Code Annotation Attributes

The JetBrains.Annotations framework provides a number of attributes described below.

To use these attributes in your code, you need to reference JetBrains.Annotations as described in the Annotations in Source Code section.

Annotation attributes

CanBeNullAttribute

Indicates that the value of the marked element could be null sometimes, so checking for null is required before its usage.

Example

            [CanBeNull] object Test() => null;
            
            void UseTest() {
              var p = Test();
              var s = p.ToString(); // Warning: Possible 'System.NullReferenceException'
            }
            

For more information, see Value and Nullability Analysis.

NotNullAttribute

Indicates that the value of the marked element can never be null.

Example

            [NotNull] object Foo() {
              return null; // Warning: Possible 'null' assignment
            }
            

For more information, see Value and Nullability Analysis.

ItemNotNullAttribute

Can be applied to symbols of types derived from IEnumerable as well as to symbols of Task and Lazy classes to indicate that the value of a collection item, of the Task.Result property or of the Lazy.Value property can never be null.

Example

            public void Foo([ItemNotNull]List<string> books)
            {
              foreach (var book in books) {
                if (book != null) // Warning: Expression is always true
                 Console.WriteLine(book.ToUpper());
              }
            }
            

For more information, see Value and Nullability Analysis.

ItemCanBeNullAttribute

Example

            public void Foo([ItemCanBeNull]List<string> books)
            {
              foreach (var book in books)
              {
                // Warning: Possible 'System.NullReferenceException'
                Console.WriteLine(book.ToUpper());
              }
            }
            

For more information, see Value and Nullability Analysis.

StringFormatMethodAttribute

Indicates that the marked method builds string by the format pattern and (optional) arguments. The parameter, which contains the format string, should be given in the constructor. The format string should be in System.String.Format(System.IFormatProvider,System.String,System.Object[]) -like form.

Example

            [StringFormatMethod("message")]
            void ShowError(string message, params object[] args) { /* do something */ }
            
            void Foo() {
              ShowError("Failed: {0}"); // Warning: Non-existing argument in format string
            }
            

Members

#ctor(System.String) Specifies which parameter of an annotated method should be treated as the format string

For more information, see Custom string formatting methods.

ValueProviderAttribute

Use this annotation to specify a type that contains static or const fields with values for the annotated property/field/parameter. The specified type will be used to improve completion suggestions.

Example

             namespace TestNamespace
             {
               public class Constants
               {
                 public static int INT_CONST = 1;
                 public const string STRING_CONST = "1";
               }
            
               public class Class1
               {
                 [ValueProvider("TestNamespace.Constants")] public int myField;
                 public void Foo([ValueProvider("TestNamespace.Constants")] string str) { }
            
                 public void Test()
                 {
                   Foo(/*try completion here*/);//
                   myField = /*try completion here*/
                 }
               }
             }
             

ValueRangeAttribute

Indicates that the integral value falls into the specified interval. It's allowed to specify multiple non-intersecting intervals. Values of interval boundaries are inclusive.

Example

            void Foo([ValueRange(0, 100)] int value) {
              if (value == -1) { // Warning: Expression is always 'false'
                ...
              }
            }
            

NonNegativeValueAttribute

Indicates that the integral value never falls below zero.

Example

            void Foo([NonNegativeValue] int value) {
              if (value == -1) { // Warning: Expression is always 'false'
                ...
              }
            }
            

InvokerParameterNameAttribute

Indicates that the function argument should be a string literal and match one of the parameters of the caller function. For example, ReSharper annotates the parameter of System.ArgumentNullException.

Example

            void Foo(string param) {
              if (param == null)
                throw new ArgumentNullException("par"); // Warning: Cannot resolve symbol
            }
            

NotifyPropertyChangedInvocatorAttribute

Indicates that the method is contained in a type that implements System.ComponentModel.INotifyPropertyChanged interface and this method is used to notify that some property value changed.

