How does mro, goto, and set_subname interact? - perl

Question

This is a complex question with regard to mro.pm, and the interplay with set_subname, and goto
In troubleshooting a problem, I think the core of my misunderstanding relates to how mro.pm works -- especially with regard to set_subname.
What is the difference between these three constructs,
Plain call to set_subname
*Foo::bar = set_subname( 'Foo::bar', $codeRef );
Anon sub which wraps a set_subname
*Foo::bar = sub {
my $codeRef2 = set_subname('Foo::bar', $codeRef);
goto $codeRef2
};
Anon sub which has its name set with set_subname
*Foo::bar = set_subname(
'Foo::bar',
sub { goto $codeRef }
);
Specifically, the Mojo test suits fails with either of these modifications with anon subs applied to Mojo::Utils's monkey_patch Running the two variants above against t/mojo/websocket_proxy.t,
With the 2 (second) option I have
*{"${class}::$k"} = sub {
my $cr = set_subname("${class}::$k", $patch{$k});
goto $cr;
};
And I get
Mojo::Reactor::Poll: Timer failed: Can't locate object method "send" via package "Mojo::Transaction::HTTP" at t/mojo/websocket_proxy.t line 66.
With the 3 (third) option I have,
*{"${class}::$k"} = set_subname("${class}::$k", sub { goto $patch{$k} })
And I get
No next::method 'new' found for Mojolicious::Routes at /usr/lib/x86_64-linux-gnu/perl/5.28/mro.pm line 30.
Obviously, the first version works (it's from the code I linked), the question is why are the other two variants giving me different errors (especially the second variant) and what's happening there -- why don't they work?

Answer 1

Your second option is not working because the sub you are using as a wrapper does not match the prototype of the inner sub. monkey_patch is not only used for methods, and this changes how some functions are parsed. In particular, Mojo::Util::steady_time has an empty prototype and is often called without using parenthesis.
*{"${class}::$k"} = Sub::Util::set_prototype(
Sub::Util::prototype( $patch{$k} ),
Sub::Util::set_subname(
"${class}::$k",
sub {
my $cr = Sub::Util::set_subname("${class}::$k", $patch{$k});
goto $cr;
}
)
);
The third construct is not working because you are using goto to remove the renamed wrapper sub from the call stack, leaving only the inner sub which has no name. This breaks next::method's ability to find the correct method name.

Answer 2

That is indeed complicated, but maybe you overcomplicated it?
Remember that MRO is only concerned with locating a method, which is just a symbol table entry to a coderef, through a defined order of package names. The internal subname only has to do with what caller() reports AFAIK.
From: Mojo
*{"${class}::$_"} = ## symbol table entry
set_subname("${class}::$_", ## an internal name
$patch{$_}) ## for a code ref
for keys %patch;
HTH
Edit After Seeing Error Messages:
The subroutines have not been validly installed. I suspect that since in option 2 and 3 you are deferring the calls to set_subname() to call time, the coderef $patch{$k} never has a subname assigned to it and that breaks a link in the chain of mro::_nextcan()'s XS magic. Particularly if $patch{$k} calls next::method. The closures seem to be valid though.
Although I must say my testing seems to show that option 2 is valid.
Enter command: my ($class, $k) = qw/W S/; my %patch = (S =>
sub {print "patch here\n"; decall;}); *{"${class}::$k"} =
sub { print "goto'r here\n"; my $cr = set_subname("${class}::$k",
$patch{$k}); goto $cr;};
Enter command: decall
0 "console"
1 "console.pl"
2 "114"
3 "(eval)"
4 "0"
5 0
6 "package W; decall"
7 ""
8 "256"
9 "\020\001\000\000\000P\004\000\000\000\000\000\000U\025U\005"
10 0
Enter command: S
goto'r here
patch here
0 "W"
1 "(eval 110)"
2 "1"
3 "W::S"
4 "1"
5 0
6 0
7 0
8 "256"
9 "\020\001\000\000\000P\004\000\000\000\000\000\000U\025U\005"
10 0
You might have to start looking farther afield for the problem with option 2.

