ReSharper DevGuide

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Existing QuickDoc providers

Overview

ReSharper ships with a number of default providers that create QuickDoc documentation for a broad range of scenarios. Some of these are themselves extensible.

XML Doc Comments

The QuickDocTypeMemberProvider and QuickDocCommentNodeProvider classes support XML DocComments.

  • QuickDocCommentNodeProvider uses a language specific implementation of IXmDocLocator to find the closest XML Doc Comment block to the text caret offset, and uses this XML block to display documentation. This is not CLR language specific - XML Doc Comments are supported in JavaScript and TypeScript.
  • QuickDocTypeMemberProvider will look to see if the declared element under the text caret implements ITypeMember (which implies a CLR element that also implements IXmlDocIdOwner). If so, it gets the XML DocComment Id and then retrieves the XML documentation via a call to IDeclaredElement.GetXMLDoc. This also handles documentation shipped with compiled code.

QuickDocTypeMemberProvider also has a fallback - if there is no XML documentation, it looks for the System.ComponentModel.DescriptionAttribute and uses this for the description of the type member.

Language specific

Some of the default providers are language specific.

  • CSharpQuickQueryRangeVariableProvider handles documentation for a variable created in LINQ from queries. It simply displays the range variable name and type, allowing navigation to the documentation of the type, and a “go to” link to navigate to the declaration of the range variable. Without this provider, the variable would not have any documentation.
  • QuickDocCssDefinitionProvider handles documentation for CSS properties and values. Interestingly, it will call IDeclaredElement.GetXMLDoc() on the CSS declared element, which creates an XML node with a member element and populates it with name, summary, description and compatibility content.
  • QuickDocJsFunctionProvider displays documentation for any element that implements IJavaScriptTypeOwner. This displays any XML Doc Comment based documentation for the code element.

Elements without documentation

Not all code elements map directly to declared elements with documentation. The QuickDocLocalSymbolProvider creates simple documentation for local symbols that don’t have actual documentation, while the QuickDocCandidatesProvider tries to map a reference in the code to a declared element that does have documentation

  • QuickDocLocalSymbolProvider provides a simple description for local symbols based on the type of local symbol (variable, parameter, etc.) and the name of the symbol. Provides “go to” navigation to the declaration of the symbol.
  • QuickDocCandidatesProvider uses the reference at the text caret position to get the declared elements to get the documentation. It will use the language specific ILanguageReferenceSelector to try and find language specific candidates (e.g. C# will see if the reference is part of an object creation expression and return the declared elements of the constructor and the type being constructed), or it will simply resolve the reference to find the normal declared element. The provider will use these declared elements to find the appropriate documentation.

    Normally, the providers and the presenters are paired - a specific provider will pass data to a matching provider. But the QuickDocCandidatesProvider will find a declared element that is then passed to QuickDocTypeMemberPresenter, which means it will look for CLR type members that have XML documentation.

High priority and fallbacks

The default providers also make use of the QuickDocProviderAttribute.Priority property. Most of the providers have a priority of 0, as they don’t overlap in the elements they handle, however, a couple do overlap, and make use of the Priority.

  • QuickDocResxProvider has a priority of -10, which means that it is called before the other default providers. It checks to see if the current declared element is an instance of IResourceItemDeclaredElement, such as the data tag in a .resx file, or it will look for a CLR property or method that belongs to a resource class. It has to be processed first, or the standard XML Doc Comments handling would take precedence.

  • QuickDocDescriptionProvider has a priority of 1, meaning it’s a fallback to the other default providers. If there isn’t a more suitable provider, this one will be used to provide a description of the current declared element. It is used as a fallback as it can only return a single string to act as the description, rather than a fuller piece of documentation like that supplied by XML Doc Comments.

    It retrieves the description by calling into IDeclaredElementDescriptionPresenter, which defers to an extensible, live collection of IDeclaredElementDescriptionProvider. You can extend this collection by implementing IDeclaredElementDescriptionProvider and decorating your class with the DeclaredElementDescriptionProviderAttribute.

    The default description providers support descriptions for XML nodes via XML schema, CSS compatibility information and HTML element descriptions stored in an internal resource file - which can itself be extended by implementing IHtmlDeclaredElementsProvider.

Extending the default providers

If you wish to extend the default providers, for example, if you’re implementing new language support, there are several ways to extend the existing providers to get QuickDoc support:

  1. If your language supports standard XML Doc Comments in source, implement IXmlDocLocator in a class marked with [Language (typeof(NewLanguage))]. The default QuickDocCommentNodeProvider class will use this interface to find the XML Doc Comment node.
  2. If your language is a CLR language and also supports standard XML Doc Comments in compiled form, your PSI tree should implement ITypeMember, and therefore IClrDeclaredElement and IXmlDocIdOwner. The default QuickDocTypeMemberProvider class will retrieve the element’s XML doc ID from IXmlDocIdOwner.XMLDocId and retrieve the XML itself from IDeclaredElement.GetXMLDoc().
  3. You can provide a simple, single string description for your IDeclaredElement derived types by implementing IDeclaredElementDescriptionProvider, which is used by QuickDocDescriptionProvider
  4. Implement ILanguageReferenceSelector and mark your class with [Language(typeof(NewLanguage))]. This class will take in an IReference and use it to find any relevant declared elements from which to find documentation. For example, the C# implementation looks for object creation expressions and returns candidates for the constructor and the type being used. This interface is used by the QuickDocCandidatesProvider.

Of course, if your requirements don’t fit any of these scenarios, you can implement IQuickDocProvider and IQuickDocPresenter directly. You should use the helper methods in XmlDocHtmlUtil and XmlDocHtmlPresenter to build the HTML.

Last modified: 10 July 2017