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[Emacs-diffs] master 495963c: * lisp/emacs-lisp/bytecomp.el (byte-compil

From: Stefan Monnier
Subject: [Emacs-diffs] master 495963c: * lisp/emacs-lisp/bytecomp.el (byte-compile-file-form-defvar-function):
Date: Fri, 20 Apr 2018 17:22:53 -0400 (EDT)

branch: master
commit 495963cfaf535646350051f47c085b84319572f0
Author: Stefan Monnier <address@hidden>
Commit: Stefan Monnier <address@hidden>

    * lisp/emacs-lisp/bytecomp.el (byte-compile-file-form-defvar-function):
    Warn about defvaralias that follows instead of precedes its var.
 lisp/emacs-lisp/bytecomp.el | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index ea9e3f0..50e6704 100644
--- 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

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