A less annoying version of the Resharper annotations for R# 8. Makes classes and enums internal, puts them in System namespace.

JetbrainsAnnotations.cs

#pragma warning disable 1591
// ReSharper disable UnusedMember.Global
// ReSharper disable UnusedParameter.Local
// ReSharper disable MemberCanBePrivate.Global
// ReSharper disable UnusedAutoPropertyAccessor.Global
// ReSharper disable IntroduceOptionalParameters.Global
// ReSharper disable MemberCanBeProtected.Global
// ReSharper disable InconsistentNaming

// ReSharper disable once CheckNamespace
namespace System
{
  /// <summary>
  /// Indicates that the value of the marked element could be <c>null</c> sometimes,
  /// so the check for <c>null</c> is necessary before its usage
  /// </summary>
  /// <example><code>
  /// [CanBeNull] public object Test() { return null; }
  /// public void UseTest() {
  ///   var p = Test();
  ///   var s = p.ToString(); // Warning: Possible 'System.NullReferenceException'
  /// }
  /// </code></example>
  [AttributeUsage(
    AttributeTargets.Method | AttributeTargets.Parameter |
    AttributeTargets.Property | AttributeTargets.Delegate |
    AttributeTargets.Field, AllowMultiple = false, Inherited = true)]
  internal sealed class CanBeNullAttribute : Attribute { }

  /// <summary>
  /// Indicates that the value of the marked element could never be <c>null</c>
  /// </summary>
  /// <example><code>
  /// [NotNull] public object Foo() {
  ///   return null; // Warning: Possible 'null' assignment
  /// }
  /// </code></example>
  [AttributeUsage(
    AttributeTargets.Method | AttributeTargets.Parameter |
    AttributeTargets.Property | AttributeTargets.Delegate |
    AttributeTargets.Field, AllowMultiple = false, Inherited = true)]
  internal sealed class NotNullAttribute : Attribute { }

  /// <summary>
  /// Indicates that the marked method builds string by format pattern and (optional) arguments.
  /// Parameter, which contains format string, should be given in constructor. The format string
  /// should be in <see cref="string.Format(IFormatProvider,string,object[])"/>-like form
  /// </summary>
  /// <example><code>
  /// [StringFormatMethod("message")]
  /// public void ShowError(string message, params object[] args) { /* do something */ }
  /// public void Foo() {
  ///   ShowError("Failed: {0}"); // Warning: Non-existing argument in format string
  /// }
  /// </code></example>
  [AttributeUsage(
    AttributeTargets.Constructor | AttributeTargets.Method,
    AllowMultiple = false, Inherited = true)]
  internal sealed class StringFormatMethodAttribute : Attribute
  {
    /// <param name="formatParameterName">
    /// Specifies which parameter of an annotated method should be treated as format-string
    /// </param>
    public StringFormatMethodAttribute(string formatParameterName)
    {
      FormatParameterName = formatParameterName;
    }

    public string FormatParameterName { get; private set; }
  }

  /// <summary>
  /// Indicates that the function argument should be string literal and match one
  /// of the parameters of the caller function. For example, ReSharper annotates
  /// the parameter of <see cref="System.ArgumentNullException"/>
  /// </summary>
  /// <example><code>
  /// public void Foo(string param) {
  ///   if (param == null)
  ///     throw new ArgumentNullException("par"); // Warning: Cannot resolve symbol
  /// }
  /// </code></example>
  [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false, Inherited = true)]
  internal sealed class InvokerParameterNameAttribute : Attribute { }

  /// <summary>
  /// Indicates that the method is contained in a type that implements
  /// <see cref="System.ComponentModel.INotifyPropertyChanged"/> interface
  /// and this method is used to notify that some property value changed
  /// </summary>
  /// <remarks>
  /// The method should be non-static and conform to one of the supported signatures:
  /// <list>
  /// <item><c>NotifyChanged(string)</c></item>
  /// <item><c>NotifyChanged(params string[])</c></item>
  /// <item><c>NotifyChanged{T}(Expression{Func{T}})</c></item>
  /// <item><c>NotifyChanged{T,U}(Expression{Func{T,U}})</c></item>
  /// <item><c>SetProperty{T}(ref T, T, string)</c></item>
  /// </list>
  /// </remarks>
  /// <example><code>
  /// public class Foo : INotifyPropertyChanged {
  ///   public event PropertyChangedEventHandler PropertyChanged;
  ///   [NotifyPropertyChangedInvocator]
  ///   protected virtual void NotifyChanged(string propertyName) { ... }
  ///
  ///   private string _name;
  ///   public string Name {
  ///     get { return _name; }
  ///     set { _name = value; NotifyChanged("LastName"); /* Warning */ }
  ///   }
  /// }
  /// </code>
  /// Examples of generated notifications:
  /// <list>
  /// <item><c>NotifyChanged("Property")</c></item>
  /// <item><c>NotifyChanged(() =&gt; Property)</c></item>
  /// <item><c>NotifyChanged((VM x) =&gt; x.Property)</c></item>
  /// <item><c>SetProperty(ref myField, value, "Property")</c></item>
  /// </list>
  /// </example>
  [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
  internal sealed class NotifyPropertyChangedInvocatorAttribute : Attribute
  {
    public NotifyPropertyChangedInvocatorAttribute() { }
    public NotifyPropertyChangedInvocatorAttribute(string parameterName)
    {
      ParameterName = parameterName;
    }

