Add perldiag entry for change #22435 (deprecate my $x if 0)

p4raw-link: @22435 on //depot/perl: 7921d0f22732c0609e6c9d21be9aaf6e52f99e6b

p4raw-id: //depot/perl@22437

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 38be87a..67869a2 100644 (file)
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -4282,6 +4282,22 @@ old way has bad side effects.
 it already went past any symlink you are presumably trying to look for.
 The operation returned C<undef>.  Use a filename instead.
 
+=item Deprecated use of my() in false conditional
+
+(D deprecated) You used a declaration similar to C<my $x if 0>.
+There has been a long-standing bug in Perl that causes a lexical variable
+not to be cleared at scope exit when its declaration includes a false
+conditional. Some people have exploited this bug to achieve a kind of
+static variable. Since we intend to fix this bug, we don't want people
+relying on this behavior. You can achieve a similar static effect by
+declaring the variable in a separate block outside the function, eg
+    
+    sub f { my $x if 0; return $x++ }
+
+becomes
+
+    { my $x; sub f { return $x++ } }
+
 =item Use of "package" with no arguments is deprecated
 
 (D deprecated) You used the C<package> keyword without specifying a package