SnippetTextEdit doesn't have an option for preserving whitespace

[DanTup]

VS Code's SnippetTextEdit has a keepWhitespace: boolean, which is not present in LSP.

After migrating some server code to use SnippetTextEdits, we found that VS Code is messing up the whitespace (trying to compensate for the lines indentation, even though the server had already done it correctly, resulting in duplicated indentation).

@dbaeumer should keepWhitespace be an option here, or should the VS Code LSP client just always set it to true?

[DanTup]

I also wonder if rather than adding flags everywhere, this should just be declarable at the server level. I imagine that servers either always do whitespace correctly, or they expect the client to, and not a mix.

[jwortmann]

FWIW, in the LSP client plugin for Sublime Text we have to strip leading indentation before applying the SnippetTextEdit, because the editor API automatically adds indentation, like you described here with VSCode. This works as long as the snippet content doesn't contain any lines with less indentation than the indentation on the starting line (think of closing brackets on a separate last line of the snippet block - in that case it would fail, but I haven't seen that in practice yet).

https://github.com/sublimelsp/LSP/blob/4e3828b9dc829977365f58454c7a34c94583a409/plugin/edit.py#L132-L138

This was also briefly discussed before in #1892 (comment)

[DanTup]

Interesting.. @dbaeumer said:

Workspace edits in general don't have support for automatic indentation. So they are always asIs.

But that's not what's happening, VS Code is absolutely changing the whitespace, and it has a keepWhitespace flag on SnippetTextEdit that prevents it.

If the intention is for it always to be asIs, then this could be fixed (for VS Code) in the VS Code LSP client by just setting keepWhitespace = true on the created SnippetTextEdits, but it sounds like that might not be great for your editor.

I am trying to find a workaround for my VS Code extension for now, but I keep hitting other issues in VS Code (like microsoft/vscode#325978). Right now the best I have is copying the LSP client's asWorkspaceEdit() into my extension and overriding it on the converter, so I can set keepWhitespace=true myself. Although, my tests can't verify this because of another VS Code issue I hit (microsoft/vscode#325990) 🙃

I think I'll probably have to go with this hack in the short-term to avoid making things worse. Our non-standard snippet implementation based on the Rust Analyzer team's spec worked a little differently, and we were in charge of the editor.insertSnippet call where we could set keepWhitespace: true easily. I don't want to revert back to that non-standard implementation just for this.