text: //===--- Stencil.cpp - Stencil implementation -------------------*- 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
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/Tooling/Transformer/Stencil.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/ASTTypeTraits.h"
  #include "clang/AST/Expr.h"
  #include "clang/ASTMatchers/ASTMatchFinder.h"
  #include "clang/ASTMatchers/ASTMatchers.h"
  #include "clang/Lex/Lexer.h"
  #include "clang/Tooling/Transformer/SourceCode.h"
  #include "clang/Tooling/Transformer/SourceCodeBuilders.h"
  #include "llvm/ADT/Twine.h"
  #include "llvm/Support/Errc.h"
  #include <atomic>
  #include <memory>
  #include <string>
  
  using namespace clang;
  using namespace tooling;
  
  using ast_matchers::MatchFinder;
  using ast_type_traits::DynTypedNode;
  using llvm::errc;
  using llvm::Error;
  using llvm::Expected;
  using llvm::StringError;
  
  // A down_cast function to safely down cast a StencilPartInterface to a subclass
  // D. Returns nullptr if P is not an instance of D.
  template <typename D> const D *down_cast(const StencilPartInterface *P) {
    if (P == nullptr || D::typeId() != P->typeId())
      return nullptr;
    return static_cast<const D *>(P);
  }
  
  static llvm::Expected<DynTypedNode>
  getNode(const ast_matchers::BoundNodes &Nodes, StringRef Id) {
    auto &NodesMap = Nodes.getMap();
    auto It = NodesMap.find(Id);
    if (It == NodesMap.end())
      return llvm::make_error<llvm::StringError>(llvm::errc::invalid_argument,
                                                 "Id not bound: " + Id);
    return It->second;
  }
  
  namespace {
  // An arbitrary fragment of code within a stencil.
  struct RawTextData {
    explicit RawTextData(std::string T) : Text(std::move(T)) {}
    std::string Text;
  };
  
  // A debugging operation to dump the AST for a particular (bound) AST node.
  struct DebugPrintNodeData {
    explicit DebugPrintNodeData(std::string S) : Id(std::move(S)) {}
    std::string Id;
  };
  
  // Operators that take a single node Id as an argument.
  enum class UnaryNodeOperator {
    Parens,
    Deref,
    Address,
  };
  
  // Generic container for stencil operations with a (single) node-id argument.
  struct UnaryOperationData {
    UnaryOperationData(UnaryNodeOperator Op, std::string Id)
        : Op(Op), Id(std::move(Id)) {}
    UnaryNodeOperator Op;
    std::string Id;
  };
  
  // The fragment of code corresponding to the selected range.
  struct SelectorData {
    explicit SelectorData(RangeSelector S) : Selector(std::move(S)) {}
    RangeSelector Selector;
  };
  
  // A stencil operation to build a member access `e.m` or `e->m`, as appropriate.
  struct AccessData {
    AccessData(StringRef BaseId, StencilPart Member)
        : BaseId(BaseId), Member(std::move(Member)) {}
    std::string BaseId;
    StencilPart Member;
  };
  
  struct IfBoundData {
    IfBoundData(StringRef Id, StencilPart TruePart, StencilPart FalsePart)
        : Id(Id), TruePart(std::move(TruePart)), FalsePart(std::move(FalsePart)) {
    }
    std::string Id;
    StencilPart TruePart;
    StencilPart FalsePart;
  };
  
  bool isEqualData(const RawTextData &A, const RawTextData &B) {
    return A.Text == B.Text;
  }
  
  bool isEqualData(const DebugPrintNodeData &A, const DebugPrintNodeData &B) {
    return A.Id == B.Id;
  }
  
  bool isEqualData(const UnaryOperationData &A, const UnaryOperationData &B) {
    return A.Op == B.Op && A.Id == B.Id;
  }
  
  // Equality is not (yet) defined for \c RangeSelector.
  bool isEqualData(const SelectorData &, const SelectorData &) { return false; }
  
  bool isEqualData(const AccessData &A, const AccessData &B) {
    return A.BaseId == B.BaseId && A.Member == B.Member;
  }
  
  bool isEqualData(const IfBoundData &A, const IfBoundData &B) {
    return A.Id == B.Id && A.TruePart == B.TruePart && A.FalsePart == B.FalsePart;
  }
  
