Deprecate describeEnum + type stricter EnumProperty (#9003)

Sequel to #8571 and
flutter/flutter#125016. This is super small, but
broke a test that copied a Flutter file (and was not modified when
Flutter got updated).

---------

Co-authored-by: Shams Zakhour (ignore Sfshaza) <[email protected]>

Author: bernaferrari

src/release/breaking-changes/describe-enum.md

@@ -1,40 +1,54 @@
 ---
-title: Migration guide for describeEnum
+title: Migration guide for describeEnum and EnumProperty
 description: Removal of describeEnum and how to migrate
 ---
 
 ## Summary
 
-The global method `describeEnum` has been deprecated. Existing uses
+The global method `describeEnum` has been deprecated. Previous uses
 of `describeEnum(Enum.something)` should use
 `Enum.something.name` instead.
 
+The class EnumProperty was modified to extend `<T extends Enum?>` instead of `<T>`. Existing uses of `EnumProperty<NotAnEnum>` should use `DiagnosticsProperty<NotAnEnum>` instead.
+
 ## Context
 
-Dart 2.17 introduced enhanced enums. With them, Enum became a type
-and all enums got a `name` getter, which made `describeEnum` redundant.
+Dart 2.17 introduced [enhanced enums][], which added `Enum` as a type.
+As a result, all enums got a `name` getter, which made `describeEnum`
+redundant. Before that, enum classes were often analyzed using an
+`EnumProperty`.
 
 The `describeEnum` method was used to convert an enum value to a string,
 since `Enum.something.toString()` would produce `Enum.something` instead
 of `something`, which a lot of users wanted. Now, the `name` getter does this.
 
+The `describeEnum` function is being deprecated, so the `EnumProperty` class is updated to only accept `Enum` objects.
+
 ## Description of change
 
 Remove `describeEnum`.
 
 - Replace `describeEnum(Enum.something)` with `Enum.something.name`.
 
+The `EnumProperty` now expects null or an `Enum`;
+you can no longer pass it a non-`Enum` class.
+
 ## Migration guide
 
-If you used `describeEnum(Enum.field)` to access the string value from an
-enum, you can now call `Enum.field.name`.
+If you previously used `describeEnum(Enum.field)` to access the string value from
+an enum, you can now call `Enum.field.name`.
+
+If you previously used `EnumProperty<NotAnEnum>`, you can now use the generic `DiagnosticsProperty<NotAnEnum>`.
 
 Code before migration:
 
 ```dart
 enum MyEnum { paper, rock }
 
 print(describeEnum(MyEnum.paper)); // output: paper
+
+// TextInputType is not an Enum
+properties.add(EnumProperty<TextInputType>( ... ));
 ```
 
 Code after migration:
@@ -43,6 +57,9 @@ Code after migration:
 enum MyEnum { paper, rock }
 
 print(MyEnum.paper.name); // output: paper
+
+// TextInputType is not an Enum
+properties.add(DiagnosticsProperty<TextInputType>( ... ));
 ```
 
 ## Timeline
@@ -56,21 +73,31 @@ API documentation:
 
 * [`describeEnum` stable][]
 * [`describeEnum` main][]
+* [`EnumProperty` stable][]
+* [`EnumProperty` main][]
+* [enhanced enums]: https://github.com/dart-lang/language/blob/main/working/0158%20-%20Enhanced%20Enum/proposal.md
 
 Relevant issues:
 
-* [☂️ Cleanup SemanticsFlag and SemanticsAction issue][]
+* [Cleanup SemanticsFlag and SemanticsAction issue][]
 
 Relevant PRs:
 
 * [Deprecate `describeEnum` PR][]
 
 [`describeEnum` stable]: {{site.api}}/flutter/lib/src/foundation/describeEnum.html
 
+[`EnumProperty` stable]: {{site.api}}/flutter/lib/src/foundation/EnumProperty.html
+
 <!-- Master channel link: -->
 {% include docs/master-api.md %}
 
 [`describeEnum` main]: {{site.master-api}}/flutter/lib/src/foundation/describeEnum.html
 
-[☂️ Cleanup SemanticsFlag and SemanticsAction issue]: {{site.repo.flutter}}/issues/123346
+[`EnumProperty` main]: {{site.master-api}}/flutter/lib/src/foundation/describeEnum.html
+
+[Cleanup SemanticsFlag and SemanticsAction issue][cleanup-issue]
+
+[cleanup-issue]: {{site.repo.flutter}}/issues/123346
+
 [Deprecate `describeEnum` PR]: {{site.repo.flutter}}/pull/125016

src/release/breaking-changes/index.md

@@ -39,6 +39,7 @@ release, and listed in alphabetical order:
 * [Customize tabs alignment using the new `TabBar.tabAlignment` property][]
 * [Updated EditableText scroll into view behavior][]
 * [Deprecate `textScaleFactor` in favor of `TextScaler`][]
+* [Deprecate describeEnum and update EnumProperty to be type strict][]
 
 [Added AppLifecycleState.hidden]: {{site.url}}/release/breaking-changes/add-applifecyclestate-hidden
 [Deprecated API removed after v3.10]: {{site.url}}/release/breaking-changes/3-10-deprecations
@@ -48,6 +49,7 @@ release, and listed in alphabetical order:
 [Customize tabs alignment using the new `TabBar.tabAlignment` property]: {{site.url}}/release/breaking-changes/tab-alignment
 [Updated EditableText scroll into view behavior]: {{site.url}}/release/breaking-changes/editable-text-scroll-into-view
 [Deprecate `textScaleFactor` in favor of `TextScaler`]: {{site.url}}/release/breaking-changes/deprecate-textscalefactor
+[Deprecate describeEnum and update EnumProperty to be type strict]: {{site.url}}/release/breaking-changes/describe-enum
 
 ### Released in Flutter 3.10