Add support for an ignore_for_file option to combining_builder.

Related to #370
Closes google/json_serializable.dart#604
Fixes google/json_serializable.dart#557

example_usage/build.yaml

@@ -14,3 +14,10 @@ targets:
       source_gen_example|property_product:
         generate_for:
           - lib/*.dart
+      # The end-user of a builder which applies "source_gen|combining_builder"
+      # may configure the builder to ignore specific lints for their project
+      source_gen|combining_builder:
+        options:
+          ignore_for_file:
+          - lint_a
+          - lint_b

source_gen/CHANGELOG.md

@@ -1,5 +1,7 @@
 ## 0.9.5-dev
 
+* Add support for an `ignore_for_file` option to `combining_builder`.
+
 * Expand documentation for `GeneratorForAnnotation` to make it clear that it
   only targets elements at the top level of a library.
 

source_gen/README.md

@@ -93,6 +93,30 @@ builders:
     applies_builders: ["source_gen|combining_builder"]
 ```
 
+### Configuring `combining_builder` `ignore_for_file`
+
+Sometimes generated code does not support all of the
+[lints](https://dart-lang.github.io/linter/) specified in the target package.
+When using a `Builder` based on `package:source_gen` which applies
+`combining_builder`, set the `ignore_for_file` option to a list of lints you
+wish to be ignored in all generated libraries.
+
+_Example `build.yaml` configuration:_
+
+```yaml
+targets:
+  $default":
+    builders:
+      source_gen|combining_builder:
+        options:
+          ignore_for_file:
+          - lint_alpha
+          - lint_beta
+```
+
+If you provide a builder that uses `SharedPartBuilder` and `combining_builder`,
+you should document this feature for your users.
+
 ## FAQ
 
 ### What is the difference between `source_gen` and [build][]?

source_gen/lib/builder.dart

@@ -27,8 +27,15 @@ const _partFiles = '.g.part';
 Builder combiningBuilder([BuilderOptions options]) {
   final optionsMap = Map<String, dynamic>.from(options?.config ?? {});
 
+  final includePartName = optionsMap.remove('include_part_name') as bool;
+  final ignoreForFile = Set<String>.from(
+    optionsMap.remove('ignore_for_file') as List ?? <String>[],
+  );
+
   final builder = CombiningBuilder(
-      includePartName: optionsMap.remove('include_part_name') as bool);
+    includePartName: includePartName,
+    ignoreForFile: ignoreForFile,
+  );
 
   if (optionsMap.isNotEmpty) {
     if (log == null) {
@@ -49,6 +56,8 @@ PostProcessBuilder partCleanup(BuilderOptions options) =>
 class CombiningBuilder implements Builder {
   final bool _includePartName;
 
+  final Set<String> _ignoreForFile;
+
   @override
   Map<String, List<String>> get buildExtensions => const {
         '.dart': [_outputExtensions]
@@ -59,8 +68,11 @@ class CombiningBuilder implements Builder {
   /// If [includePartName] is `true`, the name of each source part file
   /// is output as a comment before its content. This can be useful when
   /// debugging build issues.
-  const CombiningBuilder({bool includePartName = false})
-      : _includePartName = includePartName ?? false;
+  const CombiningBuilder({
+    bool includePartName = false,
+    Set<String> ignoreForFile,
+  })  : _includePartName = includePartName ?? false,
+        _ignoreForFile = ignoreForFile ?? const <String>{};
 
   @override
   Future build(BuildStep buildStep) async {
@@ -100,9 +112,13 @@ class CombiningBuilder implements Builder {
     if (assets.isEmpty) return;
     final partOf =
         nameOfPartial(await buildStep.inputLibrary, buildStep.inputId);
+
+    final ignoreForFile = _ignoreForFile.isEmpty
+        ? ''
+        : '\n// ignore_for_file: ${_ignoreForFile.join(', ')}\n';
     final output = '''
 $defaultFileHeader
-
+$ignoreForFile
 part of $partOf;
 
 $assets

source_gen/test/builder_test.dart

@@ -388,6 +388,33 @@ void main() {
             '// Part: a.only_whitespace.g.part\n\n')),
       });
     });
+
+    test('includes ignore for file if enabled', () async {
+      await testBuilder(
+        const CombiningBuilder(ignoreForFile: {
+          'lines_longer_than_80_chars',
+          'prefer_expression_function_bodies',
+        }),
+        {
+          '$_pkgName|lib/a.dart': 'library a; part "a.g.dart";',
+          '$_pkgName|lib/a.foo.g.part': '\n\nfoo generated content\n',
+          '$_pkgName|lib/a.only_whitespace.g.part': '\n\n\t  \n \n',
+          '$_pkgName|lib/a.bar.g.part': '\nbar generated content',
+        },
+        generateFor: {'$_pkgName|lib/a.dart'},
+        outputs: {
+          '$_pkgName|lib/a.g.dart': decodedMatches(endsWith(r'''
+// ignore_for_file: lines_longer_than_80_chars, prefer_expression_function_bodies
+
+part of a;
+
+bar generated content
+
+foo generated content
+''')),
+        },
+      );
+    });
   });
 
   test('can skip formatting with a trivial lambda', () async {