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

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> I tested your patch and discovered that it fails when two nested
>> minibuffers both use completion, e.g. C-x C-f C-h v raises the error:
>>
>>    Error in post-command-hook (icomplete-post-command-hook): (wrong-type-argument symbolp
>
> Indeed, it's nasty:
>
> - In the first step, we
>   - let-bind (globally) m-c-table to read-file-name-internal
>   - go to minibuf-1
>   - make it buffer-local in minibuf-1
>   - everything's dandy
> - In the second step, things get ugly
>   - we're in minibuf-1
>   - we let-bind m-c-table to help--symbol-completion-table which
>     only works buffer-locally in minibuf-1 (thus temporarily overriding
>     the value set just before).
>   - we go to minibuf-2 which still has no buffer-local setting so it
>     sees the global value that's still read-file-name-internal (because
>     of the very first part of the first step)
>   - we make it buffer-local but to this wrong value
>
> So in the end we get a wrong m-c-table in both buffers (the values are reversed!).

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.


        Stefan


diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 7da3c39e6b9..ce136b90449 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -3884,13 +3884,7 @@ completing-read-default
                 ;; `read-from-minibuffer' uses 1-based index.
                 (1+ (cdr initial-input)))))
 
-  (let* ((minibuffer-completion-table collection)
-         (minibuffer-completion-predicate predicate)
-         ;; FIXME: Remove/rename this var, see the next one.
-         (minibuffer-completion-confirm (unless (eq require-match t)
-                                          require-match))
-         (minibuffer--require-match require-match)
-         (base-keymap (if require-match
+  (let* ((base-keymap (if require-match
                          minibuffer-local-must-match-map
                         minibuffer-local-completion-map))
          (keymap (if (memq minibuffer-completing-file-name '(nil lambda))
@@ -3903,8 +3897,17 @@ completing-read-default
                     ;; in minibuffer-local-filename-completion-map can
                     ;; override bindings in base-keymap.
                     base-keymap)))
-         (result (read-from-minibuffer prompt initial-input keymap
-                                       nil hist def inherit-input-method)))
+         (result
+          (minibuffer-with-setup-hook
+              (lambda ()
+                (setq-local minibuffer-completion-table collection)
+                (setq-local minibuffer-completion-predicate predicate)
+                ;; FIXME: Remove/rename this var, see the next one.
+                (setq-local minibuffer-completion-confirm
+                            (unless (eq require-match t) require-match))
+                (setq-local minibuffer--require-match require-match))
+            (read-from-minibuffer prompt initial-input keymap
+                                  nil hist def inherit-input-method))))
     (when (and (equal result "") def)
       (setq result (if (consp def) (car def) def)))
     result))