//===--- ConstraintLocator.h - Constraint Locator ---------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file provides the \c ConstraintLocator class and its related types,
// which is used by the constraint-based type checker to describe how
// a particular constraint was derived.
//
//===----------------------------------------------------------------------===//
#ifndef SWIFT_SEMA_CONSTRAINTLOCATOR_H
#define SWIFT_SEMA_CONSTRAINTLOCATOR_H

#include "swift/AST/ASTNode.h"
#include "swift/AST/Type.h"
#include "swift/AST/Types.h"
#include "swift/Basic/Debug.h"
#include "swift/Basic/LLVM.h"
#include "swift/Basic/NullablePtr.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/ErrorHandling.h"
#include <utility>

namespace swift {

class Expr;
class TypeLoc;
class VarDecl;
class Pattern;
class SourceManager;
class ProtocolConformance;

/// This specifies the purpose of the contextual type, when specified to
/// typeCheckExpression.  This is used for diagnostic generation to produce more
/// specified error messages when the conversion fails.
///
enum ContextualTypePurpose : uint8_t {
  CTP_Unused,            ///< No contextual type is specified.
  CTP_Initialization,    ///< Pattern binding initialization.
  CTP_ReturnStmt,        ///< Value specified to a 'return' statement.
  CTP_YieldByValue,      ///< By-value yield operand.
  CTP_YieldByReference,  ///< By-reference yield operand.
  CTP_ThrowStmt,         ///< Value specified to a 'throw' statement.
  CTP_DiscardStmt,       ///< Value specified to a 'discard' statement.
  CTP_EnumCaseRawValue,  ///< Raw value specified for "case X = 42" in enum.
  CTP_IntGenericParam,   ///< Integer expression specified for a generic value argument.
  CTP_DefaultParameter,  ///< Default value in parameter 'foo(a : Int = 42)'.

  /// Default value in @autoclosure parameter
  /// 'foo(a : @autoclosure () -> Int = 42)'.
  CTP_AutoclosureDefaultParameter,

  CTP_CallArgument,     ///< Call to function or operator requires type.
  CTP_ClosureResult,    ///< Closure result expects a specific type.
  CTP_ArrayElement,     ///< ArrayExpr wants elements to have a specific type.
  CTP_DictionaryKey,    ///< DictionaryExpr keys should have a specific type.
  CTP_DictionaryValue,  ///< DictionaryExpr values should have a specific type.
  CTP_CoerceOperand,    ///< CoerceExpr operand coerced to specific type.
  CTP_AssignSource,     ///< AssignExpr source operand coerced to result type.
  CTP_SubscriptAssignSource, ///< AssignExpr source operand coerced to subscript
                             ///< result type.
  CTP_Condition,        ///< Condition expression of various statements e.g.
                        ///< `if`, `for`, `while` etc.
  CTP_CaseStmt,         ///< A single case statement associated with a `switch` or
                        ///  a `do-catch` statement. It has to be convertible
                        ///  to a type of a switch subject or an `Error` type.
  CTP_ForEachSequence,  ///< Sequence expression associated with `for-in` loop.
  CTP_WrappedProperty,  ///< Property type expected to match 'wrappedValue' type

  CTP_SingleValueStmtBranch, ///< The contextual type for a branch in a single
                             ///< value statement expression.

  CTP_ExprPattern,      ///< `~=` operator application associated with expression
                        /// pattern.
};

namespace constraints {

class ConstraintSystem;
enum class ConversionRestrictionKind;

/// Locates a given constraint within the expression being
/// type-checked, which may refer down into subexpressions and parts of
/// the types of those subexpressions.
///
/// Each locator as anchored at some expression, e.g., (3, (x, 3.14)),
/// and contains a path that digs further into the type of that expression.
/// For example, the path "tuple element #1" -> "tuple element #0" with the
/// above expression would refer to 'x'. If 'x' had function type, the
/// path could be further extended with either "-> argument" or "-> result",
/// to indicate constraints on its argument or result type.
class ConstraintLocator : public llvm::FoldingSetNode {
public:
  /// Describes the kind of a particular path element, e.g.,
  /// "tuple element", "call result", "base of member lookup", etc.
  enum PathElementKind : unsigned char {
#define LOCATOR_PATH_ELT(Name) Name,
#define ABSTRACT_LOCATOR_PATH_ELT(Name)
#include "ConstraintLocatorPathElts.def"
  };

  /// Flags for efficiently recording certain information about a path.
  /// All of this information should be re-derivable from the path.
  ///
  /// Values are chosen so that an empty path has value 0 and the
  /// flags for a concatenated paths is simply the bitwise-or of the
  /// flags of the component paths.
  enum Flag : unsigned {
    /// Does this path involve a function conversion, i.e. a
    /// FunctionArgument or FunctionResult node?
    IsFunctionConversion = 0x1,

    /// Does this path involve an argument being applied to a non-ephemeral
    /// parameter?
    IsNonEphemeralParam = 0x2,
  };

  /// One element in the path of a locator, which can include both
  /// a kind (PathElementKind) and a value used to describe specific
  /// kinds further (e.g., the position of a tuple element).
  class PathElement {
    PathElementKind kind;

    /// The storage for the path element value. The value stores can either
    /// be a pointer or an unsigned int. Only custom path elements store values.
    uint64_t storage;

  public:
#define LOCATOR_PATH_ELT(Name) class Name;
#include "ConstraintLocatorPathElts.def"

    PathElement(PathElementKind kind, uint64_t storage = 0)
      : kind(kind), storage(storage) {}

    /// Retrieve the kind of path element.
    PathElementKind getKind() const { return kind; }

    /// Retrieve the raw storage value.
    uint64_t getRawStorage() const { return storage; }

