Add typepair.h

Introduces typ::Type which wraps a templated pair of AST and SEM type pointers.
This is a temporary helper to ease migration of the thousands of tests that use the ProgramBuilder over from sem::Type to the new ast::Types.

Bug: tint:724
Change-Id: I4e2643a819cde97947d789fce7a74c251f837a58
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48601
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/BUILD.gn

@@ -496,6 +496,7 @@ libtint_source_set("libtint_core_all_src") {
     "symbol_table.cc",
     "symbol_table.h",
     "traits.h",
+    "typepair.h",
     "transform/binding_point.h",
     "transform/binding_remapper.cc",
     "transform/binding_remapper.h",

src/CMakeLists.txt

@@ -249,6 +249,7 @@ set(TINT_LIB_SRCS
   symbol.cc
   symbol.h
   traits.h
+  typepair.h
   transform/binding_point.h
   transform/binding_remapper.cc
   transform/binding_remapper.h

src/typepair.h

@@ -0,0 +1,91 @@
+// Copyright 2021 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.
+
+// This file contains temporary code to help implement the new `ast::Type`s.
+// Once complete, this file should be completely removed.
+// Bug: crbug.com/tint/724
+
+#ifndef SRC_TYPEPAIR_H_
+#define SRC_TYPEPAIR_H_
+
+namespace tint {
+
+namespace ast {
+class Bool;
+class F32;
+class I32;
+class U32;
+class Void;
+}  // namespace ast
+
+namespace sem {
+class Bool;
+class F32;
+class I32;
+class U32;
+class Void;
+}  // namespace sem
+
+namespace typ {  //  type-pair
+
+/// Type is a pair of ast::Type and sem::Type pointers used to simplify
+/// migration to the new ast::Type nodes.
+///
+/// Type attempts to behave as either an ast::Type or sem::Type:
+/// * Type has constructors that take either an ast::Type and sem::Type pointer
+///   pair, and single-parameter implicit constructors for either a single
+///   ast::Type or sem::Type pointer.
+/// * Type also has user-defined conversion functions for returning either an
+///   ast::Type or sem::Type pointer.
+/// * operator->() returns the sem::Type pointer. Later in the migration this
+///   will switch to returning the ast::Type pointer.
+template <typename AST, typename SEM>
+struct Type {
+  /// The ast::Type pointer
+  AST const* const ast = nullptr;
+  /// The sem::Type pointer
+  SEM const* const sem = nullptr;
+
+  /// Constructor
+  Type() = default;
+  /// Constructor
+  /// @param a the ast::Type pointer
+  Type(const AST* a) : ast(a) {}  // NOLINT: explicit
+  /// Constructor
+  /// @param s the sem::Type pointer
+  Type(const SEM* s) : sem(s) {}  // NOLINT: explicit
+  /// Constructor
+  /// @param a the ast::Type pointer
+  /// @param s the sem::Type pointer
+  Type(const AST* a, const SEM* s) : ast(a), sem(s) {}
+
+  /// @returns the ast::Type pointer
+  operator AST*() const { return const_cast<AST*>(ast); }
+  /// @returns the sem::Type pointer
+  operator SEM*() const { return const_cast<SEM*>(sem); }
+  /// @returns the sem::Type pointer
+  SEM* operator->() const { return const_cast<SEM*>(sem); }
+};
+
+using Bool = Type<ast::Bool, sem::Bool>;
+using F32 = Type<ast::F32, sem::F32>;
+using I32 = Type<ast::I32, sem::I32>;
+using U32 = Type<ast::U32, sem::U32>;
+using Void = Type<ast::Void, sem::Void>;
+
+}  // namespace typ
+
+}  // namespace tint
+
+#endif  // SRC_TYPEPAIR_H_