forcemerge 48356 49931
thanks

> When selecting a candidate the suffix after the completion boundary is
> discarded by `choose-completion`/`choose-completion-string`.
> `choose-completion` is invoked when a candidate in the *Completions*
> buffer is selected with the mouse or RET.
>
> For example when completing a file path "~/emacs/master/li|/calc", where
> "|" is the cursor, and then the candidate "lisp" is selected in the
> *Completions* buffer, the result is "~/emacs/master/lisp/". The prefix
> "~/emacs/master/" is prepended to the selected candidate, but the suffix
> "/calc" is discarded.
>
> `choose-completion-string` contains logic which checks if the resulting
> string equals the car of the completion boundary. In that case the
> minibuffer is not exited.

Strange, in your test case above, the minibuffer is not exited already.

> I propose the following change to the existing logic: When
> selecting a candidate with `choose-completion` and a suffix is present,
> the minibuffer should not be exited (completion continues) and the
> suffix is preserved.

Here is a better patch than was posted to bug#49931
to preserve the suffix.

It correctly handles at least three different cases:

1. When manually adding a suffix in the minibuffer after completions
   were displayed, choose-completion discards that suffix.

2. In file name completion in the above case the suffix is preserved.

3. 'M-! command filename TAB' and choosing a completion preserves both
   prefix and suffix.

This works only after customizing 'completion-use-base-affixes' to t: