x/tools/gopls: missing placeholder names for function parameters

[ShoshinNikita]

gopls version: master (242e5ed)

VSCode settings:

{
  "gopls": {
    "ui.completion.usePlaceholders": true,
    // ...
  }
}

Steps to reproduce:

1. Enable gopls.ui.completion.usePlaceholders.
2. Create a .go file without any imports.
3. Try to complete a function call from some package (for example, log.Printf) - the completion response has placeholder but not their names.
4. Try to complete the same function call (now with imported package) - the completion response has correct placeholders.

2023-05-17.20-01-03.mp4

---

Note: older versions of gopls didn't provide placeholders at all for cases when the package import was missing. Example:

2023-05-17.20-20-35.mp4

[findleyr]

Thank you.

CC @adonovan

This is related to the rewrite of unimported completions,

[gopherbot]

Change https://go.dev/cl/496596 mentions this issue: gopls/internal/lsp/source/completion: (unimported) add placeholders