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Define an index format for Language Servers
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Language Server Index Format

The purpose of the Language Server Index Format (LSIF) is it to define a standard format for language servers or other programming tools to dump their knowledge about a workspace. This dump can later be used to answer language server LSP requests for the same workspace without running the language server itself. Since much of the information would be invalidated by a change to the workspace, the dumped information typically excludes requests used when mutating a document. So, for example, the result of a code complete request is typically not part of such a dump.

A first draft specification can be found here.

How to Run the tools

  • > npm install -g lsif-tsc install the tsc LSIF tool.
  • > lsif-tsc -p .\tsconfig.json --stdout creates a LSIF dump for the given typescript project. Output format is new line separated JSON.

If the project provides and npm package or is depending on other npm modules the TypeScript monikers can be converted into stable npm monikers. To do so run

  • > npm install -g lsif-npm install the npm LSIF tools
  • > lsif-tsc -p .\tsconfig.json --stdout | lsif-npm --stdin --package .\package.json --stdout creates an LSIF dump and converts the monikers to npm format.

Please note that the tools are work in progress and that we have not done any extensive testing so far. Known issues are:

  1. Go to Declaration for function overloads doesn't honor the signature
  2. Go to Type Declaration is not fully implement
  3. Document link support and go to implementation is completely missing
  4. Reference results are not always inlined when possible

Both tools support --help to get information about their command line arguments.

LSIF utility tools

You can validate or visualize LSIF output using the LSIF utility tools.

LSIF extension

There is also an extension for VS Code that can serve the content of a LSIF JSON file. Consider you have dumped the content of a workspace into an LSIF JSON file then you can use the extension to serve the supported LSP requests. This works as follows:

  • follow the steps in 'How to Run the tools` above and create a dump.
  • > git clone
  • > cd vscode-lsif-extension
  • > npm install
  • > npm run compile
  • open the workspace on vscode-lsif-extension using code.
  • switch to the debug viewlet and launch Launch Client
  • in the launch version of VS Code open the command palette and execute the command: Open LSIF Database
  • in the open file picker dialog nativate to a created dump and select it.

The extension


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Licensed under the MIT License.

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