Fix package assignment with nested aliased packages

This commit fixes package assignments like *foo:: = *bar:: when both
foo and bar contain nested stashes that are aliases of each other.

mro_package_moved (actually, its auxiliary routine) need to keep a
list of stashes that have been seen as a separate list from those that
are going to have mro_isa_changed_in called on them. Otherwise, some
stashes will simply not be iterated through.

See the test that this adds and its comments. @ISA = @ISA should never
have any effect visible to Perl (with a capital), but it does in that
test case, prior to this commit.

This also fixes another bug that the test case triggered:
riter was not being reset before the second iteration in
mro_gather_and_rename.

Also, the stashes HV (aka the ‘big list’) now holds refcounts on its
elements, as that makes the code simpler as a result of the changes.

1 files changed, 29 insertions, 1 deletions

diff --git a/t/mro/package_aliases.t b/t/mro/package_aliases.t
index b4ef2027fe..f2c5c3944f 100644
--- a/t/mro/package_aliases.t
+++ b/t/mro/package_aliases.t
@@ -10,7 +10,7 @@ BEGIN {
 
 use strict;
 use warnings;
-plan(tests => 19);
+plan(tests => 20);
 
 {
     package New;
@@ -236,6 +236,34 @@ fresh_perl_is
    { stderr => 1 },
   "Assigning a nameless package over one w/subclasses updates isa caches";
 
+# mro_package_moved needs to make a distinction between replaced and
+# assigned stashes when keeping track of what it has seen so far.
+no warnings; {
+    no strict 'refs';
+
+    sub bar::blonk::blonk::phoo { "bbb" }
+    sub veclum::phoo { "lasrevinu" }
+    @feedlebomp::ISA = qw 'phoo::blonk::blonk veclum';
+    *phoo::baz:: = *bar::blonk::;   # now bar::blonk:: is on both sides
+    *phoo:: = *bar::;         # here bar::blonk:: is both deleted and added
+    *bar:: = *boo::;          # now it is only known as phoo::blonk::
+
+    # At this point, before the bug was fixed, %phoo::blonk::blonk:: ended
+    # up with no effective name, allowing it to be deleted without updating
+    # its subclasses’ caches.
+
+    my $accum = '';
+
+    $accum .= 'feedlebomp'->phoo;          # bbb
+    delete ${"phoo::blonk::"}{"blonk::"};
+    $accum .= 'feedlebomp'->phoo;          # bbb (Oops!)
+    @feedlebomp::ISA = @feedlebomp::ISA;
+    $accum .= 'feedlebomp'->phoo;          # lasrevinu
+
+    is $accum, 'bbblasrevinulasrevinu',
+      'nested classes deleted & added simultaneously';
+}
+use warnings;
 
 # mro_package_moved needs to check for self-referential packages.
 # This broke Text::Template [perl #78362].