bug#10721: 24.0.93; M-TAB for :type (file :must-match t) in Customize

[Drew Adams]

> Sounds odd.  Could yo include a recipe?

1. See also bug #8397.

2. emacs -Q

M-x customize-face font-lock-comment-delimiter-face

Delete the text in the Face: field.

Type c in that field.

M-TAB ; you see the completions for `c'

Type u in that field, so you have `cu', with point after the `u'.

M-TAB ; you see all completions for all faces, not the faces that start with
`cu' or that have substring `cu'.

Etc.

Move point to before the `c' in `cu'.  Hit M-TAB.

Now you see the completions for face names with substring `cu'.

Move point to between the `c' and `u' in `cu'. Hit M-TAB.

Point is moved after the `u'. And you see the completions for all face names,
not just those with `c' or `u' or `cu' as substring.

Etc.

Type an `r', so the field has `cur'.  With point after the `r', hit `M-TAB'.
You see all completions for all face names.

Move point before the `c'.  M-TAB completes the input to `cursor' correctly.
Put back only `cur'.  Move point before the `r'.  Hit M-TAB.  You see the face
names that have `cu' as prefix (and not as substring).

Etc.

Contrast with Emacs 23.  This surprising or "odd" behavior is a regression.