src/tint/clone_context.h - dawn - Git at Google

 // 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_TINT_CLONE_CONTEXT_H_
 #define SRC_TINT_CLONE_CONTEXT_H_

 #include <algorithm>
 #include <functional>
 #include <type_traits>
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>
 #include <vector>

 #include "src/tint/castable.h"
 #include "src/tint/debug.h"
 #include "src/tint/program_id.h"
 #include "src/tint/symbol.h"
 #include "src/tint/traits.h"

 // Forward declarations
 namespace tint {
 class CloneContext;
 class Program;
 class ProgramBuilder;
 }  // namespace tint
 namespace tint::ast {
 class FunctionList;
 class Node;
 }  // namespace tint::ast

 namespace tint {

 ProgramID ProgramIDOf(const Program*);
 ProgramID ProgramIDOf(const ProgramBuilder*);

 /// 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 const Cloneable* Clone(CloneContext* ctx) const = 0;
 };

 /// @returns an invalid ProgramID
 inline ProgramID ProgramIDOf(const Cloneable*) {
     return ProgramID();
 }

 /// CloneContext holds the state used while cloning AST nodes.
 class CloneContext {
     /// ParamTypeIsPtrOf<F, T> is true iff the first parameter of
     /// F is a pointer of (or derives from) type T.
     template <typename F, typename T>
     static constexpr bool ParamTypeIsPtrOf =
         traits::IsTypeOrDerived<typename std::remove_pointer<traits::ParameterType<F, 0>>::type, T>;

   public:
     /// SymbolTransform is a function that takes a symbol and returns a new
     /// symbol.
     using SymbolTransform = std::function<Symbol(Symbol)>;

     /// Constructor for cloning objects from `from` into `to`.
     /// @param to the target ProgramBuilder to clone into
     /// @param from the source Program to clone from
     /// @param auto_clone_symbols clone all symbols in `from` before returning
     CloneContext(ProgramBuilder* to, Program const* from, bool auto_clone_symbols = true);

     /// Constructor for cloning objects from and to the ProgramBuilder `builder`.
     /// @param builder the ProgramBuilder
     explicit CloneContext(ProgramBuilder* builder);

     /// Destructor
     ~CloneContext();

     /// Clones the Node or sem::Type `a` into the ProgramBuilder #dst if `a` is
     /// not null. If `a` is null, then Clone() returns null.
     ///
     /// Clone() may use a function registered with ReplaceAll() to create a
     /// transformed version of the object. See ReplaceAll() for more information.
     ///
     /// If the CloneContext is cloning from a Program to a ProgramBuilder, then
     /// the Node or sem::Type `a` must be owned by the Program #src.
     ///
     /// @param object the type deriving from Cloneable to clone
     /// @return the cloned node
     template <typename T>
     const T* Clone(const T* object) {
         if (src) {
             TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, object);
         }
         if (auto* cloned = CloneCloneable(object)) {
             auto* out = CheckedCast<T>(cloned);
             TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, out);
             return out;
         }
         return nullptr;
     }

     /// Clones the Node or sem::Type `a` into the ProgramBuilder #dst if `a` is
     /// not null. If `a` is null, then Clone() returns null.
     ///
     /// Unlike Clone(), this method does not invoke or use any transformations
     /// registered by ReplaceAll().
     ///
     /// If the CloneContext is cloning from a Program to a ProgramBuilder, then
     /// the Node or sem::Type `a` must be owned by the Program #src.
     ///
     /// @param a the type deriving from Cloneable to clone
     /// @return the cloned node
     template <typename T>
     const T* CloneWithoutTransform(const T* a) {
         // If the input is nullptr, there's nothing to clone - just return nullptr.
         if (a == nullptr) {
             return nullptr;
         }
         if (src) {
             TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, a);
         }
         auto* c = a->Clone(this);
         return CheckedCast<T>(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(Symbol s);

     /// 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, typename A>
     std::vector<T> Clone(const std::vector<T, A>& 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` using 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, typename A>
     std::vector<T*, A> Clone(const std::vector<T*, A>& v) {
         std::vector<T*, A> out;
         Clone(out, v);
         return out;
     }

