[google_maps_flutter_platform_interface] Convert PatternItem and Cap to typesafe structures. (#7703)

Convert `PatternItem` and `Cap` from JSON wrappers to typesafe classes.

flutter/flutter#155121

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] page, which explains my
responsibilities.
- [x] I read and followed the [relevant style guides] and ran the
auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages
repo does use `dart format`.)
- [ ] I signed the [CLA].
- [x] The title of the PR starts with the name of the package surrounded
by square brackets, e.g. `[shared_preferences]`
- [x] I [linked to at least one issue that this PR fixes] in the
description above.
- [x] I updated `pubspec.yaml` with an appropriate new version according
to the [pub versioning philosophy], or this PR is [exempt from version
changes].
- [x] I updated `CHANGELOG.md` to add a description of the change,
[following repository CHANGELOG style], or this PR is [exempt from
CHANGELOG changes].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/packages/blob/main/CONTRIBUTING.md
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md
[relevant style guides]:
https://github.com/flutter/packages/blob/main/CONTRIBUTING.md#style
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[linked to at least one issue that this PR fixes]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md#overview
[pub versioning philosophy]: https://dart.dev/tools/pub/versioning
[exempt from version changes]:
https://github.com/flutter/flutter/blob/master/docs/ecosystem/contributing/README.md#version
[following repository CHANGELOG style]:
https://github.com/flutter/flutter/blob/master/docs/ecosystem/contributing/README.md#changelog-style
[exempt from CHANGELOG changes]:
https://github.com/flutter/flutter/blob/master/docs/ecosystem/contributing/README.md#changelog
[test-exempt]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md#tests

Author: yaakovschectman

packages/google_maps_flutter/google_maps_flutter_platform_interface/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 2.9.4
+
+* Converts `PatternItem` to typesafe structure.
+* Converts `Cap` to typesafe structure.
+
 ## 2.9.3
 
 * Corrects an incorrect comment in polyline.dart file.

packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/cap.dart

@@ -6,27 +6,56 @@ import 'package:flutter/foundation.dart' show immutable;
 
 import 'types.dart';
 
+/// Enumeration of possible types of caps.
+enum CapType {
+  /// Cap that is squared off exactly at the start or end vertex of a [Polyline]
+  /// with solid stroke pattern, equivalent to having no additional cap beyond
+  /// the start or end vertex.
+  butt,
+
+  /// Cap that is a semicircle with radius equal to half the stroke width,
+  /// centered at the start or end vertex of a [Polyline] with solid stroke
+  /// pattern.
+  round,
+
+  /// Cap that is squared off after extending half the stroke width beyond the
+  /// start or end vertex of a [Polyline] with solid stroke pattern.
+  square,
+
+  /// CustomCap with a bitmap overlay centered at the start or
+  /// end vertex of a [Polyline], orientated according to the direction of the line's
+  /// first or last edge and scaled with respect to the line's stroke width.
+  custom,
+}
+
+String _capTypeToJson(CapType capType) => switch (capType) {
+      CapType.butt => 'buttCap',
+      CapType.round => 'roundCap',
+      CapType.square => 'squareCap',
+      CapType.custom => 'customCap',
+    };
+
 /// Cap that can be applied at the start or end vertex of a [Polyline].
 @immutable
 class Cap {
-  const Cap._(this._json);
+  const Cap._(this.type);
 
   /// Cap that is squared off exactly at the start or end vertex of a [Polyline]
   /// with solid stroke pattern, equivalent to having no additional cap beyond
   /// the start or end vertex.
   ///
   /// This is the default cap type at start and end vertices of Polylines with
   /// solid stroke pattern.
-  static const Cap buttCap = Cap._(<Object>['buttCap']);
+  static const Cap buttCap = Cap._(CapType.butt);
 
   /// Cap that is a semicircle with radius equal to half the stroke width,
   /// centered at the start or end vertex of a [Polyline] with solid stroke
   /// pattern.
-  static const Cap roundCap = Cap._(<Object>['roundCap']);
+  static const Cap roundCap = Cap._(CapType.round);
 
   /// Cap that is squared off after extending half the stroke width beyond the
   /// start or end vertex of a [Polyline] with solid stroke pattern.
-  static const Cap squareCap = Cap._(<Object>['squareCap']);
+  static const Cap squareCap = Cap._(CapType.square);
 
   /// Constructs a new CustomCap with a bitmap overlay centered at the start or
   /// end vertex of a [Polyline], orientated according to the direction of the line's
@@ -44,11 +73,37 @@ class Cap {
     double refWidth = 10,
   }) {
     assert(refWidth > 0.0);
-    return Cap._(<Object>['customCap', bitmapDescriptor.toJson(), refWidth]);
+    return CustomCap(bitmapDescriptor, refWidth: refWidth);
   }
 
-  final Object _json;
+  /// The type of rendering used for the cap at a start or end vertex of a
+  /// [Polyline].
+  final CapType type;
 
   /// Converts this object to something serializable in JSON.
-  Object toJson() => _json;
+  Object toJson() => <Object>[_capTypeToJson(type)];
+}
+
+/// CustomCap with a bitmap overlay centered at the start or
+/// end vertex of a [Polyline], orientated according to the direction of the line's
+/// first or last edge and scaled with respect to the line's stroke width.
+class CustomCap extends Cap {
+  /// [bitmapDescriptor] must not be null.
+  ///
+  /// [refWidth] is the reference stroke width (in pixels) - the stroke width for which
+  /// the cap bitmap at its native dimension is designed. Must be positive. Default value
+  /// is 10 pixels.
+  const CustomCap(this.bitmapDescriptor, {this.refWidth = 10})
+      : super._(CapType.custom);
+
+  /// Bitmap overlay centered at the start or end vertex of a [Polyline].
+  final BitmapDescriptor bitmapDescriptor;
+
+  /// Reference stroke width in screen pixels. See
+  /// https://developers.google.com/maps/documentation/android-sdk/reference/com/google/android/libraries/maps/model/CustomCap#refWidth
+  final double refWidth;
+
+  @override
+  Object toJson() =>
+      <Object>[_capTypeToJson(type), bitmapDescriptor.toJson(), refWidth];
 }

packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/pattern_item.dart

@@ -4,32 +4,73 @@
 
 import 'package:flutter/foundation.dart' show immutable;
 
