src/tint/ast/variable.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_VARIABLE_H_
#define SRC_TINT_AST_VARIABLE_H_

#include <utility>
#include <vector>

#include "src/tint/ast/access.h"
#include "src/tint/ast/attribute.h"
#include "src/tint/ast/expression.h"
#include "src/tint/ast/storage_class.h"

// Forward declarations
namespace tint::ast {
class BindingAttribute;
class GroupAttribute;
class LocationAttribute;
class Type;
}  // namespace tint::ast

namespace tint::ast {

/// VariableBindingPoint holds a group and binding attribute.
struct VariableBindingPoint {
    /// The `@group` part of the binding point
    const GroupAttribute* group = nullptr;
    /// The `@binding` part of the binding point
    const BindingAttribute* binding = nullptr;

    /// @returns true if the BindingPoint has a valid group and binding
    /// attribute.
    inline operator bool() const { return group && binding; }
};

/// A Variable statement.
///
/// An instance of this class represents one of four constructs in WGSL: "var"
/// declaration, "let" declaration, "override" declaration, or formal parameter
/// to a function.
///
/// 1. A "var" declaration is a name for typed storage.  Examples:
///
///       // Declared outside a function, i.e. at module scope, requires
///       // a storage class.
///       var<workgroup> width : i32;     // no initializer
///       var<private> height : i32 = 3;  // with initializer
///
///       // A variable declared inside a function doesn't take a storage class,
///       // and maps to SPIR-V Function storage.
///       var computed_depth : i32;
///       var area : i32 = compute_area(width, height);
///
/// 2. A "let" declaration is a name for a typed value.  Examples:
///
///       let twice_depth : i32 = width + width;  // Must have initializer
///
/// 3. An "override" declaration is a name for a pipeline-overridable constant.
/// Examples:
///
///       override radius : i32 = 2;       // Can be overridden by name.
///       @id(5) override width : i32 = 2; // Can be overridden by ID.
///       override scale : f32;            // No default - must be overridden.
///
/// 4. A formal parameter to a function is a name for a typed value to
///    be passed into a function.  Example:
///
///       fn twice(a: i32) -> i32 {  // "a:i32" is the formal parameter
///         return a + a;
///       }
///
/// From the WGSL draft, about "var"::
///
///   A variable is a named reference to storage that can contain a value of a
///   particular type.
///
///   Two types are associated with a variable: its store type (the type of
///   value that may be placed in the referenced storage) and its reference
///   type (the type of the variable itself).  If a variable has store type T
///   and storage class S, then its reference type is pointer-to-T-in-S.
///
/// This class uses the term "type" to refer to:
///     the value type of a "let",
///     the value type of an "override",
///     the value type of the formal parameter,
///     or the store type of the "var".
//
/// Setting is_const:
///   - "var" gets false
///   - "let" gets true
///   - "override" gets true
///   - formal parameter gets true
///
/// Setting is_overrideable:
///   - "var" gets false
///   - "let" gets false
///   - "override" gets true
///   - formal parameter gets false
///
/// Setting storage class:
///   - "var" is StorageClass::kNone when using the
///     defaulting syntax for a "var" declared inside a function.
///   - "let" is always StorageClass::kNone.
///   - formal parameter is always StorageClass::kNone.
class Variable final : public Castable<Variable, Node> {
  public:
    /// Create a variable
    /// @param program_id the identifier of the program that owns this node
    /// @param source the variable source
    /// @param sym the variable symbol
    /// @param declared_storage_class the declared storage class
    /// @param declared_access the declared access control
    /// @param type the declared variable type
    /// @param is_const true if the variable is const
    /// @param is_overridable true if the variable is pipeline-overridable
    /// @param constructor the constructor expression
    /// @param attributes the variable attributes
    Variable(ProgramID program_id,
             const Source& source,
             const Symbol& sym,
             StorageClass declared_storage_class,
             Access declared_access,
             const ast::Type* type,
             bool is_const,
             bool is_overridable,
             const Expression* constructor,
             AttributeList attributes);
    /// Move constructor
    Variable(Variable&&);

    ~Variable() override;

    /// @returns the binding point information for the variable
    VariableBindingPoint BindingPoint() const;

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

    /// The variable symbol
    const Symbol symbol;

    /// The declared variable type. This is null if the type is inferred, e.g.:
    ///   let f = 1.0;
    ///   var i = 1;
    const ast::Type* const type;

    /// True if this is a constant, false otherwise
    const bool is_const;

    /// True if this is a pipeline-overridable constant, false otherwise
    const bool is_overridable;

    /// The constructor expression or nullptr if none set
    const Expression* const constructor;

    /// The attributes attached to this variable
    const AttributeList attributes;

    /// The declared storage class
    const StorageClass declared_storage_class;

    /// The declared access control
    const Access declared_access;
};

/// A list of variables
using VariableList = std::vector<const Variable*>;

}  // namespace tint::ast

#endif  // SRC_TINT_AST_VARIABLE_H_