C++ TypeChecker::diagnose方法代码示例

static InFlightDiagnostic
diagnoseTypoCorrection(TypeChecker &tc, DeclNameLoc loc, ValueDecl *decl) {
  if (auto var = dyn_cast<VarDecl>(decl)) {
    // Suggest 'self' at the use point instead of pointing at the start
    // of the function.
    if (var->isSelfParameter())
      return tc.diagnose(loc.getBaseNameLoc(), diag::note_typo_candidate,
                         decl->getName().str());
  }

  if (!decl->getLoc().isValid() && decl->getDeclContext()->isTypeContext()) {
    Decl *parentDecl = dyn_cast<ExtensionDecl>(decl->getDeclContext());
    if (!parentDecl) parentDecl = cast<NominalTypeDecl>(decl->getDeclContext());

    if (parentDecl->getLoc().isValid()) {
      StringRef kind = (isa<VarDecl>(decl) ? "property" :
                        isa<ConstructorDecl>(decl) ? "initializer" :
                        isa<FuncDecl>(decl) ? "method" :
                        "member");

      return tc.diagnose(parentDecl, diag::note_typo_candidate_implicit_member,
                         decl->getName().str(), kind);
    }
  }

  return tc.diagnose(decl, diag::note_typo_candidate, decl->getName().str());
}

Type DerivedConformance::deriveCaseIterable(TypeChecker &tc, Decl *parentDecl,
                                            NominalTypeDecl *targetDecl,
                                            AssociatedTypeDecl *assocType) {
  // Conformance can't be synthesized in an extension.
  auto caseIterableProto
      = tc.Context.getProtocol(KnownProtocolKind::CaseIterable);
  auto caseIterableType = caseIterableProto->getDeclaredType();
  if (targetDecl != parentDecl) {
    tc.diagnose(parentDecl->getLoc(), diag::cannot_synthesize_in_extension,
                caseIterableType);
    return nullptr;
  }

  // We can only synthesize CaseIterable for enums.
  auto enumDecl = dyn_cast<EnumDecl>(targetDecl);
  if (!enumDecl)
    return nullptr;

  // Check that we can actually derive CaseIterable for this type.
  if (!canDeriveConformance(targetDecl))
    return nullptr;

  if (assocType->getName() == tc.Context.Id_AllCases) {
    return deriveCaseIterable_AllCases(tc, parentDecl, enumDecl);
  }

  tc.diagnose(assocType->getLoc(),
              diag::broken_case_iterable_requirement);
  return nullptr;
}

static InFlightDiagnostic
diagnoseTypoCorrection(TypeChecker &tc, DeclNameLoc loc, ValueDecl *decl) {
  if (auto var = dyn_cast<VarDecl>(decl)) {
    // Suggest 'self' at the use point instead of pointing at the start
    // of the function.
    if (var->isSelfParameter())
      return tc.diagnose(loc.getBaseNameLoc(), diag::note_typo_candidate,
                         decl->getName().str());
  }

  return tc.diagnose(decl, diag::note_typo_candidate, decl->getName().str());
}

/// Returns whether the given type has a valid nested \c CodingKeys enum.
///
/// If the type has an invalid \c CodingKeys entity, produces diagnostics to
/// complain about the error. In this case, the error result will be true -- in
/// the case where we don't have a valid CodingKeys enum and have produced
/// diagnostics here, we don't want to then attempt to synthesize a CodingKeys
/// enum.
///
/// \param tc The typechecker to use in validating {En,Decodable} conformance.
///
/// \param target The type decl whose nested \c CodingKeys type to validate.
///
/// \param proto The {En,De}codable protocol to ensure the properties matching
/// the keys conform to.
///
/// \returns A \c CodingKeysValidity value representing the result of the check.
static CodingKeysValidity hasValidCodingKeysEnum(TypeChecker &tc,
                                                 NominalTypeDecl *target,
                                                 ProtocolDecl *proto) {
  auto &C = tc.Context;
  auto codingKeysDecls = target->lookupDirect(DeclName(C.Id_CodingKeys));
  if (codingKeysDecls.empty())
    return CodingKeysValidity(/*hasType=*/false, /*isValid=*/true);

