Hi,

I have found out that substring and flex completion ignore the implicit
trailing ‘any’ introduced by ‘completion-pcm--optimize-pattern’.  This
is evident from the examples shown next.

My Emacs version is 28.0.50, built on 2020-07-01 from commit e98ddd6fc1.

Example 1
=========

  (completion-substring-all-completions "f" (list "f") nil 1)

and

  (completion-flex-all-completions "f" (list "f") nil 1)

both result in

  (#("f" 0 1 (face completions-common-part completion-score 0.0)) . 0)

whereas I would expect a completion score of 1.

Example 2
=========

  (completion-substring-all-completions "fo" (list "fo") nil 1)

results in

  (#("fo" 0 1 (face completions-common-part completion-score 0.5) 1 2
    (face (completions-first-difference completions-common-part))) . 0)

whereas I would again expect a completion score of 1.

Proposed Solution
=================

I propose that we make the implicit trailing ‘any’ explicit in
‘completion-substring--all-completions’.