LibMarkdown: Parse horizontal rules

A horizontal rule is generated by a line with three or more of these
characters: '*', '-', '_'.

Libraries/LibMarkdown/CMakeLists.txt

@@ -2,6 +2,7 @@ set(SOURCES
     CodeBlock.cpp
     Document.cpp
     Heading.cpp
+    HorizontalRule.cpp
     List.cpp
     Paragraph.cpp
     Table.cpp

Libraries/LibMarkdown/Document.cpp

@@ -28,6 +28,7 @@
 #include <LibMarkdown/CodeBlock.h>
 #include <LibMarkdown/Document.h>
 #include <LibMarkdown/Heading.h>
+#include <LibMarkdown/HorizontalRule.h>
 #include <LibMarkdown/List.h>
 #include <LibMarkdown/Paragraph.h>
 #include <LibMarkdown/Table.h>
@@ -105,7 +106,7 @@ OwnPtr<Document> Document::parse(const StringView& str)
         }
 
         bool any = helper<Table>(lines, blocks) || helper<List>(lines, blocks) || helper<CodeBlock>(lines, blocks)
-            || helper<Heading>(lines, blocks);
+            || helper<Heading>(lines, blocks) || helper<HorizontalRule>(lines, blocks);
 
         if (any) {
             if (!paragraph_lines.is_empty()) {

Libraries/LibMarkdown/HorizontalRule.cpp

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/String.h>
+#include <AK/StringBuilder.h>
+#include <LibMarkdown/HorizontalRule.h>
+
+namespace Markdown {
+
+String HorizontalRule::render_to_html() const
+{
+    return "<hr>\n";
+}
+
+String HorizontalRule::render_for_terminal(size_t view_width) const
+{
+    StringBuilder builder(view_width + 1);
+    for (size_t i = 0; i < view_width; ++i)
+        builder.append('-');
+    builder.append("\n\n");
+    return builder.to_string();
+}
+
+OwnPtr<HorizontalRule> HorizontalRule::parse(Vector<StringView>::ConstIterator& lines)
+{
+    if (lines.is_end())
+        return nullptr;
+
+    const StringView& line = *lines;
+
+    if (line.length() < 3)
+        return nullptr;
+    if (!line.starts_with('-') && !line.starts_with('_') && !line.starts_with('*'))
+        return nullptr;
+
+    auto first_character = line.characters_without_null_termination()[0];
+    for (auto ch : line) {
+        if (ch != first_character)
+            return nullptr;
+    }
+
+    ++lines;
+    return make<HorizontalRule>();
+}
+
+}

Libraries/LibMarkdown/HorizontalRule.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <AK/StringView.h>
+#include <AK/Vector.h>
+#include <LibMarkdown/Block.h>
+
+namespace Markdown {
+
+class HorizontalRule final : public Block {
+public:
+    HorizontalRule()
+    {
+    }
+    virtual ~HorizontalRule() override { }
+
+    virtual String render_to_html() const override;
+    virtual String render_for_terminal(size_t view_width = 0) const override;
+    static OwnPtr<HorizontalRule> parse(Vector<StringView>::ConstIterator& lines);
+};
+
+}