bug#45474: Icomplete exhibiting in recursive minibuffer when it shouldn’t

[Gregory Heytings <gregory@heytings.org>]

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>> I'm more and more thinking that we should really bite the bullet and go 
>> for a "really buffer-local" setup, such as in the patch below.
>> 
>> I'd be surprised if it doesn't introduce backward incompatibilities, 
>> but at least it's "The Right Thing" to do.
>
> Well, that's what my patch does, too, except that it delays the backward 
> incompatilibites during one Emacs major release...  (I did not include 
> minibuffer-completion-predicate and minibuffer-completion-confirm 
> because they haven't been discussed yet, but they are easy to add.)
>

And (to show that they are indeed easy to add) here is the updated patch, 
which also takes care of minibuffer-completion-predicate and 
minibuffer-completion-confirm.

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From 57ac0d5c0408bb835eb78f7497a425d8390a7460 Mon Sep 17 00:00:00 2001
From: Gregory Heytings <gregory@heytings.org>
Date: Thu, 22 Apr 2021 15:12:56 +0000
Subject: [PATCH] Make it possible to disable a completion backend in recursive
 minibuffers

---
 lisp/minibuffer.el |  1 +
 lisp/subr.el       | 17 +++++++++++++
 src/fns.c          |  6 ++---
 src/minibuf.c      | 59 +++++++++++++++++++++++++++++++++++++++++-----
 4 files changed, 74 insertions(+), 9 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 7da3c39e6b..1796b97990 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -3885,6 +3885,7 @@ completing-read-default
                 (1+ (cdr initial-input)))))
 
   (let* ((minibuffer-completion-table collection)
+         (minibuffer-local-completion t)
          (minibuffer-completion-predicate predicate)
          ;; FIXME: Remove/rename this var, see the next one.
          (minibuffer-completion-confirm (unless (eq require-match t)
diff --git a/lisp/subr.el b/lisp/subr.el
index c2be26a15f..2414f60940 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2791,6 +2791,23 @@ read-passwd
               ;; And of course, don't keep the sensitive data around.
               (erase-buffer))))))))
 
+(defmacro read-from-minibuffer (&rest body)
+  "Read a string from the minibuffer with `internal-read-from-minibuffer'.
+See `internal-read-from-minibuffer' for a description of the arguments.
+This macro exists only in Emacs 28, for the transition period during which
+the default value of `minibuffer-local-completion' is nil, and will be
+removed in Emacs 29.  Likewise, `internal-read-from-minibuffer' will be
+removed in Emacs 29, please do not use it directly."
+  `(if minibuffer-local-completion
+       (let ((minibuffer-local-completion-table minibuffer-completion-table)
+             (minibuffer-local-completion-predicate minibuffer-completion-predicate)
+             (minibuffer-local-completion-confirm minibuffer-completion-confirm))
+         (let ((minibuffer-completion-table nil)
+               (minibuffer-completion-predicate nil)
+               (minibuffer-completion-confirm nil))
+           (internal-read-from-minibuffer ,@body)))
+     (internal-read-from-minibuffer ,@body)))
+
 (defvar read-number-history nil
   "The default history for the `read-number' function.")
 
diff --git a/src/fns.c b/src/fns.c
index 1758148ff2..db6679a847 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2985,9 +2985,9 @@ DEFUN ("yes-or-no-p", Fyes_or_no_p, Syes_or_no_p, 1, 1, 0,
 
   while (1)
     {
-      ans = Fdowncase (Fread_from_minibuffer (prompt, Qnil, Qnil, Qnil,
-					      Qyes_or_no_p_history, Qnil,
-					      Qnil));
+      ans = Fdowncase (Finternal_read_from_minibuffer (prompt, Qnil, Qnil, Qnil,
+						       Qyes_or_no_p_history, Qnil,
+						       Qnil));
       if (SCHARS (ans) == 3 && !strcmp (SSDATA (ans), "yes"))
 	return unbind_to (count, Qt);
       if (SCHARS (ans) == 2 && !strcmp (SSDATA (ans), "no"))
diff --git a/src/minibuf.c b/src/minibuf.c
index 1a637c86ad..fd780bd5c1 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -865,6 +865,16 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
   if (STRINGP (input_method) && !NILP (Ffboundp (Qactivate_input_method)))
     call1 (Qactivate_input_method, input_method);
 
+  if (! EQ (Vminibuffer_local_completion, Qnil)) {
+    Fmake_local_variable (Qminibuffer_completion_table);
+    Fset (Qminibuffer_completion_table, Vminibuffer_local_completion_table);
+    Fmake_local_variable (Qminibuffer_completion_predicate);
+    Fset (Qminibuffer_completion_predicate, Vminibuffer_local_completion_predicate);
+    Fmake_local_variable (Qminibuffer_completion_confirm);
+    Fset (Qminibuffer_completion_confirm, Vminibuffer_local_completion_confirm);
+    specbind (Qminibuffer_local_completion, Qnil);
+  }
+
   run_hook (Qminibuffer_setup_hook);
 