Answer 3

After modifying Mojo/Util.pm with
foreach my $k (keys %patch) {
*{"${class}::$k"} = sub {
my $cr = set_subname("${class}::$k", $patch{$k});
goto $cr;
};
}
and isolating the test case, I get:
$ perl -MCarp::Always t/mojo/websocket_proxy2.t
Mojo::Reactor::Poll: Timer failed: Can't locate object method "send" via package "Mojo::Transaction::HTTP" at t/mojo/websocket_proxy2.t line 59.
main::__ANON__(Mojo::UserAgent=HASH(0x60280dad0), Mojo::Transaction::HTTP=HASH(0x6029ee7b0)) called at blib/lib/Mojo/UserAgent.pm line 252
Mojo::UserAgent::_finish(Mojo::UserAgent=HASH(0x60280dad0), "927210c53042c6142eda3f4010c8b17c", 1) called at blib/lib/Mojo/UserAgent.pm line 220
Mojo::UserAgent::_error(Mojo::UserAgent=HASH(0x60280dad0), "927210c53042c6142eda3f4010c8b17c", "Connect timeout") called at blib/lib/Mojo/UserAgent.pm line 128
Mojo::UserAgent::__ANON__(Mojo::IOLoop=HASH(0x601f9abb8), "Connect timeout", undef) called at blib/lib/Mojo/IOLoop.pm line 63
Mojo::IOLoop::__ANON__(Mojo::IOLoop::Client=HASH(0x601e34598)) called at blib/lib/Mojo/EventEmitter.pm line 15
Mojo::EventEmitter::emit(Mojo::IOLoop::Client=HASH(0x601e34598), "error", "Connect timeout") called at blib/lib/Mojo/IOLoop/Client.pm line 39
Mojo::IOLoop::Client::__ANON__(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 143
eval {...} called at blib/lib/Mojo/Reactor/Poll.pm line 143
Mojo::Reactor::Poll::_try(Mojo::Reactor::Poll=HASH(0x6001a8390), "Timer", CODE(0x601e24ca0)) called at blib/lib/Mojo/Reactor/Poll.pm line 81
Mojo::Reactor::Poll::one_tick(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 99
Mojo::Reactor::Poll::start(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/IOLoop.pm line 134
Mojo::IOLoop::start("Mojo::IOLoop") called at t/mojo/websocket_proxy2.t line 62
at blib/lib/Mojo/IOLoop.pm line 23.
Mojo::IOLoop::__ANON__(Mojo::Reactor::Poll=HASH(0x6001a8390), "Timer failed: Can't locate object method \"send\" via package \"Mojo::Transaction::HTTP\" at t/mojo/websocket_proxy2.t line 59.\x{a}\x{9}main::__ANON__(Mojo::UserAgent=HASH(0x60280dad0), Mojo::Transaction::HTTP=HASH(0x6029ee7b0)) called at blib/lib/Mojo/UserAgent.pm line 252\x{a}\x{9}Mojo::UserAgent::_finish(Mojo::UserAgent=HASH(0x60280dad0), \"927210c53042c6142eda3f4010c8b17c\", 1) called at blib/lib/Mojo/UserAgent.pm line 220\x{a}\x{9}Mojo::UserAgent::_error(Mojo::UserAgent=HASH(0x60280dad0), \"927210c53042c6142eda3f4010c8b17c\", \"Connect timeout\") called at blib/lib/Mojo/UserAgent.pm line 128\x{a}\x{9}Mojo::UserAgent::__ANON__(Mojo::IOLoop=HASH(0x601f9abb8), \"Connect timeout\", undef) called at blib/lib/Mojo/IOLoop.pm line 63\x{a}\x{9}Mojo::IOLoop::__ANON__(Mojo::IOLoop::Client=HASH(0x601e34598)) called at blib/lib/Mojo/EventEmitter.pm line 15\x{a}\x{9}Mojo::EventEmitter::emit(Mojo::IOLoop::Client=HASH(0x601e34598), \"error\", \"Connect timeout\") called at blib/lib/Mojo/IOLoop/Client.pm line 39\x{a}\x{9}Mojo::IOLoop::Client::__ANON__(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 143\x{a}\x{9}eval {...