  // Only ill-formed code would produce multiple results for this lookup.
  // This would get diagnosed later anyway, so we're free to only look at the
  // first result here.
  auto result = codingKeysDecls.front();

  auto *codingKeysTypeDecl = dyn_cast<TypeDecl>(result);
  if (!codingKeysTypeDecl) {
    tc.diagnose(result->getLoc(),
                diag::codable_codingkeys_type_is_not_an_enum_here,
                proto->getDeclaredType());
    return CodingKeysValidity(/*hasType=*/true, /*isValid=*/false);
  }

  // CodingKeys may be a typealias. If so, follow the alias to its canonical
  // type.
  auto codingKeysType = codingKeysTypeDecl->getDeclaredInterfaceType();
  if (isa<TypeAliasDecl>(codingKeysTypeDecl)) {
    codingKeysTypeDecl = codingKeysType->getAnyNominal();
  }

  // Ensure that the type we found conforms to the CodingKey protocol.
  auto *codingKeyProto = C.getProtocol(KnownProtocolKind::CodingKey);
  if (!tc.conformsToProtocol(codingKeysType, codingKeyProto,
                             target->getDeclContext(),
                             ConformanceCheckFlags::Used)) {
    tc.diagnose(codingKeysTypeDecl->getLoc(),
                diag::codable_codingkeys_type_does_not_conform_here,
                proto->getDeclaredType());
    return CodingKeysValidity(/*hasType=*/true, /*isValid=*/false);
  }

  // CodingKeys must be an enum for synthesized conformance.
  auto *codingKeysEnum = dyn_cast<EnumDecl>(codingKeysTypeDecl);
  if (!codingKeysEnum) {
    tc.diagnose(codingKeysTypeDecl->getLoc(),
                diag::codable_codingkeys_type_is_not_an_enum_here,
                proto->getDeclaredType());
    return CodingKeysValidity(/*hasType=*/true, /*isValid=*/false);
  }

  bool valid = validateCodingKeysEnum(tc, codingKeysEnum, target, proto);
  return CodingKeysValidity(/*hasType=*/true, /*isValid=*/valid);
}

Type DerivedConformance::deriveRawRepresentable(TypeChecker &tc,
                                                Decl *parentDecl,
                                                NominalTypeDecl *type,
                                                AssociatedTypeDecl *assocType) {
  // Check preconditions. These should already have been diagnosed by
  // type-checking but we may still get here after recovery.
  
  // The type must be an enum.
  auto enumDecl = dyn_cast<EnumDecl>(type);
  if (!enumDecl)
    return nullptr;
  
  // It must have a valid raw type.
  if (!enumDecl->hasRawType())
    return nullptr;
  if (!enumDecl->getInherited().empty() &&
      enumDecl->getInherited().front().isError())
    return nullptr;
  
  // There must be enum elements.
  if (enumDecl->getAllElements().empty())
    return nullptr;

  for (auto elt : enumDecl->getAllElements())
    tc.validateDecl(elt);

  if (assocType->getName() == tc.Context.Id_RawValue) {
    return deriveRawRepresentable_Raw(tc, parentDecl, enumDecl);
  }
  
  tc.diagnose(assocType->getLoc(),
              diag::broken_raw_representable_requirement);
  return nullptr;
}

// Suggest a default value via ?? <default value>
static void offerDefaultValueUnwrapFixit(TypeChecker &TC, DeclContext *DC, Expr *expr) {
  auto diag =
  TC.diagnose(expr->getLoc(), diag::unwrap_with_default_value);

