Enable lint unnecessary_statements. Codebase is compliant. (#20099)

* Enable lint unnecessary_statements. Codebase is compliant.

* Fix mega_gallery generated code to not generate unecessary statements

* Fix lint in mega gallery changes

* Enable unnecessary_statements for users as well as repo.

analysis_options.yaml

@@ -150,7 +150,7 @@ linter:
     - unnecessary_null_in_if_null_operators
     - unnecessary_overrides
     - unnecessary_parenthesis
-    # - unnecessary_statements # not yet tested
+    - unnecessary_statements
     - unnecessary_this
     - unrelated_type_equality_checks
     - use_rethrow_when_possible

dev/tools/mega_gallery.dart

@@ -92,11 +92,10 @@ void main(List<String> args) {
 // TODO(devoncarew): Create an entry-point that builds a UI with all `n` copies.
 void _createEntry(File mainFile, int copies) {
   final StringBuffer imports = new StringBuffer();
-  final StringBuffer importRefs = new StringBuffer();
 
   for (int i = 1; i < copies; i++) {
+    imports.writeln('// ignore: unused_import');
     imports.writeln("import 'gallery_$i/main.dart' as main_$i;");
-    importRefs.writeln('  main_$i.main;');
   }
 
   final String contents = '''
@@ -110,9 +109,6 @@ import 'gallery/app.dart';
 ${imports.toString().trim()}
 
 void main() {
-  // Make sure the imports are not marked as unused.
-  ${importRefs.toString().trim()}
-
   runApp(const GalleryApp());
 }
 ''';

packages/flutter/lib/analysis_options_user.yaml

@@ -81,5 +81,6 @@ linter:
     # - unawaited_futures
     - unnecessary_brace_in_string_interps
     - unnecessary_getters_setters
+    - unnecessary_statements
     - unrelated_type_equality_checks
     - valid_regexps