content: Parse code block data-code-language attribute

We don't currently need this -- I wrote it when I thought proper
styling depended on knowing whether the code block was declared with
a language or not -- but it took some thinking-through to get just
right, so might as well do it now in case we want it later (e.g., to
include the language attribute in Flutter Semantics for code
blocks).

Author: chrisbobbe

Diff for: lib/model/content.dart

@@ -287,9 +287,20 @@ class SpoilerNode extends BlockContentNode {
 }
 
 class CodeBlockNode extends BlockContentNode {
-  const CodeBlockNode(this.spans, {super.debugHtmlNode});
+  const CodeBlockNode(
+    this.spans, {
+    this.codeLanguage,
+    super.debugHtmlNode,
+  });
 
   final List<CodeBlockSpanNode> spans;
+  final String? codeLanguage;
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(StringProperty('codeLanguage', codeLanguage));
+  }
 
   @override
   List<DiagnosticsNode> debugDescribeChildren() {
@@ -943,9 +954,11 @@ class _ZulipContentParser {
 
   BlockContentNode parseCodeBlock(dom.Element divElement) {
     assert(_debugParserContext == _ParserContext.block);
+    String? codeLanguage;
     final mainElement = () {
       assert(divElement.localName == 'div'
           && divElement.className == "codehilite");
+      codeLanguage = divElement.attributes['data-code-language'];
 
       if (divElement.nodes.length != 1) return null;
       final child = divElement.nodes[0];
@@ -1009,7 +1022,7 @@ class _ZulipContentParser {
       spans.add(span);
     }
 
-    return CodeBlockNode(spans, debugHtmlNode: debugHtmlNode);
+    return CodeBlockNode(spans, codeLanguage: codeLanguage, debugHtmlNode: debugHtmlNode);
   }
 
   BlockContentNode parseImageNode(dom.Element divElement) {

Diff for: test/model/content_test.dart

@@ -281,7 +281,7 @@ class ContentExample {
     "```\nverb\natim\n```",
     expectedText: 'verb\natim',
     '<div class="codehilite"><pre><span></span><code>verb\natim\n</code></pre></div>', [
-      CodeBlockNode([
+      CodeBlockNode(codeLanguage: null, [
         CodeBlockSpanNode(text: 'verb\natim', type: CodeBlockSpanType.text),
       ]),
     ]);
@@ -294,7 +294,7 @@ class ContentExample {
         '<span></span><code><span class="kd">class</span><span class="w"> </span>'
         '<span class="nc">A</span><span class="w"> </span><span class="p">{}</span>'
         '\n</code></pre></div>', [
-      CodeBlockNode([
+      CodeBlockNode(codeLanguage: 'Dart', [
         CodeBlockSpanNode(text: 'class', type: CodeBlockSpanType.keywordDeclaration),
         CodeBlockSpanNode(text: ' ', type: CodeBlockSpanType.whitespace),
         CodeBlockSpanNode(text: 'A', type: CodeBlockSpanType.nameClass),
@@ -316,7 +316,7 @@ class ContentExample {
         '<span class="s">"world!</span><span class="se">\\n</span><span class="s">"</span>'
         '<span class="p">);</span>\n<span class="p">}</span>\n'
         '</code></pre></div>', [
-      CodeBlockNode([
+      CodeBlockNode(codeLanguage: 'Rust', [
         CodeBlockSpanNode(text: 'fn', type: CodeBlockSpanType.keyword),
         CodeBlockSpanNode(text: ' ', type: CodeBlockSpanType.text),
         CodeBlockSpanNode(text: 'main', type: CodeBlockSpanType.nameFunction),
@@ -378,7 +378,8 @@ class ContentExample {
     '<div class="codehilite">'
       '<pre><span></span><code>code block.\n</code></pre></div>\n\n'
     '<p>some content</p>', [
-      CodeBlockNode([CodeBlockSpanNode(text: "code block.", type: CodeBlockSpanType.text)]),
+      CodeBlockNode(codeLanguage: null,
+        [CodeBlockSpanNode(text: "code block.", type: CodeBlockSpanType.text)]),
       ParagraphNode(links: null, nodes: [TextNode("some content")]),
     ]);
 
@@ -1062,7 +1063,7 @@ void main() {
             ParagraphNode(wasImplicit: true, links: null, nodes: [TextNode('three')]),
           ]]),
         ]),
-        CodeBlockNode([
+        CodeBlockNode(codeLanguage: null, [
           CodeBlockSpanNode(text: 'four', type: CodeBlockSpanType.text),
         ]),
         ParagraphNode(wasImplicit: true, links: null, nodes: [TextNode('\n\n')]), // TODO avoid this; it renders wrong