//===--- MatchConsumer.h - MatchConsumer abstraction ------------*- 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

//

//===----------------------------------------------------------------------===//

///

/// \file This file defines the *MatchConsumer* abstraction: a computation over

/// match results, specifically the `ast_matchers::MatchFinder::MatchResult`

/// class.

///

//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_TOOLING_TRANSFORMER_MATCHCONSUMER_H

#define LLVM_CLANG_TOOLING_TRANSFORMER_MATCHCONSUMER_H

#include "clang/AST/ASTTypeTraits.h"

#include "clang/ASTMatchers/ASTMatchFinder.h"

#include "llvm/ADT/StringRef.h"

#include "llvm/Support/Errc.h"

#include "llvm/Support/Error.h"

namespace clang {

namespace transformer {

/// A failable computation over nodes bound by AST matchers.

///

/// The computation should report any errors though its return value (rather

/// than terminating the program) to enable usage in interactive scenarios like

/// clang-query.

///

/// This is a central abstraction of the Transformer framework.

template <typename T>

using MatchConsumer =

    std::function<Expected<T>(const ast_matchers::MatchFinder::MatchResult &)>;

/// Creates an error that signals that a `MatchConsumer` expected a certain node

/// to be bound by AST matchers, but it was not actually bound.

inline llvm::Error notBoundError(llvm::StringRef Id) {

  return llvm::make_error<llvm::StringError>(llvm::errc::invalid_argument,

                                             "Id not bound: " + Id);

}

/// Chooses between the two consumers, based on whether \p ID is bound in the

/// match.

template <typename T>

MatchConsumer<T> ifBound(std::string ID, MatchConsumer<T> TrueC,

                         MatchConsumer<T> FalseC) {

  return [=](const ast_matchers::MatchFinder::MatchResult &Result) {

    auto &Map = Result.Nodes.getMap();

    return (Map.find(ID) != Map.end() ? TrueC : FalseC)(Result);

  };

}

/// A failable computation over nodes bound by AST matchers, with (limited)

/// reflection via the `toString` method.

///

/// The computation should report any errors though its return value (rather

/// than terminating the program) to enable usage in interactive scenarios like

/// clang-query.

///

/// This is a central abstraction of the Transformer framework. It is a

/// generalization of `MatchConsumer` and intended to replace it.

template <typename T> class MatchComputation {

public:

  virtual ~MatchComputation() = default;

  /// Evaluates the computation and (potentially) updates the accumulator \c

  /// Result.  \c Result is undefined in the case of an error. `Result` is an

  /// out parameter to optimize case where the computation involves composing

  /// the result of sub-computation evaluations.

  virtual llvm::Error eval(const ast_matchers::MatchFinder::MatchResult &Match,

                           T *Result) const = 0;

  /// Convenience version of `eval`, for the case where the computation is being

  /// evaluated on its own.

  llvm::Expected<T> eval(const ast_matchers::MatchFinder::MatchResult &R) const;

  /// Constructs a string representation of the computation, for informational

  /// purposes. The representation must be deterministic, but is not required to

  /// be unique.

  virtual std::string toString() const = 0;

protected:

  MatchComputation() = default;

  // Since this is an abstract class, copying/assigning only make sense for

  // derived classes implementing `clone()`.

  MatchComputation(const MatchComputation &) = default;

  MatchComputation &operator=(const MatchComputation &) = default;

};

template <typename T>

llvm::Expected<T> MatchComputation<T>::eval(

    const ast_matchers::MatchFinder::MatchResult &R) const {

  T Output;

  if (auto Err = eval(R, &Output))

    return std::move(Err);

  return Output;

}

} // namespace transformer

} // namespace clang

#endif // LLVM_CLANG_TOOLING_TRANSFORMER_MATCHCONSUMER_H