Many editors are now compatible with the Language Server Protocol (LSP). Several languages (Java, TypeScript, etc) now have a full-featured LSP implementation, but a powerful XML language server is missing from the ecosystem.
The XML.LS (aka XML Language Server) project provides an LSP implementation for the XML language. It can be used with any editor that supports the protocol, to offer editing support (completion, hyperlink, validation, hover, codelens, ..) for XML documents (.xml, .xsd, .xslt…), as well as schema-based (XSD and DTD) validation.
The XML Language Server is extensible via a plugin system (based on a service provider interface - SPI) to provide completion, validation, etc.
XML.LS is an implementation of the LSP written in Java and based on the Eclipse LSP4J framework.
It implements most of the language server protocol features to provide XML editing support while also exposing extension points for 3rd party adopters to provide custom features via a plugin system.
Here are some plugin examples:
XML syntax/matched grammar validation, via the Xerces XML validator
XML completion based on grammar, via Xerces
Proof-of-Concept plugins like Maven, emmet or web.xml extensions.
XML.LS is reusable as a Language Server for downstream projects, but some components, such as the fault-tolerant parser or the service layer can also be reused directly.
The XML.LS is based on the Eclipse LSP4J project. Being part of the Eclipse Community would allow closer collaboration and consumption with/from other related projects and communities, like Eclipse Che, Eclipse LSP4E, Eclipse Wild Web Developer.
Additionally, the project would benefit from being inside the Eclipse.org community by attracting more experienced Eclipse developers who're already contributing to some related projects.
The project code currently depends on:
Eclipse LSP4J, to adhere to the LSP protocol
The Apache Xerces 2 parser, for parsing and validating XML documents
remark, an HTML-to-Markdown renderer, to provide documentation in the markdown format.
A part of the XML parser has been written as a “transcription” of some code present in the VSCode HTML Language Service (copyright @ Microsoft Corporation, MIT-licensed), from TypeScript to Java.
Such pieces of code are clearly identified in their copyright headers.
An initial release based on the initial contribution is planned after the project creation.
Continuous adoption of newer version of the Language Server Protocol and addition of new features from LSP
Performance and resource consumption
Ease integration in clients
Improve features for binding between XML and grammar https://github.com/angelozerr/lsp4xml/issues/373
Improve formatting options
Fix bugs. See a list of issues for missing features and bugs to fix in LSP4XML.