[go_router] Add encoder,decoder and compare parameters to TypedQueryParameter

packages/go_router/lib/src/route_data.dart

@@ -620,11 +620,42 @@ class NoOpPage extends Page<void> {
       throw UnsupportedError('Should never be called');
 }
 
+/// Signature of custom query parameter encoding.
+///
+/// The function takes a parameter value of type `T` and returns a string
+/// representation suitable for use in a URI. The returned string is escaped to
+/// be URL-safe.
+///
+/// For example, a parameter value of `'field with space'` will generate a query
+/// parameter value of `'field+with+space'`.
+typedef QueryParameterEncoder<T> = String Function(T value);
+
+/// Signature for custom query parameter decoding functions.
+///
+/// Converts an encoded string from the URI into a parameter value of type `T`.
+///
+/// The [value] parameter contains the encoded string from the URI. if the
+/// parameter is absent from the URI.
+typedef QueryParameterDecoder<T> = T Function(String value);
+
 /// Annotation to override the URI name for a route parameter.
+@optionalTypeArgs
 @Target({TargetKind.parameter})
-class TypedQueryParameter {
+class TypedQueryParameter<T> {
   /// Annotation to override the URI name for a route parameter.
-  const TypedQueryParameter({this.name});
+  const TypedQueryParameter({
+    this.name,
+    this.encoder,
+    this.decoder,
+    this.compare,
+  }) : assert(
+         (encoder == null) == (decoder == null),
+         'encoder and decoder must both be provided together',
+       ),
+       assert(
+         compare == null || encoder != null,
+         'compare function requires an encoder to be provided',
+       );
 
   /// The name of the parameter in the URI.
   ///
@@ -647,4 +678,26 @@ class TypedQueryParameter {
   /// It is escaped to be URL-safe. For example `'field with space'` will
   /// generate a query parameter named `'field+with+space'`.
   final String? name;
+
+  /// A function that converts a parameter value to a string for use in the URI.
+  ///
+  /// See [QueryParameterEncoder] for details.
+  final QueryParameterEncoder<T>? encoder;
+
+  /// A function that converts a string from the URI to a parameter value.
+  ///
+  /// See [QueryParameterDecoder] for details.
+  final QueryParameterDecoder<T>? decoder;
+
+  /// A function that determines if two parameter values differ.
+  ///
+  /// Returns `true` when the values differ and `false` when they match.
+  ///
+  /// Used to decide whether to include a parameter in the URI when a default
+  /// value exists. If the parameter equals its default value, it is omitted
+  /// from the URI; otherwise, it is included.
+  ///
+  /// This should be provided if the parameter has a default value and is is not
+  /// a primitive type.
+  final bool Function(T, T)? compare;
 }

packages/go_router/pending_changelogs/support_custom_types.yaml

@@ -0,0 +1,3 @@
+changelog: |
+  - Adds `encoder`, `decoder` and `compare` parameters to `TypedQueryParameter` annotation for custom encoding, decoding and comparison of query parameters in `TypedGoRoute` constructors.
+version: minor

packages/go_router/test/route_data_test.dart

@@ -259,6 +259,10 @@ final List<GoRoute> _relativeRoutes = <GoRoute>[
   ),
 ];
 
+String _coder(String? value) => '';
+
+bool _compare(String a, String b) => true;
+
 void main() {
   group('GoRouteData', () {
     testWidgets('It should build the page from the overridden build method', (
@@ -796,8 +800,23 @@ void main() {
   });
 
   test('TypedQueryParameter stores the name', () {
-    const parameter = TypedQueryParameter(name: 'customName');
+    const TypedQueryParameter<dynamic> parameter = TypedQueryParameter(
+      name: 'customName',
+    );
 
     expect(parameter.name, 'customName');
   });
+
+  test('TypedQueryParameter stores the encoder, decoder and compare', () {
+    const TypedQueryParameter<String> parameter = TypedQueryParameter(
+      name: 'customName',
+      encoder: _coder,
+      decoder: _coder,
+      compare: _compare,
+    );
+
+    expect(parameter.encoder, _coder);
+    expect(parameter.decoder, _coder);
+    expect(parameter.compare, _compare);
+  });
 }