YAMLParser.h

//===- YAMLParser.h - Simple YAML parser ------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
//  This is a YAML 1.2 parser.
//
//  See http://www.yaml.org/spec/1.2/spec.html for the full standard.
//
//  This currently does not implement the following:
//    * Tag resolution.
//    * UTF-16.
//    * BOMs anywhere other than the first Unicode scalar value in the file.
//
//  The most important class here is Stream. This represents a YAML stream with
//  0, 1, or many documents.
//
//  SourceMgr sm;
//  StringRef input = getInput();
//  yaml::Stream stream(input, sm);
//
//  for (yaml::document_iterator di = stream.begin(), de = stream.end();
//       di != de; ++di) {
//    yaml::Node *n = di->getRoot();
//    if (n) {
//      // Do something with n...
//    } else
//      break;
//  }
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_YAMLPARSER_H
#define LLVM_SUPPORT_YAMLPARSER_H

#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/SMLoc.h"
#include "llvm/Support/SourceMgr.h"
#include <cassert>
#include <cstddef>
#include <iterator>
#include <map>
#include <memory>
#include <optional>
#include <string>
#include <system_error>

namespace llvm {

class MemoryBufferRef;
class raw_ostream;
class Twine;

namespace yaml {

class Document;
class document_iterator;
class Node;
class Scanner;
struct Token;

/// Dump all the tokens in this stream to OS.
/// \returns true if there was an error, false otherwise.
bool dumpTokens(StringRef Input, raw_ostream &);

/// Scans all tokens in input without outputting anything. This is used
///        for benchmarking the tokenizer.
/// \returns true if there was an error, false otherwise.
bool scanTokens(StringRef Input);

/// Escape \a Input for a double quoted scalar; if \p EscapePrintable
/// is true, all UTF8 sequences will be escaped, if \p EscapePrintable is
/// false, those UTF8 sequences encoding printable unicode scalars will not be
/// escaped, but emitted verbatim.
std::string escape(StringRef Input, bool EscapePrintable = true);

/// Parse \p S as a bool according to https://yaml.org/type/bool.html.
std::optional<bool> parseBool(StringRef S);

/// This class represents a YAML stream potentially containing multiple
///        documents.
class Stream {
public:
  /// This keeps a reference to the string referenced by \p Input.
  Stream(StringRef Input, SourceMgr &, bool ShowColors = true,
         std::error_code *EC = nullptr);

  Stream(MemoryBufferRef InputBuffer, SourceMgr &, bool ShowColors = true,
         std::error_code *EC = nullptr);
  ~Stream();

  document_iterator begin();
  document_iterator end();
  void skip();
  bool failed();

  bool validate() {
    skip();
    return !failed();
  }

  void printError(Node *N, const Twine &Msg,
                  SourceMgr::DiagKind Kind = SourceMgr::DK_Error);
  void printError(const SMRange &Range, const Twine &Msg,
                  SourceMgr::DiagKind Kind = SourceMgr::DK_Error);

private:
  friend class Document;

  std::unique_ptr<Scanner> scanner;
  std::unique_ptr<Document> CurrentDoc;
};

/// Abstract base class for all Nodes.
class Node {
  virtual void anchor();

public:
  enum NodeKind {
    NK_Null,
    NK_Scalar,
    NK_BlockScalar,
    NK_KeyValue,
    NK_Mapping,
    NK_Sequence,
    NK_Alias
  };

  Node(unsigned int Type, std::unique_ptr<Document> &, StringRef Anchor,
       StringRef Tag);

  // It's not safe to copy YAML nodes; the document is streamed and the position
  // is part of the state.
  Node(const Node &) = delete;
  void operator=(const Node &) = delete;

  void *operator new(size_t Size, BumpPtrAllocator &Alloc,
                     size_t Alignment = 16) noexcept {
    return Alloc.Allocate(Size, Alignment);
  }

  void operator delete(void *Ptr, BumpPtrAllocator &Alloc,
                       size_t Size) noexcept {
    Alloc.Deallocate(Ptr, Size, 0);
  }

  void operator delete(void *) noexcept = delete;

  /// Get the value of the anchor attached to this node. If it does not
  ///        have one, getAnchor().size() will be 0.
  StringRef getAnchor() const { return Anchor; }

  /// Get the tag as it was written in the document. This does not
  ///   perform tag resolution.
  StringRef getRawTag() const { return Tag; }