    /// Attempts to cast the path element to a specific \c LocatorPathElt
    /// subclass, returning \c None if unsuccessful.
    template <class T>
    std::optional<T> getAs() const {
      if (auto *result = llvm::dyn_cast<T>(this))
        return *result;
      return std::nullopt;
    }

    /// Cast the path element to a specific \c LocatorPathElt subclass.
    template <class T>
    T castTo() const { return *llvm::cast<T>(this); }

    /// Checks whether the path element is a specific \c LocatorPathElt
    /// subclass.
    template <class T>
    bool is() const { return llvm::isa<T>(this); }

    /// Return the summary flags for this particular element.
    unsigned getNewSummaryFlags() const;

    bool isConditionalRequirement() const {
      return getKind() == PathElementKind::ConditionalRequirement;
    }

    bool isKeyPathDynamicMember() const {
      return getKind() == PathElementKind::KeyPathDynamicMember;
    }

    bool isKeyPathComponent() const {
      return getKind() == PathElementKind::KeyPathComponent;
    }

    bool isClosureResult() const {
      return getKind() == PathElementKind::ClosureResult;
    }

    void dump(raw_ostream &out) const LLVM_ATTRIBUTE_USED;
    SWIFT_DEBUG_DUMP {
      dump(llvm::errs());
    }
  };

  /// Return the summary flags for an entire path.
  static unsigned getSummaryFlagsForPath(ArrayRef<PathElement> path) {
    unsigned flags = 0;
    for (auto &elt : path) flags |= elt.getNewSummaryFlags();
    return flags;
  }

  /// Retrieve the expression that anchors this locator.
  ASTNode getAnchor() const { return anchor; }

  /// Retrieve the path that extends from the anchor to a specific
  /// subcomponent.
  ArrayRef<PathElement> getPath() const {
    // FIXME: Alignment.
    return llvm::ArrayRef(reinterpret_cast<const PathElement *>(this + 1),
                          numPathElements);
  }

  unsigned getSummaryFlags() const { return summaryFlags; }

  /// Determines whether this locator is part of a function
  /// conversion.
  bool isFunctionConversion() const {
    return (getSummaryFlags() & IsFunctionConversion);
  }

  /// Checks whether this locator is describing an argument application for a
  /// non-ephemeral parameter.
  bool isNonEphemeralParameterApplication() const {
    return (getSummaryFlags() & IsNonEphemeralParam);
  }

  /// Determine whether given locator points to the subscript reference
  /// e.g. `foo[0]` or `\Foo.[0]`
  bool isSubscriptMemberRef() const;

  /// Determine whether give locator points to the type of the
  /// key path expression.
  bool isKeyPathType() const;

  /// Determine whether given locator points to the keypath root
  bool isKeyPathRoot() const;

  /// Determine whether given locator points to the keypath value
  bool isKeyPathValue() const;

  /// Determine whether given locator points to the choice picked as
  /// as result of the key path dynamic member lookup operation.
  bool isResultOfKeyPathDynamicMemberLookup() const;

  /// Determine whether this locator points to a subscript component
  /// of the key path at some index.
  bool isKeyPathSubscriptComponent() const;

  /// Determine whether this locator points to a member component
  /// of the key path at some index.
  bool isKeyPathMemberComponent() const;

  /// Determine whether this locator points to an apply component of the key
  /// path at some index.
  bool isKeyPathApplyComponent() const;

  /// Determine whether this locator points to the member found
  /// via key path dynamic member lookup.
  bool isForKeyPathDynamicMemberLookup() const;

  /// Determine whether this locator points to element inside
  /// of a key path component.
  bool isInKeyPathComponent() const;

  /// Determine whether this locator points to a result type of
  /// a key path component.
  bool isForKeyPathComponentResult() const;

  /// Determine whether this locator points to a key path component.
  bool isForKeyPathComponent() const;

  /// Determine whether this locator points to the generic parameter.
  bool isForGenericParameter() const;

  /// Determine whether this locator points to any of the
  /// property wrappers' types for a given composed property
  /// wrapper, with the exception of the innermost property wrapper's
  /// type.
  bool isForWrappedValue() const;

  /// Determine whether this locator points to the element type of a
  /// sequence in a for ... in ... loop.
  bool isForSequenceElementType() const;

  /// Determine whether this locator points to the contextual type.
  bool isForContextualType() const;

  /// Determine whether this locator points to the contextual type for a given
  /// purpose.
  bool isForContextualType(ContextualTypePurpose ctp) const;

  /// Determine whether this locator points to the assignment expression.
  bool isForAssignment() const;

  /// Determine whether this locator points to the coercion expression.
  bool isForCoercion() const;

  /// Determine whether this locator points to the `try?` expression.
  bool isForOptionalTry() const;

  /// Determine whether this locator is for a macro expansion.
  bool isForMacroExpansion() const;

  /// Whether this locator identifies a conjunction for the branches of a
  /// SingleValueStmtExpr.
  bool isForSingleValueStmtConjunction() const;

  /// Whether this locator identifies a conjunction for the branches of a
  /// SingleValueStmtExpr, or a conjunction for one of the BraceStmts itself.
  bool isForSingleValueStmtConjunctionOrBrace() const;

  /// Whether this locator identifies a conversion for a SingleValueStmtExpr
  /// branch.
  bool isForSingleValueStmtBranch() const;

  /// If the locator in question is for a pattern match, returns the pattern,
  /// otherwise \c nullptr.
  NullablePtr<Pattern> getPatternMatch() const;

  /// Whether the locator in question is for a pattern match.
  bool isForPatternMatch() const;

  /// Whether the locator is for a named or `_` pattern decl.
  bool isForPatternDecl() const;

  /// Whether this locator identifies an element type of a collection literal.
  bool isForCollectionElement() const;