+/// Enumeration of types of pattern items.
+enum PatternItemType {
+  /// A dot used in the stroke pattern for a [Polyline].
+  dot,
+
+  /// A dash used in the stroke pattern for a [Polyline].
+  dash,
+
+  /// A gap used in the stroke pattern for a [Polyline].
+  gap,
+}
+
+String _patternItemTypeToJson(PatternItemType itemType) => switch (itemType) {
+      PatternItemType.dot => 'dot',
+      PatternItemType.dash => 'dash',
+      PatternItemType.gap => 'gap',
+    };
+
 /// Item used in the stroke pattern for a Polyline.
 @immutable
 class PatternItem {
-  const PatternItem._(this._json);
+  const PatternItem._(this.type);
 
   /// A dot used in the stroke pattern for a [Polyline].
-  static const PatternItem dot = PatternItem._(<Object>['dot']);
+  static const PatternItem dot = PatternItem._(PatternItemType.dot);
 
   /// A dash used in the stroke pattern for a [Polyline].
   ///
   /// [length] has to be non-negative.
   static PatternItem dash(double length) {
     assert(length >= 0.0);
-    return PatternItem._(<Object>['dash', length]);
+    return VariableLengthPatternItem._(
+        patternItemType: PatternItemType.dash, length: length);
   }
 
   /// A gap used in the stroke pattern for a [Polyline].
   ///
   /// [length] has to be non-negative.
   static PatternItem gap(double length) {
     assert(length >= 0.0);
-    return PatternItem._(<Object>['gap', length]);
+    return VariableLengthPatternItem._(
+        patternItemType: PatternItemType.gap, length: length);
   }
 
-  final Object _json;
+  /// The type of rendering used for an item in a pattern.
+  final PatternItemType type;
+
+  /// Converts this object to something serializable in JSON.
+  Object toJson() => <Object>[
+        _patternItemTypeToJson(type),
+      ];
+}
+
+/// A pattern item with a length, i.e. a dash or gap.
+@immutable
+class VariableLengthPatternItem extends PatternItem {
+  const VariableLengthPatternItem._(
+      {required PatternItemType patternItemType, required this.length})
+      : super._(patternItemType);
+
+  /// The length in pixels of a dash or gap.
+  final double length;
 
   /// Converts this object to something serializable in JSON.
-  Object toJson() => _json;
+  @override
+  Object toJson() => <Object>[
+        _patternItemTypeToJson(type),
+        length,
+      ];
 }

packages/google_maps_flutter/google_maps_flutter_platform_interface/pubspec.yaml

@@ -4,7 +4,7 @@ repository: https://github.com/flutter/packages/tree/main/packages/google_maps_f
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+maps%22
 # NOTE: We strongly prefer non-breaking changes, even at the expense of a
 # less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
-version: 2.9.3
+version: 2.9.4
 
 environment:
   sdk: ^3.3.0

packages/google_maps_flutter/google_maps_flutter_platform_interface/test/types/cap_test.dart

@@ -0,0 +1,48 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:google_maps_flutter_platform_interface/google_maps_flutter_platform_interface.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  test('buttCap', () {
+    const Cap cap = Cap.buttCap;
+    expect(cap.toJson(), equals(<Object>['buttCap']));
+  });
+
+  test('roundCap', () {
+    const Cap cap = Cap.roundCap;
+    expect(cap.toJson(), equals(<Object>['roundCap']));
+  });
+
+  test('squareCap', () {
+    const Cap cap = Cap.squareCap;
+    expect(cap.toJson(), equals(<Object>['squareCap']));
+  });
+
+  test('customCap', () {
+    final Cap cap = Cap.customCapFromBitmap(BitmapDescriptor.defaultMarker);
+    expect(
+        cap.toJson(),
+        equals(<Object>[
+          'customCap',
+          <Object>['defaultMarker'],
+          10.0
+        ]));
+  });
+
+  test('customCapWithWidth', () {
+    final Cap cap =
+        Cap.customCapFromBitmap(BitmapDescriptor.defaultMarker, refWidth: 100);
+    expect(
+        cap.toJson(),
+        equals(<Object>[
+          'customCap',
+          <Object>['defaultMarker'],
+          100.0
+        ]));
+  });
+}

packages/google_maps_flutter/google_maps_flutter_platform_interface/test/types/pattern_item_test.dart

@@ -0,0 +1,27 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:google_maps_flutter_platform_interface/google_maps_flutter_platform_interface.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  test('dot', () {
+    const PatternItem item = PatternItem.dot;
+    expect(item.toJson(), equals(<Object>['dot']));
+  });
+
+  test('dash', () {
+    final PatternItem item = PatternItem.dash(10.0);
+    expect(item, isA<VariableLengthPatternItem>());
+    expect(item.toJson(), equals(<Object>['dash', 10.0]));
+  });
+
+  test('gap', () {
+    final PatternItem item = PatternItem.gap(20.0);
+    expect(item, isA<VariableLengthPatternItem>());
+    expect(item.toJson(), equals(<Object>['gap', 20.0]));
+  });
+}