --no-dev-dependencies --up-to-date --no-dependency-overrides`.

[`flutter`]: https://pub.dev/packages/flutter
[`flutter_image_compress`]: https://pub.dev/packages/flutter_image_compress
[`image_compression`]: https://pub.dev/packages/image_compression
[`archive`]: https://pub.dev/packages/archive
[`characters`]: https://pub.dev/packages/characters
[`collection`]: https://pub.dev/packages/collection
[`crypto`]: https://pub.dev/packages/crypto
[`image`]: https://pub.dev/packages/image
[`meta`]: https://pub.dev/packages/meta
[`mime`]: https://pub.dev/packages/mime
[`path`]: https://pub.dev/packages/path
[`petitparser`]: https://pub.dev/packages/petitparser
[`sky_engine`]: https://pub.dev/packages/sky_engine
[`typed_data`]: https://pub.dev/packages/typed_data
[`vector_math`]: https://pub.dev/packages/vector_math
[`xml`]: https://pub.dev/packages/xml


### [*] 10/10 points: Package supports latest stable Dart and Flutter SDKs


## ✓ Support sound null safety (20 / 20)
### [*] 20/20 points: Package and dependencies are fully migrated to null safety!


Points: 120/120.

Edit : finally found a way to solve it

[dnfield]

I have a somewhat related issue: flutter_svg does work on web, but imports dart:io and so it gets marked as not working on web, even though it imports dart:io in a safe manner (it does so in precisely the same way that Flutter itself does for images).

[mit-mit]

This has landed, but we still need to get docs updated on https://dart.dev/tools/pub/pubspec

[jonasfj]

Missing documentation is fixed with dart-lang/site-www#3793

[sigurdm]

This is done!