The method should be non-static and conform to one of the supported signatures:

NotifyChanged(string)
NotifyChanged(params string[])
NotifyChanged{T}(Expression{Func{T}})
NotifyChanged{T,U}(Expression{Func{T,U}})
SetProperty{T}(ref T, T, string)

Example

             public class Foo : INotifyPropertyChanged {
               public event PropertyChangedEventHandler PropertyChanged;
             
               [NotifyPropertyChangedInvocator]
               protected virtual void NotifyChanged(string propertyName) { ... }
            
               string _name;
             
               public string Name {
                 get { return _name; }
                 set { _name = value; NotifyChanged("LastName"); /* Warning */ }
               }
             }
             

Examples of generated notifications:

NotifyChanged("Property")
NotifyChanged(() => Property)
NotifyChanged((VM x) => x.Property)
SetProperty(ref myField, value, "Property")

ContractAnnotationAttribute

Describes dependency between method input and output.

Syntax

Function Definition Table syntax:

FDT ::= FDTRow [;FDTRow]*
FDTRow ::= Input => Output | Output <= Input
Input ::= ParameterName: Value [, Input]*
Output ::= [ParameterName: Value]* {halt|stop|void|nothing|Value}
Value ::= true | false | null | notnull | canbenull

If the method has a single input parameter, its name could be omitted.
Using halt (or void/ nothing, which is the same) for the method output means that the method doesn't return normally (throws or terminates the process).
Value canbenull is only applicable for output parameters.
You can use multiple [ContractAnnotation] for each FDT row, or use single attribute with rows separated by the semicolon. There is no notion of order rows, all rows are checked for applicability and applied per each program state tracked by the analysis engine.

Examples

[ContractAnnotation("=> halt")] public void TerminationMethod()
[ContractAnnotation("null <= param:null")] // reverse condition syntax public string GetName(string surname)
[ContractAnnotation("s:null => true")] public bool IsNullOrEmpty(string s) // string.IsNullOrEmpty()
// 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)
[ContractAnnotation("=> true, result: notnull; => false, result: null")] public bool TryParse(string s, out Person result)

For more information, see Contract Annotations.

LocalizationRequiredAttribute

Indicates whether the marked element should be localized.

Example

            [LocalizationRequiredAttribute(true)]
            class Foo {
              string str = "my string"; // Warning: Localizable string
            }
            

CannotApplyEqualityOperatorAttribute

Indicates that the value of the marked type (or its derivatives) cannot be compared using '==' or '!=' operators and Equals() should be used instead. However, using '==' or '!=' for comparison with null is always permitted.

Example

            [CannotApplyEqualityOperator]
            class NoEquality { }
            
            class UsesNoEquality {
              void Test() {
                var ca1 = new NoEquality();
                var ca2 = new NoEquality();
                if (ca1 != null) { // OK
                  bool condition = ca1 == ca2; // Warning
                }
              }
            }
            

BaseTypeRequiredAttribute

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.

Example

            [BaseTypeRequired(typeof(IComponent)] // Specify requirement
            class ComponentAttribute : Attribute { }
            
            [Component] // ComponentAttribute requires implementing IComponent interface
            class MyComponent : IComponent { }
            

UsedImplicitlyAttribute

Indicates that the marked symbol is used implicitly (e.g. via reflection, in external library), so this symbol will be ignored by usage-checking inspections.
You can use ImplicitUseKindFlags and ImplicitUseTargetFlags to configure how this attribute is applied.

Example

            [UsedImplicitly]
            public class TypeConverter {}

            public class SummaryData
            {
              [UsedImplicitly(ImplicitUseKindFlags.InstantiatedWithFixedConstructorSignature)]
              public SummaryData() {}
            }

            [UsedImplicitly(ImplicitUseTargetFlags.WithInheritors)]
            public interface IService {}
            

MeansImplicitUseAttribute

Can be applied to attributes, type parameters, and parameters of a type assignable from System.Type. When applied to an attribute, the decorated attribute behaves the same as UsedImplicitlyAttribute. When applied to a type parameter or to a parameter of type System.Type, indicates that the corresponding type is used implicitly.

