Add support for external keyword on fields (#422)

Add `external` field to `FieldBuilder` and emit the keyword in the
visitor.

Author: Snehal-Singh174

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 4.6.0-wip
 
 * Add support for named arguments in `enum` classes
+* Add support for external keyword on fields.
 
 ## 4.5.0
 

lib/src/emitter.dart

@@ -386,6 +386,9 @@ class DartEmitter extends Object
     if (spec.late && _useNullSafetySyntax) {
       output.write('late ');
     }
+    if (spec.external) {
+      output.write('external ');
+    }
     switch (spec.modifier) {
       case FieldModifier.var$:
         if (spec.type == null) {

lib/src/specs/field.dart

@@ -41,6 +41,9 @@ abstract class Field extends Object
   /// Whether this field should be prefixed with `late`.
   bool get late;
 
+  /// Whether the field should be prefixed with `external`.
+  bool get external;
+
   /// Name of the field.
   String get name;
 
@@ -86,6 +89,9 @@ abstract class FieldBuilder extends Object
   /// Whether this field should be prefixed with `late`.
   bool late = false;
 
+  /// Whether the field should be prefixed with `external`.
+  bool external = false;
+
   /// Name of the field.
   String? name;
 

lib/src/specs/field.g.dart

@@ -96,4 +96,18 @@ void main() {
       '''),
     );
   });
+
+  test('should create a external field', () {
+    expect(
+      Field((b) => b
+        ..name = 'value'
+        ..external = true
+        ..type = refer('double')
+        ..annotations.addAll([refer('Float').call([])])),
+      equalsDart(r'''
+        @Float()
+        external double value;
+      '''),
+    );
+  });
 }