  // Figure out what we need to parenthesize.
  bool needsParensInside =
  exprNeedsParensBeforeAddingNilCoalescing(TC, DC, expr);
  bool needsParensOutside =
  exprNeedsParensAfterAddingNilCoalescing(TC, DC, expr, expr);

  llvm::SmallString<2> insertBefore;
  llvm::SmallString<32> insertAfter;
  if (needsParensOutside) {
    insertBefore += "(";
  }
  if (needsParensInside) {
    insertBefore += "(";
    insertAfter += ")";
  }
  insertAfter += " ?? <" "#default value#" ">";
  if (needsParensOutside)
    insertAfter += ")";

  if (!insertBefore.empty()) {
    diag.fixItInsert(expr->getStartLoc(), insertBefore);
  }
  diag.fixItInsertAfter(expr->getEndLoc(), insertAfter);
}

/// getInfixData - If the specified expression is an infix binary
/// operator, return its infix operator attributes.
static InfixData getInfixData(TypeChecker &TC, DeclContext *DC, Expr *E) {
  if (auto *ifExpr = dyn_cast<IfExpr>(E)) {
    // Ternary has fixed precedence.
    assert(!ifExpr->isFolded() && "already folded if expr in sequence?!");
    (void)ifExpr;
    return InfixData(IntrinsicPrecedences::IfExpr,
                     Associativity::Right,
                     /*assignment*/ false);

  }

  if (auto *assign = dyn_cast<AssignExpr>(E)) {
    // Assignment has fixed precedence.
    assert(!assign->isFolded() && "already folded assign expr in sequence?!");
    (void)assign;
    return InfixData(IntrinsicPrecedences::AssignExpr,
                     Associativity::Right,
                     /*assignment*/ true);

  }

  if (auto *as = dyn_cast<ExplicitCastExpr>(E)) {
    // 'as' and 'is' casts have fixed precedence.
    assert(!as->isFolded() && "already folded 'as' expr in sequence?!");
    (void)as;
    return InfixData(IntrinsicPrecedences::ExplicitCastExpr,
                     Associativity::None,
                     /*assignment*/ false);

  }

  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
    SourceFile *SF = DC->getParentSourceFile();
    Identifier name = DRE->getDecl()->getName();
    bool isCascading = DC->isCascadingContextForLookup(true);
    if (InfixOperatorDecl *op = SF->lookupInfixOperator(name, isCascading,
                                                        E->getLoc()))
      return op->getInfixData();

  }

  if (OverloadedDeclRefExpr *OO = dyn_cast<OverloadedDeclRefExpr>(E)) {
    SourceFile *SF = DC->getParentSourceFile();
    Identifier name = OO->getDecls()[0]->getName();
    bool isCascading = DC->isCascadingContextForLookup(true);
    if (InfixOperatorDecl *op = SF->lookupInfixOperator(name, isCascading,
                                                        E->getLoc()))
      return op->getInfixData();
  }

  // If E is already an ErrorExpr, then we've diagnosed it as invalid already,
  // otherwise emit an error.
  if (!isa<ErrorExpr>(E))
    TC.diagnose(E->getLoc(), diag::unknown_binop);

  // Recover with an infinite-precedence left-associative operator.
  return InfixData((unsigned char)~0U, Associativity::Left,
                   /*assignment*/ false);
}

static InFlightDiagnostic
noteTypoCorrection(TypeChecker &tc, DeclNameLoc loc, ValueDecl *decl,
                   bool wasClaimed) {
  if (auto var = dyn_cast<VarDecl>(decl)) {
    // Suggest 'self' at the use point instead of pointing at the start
    // of the function.
    if (var->isSelfParameter()) {
      if (wasClaimed) {
        // We don't need an extra note for this case because the programmer
        // knows what 'self' refers to.
        return InFlightDiagnostic();
      }

      return tc.diagnose(loc.getBaseNameLoc(), diag::note_typo_candidate,
                         var->getName().str());
    }
  }

  if (Decl *parentDecl = findExplicitParentForImplicitDecl(decl)) {
    StringRef kind = (isa<VarDecl>(decl) ? "property" :
                      isa<ConstructorDecl>(decl) ? "initializer" :
                      isa<FuncDecl>(decl) ? "method" :
                      "member");

