bug#40152: 27.0.90; icomplete vs recursive prompts

[Kévin Le Gouguec]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
>> Date: Fri, 20 Mar 2020 19:21:01 +0100
>> 
>> - "Synthetic" reproduction recipe:
>>     - (completing-read "Foo? " (tags-lazy-completion-table))
>> 
>> - With actual user commands:
>>     - C-x b foo RET
>>       - or any non-Lisp buffer, so that xref picks the etags backend
>>     - M-.
>> 
>> From there:
>> 
>> - Try to input a character.
>>     - The identifier prompt is interrupted by the etags prompt ("Visit
>>       tags table").
>> - Try to input a character.
>>     - The etags prompt disappears and we're back to the identifier
>>       prompt.
>> 
>> The identifier prompt is replaced with the etags prompt as soon as a
>> single character is typed.  While in the etags prompt, one can use
>> icomplete commands (e.g. TAB, C-.) as well as C-q CHAR to input
>> characters one-by-one.
>
> What would you like to happen instead?

When the etags prompt interrupts the xref prompt, I'd like the etags
prompt to remain uninterrupted until I exit it (with e.g. RET/C-j).  In
particular, self-inserting characters do not cause the xref prompt to
come back.

For example, if I'm in a buffer whose default-directory is the root of
the Emacs source repository (e.g. in a Dired buffer, visiting the
Makefile…) and I hit C-. (and point is not on something that looks like
an identifier), here's what happens:

1. the "Find definitions of" prompt appears,
2. I start typing an identifier,
3. the "Visit tags table" prompt interrupts,
4. I'd like to input "src/ C-j", but every self-inserting character
   makes the prompt go back-and-forth between "Find definitions of" and
   "Visit tags table".  Worse, when the prompt comes back to "Visit tags
   table", any character I had previously input has disappeared.

I just found out that there is a workaround: in step 2, if I hit TAB
(minibuffer-complete) instead of typing an identifier, the "Visit tags
table" prompt comes up *and stays until I exit it*.  The back-and-forth
only starts if

1. I input a self-inserting char during the first prompt, or
2. if icomplete-show-matches-on-no-input is t.