  /// Returns true if \p locator is ending with either of the following
  ///  - Member
  ///  - Member -> KeyPathDynamicMember
  bool isMemberRef() const;

  /// Determine whether this locator points directly to a given expression.
  template <typename E> bool directlyAt() const {
    if (auto *expr = getAnchor().dyn_cast<Expr *>())
      return isa<E>(expr) && getPath().empty();
    return false;
  }

  /// Check whether the first element in the path of this locator (if any)
  /// is a given \c LocatorPathElt subclass.
  template <class T>
  bool isFirstElement() const {
    auto path = getPath();
    return !path.empty() && path.front().is<T>();
  }

  /// Attempts to cast the first path element of the locator to a specific
  /// \c LocatorPathElt subclass, returning \c None if either unsuccessful or
  /// the locator has no path elements.
  template <class T>
  std::optional<T> getFirstElementAs() const {
    auto path = getPath();
    if (path.empty())
      return std::nullopt;

    return path[0].getAs<T>();
  }

  /// Casts the first path element of the locator to a specific
  /// \c LocatorPathElt subclass, asserting that it has at least one element.
  template <class T>
  T castFirstElementTo() const {
    auto path = getPath();
    assert(!path.empty() && "Expected at least one path element!");
    return path[0].castTo<T>();
  }

  /// Check whether the last element in the path of this locator (if any)
  /// is a given \c LocatorPathElt subclass.
  template <class T>
  bool isLastElement() const {
    auto path = getPath();
    return !path.empty() && path.back().is<T>();
  }

  /// Attempts to cast the last path element of the locator to a specific
  /// \c LocatorPathElt subclass, returning \c None if either unsuccessful or
  /// the locator has no path elements.
  template <class T>
  std::optional<T> getLastElementAs() const {
    auto path = getPath();
    if (path.empty())
      return std::nullopt;

    return path.back().getAs<T>();
  }

  /// Casts the last path element of the locator to a specific \c LocatorPathElt
  /// subclass, asserting that it has at least one element.
  template <class T>
  T castLastElementTo() const {
    auto path = getPath();
    assert(!path.empty() && "Expected at least one path element!");
    return path.back().castTo<T>();
  }

  using PathIterator = ArrayRef<PathElement>::iterator;
  using PathReverseIterator = ArrayRef<PathElement>::reverse_iterator;

  /// Attempts to find the first element in the locator's path that is a
  /// specific \c LocatorPathElt subclass, returning \c None if no such element
  /// exists.
  ///
  /// \param iter A reference to an iterator which will be used to iterate
  /// over the locator's path.
  template <class T>
  std::optional<T> findFirst(PathIterator &iter) const {
    auto path = getPath();
    auto end = path.end();
    assert(iter >= path.begin() && iter <= end);

    for (; iter != end; ++iter)
      if (auto elt = iter->getAs<T>())
        return elt;
    return std::nullopt;
  }

  /// Attempts to find the first element in the locator's path that is a
  /// specific \c LocatorPathElt subclass, returning \c None if no such element
  /// exists.
  template <class T>
  std::optional<T> findFirst() const {
    auto iter = getPath().begin();
    return findFirst<T>(iter);
  }

  /// Attempts to find the last element in the locator's path that is a
  /// specific \c LocatorPathElt subclass, returning \c None if no such element
  /// exists.
  ///
  /// \param iter A reference to a reverse iterator which will be used to
  /// iterate over the locator's path.
  template <class T>
  std::optional<T> findLast(PathReverseIterator &iter) const {
    auto path = getPath();
    auto end = path.rend();
    assert(iter >= path.rbegin() && iter <= end);

    for (; iter != end; ++iter)
      if (auto elt = iter->getAs<T>())
        return elt;
    return std::nullopt;
  }

  /// Attempts to find the last element in the locator's path that is a
  /// specific \c LocatorPathElt subclass, returning \c None if no such element
  /// exists.
  template <class T>
  std::optional<T> findLast() const {
    auto iter = getPath().rbegin();
    return findLast<T>(iter);
  }

  /// If this locator points to generic parameter return its type.
  GenericTypeParamType *getGenericParameter() const;

  /// If this locator points to any of the property wrappers' types
  /// for a given composed property wrapper, with the exception
  /// of the innermost property wrapper's type.
  Type getWrappedValue() const;

  /// Produce a profile of this locator, for use in a folding set.
  static void Profile(llvm::FoldingSetNodeID &id, ASTNode anchor,
                      ArrayRef<PathElement> path);

  /// Produce a profile of this locator, for use in a folding set.
  void Profile(llvm::FoldingSetNodeID &id) {
    Profile(id, anchor, getPath());
  }
  
  /// Produce a debugging dump of this locator.
  SWIFT_DEBUG_DUMPER(dump(SourceManager *SM));
  SWIFT_DEBUG_DUMPER(dump(ConstraintSystem *CS));

  void dump(SourceManager *SM, raw_ostream &OS) const LLVM_ATTRIBUTE_USED;

private:
  /// Initialize a constraint locator with an anchor and a path.
  ConstraintLocator(ASTNode anchor, ArrayRef<PathElement> path, unsigned flags)
      : anchor(anchor), numPathElements(path.size()), summaryFlags(flags) {
    // FIXME: Alignment.
    std::copy(path.begin(), path.end(),
              reinterpret_cast<PathElement *>(this + 1));
  }

  /// Create a new locator from an anchor and an array of path
  /// elements.
  ///
  /// Note that this routine only handles the allocation and initialization
  /// of the locator. The ConstraintSystem object is responsible for
  /// uniquing via the FoldingSet.
  static ConstraintLocator *create(llvm::BumpPtrAllocator &allocator,
                                   ASTNode anchor, ArrayRef<PathElement> path,
                                   unsigned flags) {
    // FIXME: Alignment.
    unsigned size = sizeof(ConstraintLocator)
                  + path.size() * sizeof(PathElement);
    void *mem = allocator.Allocate(size, alignof(ConstraintLocator));
    return new (mem) ConstraintLocator(anchor, path, flags);
  }