PublicAPIAttribute

This attribute is intended to mark publicly available API, which should not be removed and so is treated as used.

InstantHandleAttribute

Tells the 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.

PureAttribute

Indicates that a method does not make any observable state changes. The same as System.Diagnostics.Contracts.PureAttribute.

Example

            [Pure] int Multiply(int x, int y) => x * y;
            
            void M() {
              Multiply(123, 42); // Warning: Return value of pure method is not used
            }
            

MustUseReturnValueAttribute

Indicates that the return value of the method invocation must be used.

Methods decorated with this attribute (in contrast to pure methods) might change state, but make no sense without using their return value.
Similarly to PureAttribute, this attribute will help to detect usages of the method when the return value is not used. Additionally, you can optionally specify a custom message, which will be used when showing warnings, e.g.

[MustUseReturnValue("Use the return value to...")]

ProvidesContextAttribute

Indicates the type member or parameter of some type, that should be used instead of all other ways to get the value of that type. This annotation is useful when you have some "context" value evaluated and stored somewhere, meaning that all other ways to get this value must be consolidated with existing one.

Example

            class Foo {
              [ProvidesContext] IBarService _barService = ...;
            
              void ProcessNode(INode node) {
                DoSomething(node, node.GetGlobalServices().Bar);
                //              ^ Warning: use value of '_barService' field
              }
            }
            

PathReferenceAttribute

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 (~).

SourceTemplateAttribute

An extension method marked with this attribute is processed by code completion as a 'Source Template'. When the extension method is completed over some expression, its source code is automatically expanded like a template at call site.

Template method body can contain valid source code and/or special comments starting with '$'. Text inside these comments is added as source code when the template is applied. Template parameters can be used either as additional method parameters or as identifiers wrapped in two '$' signs. Use the MacroAttribute attribute to specify macros for parameters.

Example

In this example, the 'forEach' method is a source template available over all values of enumerable types, producing ordinary C# 'foreach' statement and placing caret inside block:

            [SourceTemplate]
            public static void forEach<T>(this IEnumerable<T> xs) {
              foreach (var x in xs) {
                 //$ $END$
              }
            }
            

MacroAttribute

Allows specifying a macro for a parameter of a SourceTemplateAttribute.

You can apply the attribute on the whole method or on any of its additional parameters. The macro expression is defined in the Expression property. When applied on a method, the target template parameter is defined in the Target property. To apply the macro silently for the parameter, set the Editable property value = -1.

Example

Applying the attribute on a source template method:

            [SourceTemplate, Macro(Target = "item", Expression = "suggestVariableName()")]
            public static void forEach<T>(this IEnumerable<T> collection) {
              foreach (var item in collection) {
                //$ $END$
              }
            }
            

Applying the attribute on a template method parameter:

            [SourceTemplate]
            public static void something(this Entity x, [Macro(Expression = "guid()", Editable = -1)] string newguid) {
              /*$ var $x$Id = "$newguid$" + x.ToString();
              x.DoSomething($x$Id); */
            }
            

Members

Expression
Allows specifying a macro that will be executed for a SourceTemplateAttribute parameter when the template is expanded.
Editable
Allows specifying which occurrence of the target parameter becomes editable when the template is deployed.
If the target parameter is used several times in the template, only one occurrence becomes editable; other occurrences are changed synchronously. To specify the zero-based index of the editable occurrence, use values >= 0. To make the parameter non-editable when the template is expanded, use -1.
Target
Identifies the target parameter of a SourceTemplateAttribute if the MacroAttribute is applied on a template method.

AspMvcActionAttribute

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 System.Web.Mvc.Html.ChildActionExtensions.RenderAction(HtmlHelper, String).