     /// Clones each of the elements of the vector `from` into the vector `to`,
     /// inserting any additional elements into the list that were registered with
     /// calls to InsertBefore().
     ///
     /// All the elements of the vector `from` must be owned by the Program #src.
     ///
     /// @param from the vector to clone
     /// @param to the cloned result
     template <typename T, typename A>
     void Clone(std::vector<T*, A>& to, const std::vector<T*, A>& from) {
         to.reserve(from.size());

         auto list_transform_it = list_transforms_.find(&from);
         if (list_transform_it != list_transforms_.end()) {
             const auto& transforms = list_transform_it->second;
             for (auto* o : transforms.insert_front_) {
                 to.emplace_back(CheckedCast<T>(o));
             }
             for (auto& el : from) {
                 auto insert_before_it = transforms.insert_before_.find(el);
                 if (insert_before_it != transforms.insert_before_.end()) {
                     for (auto insert : insert_before_it->second) {
                         to.emplace_back(CheckedCast<T>(insert));
                     }
                 }
                 if (transforms.remove_.count(el) == 0) {
                     to.emplace_back(Clone(el));
                 }
                 auto insert_after_it = transforms.insert_after_.find(el);
                 if (insert_after_it != transforms.insert_after_.end()) {
                     for (auto insert : insert_after_it->second) {
                         to.emplace_back(CheckedCast<T>(insert));
                     }
                 }
             }
             for (auto* o : transforms.insert_back_) {
                 to.emplace_back(CheckedCast<T>(o));
             }
         } else {
             for (auto& el : from) {
                 to.emplace_back(Clone(el));

                 // Clone(el) may have inserted after
                 list_transform_it = list_transforms_.find(&from);
                 if (list_transform_it != list_transforms_.end()) {
                     const auto& transforms = list_transform_it->second;

                     auto insert_after_it = transforms.insert_after_.find(el);
                     if (insert_after_it != transforms.insert_after_.end()) {
                         for (auto insert : insert_after_it->second) {
                             to.emplace_back(CheckedCast<T>(insert));
                         }
                     }
                 }
             }

             // Clone(el)s may have inserted back
             list_transform_it = list_transforms_.find(&from);
             if (list_transform_it != list_transforms_.end()) {
                 const auto& transforms = list_transform_it->second;

                 for (auto* o : transforms.insert_back_) {
                     to.emplace_back(CheckedCast<T>(o));
                 }
             }
         }
     }

     /// 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 Cloneable type that matches (or derives from) the type of
     /// the single parameter of `replacer`.
     /// The returned Cloneable of `replacer` will be used as the replacement for
     /// all references to the object that's being cloned. This returned Cloneable
     /// must be owned by the Program #dst.
     ///
     /// `replacer` must be function-like with the signature: `T* (T*)`
     ///  where `T` is a type deriving from Cloneable.
     ///
     /// If `replacer` returns a nullptr then Clone() will call `T::Clone()` to
     /// clone the object.
     ///
     /// Example:
     ///
     /// ```
     ///   // Replace all ast::UintLiteralExpressions with the number 42
     ///   CloneCtx ctx(&out, in);
     ///   ctx.ReplaceAll([&] (ast::UintLiteralExpression* l) {
     ///       return ctx->dst->create<ast::UintLiteralExpression>(
     ///           ctx->Clone(l->source),
     ///           ctx->Clone(l->type),
     ///           42);
     ///     });
     ///   ctx.Clone();
     /// ```
     ///
     /// @warning a single handler can only be registered for any given type.
     /// Attempting to register two handlers for the same type will result in an
     /// ICE.
     /// @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* (T*)`, where `T` derives from Cloneable
     /// @returns this CloneContext so calls can be chained
     template <typename F>
     traits::EnableIf<ParamTypeIsPtrOf<F, Cloneable>, CloneContext>& ReplaceAll(F&& replacer) {
         using TPtr = traits::ParameterType<F, 0>;
         using T = typename std::remove_pointer<TPtr>::type;
         for (auto& transform : transforms_) {
             if (transform.typeinfo->Is(&TypeInfo::Of<T>()) ||
                 TypeInfo::Of<T>().Is(transform.typeinfo)) {
                 TINT_ICE(Clone, Diagnostics())
                     << "ReplaceAll() called with a handler for type " << TypeInfo::Of<T>().name
                     << " that is already handled by a handler for type "
                     << transform.typeinfo->name;
                 return *this;
             }
         }
         CloneableTransform transform;
         transform.typeinfo = &TypeInfo::Of<T>();
         transform.function = [=](const Cloneable* in) { return replacer(in->As<T>()); };
         transforms_.emplace_back(std::move(transform));
         return *this;
     }

