KaTeX (1/n): Initial support for displaying basic KaTeX content

assets/KaTeX/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2013-2020 Khan Academy and other contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

lib/licenses.dart

@@ -12,6 +12,9 @@ import 'package:flutter/services.dart';
 Stream<LicenseEntry> additionalLicenses() async* {
   // Alphabetic by path.
 
+  yield LicenseEntryWithLineBreaks(
+    ['KaTeX'],
+    await rootBundle.loadString('assets/KaTeX/LICENSE'));
   yield LicenseEntryWithLineBreaks(
     ['Noto Color Emoji'],
     await rootBundle.loadString('assets/Noto_Color_Emoji/LICENSE'));

lib/model/content.dart

@@ -5,7 +5,9 @@ import 'package:html/parser.dart';
 
 import '../api/model/model.dart';
 import '../api/model/submessage.dart';
+import '../log.dart';
 import 'code_block.dart';
+import 'katex.dart';
 
 /// A node in a parse tree for Zulip message-style content.
 ///
@@ -341,22 +343,58 @@ class CodeBlockSpanNode extends ContentNode {
 }
 
 class MathBlockNode extends BlockContentNode {
-  const MathBlockNode({super.debugHtmlNode, required this.texSource});
+  const MathBlockNode({
+    super.debugHtmlNode,
+    this.debugHasError = false,
+    required this.texSource,
+    required this.nodes,
+  });
 
+  final bool debugHasError;
   final String texSource;
+  final List<KatexNode>? nodes;
 
   @override
-  bool operator ==(Object other) {
-    return other is MathBlockNode && other.texSource == texSource;
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(StringProperty('texSource', texSource));
   }
 
   @override
-  int get hashCode => Object.hash('MathBlockNode', texSource);
+  List<DiagnosticsNode> debugDescribeChildren() {
+    return nodes?.map((node) => node.toDiagnosticsNode()).toList() ?? const [];
+  }
+}
+
+class KatexNode extends ContentNode {
+  const KatexNode({
+    required this.styles,
+    required this.text,
+    required this.nodes,
+    super.debugHtmlNode,
+  }) : assert((text != null) ^ (nodes != null));
+
+  final KatexSpanStyles styles;
+
+  /// The text or a single character this KaTeX span contains, generally
+  /// observed to be the leaf node in the KaTeX HTML tree.
+  /// It will be null if this span has child nodes.
+  final String? text;
+
+  /// The child nodes of this span in the KaTeX HTML tree.
+  /// It will be null if this span is a text node.
+  final List<KatexNode>? nodes;
 
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
-    properties.add(StringProperty('texSource', texSource));
+    properties.add(KatexSpanStylesProperty('styles', styles));
+    properties.add(StringProperty('text', text));
+  }
+
+  @override
+  List<DiagnosticsNode> debugDescribeChildren() {
+    return nodes?.map((node) => node.toDiagnosticsNode()).toList() ?? const [];
   }
 }
 
@@ -822,23 +860,27 @@ class ImageEmojiNode extends EmojiNode {
 }
 
 class MathInlineNode extends InlineContentNode {
-  const MathInlineNode({super.debugHtmlNode, required this.texSource});
+  const MathInlineNode({
+    super.debugHtmlNode,
+    this.debugHasError = false,
+    required this.texSource,
+    required this.nodes,
+  });
 
+  final bool debugHasError;
   final String texSource;
-
-  @override
-  bool operator ==(Object other) {
-    return other is MathInlineNode && other.texSource == texSource;
-  }
-
-  @override
-  int get hashCode => Object.hash('MathInlineNode', texSource);
+  final List<KatexNode>? nodes;
 
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     properties.add(StringProperty('texSource', texSource));
   }
+
+  @override
+  List<DiagnosticsNode> debugDescribeChildren() {
+    return nodes?.map((node) => node.toDiagnosticsNode()).toList() ?? const [];
+  }
 }
 
 class GlobalTimeNode extends InlineContentNode {
@@ -864,7 +906,10 @@ class GlobalTimeNode extends InlineContentNode {
 
 ////////////////////////////////////////////////////////////////
 
-String? _parseMath(dom.Element element, {required bool block}) {
+({List<KatexNode>? spans, bool debugHasError, String texSource})? _parseMath(
+  dom.Element element, {
+  required bool block,
+}) {
   final dom.Element katexElement;
   if (!block) {
     assert(element.localName == 'span' && element.className == 'katex');
@@ -873,41 +918,60 @@ String? _parseMath(dom.Element element, {required bool block}) {
   } else {
     assert(element.localName == 'span' && element.className == 'katex-display');
 
