Attaching source for LSP APIs

IntelliJ Platform
1

The documentation has this guide:

Since 2024.2, LSP API sources are provided with the IntelliJ IDEA Ultimate sources artifact. See Attaching Sources on how to enable downloading sources. Then, use Navigate | Class… to open the LspServerManager class. In the opened editor, invoke Download IntelliJ Platform sources to download and attach sources.

This doesn’t work. Download IntelliJ Platform sources terminates in a few seconds, saying “Sources were downloaded”.

2

The problem is tracked here. The suggested workaround is as follow:

As a workaround, download IU sources manually, i.e. from:

https://www.jetbrains.com/intellij-repository/releases/com/jetbrains/intellij/idea/ideaIU/2024.3/ideaIU-2024.3-sources.jar

and then use Choose Sources… basic action instead of Download IntelliJ Platform sources and point to the download IU sources artifact.

For 2025.3 and later, the URL looks like this:

https://www.jetbrains.com/intellij-repository/releases/com/jetbrains/intellij/idea/idea/2025.3/idea-2025.3-sources.jar

An extensive list of links can be found here. Look for idea-sources.jar (2025.3+) or ideaIU-sources.jar.

3

Please try using 2025.1 EAP with latest Plugin DevKit plugin for your development instance, there were some fixes.

4

I’m on 2025.1 now with DevKit 251.23774.460. Running Download IntelliJ Platform sources shows:

Artifact was downloaded to ~\.gradle\caches\modules-2\files-2.1\com.jetbrains.intellij.pycharm\pycharmPC\2025.1\<hash>\pycharmPC-2025.1-sources.jar

The .jar file still doesn’t have anything at com.intellij.platform.lsp.

6

To retrieve the corresponding intellij.platform.lsp[.impl].xml file:

  1. Navigate to the ZIP file of the development instance. On Windows 11, the path looks something like this:

    ~\.gradle\caches\modules-2\files-2.1\com.jetbrains.intellij.pycharm\pycharmPY\2025.3.1.1\<hash>\pycharmPY-2025.3.1.1.zip

  2. Extract it, then go to lib. The XML file is placed at the topmost level of product-backend.jar (as of 2025.3.1.1; IIRC, it used to be in another JAR).