    return tc.diagnose(parentDecl,
                       wasClaimed ? diag::implicit_member_declared_here
                                  : diag::note_typo_candidate_implicit_member,
                       decl->getBaseName().userFacingName(), kind);
  }

  if (wasClaimed) {
    return tc.diagnose(decl, diag::decl_declared_here, decl->getBaseName());
  } else {
    return tc.diagnose(decl, diag::note_typo_candidate,
                       decl->getBaseName().userFacingName());
  }
}

static bool canSynthesizeRawRepresentable(TypeChecker &tc, Decl *parentDecl, EnumDecl *enumDecl) {

  // It must have a valid raw type.
  Type rawType = enumDecl->getRawType();
  if (!rawType)
    return false;
  auto parentDC = cast<DeclContext>(parentDecl);
  rawType       = ArchetypeBuilder::mapTypeIntoContext(parentDC, rawType);

  if (!enumDecl->getInherited().empty() &&
      enumDecl->getInherited().front().isError())
    return false;

  // The raw type must be Equatable, so that we have a suitable ~= for synthesized switch statements.
  auto equatableProto = tc.getProtocol(enumDecl->getLoc(),
                                       KnownProtocolKind::Equatable);
  if (!equatableProto)
    return false;

  if (!tc.conformsToProtocol(rawType, equatableProto, enumDecl, None)) {
    SourceLoc loc = enumDecl->getInherited()[0].getSourceRange().Start;
    tc.diagnose(loc, diag::enum_raw_type_not_equatable, rawType);
    return false;
  }
  
  // There must be enum elements.
  if (enumDecl->getAllElements().empty())
    return false;

  // Have the type-checker validate that:
  // - the enum elements all have the same type
  // - they all match the enum type
  for (auto elt : enumDecl->getAllElements()) {
    tc.validateDecl(elt);
    if (elt->isInvalid()) {
      return false;
    }
  }

  // If it meets all of those requirements, we can synthesize RawRepresentable conformance.
  return true;
}

Type DerivedConformance::deriveRawRepresentable(TypeChecker &tc,
                                                Decl *parentDecl,
                                                NominalTypeDecl *type,
                                                AssociatedTypeDecl *assocType) {

  // We can only synthesize RawRepresentable for enums.
  auto enumDecl = dyn_cast<EnumDecl>(type);
  if (!enumDecl)
    return nullptr;

  // Check other preconditions for synthesized conformance.
  if (!canSynthesizeRawRepresentable(tc, parentDecl, enumDecl))
    return nullptr;

  if (assocType->getName() == tc.Context.Id_RawValue) {
    return deriveRawRepresentable_Raw(tc, parentDecl, enumDecl);
  }
  
  tc.diagnose(assocType->getLoc(),
              diag::broken_raw_representable_requirement);
  return nullptr;
}

// For a generic requirement in a protocol, make sure that the requirement
// set didn't add any requirements to Self or its associated types.
static bool checkProtocolSelfRequirements(GenericSignature *sig,
                                          ValueDecl *decl,
                                          TypeChecker &TC) {
  // For a generic requirement in a protocol, make sure that the requirement
  // set didn't add any requirements to Self or its associated types.
  if (auto *proto = dyn_cast<ProtocolDecl>(decl->getDeclContext())) {
    auto protoSelf = proto->getSelfInterfaceType();
    for (auto req : sig->getRequirements()) {
      // If one of the types in the requirement is dependent on a non-Self
      // type parameter, this requirement is okay.
      if (!isSelfDerivedOrConcrete(protoSelf, req.getFirstType()) ||
          !isSelfDerivedOrConcrete(protoSelf, req.getSecondType()))
        continue;

      // The conformance of 'Self' to the protocol is okay.
      if (req.getKind() == RequirementKind::Conformance &&
          req.getSecondType()->getAs<ProtocolType>()->getDecl() == proto &&
          req.getFirstType()->is<GenericTypeParamType>())
        continue;