  /// Get the verbatium tag for a given Node. This performs tag resoluton
  ///   and substitution.
  std::string getVerbatimTag() const;

  SMRange getSourceRange() const { return SourceRange; }
  void setSourceRange(SMRange SR) { SourceRange = SR; }

  // These functions forward to Document and Scanner.
  Token &peekNext();
  Token getNext();
  Node *parseBlockNode();
  BumpPtrAllocator &getAllocator();
  void setError(const Twine &Message, Token &Location) const;
  bool failed() const;

  virtual void skip() {}

  unsigned int getType() const { return TypeID; }

protected:
  std::unique_ptr<Document> &Doc;
  SMRange SourceRange;

  ~Node() = default;

private:
  unsigned int TypeID;
  StringRef Anchor;
  /// The tag as typed in the document.
  StringRef Tag;
};

/// A null value.
///
/// Example:
///   !!null null
class NullNode final : public Node {
  void anchor() override;

public:
  NullNode(std::unique_ptr<Document> &D)
      : Node(NK_Null, D, StringRef(), StringRef()) {}

  static bool classof(const Node *N) { return N->getType() == NK_Null; }
};

/// A scalar node is an opaque datum that can be presented as a
///        series of zero or more Unicode scalar values.
///
/// Example:
///   Adena
class ScalarNode final : public Node {
  void anchor() override;

public:
  ScalarNode(std::unique_ptr<Document> &D, StringRef Anchor, StringRef Tag,
             StringRef Val)
      : Node(NK_Scalar, D, Anchor, Tag), Value(Val) {
    SMLoc Start = SMLoc::getFromPointer(Val.begin());
    SMLoc End = SMLoc::getFromPointer(Val.end());
    SourceRange = SMRange(Start, End);
  }

  // Return Value without any escaping or folding or other fun YAML stuff. This
  // is the exact bytes that are contained in the file (after conversion to
  // utf8).
  StringRef getRawValue() const { return Value; }

  /// Gets the value of this node as a StringRef.
  ///
  /// \param Storage is used to store the content of the returned StringRef if
  ///        it requires any modification from how it appeared in the source.
  ///        This happens with escaped characters and multi-line literals.
  StringRef getValue(SmallVectorImpl<char> &Storage) const;

  static bool classof(const Node *N) {
    return N->getType() == NK_Scalar;
  }

private:
  StringRef Value;

  StringRef unescapeDoubleQuoted(StringRef UnquotedValue,
                                 StringRef::size_type Start,
                                 SmallVectorImpl<char> &Storage) const;
};

/// A block scalar node is an opaque datum that can be presented as a
///        series of zero or more Unicode scalar values.
///
/// Example:
///   |
///     Hello
///     World
class BlockScalarNode final : public Node {
  void anchor() override;

public:
  BlockScalarNode(std::unique_ptr<Document> &D, StringRef Anchor, StringRef Tag,
                  StringRef Value, StringRef RawVal)
      : Node(NK_BlockScalar, D, Anchor, Tag), Value(Value) {
    SMLoc Start = SMLoc::getFromPointer(RawVal.begin());
    SMLoc End = SMLoc::getFromPointer(RawVal.end());
    SourceRange = SMRange(Start, End);
  }

  /// Gets the value of this node as a StringRef.
  StringRef getValue() const { return Value; }

  static bool classof(const Node *N) {
    return N->getType() == NK_BlockScalar;
  }

private:
  StringRef Value;
};

/// A key and value pair. While not technically a Node under the YAML
///        representation graph, it is easier to treat them this way.
///
/// TODO: Consider making this not a child of Node.
///
/// Example:
///   Section: .text
class KeyValueNode final : public Node {
  void anchor() override;

public:
  KeyValueNode(std::unique_ptr<Document> &D)
      : Node(NK_KeyValue, D, StringRef(), StringRef()) {}

  /// Parse and return the key.
  ///
  /// This may be called multiple times.
  ///
  /// \returns The key, or nullptr if failed() == true.
  Node *getKey();

  /// Parse and return the value.
  ///
  /// This may be called multiple times.
  ///
  /// \returns The value, or nullptr if failed() == true.
  Node *getValue();

  void skip() override {
    if (Node *Key = getKey()) {
      Key->skip();
      if (Node *Val = getValue())
        Val->skip();
    }
  }

  static bool classof(const Node *N) {
    return N->getType() == NK_KeyValue;
  }

private:
  Node *Key = nullptr;
  Node *Value = nullptr;
};

