Debugger page fails to auto-open main.dart when connected to web app

[elliette]

When DevTools is connected to a web app, the debugger page auto-opens the Flutter bootstrap file, instead of the app's main.dart file:

We should make sure the debugger page opens the main.dart file instead of this bootstrap file, which is the intended behavior.

However, there is also the question of discoverability of the file search bar. Instead of loading main.dart, we could default to showing a page that tells the user how to open a file. See dart-lang/webdev#2010

[elliette]

I know why this is happening:

• In DevTools, we open up to whatever the rootLib is (as set by the VM service / DWDS):

  devtools/packages/devtools_app/lib/src/screens/debugger/debugger_controller.dart

  Line 473 in f895e18

  return ref.uri == isolate.rootLib?.uri;

• In DWDS, we set the rootLib to be org-dartlang-app:/web_entrypoint.dart. The reasoning for this is explained in: [vm_service] isolate.rootLib returns the wrong library on the web. dart-lang/sdk#44760. However, I think we intended to change it to main.dart in the future, see: [vm_service] isolate.rootLib returns the wrong library on the web. dart-lang/sdk#44760 (comment) @annagrin Do you know where that stands? I think this would be our best option.

The other option is to have DevTools try to find the main.dart file in the list of scripts, but I don't like that solution and think it should be determined by the VM service / DWDS.

[annagrin]

Unfortunately this is tricky - in dwds we set the rootLib of the VM incorrectly to the wrapper of the main since we don't know what is the correct one. One of the solutions we were thinking about is adding build metadata (constructed by the build, or frontend server in this case) to send all kinds of useful information to dwds (including main module, main module to show in the debugger, locations of dill files, compilation flags etc)

For now we can think of hacking it somehow - if we have an easy way to detect the main module in flutter tools, just pass it as a parameter to dwds? But I am not sure if we do.

I think this should be possible - flutter tools creates a bootstrap to start the main wrapper, is we can find what created the wrapper we can find the main:)

Starting point would be:

https://github.com/flutter/flutter/blob/26b6c1bedda2a62bb0ce84cdd7932769d99f1e52/packages/flutter_tools/lib/src/web/bootstrap.dart#L16

[elliette]

Note: Also investigated how to sort the scripts shown to the user when they open their file search. Started making changes in dart-lang/webdev@master...elliette:sort-scripts, but I think it will also require DevTools changes.

[elliette]

This was fixed in dart-lang/webdev#2047