  /// The expression at which this locator is anchored.
  ASTNode anchor;

  /// The number of path elements in this locator.
  ///
  /// The actual path elements are stored after the locator.
  unsigned numPathElements : 24;

  /// A set of flags summarizing interesting properties of the path.
  unsigned summaryFlags : 7;
  
  friend class ConstraintSystem;
};

using LocatorPathElt = ConstraintLocator::PathElement;

// Disallow direct uses of isa/cast/dyn_cast on LocatorPathElt in favor of using
// is/castTo/getAs. This allows us to work with Optional<T> rather than pointers
// for getAs, and maintains consistency with ConstraintLocator's
// isLastElement/castLastElementTo/getLastElementAs members.
template <class X>
inline bool
isa(const LocatorPathElt &) = delete; // Use LocatorPathElt::is instead.

template <class X>
inline typename llvm::cast_retty<X, LocatorPathElt>::ret_type
cast(const LocatorPathElt &) = delete; // Use LocatorPathElt::castTo instead.

template <class X>
inline typename llvm::cast_retty<X, LocatorPathElt>::ret_type
dyn_cast(const LocatorPathElt &) = delete; // Use LocatorPathElt::getAs instead.

#define SIMPLE_LOCATOR_PATH_ELT(Name) \
class LocatorPathElt:: Name final : public LocatorPathElt { \
public: \
  Name () : LocatorPathElt(ConstraintLocator:: Name) {} \
                                                        \
  static bool classof(const LocatorPathElt *elt) { \
    return elt->getKind() == ConstraintLocator:: Name; \
  } \
};
#include "ConstraintLocatorPathElts.def"

/// A base class for custom path elements that store numeric values.
template <unsigned NumValues>
class StoredIntegerElement: public LocatorPathElt {
  static constexpr unsigned valueWidth() {
    switch (NumValues) {
    default:
      return 16;
    case 1:
      return 64;
    case 2:
      return 32;
    }
  }

  template <unsigned Index = 0,
            typename = typename std::enable_if<(Index < NumValues)>::type>
  static uint64_t packValue(uint64_t value) {
    return value << (valueWidth() * (NumValues - Index - 1));
  }

  static constexpr uint64_t valueMask =
    valueWidth() < 64 ? (1ULL << valueWidth()) - 1 : -1ULL;

public:
  template <unsigned NumNumericInputs = NumValues,
            typename = typename std::enable_if<NumNumericInputs == 1>::type>
  StoredIntegerElement(ConstraintLocator::PathElementKind kind, uint64_t value)
    : LocatorPathElt(kind, value) { }

  template <unsigned NumNumericInputs = NumValues,
            typename = typename std::enable_if<NumNumericInputs == 2>::type>
  StoredIntegerElement(ConstraintLocator::PathElementKind kind, uint32_t value0, uint32_t value1)
    : LocatorPathElt(kind, packValue<0>(value0) | packValue<1>(value1)) { }

  template <unsigned NumNumericInputs = NumValues,
            typename = typename std::enable_if<NumNumericInputs == 3>::type>
  StoredIntegerElement(ConstraintLocator::PathElementKind kind,
                       uint16_t value0, uint16_t value1, uint16_t value2)
    : LocatorPathElt(kind,
                     packValue<0>(value0) | packValue<1>(value1) | packValue<2>(value2)) { }

  /// Retrieve a value associated with the path element.
  template <unsigned Index = 0,
            typename = typename std::enable_if<(Index < NumValues)>::type>
  uint64_t getValue() const {
    // We pack values into equally-sized components of the storage, with value0
    // being stored in the upper bits, valueN in the lower bits. Therefore we
    // need to shift out any extra values in the lower bits.
    auto extraValues = NumValues - Index - 1;
    auto value = getRawStorage() >> (extraValues * valueWidth());
    return value & valueMask;
  }
};

/// A base class for custom path elements that store a pointer.
template <typename T>
class StoredPointerElement: public LocatorPathElt {
public:
  StoredPointerElement(ConstraintLocator::PathElementKind kind, const T *ptr)
      : LocatorPathElt(kind, reinterpret_cast<uintptr_t>(ptr)) {
    assert(ptr == getStoredPointer());
  }

  /// Retrieve the associated pointer for the element.
  T *getStoredPointer() const { return reinterpret_cast<T *>(getRawStorage()); }
};

// The following LocatorPathElt subclasses are used to expose accessors for
// specific path element information. They shouldn't introduce additional
// storage, as LocatorPathElt gets passed about by value. Custom path elements
// should subclass StoredIntegerElement to store unsigned values, or StoredPointerElement
// to store pointer values.

class LocatorPathElt::ApplyArgToParam final : public StoredIntegerElement<3> {
public:
  ApplyArgToParam(uint16_t argIdx, uint16_t paramIdx, ParameterTypeFlags flags)
      : StoredIntegerElement(ConstraintLocator::ApplyArgToParam, argIdx, paramIdx, flags.toRaw()) {}

  unsigned getArgIdx() const { return getValue<0>(); }
  unsigned getParamIdx() const { return getValue<1>(); }
  ParameterTypeFlags getParameterFlags() const {
    return ParameterTypeFlags::fromRaw(getValue<2>());
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ApplyArgToParam;
  }
};

class LocatorPathElt::SynthesizedArgument final : public StoredIntegerElement<2> {
public:
  SynthesizedArgument(unsigned index, bool afterCodeCompletionLoc = false)
      : StoredIntegerElement(ConstraintLocator::SynthesizedArgument, index,
                             afterCodeCompletionLoc) {}

  unsigned getIndex() const { return getValue<0>(); }
  bool isAfterCodeCompletionLoc() const { return getValue<1>(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::SynthesizedArgument;
  }
};

class LocatorPathElt::TupleType : public StoredPointerElement<TypeBase> {
public:
  TupleType(Type type)
      : StoredPointerElement(PathElementKind::TupleType, type.getPointer()) {
    assert(type->getDesugaredType()->is<swift::TupleType>());
  }

