[transform] Add a simple transform manager.

This CL holds a simpler manager to hold and execute multiple transforms.

Bug: tint:206
Change-Id: I45f6b55134f871167704f3549c4e4c72ef806c3a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/29121
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>

BUILD.gn

@@ -375,6 +375,8 @@ source_set("libtint_core_src") {
     "src/source.h",
     "src/transform/bound_array_accessors_transform.cc",
     "src/transform/bound_array_accessors_transform.h",
+    "src/transform/manager.cc",
+    "src/transform/manager.h",
     "src/transform/transformer.cc",
     "src/transform/transformer.h",
     "src/transform/vertex_pulling_transform.cc",

src/CMakeLists.txt

@@ -196,6 +196,8 @@ set(TINT_LIB_SRCS
   source.h
   transform/bound_array_accessors_transform.cc
   transform/bound_array_accessors_transform.h
+  transform/manager.cc
+  transform/manager.h
   transform/transformer.cc
   transform/transformer.h
   transform/vertex_pulling_transform.cc

src/transform/manager.cc

@@ -0,0 +1,35 @@
+// 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.
+
+#include "src/transform/manager.h"
+
+namespace tint {
+namespace transform {
+
+Manager::Manager() = default;
+
+Manager::~Manager() = default;
+
+bool Manager::Run() {
+  for (auto& transform : transforms_) {
+    if (!transform->Run()) {
+      error_ = transform->error();
+      return false;
+    }
+  }
+  return true;
+}
+
+}  // namespace transform
+}  // namespace tint

src/transform/manager.h

@@ -0,0 +1,57 @@
+// 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_TRANSFORM_MANAGER_H_
+#define SRC_TRANSFORM_MANAGER_H_
+
+#include <memory>
+#include <string>
+
+#include "src/transform/transformer.h"
+
+namespace tint {
+namespace transform {
+
+/// Manager for the provided passes. The passes will be execute in the
+/// appended order. If any pass fails the manager will return immediately and
+/// the error can be retrieved with the |error| method.
+class Manager {
+ public:
+  /// Constructor
+  Manager();
+  ~Manager();
+
+  /// Add pass to the manager
+  /// @param transform the transform to append
+  void append(std::unique_ptr<Transformer> transform) {
+    transforms_.push_back(std::move(transform));
+  }
+
+  /// Runs the transforms
+  /// @returns true on success; false otherwise
+  bool Run();
+
+  /// @returns the error, or blank if none set
+  std::string error() const { return error_; }
+
+ private:
+  std::vector<std::unique_ptr<Transformer>> transforms_;
+
+  std::string error_;
+};
+
+}  // namespace transform
+}  // namespace tint
+
+#endif  // SRC_TRANSFORM_MANAGER_H_