     /// ReplaceAll() registers `replacer` to be called whenever the Clone() method
     /// is called with a Symbol.
     /// The returned symbol of `replacer` will be used as the replacement for
     /// all references to the symbol that's being cloned. This returned Symbol
     /// must be owned by the Program #dst.
     /// @param replacer a function the signature `Symbol(Symbol)`.
     /// @warning a SymbolTransform can only be registered once. Attempting to
     /// register a SymbolTransform more than once will result in an ICE.
     /// @returns this CloneContext so calls can be chained
     CloneContext& ReplaceAll(const SymbolTransform& replacer) {
         if (symbol_transform_) {
             TINT_ICE(Clone, Diagnostics()) << "ReplaceAll(const SymbolTransform&) called "
                                               "multiple times on the same CloneContext";
             return *this;
         }
         symbol_transform_ = replacer;
         return *this;
     }

     /// Replace replaces all occurrences of `what` in #src with the pointer `with`
     /// in #dst when calling Clone().
     /// [DEPRECATED]: This function cannot handle nested replacements. Use the
     /// overload of Replace() that take a function for the `WITH` argument.
     /// @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, typename = traits::EnableIfIsType<WITH, Cloneable>>
     CloneContext& Replace(const WHAT* what, const WITH* with) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, what);
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, with);
         replacements_[what] = [with]() -> const Cloneable* { return with; };
         return *this;
     }

     /// Replace replaces all occurrences of `what` in #src with the result of the
     /// function `with` in #dst when calling Clone(). `with` will be called each
     /// time `what` is cloned by this context. If `what` is not cloned, then
     /// `with` may never be called.
     /// @param what a pointer to the object in #src that will be replaced with
     /// `with`
     /// @param with a function that takes no arguments and returns a pointer to
     /// the replacement object owned by #dst. The returned pointer 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, typename = std::invoke_result_t<WITH>>
     CloneContext& Replace(const WHAT* what, WITH&& with) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, what);
         replacements_[what] = with;
         return *this;
     }

     /// Removes `object` from the cloned copy of `vector`.
     /// @param vector the vector in #src
     /// @param object a pointer to the object in #src that will be omitted from
     /// the cloned vector.
     /// @returns this CloneContext so calls can be chained
     template <typename T, typename A, typename OBJECT>
     CloneContext& Remove(const std::vector<T, A>& vector, OBJECT* object) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, object);
         if (std::find(vector.begin(), vector.end(), object) == vector.end()) {
             TINT_ICE(Clone, Diagnostics())
                 << "CloneContext::Remove() vector does not contain object";
             return *this;
         }

         list_transforms_[&vector].remove_.emplace(object);
         return *this;
     }

     /// Inserts `object` before any other objects of `vector`, when it is cloned.
     /// @param vector the vector in #src
     /// @param object a pointer to the object in #dst that will be inserted at the
     /// front of the vector
     /// @returns this CloneContext so calls can be chained
     template <typename T, typename A, typename OBJECT>
     CloneContext& InsertFront(const std::vector<T, A>& vector, OBJECT* object) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
         auto& transforms = list_transforms_[&vector];
         auto& list = transforms.insert_front_;
         list.emplace_back(object);
         return *this;
     }

     /// Inserts `object` after any other objects of `vector`, when it is cloned.
     /// @param vector the vector in #src
     /// @param object a pointer to the object in #dst that will be inserted at the
     /// end of the vector
     /// @returns this CloneContext so calls can be chained
     template <typename T, typename A, typename OBJECT>
     CloneContext& InsertBack(const std::vector<T, A>& vector, OBJECT* object) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
         auto& transforms = list_transforms_[&vector];
         auto& list = transforms.insert_back_;
         list.emplace_back(object);
         return *this;
     }

