Architectural Overview

The Platform part of ReSharper typically relates to features that interact directly with Visual Studio. As a result, plugin developers are unlikely to work with Platform components directly. However, it's important to have a general idea of some platform components in order to be able to understand and investigate, if necessary, the ways in which interactions happen. Here are a few Platform elements that are worth knowing about:

• ActionManagement - this assembly concerns itself with managing actions, i.e., executable pieces of code that appear in Visual Studio's Command system. See Actions and Menu Items for more information on creating actions.

• Annotations - relates to the Annotations subsystem. The idea of annotations is being able to use attributes to give ReSharper hints as to how the code behaves. Frequently encountered attributes such as [NotNull] are examples of annotations.

• ComponentModel - relates to ReSharper's component model. Understanding of the component model is critical to be able to use various ReSharper's subsystems. See Component Model for more details.

• DocumentManager and DocumentModel - contains mechanisms for managing documents. Encapsulates important concepts (e.g., RangeMarker) used for correctly modifying documents.

• ProjectModel - used for interacting with Visual Studio's project model.

• TextControl - used for interacting with Visual Studio's text editor control.

• Util - contains a large number of important ReSharper utility entities, including specialized collections, DataFlow classes (Lifetime) and many others.

Please note that Platform elements typically live in namespaces unrelated to ReSharper itself. The reason for this is that the Platform components are used not only in ReSharper, but also in other products such as dotTrace, dotCover and dotPeek.

The PSI or the Program Structure Interface, is the part of ReSharper responsible for lexing and parsing the languages that ReSharper supports. It is also responsible for resolving types and such practicalities as, e.g., overload resolution, type inference, etc.

The PSI exists in several assemblies: the general Psi assembly, language-specific assemblies (e.g., Psi.CSharp), platform-specific assemblies (e.g., Psi.Web) as well as specialized multi-language assemblies such as Psi.Html.JavaScript. The latter assemblies are used specifically for situations where files containing several languages are parsed. Such files (e.g., .cshtml files of Razor view) are typically found in web development projects.

Central to the PSI is the notion of a Language Service, a component which actually adds ReSharper support for a particular language. The ReSharper PSI assemblies actually contain language services for all languages that ReSharper supports as well as the infrastructure which allows plugin developers to develop new languages.

In ReSharper's terminology, a 'feature' is an aspect of functionality that is provided by ReSharper at the outer, user-visible level. This includes things like code completion, navigation, code cleanup, and many more.

Please note that in developing your own features, you are more likely to be interacting with feature services than with actual features, although feature assemblies are good for learning how to implement certain things.

As the name suggests, ReSharper's Feature Services contain a large number of services that support ReSharper's features. For example, the component that provides the Code Inspection Wiki data at start-up time is a feature service. Another example would be the various data provider and builder classes that are used in bulb items that ReSharper presents. Support for the Generate Menu and many other features is also contained here.

Please note that feature services do not contain features themselves. Quite often they contain components which are used by more than one feature.