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

[Neil Nair via cfe-commits]

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+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Defines the Markdown AST node hierarchy for the clang-doc Markdown parser.
+///
+/// Block nodes represent structural constructs (paragraphs, headings, lists,
+/// fenced code blocks, etc). Inline nodes represent span-level content (text,
+/// emphasis, inline code) that appears inside block nodes.
+///
+/// All nodes are arena-allocated via ASTContext, which owns their lifetime.
+/// The parser builds the tree by calling push_back() on simple_ilist members.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_DOC_SUPPORT_MARKDOWN_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_DOC_SUPPORT_MARKDOWN_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/simple_ilist.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <type_traits>
+#include <utility>
+
+namespace clang::doc::markdown {
+
+enum class NodeKind {
+  // Inline nodes
+  NK_Text,
+  NK_InlineCode,
+  NK_Emphasis,
+  NK_Strong,
+  // Block nodes
+  NK_Paragraph,
+  NK_Heading,
+  NK_FencedCode,
+  NK_Table, // TODO: add TableNode
+  NK_UnorderedList,
+  NK_OrderedList,
+  NK_BlockQuote,
+  NK_ThematicBreak,
+  NK_Document,
+};
+
+struct InlineNode;
+struct BlockNode;
+
+//===----------------------------------------------------------------------===//
+// Inline nodes -- span-level content inside block nodes
+//===----------------------------------------------------------------------===//
+
+/// Base class for all inline nodes. Inline nodes represent span-level content
+/// such as text, emphasis, and inline code. They live in InlineList members
+/// of block nodes.
+struct InlineNode : llvm::ilist_node<InlineNode> {
+  NodeKind Kind;
+  explicit InlineNode(NodeKind K) : Kind(K) {}
+  virtual ~InlineNode() = default;
+  virtual void print(llvm::raw_ostream &OS) const = 0;
+  LLVM_DUMP_METHOD void dump() const;
+};
+
+using InlineList = llvm::simple_ilist<InlineNode>;
+
+/// A plain text run.
+struct TextNode : InlineNode {
+private:
+  llvm::StringRef Text;
+
+public:
+  explicit TextNode(llvm::StringRef T)
+      : InlineNode(NodeKind::NK_Text), Text(T) {}
+  llvm::StringRef getText() const { return Text; }
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const InlineNode *N) {
+    return N->Kind == NodeKind::NK_Text;
+  }
+};
+
+/// A backtick-delimited inline code span.
+struct InlineCodeNode : InlineNode {
+private:
+  llvm::StringRef Code;
+
+public:
+  explicit InlineCodeNode(llvm::StringRef C)
+      : InlineNode(NodeKind::NK_InlineCode), Code(C) {}
+  llvm::StringRef getCode() const { return Code; }
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const InlineNode *N) {
+    return N->Kind == NodeKind::NK_InlineCode;
+  }
+};
+
+/// An emphasis span (* or _).
+struct EmphasisNode : InlineNode {
+  InlineList Children;
+  EmphasisNode() : InlineNode(NodeKind::NK_Emphasis) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const InlineNode *N) {
+    return N->Kind == NodeKind::NK_Emphasis;
+  }
+};
+
+/// A strong emphasis span (** or __).
+struct StrongNode : InlineNode {
+  InlineList Children;
+  StrongNode() : InlineNode(NodeKind::NK_Strong) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const InlineNode *N) {
+    return N->Kind == NodeKind::NK_Strong;
+  }
+};
+
+//===----------------------------------------------------------------------===//
+// Block nodes -- structural constructs
+//===----------------------------------------------------------------------===//
+
+/// Base class for all block nodes. Block nodes represent structural constructs
+/// such as paragraphs, headings, and lists. They live in BlockList members of
+/// container block nodes.
+struct BlockNode : llvm::ilist_node<BlockNode> {
+  NodeKind Kind;
+  explicit BlockNode(NodeKind K) : Kind(K) {}
+  virtual ~BlockNode() = default;
+  virtual void print(llvm::raw_ostream &OS) const = 0;
+  LLVM_DUMP_METHOD void dump() const;
+};
+
+using BlockList = llvm::simple_ilist<BlockNode>;
+
+/// A paragraph of inline content.
+struct ParagraphNode : BlockNode {
+  InlineList Children;
