‘Subroutine (not var) "&x" will not stay shared’

Another ‘variable’ warning about lexical subs that I missed.

3 files changed, 32 insertions, 2 deletions

diff --git a/pad.c b/pad.c
index e7392aba4b..6707542d3f 100644
--- a/pad.c
+++ b/pad.c
@@ -1233,8 +1233,11 @@ S_pad_findlex(pTHX_ const char *namepv, STRLEN namelen, U32 flags, const CV* cv,
 			 && !PadnameIsSTATE(name_p[offset])
 			 && warn && ckWARN(WARN_CLOSURE)) {
 			newwarn = 0;
+			/* diag_listed_as: Variable "%s" will not stay
+					   shared */
 			Perl_warner(aTHX_ packWARN(WARN_CLOSURE),
-			    "Variable \"%"UTF8f"\" will not stay shared",
+			    "%se \"%"UTF8f"\" will not stay shared",
+			     *namepv == '&' ? "Subroutin" : "Variabl",
 			     UTF8fARG(1, namelen, namepv));
 		    }
 
diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index a369a70540..f9a56fa3a1 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -5438,6 +5438,25 @@ the previous instance.  This is almost always a typographical error.
 Note that the earlier subroutine will still exist until the end of
 the scope or until all closure references to it are destroyed.
 
+=item Subroutine "%s" will not stay shared
+
+(W closure) An inner (nested) I<named> subroutine is referencing a "my"
+subroutine defined in an outer named subroutine.
+
+When the inner subroutine is called, it will see the value of the outer
+subroutine's lexical subroutine as it was before and during the *first*
+call to the outer subroutine; in this case, after the first call to the
+outer subroutine is complete, the inner and outer subroutines will no
+longer share a common value for the lexical subroutine.  In other words,
+it will no longer be shared.  This will especially make a difference
+if the lexical subroutines accesses lexical variables declared in its
+surrounding scope.
+
+This problem can usually be solved by making the inner subroutine
+anonymous, using the C<sub {}> syntax.  When inner anonymous subs that
+reference lexical subroutines in outer subroutines are created, they
+are automatically rebound to the current values of such lexical subs.
+
 =item Subroutine %s redefined
 
 (W redefine) You redefined a subroutine.  To suppress this warning, say
diff --git a/t/op/lexsub.t b/t/op/lexsub.t
index 32f8bc7eac..f43285f115 100644
--- a/t/op/lexsub.t
+++ b/t/op/lexsub.t
@@ -7,7 +7,7 @@ BEGIN {
     *bar::is = *is;
     *bar::like = *like;
 }
-plan 146;
+plan 147;
 
 # -------------------- Errors with feature disabled -------------------- #
 
@@ -807,6 +807,14 @@ is runperl(switches => ['-lXMfeature=:all'],
   like $@, qr/^Undefined subroutine &φου called at /,
     'my sub with utf8 name';
 }
+{
+  my $w;
+  local $SIG{__WARN__} = sub { $w = shift };
+  use warnings 'closure';
+  eval 'sub stayshared { my sub x; sub notstayshared { x } } 1' or die;
+  like $w, qr/^Subroutine "&x" will not stay shared at /,
+          'Subroutine will not stay shared';
+}
 
 # -------------------- Interactions (and misc tests) -------------------- #