I can reproduce this bug easily.
webdev says the following things.
[INFO] ------------------------------------------------------------------------
[INFO] Starting Build
[INFO] Updating asset graph completed, took 5ms
[INFO] Running build completed, took 189ms
[INFO] Caching finalized dependency graph completed, took 140ms
[SEVERE] build_web_compilers|ddc on web/main.module (cached):
Error compiling dartdevc module:angular_tour_of_heroes|web/main.ddc.js
[error] Target of URI doesn't exist: 'package:angular_forms/angular_forms.dart'. (package:angular_tour_of_heroes/app_component.dart, line 2, col 8)
[error] Arguments of a constant creation must be constant expressions. (package:angular_tour_of_heroes/app_component.dart, line 11, col 32)
[error] The values in a const list literal must be constants. (package:angular_tour_of_heroes/app_component.dart, line 11, col 32)
[error] Undefined name 'formDirectives'. (package:angular_tour_of_heroes/app_component.dart, line 11, col 32)
[error] Target of URI doesn't exist: 'package:angular_forms/angular_forms.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 9, col 8)
[error] Target of URI hasn't been generated: 'package:angular/angular.template.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 13,col 8)
[error] Target of URI hasn't been generated: 'package:angular_forms/angular_forms.template.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 14, col 8)
[error] Target of URI doesn't exist: 'package:angular_tour_of_heroes/app_component.css.shim.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 17, col 8)
[error] Target of URI doesn't exist: 'package:angular_forms/src/directives/default_value_accessor.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 32, col 8)
[error] Target of URI doesn't exist: 'package:angular_forms/src/directives/control_value_accessor.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 33, col 8)
[error] Target of URI doesn't exist: 'package:angular_forms/src/directives/ng_model.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 34, col 8)
[error] Target of URI doesn't exist: 'package:angular_forms/src/directives/control_value_accessor.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 36, col 8)
[error] Target of URI doesn't exist: 'package:angular_forms/src/directives/ng_control.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 37, col 8)
Please fix all errors before compiling (warnings are okay).
}
[SEVERE] build_web_compilers|ddc on test/app_test.module (cached):
Error compiling dartdevc module:angular_tour_of_heroes|test/app_test.ddc.js
[error] Target of URI hasn't been generated: 'package:angular/angular.template.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 13,col 8)
[error] Target of URI hasn't been generated: 'package:angular_forms/angular_forms.template.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 14, col 8)
[error] Target of URI doesn't exist: 'package:angular_tour_of_heroes/app_component.css.shim.dart'. (package:angular_tour_of_heroes/app_component.template.dart, line 17, col 8)
Please fix all errors before compiling (warnings are okay).
}
[SEVERE] Failed after 340ms
Note that I can build the same code successful if I delete .dart_tool and build it again.