Debug language server

Contents

• Using output channel
• Using Chrome developer tools

Using output channel

The same as VSCode, each language server has it's own output channel, the output channel can be opened by

:CocCommand workspace.showOutput

To make an output channel track all LSP communication, set [languageserverId].trace.server to verbose in your coc-settings.json.

For example, to make tsserver track LSP communication, use:

  "tsserver.trace.server": "verbose",

to make a custom language server track LSP communication, add a trace.server section in your language server configuration, like:

"languageserver":{
   "ccls": {
    "command": "ccls",
    "filetypes": ["c", "cpp", "objc", "objcpp"],
    "trace.server": "verbose",
    "initializationOptions": {
      "cacheDirectory": "/tmp/ccls"
    }
  }
}

However, the output of LSP communication is difficult for humans to read. You can upload the content to the LSP inspector: https://microsoft.github.io/language-server-protocol/inspector/, which looks like this:

Using Chrome developer tools

You can use Chrome to debug a language server which is using node IPC for communication.

First, add execArgv to the language server settings like:

 "css.execArgv": ["--nolazy", "--inspect-brk=6045"]

After the css service starts, open Chrome with the url chrome://inspect

Make sure the Discover network targets option is checked and you have the address added to Target discovery settings, and then you will have the debugging target.