    public string ParameterName { get; private set; }
  }

  /// <summary>
  /// Describes dependency between method input and output
  /// </summary>
  /// <syntax>
  /// <p>Function Definition Table syntax:</p>
  /// <list>
  /// <item>FDT      ::= FDTRow [;FDTRow]*</item>
  /// <item>FDTRow   ::= Input =&gt; Output | Output &lt;= Input</item>
  /// <item>Input    ::= ParameterName: Value [, Input]*</item>
  /// <item>Output   ::= [ParameterName: Value]* {halt|stop|void|nothing|Value}</item>
  /// <item>Value    ::= true | false | null | notnull | canbenull</item>
  /// </list>
  /// If method has single input parameter, it's name could be omitted.<br/>
  /// Using <c>halt</c> (or <c>void</c>/<c>nothing</c>, which is the same)
  /// for method output means that the methos doesn't return normally.<br/>
  /// <c>canbenull</c> annotation is only applicable for output parameters.<br/>
  /// You can use multiple <c>[ContractAnnotation]</c> for each FDT row,
  /// or use single attribute with rows separated by semicolon.<br/>
  /// </syntax>
  /// <examples><list>
  /// <item><code>
  /// [ContractAnnotation("=> halt")]
  /// public void TerminationMethod()
  /// </code></item>
  /// <item><code>
  /// [ContractAnnotation("halt &lt;= condition: false")]
  /// public void Assert(bool condition, string text) // regular assertion method
  /// </code></item>
  /// <item><code>
  /// [ContractAnnotation("s:null => true")]
  /// public bool IsNullOrEmpty(string s) // string.IsNullOrEmpty()
  /// </code></item>
  /// <item><code>
  /// // A method that returns null if the parameter is null, and not null if the parameter is not null
  /// [ContractAnnotation("null => null; notnull => notnull")]
  /// public object Transform(object data) 
  /// </code></item>
  /// <item><code>
  /// [ContractAnnotation("s:null=>false; =>true,result:notnull; =>false, result:null")]
  /// public bool TryParse(string s, out Person result)
  /// </code></item>
  /// </list></examples>
  [AttributeUsage(AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
  internal sealed class ContractAnnotationAttribute : Attribute
  {
    public ContractAnnotationAttribute([NotNull] string contract)
      : this(contract, false) { }

    public ContractAnnotationAttribute([NotNull] string contract, bool forceFullStates)
    {
      Contract = contract;
      ForceFullStates = forceFullStates;
    }

    public string Contract { get; private set; }
    public bool ForceFullStates { get; private set; }
  }

  /// <summary>
  /// Indicates that marked element should be localized or not
  /// </summary>
  /// <example><code>
  /// [LocalizationRequiredAttribute(true)]
  /// public class Foo {
  ///   private string str = "my string"; // Warning: Localizable string
  /// }
  /// </code></example>
  [AttributeUsage(AttributeTargets.All, AllowMultiple = false, Inherited = true)]
  internal sealed class LocalizationRequiredAttribute : Attribute
  {
    public LocalizationRequiredAttribute() : this(true) { }
    public LocalizationRequiredAttribute(bool required)
    {
      Required = required;
    }

    public bool Required { get; private set; }
  }

  /// <summary>
  /// Indicates that the value of the marked type (or its derivatives)
  /// cannot be compared using '==' or '!=' operators and <c>Equals()</c>
  /// should be used instead. However, using '==' or '!=' for comparison
  /// with <c>null</c> is always permitted.
  /// </summary>
  /// <example><code>
  /// [CannotApplyEqualityOperator]
  /// class NoEquality { }
  /// class UsesNoEquality {
  ///   public void Test() {
  ///     var ca1 = new NoEquality();
  ///     var ca2 = new NoEquality();
  ///     if (ca1 != null) { // OK
  ///       bool condition = ca1 == ca2; // Warning
  ///     }
  ///   }
  /// }
  /// </code></example>
  [AttributeUsage(
    AttributeTargets.Interface | AttributeTargets.Class |
    AttributeTargets.Struct, AllowMultiple = false, Inherited = true)]
  internal sealed class CannotApplyEqualityOperatorAttribute : Attribute { }

