Lexer Factories

ReSharper requires a custom language to implement ILexerFactory, which is exposed via IProjectFileLanguageService.GetMixedLexerFactory and the LanguageService.GetPrimaryLexerFactory abstract method.

The lexer factory is assigned to the IFile root node of the PSI tree, via the IFileImpl interface, which exposes implementation details rather than PSI tree information. This is made available so that various parts of ReSharper can easily create a fresh lexer on a new buffer.

public interface ILexerFactory
{
  ILexer CreateLexer(IBuffer buffer);
}

This class is usually trivial to implement, simply returning a new instance of a class that implements the ILexer interface.

note

The LanguageService.GetPrimaryLexerFactory method should be implemented by creating a new instance of this class, and typically, the IProjectFileLanguageService.GetMixedLexerFactory will just call GetPrimaryLexerFactory.

However, if the custom language hosts "secondary" PSI trees (such as HTML, which can also contain CSS and JavaScript), the IProjectFileLanguageService should inherit form MixedProjectLanguageService, which provides an implementation of GetMixedLexerFactory that returns an instance of MixedLexerFactory using the lexer factory returned from GetPrimaryLexerFactory.

The IBuffer interface is an abstraction of a text based buffer that a lexer uses to get the contents of the file (persistent or in-memory). See the guide on Text Buffers for more details.