AspMvcAreaAttribute

ASP.NET MVC attribute. Indicates that the marked parameter is an MVC area. Use this attribute for custom wrappers similar to System.Web.Mvc.Html.ChildActionExtensions.RenderAction(HtmlHelper, String).

AspMvcControllerAttribute

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 System.Web.Mvc.Html.ChildActionExtensions.RenderAction(HtmlHelper, String, String).

AspMvcMasterAttribute

ASP.NET MVC attribute. Indicates that the marked parameter is an MVC Master. Use this attribute for custom wrappers similar to System.Web.Mvc.Controller.View(String, String).

AspMvcModelTypeAttribute

ASP.NET MVC attribute. Indicates that the marked parameter is an MVC model type. Use this attribute for custom wrappers similar to System.Web.Mvc.Controller.View(String, Object).

AspMvcPartialViewAttribute

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 System.Web.Mvc.Html.RenderPartialExtensions.RenderPartial(HtmlHelper, String).

AspMvcSuppressViewErrorAttribute

ASP.NET MVC attribute. Allows disabling inspections for MVC views within a class or a method.

AspMvcDisplayTemplateAttribute

ASP.NET MVC attribute. Indicates that a parameter is an MVC display template. Use this attribute for custom wrappers similar to System.Web.Mvc.Html.DisplayExtensions.DisplayForModel(HtmlHelper, String).

AspMvcEditorTemplateAttribute

ASP.NET MVC attribute. Indicates that the marked parameter is an MVC editor template. Use this attribute for custom wrappers similar to System.Web.Mvc.Html.EditorExtensions.EditorForModel(HtmlHelper, String).

AspMvcTemplateAttribute

ASP.NET MVC attribute. Indicates that the marked parameter is an MVC template. Use this attribute for custom wrappers similar to System.ComponentModel.DataAnnotations.UIHintAttribute(System.String).

AspMvcViewAttribute

ASP.NET MVC attribute. If applied to a parameter, indicates that the parameter is an MVC view component. If applied to a method, the MVC view name is calculated implicitly from the context. Use this attribute for custom wrappers similar to System.Web.Mvc.Controller.View(Object).

AspMvcViewComponentAttribute

ASP.NET MVC attribute. If applied to a parameter, indicates that the parameter is an MVC view component name.

AspMvcViewComponentViewAttribute

ASP.NET MVC attribute. If applied to a parameter, indicates that the parameter is an MVC view component view. If applied to a method, the MVC view component view name is default.

AspMvcActionSelectorAttribute

ASP.NET MVC attribute. When applied to a parameter of an attribute, indicates that this parameter is an MVC action name.

Example

            [ActionName("Foo")]
            public ActionResult Login(string returnUrl) {
              ViewBag.ReturnUrl = Url.Action("Foo"); // OK
              return RedirectToAction("Bar"); // Error: Cannot resolve action
            }
            

RazorSectionAttribute

Razor attribute. Indicates that the marked parameter or method is a Razor section. Use this attribute for custom wrappers similar to System.Web.WebPages.WebPageBase.RenderSection(String).

CollectionAccessAttribute

Indicates how method, constructor invocation, or property access over collection type affects the contents of the collection. Use CollectionAccessType to specify the access type.

Using this attribute only makes sense if all collection methods are marked with this attribute.

Example

            public class MyStringCollection : List<string>
            {
              [CollectionAccess(CollectionAccessType.Read)]
              public string GetFirstString()
              {
                return this.ElementAt(0);
              }
            }
            class Test
            {
              public void Foo()
              {
                // Warning: Contents of the collection is never updated
                var col = new MyStringCollection();
                string x = col.GetFirstString();
              }
            }
            

AssertionMethodAttribute

Indicates that the marked method is assertion method, i.e. it halts the control flow if one of the conditions is satisfied. To set the condition, mark one of the parameters with AssertionConditionAttribute attribute.

