Use builders to run the generator instead of just as a script.

build.yaml

@@ -0,0 +1,14 @@
+targets:
+  $default:
+    builders:
+      'environment_config:env_config_generator':
+        enabled: true
+
+
+builders:
+  env_config_generator:
+    import: 'package:environment_config/builder.dart'
+    builder_factories: ["generateConfig"]
+    build_extensions:
+      '.yaml': ['.dart']
+    auto_apply: dependents

example/.gitignore

@@ -0,0 +1,30 @@
+# Created by .ignore support plugin (hsz.mobi)
+### Dart template
+# See https://www.dartlang.org/guides/libraries/private-files
+
+# Files and directories created by pub
+.dart_tool/
+.packages
+build/
+# If you're building an application, you may want to check-in your pubspec.lock
+pubspec.lock
+
+# Directory created by dartdoc
+# If you don't generate documentation locally you can remove this line.
+doc/api/
+
+# Avoid committing generated Javascript files:
+*.dart.js
+*.info.json      # Produced by the --dump-info flag.
+*.js             # When generated by dart2js. Don't specify *.js if your
+                 # project includes source files written in JavaScript.
+*.js_
+*.js.deps
+*.js.map
+
+.flutter-plugins
+.flutter-plugins-dependencies
+
+!lib/generated
+lib/generated/**
+!**/.gitkeep

example/build.yaml

@@ -0,0 +1,6 @@
+targets:
+  $default:
+    builders:
+      'environment_config:env_config_generator':
+        options:
+          "--config-extension": "dev"

example/environment_config.yaml

@@ -0,0 +1,17 @@
+# Config example. Run `flutter pub run environment_config:generate --env=YOUR_VALUE` to see example
+environment_config:
+  path: generated/environment_config.dart
+  fields:
+    hello:
+
+  imports:
+    - dart:io
+
+  extensions:
+    dev:
+      fields:
+        hello:
+          default: 'Hello, Config!'
+
+      imports:
+        - dart:async

example/lib/example.dart

@@ -0,0 +1 @@
+export 'package:environment_config_example/generated/environment_config.dart';

example/main.dart

@@ -1,8 +1,5 @@
-/// 1. Install your project dependencies
-///
-/// 2. Run `flutter pub run environment_config:generate` with key and values specified
-/// in your YAML config
-///
-/// 3. Import generated file
+import 'package:environment_config_example/example.dart';
 
-import 'environment_config.dart';
+void main() {
+  print(EnvironmentConfig.hello);
+}

example/pubspec.yaml

@@ -0,0 +1,6 @@
+name: environment_config_example
+
+dev_dependencies:
+  build_runner: "^1.10.0"
+  environment_config:
+    path: ../

lib/builder.dart

@@ -0,0 +1,24 @@
+import 'dart:async';
+
+import 'package:build/build.dart';
+import 'package:environment_config/generator.dart' as gen;
+
+Builder generateConfig(BuilderOptions builderOptions) =>
+    _GenerateConfig(builderOptions);
+
+class _GenerateConfig extends Builder {
+  final List<String> arguments;
+
+  _GenerateConfig(BuilderOptions builderOptions)
+      : arguments = builderOptions.config.entries
+            .map((e) => e.value != null ? '${e.key}=${e.value}' : e.key)
+            .toList(growable: false);
+
+  @override
+  final buildExtensions = const {
+    '.yaml': ['.dart']
+  };
+
+  @override
+  Future<void> build(BuildStep buildStep) => gen.generateConfig(arguments);
+}

pubspec.lock

@@ -7,14 +7,14 @@ packages:
       name: _fe_analyzer_shared
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.1"
+    version: "7.0.0"
   analyzer:
     dependency: transitive
     description:
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.39.2+1"
+    version: "0.39.17"
   args:
     dependency: "direct main"
     description:
@@ -29,6 +29,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.4.1"
+  build:
+    dependency: "direct main"
+    description:
+      name: build
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.3.0"
   built_collection:
     dependency: transitive
     description:
@@ -50,6 +57,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.1.3"
+  cli_util:
+    dependency: transitive
+    description:
+      name: cli_util
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.2.0"
   code_builder:
     dependency: "direct main"
     description:
@@ -91,7 +105,7 @@ packages:
       name: dart_style
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.3"
+    version: "1.3.6"
   fixnum:
     dependency: transitive
     description:
@@ -120,6 +134,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.6.1+1"
+  logging:
+    dependency: transitive
+    description:
+      name: logging
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.11.4"
   matcher:
     dependency: transitive
     description:
@@ -183,6 +204,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.1.3"
+  source_gen:
+    dependency: "direct main"
+    description:
+      name: source_gen
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.9.5"
   source_span:
     dependency: transitive
     description:
@@ -233,4 +261,4 @@ packages:
     source: hosted
     version: "2.2.0"
 sdks:
-  dart: ">=2.3.0 <3.0.0"
+  dart: ">=2.7.0 <3.0.0"

pubspec.yaml

@@ -13,20 +13,5 @@ dependencies:
   code_builder: ">=3.0.0 <4.0.0"
   args: ">=1.0.0 <2.0.0"
   yaml: ">=2.0.0 <3.0.0"
-
-# Config example. Run `flutter pub run environment_config:generate --env=YOUR_VALUE` to see example
-environment_config:
-  fields:
-    env:
-
-  imports:
-    - some:package
-
-  extensions:
-    dev:
-      fields:
-        env:
-          default: some value
-
-      imports:
-        - other:package
+  build: ">=1.3.0"
+  source_gen: ">=0.9.5"