content: Render KaTeX by default, the way we have in recent releases

This is cherry-picked from commits we included in each of the last
several releases, starting with 8f37237 in v0.0.31.

Author: gnprice

lib/model/settings.dart

@@ -178,7 +178,7 @@ enum BoolGlobalSetting {
   upgradeWelcomeDialogShown(GlobalSettingType.internal, false),
 
   /// An experimental flag to toggle rendering KaTeX content in messages.
-  renderKatex(GlobalSettingType.experimentalFeatureFlag, false),
+  renderKatex(GlobalSettingType.experimentalFeatureFlag, true),
 
   /// An experimental flag to enable rendering KaTeX even when some
   /// errors are encountered.

test/model/content_test.dart

@@ -512,7 +512,7 @@ class ContentExample {
   static final mathInline = ContentExample.inline(
     'inline math',
     r"$$ \lambda $$",
-    expectedText: r'\lambda',
+    expectedText: r'λ',
     '<p><span class="katex">'
       '<span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>λ</mi></mrow>'
         '<annotation encoding="application/x-tex"> \\lambda </annotation></semantics></math></span>'
@@ -532,7 +532,7 @@ class ContentExample {
   static const mathBlock = ContentExample(
     'math block',
     "```math\n\\lambda\n```",
-    expectedText: r'\lambda',
+    expectedText: r'λ',
     '<p><span class="katex-display"><span class="katex">'
       '<span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><semantics><mrow><mi>λ</mi></mrow>'
         '<annotation encoding="application/x-tex">\\lambda</annotation></semantics></math></span>'

test/widgets/content_test.dart

@@ -558,7 +558,11 @@ void main() {
   group('MathBlock', () {
     testContentSmoke(ContentExample.mathBlock);
 
-    testWidgets('displays KaTeX source; experimental flag default', (tester) async {
+    testWidgets('displays KaTeX source; experimental flag disabled', (tester) async {
+      addTearDown(testBinding.reset);
+      final globalSettings = testBinding.globalStore.settings;
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, false);
+
       await prepareContent(tester, plainContent(ContentExample.mathBlock.html));
       tester.widget(find.text(r'\lambda', findRichText: true));
     });
@@ -1102,6 +1106,23 @@ void main() {
     });
 
     testWidgets('maintains font-size ratio with surrounding text, when showing TeX source', (tester) async {
+      const html = '<span class="katex">'
+        '<span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>λ</mi></mrow>'
+          '<annotation encoding="application/x-tex"> \\lambda </annotation></semantics></math></span>'
+        '<span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">λ</span></span></span></span>';
+      await checkFontSizeRatio(tester,
+        targetHtml: html,
+        targetFontSizeFinder: mkTargetFontSizeFinderFromPattern(r'λ'));
+    }, skip: true // TODO(#46): adapt this test
+                  //   (it needs a more complex targetFontSizeFinder;
+                  //    see other uses in this file for examples.)
+    );
+
+    testWidgets('maintains font-size ratio with surrounding text, when showing TeX source', (tester) async {
+      addTearDown(testBinding.reset);
+      final globalSettings = testBinding.globalStore.settings;
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, false);
+
       const html = '<span class="katex">'
         '<span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>λ</mi></mrow>'
           '<annotation encoding="application/x-tex"> \\lambda </annotation></semantics></math></span>'
@@ -1111,7 +1132,11 @@ void main() {
         targetFontSizeFinder: mkTargetFontSizeFinderFromPattern(r'\lambda'));
     });
 
-    testWidgets('displays KaTeX source; experimental flag default', (tester) async {
+    testWidgets('displays KaTeX source; experimental flag disabled', (tester) async {
+      addTearDown(testBinding.reset);
+      final globalSettings = testBinding.globalStore.settings;
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, false);
+
       await prepareContent(tester, plainContent(ContentExample.mathInline.html));
       tester.widget(find.text(r'\lambda', findRichText: true));
     });