+  ParagraphNode() : BlockNode(NodeKind::NK_Paragraph) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_Paragraph;
+  }
+};
+
+/// An ATX heading (# through ######).
+struct HeadingNode : BlockNode {
+private:
+  unsigned Level;
+
+public:
+  InlineList Children;
+  explicit HeadingNode(unsigned L)
+      : BlockNode(NodeKind::NK_Heading), Level(L) {}
+  unsigned getLevel() const { return Level; }
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_Heading;
+  }
+};
+
+/// A fenced code block (``` or ~~~). Lang holds the info string.
+struct FencedCodeNode : BlockNode {
+private:
+  llvm::StringRef Lang;
+  llvm::StringRef Code;
+
+public:
+  FencedCodeNode(llvm::StringRef L, llvm::StringRef C)
+      : BlockNode(NodeKind::NK_FencedCode), Lang(L), Code(C) {}
+  llvm::StringRef getLang() const { return Lang; }
+  llvm::StringRef getCode() const { return Code; }
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_FencedCode;
+  }
+};
+
+/// A single item in an unordered or ordered list.
+/// ListItemNode is not a BlockNode -- it only lives inside list nodes.
+struct ListItemNode : llvm::ilist_node<ListItemNode> {
+  InlineList Children;
+  ListItemNode() = default;
+  void print(llvm::raw_ostream &OS) const;
+  LLVM_DUMP_METHOD void dump() const;
+};
+
+/// An unordered list (-, *, or + markers).
+struct UnorderedListNode : BlockNode {
+  llvm::simple_ilist<ListItemNode> Items;
+  UnorderedListNode() : BlockNode(NodeKind::NK_UnorderedList) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_UnorderedList;
+  }
+};
+
+/// An ordered list (1. 2. 3. markers). Start holds the first item number.
+struct OrderedListNode : BlockNode {
+private:
+  unsigned Start;
+
+public:
+  llvm::simple_ilist<ListItemNode> Items;
+  explicit OrderedListNode(unsigned S = 1)
+      : BlockNode(NodeKind::NK_OrderedList), Start(S) {}
+  unsigned getStart() const { return Start; }
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_OrderedList;
+  }
+};
+
+/// A block quote (> marker).
+struct BlockQuoteNode : BlockNode {
+  BlockList Children;
+  BlockQuoteNode() : BlockNode(NodeKind::NK_BlockQuote) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_BlockQuote;
+  }
+};
+
+/// A thematic break (---, ***, or ___).
+struct ThematicBreakNode : BlockNode {
+  ThematicBreakNode() : BlockNode(NodeKind::NK_ThematicBreak) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_ThematicBreak;
+  }
+};
+
+/// The root document node. Contains all top-level block nodes.
+/// Children are added by the parser via push_back on the Children ilist.
+struct DocumentNode : BlockNode {
+  BlockList Children;
+  DocumentNode() : BlockNode(NodeKind::NK_Document) {}
+  void print(llvm::raw_ostream &OS) const override;
+  static bool classof(const BlockNode *N) {
+    return N->Kind == NodeKind::NK_Document;
+  }
+};
+
+//===----------------------------------------------------------------------===//
+// ASTContext -- owns the arena and all allocated nodes
+//===----------------------------------------------------------------------===//
+
+template <typename T>
+using IsMarkdownNode = std::enable_if_t<std::is_base_of_v<InlineNode, T> ||
+                                        std::is_base_of_v<BlockNode, T> ||
+                                        std::is_same_v<T, ListItemNode>>;
+
+/// Owns the bump pointer arena for all Markdown AST nodes. Nodes allocated
+/// via allocate() have their lifetime tied to the ASTContext.
+class ASTContext {
+  llvm::BumpPtrAllocator Arena;
+  DocumentNode *Root = nullptr;
+
+public:
+  ASTContext() = default;
+
+  template <typename T, typename... Args, typename = IsMarkdownNode<T>>
+  T *allocate(Args &&...args) {
+    return new (Arena.Allocate<T>()) T(std::forward<Args>(args)...);
+  }
+
+  /// Copy a string into the arena so its lifetime matches the ASTContext.
+  llvm::StringRef internString(llvm::StringRef S) {
+    char *Buf = Arena.Allocate<char>(S.size());
+    std::copy(S.begin(), S.end(), Buf);
+    return llvm::StringRef(Buf, S.size());
+  }
----------------
Neil-N4 wrote:

Removed along with ASTContext. the copies were needed in the parser for joining paragraph lines but since ASTContext is now in the parser PR that's handled there

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