  Type getType() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::TupleType;
  }
};

class LocatorPathElt::GenericType : public StoredPointerElement<TypeBase> {
public:
  GenericType(Type type)
      : StoredPointerElement(PathElementKind::GenericType, type.getPointer()) {
    assert(type->getDesugaredType()->is<BoundGenericType>());
  }

  Type getType() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::GenericType;
  }
};

/// Abstract superclass for any kind of tuple element.
class LocatorPathElt::AnyTupleElement : public StoredIntegerElement<1> {
protected:
  AnyTupleElement(PathElementKind kind, unsigned index)
      : StoredIntegerElement(kind, index) {
    assert(classof(this) && "classof needs updating");
  }

public:
  unsigned getIndex() const { return getValue(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->is<LocatorPathElt::TupleElement>() ||
           elt->is<LocatorPathElt::NamedTupleElement>();
  }
};

class LocatorPathElt::TupleElement final
    : public LocatorPathElt::AnyTupleElement {
public:
  TupleElement(unsigned index)
      : AnyTupleElement(ConstraintLocator::TupleElement, index) {}

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::TupleElement;
  }
};

class LocatorPathElt::NamedTupleElement final
    : public LocatorPathElt::AnyTupleElement {
public:
  NamedTupleElement(unsigned index)
      : AnyTupleElement(ConstraintLocator::NamedTupleElement, index) {}

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::NamedTupleElement;
  }
};

class LocatorPathElt::PackType : public StoredPointerElement<TypeBase> {
public:
  PackType(Type type)
      : StoredPointerElement(PathElementKind::PackType, type.getPointer()) {
    assert(type->getDesugaredType()->is<swift::PackType>());
  }

  Type getType() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::PackType;
  }
};

class LocatorPathElt::PackElement final : public StoredIntegerElement<1> {
public:
  PackElement(unsigned index)
      : StoredIntegerElement(ConstraintLocator::PackElement, index) {}

  unsigned getIndex() const { return getValue<0>(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::PackElement;
  }
};

class LocatorPathElt::KeyPathComponent final : public StoredIntegerElement<1> {
public:
  KeyPathComponent(unsigned index)
      : StoredIntegerElement(ConstraintLocator::KeyPathComponent, index) {}

  unsigned getIndex() const { return getValue(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::KeyPathComponent;
  }
};

class LocatorPathElt::ProtocolCompositionMemberType final : public StoredIntegerElement<1> {
public:
  ProtocolCompositionMemberType(unsigned index)
      : StoredIntegerElement(ConstraintLocator::GenericArgument, index) {}

  unsigned getIndex() const { return getValue(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ProtocolCompositionMemberType;
  }
};

class LocatorPathElt::GenericArgument final : public StoredIntegerElement<1> {
public:
  GenericArgument(unsigned index)
      : StoredIntegerElement(ConstraintLocator::GenericArgument, index) {}

  unsigned getIndex() const { return getValue(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::GenericArgument;
  }
};

/// Abstract superclass for any kind of element that describes a requirement
/// placed on a type within a requirements clause.
class LocatorPathElt::AnyRequirement : public StoredIntegerElement<2> {
protected:
  AnyRequirement(PathElementKind kind, unsigned index, RequirementKind reqKind)
      : StoredIntegerElement(kind, index, static_cast<unsigned>(reqKind)) {
    assert(classof(this) && "classof needs updating");
  }

public:
  unsigned getIndex() const { return getValue<0>(); }
  RequirementKind getRequirementKind() const {
    return static_cast<RequirementKind>(getValue<1>());
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->is<LocatorPathElt::ConditionalRequirement>() ||
           elt->is<LocatorPathElt::TypeParameterRequirement>();
  }
};

class LocatorPathElt::ConditionalRequirement final
    : public LocatorPathElt::AnyRequirement {
public:
  ConditionalRequirement(unsigned index, RequirementKind reqKind)
      : AnyRequirement(ConstraintLocator::ConditionalRequirement, index,
                       reqKind) {}

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ConditionalRequirement;
  }
};

class LocatorPathElt::TypeParameterRequirement final
    : public LocatorPathElt::AnyRequirement {
public:
  TypeParameterRequirement(unsigned index, RequirementKind reqKind)
      : AnyRequirement(ConstraintLocator::TypeParameterRequirement, index,
                       reqKind) {}

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::TypeParameterRequirement;
  }
};

class LocatorPathElt::Witness final : public StoredPointerElement<ValueDecl> {
public:
  Witness(ValueDecl *witness)
      : StoredPointerElement(PathElementKind::Witness, witness) {}

  ValueDecl *getDecl() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::Witness;
  }
};

class LocatorPathElt::GenericParameter final : public StoredPointerElement<GenericTypeParamType> {
public:
  GenericParameter(GenericTypeParamType *type)
      : StoredPointerElement(PathElementKind::GenericParameter, type) {
    static_assert(alignof(GenericTypeParamType) >= 4,
                  "archetypes insufficiently aligned");
  }

  GenericTypeParamType *getType() const {
    return getStoredPointer();
  }

  bool isParameterPack() const {
    return getType()->isParameterPack();
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::GenericParameter;
  }
};

class LocatorPathElt::WrappedValue final : public StoredPointerElement<TypeBase> {
public:
  WrappedValue(Type type)
      : StoredPointerElement(PathElementKind::WrappedValue, type.getPointer()) {
    assert(type.getPointer() != nullptr);
  }