   /* Don't allow the user to undo past this point.  */
@@ -1231,9 +1241,16 @@ barf_if_interaction_inhibited (void)
     xsignal0 (Qinhibited_interaction);
 }
 
-DEFUN ("read-from-minibuffer", Fread_from_minibuffer,
-       Sread_from_minibuffer, 1, 7, 0,
+DEFUN ("internal-read-from-minibuffer", Finternal_read_from_minibuffer,
+       Sinternal_read_from_minibuffer, 1, 7, 0,
        doc: /* Read a string from the minibuffer, prompting with string PROMPT.
+
+Note: Do not use this function directly, use `read-from-minibuffer' instead,
+whith the arguments described below.  The `read-from-minibuffer' macro exists
+only in Emacs 28 for the transition period during which the default value of
+`minibuffer-local-completion' is nil, it will be removed in Emacs 29, and
+`internal-read-from-minibuffer' will become `read-from-minibuffer' again.
+
 The optional second arg INITIAL-CONTENTS is an obsolete alternative to
   DEFAULT-VALUE.  It normally should be nil in new code, except when
   HIST is a cons.  It is discussed in more detail below.
@@ -1352,9 +1369,9 @@ DEFUN ("read-string", Fread_string, Sread_string, 1, 5, 0,
      FIXME: `minibuffer-completion-table' should be buffer-local instead.  */
   specbind (Qminibuffer_completion_table, Qnil);
 
-  val = Fread_from_minibuffer (prompt, initial_input, Qnil,
-			       Qnil, history, default_value,
-			       inherit_input_method);
+  val = Finternal_read_from_minibuffer (prompt, initial_input, Qnil,
+				        Qnil, history, default_value,
+				        inherit_input_method);
   if (STRINGP (val) && SCHARS (val) == 0 && ! NILP (default_value))
     val = CONSP (default_value) ? XCAR (default_value) : default_value;
   return unbind_to (count, val);
@@ -2282,6 +2299,9 @@ syms_of_minibuf (void)
   Fset (Qminibuffer_default, Qnil);
 
   DEFSYM (Qminibuffer_completion_table, "minibuffer-completion-table");
+  DEFSYM (Qminibuffer_completion_predicate, "minibuffer-completion-predicate");
+  DEFSYM (Qminibuffer_completion_confirm, "minibuffer-completion-confirm");
+  DEFSYM (Qminibuffer_local_completion, "minibuffer-local-completion");
 
   staticpro (&last_minibuf_string);
 
@@ -2415,6 +2435,33 @@ syms_of_minibuf (void)
  completion commands listed in `minibuffer-confirm-exit-commands'.  */);
   Vminibuffer_completion_confirm = Qnil;
 
+  DEFVAR_LISP ("minibuffer-local-completion", Vminibuffer_local_completion,
+	       doc: /* Whether minibuffer completion elements should become buffer-local.
+The default is nil for Emacs 28.  Setting this variable in Emacs 29 will have no effect;
+the value t will be assumed.
+When t, `minibuffer-completion-table', `minibuffer-completion-predicate' and
+`minibuffer-completion-confirm' become buffer-local upon entering the minibuffer,
+and are nil in recursive invocations of the minibuffer, unless they have been let-bound
+to a value.
+When nil, their values is shared between the recursive invocations of the minibuffer,
+unless they have been let-bound to another value.  */);
+  Vminibuffer_local_completion = Qnil;
+
+  DEFVAR_LISP ("minibuffer-local-completion-table", Vminibuffer_local_completion_table,
+	       doc: /* The local completion table used in the minibuffer.
+See `minibuffer-local-completion'.  */);
+  Vminibuffer_local_completion_table = Qnil;
+
+  DEFVAR_LISP ("minibuffer-local-completion-predicate", Vminibuffer_local_completion_predicate,
+	       doc: /* The local completion predicate used in the minibuffer.
+See `minibuffer-local-completion'.  */);
+  Vminibuffer_local_completion_predicate = Qnil;
+
+  DEFVAR_LISP ("minibuffer-local-completion-confirm", Vminibuffer_local_completion_confirm,
+	       doc: /* The local completion confirm used in the minibuffer.
+See `minibuffer-local-completion'.  */);
+  Vminibuffer_local_completion_confirm = Qnil;
+
   DEFVAR_LISP ("minibuffer-completing-file-name",
 	       Vminibuffer_completing_file_name,
 	       doc: /* Non-nil means completing file names.  */);
@@ -2487,7 +2534,7 @@ syms_of_minibuf (void)
 
   defsubr (&Sactive_minibuffer_window);
   defsubr (&Sset_minibuffer_window);
-  defsubr (&Sread_from_minibuffer);
+  defsubr (&Sinternal_read_from_minibuffer);
   defsubr (&Sread_string);
   defsubr (&Sread_command);
   defsubr (&Sread_variable);
-- 
2.30.2