[flutter_markdown] Custom fontfeature superscript (flutter#5874)

Fix not solved issue from another PR: flutter#5058 (comment).

I chose the 2nd option with custom font feature.

Author: dawidope

packages/flutter_markdown/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 0.7.1
+
+* Allows for choosing a custom font feature to create superscript in footnotes when the font does not support the `supr` font feature.
+  * Use the `superscriptFontFeatureTag` property in `MarkdownStyleSheet`.
+  * For example, for the `Roboto` font which doesn't support `supr`, you can set `numr`.
+
 ## 0.7.0
 
 * **BREAKING CHANGES**:

packages/flutter_markdown/lib/src/builder.dart

@@ -537,6 +537,8 @@ class MarkdownBuilder implements md.NodeVisitor {
               style: textSpan.style?.copyWith(
                 fontFeatures: <FontFeature>[
                   const FontFeature.enable('sups'),
+                  if (styleSheet.superscriptFontFeatureTag != null)
+                    FontFeature.enable(styleSheet.superscriptFontFeatureTag!),
                 ],
               ),
             ),

packages/flutter_markdown/lib/src/style_sheet.dart

@@ -59,6 +59,7 @@ class MarkdownStyleSheet {
     this.orderedListAlign = WrapAlignment.start,
     this.blockquoteAlign = WrapAlignment.start,
     this.codeblockAlign = WrapAlignment.start,
+    this.superscriptFontFeatureTag,
     @Deprecated('Use textScaler instead.') this.textScaleFactor,
     TextScaler? textScaler,
   })  : assert(
@@ -391,6 +392,7 @@ class MarkdownStyleSheet {
     WrapAlignment? orderedListAlign,
     WrapAlignment? blockquoteAlign,
     WrapAlignment? codeblockAlign,
+    String? superscriptFontFeatureTag,
     @Deprecated('Use textScaler instead.') double? textScaleFactor,
     TextScaler? textScaler,
   }) {
@@ -457,6 +459,8 @@ class MarkdownStyleSheet {
       orderedListAlign: orderedListAlign ?? this.orderedListAlign,
       blockquoteAlign: blockquoteAlign ?? this.blockquoteAlign,
       codeblockAlign: codeblockAlign ?? this.codeblockAlign,
+      superscriptFontFeatureTag:
+          superscriptFontFeatureTag ?? this.superscriptFontFeatureTag,
       textScaler: newTextScaler,
       textScaleFactor: nextTextScaleFactor,
     );
@@ -520,6 +524,7 @@ class MarkdownStyleSheet {
       blockquoteAlign: other.blockquoteAlign,
       codeblockAlign: other.codeblockAlign,
       textScaleFactor: other.textScaleFactor,
+      superscriptFontFeatureTag: other.superscriptFontFeatureTag,
       // Only one of textScaler and textScaleFactor can be passed. If
       // other.textScaleFactor is non-null, then the sheet was created with a
       // textScaleFactor and the textScaler was derived from that, so should be
@@ -688,6 +693,10 @@ class MarkdownStyleSheet {
   @Deprecated('Use textScaler instead.')
   final double? textScaleFactor;
 
+  /// Custom font feature tag for font which does not support `sups'
+  /// feature to create superscript in footnotes.
+  final String? superscriptFontFeatureTag;
+
   /// A [Map] from element name to the corresponding [TextStyle] object.
   Map<String, TextStyle?> get styles => _styles;
   Map<String, TextStyle?> _styles;
@@ -752,6 +761,7 @@ class MarkdownStyleSheet {
         other.orderedListAlign == orderedListAlign &&
         other.blockquoteAlign == blockquoteAlign &&
         other.codeblockAlign == codeblockAlign &&
+        other.superscriptFontFeatureTag == superscriptFontFeatureTag &&
         other.textScaler == textScaler;
   }
 
@@ -811,6 +821,7 @@ class MarkdownStyleSheet {
       codeblockAlign,
       textScaler,
       textScaleFactor,
+      superscriptFontFeatureTag,
     ]);
   }
 }

packages/flutter_markdown/pubspec.yaml

@@ -4,7 +4,7 @@ description: A Markdown renderer for Flutter. Create rich text output,
   formatted with simple Markdown tags.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_markdown
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_markdown%22
-version: 0.7.0
+version: 0.7.1
 
 environment:
   sdk: ^3.3.0

packages/flutter_markdown/test/footnote_test.dart

@@ -158,7 +158,7 @@ void defineTests() {
     'superscript textstyle replacing',
     () {
       testWidgets(
-        'superscript has correct fontfeature',
+        'superscript has correct default fontfeature',
         (WidgetTester tester) async {
           const String data = 'Foo[^a]\n[^a]: Bar';
           await tester.pumpWidget(
@@ -184,6 +184,35 @@ void defineTests() {
         },
       );
 
+      testWidgets(
+        'superscript has correct custom fontfeature',
+        (WidgetTester tester) async {
+          const String data = 'Foo[^a]\n[^a]: Bar';
+          await tester.pumpWidget(
+            boilerplate(
+              MarkdownBody(
+                data: data,
+                styleSheet:
+                    MarkdownStyleSheet(superscriptFontFeatureTag: 'numr'),
+              ),
+            ),
+          );
+
+          final Iterable<Widget> widgets = tester.allWidgets;
+          final Text text =
+              widgets.firstWhere((Widget widget) => widget is Text) as Text;
+
+          final TextSpan span = text.textSpan! as TextSpan;
+          final List<InlineSpan>? children = span.children;
+
+          expect(children, isNotNull);
+          expect(children!.length, 2);
+          expect(children[1].style, isNotNull);
+          expect(children[1].style!.fontFeatures?.length, 2);
+          expect(children[1].style!.fontFeatures?[1].feature, 'numr');
+        },
+      );
+
       testWidgets(
         'superscript index has the same font style like text',
         (WidgetTester tester) async {