trim_trailing_whitespace moves caret

( ported from Microsoft/vscode-editorconfig#24 )

Repro’d on editorconfig v0.2.7:

1. Enable autosave in VS Code (e.g. in user settings) - great for users who are used to using Git to back up their code.
2. Open up a workspace that lacks VS Code workspace settings for files.trimTrailingWhitespace.
3. In the same workspace, create a .editorconfig, setting trim_trailing_whitespace = true

Type some code with spaces, then rest (wait for autosave delay).

Expected: Caret position remains, trailing whitespace preceding the caret is not trimmed Actual: All trailing whitespace is trimmed, causing the caret to move and the code (whitespace) that was under composition to be deleted.

Note, this caused me to stop using trim_trailing_whitespace for a while, before I realised that enabling the matching VS Code option overrode the behaviour to be correct. However, figured it was worth reporting so that this could be improved for new users.

[NinoFloris]

Nice to find this issue

I would love it if you could at least not trim it if there is no text in front of it?

As currently if I want to start by indenting a line and then type my text I have to be faster than my autosave or I will be yanked back to the start. Very unpleasant and currently my trim_trailing_whitespace is commented out because of this.

[dgileadi]

I’ve done some looking into this and I know why it’s happening. The vscode function trimTrailingWhitespace correctly ignores trailing whitespace at all of the cursors that are passed into it. The problem is the editor.action.trimTrailingWhitespace command that this extension uses (which is the same as the Ctrl+K Ctrl+X menu command). Internally that TrimTrailingWhitespaceCommand object calls the trimTrailingWhitespace function and always passes it an empty array of cursors. This behavior makes sense in the context of a menu command, but of course doesn’t make sense when the command is generated by an auto-save.

Incidentally The reason the files.trimTrailingWhitespace setting doesn’t trim whitespace at the cursor(s) is that it doesn’t use the TrimTrailingWhitespaceCommand. Instead it calls trimTrailingWhitespace directly and passes it an array of cursors.

The best fix I can think of is to implement vscode #24400, passing along a reason of auto-save. I’ve implemented this locally and it solves the problem for me. I plan on making a PR for vscode and a PR for this extension.