How to import generated source in dart2 using build_runner?

Question

I want to create a Builder that would create Env class on the fly. That class should be available for import anywhere in my project. It is as container for environment constants defined in build.yml

Builder itself works fine, it generates desired output, however when I run

pub run build_runner build

build fails with following message

[SEVERE] build_web_compilers:entrypoint on web/main.dart: Unable to find modules for some sources, this is usually the result of either a bad import, a missing dependency in a package (or possibly a dev_dependency needs to move to a real dependency), or a build failure (if importing a generated file).

Please check the following imports:

import '../.dart_tool/build/generated/buildertest/lib/environment.g.dart'; from buildertest|web/main.dart at 2:1

[INFO] Running build completed, took 4.1s [INFO] Caching finalized dependency graph completed, took 450ms [SEVERE] Failed after 4.6s

import by itself is ok, as it works fine when I run following snippet

import '../.dart_tool/build/generated/buildertest/lib/environment.g.dart';


void main() {

  print("Name:${Environment.name}");
  print("Endpoint:${Environment.endpoint}");
}

with

dart web/main.dart

What should be done to make this import valid??

Here is build.yaml

targets:
  $default:
    builders:
      angular_components|scss_builder:
        enabled: True
      env|builder:
        options:
          name: "default"
          endpoint: "http://example.org"
        enabled: true

builders:
  env|builder:
    import: "env/EnvBuilder.dart"
    builder_factories: ["builderFactory"]
    is_optional: false
    build_extensions:
      "$lib$": ["environment.g.dart"]
    auto_apply: root_package
    runs_before: ["build_test:test_bootstrap","build_modules:module_library","build_modules:dartdevc","build_web_compilers:ddc","build_modules:vm","build_modules:dart2js","build_web_compilers:entrypoint"]