      TC.diagnose(decl,
                  TC.Context.LangOpts.EffectiveLanguageVersion[0] >= 4
                    ? diag::requirement_restricts_self
                    : diag::requirement_restricts_self_swift3,
                  decl->getDescriptiveKind(), decl->getFullName(),
                  req.getFirstType().getString(),
                  static_cast<unsigned>(req.getKind()),
                  req.getSecondType().getString());

      if (TC.Context.LangOpts.EffectiveLanguageVersion[0] >= 4)
        return true;
    }
  }

  return false;
}

/// Validates the given CodingKeys enum decl by ensuring its cases are a 1-to-1
/// match with the stored vars of the given type.
///
/// \param tc The typechecker to use in validating {En,De}codable conformance.
///
/// \param codingKeysDecl The \c CodingKeys enum decl to validate.
///
/// \param target The nominal type decl to validate the \c CodingKeys against.
///
/// \param proto The {En,De}codable protocol to validate all the keys conform
/// to.
static bool
validateCodingKeysEnum(TypeChecker &tc, EnumDecl *codingKeysDecl,
                       NominalTypeDecl *target, ProtocolDecl *proto) {
  // Look through all var decls in the given type.
  // * Filter out lazy/computed vars (currently already done by
  //   getStoredProperties).
  // * Filter out ones which are present in the given decl (by name).
  //
  // If any of the entries in the CodingKeys decl are not present in the type
  // by name, then this decl doesn't match.
  // If there are any vars left in the type which don't have a default value
  // (for Decodable), then this decl doesn't match.

  // Here we'll hold on to properties by name -- when we've validated a property
  // against its CodingKey entry, it will get removed.
  llvm::SmallDenseMap<Identifier, VarDecl *, 8> properties;
  for (auto *varDecl : target->getStoredProperties(/*skipInaccessible=*/true)) {
    properties[varDecl->getName()] = varDecl;
  }

  bool propertiesAreValid = true;
  for (auto elt : codingKeysDecl->getAllElements()) {
    auto it = properties.find(elt->getName());
    if (it == properties.end()) {
      tc.diagnose(elt->getLoc(), diag::codable_extraneous_codingkey_case_here,
                  elt->getName());
      // TODO: Investigate typo-correction here; perhaps the case name was
      //       misspelled and we can provide a fix-it.
      propertiesAreValid = false;
      continue;
    }

    // We have a property to map to. Ensure it's {En,De}codable.
    auto conformance = varConformsToCodable(tc, target->getDeclContext(),
                                            it->second, proto);
    switch (conformance) {
      case Conforms:
        // The property was valid. Remove it from the list.
        properties.erase(it);
        break;

      case DoesNotConform:
        tc.diagnose(it->second->getLoc(),
                    diag::codable_non_conforming_property_here,
                    proto->getDeclaredType(), it->second->getType());
        LLVM_FALLTHROUGH;

      case TypeNotValidated:
        // We don't produce a diagnostic for a type which failed to validate.
        // This will produce a diagnostic elsewhere anyway.
        propertiesAreValid = false;
        continue;
    }
  }

  if (!propertiesAreValid)
    return false;

  // If there are any remaining properties which the CodingKeys did not cover,
  // we can skip them on encode. On decode, though, we can only skip them if
  // they have a default value.
  if (!properties.empty() &&
      proto == tc.Context.getProtocol(KnownProtocolKind::Decodable)) {
    for (auto it = properties.begin(); it != properties.end(); ++it) {
      if (it->second->getParentInitializer() != nullptr) {
        // Var has a default value.
        continue;
      }

      propertiesAreValid = false;
      tc.diagnose(it->second->getLoc(), diag::codable_non_decoded_property_here,
                  proto->getDeclaredType(), it->first);
    }
  }

  return propertiesAreValid;
}

static void bindExtensionDecl(ExtensionDecl *ED, TypeChecker &TC) {
  if (ED->getExtendedType())
    return;

