[cfe] process .dart_tool/build/generated folder

[asashour]

This is the CFE part of #51087, to support build

The below cases don't find the part, on running main(), taken from the sample package:

// example/foo.dart
part 'foo.g.dart';

void main() {
  print(_abc);
}

// .dart_tool/build/generated/<project_name>/example/foo.g.dart
part of 'foo.dart';

var _abc = 'hello';

error

example/foo.dart:1:6: Error: Error when reading 'example/foo.g.dart': The system cannot find the file specified.

part 'foo.g.dart';
     ^
example/foo.dart:1:6: Error: Can't use 'example/foo.g.dart' as a part, because it has no 'part of' declaration.
part 'foo.g.dart';
     ^
example/foo.dart:4:9: Error: Undefined name '_abc'.
  print(_abc);
        ^^^^

---

Having library also gives similar error.

// example/foo_lib.dart
library foo_library;

part 'foo_lib.g.dart';

void main() {
  print(_abc);
}

// .dart_tool/build/generated/example/foo_lib.g.dart
part of 'foo_lib.dart';

var _abc = 'hello';

/cc @greglittlefield-wf

[johnniwinther]

@asashour @jakemac53 Where is it specified that we are supposed to handle this?

[jakemac53]

@johnniwinther I am not aware of any plan to support this in the CFE (if we were going to do that I would probably try and do it through some feature in the package_config.json so it was more general).

[jakemac53]

Note that you should be able to use dart run build_runner run <script> instead of dart <script> and that should work for build to cache files.

[asashour]

should be able to use dart run build_runner run <script> instead

You are right, sorry that I didn't test it this way.

Apologies for the disturbance.