  /// <summary>
  /// When applied to a target attribute, specifies a requirement for any type marked
  /// with the target attribute to implement or inherit specific type or types.
  /// </summary>
  /// <example><code>
  /// [BaseTypeRequired(typeof(IComponent)] // Specify requirement
  /// public class ComponentAttribute : Attribute { }
  /// [Component] // ComponentAttribute requires implementing IComponent interface
  /// public class MyComponent : IComponent { }
  /// </code></example>
  [AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
  [BaseTypeRequired(typeof(Attribute))]
  internal sealed class BaseTypeRequiredAttribute : Attribute
  {
    public BaseTypeRequiredAttribute([NotNull] Type baseType)
    {
      BaseType = baseType;
    }

    [NotNull] public Type BaseType { get; private set; }
  }

  /// <summary>
  /// Indicates that the marked symbol is used implicitly
  /// (e.g. via reflection, in external library), so this symbol
  /// will not be marked as unused (as well as by other usage inspections)
  /// </summary>
  [AttributeUsage(AttributeTargets.All, AllowMultiple = false, Inherited = true)]
  internal sealed class UsedImplicitlyAttribute : Attribute
  {
    public UsedImplicitlyAttribute()
      : this(ImplicitUseKindFlags.Default, ImplicitUseTargetFlags.Default) { }

    public UsedImplicitlyAttribute(ImplicitUseKindFlags useKindFlags)
      : this(useKindFlags, ImplicitUseTargetFlags.Default) { }

    public UsedImplicitlyAttribute(ImplicitUseTargetFlags targetFlags)
      : this(ImplicitUseKindFlags.Default, targetFlags) { }

    public UsedImplicitlyAttribute(
      ImplicitUseKindFlags useKindFlags, ImplicitUseTargetFlags targetFlags)
    {
      UseKindFlags = useKindFlags;
      TargetFlags = targetFlags;
    }

    public ImplicitUseKindFlags UseKindFlags { get; private set; }
    public ImplicitUseTargetFlags TargetFlags { get; private set; }
  }

  /// <summary>
  /// Should be used on attributes and causes ReSharper
  /// to not mark symbols marked with such attributes as unused
  /// (as well as by other usage inspections)
  /// </summary>
  [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
  internal sealed class MeansImplicitUseAttribute : Attribute
  {
    public MeansImplicitUseAttribute() 
      : this(ImplicitUseKindFlags.Default, ImplicitUseTargetFlags.Default) { }

    public MeansImplicitUseAttribute(ImplicitUseKindFlags useKindFlags)
      : this(useKindFlags, ImplicitUseTargetFlags.Default) { }

    public MeansImplicitUseAttribute(ImplicitUseTargetFlags targetFlags)
      : this(ImplicitUseKindFlags.Default, targetFlags) { }

    public MeansImplicitUseAttribute(
      ImplicitUseKindFlags useKindFlags, ImplicitUseTargetFlags targetFlags)
    {
      UseKindFlags = useKindFlags;
      TargetFlags = targetFlags;
    }

    [UsedImplicitly] public ImplicitUseKindFlags UseKindFlags { get; private set; }
    [UsedImplicitly] public ImplicitUseTargetFlags TargetFlags { get; private set; }
  }
  
  [Flags]
  internal enum ImplicitUseKindFlags
  {
    Default = Access | Assign | InstantiatedWithFixedConstructorSignature,
    /// <summary>Only entity marked with attribute considered used</summary>
    Access = 1,
    /// <summary>Indicates implicit assignment to a member</summary>
    Assign = 2,
    /// <summary>
    /// Indicates implicit instantiation of a type with fixed constructor signature.
    /// That means any unused constructor parameters won't be reported as such.
    /// </summary>
    InstantiatedWithFixedConstructorSignature = 4,
    /// <summary>Indicates implicit instantiation of a type</summary>
    InstantiatedNoFixedConstructorSignature = 8,
  }

