content: Include inline styles (italic etc.) in what we pass to WidgetSpans

Fixes #1813.
Fixes #1819.

This is NFC for inline math, since all the inline styles are
overridden there. But see the previous commit for where we
consolidated those overrides, making a natural place to add more if
needed in the future, with TODOs for some existing ones we might not
want to keep.

Author: chrisbobbe

lib/widgets/content.dart

@@ -1081,10 +1081,21 @@ class _InlineContentBuilder {
     _recognizer = _recognizerStack!.removeLast();
   }
 
-  InlineSpan _buildNodes(List<InlineContentNode> nodes, {required TextStyle? style}) {
+  final List<TextStyle> _styleStack = [];
+
+  TextStyle _resolveStyleStack() {
+    assert(_styleStack.isNotEmpty); // first item is `widget.style`
+    return _styleStack.reduce((value, element) => value.merge(element));
+  }
+
+  InlineSpan _buildNodes(List<InlineContentNode> nodes, {required TextStyle style}) {
+    _styleStack.add(style);
+    final children = nodes.map(_buildNode).toList(growable: false);
+    _styleStack.removeLast();
+
     return TextSpan(
       style: style,
-      children: nodes.map(_buildNode).toList(growable: false));
+      children: children);
   }
 
   InlineSpan _buildNode(InlineContentNode node) {
@@ -1123,7 +1134,7 @@ class _InlineContentBuilder {
 
       case UserMentionNode():
         return WidgetSpan(alignment: PlaceholderAlignment.middle,
-          child: UserMention(ambientTextStyle: widget.style, node: node));
+          child: UserMention(ambientTextStyle: _resolveStyleStack(), node: node));
 
       case UnicodeEmojiNode():
         return TextSpan(text: node.emojiUnicode, recognizer: _recognizer,
@@ -1145,11 +1156,11 @@ class _InlineContentBuilder {
           : WidgetSpan(
               alignment: PlaceholderAlignment.baseline,
               baseline: TextBaseline.alphabetic,
-              child: KatexWidget(ambientTextStyle: widget.style, nodes: nodes));
+              child: KatexWidget(ambientTextStyle: _resolveStyleStack(), nodes: nodes));
 
       case GlobalTimeNode():
         return WidgetSpan(alignment: PlaceholderAlignment.middle,
-          child: GlobalTime(node: node, ambientTextStyle: widget.style));
+          child: GlobalTime(node: node, ambientTextStyle: _resolveStyleStack()));
 
       case UnimplementedInlineContentNode():
         return _errorUnimplemented(node, context: _context!);
@@ -1341,7 +1352,7 @@ class GlobalTime extends StatelessWidget {
                 size: ambientTextStyle.fontSize!,
                 // (When GlobalTime appears in a link, it should be blue
                 // like the text.)
-                color: DefaultTextStyle.of(context).style.color!,
+                color: ambientTextStyle.color,
                 ZulipIcons.clock),
               // Ad-hoc spacing adjustment per feedback:
               //   https://chat.zulip.org/#narrow/stream/101-design/topic/clock.20icons/near/1729345

test/widgets/content_test.dart

@@ -763,6 +763,14 @@ void main() {
         });
     });
 
+    testWidgets('is italic in italic span', (tester) async {
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/1813
+      await prepareContent(tester,
+        plainContent('<p><em><span class="user-mention" data-user-id="13313">@Chris Bobbe</span></em></p>'));
+      final style = mergedStyleOf(tester, '@Chris Bobbe');
+      check(style!.fontStyle).equals(FontStyle.italic);
+    });
+
     testFontWeight('silent or non-self mention in plain paragraph',
       expectedWght: 400,
       // @_**Greg Price**
@@ -1081,7 +1089,19 @@ void main() {
       check(find.textContaining(renderedTextRegexpTwelveHour)).findsOne();
     });
 
-    void testIconAndTextSameColor(String description, String html) {
+    testWidgets('is italic in italic span', (tester) async {
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/1813
+      await prepareContent(tester,
+        // We use the self-account's time-format setting.
+        wrapWithPerAccountStoreWidget: true,
+        initialSnapshot: eg.initialSnapshot(),
+        plainContent('<p><em>$timeSpanHtml</em></p>'));
+      final style = mergedStyleOf(tester,
+        findAncestor: find.byType(GlobalTime), renderedTextRegexp);
+      check(style!.fontStyle).equals(FontStyle.italic);
+    });
+
+    void testIconAndTextSameColor(String description, String html, {Color? expectedColor}) {
       testWidgets('clock icon and text are the same color: $description', (tester) async {
         await prepareContent(tester,
           // We use the self-account's time-format setting.
@@ -1097,11 +1117,16 @@ void main() {
         check(textColor).isNotNull();
 
         check(icon).color.isNotNull().isSameColorAs(textColor!);
+        if (expectedColor != null) {
+          check(icon).color.equals(expectedColor);
+        }
       });
     }
 
     testIconAndTextSameColor('common case', '<p>$timeSpanHtml</p>');
-    testIconAndTextSameColor('inside link', '<p><a href="https://example/">$timeSpanHtml</a></p>');
+    // Regression test for: https://github.com/zulip/zulip-flutter/issues/1819
+    testIconAndTextSameColor('inside link', '<p><a href="https://example/">$timeSpanHtml</a></p>',
+      expectedColor: const HSLColor.fromAHSL(1, 200, 1, 0.4).toColor());
 
     group('maintains font-size ratio with surrounding text', () {
       Future<void> doCheck(WidgetTester tester, double Function(GlobalTime widget) sizeFromWidget) async {