luau/Analysis/include/Luau/Instantiation.h

// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
#pragma once

#include "Luau/NotNull.h"
#include "Luau/Substitution.h"
#include "Luau/TypeFwd.h"
#include "Luau/Unifiable.h"

namespace Luau
{

struct TxnLog;
struct TypeArena;
struct TypeCheckLimits;

// A substitution which replaces generic types in a given set by free types.
struct ReplaceGenerics : Substitution
{
    ReplaceGenerics(const TxnLog* log, TypeArena* arena, NotNull<BuiltinTypes> builtinTypes, TypeLevel level, Scope* scope,
        const std::vector<TypeId>& generics, const std::vector<TypePackId>& genericPacks)
        : Substitution(log, arena)
        , builtinTypes(builtinTypes)
        , level(level)
        , scope(scope)
        , generics(generics)
        , genericPacks(genericPacks)
    {
    }

    NotNull<BuiltinTypes> builtinTypes;

    TypeLevel level;
    Scope* scope;
    std::vector<TypeId> generics;
    std::vector<TypePackId> genericPacks;
    bool ignoreChildren(TypeId ty) override;
    bool isDirty(TypeId ty) override;
    bool isDirty(TypePackId tp) override;
    TypeId clean(TypeId ty) override;
    TypePackId clean(TypePackId tp) override;
};

// A substitution which replaces generic functions by monomorphic functions
struct Instantiation : Substitution
{
    Instantiation(const TxnLog* log, TypeArena* arena, NotNull<BuiltinTypes> builtinTypes, TypeLevel level, Scope* scope)
        : Substitution(log, arena)
        , builtinTypes(builtinTypes)
        , level(level)
        , scope(scope)
    {
    }

    NotNull<BuiltinTypes> builtinTypes;

    TypeLevel level;
    Scope* scope;
    bool ignoreChildren(TypeId ty) override;
    bool isDirty(TypeId ty) override;
    bool isDirty(TypePackId tp) override;
    TypeId clean(TypeId ty) override;
    TypePackId clean(TypePackId tp) override;
};

/** Attempt to instantiate a type.  Only used under local type inference.
 *
 * When given a generic function type, instantiate() will return a copy with the
 * generics replaced by fresh types.  Instantiation will return the same TypeId
 * back if the function does not have any generics.
 *
 * All higher order generics are left as-is.  For example, instantiation of
 * <X>(<Y>(Y) -> (X, Y)) -> (X, Y) is (<Y>(Y) -> ('x, Y)) -> ('x, Y)
 *
 * We substitute the generic X for the free 'x, but leave the generic Y alone.
 *
 * Instantiation fails only when processing the type causes internal recursion
 * limits to be exceeded.
 */
std::optional<TypeId> instantiate(
    NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, NotNull<TypeCheckLimits> limits, NotNull<Scope> scope, TypeId ty);

} // namespace Luau