Wow, it seems that there’s a lot of confusion going on…
I recorded a gif to better explain, but you could also test it locally by doing the same steps:

• Install elixir-ls
• Add the config "files.trimTrailingWhitespace": true and "editor.formatOnSave": true
• Add documentation to a function with multiple lines
• Save the file and see the markup getting messed up because vscode removes all spaces around a line and there’s no counterpart option to prevent that (like only removing spaces at the start of the line and not the end)

https://gifyu.com/image/Z5fz

I think there is some confusion about the “leading” word. The only “leading” whitespace on your 3rd image is the one that is still there on the 4th image.

Whitespace is considered “per line”. The editor doesn’t care about what the code means, it just removes whitespace at the end of the line, except for the line break.

On line 1 there is none leading or trailing.
On line 2, there are only spaces, and no content. The editors considers this space to be at the end of the line (trailing), and removes it.
On line 3 there are two leading spaces before @doc, and they are still there after the cleanup.
On line 4, there are two leading spaces too, before “Some”, and they are still there. After the content (after the word “here”) there is trailing whitespace, and it gets removed.
And so on.

So no, the editor does not consider all whistespace as trailing. It does not remove leading whitespace.

Thanks to everyone that contributed, we reached our goal!

While we are here jousting about semantics, there are at least 27 people (so far) that shared our pain, regardless of the “proposed” solution.

I hope this gets picked up and the team back at Microsoft can propose a nice solution that helps us solve this issue. So, thanks to you all!