content: Remove TextStyle merge in rendering inline code

Also in rendering inline TeX source when it doesn't parse...but
that's decreasingly visible as we implement more TeX. :)

Fixes #806.
Fixes #1812.

Similar reasoning as in the previous commits; see there. The
inline-code span-node was clobbering the link-color and font-weight
attributes when those are set by ancestor link and emphasis nodes.

Author: chrisbobbe

lib/widgets/content.dart

@@ -1137,9 +1137,8 @@ class _InlineContentBuilder {
         final nodes = node.nodes;
         return nodes == null
           ? TextSpan(
-              style: widget.style
-                .merge(ContentTheme.of(_context!).textStyleInlineMath)
-                .apply(fontSizeFactor: kInlineCodeFontSizeFactor),
+              style: ContentTheme.of(_context!).textStyleInlineMath
+                .copyWith(fontSize: widget.style.fontSize! * kInlineCodeFontSizeFactor),
               children: [TextSpan(text: node.texSource)])
           : WidgetSpan(
               alignment: PlaceholderAlignment.baseline,
@@ -1180,11 +1179,9 @@ class _InlineContentBuilder {
     // TODO `code`: find equivalent of web's `unicode-bidi: embed; direction: ltr`
 
     return _buildNodes(
-      style: widget.style
-        .merge(ContentTheme.of(_context!).textStyleInlineCode)
-        .apply(fontSizeFactor: kInlineCodeFontSizeFactor),
-      node.nodes,
-    );
+      style: ContentTheme.of(_context!).textStyleInlineCode
+        .copyWith(fontSize: widget.style.fontSize! * kInlineCodeFontSizeFactor),
+      node.nodes);
 
     // Another fun solution -- we can in fact have a border!  Like so:
     //   TextStyle(

test/widgets/content_test.dart

@@ -729,6 +729,22 @@ void main() {
         targetHtml: '<code>code</code>',
         targetFontSizeFinder: mkTargetFontSizeFinderFromPattern('code'));
     });
+
+    testFontWeight('is bold in bold span',
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/1812
+      expectedWght: 600,
+      // **`bold`**
+      content: plainContent('<p><strong><code>bold</code></strong></p>'),
+      styleFinder: (tester) => mergedStyleOf(tester, 'bold')!,
+    );
+
+    testWidgets('is link-colored in link span', (tester) async {
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/806
+      await prepareContent(tester,
+        plainContent('<p><a href="https://example/"><code>code</code></a></p>'));
+      final style = mergedStyleOf(tester, 'code');
+      check(style!.color).equals(const HSLColor.fromAHSL(1, 200, 1, 0.4).toColor());
+    });
   });
 
   group('UserMention', () {
@@ -1046,8 +1062,29 @@ void main() {
       tester.widget(find.text('λ', findRichText: true));
     });
 
-    testWidgets('fallback to displaying KaTeX source if unsupported KaTeX HTML', (tester) async {
+    group('fallback to displaying KaTeX source if unsupported KaTeX HTML', () {
       testContentSmoke(ContentExample.mathInlineUnknown);
+
+      assert(ContentExample.mathInlineUnknown.html.startsWith('<p>'));
+      assert(ContentExample.mathInlineUnknown.html.endsWith('</p>'));
+      final unsupportedKatexHtml = ContentExample.mathInlineUnknown.html
+        .substring(3, ContentExample.mathInlineUnknown.html.length - 4);
+
+      testFontWeight('is bold in bold span',
+        // Regression test for: https://github.com/zulip/zulip-flutter/issues/1812
+        expectedWght: 600,
+        // **$$ \lambda $$**
+        content: plainContent('<p><strong>$unsupportedKatexHtml</strong></p>'),
+        styleFinder: (tester) => mergedStyleOf(tester, r'\lambda')!,
+      );
+
+      testWidgets('is link-colored in link span', (tester) async {
+        // Regression test for: https://github.com/zulip/zulip-flutter/issues/806
+        await prepareContent(tester,
+          plainContent('<p><a href="https://example/">$unsupportedKatexHtml</a></p>'));
+        final style = mergedStyleOf(tester, r'\lambda');
+        check(style!.color).equals(const HSLColor.fromAHSL(1, 200, 1, 0.4).toColor());
+      });
     });
   });