[clang-tools-extra] [clang-doc] Add Markdown AST node type definitions (PR #205609)

[Paul Kirth via cfe-commits]

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@@ -0,0 +1,182 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_DOC_SUPPORT_MARKDOWN_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_DOC_SUPPORT_MARKDOWN_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Allocator.h"
+#include <type_traits>
+
+namespace clang::doc::markdown {
+
+enum class NodeKind {
+  NK_Text,
+  NK_InlineCode,
+  NK_Emphasis,
+  NK_Strong,
+  NK_Paragraph,
+  NK_Heading,
+  NK_FencedCode,
+  NK_Table,
+  NK_UnorderedList,
+  NK_OrderedList,
+  NK_ListItem,
+  NK_BlockQuote,
+  NK_ThematicBreak,
+};
+
+struct MDNode {
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ilovepi wrote:

This type needs a new name. MDNode is used heavily in LLVM for MetaData. Its going to be very confusing since its such a core data structure across clang and llvm. So lets use something else. `MarkdownNode` or `MDAstNode` are potentially OK, but naming is hard, so whatever you want is probably fine if its not easy to confuse. ... Maybe just `Node`? 🤷 

https://github.com/llvm/llvm-project/pull/205609