src/clone_context.h

// Copyright 2020 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef SRC_CLONE_CONTEXT_H_
#define SRC_CLONE_CONTEXT_H_

#include <cassert>
#include <functional>
#include <unordered_map>
#include <vector>

#include "src/castable.h"
#include "src/debug.h"
#include "src/source.h"
#include "src/symbol.h"
#include "src/traits.h"

namespace tint {

// Forward declarations
class CloneContext;
class Program;
class ProgramBuilder;

namespace ast {
class FunctionList;
}  // namespace ast

/// Cloneable is the base class for all objects that can be cloned
class Cloneable : public Castable<Cloneable> {
 public:
  /// Performs a deep clone of this object using the CloneContext `ctx`.
  /// @param ctx the clone context
  /// @return the newly cloned object
  virtual Cloneable* Clone(CloneContext* ctx) const = 0;
};

/// CloneContext holds the state used while cloning AST nodes and types.
class CloneContext {
 public:
  /// Constructor
  /// @param to the target ProgramBuilder to clone into
  /// @param from the source Program to clone from
  CloneContext(ProgramBuilder* to, Program const* from);

  /// Destructor
  ~CloneContext();

  /// Clones the Node or type::Type `a` into the ProgramBuilder #dst if `a` is
  /// not null. If `a` is null, then Clone() returns null. If `a` has been
  /// cloned already by this CloneContext then the same cloned pointer is
  /// returned.
  ///
  /// Clone() may use a function registered with ReplaceAll() to create a
  /// transformed version of the object. See ReplaceAll() for more information.
  ///
  /// The Node or type::Type `a` must be owned by the Program #src.
  ///
  /// @param a the `Node` or `type::Type` to clone
  /// @return the cloned node
  template <typename T>
  T* Clone(T* a) {
    // If the input is nullptr, there's nothing to clone - just return nullptr.
    if (a == nullptr) {
      return nullptr;
    }

    // See if we've already cloned this object - if we have return the
    // previously cloned pointer.
    // If we haven't cloned this before, try cloning using a replacer transform.
    if (auto* c = LookupOrTransform(a)) {
      return CheckedCast<T>(c);
    }

    // First time clone and no replacer transforms matched.
    // Clone with T::Clone().
    auto* c = a->Clone(this);
    cloned_.emplace(a, c);
    return CheckedCast<T>(c);
  }

  /// Clones the Node or type::Type `a` into the ProgramBuilder #dst if `a` is
  /// not null. If `a` is null, then Clone() returns null. If `a` has been
  /// cloned already by this CloneContext then the same cloned pointer is
  /// returned.
  ///
  /// Unlike Clone(), this method does not invoke or use any transformations
  /// registered by ReplaceAll().
  ///
  /// The Node or type::Type `a` must be owned by the Program #src.
  ///
  /// @param a the `Node` or `type::Type` to clone
  /// @return the cloned node
  template <typename T>
  T* CloneWithoutTransform(T* a) {
    // If the input is nullptr, there's nothing to clone - just return nullptr.
    if (a == nullptr) {
      return nullptr;
    }

    // Have we seen this object before? If so, return the previously cloned
    // version instead of making yet another copy.
    auto it = cloned_.find(a);
    if (it != cloned_.end()) {
      return CheckedCast(it->second);
    }

    // First time clone and no replacer transforms matched.
    // Clone with T::Clone().
    auto* c = a->Clone(this);
    cloned_.emplace(a, c);
    return CheckedCast(c);
  }

  /// Clones the Source `s` into `dst`
  /// TODO(bclayton) - Currently this 'clone' is a shallow copy. If/when
  /// `Source.File`s are owned by the Program this should make a copy of the
  /// file.
  /// @param s the `Source` to clone
  /// @return the cloned source
  Source Clone(const Source& s) const { return s; }

  /// Clones the Symbol `s` into `dst`
  ///
  /// The Symbol `s` must be owned by the Program #src.
  ///
  /// @param s the Symbol to clone
  /// @return the cloned source
  Symbol Clone(const Symbol& s) const;

  /// Clones each of the elements of the vector `v` into the ProgramBuilder
  /// #dst.
  ///
  /// All the elements of the vector `v` must be owned by the Program #src.
  ///
  /// @param v the vector to clone
  /// @return the cloned vector
  template <typename T>
  std::vector<T> Clone(const std::vector<T>& v) {
    std::vector<T> out;
    out.reserve(v.size());
    for (auto& el : v) {
      out.emplace_back(Clone(el));
    }
    return out;
  }

  /// Clones each of the elements of the vector `v` into the ProgramBuilder
  /// #dst, inserting any additional elements into the list that were registered
  /// with calls to InsertBefore().
  ///
  /// All the elements of the vector `v` must be owned by the Program #src.
  ///
  /// @param v the vector to clone
  /// @return the cloned vector
  template <typename T>
  std::vector<T*> Clone(const std::vector<T*>& v) {
    std::vector<T*> out;
    out.reserve(v.size());
    for (auto& el : v) {
      auto it = insert_before_.find(el);
      if (it != insert_before_.end()) {
        for (auto insert : it->second) {
          out.emplace_back(CheckedCast<T>(insert));
        }
      }
      out.emplace_back(Clone(el));
    }
    return out;
  }

  /// Clones each of the elements of the vector `v` into the ProgramBuilder
  /// #dst.
  ///
  /// All the elements of the vector `v` must be owned by the Program #src.
  ///
  /// @param v the vector to clone
  /// @return the cloned vector
  ast::FunctionList Clone(const ast::FunctionList& v);

