Formatting depends on both file and buffer content

[namedots]

It seems to me like content is read from the buffer, then diffed against the file and then changes are applied to the buffer. But if the file doesn't match the buffer, then applying that diff to the buffer doesn't make sense.
That might not be entirely accurate. That is my rough impression of what's happening.

this is what that looks like: https://asciinema.org/a/ydOkICrct6uhjXTQ3iik5S3cF

-module(hello).


five() -> 5.

this is reproduced by saving the above content (plus a blank line above it which github leaves out) to hello.erl, and repeatedly formatting it. the buffer ends up having this content after having formatted 3 times:

five() ->
five() ->
five() ->
    5.

expected behaviour: format the buffer and ignore the file, formatting again should have no further effect

work-around: save before formatting and only format once, or use other method of formatting

Context

• erlang_ls version (tag/sha): 0.46.1 / 1a66e87
• Editor used: nvim
• LSP client used: coc

same thing with vscode and https://marketplace.visualstudio.com/items?itemName=erlang-ls.erlang-ls