TypeCheckConcurrency.h

//===--- TypeCheckConcurrency.h - Concurrency -------------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 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 type checking support for Swift's concurrency model.
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_SEMA_TYPECHECKCONCURRENCY_H
#define SWIFT_SEMA_TYPECHECKCONCURRENCY_H

#include "swift/AST/ASTContext.h"
#include "swift/AST/ConcreteDeclRef.h"
#include "swift/AST/DiagnosticEngine.h"
#include "swift/AST/Expr.h"
#include "swift/AST/Module.h"
#include "swift/AST/Type.h"
#include <cassert>

namespace swift {

class AbstractFunctionDecl;
class ConstructorDecl;
class ActorIsolation;
class AnyFunctionType;
class ASTContext;
class ClassDecl;
class ClosureActorIsolation;
class ClosureExpr;
class ConcreteDeclRef;
class CustomAttr;
class Decl;
class DeclContext;
class EnumElementDecl;
class Expr;
class FuncDecl;
class Initializer;
class PatternBindingDecl;
class ProtocolConformance;
class TopLevelCodeDecl;
class TypeBase;
class ValueDecl;
class VarDecl;

/// Add notes suggesting the addition of 'async', as appropriate,
/// to a diagnostic for a function that isn't an async context.
void addAsyncNotes(AbstractFunctionDecl const* func);

/// Check actor isolation rules.
void checkTopLevelActorIsolation(TopLevelCodeDecl *decl);
void checkFunctionActorIsolation(AbstractFunctionDecl *decl);
void checkInitializerActorIsolation(Initializer *init, Expr *expr);
void checkEnumElementActorIsolation(EnumElementDecl *element, Expr *expr);
void checkPropertyWrapperActorIsolation(VarDecl *wrappedVar, Expr *expr);

/// States the reason for checking the Sendability of a given declaration.
enum class SendableCheckReason {
  /// A reference to an actor from outside that actor.
  CrossActor,

  /// Exiting an actor to non-isolated async code.
  ExitingActor,

  /// A synchronous operation that was "promoted" to an asynchronous one
  /// because it was out of the actor's domain.
  SynchronousAsAsync,

  /// A protocol conformance where the witness/requirement have different
  /// actor isolation.
  Conformance,

  /// An override of a function.
  Override,

  /// The declaration is being exposed to Objective-C.
  ObjC,
};

/// Check that the actor isolation of an override matches that of its
/// overridden declaration.
void checkOverrideActorIsolation(ValueDecl *value);

/// Determine whether the given context requires strict concurrency checking,
/// e.g., because it uses concurrency features directly or because it's in
/// code where strict checking has been enabled.
bool contextRequiresStrictConcurrencyChecking(
    const DeclContext *dc,
    llvm::function_ref<Type(const AbstractClosureExpr *)> getType,
    llvm::function_ref<bool(const ClosureExpr *)> isolatedByPreconcurrency);

/// Describes a referenced actor variable and whether it is isolated.
struct ReferencedActor {
  /// Describes whether the actor variable is isolated or, if it is not
  /// isolated, why it is not isolated.
  enum Kind {
    /// It is isolated.
    Isolated = 0,

    /// It is not an isolated parameter at all.
    NonIsolatedParameter,

    // It is within a Sendable function.
    SendableFunction,

    // It is within a Sendable closure.
    SendableClosure,

    // It is within an 'async let' initializer.
    AsyncLet,

    // It is within a global actor.
    GlobalActor,

    // It is within the main actor.
    MainActor,

    // It is within a nonisolated context.
    NonIsolatedContext,

    // It is within a nonisolated autoclosure argument. This is primarily here
    // to aid in giving specific diagnostics, because autoclosures are not
    // always easy for programmers to notice.
    NonIsolatedAutoclosure
  };

  VarDecl * const actor;
  /// The outer scope is known to be running on an actor.
  /// We may be isolated to the actor or not, depending on the exact expression
  const bool isPotentiallyIsolated;
  const Kind kind;
  const Type globalActor;