     /// Inserts `object` before `before` whenever `vector` is cloned.
     /// @param vector the vector in #src
     /// @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 T, typename A, typename BEFORE, typename OBJECT>
     CloneContext& InsertBefore(const std::vector<T, A>& vector,
                                const BEFORE* before,
                                const OBJECT* object) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, before);
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
         if (std::find(vector.begin(), vector.end(), before) == vector.end()) {
             TINT_ICE(Clone, Diagnostics())
                 << "CloneContext::InsertBefore() vector does not contain before";
             return *this;
         }

         auto& transforms = list_transforms_[&vector];
         auto& list = transforms.insert_before_[before];
         list.emplace_back(object);
         return *this;
     }

     /// Inserts `object` after `after` whenever `vector` is cloned.
     /// @param vector the vector in #src
     /// @param after a pointer to the object in #src
     /// @param object a pointer to the object in #dst that will be inserted after
     /// any occurrence of the clone of `after`
     /// @returns this CloneContext so calls can be chained
     template <typename T, typename A, typename AFTER, typename OBJECT>
     CloneContext& InsertAfter(const std::vector<T, A>& vector,
                               const AFTER* after,
                               const OBJECT* object) {
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, after);
         TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
         if (std::find(vector.begin(), vector.end(), after) == vector.end()) {
             TINT_ICE(Clone, Diagnostics())
                 << "CloneContext::InsertAfter() vector does not contain after";
             return *this;
         }

         auto& transforms = list_transforms_[&vector];
         auto& list = transforms.insert_after_[after];
         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:
     struct CloneableTransform {
         /// Constructor
         CloneableTransform();
         /// Copy constructor
         /// @param other the CloneableTransform to copy
         CloneableTransform(const CloneableTransform& other);
         /// Destructor
         ~CloneableTransform();

         // TypeInfo of the Cloneable that the transform operates on
         const TypeInfo* typeinfo;
         std::function<const Cloneable*(const Cloneable*)> function;
     };

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

     /// 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>
     const TO* CheckedCast(const FROM* obj) {
         if (obj == nullptr) {
             return nullptr;
         }
         if (const TO* cast = obj->template As<TO>()) {
             return cast;
         }
         CheckedCastFailure(obj, TypeInfo::Of<TO>());
         return nullptr;
     }

     /// Clones a Cloneable object, using any replacements or transforms that have
     /// been configured.
     const Cloneable* CloneCloneable(const Cloneable* object);

     /// Adds an error diagnostic to Diagnostics() that the cloned object was not
     /// of the expected type.
     void CheckedCastFailure(const Cloneable* got, const TypeInfo& expected);

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

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

     /// Transformations to be applied to a list (vector)
     struct ListTransforms {
         /// Constructor
         ListTransforms();
         /// Destructor
         ~ListTransforms();

         /// A map of object in #src to omit when cloned into #dst.
         std::unordered_set<const Cloneable*> remove_;

         /// A list of objects in #dst to insert before any others when the vector is
         /// cloned.
         CloneableList insert_front_;

         /// A list of objects in #dst to insert befor after any others when the
         /// vector is cloned.
         CloneableList insert_back_;

         /// 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<const Cloneable*, CloneableList> insert_before_;

         /// 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 after cloning and inserting the map-key.
         std::unordered_map<const Cloneable*, CloneableList> insert_after_;
     };

     /// A map of object in #src to functions that create their replacement in
     /// #dst
     std::unordered_map<const Cloneable*, std::function<const Cloneable*()>> replacements_;

     /// A map of symbol in #src to their cloned equivalent in #dst
     std::unordered_map<Symbol, Symbol> cloned_symbols_;

     /// Cloneable transform functions registered with ReplaceAll()
     std::vector<CloneableTransform> transforms_;

     /// Map of std::vector pointer to transforms for that list
     std::unordered_map<const void*, ListTransforms> list_transforms_;

     /// Symbol transform registered with ReplaceAll()
     SymbolTransform symbol_transform_;
 };

