Standardize Flutter bootstrap code

[parlough]

Closes #2966

[daohoangson]

I would love to see PR merged. At the moment, registerPlugins is being called before bootstrapEngine, which is causing issues with package_info_plus. That plugin needs the asset manager during registration.

[parlough]

@daohoangson Could you provide more details on the issue you're seeing or where? I don't believe package: package_info_plus is supported in DartPad.

[daohoangson]

Sorry for not being clear, I have been maintaining my own version of DartPad with additional packages. The build starts failing after adding package_info_plus so I tried to debug it.

The plugin tries to get the asset manager:

https://github.com/fluttercommunity/plus_plugins/blob/c71730e65a0ea59bc177d3dcb2da2abbaa1bcc61/packages/package_info_plus/package_info_plus/lib/src/package_info_plus_web.dart#L20

_assetManager = assetManagerMock ?? assetManager;

The getter looks like this:

https://github.com/flutter/engine/blob/c6fecf65fbf385c5e9168c5b40526c9ae998045b/lib/web_ui/lib/ui_web/src/ui_web/asset_manager.dart#L11

AssetManager get assetManager => engineAssetManager;

It calls another getter:

https://github.com/flutter/engine/blob/c6fecf65fbf385c5e9168c5b40526c9ae998045b/lib/web_ui/lib/src/engine/initialization.dart#L242

ui_web.AssetManager get engineAssetManager => _debugAssetManager ?? _assetManager!;

Because registerPlugins was called before bootstrapEngine, _assetManager is null so the ! operator throws an error.

[devoncarew]

👍

[johnpryan]

What does this change do?

[mmcdon20]

@johnpryan fixes #2966

[johnpryan]

Got it... We might not need to maintain this code any more. The comment above is old and out of date since flutter/flutter#144434 landed and we integrated the new bootstrapping (#2960)

[johnpryan]

Do we even need to call registerPlugins anymore? I think we might be able to remove kBootstrapFlutterCode and rely on the new bootstrapping improvements to initialize plugins.

cc: @eyebrowsoffire @ditman

[ditman]

@johnpryan I don't remember dartpad code very well, but I think the new bootstrapping code is NOT generating the actual main.dart file that contains the registerPlugins call, it's done by the flutter tool here:

https://github.com/flutter/flutter/blob/main/packages/flutter_tools/lib/src/web/file_generators/main_dart.dart

That generated file is the thing that glues the framework + engine + plugins + user code, so users only have to worry about writing the latter.