Make lock(&foo) syntax nominally lock the subroutine
In 5.10, lock(&foo) was an error for non-lvalue subs. For lvalue
subs, it passed &foo to the lockhook and return \&foo.
In 5.12, lock(&foo) was still an error for non-lvalue subs. For
lvalue subs, it would pass &foo to the lockhook and then either
trip an assertion (-DDEBUGGING) or return &foo, resulting in inter-
esting bugs.
Commit
f4df43b5e changed lock(&lvalue_sub) to call the sub and lock
its return value.
As Reini Urban pointed out in
<CAHiT=DE5cVZbuCR3kb=Q5oCa18vo3jr5jZKmURHYha2PwF4pEQ@mail.gmail.com>,
locking a subroutine does have its uses.
Since lock(&foo) has never really worked anyway, we can still
change this.
So, for lvalue subs, this reverts back to the 5.10 behaviour. For
non-lvalue subs, it now behaves the same way, the lvalue flag making
no difference. Note that it still causes an error at run-time, if
threads::shared is loaded, as its lockhook is conservative in what
it accepts.
But this change allows for future extensibility, unlike
f4df43b5e.
A note about the implementation: There are two pieces of code (at
least) in op.c that convert an entersub op into an rv2cv, one in
S_doref and the other in Perl_op_lvalue_flags. Originally (before
f4df43b5e) it was S_doref that took care of that for OP_LOCK. But
Perl_op_lvalue_flags is called first, so it would assume it was an
assignment to a sub call and croak if there was no lvalue sub in the
symbol table. This commit adds back the special case for OP_LOCK, but
in Perl_op_lvalue_flags, not S_doref.