/// This is an iterator abstraction over YAML collections shared by both
///        sequences and maps.
///
/// BaseT must have a ValueT* member named CurrentEntry and a member function
/// increment() which must set CurrentEntry to 0 to create an end iterator.
template <class BaseT, class ValueT> class basic_collection_iterator {
public:
  using iterator_category = std::input_iterator_tag;
  using value_type = ValueT;
  using difference_type = std::ptrdiff_t;
  using pointer = value_type *;
  using reference = value_type &;

  basic_collection_iterator() = default;
  basic_collection_iterator(BaseT *B) : Base(B) {}

  ValueT *operator->() const {
    assert(Base && Base->CurrentEntry && "Attempted to access end iterator!");
    return Base->CurrentEntry;
  }

  ValueT &operator*() const {
    assert(Base && Base->CurrentEntry &&
           "Attempted to dereference end iterator!");
    return *Base->CurrentEntry;
  }

  operator ValueT *() const {
    assert(Base && Base->CurrentEntry && "Attempted to access end iterator!");
    return Base->CurrentEntry;
  }

  /// Note on EqualityComparable:
  ///
  /// The iterator is not re-entrant,
  /// it is meant to be used for parsing YAML on-demand
  /// Once iteration started - it can point only to one entry at a time
  /// hence Base.CurrentEntry and Other.Base.CurrentEntry are equal
  /// iff Base and Other.Base are equal.
  bool operator==(const basic_collection_iterator &Other) const {
    if (Base && (Base == Other.Base)) {
      assert((Base->CurrentEntry == Other.Base->CurrentEntry)
             && "Equal Bases expected to point to equal Entries");
    }

    return Base == Other.Base;
  }

  bool operator!=(const basic_collection_iterator &Other) const {
    return !(Base == Other.Base);
  }

  basic_collection_iterator &operator++() {
    assert(Base && "Attempted to advance iterator past end!");
    Base->increment();
    // Create an end iterator.
    if (!Base->CurrentEntry)
      Base = nullptr;
    return *this;
  }

private:
  BaseT *Base = nullptr;
};

// The following two templates are used for both MappingNode and Sequence Node.
template <class CollectionType>
typename CollectionType::iterator begin(CollectionType &C) {
  assert(C.IsAtBeginning && "You may only iterate over a collection once!");
  C.IsAtBeginning = false;
  typename CollectionType::iterator ret(&C);
  ++ret;
  return ret;
}

template <class CollectionType> void skip(CollectionType &C) {
  // TODO: support skipping from the middle of a parsed collection ;/
  assert((C.IsAtBeginning || C.IsAtEnd) && "Cannot skip mid parse!");
  if (C.IsAtBeginning)
    for (typename CollectionType::iterator i = begin(C), e = C.end(); i != e;
         ++i)
      i->skip();
}

/// Represents a YAML map created from either a block map for a flow map.
///
/// This parses the YAML stream as increment() is called.
///
/// Example:
///   Name: _main
///   Scope: Global
class MappingNode final : public Node {
  void anchor() override;

public:
  enum MappingType {
    MT_Block,
    MT_Flow,
    MT_Inline ///< An inline mapping node is used for "[key: value]".
  };

  MappingNode(std::unique_ptr<Document> &D, StringRef Anchor, StringRef Tag,
              MappingType MT)
      : Node(NK_Mapping, D, Anchor, Tag), Type(MT) {}

  friend class basic_collection_iterator<MappingNode, KeyValueNode>;

  using iterator = basic_collection_iterator<MappingNode, KeyValueNode>;

  template <class T> friend typename T::iterator yaml::begin(T &);
  template <class T> friend void yaml::skip(T &);

  iterator begin() { return yaml::begin(*this); }

  iterator end() { return iterator(); }

  void skip() override { yaml::skip(*this); }

  static bool classof(const Node *N) {
    return N->getType() == NK_Mapping;
  }

private:
  MappingType Type;
  bool IsAtBeginning = true;
  bool IsAtEnd = false;
  KeyValueNode *CurrentEntry = nullptr;

  void increment();
};