  Type getType() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::WrappedValue;
  }
};

class LocatorPathElt::OpenedGeneric final : public StoredPointerElement<GenericSignatureImpl> {
public:
  OpenedGeneric(GenericSignature sig)
      : StoredPointerElement(PathElementKind::OpenedGeneric, sig.getPointer()) {}

  GenericSignature getSignature() const {
    return getStoredPointer();
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::OpenedGeneric;
  }
};

class LocatorPathElt::OpenedOpaqueArchetype final
    : public StoredPointerElement<OpaqueTypeDecl> {
public:
  OpenedOpaqueArchetype(OpaqueTypeDecl *decl)
      : StoredPointerElement(PathElementKind::OpenedOpaqueArchetype, decl) {}

  OpaqueTypeDecl *getDecl() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::OpenedOpaqueArchetype;
  }
};

class LocatorPathElt::KeyPathDynamicMember final : public StoredPointerElement<NominalTypeDecl> {
public:
  KeyPathDynamicMember(NominalTypeDecl *keyPathDecl)
      : StoredPointerElement(PathElementKind::KeyPathDynamicMember, keyPathDecl) {}

  NominalTypeDecl *getKeyPathDecl() const {
    return getStoredPointer();
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::KeyPathDynamicMember;
  }
};

class LocatorPathElt::TernaryBranch final : public StoredIntegerElement<1> {
public:
  TernaryBranch(bool side)
      : StoredIntegerElement(ConstraintLocator::TernaryBranch, side) {}

  bool forThen() const { return bool(getValue()); }

  bool forElse() const { return !bool(getValue()); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::TernaryBranch;
  }
};

/// A particular result of a ThenStmt at a given index in a SingleValueStmtExpr.
/// The stored index corresponds to the \c getResultExprs array.
class LocatorPathElt::SingleValueStmtResult final
    : public StoredIntegerElement<1> {
public:
  SingleValueStmtResult(unsigned exprIdx)
      : StoredIntegerElement(ConstraintLocator::SingleValueStmtResult,
                             exprIdx) {}

  unsigned getIndex() const { return getValue(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::SingleValueStmtResult;
  }
};

class LocatorPathElt::PatternMatch final : public StoredPointerElement<Pattern> {
public:
  PatternMatch(Pattern *pattern)
      : StoredPointerElement(PathElementKind::PatternMatch, pattern) {}

  Pattern *getPattern() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::PatternMatch;
  }
};

class LocatorPathElt::ArgumentAttribute final : public StoredIntegerElement<1> {
public:
  enum Attribute : uint8_t { InOut, Escaping, Concurrent, GlobalActor };

private:
  ArgumentAttribute(Attribute attr)
      : StoredIntegerElement(ConstraintLocator::ArgumentAttribute, static_cast<uint8_t>(attr)) {}

public:
  Attribute getAttr() const { return static_cast<Attribute>(getValue()); }

  static ArgumentAttribute forInOut() {
    return ArgumentAttribute(Attribute::InOut);
  }

  static ArgumentAttribute forEscaping() {
    return ArgumentAttribute(Attribute::Escaping);
  }

  static ArgumentAttribute forConcurrent() {
    return ArgumentAttribute(Attribute::Concurrent);
  }

  static ArgumentAttribute forGlobalActor() {
    return ArgumentAttribute(Attribute::GlobalActor);
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ArgumentAttribute;
  }
};

class LocatorPathElt::ConformanceRequirement final
    : public StoredPointerElement<ProtocolConformance> {
public:
  ConformanceRequirement(ProtocolConformance *conformance)
      : StoredPointerElement(PathElementKind::ConformanceRequirement,
                             conformance) {}

  ProtocolConformance *getConformance() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ConformanceRequirement;
  }
};

class LocatorPathElt::PlaceholderType final
    : public StoredPointerElement<TypeRepr> {
public:
  PlaceholderType(TypeRepr *placeholderRepr)
      : StoredPointerElement(PathElementKind::PlaceholderType,
                             placeholderRepr) {}

  TypeRepr *getPlaceholderRepr() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::PlaceholderType;
  }
};

class LocatorPathElt::ContextualType final : public StoredIntegerElement<1> {
public:
  ContextualType(ContextualTypePurpose purpose)
      : StoredIntegerElement(ConstraintLocator::ContextualType,
                             static_cast<unsigned>(purpose)) {}

  ContextualTypePurpose getPurpose() const {
    return static_cast<ContextualTypePurpose>(getValue());
  }

  bool isFor(ContextualTypePurpose purpose) const {
    return getPurpose() == purpose;
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ContextualType;
  }
};

class LocatorPathElt::ConstructorMemberType final
    : public StoredIntegerElement<1> {
public:
  ConstructorMemberType(bool isShortFormOrSelfDelegating = false)
      : StoredIntegerElement(ConstraintLocator::ConstructorMemberType,
                             isShortFormOrSelfDelegating) {}

  /// Whether this constructor overload is for a short-form init call such as
  /// 'X(...)', or a 'self.init(...)' call. Such calls have additional ranking
  /// rules.
  bool isShortFormOrSelfDelegatingConstructor() const {
    return bool(getValue());
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::ConstructorMemberType;
  }
};

class LocatorPathElt::SyntacticElement final
    : public StoredPointerElement<void> {
public:
  SyntacticElement(ASTNode element)
      : StoredPointerElement(PathElementKind::SyntacticElement,
                             element.getOpaqueValue()) {
    assert(element);
  }

