NB: This problem seems to be limited to mma-mode (for Mathematica).

For example, suppose I define a snippet like this:

# key: test
# name: test
# --

Then, I test it (with C-c C-t). After I type the first character (x), my terminal looks like this (the indicates the position of the cursor).


Note that a couple of spurious spaces were added in front of the mirrored x.

This behavior continues with every additional keystroke, as long as mirroring is taking place:


It happens even if the keystroke is for a backspace:


As I said at the beginning, I see this problem only with mma-mode.

Now, mma-mode is not maintained, AFAICT. Therefore, the most I can hope for is some workaround.

Any ideas on how I could prevent the addition of spurious spaces before mirrors?

  • 1
    Does setting yas-indent-line to fixed help? If you have those 2 lines in a .m file, does M-x indent-according-to-mode on the second line also cause indentation?
    – npostavs
    Apr 3, 2017 at 17:51
  • @npostavs: indent-according-to-mode does give a clue: if I run it on an empty buffer under mma-mode, two spaces get inserted. Unfortunately, however, if I add the line # expand-env: ((yas-indent-line 'fixed)) to the snippet's header, I still get the behavior I showed before.
    – kjo
    Apr 3, 2017 at 18:08
  • 1
    What yasnippet version are you using? I think older versions wouldn't apply expand-env at the right time (see github.com/joaotavora/yasnippet/pull/743). Setting yas-indent-line in mma-mode-hook should be okay.
    – npostavs
    Apr 3, 2017 at 18:31
  • 1
    Actually these comments near the top of mma-mode.el give a hint, "If point is not on the leading whitespace of the current line, indents by steps of `mma-indentation'" - yasnippet calls the indent function with point sitting just after the leading whitespace. Perhaps replacing (back-to-indentation) with (beginning-of-line) in yas--indent-region would help.
    – npostavs
    Apr 3, 2017 at 21:16
  • @npostavs: Thanks for your suggestions. I'm using version 0.11.0 of yasnippet. In any case, setting yas-indent-line in mma-mode-hook did not help. I don't entirely understand you last suggestion. Do you mean that I should redefine yas--indent-region? If so, is there a way to do this "buffer-locally", for mma-mode buffers only?
    – kjo
    Apr 4, 2017 at 10:31

1 Answer 1


mma-mode seems to have a strange (non-idempotent) indentation function. Therefore you should stop yasnippet from trying to use it when in mma-mode:

(defun my-mma-mode-hook ()
  (setq-local yas-indent-line 'fixed))
(add-hook 'mma-mode-hook #'my-mma-mode-hook)

Unfortunately, this doesn't work in yasnippet versions 0.11 and earlier because it doesn't respect yas-indent-line for mirror updates. This will be fixed in the upcoming 0.12, but you can use this advice to fix it in the meantime:

;; NOTE: this also disables `$>' indent markers in snippets,
;; but hardly anyone uses those anyway.
(defun yas-indent-line-is-auto-p (&rest _)
  (eq yas-indent-line 'auto))
(advice-add 'yas--indent-region :before-while #'yas-indent-line-is-auto-p)

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