luau/Analysis/include/Luau/Unifier.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/Error.h"
#include "Luau/Location.h"
#include "Luau/ParseOptions.h"
#include "Luau/Scope.h"
#include "Luau/Substitution.h"
#include "Luau/TxnLog.h"
#include "Luau/TypeArena.h"
#include "Luau/UnifierSharedState.h"
#include "Luau/Normalize.h"

#include <unordered_set>

namespace Luau
{

enum Variance
{
    Covariant,
    Invariant
};

// A substitution which replaces singleton types by their wider types
struct Widen : Substitution
{
    Widen(TypeArena* arena, NotNull<BuiltinTypes> builtinTypes)
        : Substitution(TxnLog::empty(), arena)
        , builtinTypes(builtinTypes)
    {
    }

    NotNull<BuiltinTypes> builtinTypes;

    bool isDirty(TypeId ty) override;
    bool isDirty(TypePackId ty) override;
    TypeId clean(TypeId ty) override;
    TypePackId clean(TypePackId ty) override;
    bool ignoreChildren(TypeId ty) override;

    TypeId operator()(TypeId ty);
    TypePackId operator()(TypePackId ty);
};

/**
 * Normally, when we unify table properties, we must do so invariantly, but we
 * can introduce a special exception: If the table property in the subtype
 * position arises from a literal expression, it is safe to instead perform a
 * covariant check.
 *
 * This is very useful for typechecking cases where table literals (and trees of
 * table literals) are passed directly to functions.
 *
 * In this case, we know that the property has no other name referring to it and
 * so it is perfectly safe for the function to mutate the table any way it
 * wishes.
 */
using LiteralProperties = DenseHashSet<Name>;

// TODO: Use this more widely.
struct UnifierOptions
{
    bool isFunctionCall = false;
};

struct Unifier
{
    TypeArena* const types;
    NotNull<BuiltinTypes> builtinTypes;
    NotNull<Normalizer> normalizer;

    NotNull<Scope> scope; // const Scope maybe
    TxnLog log;
    bool failure = false;
    ErrorVec errors;
    Location location;
    Variance variance = Covariant;
    bool normalize = true;      // Normalize unions and intersections if necessary
    bool checkInhabited = true; // Normalize types to check if they are inhabited
    CountMismatch::Context ctx = CountMismatch::Arg;

    // If true, generics act as free types when unifying.
    bool hideousFixMeGenericsAreActuallyFree = false;

    UnifierSharedState& sharedState;

    // When the Unifier is forced to unify two blocked types (or packs), they
    // get added to these vectors.  The ConstraintSolver can use this to know
    // when it is safe to reattempt dispatching a constraint.
    std::vector<TypeId> blockedTypes;
    std::vector<TypePackId> blockedTypePacks;

    Unifier(NotNull<Normalizer> normalizer, NotNull<Scope> scope, const Location& location, Variance variance, TxnLog* parentLog = nullptr);

    // Configure the Unifier to test for scope subsumption via embedded Scope
    // pointers rather than TypeLevels.
    void enableNewSolver();

    // Test whether the two type vars unify.  Never commits the result.
    ErrorVec canUnify(TypeId subTy, TypeId superTy);
    ErrorVec canUnify(TypePackId subTy, TypePackId superTy, bool isFunctionCall = false);

    /** Attempt to unify.
     * Populate the vector errors with any type errors that may arise.
     * Populate the transaction log with the set of TypeIds that need to be reset to undo the unification attempt.
     */
    void tryUnify(
        TypeId subTy,
        TypeId superTy,
        bool isFunctionCall = false,
        bool isIntersection = false,
        const LiteralProperties* aliasableMap = nullptr
    );

private:
    void tryUnify_(
        TypeId subTy,
        TypeId superTy,
        bool isFunctionCall = false,
        bool isIntersection = false,
        const LiteralProperties* aliasableMap = nullptr
    );
    void tryUnifyUnionWithType(TypeId subTy, const UnionType* uv, TypeId superTy);

