Fix display of minibuffer prompt in ido.el

* lisp/minibuffer.el (minibuffer--message-overlay-pos): New
function.
(set-minibuffer-message): Use it to determine where to show the
overlay with the temporary message.
* lisp/ido.el (ido-exhibit): Revert "Render Ido suggestions using
an overlay"; this restores the original code which inserted the
match-status information into the minibuffer, instead of
displaying it in an overlay with an after-string.  Put the special
'minibuffer-message' text property at the beginning of the
inserted text.  (Bug#39379)

* etc/NEWS:
* doc/lispref/display.texi (Displaying Messages):
* doc/lispref/text.texi (Special Properties): Document the
'minibuffer-message' text property and its effect.

2 files changed, 23 insertions, 14 deletions

diff --git a/lisp/ido.el b/lisp/ido.el
index 6707d814077..7198649e5a5 100644
--- a/lisp/ido.el
+++ b/lisp/ido.el
@@ -4492,8 +4492,6 @@ For details of keybindings, see `ido-find-file'."
         (ido-tidy))
       (throw 'ido contents))))
 
-(defvar ido--overlay nil)
-
 (defun ido-exhibit ()
   "Post command hook for Ido."
   ;; Find matching files and display a list in the minibuffer.
@@ -4728,16 +4726,13 @@ For details of keybindings, see `ido-find-file'."
         (let ((inf (ido-completions contents)))
           (setq ido-show-confirm-message nil)
           (ido-trace "inf" inf)
-          (when ido--overlay
-            (delete-overlay ido--overlay))
-          (let ((o (make-overlay (point-max) (point-max) nil t t)))
-            (when (> (length inf) 0)
-              ;; For hacks that redefine ido-completions function (bug#39379)
-              (when (eq (aref inf 0) ?\n)
-                (setq inf (concat " " inf)))
-              (put-text-property 0 1 'cursor t inf))
-            (overlay-put o 'after-string inf)
-            (setq ido--overlay o)))
+          (let ((pos (point)))
+            (insert inf)
+            (if (< pos (point-max))
+                ;; Tell set-minibuffer-message where to display the
+                ;; overlay with temporary messages.
+                (put-text-property pos (1+ pos) 'minibuffer-message t)))
+          )
         ))))
 
 (defun ido-completions (name)
diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 0589211877a..49daabc44e3 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -763,8 +763,21 @@ and `clear-minibuffer-message' called automatically via
 (defvar minibuffer-message-timer nil)
 (defvar minibuffer-message-overlay nil)
 
+(defun minibuffer--message-overlay-pos ()
+  "Return position where `set-minibuffer-message' shall put message overlay."
+  ;; Starting from point, look for non-nil 'minibuffer-message'
+  ;; property, and return its position.  If none found, return the EOB
+  ;; position.
+  (let* ((pt (point))
+         (propval (get-text-property pt 'minibuffer-message)))
+    (if propval pt
+      (next-single-property-change pt 'minibuffer-message nil (point-max)))))
+
 (defun set-minibuffer-message (message)
   "Temporarily display MESSAGE at the end of the minibuffer.
+If some part of the minibuffer text has the `minibuffer-message' property,
+the message will be displayed before the first such character, instead of
+at the end of the minibuffer.
 The text is displayed for `minibuffer-message-clear-timeout' seconds
 \(if the value is a number), or until the next input event arrives,
 whichever comes first.
@@ -784,8 +797,9 @@ via `set-message-function'."
 
       (clear-minibuffer-message)
 
-      (setq minibuffer-message-overlay
-            (make-overlay (point-max) (point-max) nil t t))
+      (let ((ovpos (minibuffer--message-overlay-pos)))
+        (setq minibuffer-message-overlay
+              (make-overlay ovpos ovpos nil t t)))
       (unless (zerop (length message))
         ;; The current C cursor code doesn't know to use the overlay's
         ;; marker's stickiness to figure out whether to place the cursor