  ASTNode getElement() const {
    // Unfortunately \c getFromOpaqueValue doesn't produce an ASTNode.
    auto node = ASTNode::getFromOpaqueValue(getStoredPointer());
    if (auto *expr = node.dyn_cast<Expr *>())
      return expr;

    if (auto *stmt = node.dyn_cast<Stmt *>())
      return stmt;

    if (auto *decl = node.dyn_cast<Decl *>())
      return decl;

    if (auto *pattern = node.dyn_cast<Pattern *>())
      return pattern;

    if (auto *repr = node.dyn_cast<TypeRepr *>())
      return repr;

    if (auto *cond = node.dyn_cast<StmtConditionElement *>())
      return cond;

    if (auto *caseItem = node.dyn_cast<CaseLabelItem *>())
      return caseItem;

    llvm_unreachable("unhandled ASTNode element kind");
  }

  Stmt *asStmt() const {
    auto node = ASTNode::getFromOpaqueValue(getStoredPointer());
    return cast<Stmt *>(node);
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::SyntacticElement;
  }
};

class LocatorPathElt::PatternBindingElement final
    : public StoredIntegerElement<1> {
public:
  PatternBindingElement(unsigned index)
      : StoredIntegerElement(ConstraintLocator::PatternBindingElement, index) {}

  unsigned getIndex() const { return getValue(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::PatternBindingElement;
  }
};

class LocatorPathElt::PatternDecl : public StoredIntegerElement<1> {
public:
  PatternDecl(ConstraintLocator::PathElementKind kind)
      : StoredIntegerElement(kind, /*placeholder=*/0) {
    assert(classof(this) && "classof needs updating");
  }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::NamedPatternDecl ||
           elt->getKind() == ConstraintLocator::AnyPatternDecl;
  }
};

class LocatorPathElt::NamedPatternDecl final
    : public LocatorPathElt::PatternDecl {
public:
  NamedPatternDecl() : PatternDecl(ConstraintLocator::NamedPatternDecl) {}

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::NamedPatternDecl;
  }
};

class LocatorPathElt::AnyPatternDecl final
    : public LocatorPathElt::PatternDecl {
public:
  AnyPatternDecl() : PatternDecl(ConstraintLocator::AnyPatternDecl) {}

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == ConstraintLocator::AnyPatternDecl;
  }
};

class LocatorPathElt::PackExpansionType final
    : public StoredPointerElement<swift::PackExpansionType> {
public:
  PackExpansionType(swift::PackExpansionType *openedPackExpansionTy)
      : StoredPointerElement(PathElementKind::PackExpansionType,
                             openedPackExpansionTy) {
    assert(openedPackExpansionTy);
  }

  swift::PackExpansionType *getOpenedType() const { return getStoredPointer(); }

  static bool classof(const LocatorPathElt *elt) {
    return elt->getKind() == PathElementKind::PackExpansionType;
  }
};

namespace details {
  template <typename CustomPathElement>
  class PathElement {
    static constexpr bool hasStoredValueImpl(...) { return false; }

    template <unsigned N>
    static constexpr bool hasStoredValueImpl(StoredIntegerElement<N> *) { return true; }

    template <typename T>
    static constexpr bool hasStoredValueImpl(StoredPointerElement<T> *) { return true; }

  public:
    static constexpr bool hasStoredValue() {
      return hasStoredValueImpl(static_cast<CustomPathElement *>(nullptr));
    }
  };
}

template <typename CustomPathElement>
constexpr bool isValidCustomPathElement() {
  return details::PathElement<CustomPathElement>::hasStoredValue();
}

// All custom path element classes must inherit from StoredIntegerElement or StoredPointerElement
#define CUSTOM_LOCATOR_PATH_ELT(Name) \
static_assert(isValidCustomPathElement<LocatorPathElt::Name>(), \
    "Custom path elements must inherit from StoredIntegerElement or StoredPointerElement");
#include "ConstraintLocatorPathElts.def"


/// A simple stack-only builder object that constructs a
/// constraint locator without allocating memory.
///
/// Use this object to build a path when passing components down the
/// stack, e.g., when recursively breaking apart types as in \c matchTypes().
class ConstraintLocatorBuilder {
  /// The constraint locator that this builder extends or the
  /// previous builder in the chain.
  llvm::PointerUnion<ConstraintLocator *, ConstraintLocatorBuilder *>
    previous;

  /// The current path element, if there is one.
  std::optional<LocatorPathElt> element;

  /// The current set of flags.
  unsigned summaryFlags;

  ConstraintLocatorBuilder(llvm::PointerUnion<ConstraintLocator *,
                                              ConstraintLocatorBuilder *>
                             previous,
                           LocatorPathElt element,
                           unsigned flags)
    : previous(previous), element(element), summaryFlags(flags) { }

public:
  ConstraintLocatorBuilder(ConstraintLocator *locator)
    : previous(locator), element(),
      summaryFlags(locator ? locator->getSummaryFlags() : 0) { }

  /// Retrieve a new path with the given path element added to it. Note that
  /// the produced locator stores a reference to this locator, and therefore
  /// must not outlive it.
  ConstraintLocatorBuilder withPathElement(LocatorPathElt newElt) & {
    unsigned newFlags = summaryFlags | newElt.getNewSummaryFlags();
    if (!element)
      return ConstraintLocatorBuilder(previous, newElt, newFlags);

    return ConstraintLocatorBuilder(this, newElt, newFlags);
  }

  /// Determine whether this locator builder points directly to a
  /// given expression.
  template <typename E>
  bool directlyAt() const {
    if (auto *expr = getAnchor().dyn_cast<Expr *>())
      return isa<E>(expr) && !last();
    return false;
  }

  /// Determine whether this builder has an empty path (no new elements).
  bool hasEmptyPath() const {
    return !element;
  }