  ReferencedActor(VarDecl *actor, bool isPotentiallyIsolated, Kind kind, Type globalActor = Type())
    : actor(actor),
      isPotentiallyIsolated(isPotentiallyIsolated),
      kind(kind),
      globalActor(globalActor) {}

  static ReferencedActor forGlobalActor(VarDecl *actor,
                                        bool isPotentiallyIsolated,
                                        Type globalActor);

  bool isIsolated() const { return kind == Isolated; }

  /// Whether the variable is "self" or a capture therefore.
  bool isSelf() const {
    if (!actor)
      return false;

    return actor->isSelfParameter() || actor->isSelfParamCapture();
  }

  /// Whether the referenced actor is known to be local.
  bool isKnownToBeLocal() const;

  explicit operator bool() const { return isIsolated(); }
};

/// The values for each case in this enum correspond to %select numbers
/// in a diagnostic, so be sure to update it if you add new cases.
enum class VarRefUseEnv {
  Read = 0,
  Mutating = 1,
  Inout = 2 // means Mutating; having a separate kind helps diagnostics
};

/// Describes the result of referencing a declaration.
struct ActorReferenceResult {
  enum Kind: uint8_t {
    /// The declaration being referenced is within the same concurrency
    /// domain as where the reference occurs, so no checking is required.
    SameConcurrencyDomain,
    /// Using the declaration requires entering a new actor, which might also
    /// mean switching away from the current actor.
    EntersActor,
    /// Using the declaration means leaving the current actor, exiting to
    /// a nonisolated context.
    ExitsActorToNonisolated,
  };

  /// Flags describing any additional adjustments or requirements when
  /// accessing the declaration.
  enum class Flags: uint8_t {
    /// A synchronous declaration must be accessed asynchronously to enter its
    /// actor.
    AsyncPromotion = 1 << 0,

    /// A non-throwing declaration that is potentially being accessed from
    /// another node, and can therefore throw an error due to transport
    /// failure.
    ThrowsPromotion = 1 << 1,

    /// The declaration is being accessed from outside the actor and
    /// potentially from a different node, so it must be marked 'distributed'.
    Distributed = 1 << 2,

    /// The declaration is being accessed from a @preconcurrency context.
    Preconcurrency = 1 << 3,
  };

  using Options = OptionSet<Flags>;

  const Kind kind;
  const Options options;
  const ActorIsolation isolation;

private:
  static ActorReferenceResult forSameConcurrencyDomain(
      ActorIsolation isolation);

  static ActorReferenceResult forEntersActor(
      ActorIsolation isolation, Options options);

  static ActorReferenceResult forExitsActorToNonisolated(
      ActorIsolation isolation);

public:
  /// Determine what happens when referencing the given declaration from the
  /// given declaration context.
  ///
  ///
  /// \param declRef The declaration that is being referenced.
  ///
  /// \param fromDC The declaration context from which the reference occurs.
  ///
  /// \param actorInstance When not \c None, the actor instance value that is
  /// provided when referencing the declaration. This can be either the base
  /// of a member access or a parameter passed to a function.
  static ActorReferenceResult forReference(
      ConcreteDeclRef declRef, SourceLoc declRefLoc, const DeclContext *fromDC,
      Optional<VarRefUseEnv> useKind = None,
      Optional<ReferencedActor> actorInstance = None,
      Optional<ActorIsolation> knownDeclIsolation = None,
      Optional<ActorIsolation> knownContextIsolation = None,
      llvm::function_ref<ClosureActorIsolation(AbstractClosureExpr *)>
          getClosureActorIsolation = __AbstractClosureExpr_getActorIsolation);

  operator Kind() const { return kind; }
};

/// Diagnose the presence of any non-sendable types when referencing a
/// given declaration from a particular declaration context.
///
/// This function should be invoked any time that the given declaration
/// reference is will move values of the declaration's types across a
/// concurrency domain, whether in/out of an actor or in/or of a concurrent
/// function or closure.
///
/// \param declRef The declaration being referenced from another concurrency
/// domain, including the substitutions so that (e.g.) we can consider the
/// specific types at the use site.
///
/// \param fromDC The context from which the reference occurs.
///
/// \param loc The location at which the reference occurs, which will be
/// used when emitting diagnostics.
///
/// \param refKind Describes what kind of reference is being made, which is
/// used to tailor the diagnostic.
///
/// \returns true if an problem was detected, false otherwise.
bool diagnoseNonSendableTypesInReference(
    ConcreteDeclRef declRef, const DeclContext *fromDC, SourceLoc loc,
    SendableCheckReason refKind,
    Optional<ActorIsolation> knownIsolation = None);