  /// <summary>
  /// Specify what is considered used implicitly
  /// when marked with <see cref="MeansImplicitUseAttribute"/>
  /// or <see cref="UsedImplicitlyAttribute"/>
  /// </summary>
  [Flags]
  internal enum ImplicitUseTargetFlags
  {
    Default = Itself,
    Itself = 1,
    /// <summary>Members of entity marked with attribute are considered used</summary>
    Members = 2,
    /// <summary>Entity marked with attribute and all its members considered used</summary>
    WithMembers = Itself | Members
  }

  /// <summary>
  /// This attribute is intended to mark publicly available API
  /// which should not be removed and so is treated as used
  /// </summary>
  [MeansImplicitUse]
  internal sealed class PublicAPIAttribute : Attribute
  {
    public PublicAPIAttribute() { }
    public PublicAPIAttribute([NotNull] string comment)
    {
      Comment = comment;
    }

    [NotNull] public string Comment { get; private set; }
  }

  /// <summary>
  /// Tells code analysis engine if the parameter is completely handled
  /// when the invoked method is on stack. If the parameter is a delegate,
  /// indicates that delegate is executed while the method is executed.
  /// If the parameter is an enumerable, indicates that it is enumerated
  /// while the method is executed
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter, Inherited = true)]
  internal sealed class InstantHandleAttribute : Attribute { }

  /// <summary>
  /// Indicates that a method does not make any observable state changes.
  /// The same as <c>System.Diagnostics.Contracts.PureAttribute</c>
  /// </summary>
  /// <example><code>
  /// [Pure] private int Multiply(int x, int y) { return x * y; }
  /// public void Foo() {
  ///   const int a = 2, b = 2;
  ///   Multiply(a, b); // Waring: Return value of pure method is not used
  /// }
  /// </code></example>
  [AttributeUsage(AttributeTargets.Method, Inherited = true)]
  internal sealed class PureAttribute : Attribute { }

  /// <summary>
  /// Indicates that a parameter is a path to a file or a folder
  /// within a web project. Path can be relative or absolute,
  /// starting from web root (~)
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal class PathReferenceAttribute : Attribute
  {
    public PathReferenceAttribute() { }
    public PathReferenceAttribute([PathReference] string basePath)
    {
      BasePath = basePath;
    }

    [NotNull] public string BasePath { get; private set; }
  }

  // ASP.NET MVC attributes

  [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
  internal sealed class AspMvcAreaMasterLocationFormatAttribute : Attribute
  {
    public AspMvcAreaMasterLocationFormatAttribute(string format) { }
  }

  [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
  internal sealed class AspMvcAreaPartialViewLocationFormatAttribute : Attribute
  {
    public AspMvcAreaPartialViewLocationFormatAttribute(string format) { }
  }

  [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
  internal sealed class AspMvcAreaViewLocationFormatAttribute : Attribute
  {
    public AspMvcAreaViewLocationFormatAttribute(string format) { }
  }

  [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
  internal sealed class AspMvcMasterLocationFormatAttribute : Attribute
  {
    public AspMvcMasterLocationFormatAttribute(string format) { }
  }

  [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
  internal sealed class AspMvcPartialViewLocationFormatAttribute : Attribute
  {
    public AspMvcPartialViewLocationFormatAttribute(string format) { }
  }

  [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
  internal sealed class AspMvcViewLocationFormatAttribute : Attribute
  {
    public AspMvcViewLocationFormatAttribute(string format) { }
  }
  
  /// <summary>
  /// ASP.NET MVC attribute. If applied to a parameter, indicates that the parameter
  /// is an MVC action. If applied to a method, the MVC action name is calculated
  /// implicitly from the context. Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Html.ChildActionExtensions.RenderAction(HtmlHelper, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Method)]
  internal sealed class AspMvcActionAttribute : Attribute
  {
    public AspMvcActionAttribute() { }
    public AspMvcActionAttribute([NotNull] string anonymousProperty)
    {
      AnonymousProperty = anonymousProperty;
    }

    [NotNull] public string AnonymousProperty { get; private set; }
  }

  /// <summary>
  /// ASP.NET MVC attribute. Indicates that a parameter is an MVC area.
  /// Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Html.ChildActionExtensions.RenderAction(HtmlHelper, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal sealed class AspMvcAreaAttribute : PathReferenceAttribute
  {
    public AspMvcAreaAttribute() { }
    public AspMvcAreaAttribute([NotNull] string anonymousProperty)
    {
      AnonymousProperty = anonymousProperty;
    }

