src/tint/lang/wgsl/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,
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// See the License for the specific language governing permissions and
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#ifndef SRC_TINT_LANG_WGSL_AST_STRUCT_MEMBER_OFFSET_ATTRIBUTE_H_
#define SRC_TINT_LANG_WGSL_AST_STRUCT_MEMBER_OFFSET_ATTRIBUTE_H_

#include <string>

#include "src/tint/lang/wgsl/ast/attribute.h"
#include "src/tint/lang/wgsl/ast/expression.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 nid the unique node identifier
    /// @param src the source of this node
    /// @param expr the offset expression
    StructMemberOffsetAttribute(GenerationID pid,
                                NodeID nid,
                                const Source& src,
                                const Expression* expr);
    ~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 expression
    const Expression* const expr;
};

}  // namespace tint::ast

#endif  // SRC_TINT_LANG_WGSL_AST_STRUCT_MEMBER_OFFSET_ATTRIBUTE_H_