* lisp/emacs-lisp/bytecomp.el (byte-compile-file-form-defvar-function):

Warn about defvaralias that follows instead of precedes its var.

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index ea9e3f06555afd533597f031b1d7a6a66aa4aaca..50e67046e8b9429d2c022a8a67159d9be56fc696 100644 (file)
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -2426,6 +2426,15 @@ list that represents a doc string reference.
 (defun byte-compile-file-form-defvar-function (form)
   (pcase-let (((or `',name (let name nil)) (nth 1 form)))
     (if name (byte-compile--declare-var name)))
+  ;; Variable aliases are better declared before the corresponding variable,
+  ;; since it makes it more likely that only one of the two vars has a value
+  ;; before the `defvaralias' gets executed, which avoids the need to
+  ;; merge values.
+  (pcase form
+    (`(defvaralias ,_ ',newname . ,_)
+     (when (memq newname byte-compile-bound-variables)
+       (byte-compile-warn
+        "Alias for `%S' should be declared before its referent" newname))))
   (byte-compile-keep-pending form))
 
 (put 'custom-declare-variable 'byte-hunk-handler