When calling org-refile with org-completion-use-ido set to t, pressing TAB in ido-mode results in an error. This is because ido-completion-help expects a list of strings. However, org-refile sends ido-completing-read a list of lists.
To replicate: 1. /usr/bin/emacs -Q -l ~/.minimal.el --8<---------------cut here---------------start------------->8--- (add-to-list 'load-path "~/org-mode/lisp") (add-to-list 'load-path "~/org-mode/contrib/lisp") (ido-mode) (setq org-completion-use-ido 1) --8<---------------cut here---------------end--------------->8--- Go to an org file with headlines: --8<---------------cut here---------------start------------->8--- * One * Two * Three --8<---------------cut here---------------end--------------->8--- 2. Call org-refile on the first headline. 3. Press TAB within the ido minibuffer. (See the backtrace at the bottom of this post). A git bisect revealed that the change was introduced in 2015 with the following commit: ,---- | commit 50ba0a5ed609f3600f2590f3ba22b8ab3ff3331c | Author: Nicolas Goaziou <m...@nicolasgoaziou.fr> | Date: Sun Jun 7 00:38:58 2015 +0200 | | Fix 1a7364177046b8a57ade0aeb9f52bacfc0b8b088 | | * lisp/org.el (org-icompleting-read): Let `completing-read' or | equivalent sort out type of completion. | (org-olpath-completing-read): Revert partially | 1a7364177046b8a57ade0aeb9f52bacfc0b8b088. `---- It looks like this commit removed some functionality from the now obsolete org-icompleting-read that made sure that the items in the completion list passed to the completing read function were strings. Matt --8<---------------cut here---------------start------------->8--- Debugger entered--Lisp error: (wrong-type-argument arrayp (#("Three" 0 5 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Three\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 14)) ido-no-final-slash((#("Three" 0 5 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Three\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 14)) ido-file-lessp((#("Three" 0 5 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Three\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 14) (#("Two" 0 3 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Two\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 8)) sort(((#("Two" 0 3 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Two\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 8)) ido-file-lessp) ido-completion-help() funcall-interactively(ido-completion-help) call-interactively(ido-completion-help) ido-complete() funcall-interactively(ido-complete) call-interactively(ido-complete nil nil) command-execute(ido-complete) read-from-minibuffer("Refile subtree \"One\" to: " nil (keymap keymap (4 . ido-magic-delete-char) (6 . ido-magic-forward-char) (2 . ido-magic-backward-char) (63 . ido-completion-help) (left . ido-prev-match) (right . ido-next-match) (0 . ido-restrict-to-matches) (27 keymap (32 . ido-take-first-match)) (67108896 . ido-restrict-to-matches) (26 . ido-undo-merge-work-directory) (20 . ido-toggle-regexp) (67108908 . ido-prev-match) (67108910 . ido-next-match) (19 . ido-next-match) (18 . ido-prev-match) (16 . ido-toggle-prefix) (13 . ido-exit-minibuffer) (10 . ido-select-text) (32 . ido-complete-space) (9 . ido-complete) (5 . ido-edit-input) (3 . ido-toggle-case) (1 . ido-toggle-ignore) keymap (menu-bar keymap (minibuf "Minibuf" keymap (previous menu-item "Previous History Item" previous-history-element :help "Put previous minibuffer history element in the minibuffer") (next menu-item "Next History Item" next-history-element :help "Put next minibuffer history element in the minibuffer") (isearch-backward menu-item "Isearch History Backward" isearch-backward :help "Incrementally search minibuffer history backward") (isearch-forward menu-item "Isearch History Forward" isearch-forward :help "Incrementally search minibuffer history forward") (return menu-item "Enter" exit-minibuffer :key-sequence "" :help "Terminate input and exit minibuffer") (quit menu-item "Quit" abort-recursive-edit :help "Abort input and exit minibuffer") "Minibuf")) (10 . exit-minibuffer) (13 . exit-minibuffer) (7 . abort-recursive-edit) (C-tab . file-cache-minibuffer-complete) (9 . self-insert-command) (XF86Back . previous-history-element) (up . previous-line-or-history-element) (prior . previous-history-element) (XF86Forward . next-history-element) (down . next-line-or-history-element) (next . next-history-element) (27 keymap (114 . previous-matching-history-element) (115 . next-matching-history-element) (112 . previous-history-element) (110 . next-history-element))) nil org-refile-history) ido-read-internal(list "Refile subtree \"One\" to: " org-refile-history nil t nil) ido-completing-read("Refile subtree \"One\" to: " ((#("Two" 0 3 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Two\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 8) (#("Three" 0 5 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Three\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 14)) nil t nil org-refile-history nil) apply(ido-completing-read ("Refile subtree \"One\" to: " ((#("Two" 0 3 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Two\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 8) (#("Three" 0 5 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Three\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 14)) nil t nil org-refile-history nil)) org-icompleting-read("Refile subtree \"One\" to: " ((#("Two" 0 3 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Two\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 8) (#("Three" 0 5 (face org-level-1 fontified t)) "/home/matt/test.org" "^\\(\\*+\\)\\(?: +\\(DONE\\|TODO\\)\\)?\\(?: +\\(\\[#.\\]\\)\\)?\\(?: +\\(?:\\[[0-9%/]+\\] *\\)*\\(Three\\)\\(?: *\\[[0-9%/]+\\]\\)*\\)\\(?:[ ]+\\(:[[:alnum:]_@#%:]+:\\)\\)?[ ]*$" 14)) nil t nil org-refile-history nil) org-refile-get-location("Refile subtree \"One\" to" nil nil nil) org-refile(nil) funcall-interactively(org-refile nil) call-interactively(org-refile record nil) command-execute(org-refile record) execute-extended-command(nil "org-refile" nil) funcall-interactively(execute-extended-command nil "org-refile" nil) call-interactively(execute-extended-command nil nil) command-execute(execute-extended-command) --8<---------------cut here---------------end--------------->8---