  // If we didn't parse a type, fill in an error type and bail out.
  if (!ED->getExtendedTypeLoc().getTypeRepr()) {
    ED->setInvalid();
    ED->getExtendedTypeLoc().setInvalidType(TC.Context);
    return;
  }

  auto dc = ED->getDeclContext();

  // Validate the representation.
  // FIXME: Perform some kind of "shallow" validation here?
  TypeResolutionOptions options;
  options |= TR_AllowUnboundGenerics;
  options |= TR_ExtensionBinding;
  if (TC.validateType(ED->getExtendedTypeLoc(), dc, options)) {
    ED->setInvalid();
    return;
  }

  // Dig out the extended type.
  auto extendedType = ED->getExtendedType();

  // Hack to allow extending a generic typealias.
  if (auto *unboundGeneric = extendedType->getAs<UnboundGenericType>()) {
    if (auto *aliasDecl = dyn_cast<TypeAliasDecl>(unboundGeneric->getDecl())) {
      auto extendedNominal = aliasDecl->getDeclaredInterfaceType()->getAnyNominal();
      if (extendedNominal) {
        extendedType = extendedNominal->getDeclaredType();
        ED->getExtendedTypeLoc().setType(extendedType);
      }
    }
  }

  // Handle easy cases.

  // Cannot extend a metatype.
  if (extendedType->is<AnyMetatypeType>()) {
    TC.diagnose(ED->getLoc(), diag::extension_metatype, extendedType)
      .highlight(ED->getExtendedTypeLoc().getSourceRange());
    ED->setInvalid();
    ED->getExtendedTypeLoc().setInvalidType(TC.Context);
    return;
  }

  // Cannot extend a bound generic type.
  if (extendedType->isSpecialized()) {
    TC.diagnose(ED->getLoc(), diag::extension_specialization,
                extendedType->getAnyNominal()->getName())
      .highlight(ED->getExtendedTypeLoc().getSourceRange());
    ED->setInvalid();
    ED->getExtendedTypeLoc().setInvalidType(TC.Context);
    return;
  }

  // Dig out the nominal type being extended.
  NominalTypeDecl *extendedNominal = extendedType->getAnyNominal();
  if (!extendedNominal) {
    TC.diagnose(ED->getLoc(), diag::non_nominal_extension, extendedType)
      .highlight(ED->getExtendedTypeLoc().getSourceRange());
    ED->setInvalid();
    ED->getExtendedTypeLoc().setInvalidType(TC.Context);
    return;
  }
  assert(extendedNominal && "Should have the nominal type being extended");

  // If the extended type is generic or is a protocol. Clone or create
  // the generic parameters.
  if (extendedNominal->isGenericContext()) {
    if (auto proto = dyn_cast<ProtocolDecl>(extendedNominal)) {
      // For a protocol extension, build the generic parameter list.
      ED->setGenericParams(proto->createGenericParams(ED));
    } else {
      // Clone the existing generic parameter list.
      ED->setGenericParams(
        cloneGenericParams(TC.Context, ED,
                           extendedNominal->getGenericParamsOfContext()));
    }
  }

  // If we have a trailing where clause, deal with it now.
  // For now, trailing where clauses are only permitted on protocol extensions.
  if (auto trailingWhereClause = ED->getTrailingWhereClause()) {
    if (!extendedNominal->isGenericContext()) {
      // Only generic and protocol types are permitted to have
      // trailing where clauses.
      TC.diagnose(ED, diag::extension_nongeneric_trailing_where, extendedType)
        .highlight(trailingWhereClause->getSourceRange());
      ED->setTrailingWhereClause(nullptr);
    } else {
      // Merge the trailing where clause into the generic parameter list.
      // FIXME: Long-term, we'd like clients to deal with the trailing where
      // clause explicitly, but for now it's far more direct to represent
      // the trailing where clause as part of the requirements.
      ED->getGenericParams()->addTrailingWhereClause(
        TC.Context,
        trailingWhereClause->getWhereLoc(),
//.........这里部分代码省略.........