  /// Return the set of flags that summarize this path.
  unsigned getSummaryFlags() const {
    return summaryFlags;
  }

  bool isFunctionConversion() const {
    return (getSummaryFlags() & ConstraintLocator::IsFunctionConversion);
  }

  bool isForAutoclosureResult() const {
    SmallVector<LocatorPathElt, 4> path;
    getLocatorParts(path);

    auto last = std::find_if(
        path.rbegin(), path.rend(), [](LocatorPathElt &elt) -> bool {
          return elt.getKind() != ConstraintLocator::OptionalInjection &&
                 elt.getKind() != ConstraintLocator::GenericArgument;
        });

    if (last != path.rend())
      return last->getKind() == ConstraintLocator::AutoclosureResult;

    return false;
  }

  bool isForRequirement(RequirementKind kind) const {
    if (auto lastElt = last()) {
      auto requirement = lastElt->getAs<LocatorPathElt::AnyRequirement>();
      return requirement && kind == requirement->getRequirementKind();
    }
    return false;
  }

  bool isForExistentialMemberAccessConversion() const {
    for (auto prev = this; prev;
         prev = prev->previous.dyn_cast<ConstraintLocatorBuilder *>()) {
      if (auto elt = prev->element) {
        if (elt->is<LocatorPathElt::ExistentialMemberAccessConversion>())
          return true;
      }

      if (auto locator = prev->previous.dyn_cast<ConstraintLocator *>())
        return bool(locator->findLast<
                    LocatorPathElt::ExistentialMemberAccessConversion>());
    }
    return false;
  }

  std::optional<std::pair</*witness=*/ValueDecl *, GenericTypeParamType *>>
  isForWitnessGenericParameterRequirement() const {
    SmallVector<LocatorPathElt, 2> path;
    getLocatorParts(path);

    // -> witness -> generic env -> requirement
    if (path.size() < 3)
      return std::nullopt;

    GenericTypeParamType *GP = nullptr;
    if (auto reqLoc =
            path.back().getAs<LocatorPathElt::TypeParameterRequirement>()) {
      path.pop_back();
      if (auto openedGeneric =
              path.back().getAs<LocatorPathElt::OpenedGeneric>()) {
        auto signature = openedGeneric->getSignature();
        auto requirement = signature.getRequirements()[reqLoc->getIndex()];
        GP = requirement.getFirstType()->getAs<GenericTypeParamType>();
      }
    }

    if (!GP)
      return std::nullopt;

    auto witness = path.front().getAs<LocatorPathElt::Witness>();
    if (!witness)
      return std::nullopt;

    return std::make_pair(witness->getDecl(), GP);
  }

  /// Checks whether this locator is describing an argument application for a
  /// non-ephemeral parameter.
  bool isNonEphemeralParameterApplication() const {
    return (getSummaryFlags() & ConstraintLocator::IsNonEphemeralParam);
  }

  /// Retrieve the base constraint locator, on which this builder's
  /// path is based.
  ConstraintLocator *getBaseLocator() const {
    for (auto prev = this;
         prev;
         prev = prev->previous.dyn_cast<ConstraintLocatorBuilder *>()) {
      if (auto locator = prev->previous.dyn_cast<ConstraintLocator *>())
        return locator;
    }

    return nullptr;
  }

  /// Get anchor expression associated with this locator builder.
  ASTNode getAnchor() const {
    for (auto prev = this; prev;
         prev = prev->previous.dyn_cast<ConstraintLocatorBuilder *>()) {
      if (auto *locator = prev->previous.dyn_cast<ConstraintLocator *>())
        return locator->getAnchor();
    }

    return {};
  }

  /// Retrieve the components of the complete locator, which includes
  /// the anchor expression and the path.
  ASTNode getLocatorParts(SmallVectorImpl<LocatorPathElt> &path) const {
    for (auto prev = this;
         prev;
         prev = prev->previous.dyn_cast<ConstraintLocatorBuilder *>()) {
      // If there is an element at this level, add it.
      if (prev->element)
        path.push_back(*prev->element);

      if (auto locator = prev->previous.dyn_cast<ConstraintLocator *>()) {
        // We found the end of the chain. Reverse the path we've built up,
        // then prepend the locator's path.
        std::reverse(path.begin(), path.end());
        path.insert(path.begin(),
                    locator->getPath().begin(),
                    locator->getPath().end());
        return locator->getAnchor();
      }
    }

    // There was no locator. Just reverse the path.
    std::reverse(path.begin(), path.end());
    return nullptr;
  }

  /// Attempt to simplify this locator to a single expression.
  Expr *trySimplifyToExpr() const;

  /// Retrieve the last element in the path, if there is one.
  std::optional<LocatorPathElt> last() const {
    // If we stored a path element here, grab it.
    if (element) return *element;

    // Otherwise, look in the previous builder if there is one.
    if (auto prevBuilder = previous.dyn_cast<ConstraintLocatorBuilder *>())
      return prevBuilder->last();

    // Next, check the constraint locator itself.
    if (auto locator = previous.dyn_cast<ConstraintLocator *>()) {
      auto path = locator->getPath();
      if (path.empty())
        return std::nullopt;
      return path.back();
    }

    return std::nullopt;
  }

  /// Check whether this locator has the given locator path element
  /// at the end of its path.
  template <class Kind>
  bool endsWith() const {
    if (auto lastElt = last()) {
      return lastElt->is<Kind>();
    }
    return false;
  }

  /// Produce a debugging dump of this locator.
  SWIFT_DEBUG_DUMPER(dump(SourceManager *SM));
  SWIFT_DEBUG_DUMPER(dump(ConstraintSystem *CS));

  void dump(SourceManager *SM, raw_ostream &OS) const LLVM_ATTRIBUTE_USED;
};

} // end namespace constraints
} // end namespace swift

#endif // LLVM_SWIFT_SEMA_CONSTRAINTLOCATOR_H