 }  // namespace tint

 #endif  // SRC_TINT_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_TINT_CLONE_CONTEXT_H_
	#define SRC_TINT_CLONE_CONTEXT_H_

	#include <algorithm>
	#include <functional>
	#include <type_traits>
	#include <unordered_map>
	#include <unordered_set>
	#include <utility>
	#include <vector>

	#include "src/tint/castable.h"
	#include "src/tint/debug.h"
	#include "src/tint/program_id.h"
	#include "src/tint/symbol.h"
	#include "src/tint/traits.h"

	// Forward declarations
	namespace tint {
	class CloneContext;
	class Program;
	class ProgramBuilder;
	} // namespace tint
	namespace tint::ast {
	class FunctionList;
	class Node;
	} // namespace tint::ast

	namespace tint {

	ProgramID ProgramIDOf(const Program*);
	ProgramID ProgramIDOf(const ProgramBuilder*);

	/// 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 const Cloneable* Clone(CloneContext* ctx) const = 0;
	};

	/// @returns an invalid ProgramID
	inline ProgramID ProgramIDOf(const Cloneable*) {
	return ProgramID();
	}

	/// CloneContext holds the state used while cloning AST nodes.
	class CloneContext {
	/// ParamTypeIsPtrOf<F, T> is true iff the first parameter of
	/// F is a pointer of (or derives from) type T.
	template <typename F, typename T>
	static constexpr bool ParamTypeIsPtrOf =
	traits::IsTypeOrDerived<typename std::remove_pointer<traits::ParameterType<F, 0>>::type, T>;

	public:
	/// SymbolTransform is a function that takes a symbol and returns a new
	/// symbol.
	using SymbolTransform = std::function<Symbol(Symbol)>;

	/// Constructor for cloning objects from `from` into `to`.
	/// @param to the target ProgramBuilder to clone into
	/// @param from the source Program to clone from
	/// @param auto_clone_symbols clone all symbols in `from` before returning
	CloneContext(ProgramBuilder* to, Program const* from, bool auto_clone_symbols = true);

	/// Constructor for cloning objects from and to the ProgramBuilder `builder`.
	/// @param builder the ProgramBuilder
	explicit CloneContext(ProgramBuilder* builder);

	/// Destructor
	~CloneContext();

	/// Clones the Node or sem::Type `a` into the ProgramBuilder #dst if `a` is
	/// not null. If `a` is null, then Clone() returns null.
	///
	/// Clone() may use a function registered with ReplaceAll() to create a
	/// transformed version of the object. See ReplaceAll() for more information.
	///
	/// If the CloneContext is cloning from a Program to a ProgramBuilder, then
	/// the Node or sem::Type `a` must be owned by the Program #src.
	///
	/// @param object the type deriving from Cloneable to clone
	/// @return the cloned node
	template <typename T>
	const T* Clone(const T* object) {
	if (src) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, object);
	}
	if (auto* cloned = CloneCloneable(object)) {
	auto* out = CheckedCast<T>(cloned);
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, out);
	return out;
	}
	return nullptr;
	}

	/// Clones the Node or sem::Type `a` into the ProgramBuilder #dst if `a` is
	/// not null. If `a` is null, then Clone() returns null.
	///
	/// Unlike Clone(), this method does not invoke or use any transformations
	/// registered by ReplaceAll().
	///
	/// If the CloneContext is cloning from a Program to a ProgramBuilder, then
	/// the Node or sem::Type `a` must be owned by the Program #src.
	///
	/// @param a the type deriving from Cloneable to clone
	/// @return the cloned node
	template <typename T>
	const T* CloneWithoutTransform(const T* a) {
	// If the input is nullptr, there's nothing to clone - just return nullptr.
	if (a == nullptr) {
	return nullptr;
	}
	if (src) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, a);
	}
	auto* c = a->Clone(this);
	return CheckedCast<T>(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(Symbol s);

	/// 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, typename A>
	std::vector<T> Clone(const std::vector<T, A>& 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` using 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, typename A>
	std::vector<T, A> Clone(const std::vector<T, A>& v) {
	std::vector<T*, A> out;
	Clone(out, v);
	return out;
	}