    [NotNull] public string AnonymousProperty { get; private set; }
  }

  /// <summary>
  /// ASP.NET MVC attribute. If applied to a parameter, indicates that
  /// the parameter is an MVC controller. If applied to a method,
  /// the MVC controller name is calculated implicitly from the context.
  /// Use this attribute for custom wrappers similar to 
  /// <c>System.Web.Mvc.Html.ChildActionExtensions.RenderAction(HtmlHelper, String, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Method)]
  internal sealed class AspMvcControllerAttribute : Attribute
  {
    public AspMvcControllerAttribute() { }
    public AspMvcControllerAttribute([NotNull] string anonymousProperty)
    {
      AnonymousProperty = anonymousProperty;
    }

    [NotNull] public string AnonymousProperty { get; private set; }
  }

  /// <summary>
  /// ASP.NET MVC attribute. Indicates that a parameter is an MVC Master.
  /// Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Controller.View(String, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal sealed class AspMvcMasterAttribute : Attribute { }

  /// <summary>
  /// ASP.NET MVC attribute. Indicates that a parameter is an MVC model type.
  /// Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Controller.View(String, Object)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal sealed class AspMvcModelTypeAttribute : Attribute { }

  /// <summary>
  /// ASP.NET MVC attribute. If applied to a parameter, indicates that
  /// the parameter is an MVC partial view. If applied to a method,
  /// the MVC partial view name is calculated implicitly from the context.
  /// Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(HtmlHelper, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Method)]
  internal sealed class AspMvcPartialViewAttribute : PathReferenceAttribute { }

  /// <summary>
  /// ASP.NET MVC attribute. Allows disabling all inspections
  /// for MVC views within a class or a method.
  /// </summary>
  [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
  internal sealed class AspMvcSupressViewErrorAttribute : Attribute { }

  /// <summary>
  /// ASP.NET MVC attribute. Indicates that a parameter is an MVC display template.
  /// Use this attribute for custom wrappers similar to 
  /// <c>System.Web.Mvc.Html.DisplayExtensions.DisplayForModel(HtmlHelper, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal sealed class AspMvcDisplayTemplateAttribute : Attribute { }

  /// <summary>
  /// ASP.NET MVC attribute. Indicates that a parameter is an MVC editor template.
  /// Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Html.EditorExtensions.EditorForModel(HtmlHelper, String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal sealed class AspMvcEditorTemplateAttribute : Attribute { }

  /// <summary>
  /// ASP.NET MVC attribute. Indicates that a parameter is an MVC template.
  /// Use this attribute for custom wrappers similar to
  /// <c>System.ComponentModel.DataAnnotations.UIHintAttribute(System.String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  internal sealed class AspMvcTemplateAttribute : Attribute { }

  /// <summary>
  /// ASP.NET MVC attribute. If applied to a parameter, indicates that the parameter
  /// is an MVC view. If applied to a method, the MVC view name is calculated implicitly
  /// from the context. Use this attribute for custom wrappers similar to
  /// <c>System.Web.Mvc.Controller.View(Object)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Method)]
  internal sealed class AspMvcViewAttribute : PathReferenceAttribute { }

  /// <summary>
  /// ASP.NET MVC attribute. When applied to a parameter of an attribute,
  /// indicates that this parameter is an MVC action name
  /// </summary>
  /// <example><code>
  /// [ActionName("Foo")]
  /// public ActionResult Login(string returnUrl) {
  ///   ViewBag.ReturnUrl = Url.Action("Foo"); // OK
  ///   return RedirectToAction("Bar"); // Error: Cannot resolve action
  /// }
  /// </code></example>
  [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property)]
  internal sealed class AspMvcActionSelectorAttribute : Attribute { }

  [AttributeUsage(
    AttributeTargets.Parameter | AttributeTargets.Property |
    AttributeTargets.Field, Inherited = true)]
  internal sealed class HtmlElementAttributesAttribute : Attribute
  {
    public HtmlElementAttributesAttribute() { }
    public HtmlElementAttributesAttribute([NotNull] string name)
    {
      Name = name;
    }

    [NotNull] public string Name { get; private set; }
  }

  [AttributeUsage(
    AttributeTargets.Parameter | AttributeTargets.Field |
    AttributeTargets.Property, Inherited = true)]
  internal sealed class HtmlAttributeValueAttribute : Attribute
  {
    public HtmlAttributeValueAttribute([NotNull] string name)
    {
      Name = name;
    }

    [NotNull] public string Name { get; private set; }
  }

  // Razor attributes

  /// <summary>
  /// Razor attribute. Indicates that a parameter or a method is a Razor section.
  /// Use this attribute for custom wrappers similar to 
  /// <c>System.Web.WebPages.WebPageBase.RenderSection(String)</c>
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Method, Inherited = true)]
  internal sealed class RazorSectionAttribute : Attribute { }
}