[perl #19135] string eval turns off readonlyness on lexicals

Don’t turn off readonliness on lexicals when freeing pad entries.

The readonliness is (prior to this commit) turned off explicitly in
pad_free under ithreads. See also bug #19022, which resulted from the
same change. There is some discussion there, too, but nobody seemed to
know exactly why the readonliness needed to be turned off.

Change 4761/2aa1bed, from January of 2000, added that SvREADONLY_off.
It is supposed to make sure that pad entries that were constants will
not be constants the next time they are used.

Dave Mitchell writes:
> I think...[this]...fix is correct (just removing the SvREADONLY_off).
> The issue it was trying to fix appears to have been properly fixed
> later by 3b1c21fabed159100271bd60bac3f870f5ac16af, which is why it's
> safe to remove it.

So this commit just deletes that code.

2 files changed, 7 insertions, 6 deletions

diff --git a/pad.c b/pad.c
index 9b8cda5df2..8ab34ff465 100644
--- a/pad.c
+++ b/pad.c
@@ -1450,11 +1450,6 @@ Perl_pad_free(pTHX_ PADOFFSET po)
 
     if (PL_curpad[po] && PL_curpad[po] != &PL_sv_undef) {
 	SvPADTMP_off(PL_curpad[po]);
-#ifdef USE_ITHREADS
-	/* SV could be a shared hash key (eg bugid #19022) */
-	if (!SvIsCOW(PL_curpad[po]))
-	    SvREADONLY_off(PL_curpad[po]);	/* could be a freed constant */
-#endif
     }
     if ((I32)po < PL_padix)
 	PL_padix = po - 1;
diff --git a/t/op/eval.t b/t/op/eval.t
index 0a5fadc1e0..a1c1c1a94c 100644
--- a/t/op/eval.t
+++ b/t/op/eval.t
@@ -6,7 +6,7 @@ BEGIN {
     require './test.pl';
 }
 
-print "1..107\n";
+print "1..108\n";
 
 eval 'print "ok 1\n";';
 
@@ -611,3 +611,9 @@ eval $ov;
 print "ok\n";
 EOP
 
+for my $k (!0) {
+  eval 'my $do_something_with = $k';
+  eval { $k = 'mon' };
+  is "a" =~ /a/, "1",
+    "string eval leaves readonly lexicals readonly [perl #19135]";
+}