src/tint/ast/struct_member_offset_attribute.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_AST_STRUCT_MEMBER_OFFSET_ATTRIBUTE_H_
#define SRC_TINT_AST_STRUCT_MEMBER_OFFSET_ATTRIBUTE_H_

#include <string>

#include "src/tint/ast/attribute.h"

namespace tint::ast {

/// A struct member offset attribute
/// @note The WGSL spec removed the `@offset(n)` attribute for `@size(n)`
/// and `@align(n)` in https://github.com/gpuweb/gpuweb/pull/1447. However
/// this attribute is kept because the SPIR-V reader has to deal with absolute
/// offsets, and transforming these to size / align is complex and can be done
/// in a number of ways. The Resolver is responsible for consuming the size and
/// align attributes and transforming these into absolute offsets. It is
/// trivial for the Resolver to handle `@offset(n)` or `@size(n)` /
/// `@align(n)` attributes, so this is what we do, keeping all the layout
/// logic in one place.
class StructMemberOffsetAttribute final
    : public Castable<StructMemberOffsetAttribute, Attribute> {
 public:
  /// constructor
  /// @param pid the identifier of the program that owns this node
  /// @param src the source of this node
  /// @param offset the offset value
  StructMemberOffsetAttribute(ProgramID pid,
                              const Source& src,
                              uint32_t offset);
  ~StructMemberOffsetAttribute() override;

  /// @returns the WGSL name for the attribute
  std::string Name() const override;

  /// Clones this node and all transitive child nodes using the `CloneContext`
  /// `ctx`.
  /// @param ctx the clone context
  /// @return the newly cloned node
  const StructMemberOffsetAttribute* Clone(CloneContext* ctx) const override;

  /// The offset value
  const uint32_t offset;
};

}  // namespace tint::ast

#endif  // SRC_TINT_AST_STRUCT_MEMBER_OFFSET_ATTRIBUTE_H_