Error message after setting 'pdf-annot-activate-created-annotations t' about pdf-tools HOT 1 CLOSED

Thanks for reporting this! I can reproduce this bug. In general, to debug an error it is helpful to enable debug on error by running M-x toggle-debug-on-error before doing whatever causes the error and then reporting the contents of the *Backtrace* buffer.

The error message means that the function nth expected a number but wrongly received nil instead. The *Backtrace* shows at which call to nth the error happens. The problem is that pdf-keynav adds advice to pdf-annot-add-markup-annotation to ensure that the cursor is displayed again after markup is added. With (setq pdf-annot-activate-created-annotations t), however, pdf-annot-add-markup-annotation activates a new buffer for the annotation, while pdf-keynav-after-markup-advice assumes that the active buffer is still the pdf buffer.

One workaround is to not use (setq pdf-annot-activate-created-annotations t) and instead just press enter after adding an annotation to activate it.

Another workaround (for now) is to overwrite pdf-keynav-after-markup-advice, for example by adding the following to your :config block of (use-package pdf-tools..:

(defun pdf-keynav-after-markup-advice (&rest _arg)
  "Deactivate region and display cursor."
  (when (equal major-mode 'pdf-view-mode)
    (when pdf-keynav-transient-mark-mode
      (setq pdf-keynav-mark-active-p nil))
    (pdf-keynav-display-region-cursor)))

so that it only tries to display the cursor when in a buffer in pdf-view-mode.

A more general bug is that after one edits the text of an annotation, the cursor is gone. A workaround is to add this:

(advice-add 'pdf-annot-edit-contents-finalize :after
	    #'pdf-keynav-after-markup-advice)

But this also displays the cursor in some situations where one might want it.

I'll close this issue once I've pushed a more permanent fix.

from pdf-tools.