Don't autovivify stashes as soon as the lexer sees them.

This makes defined %foo::bar:: work again.
Add tests for it, remove note in perldelta about having broken it.

p4raw-id: //depot/perl@26370

pod/perl593delta.pod

@@ -15,16 +15,6 @@ L<perl592delta> for the differences between 5.8.0 and 5.9.2.
 C<_> is now forced to be a bareword after a filetest operator. This solves
 a number of misparsing issues when a global C<_> subroutine is defined.
 
-=head2 C<defined %foo::bar::>
-
-This used to report whether the C<foo::bar> package was created. Now it's
-always true, as a side-effect of a change to shrink the internal size of
-hash structures. Note that using C<defined> on hashes was deprecated
-anyway. To achieve the same result, you can use a symbolic reference
-instead (and this is backwards-compatible):
-
-    defined %{"foo::bar::"}
-
 =head1 Core Enhancements
 
 =head1 Modules and Pragmata

t/op/stash.t

@@ -7,7 +7,7 @@ BEGIN {
 
 require "./test.pl";
 
-plan( tests => 2 );
+plan( tests => 8 );
 
 # Used to segfault (bug #15479)
 fresh_perl_is(
@@ -24,3 +24,15 @@ fresh_perl_is(
     { switches => [ '-w' ] },
     q(Insert a non-GV in a stash, under warnings 'once'),
 );
+
+ok( !defined %oedipa::maas::, q(stashes aren't defined if not used) );
+ok( !defined %{"oedipa::maas::"}, q(- work with hard refs too) );
+
+ok( defined %tyrone::slothrop::, q(stashes are defined if seen at compile time) );
+ok( defined %{"tyrone::slothrop::"}, q(- work with hard refs too) );
+
+ok( defined %bongo::shaftsbury::, q(stashes are defined if a var is seen at compile time) );
+ok( defined %{"bongo::shaftsbury::"}, q(- work with hard refs too) );
+
+package tyrone::slothrop;
+$bongo::shaftsbury::scalar = 1;

toke.c

@@ -5661,10 +5661,15 @@ S_pending_ident(pTHX)
     /* build ops for a bareword */
     yylval.opval = (OP*)newSVOP(OP_CONST, 0, newSVpv(PL_tokenbuf+1, 0));
     yylval.opval->op_private = OPpCONST_ENTERED;
-    gv_fetchpv(PL_tokenbuf+1, PL_in_eval ? (GV_ADDMULTI | GV_ADDINEVAL) : TRUE,
-               ((PL_tokenbuf[0] == '$') ? SVt_PV
-                : (PL_tokenbuf[0] == '@') ? SVt_PVAV
-                : SVt_PVHV));
+    gv_fetchpv(
+	    PL_tokenbuf+1,
+	    PL_in_eval
+		? (GV_ADDMULTI | GV_ADDINEVAL)
+		/* if the identifier refers to a stash, don't autovivify it */
+		: !(*PL_tokenbuf == '%' && *(d = PL_tokenbuf + strlen(PL_tokenbuf) - 1) == ':' && d[-1] == ':'),
+	    ((PL_tokenbuf[0] == '$') ? SVt_PV
+	     : (PL_tokenbuf[0] == '@') ? SVt_PVAV
+	     : SVt_PVHV));
     return WORD;
 }