  /// ReplaceAll() registers `replacer` to be called whenever the Clone() method
  /// is called with a type that matches (or derives from) the type of the
  /// second parameter of `replacer`.
  ///
  /// `replacer` must be function-like with the signature:
  ///   `T* (CloneContext*, T*)`
  ///  where `T` is a type deriving from Cloneable.
  ///
  /// If `replacer` returns a nullptr then Clone() will attempt the next
  /// registered replacer function that matches the object type. If no replacers
  /// match the object type, or all returned nullptr then Clone() will call
  /// `T::Clone()` to clone the object.
  ///
  /// Example:
  ///
  /// ```
  ///   // Replace all ast::UintLiterals with the number 42
  ///   CloneCtx ctx(&out, in)
  ///     .ReplaceAll([&] (CloneContext* ctx, ast::UintLiteral* l) {
  ///       return ctx->dst->create<ast::UintLiteral>(
  ///           ctx->Clone(l->source()),
  ///           ctx->Clone(l->type()),
  ///           42);
  ///     }).Clone();
  /// ```
  ///
  /// @warning The replacement object must be of the correct type for all
  /// references of the original object. A type mismatch will result in an
  /// assertion in debug builds, and undefined behavior in release builds.
  /// @param replacer a function or function-like object with the signature
  ///        `T* (CloneContext*, T*)`, where `T` derives from Cloneable
  /// @returns this CloneContext so calls can be chained
  template <typename F>
  CloneContext& ReplaceAll(F replacer) {
    using TPtr = traits::ParamTypeT<F, 1>;
    using T = typename std::remove_pointer<TPtr>::type;
    transforms_.emplace_back([=](Cloneable* in) {
      auto* in_as_t = in->As<T>();
      return in_as_t != nullptr ? replacer(this, in_as_t) : nullptr;
    });
    return *this;
  }

  /// Replace replaces all occurrences of `what` in #src with `with` in #dst
  /// when calling Clone().
  /// @param what a pointer to the object in #src that will be replaced with
  /// `with`
  /// @param with a pointer to the replacement object owned by #dst that will be
  /// used as a replacement for `what`
  /// @warning The replacement object must be of the correct type for all
  /// references of the original object. A type mismatch will result in an
  /// assertion in debug builds, and undefined behavior in release builds.
  /// @returns this CloneContext so calls can be chained
  template <typename WHAT, typename WITH>
  CloneContext& Replace(WHAT* what, WITH* with) {
    cloned_[what] = with;
    return *this;
  }

  /// Inserts `object` before `before` whenever a vector containing `object` is
  /// cloned.
  /// @param before a pointer to the object in #src
  /// @param object a pointer to the object in #dst that will be inserted before
  /// any occurrence of the clone of `before`
  /// @returns this CloneContext so calls can be chained
  template <typename BEFORE, typename OBJECT>
  CloneContext& InsertBefore(BEFORE* before, OBJECT* object) {
    auto& list = insert_before_[before];
    list.emplace_back(object);
    return *this;
  }

  /// Clone performs the clone of the Program's AST nodes, types and symbols
  /// from #src to #dst. Semantic nodes are not cloned, as these will be rebuilt
  /// when the ProgramBuilder #dst builds its Program.
  void Clone();

  /// The target ProgramBuilder to clone into.
  ProgramBuilder* const dst;

  /// The source Program to clone from.
  Program const* const src;

 private:
  using Transform = std::function<Cloneable*(Cloneable*)>;

  CloneContext(const CloneContext&) = delete;
  CloneContext& operator=(const CloneContext&) = delete;

  /// LookupOrTransform is the template-independent logic of Clone().
  /// This is outside of Clone() to reduce the amount of template-instantiated
  /// code.
  Cloneable* LookupOrTransform(Cloneable* a) {
    // Have we seen this object before? If so, return the previously cloned
    // version instead of making yet another copy.
    auto it = cloned_.find(a);
    if (it != cloned_.end()) {
      return it->second;
    }

    // Attempt to clone using the registered replacer functions.
    for (auto& f : transforms_) {
      if (Cloneable* c = f(a)) {
        cloned_.emplace(a, c);
        return c;
      }
    }

    // No luck, Clone() will have to call T::Clone().
    return nullptr;
  }

  /// Cast `obj` from type `FROM` to type `TO`, returning the cast object.
  /// Reports an internal compiler error if the cast failed.
  template <typename TO, typename FROM>
  TO* CheckedCast(FROM* obj) {
    TO* cast = obj->template As<TO>();
    if (!cast) {
      TINT_ICE(Diagnostics()) << "Cloned object was not of the expected type";
    }
    return cast;
  }

  /// @returns the diagnostic list of #dst
  diag::List& Diagnostics() const;

  /// A vector of Cloneable*
  using CloneableList = std::vector<Cloneable*>;

  /// A map of object in #src to their cloned equivalent in #dst
  std::unordered_map<Cloneable*, Cloneable*> cloned_;

  /// A map of object in #src to the list of cloned objects in #dst.
  /// Clone(const std::vector<T*>& v) will use this to insert the map-value list
  /// into the target vector/ before cloning and inserting the map-key.
  std::unordered_map<Cloneable*, CloneableList> insert_before_;

  /// Transform functions registered with ReplaceAll()
  std::vector<Transform> transforms_;
};

}  // namespace tint

#endif  // SRC_CLONE_CONTEXT_H_