♻️ Fighting with the Dart formatter (#697)

## What does this change?

Generated files are being formatted based on confusing conditions. The
PR refactored how we construct the Dart formatter in a more elegant
manner.

1. The formatter will try to find a valid Dart SDK constraint from
`pubspec.yaml` / `pubspec.lock`. Otherwise, it will fall back to using
the current Dart SDK version as the constraint. The behavior is like:
1. When the user is using Dart SDK 3.8.0, `pubspec.yaml` has `^3.4.0`,
and `pubspec.lock` resolves `^3.7.0`, the formatter will format like
3.4.0.
2. When the runner is being used for testing purposes, which the
specified pubspec file does not contain `environment - sdk` (and likely
does not have a `pubspec.lock`), the formatter will format based on the
current Dart SDK version.
2. The formatter will try to find a valid page width from
`analysis_options.yaml - formatter - page_width` / `pubspec.yaml -
flutter_gen - line_length`, then prepend the format width header to make
all format tools respect the config.

- Fixes
#685 (comment)
- Fixes
#659 (comment)
- Fixes #620

## Type of change

- [x] New feature (non-breaking change which adds functionality)

Author: AlexV525

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -52,7 +52,7 @@ body:
 
         flutter_gen:
           output: lib/gen/
-          line_length: 80
+        #  line_length: 80
 
           integrations:
             flutter_svg: true

.idea/runConfigurations/build_runner_build_example.xml

@@ -143,7 +143,7 @@ Default configuration can be found [here](https://github.com/FlutterGen/flutter_
 
 flutter_gen:
   output: lib/gen/ # Optional (default: lib/gen/)
-  line_length: 80 # Optional (default: 80)
+  # line_length: 80 # Optional
 
   # Optional
   integrations:
@@ -184,7 +184,7 @@ targets:
       flutter_gen_runner: # or flutter_gen
         options: 
           output: lib/build_gen/ # Optional (default: lib/gen/)
-          line_length: 120 # Optional (default: 80)
+          line_length: 120 # Optional
 ```
 
 ## Available Parsers

.idea/runConfigurations/build_runner_build_example_resources.xml

@@ -1,11 +1,13 @@
+// dart format width=80
+
 /// GENERATED CODE - DO NOT MODIFY BY HAND
 /// *****************************************************
 ///  FlutterGen
 /// *****************************************************
 
 // coverage:ignore-file
 // ignore_for_file: type=lint
-// ignore_for_file: directives_ordering,unnecessary_import,implicit_dynamic_list_literal,deprecated_member_use
+// ignore_for_file: deprecated_member_use,directives_ordering,implicit_dynamic_list_literal,unnecessary_import
 
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';

README.md

@@ -1,11 +1,12 @@
+// dart format width=80
 /// GENERATED CODE - DO NOT MODIFY BY HAND
 /// *****************************************************
 ///  FlutterGen
 /// *****************************************************
 
 // coverage:ignore-file
 // ignore_for_file: type=lint
-// ignore_for_file: directives_ordering,unnecessary_import,implicit_dynamic_list_literal,deprecated_member_use
+// ignore_for_file: deprecated_member_use,directives_ordering,implicit_dynamic_list_literal,unnecessary_import
 
 import 'package:flutter/painting.dart';
 import 'package:flutter/material.dart';

examples/example/lib/gen/assets.gen.dart

@@ -1,11 +1,12 @@
+// dart format width=80
 /// GENERATED CODE - DO NOT MODIFY BY HAND
 /// *****************************************************
 ///  FlutterGen
 /// *****************************************************
 
 // coverage:ignore-file
 // ignore_for_file: type=lint
-// ignore_for_file: directives_ordering,unnecessary_import,implicit_dynamic_list_literal,deprecated_member_use
+// ignore_for_file: deprecated_member_use,directives_ordering,implicit_dynamic_list_literal,unnecessary_import
 
 class MyFontFamily {
   MyFontFamily._();

examples/example/lib/gen/colors.gen.dart

@@ -14,20 +14,21 @@ dependencies:
 
   flutter_svg: ^2.0.0
   lottie: ^3.0.0
-  rive: ^0.11.0
+  rive: ^0.13.20
 
 dev_dependencies:
+  lints: any
   flutter_test:
     sdk: flutter
+
   flutter_gen_runner:
     path: ../../packages/runner
 
-  lints: ^2.0.0
   build_runner: ^2.0.0
 
 flutter_gen:
   output: lib/gen/ # Optional (default: lib/gen/)
-  line_length: 80 # Optional (default: 80)
+#  line_length: 80 # Optional
 
   integrations:
     flutter_svg: true

examples/example/lib/gen/fonts.gen.dart

@@ -1,11 +1,13 @@
+// dart format width=80
+
 /// GENERATED CODE - DO NOT MODIFY BY HAND
 /// *****************************************************
 ///  FlutterGen
 /// *****************************************************
 
 // coverage:ignore-file
 // ignore_for_file: type=lint
-// ignore_for_file: directives_ordering,unnecessary_import,implicit_dynamic_list_literal,deprecated_member_use
+// ignore_for_file: deprecated_member_use,directives_ordering,implicit_dynamic_list_literal,unnecessary_import
 
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';

examples/example/pubspec.yaml

@@ -1,11 +1,12 @@
+// dart format width=80
 /// GENERATED CODE - DO NOT MODIFY BY HAND
 /// *****************************************************
 ///  FlutterGen
 /// *****************************************************
 
 // coverage:ignore-file
 // ignore_for_file: type=lint
-// ignore_for_file: directives_ordering,unnecessary_import,implicit_dynamic_list_literal,deprecated_member_use
+// ignore_for_file: deprecated_member_use,directives_ordering,implicit_dynamic_list_literal,unnecessary_import
 
 import 'package:flutter/painting.dart';
 import 'package:flutter/material.dart';