	/// Clones each of the elements of the vector `from` into the vector `to`,
	/// inserting any additional elements into the list that were registered with
	/// calls to InsertBefore().
	///
	/// All the elements of the vector `from` must be owned by the Program #src.
	///
	/// @param from the vector to clone
	/// @param to the cloned result
	template <typename T, typename A>
	void Clone(std::vector<T, A>& to, const std::vector<T, A>& from) {
	to.reserve(from.size());

	auto list_transform_it = list_transforms_.find(&from);
	if (list_transform_it != list_transforms_.end()) {
	const auto& transforms = list_transform_it->second;
	for (auto* o : transforms.insert_front_) {
	to.emplace_back(CheckedCast<T>(o));
	}
	for (auto& el : from) {
	auto insert_before_it = transforms.insert_before_.find(el);
	if (insert_before_it != transforms.insert_before_.end()) {
	for (auto insert : insert_before_it->second) {
	to.emplace_back(CheckedCast<T>(insert));
	}
	}
	if (transforms.remove_.count(el) == 0) {
	to.emplace_back(Clone(el));
	}
	auto insert_after_it = transforms.insert_after_.find(el);
	if (insert_after_it != transforms.insert_after_.end()) {
	for (auto insert : insert_after_it->second) {
	to.emplace_back(CheckedCast<T>(insert));
	}
	}
	}
	for (auto* o : transforms.insert_back_) {
	to.emplace_back(CheckedCast<T>(o));
	}
	} else {
	for (auto& el : from) {
	to.emplace_back(Clone(el));

	// Clone(el) may have inserted after
	list_transform_it = list_transforms_.find(&from);
	if (list_transform_it != list_transforms_.end()) {
	const auto& transforms = list_transform_it->second;

	auto insert_after_it = transforms.insert_after_.find(el);
	if (insert_after_it != transforms.insert_after_.end()) {
	for (auto insert : insert_after_it->second) {
	to.emplace_back(CheckedCast<T>(insert));
	}
	}
	}
	}

	// Clone(el)s may have inserted back
	list_transform_it = list_transforms_.find(&from);
	if (list_transform_it != list_transforms_.end()) {
	const auto& transforms = list_transform_it->second;

	for (auto* o : transforms.insert_back_) {
	to.emplace_back(CheckedCast<T>(o));
	}
	}
	}
	}

	/// 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 Cloneable type that matches (or derives from) the type of
	/// the single parameter of `replacer`.
	/// The returned Cloneable of `replacer` will be used as the replacement for
	/// all references to the object that's being cloned. This returned Cloneable
	/// must be owned by the Program #dst.
	///
	/// `replacer` must be function-like with the signature: `T* (T*)`
	/// where `T` is a type deriving from Cloneable.
	///
	/// If `replacer` returns a nullptr then Clone() will call `T::Clone()` to
	/// clone the object.
	///
	/// Example:
	///
	/// ```
	/// // Replace all ast::UintLiteralExpressions with the number 42
	/// CloneCtx ctx(&out, in);
	/// ctx.ReplaceAll([&] (ast::UintLiteralExpression* l) {
	/// return ctx->dst->create<ast::UintLiteralExpression>(
	/// ctx->Clone(l->source),
	/// ctx->Clone(l->type),
	/// 42);
	/// });
	/// ctx.Clone();
	/// ```
	///
	/// @warning a single handler can only be registered for any given type.
	/// Attempting to register two handlers for the same type will result in an
	/// ICE.
	/// @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* (T*)`, where `T` derives from Cloneable
	/// @returns this CloneContext so calls can be chained
	template <typename F>
	traits::EnableIf<ParamTypeIsPtrOf<F, Cloneable>, CloneContext>& ReplaceAll(F&& replacer) {
	using TPtr = traits::ParameterType<F, 0>;
	using T = typename std::remove_pointer<TPtr>::type;
	for (auto& transform : transforms_) {
	if (transform.typeinfo->Is(&TypeInfo::Of<T>()) \|\|
	TypeInfo::Of<T>().Is(transform.typeinfo)) {
	TINT_ICE(Clone, Diagnostics())
	<< "ReplaceAll() called with a handler for type " << TypeInfo::Of<T>().name
	<< " that is already handled by a handler for type "
	<< transform.typeinfo->name;
	return *this;
	}
	}
	CloneableTransform transform;
	transform.typeinfo = &TypeInfo::Of<T>();
	transform.function = [=](const Cloneable* in) { return replacer(in->As<T>()); };
	transforms_.emplace_back(std::move(transform));
	return *this;
	}