/// Produce a diagnostic for a missing conformance to Sendable.
void diagnoseMissingSendableConformance(
    SourceLoc loc, Type type, const DeclContext *fromDC);

/// If the given nominal type is public and does not explicitly
/// state whether it conforms to Sendable, provide a diagnostic.
void diagnoseMissingExplicitSendable(NominalTypeDecl *nominal);

/// How the Sendable check should be performed.
enum class SendableCheck {
  /// Sendable conformance was explicitly stated and should be
  /// fully checked.
  Explicit,

  /// Sendable conformance was implied by a protocol that inherits from
  /// Sendable and also predates concurrency.
  ImpliedByStandardProtocol,

  /// Implicit conformance to Sendable.
  Implicit,

  /// Implicit conformance to Sendable that would be externally-visible, i.e.,
  /// for a public @_frozen type.
  ImplicitForExternallyVisible,
};

/// Whether this sendable check is implicit.
static inline bool isImplicitSendableCheck(SendableCheck check) {
  switch (check) {
  case SendableCheck::Explicit:
  case SendableCheck::ImpliedByStandardProtocol:
    return false;

  case SendableCheck::Implicit:
  case SendableCheck::ImplicitForExternallyVisible:
    return true;
  }
}

/// Describes the context in which a \c Sendable check occurs.
struct SendableCheckContext {
  const DeclContext * const fromDC;
  const Optional<SendableCheck> conformanceCheck;

  SendableCheckContext(
      const DeclContext * fromDC,
      Optional<SendableCheck> conformanceCheck = None
  ) : fromDC(fromDC), conformanceCheck(conformanceCheck) { }

  /// Determine the default diagnostic behavior for a missing/unavailable
  /// Sendable conformance in this context.
  DiagnosticBehavior defaultDiagnosticBehavior() const;

  /// Determine the diagnostic behavior for an implicitly non-Sendable type.
  DiagnosticBehavior implicitSendableDiagnosticBehavior() const;

  /// Determine the diagnostic behavior when referencing the given nominal
  /// type in this context.
  DiagnosticBehavior diagnosticBehavior(NominalTypeDecl *nominal) const;

  /// Whether we are in an explicit conformance to Sendable.
  bool isExplicitSendableConformance() const;
};

/// Diagnose any non-Sendable types that occur within the given type, using
/// the given diagnostic.
///
/// \param diagnose Emit a diagnostic indicating that the current type
/// is non-Sendable, with the suggested behavior limitation. Returns \c true
/// if it did not emit any diagnostics.
///
/// \returns \c true if any errors were produced, \c false if no diagnostics or
/// only warnings and notes were produced.
bool diagnoseNonSendableTypes(
    Type type, SendableCheckContext fromContext, SourceLoc loc,
    llvm::function_ref<bool(Type, DiagnosticBehavior)> diagnose);

namespace detail {
  template<typename T>
  struct Identity {
    typedef T type;
  };
}

/// Diagnose any non-Sendable types that occur within the given type, using
/// the given diagnostic.
///
/// \returns \c true if any errors were produced, \c false if no diagnostics or
/// only warnings and notes were produced.
template<typename ...DiagArgs>
bool diagnoseNonSendableTypes(
    Type type, SendableCheckContext fromContext, SourceLoc loc,
    Diag<Type, DiagArgs...> diag,
    typename detail::Identity<DiagArgs>::type ...diagArgs) {
  ASTContext &ctx = fromContext.fromDC->getASTContext();
  return diagnoseNonSendableTypes(
      type, fromContext, loc, [&](Type specificType,
      DiagnosticBehavior behavior) {
    if (behavior != DiagnosticBehavior::Ignore) {
      ctx.Diags.diagnose(loc, diag, type, diagArgs...)
        .limitBehavior(behavior);
    }

