Recommend not modifying :set's value arg in defcustom (bug#16755).

* doc/lispref/customize.texi (Variable Definitions):
* lisp/custom.el (defcustom): Recommend avoiding
  destructive modification of the value argument of :set.

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 723bd1188c6038bafbbbc22c35f953754aab5f09..2749a521c9aab45ed52e72bee3eed616a2fce23d 100644 (file)
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2014-03-18  Juanma Barranquero  <lekktu@gmail.com>
+
+       * customize.texi (Variable Definitions): Recommend avoiding
+       destructive modification of the value argument of :set (bug#16755).
+
 2014-03-18  Stefan Monnier  <monnier@iro.umontreal.ca>
 
        * modes.texi (Auto-Indentation): Mention electric-indent variables.

diff --git a/doc/lispref/customize.texi b/doc/lispref/customize.texi
index 094beef01ec2bbcede03004a09e43da3890e71a9..0c6497fb4ef3b5dc379a04f9dcd6da32d0235eaa 100644 (file)
--- a/doc/lispref/customize.texi
+++ b/doc/lispref/customize.texi
@@ -353,8 +353,9 @@ option when using the Customize interface.  The function
 @var{setfunction} should take two arguments, a symbol (the option
 name) and the new value, and should do whatever is necessary to update
 the value properly for this option (which may not mean simply setting
-the option as a Lisp variable).  The default for @var{setfunction} is
-@code{set-default}.
+the option as a Lisp variable); preferably, though, it should not
+modify its value argument destructively.  The default for
+@var{setfunction} is @code{set-default}.
 
 If you specify this keyword, the variable's documentation string
 should describe how to do the same job in hand-written Lisp code.

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 70b557ad36b0517f5bb5438dad46fd142348e945..4308d4085fa894d3087a0f2816f10712dead7fce 100644 (file)
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2014-03-18  Juanma Barranquero  <lekktu@gmail.com>
+
+       * custom.el (defcustom): Doc fix: recommend avoiding destructive
+       modification of the value argument of :set (bug#16755).
+
 2014-03-18  Stefan Monnier  <monnier@iro.umontreal.ca>
 
        * simple.el (newline-and-indent): Do autofill (bug#17031).

diff --git a/lisp/custom.el b/lisp/custom.el
index 09431c454ec8209c8a434e4438ea528c21a2be85..c30ad7cb2136901325c1fefc0732eafdadb9f3ac 100644 (file)
--- a/lisp/custom.el
+++ b/lisp/custom.el
@@ -232,9 +232,10 @@ The following keywords are meaningful:
        given in the `defcustom' call.  The default is
        `custom-initialize-reset'.
 :set   VALUE should be a function to set the value of the symbol
-        when using the Customize user interface.
-       It takes two arguments, the symbol to set and the value to
-       give it.  The default choice of function is `set-default'.
+       when using the Customize user interface.  It takes two arguments,
+       the symbol to set and the value to give it.  The function should
+       not modify its value argument destructively.  The default choice
+       of function is `set-default'.
 :get   VALUE should be a function to extract the value of symbol.
        The function takes one argument, a symbol, and should return
        the current value for that symbol.  The default choice of function