Indentation (tabs vs. spaces) with `lsp-format-buffer` and `lua-mode`

[AndreasMatthias]

Thank you for the bug report

• I am using the latest version of lsp-mode related packages.
• I checked FAQ and Troubleshooting sections
• You may also try reproduce the issue using clean environment using the following command: M-x lsp-start-plain

Bug description

lua-mode in default configuration uses spaces for indentation, but (lsp-format-buffer) uses tabs.

Steps to reproduce

Take this example:

function foo()
print('foo')
end

With point at line 2, (indent-for-tab-command) indents this line by 3 spaces, because lua-indent-level is set to 3. This verifies that lua-mode is using spaces and not tabs (in the default configuration).

But if I let lua-language-server format the buffer with (lsp-format-buffer), the second line gets indented by one tab and not by 3 spaces.

If I understand correctly lua-language-server does not decide by itself whether to use spaces or tabs for indentation, but gets this information from the client.

Expected behavior

Indentation of lua-mode and (lsp-format-buffer) should be the same.

Which Language Server did you use?

lua-language-server

OS

Linux

Error callstack

No response

Anything else?

No response

[yyoncho]

We use lua-indent-level to get the tab size. (see https://github.com/yyoncho/lsp-mode/blob/inlay-hints/lsp-mode.el#L5910 )
We use indent-tabs-mode to determine whether to ask the server to indent with tabs or not.