Convert +snippets/expand-on-region to advice

It's meant to be corrective, not alternative behavior.

modules/editor/snippets/autoload/evil.el

@@ -1,16 +0,0 @@
-;;; editor/snippets/autoload/evil.el -*- lexical-binding: t; -*-
-;;;###if (featurep! :editor evil)
-
-;;;###autoload
-(defun +snippets/expand-on-region ()
-  "Only use this with `evil-mode'. Expands a snippet around a selected region
-and switches to insert mode if there are editable fields."
-  (interactive)
-  (when (evil-visual-state-p)
-    (evil-visual-select evil-visual-beginning evil-visual-end 'inclusive))
-  (cl-letf (((symbol-function 'region-beginning) (lambda () evil-visual-beginning))
-            ((symbol-function 'region-end)       (lambda () evil-visual-end)))
-    (yas-insert-snippet))
-  (when (yas-active-snippets)
-    (evil-insert-state +1)))
-

modules/editor/snippets/autoload/snippets.el

@@ -110,6 +110,26 @@ buggy behavior when <delete> is pressed in an empty field."
     (message "This is a built-in snippet, enabling read only mode. Use `yas-new-snippet' to redefine snippets")))
 
 
+;;
+;;; Advice
+
+;;;###autoload
+(defun +snippets*expand-on-region (orig-fn &optional no-condition)
+  "Fix off-by-one issue with expanding snippets on an evil visual region, and
+switches to insert mode.
+
+If evil-local-mode isn't enabled, run ORIG-FN as is."
+  (if (not (and (bound-and-true-p evil-local-mode)
+                (evil-visual-state-p)))
+      (funcall orig-fn no-condition)
+    (evil-visual-select evil-visual-beginning evil-visual-end 'inclusive)
+    (cl-letf (((symbol-function 'region-beginning) (lambda () evil-visual-beginning))
+              ((symbol-function 'region-end)       (lambda () evil-visual-end)))
+      (funcall orig-fn no-condition))
+    (when (yas-active-snippets)
+      (evil-insert-state +1))))
+
+
 ;;
 ;; Commands