[#35] Allow fixed-height minibuffer

CHANGELOG.md

@@ -40,6 +40,9 @@ The format is based on [Keep a Changelog].
   retrieve history elements. The Isearch entry-point bindings now work
   properly in Selectrum too, except that they allow you to select a
   history element using Selectrum. See [#49].
+* You can now cause the minibuffer to always have the same height,
+  even if there are fewer candidates, by enabling
+  `selectrum-fix-minibuffer-height` ([#35]).
 
 ### Enhancements
 * In `read-file-name`, when a default is provided (for example in the

README.md

@@ -238,6 +238,11 @@ matching and case-insensitive matching.
 * By default, ten candidates are shown in the minibuffer at any given
   time. You can customize that by changing
   `selectrum-num-candidates-displayed`.
+    * Normally `selectrum-num-candidates-displayed` acts as just a
+      maximum for the height of the minibuffer. You might prefer for
+      the minibuffer to *always* have that height, even if there are
+      fewer candidates. This behavior may be achieved by setting
+      `selectrum-fix-minibuffer-height` to a non-nil value.
 * The currently selected candidate is highlighted with the face
   `selectrum-current-candidate`. If you don't like the color, you can
   adjust it to taste.

selectrum.el

@@ -247,6 +247,11 @@ This option is a workaround for 2 problems:
   wrapping."
   :type 'integer)
 
+(defcustom selectrum-fix-minibuffer-height nil
+  "Non-nil means the minibuffer always has the same height.
+Even if there are fewer candidates."
+  :type 'boolean)
+
 ;;;; Utility functions
 
 ;;;###autoload
@@ -667,7 +672,12 @@ just rendering it to the screen and then checking."
                                             selectrum-right-margin-padding)))
                       right-margin))
                     (push ol selectrum--right-margin-overlays))))
-              (cl-incf index))))
+              (cl-incf index))
+            ;; Simplest way to grow the minibuffer to size is to just
+            ;; insert some extra newlines :P
+            (when selectrum-fix-minibuffer-height
+              (dotimes (_ (- selectrum-num-candidates-displayed index))
+                (insert "\n")))))
         (add-text-properties bound (point-max) '(read-only t))
         (setq selectrum--end-of-input-marker (set-marker (make-marker) bound))
         (set-marker-insertion-type selectrum--end-of-input-marker t)