    // Traverse the two types provided and block on any BlockedTypes we find.
    // Returns true if any types were blocked on.
    bool DEPRECATED_blockOnBlockedTypes(TypeId subTy, TypeId superTy);

    void tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionType* uv, bool cacheEnabled, bool isFunctionCall);
    void tryUnifyTypeWithIntersection(TypeId subTy, TypeId superTy, const IntersectionType* uv);
    void tryUnifyIntersectionWithType(TypeId subTy, const IntersectionType* uv, TypeId superTy, bool cacheEnabled, bool isFunctionCall);
    void tryUnifyNormalizedTypes(
        TypeId subTy,
        TypeId superTy,
        const NormalizedType& subNorm,
        const NormalizedType& superNorm,
        std::string reason,
        std::optional<TypeError> error = std::nullopt
    );
    void tryUnifyPrimitives(TypeId subTy, TypeId superTy);
    void tryUnifySingletons(TypeId subTy, TypeId superTy);
    void tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCall = false);
    void tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection = false, const LiteralProperties* aliasableMap = nullptr);
    void tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed);
    void tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed);
    void tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed);
    void tryUnifyNegations(TypeId subTy, TypeId superTy);

    TypePackId tryApplyOverloadedFunction(TypeId function, const NormalizedFunctionType& overloads, TypePackId args);

    TypeId widen(TypeId ty);
    TypePackId widen(TypePackId tp);

    TypeId deeplyOptional(TypeId ty, std::unordered_map<TypeId, TypeId> seen = {});

    bool canCacheResult(TypeId subTy, TypeId superTy);
    void cacheResult(TypeId subTy, TypeId superTy, size_t prevErrorCount);

public:
    void tryUnify(TypePackId subTy, TypePackId superTy, bool isFunctionCall = false);

private:
    void tryUnify_(TypePackId subTy, TypePackId superTy, bool isFunctionCall = false);
    void tryUnifyVariadics(TypePackId subTy, TypePackId superTy, bool reversed, int subOffset = 0);

    void tryUnifyWithAny(TypeId subTy, TypeId anyTy);
    void tryUnifyWithAny(TypePackId subTy, TypePackId anyTp);

    std::optional<TypeId> findTablePropertyRespectingMeta(TypeId lhsType, Name name);

    TxnLog combineLogsIntoIntersection(std::vector<TxnLog> logs);
    TxnLog combineLogsIntoUnion(std::vector<TxnLog> logs);

public:
    // Returns true if the type "needle" already occurs within "haystack" and reports an "infinite type error"
    bool occursCheck(TypeId needle, TypeId haystack, bool reversed);
    bool occursCheck(DenseHashSet<TypeId>& seen, TypeId needle, TypeId haystack);
    bool occursCheck(TypePackId needle, TypePackId haystack, bool reversed);
    bool occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, TypePackId haystack);

    std::unique_ptr<Unifier> makeChildUnifier();

    void reportError(TypeError err);
    LUAU_NOINLINE void reportError(Location location, TypeErrorData data);

private:
    TypeMismatch::Context mismatchContext();

    void checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, TypeId wantedType, TypeId givenType);
    void checkChildUnifierTypeMismatch(const ErrorVec& innerErrors, const std::string& prop, TypeId wantedType, TypeId givenType);

    [[noreturn]] void ice(const std::string& message, const Location& location);
    [[noreturn]] void ice(const std::string& message);

    // Available after regular type pack unification errors
    std::optional<int> firstPackErrorPos;

    // If true, we do a bunch of small things differently to work better with
    // the new type inference engine. Most notably, we use the Scope hierarchy
    // directly rather than using TypeLevels.
    bool useNewSolver = false;
};

void promoteTypeLevels(TxnLog& log, const TypeArena* arena, TypeLevel minLevel, Scope* outerScope, bool useScope, TypePackId tp);
std::optional<TypeError> hasUnificationTooComplex(const ErrorVec& errors);
std::optional<TypeError> hasCountMismatch(const ErrorVec& errors);

} // namespace Luau