    return false;
  });
}

/// Diagnose this sendability error with behavior based on the import of
/// \p nominal . For instance, depending on how \p nominal is imported into
/// \p fromContext , the diagnostic behavior limitation may be lower or the
/// compiler might emit a fix-it adding \c \@preconcurrency to the \c import .
///
/// \param nominal The declaration whose import we should check, or \c nullptr
/// to get behavior for a non-nominal type.
///
/// \param fromContext The context where the error will be emitted.
///
/// \param diagnose Emit a diagnostic indicating a sendability problem,
/// with the suggested behavior limitation. Returns \c true
/// if it did \em not emit any diagnostics.
///
/// \returns \c true if any errors were produced, \c false if no diagnostics or
/// only warnings and notes were produced.
bool diagnoseSendabilityErrorBasedOn(
    NominalTypeDecl *nominal, SendableCheckContext fromContext,
    llvm::function_ref<bool(DiagnosticBehavior)> diagnose);

/// Given a set of custom attributes, pick out the global actor attributes
/// and perform any necessary resolution and diagnostics, returning the
/// global actor attribute and type it refers to (or \c None).
Optional<std::pair<CustomAttr *, NominalTypeDecl *>>
checkGlobalActorAttributes(
    SourceLoc loc, DeclContext *dc, ArrayRef<CustomAttr *> attrs);

/// Get the explicit global actor specified for a closure.
Type getExplicitGlobalActor(ClosureExpr *closure);

/// Adjust the type of the variable for concurrency.
Type adjustVarTypeForConcurrency(
    Type type, VarDecl *var, DeclContext *dc,
    llvm::function_ref<Type(const AbstractClosureExpr *)> getType,
    llvm::function_ref<bool(const ClosureExpr *)> isolatedByPreconcurrency);

/// Adjust the given function type to account for concurrency-specific
/// attributes whose affect on the type might differ based on context.
/// This includes adjustments for unsafe parameter attributes like
/// `@_unsafeSendable` and `@_unsafeMainActor` as well as a global actor
/// on the declaration itself.
AnyFunctionType *adjustFunctionTypeForConcurrency(
    AnyFunctionType *fnType, ValueDecl *decl, DeclContext *dc,
    unsigned numApplies, bool isMainDispatchQueue,
    llvm::function_ref<Type(const AbstractClosureExpr *)> getType,
    llvm::function_ref<bool(const ClosureExpr *)> isolatedByPreconcurrency,
    llvm::function_ref<Type(Type)> openType);

/// Determine whether the given name is that of a DispatchQueue operation that
/// takes a closure to be executed on the queue.
bool isDispatchQueueOperationName(StringRef name);

/// Check the correctness of the given Sendable conformance.
///
/// \returns true if an error occurred.
bool checkSendableConformance(
    ProtocolConformance *conformance, SendableCheck check);

/// Check whether we are in an actor's initializer or deinitializer.
/// \returns nullptr iff we are not in such a declaration. Otherwise,
///          returns a pointer to the declaration.
AbstractFunctionDecl const *isActorInitOrDeInitContext(
    const DeclContext *dc,
    llvm::function_ref<bool(const AbstractClosureExpr *)> isSendable);

/// Determine whether this declaration is always accessed asynchronously.
bool isAsyncDecl(ConcreteDeclRef declRef);

/// Determine whether this declaration can throw errors.
bool isThrowsDecl(ConcreteDeclRef declRef);

/// Find the directly-referenced parameter or capture of a parameter for
/// for the given expression.
VarDecl *getReferencedParamOrCapture(
    Expr *expr,
    llvm::function_ref<Expr *(OpaqueValueExpr *)> getExistentialValue);

/// Determine whether the given value can be accessed across actors
/// without from normal synchronous code.
///
/// \param value The value we are checking.
/// \param isolation The actor isolation of the value.
/// \param fromDC The context where we are performing the access.
bool isAccessibleAcrossActors(
    ValueDecl *value, const ActorIsolation &isolation,
    const DeclContext *fromDC, Optional<ReferencedActor> actorInstance = None);

/// Check whether given variable references to a potentially
/// isolated actor.
bool isPotentiallyIsolatedActor(
    VarDecl *var, llvm::function_ref<bool(ParamDecl *)> isIsolated =
                      [](ParamDecl *P) { return P->isIsolated(); });

} // end namespace swift

#endif /* SWIFT_SEMA_TYPECHECKCONCURRENCY_H */