//.........这里部分代码省略.........
      break;
    }

    // Collect generic parameter types referenced by types used in a requirement.
    ReferencedGenericTypeWalker walker;
    if (first && first->hasTypeParameter())
      first.walk(walker);
    if (second && second->hasTypeParameter())
      second.walk(walker);
    auto &genericParamsUsedByRequirementTypes =
        walker.getReferencedGenericParams();

    // If at least one of the collected generic types or a root generic
    // parameter of dependent member types is known to be referenced by
    // parameter types, return types or other types known to be "referenced",
    // then all the types used in the requirement are considered to be
    // referenced, because they are used to defined something that is known
    // to be referenced.
    bool foundNewReferencedGenericParam = false;
    if (std::any_of(genericParamsUsedByRequirementTypes.begin(),
                    genericParamsUsedByRequirementTypes.end(),
                    [&referencedGenericParams](CanType t) {
                      assert(t->isTypeParameter());
                      return referencedGenericParams.find(
                                 t->getRootGenericParam()
                                     ->getCanonicalType()) !=
                             referencedGenericParams.end();
                    })) {
      std::for_each(genericParamsUsedByRequirementTypes.begin(),
                    genericParamsUsedByRequirementTypes.end(),
                    [&referencedGenericParams,
                     &foundNewReferencedGenericParam](CanType t) {
                      // Add only generic type parameters, but ignore any
                      // dependent member types, because requirement
                      // on a dependent member type does not provide enough
                      // information to infer the base generic type
                      // parameter.
                      if (!t->is<GenericTypeParamType>())
                        return;
                      if (referencedGenericParams.insert(t).second)
                        foundNewReferencedGenericParam = true;
                    });
    }
    return foundNewReferencedGenericParam;
  };

  ArrayRef<Requirement> requirements;

  auto FindReferencedGenericParamsInRequirements = [&requirements, sig, &reqTypesVisitor] {
    requirements = sig->getRequirements();
    // Try to find new referenced generic parameter types in requirements until
    // we reach a fix point. We need to iterate until a fix point, because we
    // may have e.g. chains of same-type requirements like:
    // not-yet-referenced-T1 == not-yet-referenced-T2.DepType2,
    // not-yet-referenced-T2 == not-yet-referenced-T3.DepType3,
    // not-yet-referenced-T3 == referenced-T4.DepType4.
    // When we process the first of these requirements, we don't know yet that
    // T2
    // will be referenced, because T3 will be referenced,
    // because T3 == T4.DepType4.
    while (true) {
      bool foundNewReferencedGenericParam = false;
      for (auto req : requirements) {
        if (reqTypesVisitor(req))
          foundNewReferencedGenericParam = true;
      }
      if (!foundNewReferencedGenericParam)
        break;
    }
  };

  // Find the depth of the function's own generic parameters.
  unsigned fnGenericParamsDepth = genericParams->getDepth();

  // Check that every generic parameter type from the signature is
  // among referencedGenericParams.
  for (auto *genParam : sig->getGenericParams()) {
    auto *paramDecl = genParam->getDecl();
    if (paramDecl->getDepth() != fnGenericParamsDepth)
      continue;
    if (!referencedGenericParams.count(genParam->getCanonicalType())) {
      // Lazily search for generic params that are indirectly used in the
      // function signature. Do it only if there is a generic parameter
      // that is not known to be referenced yet.
      if (requirements.empty()) {
        FindReferencedGenericParamsInRequirements();
        // Nothing to do if this generic parameter is considered to be
        // referenced after analyzing the requirements from the generic
        // signature.
        if (referencedGenericParams.count(genParam->getCanonicalType()))
          continue;
      }
      // Produce an error that this generic parameter cannot be bound.
      TC.diagnose(paramDecl->getLoc(), diag::unreferenced_generic_parameter,
                  paramDecl->getNameStr());
      decl->setInterfaceType(ErrorType::get(TC.Context));
      decl->setInvalid();
    }
  }
}