🧹 Remove dead code in _enumFieldsMap (#194)

Refactor `_enumFieldsMap` and `enumValueMapFromType` in `build_cli/lib/src/enum_helpers.dart` to eliminate an unreachable `return null` and redundant null checks.

- Changed `_enumFieldsMap` to return `Map<FieldElement, String>` (non-nullable) and use an explicit cast to `EnumElement` for the target type's element, as it's only called for enums.
- Updated `enumValueMapFromType` to return `String` (non-nullable) and removed the now unnecessary null check.
- Cleaned up the call site in `build_cli/lib/src/build_cli_generator.dart` to remove a redundant bang operator.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: kevmoo

build_cli/lib/src/build_cli_generator.dart

@@ -153,9 +153,12 @@ ${element.name} $resultParserName(ArgResults result) =>''');
         'ArgParser $populateParserName(ArgParser parser$overrideArgs) => '
         'parser',
       );
+    final enumTypes = <DartType>{};
     for (var f in fields.values) {
       if (f.type.isEnum) {
-        yield enumValueMapFromType(f.type)!;
+        if (enumTypes.add(f.type)) {
+          yield enumValueMapFromType(f.type);
+        }
       }
 
       _parserOptionFor(buffer, f);

build_cli/lib/src/enum_helpers.dart

@@ -4,13 +4,9 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:source_helper/source_helper.dart';
 
-String? enumValueMapFromType(DartType targetType) {
+String enumValueMapFromType(DartType targetType) {
   final enumMap = _enumFieldsMap(targetType);
 
-  if (enumMap == null) {
-    return null;
-  }
-
   final items = enumMap.entries.map(
     (e) =>
         '  ${targetType.element!.name}.${e.key.name}: '
@@ -24,16 +20,9 @@ String? enumValueMapFromType(DartType targetType) {
 String enumConstMapName(DartType targetType) =>
     '_\$${targetType.element!.name}EnumMapBuildCli';
 
-/// If [targetType] is not an enum, `null` is returned.
-Map<FieldElement, String>? _enumFieldsMap(DartType targetType) {
-  if (targetType is InterfaceType && targetType.element is EnumElement) {
-    return Map<FieldElement, String>.fromEntries(
-      targetType.element.fields
-          .where((p) => p.isOriginDeclaration)
-          .map((p) => MapEntry(p, p.name!)),
-    );
-  }
-  return null;
+Map<FieldElement, String> _enumFieldsMap(DartType targetType) {
+  final element = targetType.element as EnumElement;
+  return {for (final p in element.constants) p: p.name!};
 }
 
 const enumValueHelperFunctionName = r'_$enumValueHelper';