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Enable Experimental Background Indexing.md

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Enable Experimental Background Indexing

Background indexing in SourceKit-LSP is available as an experimental feature. This guide shows how to set up background indexing and which caveats to expect.

Behavior Without Background Indexing

By default SourceKit-LSP does not update its global index in the background or build Swift modules in the background. Thus, a lot of cross-module or global functionality is limited if the project hasn't been built recently. For example consider two modules: Lib and Exec, where Exec depends on Lib: Without background indexing, if a function is added to Lib, completion/jump to definition/etc in Exec would not be able to see that function until after a build. Background indexing solves that issue.

Set Up

  1. Install a main or release/6.0 Swift Development Snapshot from https://www.swift.org/install or install the Xcode 16 beta.
  2. Point your editor to the newly installed toolchain.
    • In VS Code on macOS this can be done by adding the following to your settings.json:
      • For open source toolchains "swift.path": "/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/bin"
      • When installing the Xcode 16 beta "swift.path": "/Applications/Xcode-beta.app/Library/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin"
    • In VS Code on other platforms, you need to set the swift.path to the usr/bin directory of your toolchain’s install location.
    • Other editors likely also have a way to pick the Swift toolchain, the exact steps vary by your setup.
  3. Enable the experimental background-indexing feature by creating a configuration file with the following contents at ~/.sourcekit-lsp/config.json with the following contents:
{
  "backgroundIndexing": true
}

Known issues

  • Background Indexing is only supported for SwiftPM projects #1269, #1271
  • If you change a function in a way that changes its USR but keeps it API compatible (such as adding a defaulted parameter), references to it will be lost and not re-indexed automatically #1264
    • Workaround: Make some edit to the files that had references to re-index them
  • The index build is currently completely separate from the command line build generated using swift build. Building does not update the index (break your habits of always building!) #1270
  • The initial indexing might take 2-3x more time than a regular build #1262, #1268

Filing issues

If you hit any issues that are not mentioned above, please file a GitHub issue and attach the following information, if possible:

  • A diagnostic bundle generated by running path/to/sourcekit-lsp diagnose.
  • Your project including the .index-build folder, if possible.