Is there an existing issue for this?

• I have searched the existing issues
• I have read the guide to filing a bug

Use case

When using flutter assemble command, there are many undocumented features / options.

for instance, this is the sequence I use to generate an app bundle for windows-x64

flutter create test_module1 --template=module --local-engine-src-path /d/workspace/engine/src --local-engine=host_debug

cd test_module1
flutter assemble --local-engine=host_debug -dTargetPlatform=windows-x64 '-dBuildMode=debug' -dTrackWidgetCreation=true --output="jit_bundle" -dTargetFile="lib/main.dart" debug_bundle_windows_assets
flutter assemble --local-engine=host_release -dTargetPlatform=windows-x64 '-dBuildMode=release' --output="aot_bundle" -dTargetFile="lib/main.dart" release_bundle_windows_assets

• the target name (release_bundle_windows_assets / debug_bundle_windows_assets) are not documented and had to be deduced by looking at the src code for the command
• non of the options TargetPlatform, BuildMode are documented.
• in case of a missing option, there is no way to know which valid options are available.

Proposal

• There should be a documentation for all options that are required to successfully run the command.
• The user should be able to get list valid options for each argument.
• Error messages should list valid options instead of just saying an option is missing.