/// Represents a YAML sequence created from either a block sequence for a
///        flow sequence.
///
/// This parses the YAML stream as increment() is called.
///
/// Example:
///   - Hello
///   - World
class SequenceNode final : public Node {
  void anchor() override;

public:
  enum SequenceType {
    ST_Block,
    ST_Flow,
    // Use for:
    //
    // key:
    // - val1
    // - val2
    //
    // As a BlockMappingEntry and BlockEnd are not created in this case.
    ST_Indentless
  };

  SequenceNode(std::unique_ptr<Document> &D, StringRef Anchor, StringRef Tag,
               SequenceType ST)
      : Node(NK_Sequence, D, Anchor, Tag), SeqType(ST) {}

  friend class basic_collection_iterator<SequenceNode, Node>;

  using iterator = basic_collection_iterator<SequenceNode, Node>;

  template <class T> friend typename T::iterator yaml::begin(T &);
  template <class T> friend void yaml::skip(T &);

  void increment();

  iterator begin() { return yaml::begin(*this); }

  iterator end() { return iterator(); }

  void skip() override { yaml::skip(*this); }

  static bool classof(const Node *N) {
    return N->getType() == NK_Sequence;
  }

private:
  SequenceType SeqType;
  bool IsAtBeginning = true;
  bool IsAtEnd = false;
  bool WasPreviousTokenFlowEntry = true; // Start with an imaginary ','.
  Node *CurrentEntry = nullptr;
};

/// Represents an alias to a Node with an anchor.
///
/// Example:
///   *AnchorName
class AliasNode final : public Node {
  void anchor() override;

public:
  AliasNode(std::unique_ptr<Document> &D, StringRef Val)
      : Node(NK_Alias, D, StringRef(), StringRef()), Name(Val) {}

  StringRef getName() const { return Name; }

  static bool classof(const Node *N) { return N->getType() == NK_Alias; }

private:
  StringRef Name;
};

/// A YAML Stream is a sequence of Documents. A document contains a root
///        node.
class Document {
public:
  Document(Stream &ParentStream);

  /// Root for parsing a node. Returns a single node.
  Node *parseBlockNode();

  /// Finish parsing the current document and return true if there are
  ///        more. Return false otherwise.
  bool skip();

  /// Parse and return the root level node.
  Node *getRoot() {
    if (Root)
      return Root;
    return Root = parseBlockNode();
  }

  const std::map<StringRef, StringRef> &getTagMap() const { return TagMap; }

private:
  friend class Node;
  friend class document_iterator;

  /// Stream to read tokens from.
  Stream &stream;

  /// Used to allocate nodes to. All are destroyed without calling their
  ///        destructor when the document is destroyed.
  BumpPtrAllocator NodeAllocator;

  /// The root node. Used to support skipping a partially parsed
  ///        document.
  Node *Root;

  /// Maps tag prefixes to their expansion.
  std::map<StringRef, StringRef> TagMap;

  Token &peekNext();
  Token getNext();
  void setError(const Twine &Message, Token &Location) const;
  bool failed() const;

  /// Parse %BLAH directives and return true if any were encountered.
  bool parseDirectives();

  /// Parse %YAML
  void parseYAMLDirective();

  /// Parse %TAG
  void parseTAGDirective();

  /// Consume the next token and error if it is not \a TK.
  bool expectToken(int TK);
};

/// Iterator abstraction for Documents over a Stream.
class document_iterator {
public:
  document_iterator() = default;
  document_iterator(std::unique_ptr<Document> &D) : Doc(&D) {}

  bool operator==(const document_iterator &Other) const {
    if (isAtEnd() || Other.isAtEnd())
      return isAtEnd() && Other.isAtEnd();

    return Doc == Other.Doc;
  }
  bool operator!=(const document_iterator &Other) const {
    return !(*this == Other);
  }

  document_iterator operator++() {
    assert(Doc && "incrementing iterator past the end.");
    if (!(*Doc)->skip()) {
      Doc->reset(nullptr);
    } else {
      Stream &S = (*Doc)->stream;
      Doc->reset(new Document(S));
    }
    return *this;
  }

  Document &operator*() { return **Doc; }

  std::unique_ptr<Document> &operator->() { return *Doc; }

private:
  bool isAtEnd() const { return !Doc || !*Doc; }

  std::unique_ptr<Document> *Doc = nullptr;
};

} // end namespace yaml

} // end namespace llvm

#endif // LLVM_SUPPORT_YAMLPARSER_H