	/// ReplaceAll() registers `replacer` to be called whenever the Clone() method
	/// is called with a Symbol.
	/// The returned symbol of `replacer` will be used as the replacement for
	/// all references to the symbol that's being cloned. This returned Symbol
	/// must be owned by the Program #dst.
	/// @param replacer a function the signature `Symbol(Symbol)`.
	/// @warning a SymbolTransform can only be registered once. Attempting to
	/// register a SymbolTransform more than once will result in an ICE.
	/// @returns this CloneContext so calls can be chained
	CloneContext& ReplaceAll(const SymbolTransform& replacer) {
	if (symbol_transform_) {
	TINT_ICE(Clone, Diagnostics()) << "ReplaceAll(const SymbolTransform&) called "
	"multiple times on the same CloneContext";
	return *this;
	}
	symbol_transform_ = replacer;
	return *this;
	}

	/// Replace replaces all occurrences of `what` in #src with the pointer `with`
	/// in #dst when calling Clone().
	/// [DEPRECATED]: This function cannot handle nested replacements. Use the
	/// overload of Replace() that take a function for the `WITH` argument.
	/// @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, typename = traits::EnableIfIsType<WITH, Cloneable>>
	CloneContext& Replace(const WHAT* what, const WITH* with) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, what);
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, with);
	replacements_[what] = [with]() -> const Cloneable* { return with; };
	return *this;
	}

	/// Replace replaces all occurrences of `what` in #src with the result of the
	/// function `with` in #dst when calling Clone(). `with` will be called each
	/// time `what` is cloned by this context. If `what` is not cloned, then
	/// `with` may never be called.
	/// @param what a pointer to the object in #src that will be replaced with
	/// `with`
	/// @param with a function that takes no arguments and returns a pointer to
	/// the replacement object owned by #dst. The returned pointer 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, typename = std::invoke_result_t<WITH>>
	CloneContext& Replace(const WHAT* what, WITH&& with) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, what);
	replacements_[what] = with;
	return *this;
	}

	/// Removes `object` from the cloned copy of `vector`.
	/// @param vector the vector in #src
	/// @param object a pointer to the object in #src that will be omitted from
	/// the cloned vector.
	/// @returns this CloneContext so calls can be chained
	template <typename T, typename A, typename OBJECT>
	CloneContext& Remove(const std::vector<T, A>& vector, OBJECT* object) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, object);
	if (std::find(vector.begin(), vector.end(), object) == vector.end()) {
	TINT_ICE(Clone, Diagnostics())
	<< "CloneContext::Remove() vector does not contain object";
	return *this;
	}

	list_transforms_[&vector].remove_.emplace(object);
	return *this;
	}

	/// Inserts `object` before any other objects of `vector`, when it is cloned.
	/// @param vector the vector in #src
	/// @param object a pointer to the object in #dst that will be inserted at the
	/// front of the vector
	/// @returns this CloneContext so calls can be chained
	template <typename T, typename A, typename OBJECT>
	CloneContext& InsertFront(const std::vector<T, A>& vector, OBJECT* object) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
	auto& transforms = list_transforms_[&vector];
	auto& list = transforms.insert_front_;
	list.emplace_back(object);
	return *this;
	}

	/// Inserts `object` after any other objects of `vector`, when it is cloned.
	/// @param vector the vector in #src
	/// @param object a pointer to the object in #dst that will be inserted at the
	/// end of the vector
	/// @returns this CloneContext so calls can be chained
	template <typename T, typename A, typename OBJECT>
	CloneContext& InsertBack(const std::vector<T, A>& vector, OBJECT* object) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
	auto& transforms = list_transforms_[&vector];
	auto& list = transforms.insert_back_;
	list.emplace_back(object);
	return *this;
	}