-    if (element.nodes.length != 1) return null;
-    final child = element.nodes.single;
-    if (child is! dom.Element) return null;
-    if (child.localName != 'span') return null;
-    if (child.className != 'katex') return null;
-    katexElement = child;
-  }
-
-  // Expect two children span.katex-mathml, span.katex-html .
-  // For now we only care about the .katex-mathml .
-  if (katexElement.nodes.isEmpty) return null;
-  final child = katexElement.nodes.first;
-  if (child is! dom.Element) return null;
-  if (child.localName != 'span') return null;
-  if (child.className != 'katex-mathml') return null;
-
-  if (child.nodes.length != 1) return null;
-  final grandchild = child.nodes.single;
-  if (grandchild is! dom.Element) return null;
-  if (grandchild.localName != 'math') return null;
-  if (grandchild.attributes['display'] != (block ? 'block' : null)) return null;
-  if (grandchild.namespaceUri != 'http://www.w3.org/1998/Math/MathML') return null;
-
-  if (grandchild.nodes.length != 1) return null;
-  final greatgrand = grandchild.nodes.single;
-  if (greatgrand is! dom.Element) return null;
-  if (greatgrand.localName != 'semantics') return null;
-
-  if (greatgrand.nodes.isEmpty) return null;
-  final descendant4 = greatgrand.nodes.last;
-  if (descendant4 is! dom.Element) return null;
-  if (descendant4.localName != 'annotation') return null;
-  if (descendant4.attributes['encoding'] != 'application/x-tex') return null;
-
-  return descendant4.text.trim();
+    if (element.nodes case [
+      dom.Element(localName: 'span', className: 'katex') && final child,
+    ]) {
+      katexElement = child;
+    } else {
+      return null;
+    }
+  }
+
+  if (katexElement.nodes case [
+    dom.Element(localName: 'span', className: 'katex-mathml', nodes: [
+      dom.Element(
+        localName: 'math',
+        namespaceUri: 'http://www.w3.org/1998/Math/MathML')
+          && final mathElement,
+    ]),
+    dom.Element(localName: 'span', className: 'katex-html', nodes: [...])
+      && final katexHtmlElement,
+  ]) {
+    if (mathElement.attributes['display'] != (block ? 'block' : null)) {
+      return null;
+    }
+
+    final String texSource;
+    if (mathElement.nodes case [
+      dom.Element(localName: 'semantics', nodes: [
+        ...,
+        dom.Element(
+          localName: 'annotation',
+          attributes: {'encoding': 'application/x-tex'},
+          :final text),
+      ]),
+    ]) {
+      texSource = text.trim();
+    } else {
+      return null;
+    }
+
+    List<KatexNode>? spans;
+    final parser = KatexParser();
+    try {
+      spans = parser.parseKatexHTML(katexHtmlElement);
+    } on KatexHtmlParseError catch (e, st) {
+      assert(debugLog('$e\n$st'));
+    }
+
+    return (
+      spans: spans,
+      debugHasError: parser.debugHasError,
+      texSource: texSource,
+    );
+  } else {
+    return null;
+  }
 }
 
 /// Parser for the inline-content subtrees within Zulip content HTML.
@@ -920,9 +984,13 @@ String? _parseMath(dom.Element element, {required bool block}) {
 class _ZulipInlineContentParser {
   InlineContentNode? parseInlineMath(dom.Element element) {
     final debugHtmlNode = kDebugMode ? element : null;
-    final texSource = _parseMath(element, block: false);
-    if (texSource == null) return null;
-    return MathInlineNode(texSource: texSource, debugHtmlNode: debugHtmlNode);
+    final parsed = _parseMath(element, block: false);
+    if (parsed == null) return null;
+    return MathInlineNode(
+      texSource: parsed.texSource,
+      nodes: parsed.spans,
+      debugHasError: parsed.debugHasError,
+      debugHtmlNode: debugHtmlNode);
   }
 
   UserMentionNode? parseUserMention(dom.Element element) {
@@ -1624,10 +1692,12 @@ class _ZulipContentParser {
     })());
 
     final firstChild = nodes.first as dom.Element;
-    final texSource = _parseMath(firstChild, block: true);
-    if (texSource != null) {
+    final parsed = _parseMath(firstChild, block: true);
+    if (parsed != null) {
       result.add(MathBlockNode(
-        texSource: texSource,
+        texSource: parsed.texSource,
+        nodes: parsed.spans,
+        debugHasError: parsed.debugHasError,
         debugHtmlNode: kDebugMode ? firstChild : null));
     } else {
       result.add(UnimplementedBlockContentNode(htmlNode: firstChild));
@@ -1659,10 +1729,11 @@ class _ZulipContentParser {
       if (child case dom.Text(text: '\n\n')) continue;
 
       if (child case dom.Element(localName: 'span', className: 'katex-display')) {
-        final texSource = _parseMath(child, block: true);
-        if (texSource != null) {
+        final parsed = _parseMath(child, block: true);
+        if (parsed != null) {
           result.add(MathBlockNode(
-            texSource: texSource,
+            texSource: parsed.texSource,
+            nodes: parsed.spans,
             debugHtmlNode: debugHtmlNode));
           continue;
         }