  // Equality is not defined over MatchConsumers, which are opaque.
  bool isEqualData(const MatchConsumer<std::string> &A,
                   const MatchConsumer<std::string> &B) {
    return false;
  }
  
  std::string toStringData(const RawTextData &Data) {
    std::string Result;
    llvm::raw_string_ostream OS(Result);
    OS << "\"";
    OS.write_escaped(Data.Text);
    OS << "\"";
    OS.flush();
    return Result;
  }
  
  std::string toStringData(const DebugPrintNodeData &Data) {
    return (llvm::Twine("dPrint(\"") + Data.Id + "\")").str();
  }
  
  std::string toStringData(const UnaryOperationData &Data) {
    StringRef OpName;
    switch (Data.Op) {
    case UnaryNodeOperator::Parens:
      OpName = "expression";
      break;
    case UnaryNodeOperator::Deref:
      OpName = "deref";
      break;
    case UnaryNodeOperator::Address:
      OpName = "addressOf";
      break;
    }
    return (OpName + "(\"" + Data.Id + "\")").str();
  }
  
  std::string toStringData(const SelectorData &) { return "SelectorData()"; }
  
  std::string toStringData(const AccessData &Data) {
    return (llvm::Twine("access(\"") + Data.BaseId + "\", " +
            Data.Member.toString() + ")")
        .str();
  }
  
  std::string toStringData(const IfBoundData &Data) {
    return (llvm::Twine("ifBound(\"") + Data.Id + "\", " +
            Data.TruePart.toString() + ", " + Data.FalsePart.toString() + ")")
        .str();
  }
  
  std::string toStringData(const MatchConsumer<std::string> &) {
    return "MatchConsumer<std::string>()";
  }
  
  // The `evalData()` overloads evaluate the given stencil data to a string, given
  // the match result, and append it to `Result`. We define an overload for each
  // type of stencil data.
  
  Error evalData(const RawTextData &Data, const MatchFinder::MatchResult &,
                 std::string *Result) {
    Result->append(Data.Text);
    return Error::success();
  }
  
  Error evalData(const DebugPrintNodeData &Data,
                 const MatchFinder::MatchResult &Match, std::string *Result) {
    std::string Output;
    llvm::raw_string_ostream Os(Output);
    auto NodeOrErr = getNode(Match.Nodes, Data.Id);
    if (auto Err = NodeOrErr.takeError())
      return Err;
    NodeOrErr->print(Os, PrintingPolicy(Match.Context->getLangOpts()));
    *Result += Os.str();
    return Error::success();
  }
  
  Error evalData(const UnaryOperationData &Data,
                 const MatchFinder::MatchResult &Match, std::string *Result) {
    const auto *E = Match.Nodes.getNodeAs<Expr>(Data.Id);
    if (E == nullptr)
      return llvm::make_error<StringError>(
          errc::invalid_argument, "Id not bound or not Expr: " + Data.Id);
    llvm::Optional<std::string> Source;
    switch (Data.Op) {
    case UnaryNodeOperator::Parens:
      Source = buildParens(*E, *Match.Context);
      break;
    case UnaryNodeOperator::Deref:
      Source = buildDereference(*E, *Match.Context);
      break;
    case UnaryNodeOperator::Address:
      Source = buildAddressOf(*E, *Match.Context);
      break;
    }
    if (!Source)
      return llvm::make_error<StringError>(
          errc::invalid_argument,
          "Could not construct expression source from ID: " + Data.Id);
    *Result += *Source;
    return Error::success();
  }
  
  Error evalData(const SelectorData &Data, const MatchFinder::MatchResult &Match,
                 std::string *Result) {
    auto Range = Data.Selector(Match);
    if (!Range)
      return Range.takeError();
    *Result += getText(*Range, *Match.Context);
    return Error::success();
  }
  
  Error evalData(const AccessData &Data, const MatchFinder::MatchResult &Match,
                 std::string *Result) {
    const auto *E = Match.Nodes.getNodeAs<Expr>(Data.BaseId);
    if (E == nullptr)
      return llvm::make_error<StringError>(errc::invalid_argument,
                                           "Id not bound: " + Data.BaseId);
    if (!E->isImplicitCXXThis()) {
      if (llvm::Optional<std::string> S = E->getType()->isAnyPointerType()
                                              ? buildArrow(*E, *Match.Context)
                                              : buildDot(*E, *Match.Context))
        *Result += *S;
      else
        return llvm::make_error<StringError>(
            errc::invalid_argument,
            "Could not construct object text from ID: " + Data.BaseId);
    }
    return Data.Member.eval(Match, Result);
  }
  