	/// Inserts `object` before `before` whenever `vector` is cloned.
	/// @param vector the vector in #src
	/// @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 T, typename A, typename BEFORE, typename OBJECT>
	CloneContext& InsertBefore(const std::vector<T, A>& vector,
	const BEFORE* before,
	const OBJECT* object) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, before);
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
	if (std::find(vector.begin(), vector.end(), before) == vector.end()) {
	TINT_ICE(Clone, Diagnostics())
	<< "CloneContext::InsertBefore() vector does not contain before";
	return *this;
	}

	auto& transforms = list_transforms_[&vector];
	auto& list = transforms.insert_before_[before];
	list.emplace_back(object);
	return *this;
	}

	/// Inserts `object` after `after` whenever `vector` is cloned.
	/// @param vector the vector in #src
	/// @param after a pointer to the object in #src
	/// @param object a pointer to the object in #dst that will be inserted after
	/// any occurrence of the clone of `after`
	/// @returns this CloneContext so calls can be chained
	template <typename T, typename A, typename AFTER, typename OBJECT>
	CloneContext& InsertAfter(const std::vector<T, A>& vector,
	const AFTER* after,
	const OBJECT* object) {
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, src, after);
	TINT_ASSERT_PROGRAM_IDS_EQUAL_IF_VALID(Clone, dst, object);
	if (std::find(vector.begin(), vector.end(), after) == vector.end()) {
	TINT_ICE(Clone, Diagnostics())
	<< "CloneContext::InsertAfter() vector does not contain after";
	return *this;
	}

	auto& transforms = list_transforms_[&vector];
	auto& list = transforms.insert_after_[after];
	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:
	struct CloneableTransform {
	/// Constructor
	CloneableTransform();
	/// Copy constructor
	/// @param other the CloneableTransform to copy
	CloneableTransform(const CloneableTransform& other);
	/// Destructor
	~CloneableTransform();

	// TypeInfo of the Cloneable that the transform operates on
	const TypeInfo* typeinfo;
	std::function<const Cloneable(const Cloneable)> function;
	};

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

	/// 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>
	const TO* CheckedCast(const FROM* obj) {
	if (obj == nullptr) {
	return nullptr;
	}
	if (const TO* cast = obj->template As<TO>()) {
	return cast;
	}
	CheckedCastFailure(obj, TypeInfo::Of<TO>());
	return nullptr;
	}

	/// Clones a Cloneable object, using any replacements or transforms that have
	/// been configured.
	const Cloneable* CloneCloneable(const Cloneable* object);

	/// Adds an error diagnostic to Diagnostics() that the cloned object was not
	/// of the expected type.
	void CheckedCastFailure(const Cloneable* got, const TypeInfo& expected);

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

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

	/// Transformations to be applied to a list (vector)
	struct ListTransforms {
	/// Constructor
	ListTransforms();
	/// Destructor
	~ListTransforms();

	/// A map of object in #src to omit when cloned into #dst.
	std::unordered_set<const Cloneable*> remove_;

	/// A list of objects in #dst to insert before any others when the vector is
	/// cloned.
	CloneableList insert_front_;

	/// A list of objects in #dst to insert befor after any others when the
	/// vector is cloned.
	CloneableList insert_back_;

	/// 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<const Cloneable*, CloneableList> insert_before_;

	/// 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 after cloning and inserting the map-key.
	std::unordered_map<const Cloneable*, CloneableList> insert_after_;
	};

	/// A map of object in #src to functions that create their replacement in
	/// #dst
	std::unordered_map<const Cloneable, std::function<const Cloneable()>> replacements_;

	/// A map of symbol in #src to their cloned equivalent in #dst
	std::unordered_map<Symbol, Symbol> cloned_symbols_;

	/// Cloneable transform functions registered with ReplaceAll()
	std::vector<CloneableTransform> transforms_;

	/// Map of std::vector pointer to transforms for that list
	std::unordered_map<const void*, ListTransforms> list_transforms_;

	/// Symbol transform registered with ReplaceAll()
	SymbolTransform symbol_transform_;
	};

	} // namespace tint

	#endif // SRC_TINT_CLONE_CONTEXT_H_