Rename of variables (with rope) fails bluntly if there is a SyntaxError

[krassowski]

If I rename a function or variable in a document which contains a SytnaxError (or IndentationError, or anything else which causes the document not to be a valid Python source code), the rename fails with IndexError: list index out of range. The failing rename is not a problem in itself, but the unclear error may cause distress in users trying to understand what is going on.

Full backtrace is attached here. From what I understand, this is because rope cannot load the file (as it is not a valid Python source) thus lines list remain empty (so the requested position is out of range).

Expected behaviour: an informative error is passed to the client, e.g.

"Rename could not be performed due to a SyntaxError at line X"

Question: should it be solved in pyls or in rope?

Proposed solution: the code in rope_rename.py could by wrapped in try-except to catch rope errors, or (if you advise such) I could fill an issue in rope repository.

References: https://github.com/krassowski/jupyterlab-lsp/pull/115, https://github.com/krassowski/jupyterlab-lsp/pull/127 (while we already got a UX workaround, I thought that reporting it here may help others who implement LSP/use the pyls server).

[ccordoba12]

the code in rope_rename.py could by wrapped in try-except to catch rope errors

I'm fine with that. Please submit a PR to do it

[mcepl]

Or you can send PR to me at python-rope/rope, I will happily consider anything you throw my way.