AssertionConditionAttribute

Indicates the condition parameter of the assertion method. The method itself should be marked by AssertionMethodAttribute attribute. The mandatory argument of the attribute is the assertion type.

TerminatesProgramAttribute

Indicates that the marked method unconditionally terminates control flow execution. For example, it could unconditionally throw exception.

LinqTunnelAttribute

Indicates that the method is a pure LINQ method, with postponed enumeration (like Enumerable.Select, .Where). This annotation allows inference of [InstantHandle] annotation for parameters of delegate type by analyzing LINQ method chains.

NoEnumerationAttribute

Indicates that IEnumerable passed as a parameter is not enumerated. Use this annotation to suppress the 'Possible multiple enumeration of IEnumerable' inspection.

Example

            static void ThrowIfNull<T>([NoEnumeration] T v, string n) where T : class
            {
              // custom check for null but no enumeration
            }
            
            void Foo(IEnumerable<string> values)
            {
              ThrowIfNull(values, nameof(values));
              var x = values.ToList(); // No warnings about multiple enumeration
            }
            

RegexPatternAttribute

Indicates that the marked parameter, field, or property is a regular expression pattern.

For more information, see Regular Expressions Assistance.

NoReorderAttribute

Prevents the Member Reordering feature from tossing members of the marked class.

The attribute must be mentioned in your member reordering patterns.

For more information, see Rearrange Members with File and Type Layout Patterns

XamlItemsControlAttribute

XAML attribute. Indicates the type that has ItemsSource property and should be treated as ItemsControl -derived type, to enable inner items DataContext type resolve.

XamlItemBindingOfItemsControlAttribute

XAML attribute. Indicates the property of some BindingBase -derived type, that is used to bind some item of ItemsControl -derived type. This annotation will enable the DataContext type resolve for XAML bindings for such properties.

Property should have the tree ancestor of the ItemsControl type or marked with the XamlItemsControlAttribute attribute.

XamlItemStyleOfItemsControlAttribute

XAML attribute. Indicates the property of some Style -derived type, that is used to style items of ItemsControl -derived type. This annotation will enable the DataContext type resolve for XAML bindings for such properties.

Property should have the tree ancestor of the ItemsControl type or marked with the XamlItemsControlAttribute attribute.

Helper types

ImplicitUseKindFlags

Specifies the details of implicitly used symbol when it is marked with MeansImplicitUseAttribute or UsedImplicitlyAttribute.

Members

Access
Only entity marked with attribute considered used.
Assign
Indicates implicit assignment to a member.
InstantiatedWithFixedConstructorSignature
Indicates implicit instantiation of a type with fixed constructor signature. That means any unused constructor parameters won't be reported as such.
InstantiatedNoFixedConstructorSignature
Indicates implicit instantiation of a type.

ImplicitUseTargetFlags

Specifies what is considered to be used implicitly when marked with MeansImplicitUseAttribute or UsedImplicitlyAttribute.

Members

Members
Members of the type marked with the attribute are considered used.
WithInheritors
Inherited entities are considered used.
WithMembers
Entity marked with the attribute and all its members considered used.

CollectionAccessType

Provides a value for the CollectionAccessAttribute to define how the collection method invocation affects the contents of the collection.

Members

None
Method does not use or modify content of the collection.
Read
Method only reads content of the collection but does not modify it.
ModifyExistingContent
Method can change content of the collection but does not add new elements.
UpdatedContent
Method can add new elements to the collection.

AssertionConditionType

Specifies assertion type. If the assertion method argument satisfies the condition, then the execution continues. Otherwise, execution is assumed to be halted.

Members

IS_TRUE
Marked parameter should be evaluated to true.
IS_FALSE
Marked parameter should be evaluated to false.
IS_NULL
Marked parameter should be evaluated to null value.
IS_NOT_NULL
Marked parameter should be evaluated to not null value.

Last modified: 08 March 2021