RE: how to determine the current table (really) being used for minibuffer completion?

[Drew Adams]

Hypothetical example that might make the request clearer:

(completion-all-completions
 STRING 'read-file-name-internal nil (length STRING))

The result returned might be a list of relative file names, or it might be a
list of env vars. A result such as ("CATACOMBS" "CATAPHILE" "CATASTROPHE" . 4)
could be either.

I would like (via Lisp) to know which kind of completion was in fact used
successfully: file-name completion per se or env var completion.

I don't want to analyze STRING (e.g. check for `$') to figure out what might be
the case. (completion-boundaries STRING 'read-file-name-internal nil "") just
gives something like (0 . 0), indicating the whole STRING.

Emacs should be able to tell me directly what the last completion table/function
used was. It should be easy to make this info available somehow, e.g. in a
global variable.

Similarly, for multiple, successive completion types using `completion-styles',
I would like to know which type (style) was in fact successful.

This is the kind of thing I'm talking about.