} called at blib/lib/Mojo/Reactor/Poll.pm line 143\x{a}\x{9}Mojo::Reactor::Poll::_try(Mojo::Reactor::Poll=HASH(0x6001a8390), \"Timer\", CODE(0x601e24ca0)) called at blib/lib/Mojo/Reactor/Poll.pm line 81\x{a}\x{9}Mojo::Reactor::Poll::one_tick(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 99\x{a}\x{9}Mojo::Reactor::Poll::start(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/IOLoop.pm line 134\x{a}\x{9}Mojo::IOLoop::start(\"Mojo::IOLoop\") called at t/mojo/websocket_proxy2.t line 62\x{a}") called at blib/lib/Mojo/EventEmitter.pm line 15
Mojo::EventEmitter::emit(Mojo::Reactor::Poll=HASH(0x6001a8390), "error", "Timer failed: Can't locate object method \"send\" via package \"Mojo::Transaction::HTTP\" at t/mojo/websocket_proxy2.t line 59.\x{a}\x{9}main::__ANON__(Mojo::UserAgent=HASH(0x60280dad0), Mojo::Transaction::HTTP=HASH(0x6029ee7b0)) called at blib/lib/Mojo/UserAgent.pm line 252\x{a}\x{9}Mojo::UserAgent::_finish(Mojo::UserAgent=HASH(0x60280dad0), \"927210c53042c6142eda3f4010c8b17c\", 1) called at blib/lib/Mojo/UserAgent.pm line 220\x{a}\x{9}Mojo::UserAgent::_error(Mojo::UserAgent=HASH(0x60280dad0), \"927210c53042c6142eda3f4010c8b17c\", \"Connect timeout\") called at blib/lib/Mojo/UserAgent.pm line 128\x{a}\x{9}Mojo::UserAgent::__ANON__(Mojo::IOLoop=HASH(0x601f9abb8), \"Connect timeout\", undef) called at blib/lib/Mojo/IOLoop.pm line 63\x{a}\x{9}Mojo::IOLoop::__ANON__(Mojo::IOLoop::Client=HASH(0x601e34598)) called at blib/lib/Mojo/EventEmitter.pm line 15\x{a}\x{9}Mojo::EventEmitter::emit(Mojo::IOLoop::Client=HASH(0x601e34598), \"error\", \"Connect timeout\") called at blib/lib/Mojo/IOLoop/Client.pm line 39\x{a}\x{9}Mojo::IOLoop::Client::__ANON__(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 143\x{a}\x{9}eval {...} called at blib/lib/Mojo/Reactor/Poll.pm line 143\x{a}\x{9}Mojo::Reactor::Poll::_try(Mojo::Reactor::Poll=HASH(0x6001a8390), \"Timer\", CODE(0x601e24ca0)) called at blib/lib/Mojo/Reactor/Poll.pm line 81\x{a}\x{9}Mojo::Reactor::Poll::one_tick(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 99\x{a}\x{9}Mojo::Reactor::Poll::start(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/IOLoop.pm line 134\x{a}\x{9}Mojo::IOLoop::start(\"Mojo::IOLoop\") called at t/mojo/websocket_proxy2.t line 62\x{a}") called at blib/lib/Mojo/Reactor/Poll.pm line 143
Mojo::Reactor::Poll::_try(Mojo::Reactor::Poll=HASH(0x6001a8390), "Timer", CODE(0x601e24ca0)) called at blib/lib/Mojo/Reactor/Poll.pm line 81
Mojo::Reactor::Poll::one_tick(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/Reactor/Poll.pm line 99
Mojo::Reactor::Poll::start(Mojo::Reactor::Poll=HASH(0x6001a8390)) called at blib/lib/Mojo/IOLoop.pm line 134
Mojo::IOLoop::start("Mojo::IOLoop") called at t/mojo/websocket_proxy2.t line 62
I can also confirm that setting the prototype fixes it.