  Error evalData(const IfBoundData &Data, const MatchFinder::MatchResult &Match,
                 std::string *Result) {
    auto &M = Match.Nodes.getMap();
    return (M.find(Data.Id) != M.end() ? Data.TruePart : Data.FalsePart)
        .eval(Match, Result);
  }
  
  Error evalData(const MatchConsumer<std::string> &Fn,
                 const MatchFinder::MatchResult &Match, std::string *Result) {
    Expected<std::string> Value = Fn(Match);
    if (!Value)
      return Value.takeError();
    *Result += *Value;
    return Error::success();
  }
  
  template <typename T>
  class StencilPartImpl : public StencilPartInterface {
    T Data;
  
  public:
    template <typename... Ps>
    explicit StencilPartImpl(Ps &&... Args)
        : StencilPartInterface(StencilPartImpl::typeId()),
          Data(std::forward<Ps>(Args)...) {}
  
    // Generates a unique identifier for this class (specifically, one per
    // instantiation of the template).
    static const void* typeId() {
      static bool b;
      return &b;
    }
  
    Error eval(const MatchFinder::MatchResult &Match,
               std::string *Result) const override {
      return evalData(Data, Match, Result);
    }
  
    bool isEqual(const StencilPartInterface &Other) const override {
      if (const auto *OtherPtr = down_cast<StencilPartImpl>(&Other))
        return isEqualData(Data, OtherPtr->Data);
      return false;
    }
  
    std::string toString() const override { return toStringData(Data); }
  };
  } // namespace
  
  StencilPart Stencil::wrap(StringRef Text) {
    return stencil::text(Text);
  }
  
  StencilPart Stencil::wrap(RangeSelector Selector) {
    return stencil::selection(std::move(Selector));
  }
  
  void Stencil::append(Stencil OtherStencil) {
    for (auto &Part : OtherStencil.Parts)
      Parts.push_back(std::move(Part));
  }
  
  llvm::Expected<std::string>
  Stencil::eval(const MatchFinder::MatchResult &Match) const {
    std::string Result;
    for (const auto &Part : Parts)
      if (auto Err = Part.eval(Match, &Result))
        return std::move(Err);
    return Result;
  }
  
  StencilPart stencil::text(StringRef Text) {
    return StencilPart(std::make_shared<StencilPartImpl<RawTextData>>(Text));
  }
  
  StencilPart stencil::selection(RangeSelector Selector) {
    return StencilPart(
        std::make_shared<StencilPartImpl<SelectorData>>(std::move(Selector)));
  }
  
  StencilPart stencil::dPrint(StringRef Id) {
    return StencilPart(std::make_shared<StencilPartImpl<DebugPrintNodeData>>(Id));
  }
  
  StencilPart stencil::expression(llvm::StringRef Id) {
    return StencilPart(std::make_shared<StencilPartImpl<UnaryOperationData>>(
        UnaryNodeOperator::Parens, Id));
  }
  
  StencilPart stencil::deref(llvm::StringRef ExprId) {
    return StencilPart(std::make_shared<StencilPartImpl<UnaryOperationData>>(
        UnaryNodeOperator::Deref, ExprId));
  }
  
  StencilPart stencil::addressOf(llvm::StringRef ExprId) {
    return StencilPart(std::make_shared<StencilPartImpl<UnaryOperationData>>(
        UnaryNodeOperator::Address, ExprId));
  }
  
  StencilPart stencil::access(StringRef BaseId, StencilPart Member) {
    return StencilPart(
        std::make_shared<StencilPartImpl<AccessData>>(BaseId, std::move(Member)));
  }
  
  StencilPart stencil::ifBound(StringRef Id, StencilPart TruePart,
                               StencilPart FalsePart) {
    return StencilPart(std::make_shared<StencilPartImpl<IfBoundData>>(
        Id, std::move(TruePart), std::move(FalsePart)));
  }
  
  StencilPart stencil::run(MatchConsumer<std::string> Fn) {
    return StencilPart(
        std::make_shared<StencilPartImpl<MatchConsumer<std::string>>>(
            std::move(Fn)));
  }
  