LibMarkdown: Add start numbers for ordered lists

5. hey -> <ol start="5"><li>hey</li></ol>

Userland/Libraries/LibMarkdown/List.cpp

@@ -16,7 +16,12 @@ String List::render_to_html(bool) const
     StringBuilder builder;
 
     const char* tag = m_is_ordered ? "ol" : "ul";
-    builder.appendff("<{}>\n", tag);
+    builder.appendff("<{}", tag);
+
+    if (m_start_number != 1)
+        builder.appendff(" start=\"{}\"", m_start_number);
+
+    builder.append(">\n");
 
     for (auto& item : m_items) {
         builder.append("<li>");
@@ -59,6 +64,7 @@ OwnPtr<List> List::parse(LineIterator& lines)
 
     bool is_tight = true;
     bool has_trailing_blank_lines = false;
+    size_t start_number = 1;
 
     while (!lines.is_end()) {
 
@@ -85,6 +91,11 @@ OwnPtr<List> List::parse(LineIterator& lines)
                 continue;
             if (ch == '.' || ch == ')')
                 if (i + 1 < line.length() && line[i + 1] == ' ') {
+                    auto maybe_start_number = line.substring_view(offset, i - offset).to_uint<size_t>();
+                    if (!maybe_start_number.has_value())
+                        break;
+                    if (first)
+                        start_number = maybe_start_number.value();
                     appears_ordered = true;
                     offset = i + 1;
                 }
@@ -124,7 +135,7 @@ OwnPtr<List> List::parse(LineIterator& lines)
         first = false;
     }
 
-    return make<List>(move(items), is_ordered, is_tight);
+    return make<List>(move(items), is_ordered, is_tight, start_number);
 }
 
 }

Userland/Libraries/LibMarkdown/List.h

@@ -15,10 +15,11 @@ namespace Markdown {
 
 class List final : public Block {
 public:
-    List(Vector<OwnPtr<ContainerBlock>> items, bool is_ordered, bool is_tight)
+    List(Vector<OwnPtr<ContainerBlock>> items, bool is_ordered, bool is_tight, size_t start_number)
         : m_items(move(items))
         , m_is_ordered(is_ordered)
         , m_is_tight(is_tight)
+        , m_start_number(start_number)
     {
     }
     virtual ~List() override { }
@@ -32,6 +33,7 @@ private:
     Vector<OwnPtr<ContainerBlock>> m_items;
     bool m_is_ordered { false };
     bool m_is_tight { false };
+    size_t m_start_number { 1 };
 };
 
 }