Here is the backtrace from my current build as requested. I will also try applying the fix from 8d7e58ce9f389d77323e0237c22c4e and test again.
I ran "emacs -Q -l tramp", then in the *scratch* buffer:
(emacs-version)
"GNU Emacs 26.1.90 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.10 Version 10.14.1 (Build 18B75))\n of 2018-12-03"
(tramp-change-syntax 'simplified)
simplified
(setq debug-on-error t)
t
Then when I typed (from "view-lossage"):
C-x C-f [find-file]
/ [self-insert-command]
c [self-insert-command]
o [self-insert-command]
s [self-insert-command]
6 [self-insert-command]
: [self-insert-command]
s [self-insert-command]
r [self-insert-command]
c [self-insert-command]
/ [self-insert-command]
s [self-insert-command]
s [self-insert-command]
<tab> [minibuffer-complete]
I got the error:
Debugger entered--Lisp error: (wrong-type-argument stringp "")
signal(wrong-type-argument (stringp ""))
completion--some(#f(compiled-function (style) #<bytecode 0x40e7eafd>) (basic partial-completion emacs22))
completion--nth-completion(1 "~//cos6:src/ss" read-file-name-internal file-exists-p 14 (metadata (category . file) (completion--unquote-requote . t)))
completion-try-completion("~//cos6:src/ss" read-file-name-internal file-exists-p 14 (metadata (category . file) (completion--unquote-requote . t)))
completion--do-completion(12 26)
completion--in-region-1(12 26)
#f(compiled-function (start end collection predicate) #<bytecode 0x400c2e6b>)(12 26 read-file-name-internal file-exists-p)
apply(#f(compiled-function (start end collection predicate) #<bytecode 0x400c2e6b>) (12 26 read-file-name-internal file-exists-p))
#f(compiled-function (funs global args) #<bytecode 0x40e6bd1d>)(nil nil (12 26 read-file-name-internal file-exists-p))
completion--in-region(12 26 read-file-name-internal file-exists-p)
completion-in-region(12 26 read-file-name-internal file-exists-p)
minibuffer-complete()
funcall-interactively(minibuffer-complete)
call-interactively(minibuffer-complete nil nil)
command-execute(minibuffer-complete)
read-from-minibuffer("Find file: " "~/" (keymap (keymap (32)) keymap (10 . minibuffer-complete-and-exit) (13 . minibuffer-complete-and-exit) keymap (menu-bar keymap (minibuf "Minibuf" keymap (tab menu-item "Complete" minibuffer-complete :help "Complete as far as possible") (space menu-item "Complete Word" minibuffer-complete-word :help "Complete at most one word") (63 menu-item "List Completions" minibuffer-completion-help :help "Display all possible completions") "Minibuf")) (27 keymap (118 . switch-to-completions)) (prior . switch-to-completions) (63 . minibuffer-completion-help) (32 . minibuffer-complete-word) (9 . minibuffer-complete) 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 "\015" :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 file-name-history "~/" nil)
completing-read-default("Find file: " read-file-name-internal file-exists-p confirm-after-completion "~/" file-name-history "~/" nil)
completing-read("Find file: " read-file-name-internal file-exists-p confirm-after-completion "~/" file-name-history "~/")
read-file-name-default("Find file: " nil "~/" confirm-after-completion nil nil)
read-file-name("Find file: " nil "~/" confirm-after-completion)
find-file-read-args("Find file: " confirm-after-completion)
byte-code("\300\301\302 \"\207" [find-file-read-args "Find file: " confirm-nonexistent-file-or-buffer] 3)
call-interactively(find-file nil nil)
command-execute(find-file)