From @masak

$ perl6 --version
This is rakudo version 2015.11-379-gfdec627 built on MoarVM version
2015.11-34-gc3eea17 implementing Perl v6.b.

$ cat foo.t
use B;

say X​::Y​::B;

$ cat bar.t
use B;
use C;

say X​::Y​::B;

$ cat lib/B.pm
class X​::Y​::B {}

$ cat lib/C.pm
class X​::Y​::C {}

$ perl6 foo.t
(B)

$ perl6 bar.t
Could not find symbol '&B'
  in block <unit> at bar.t​:4

Actually thrown at​:
  in block <unit> at bar.t​:4

Expected behavior​: bar.t should work, and print what foo.t prints.

I did a quick bisect of Rakudo, and
87288285f6f398ec7cba0900312ced4b580d79ed turns out to be the commit
that introduces the above bug.

From @masak

<nine> masak​: if 87288285f6f398ec7cba0900312ced4b580d79ed is to blame, it may just be an older precompilation issue that surfaced because we precompile everything that's too slow to run away now...
<nine> masak​: to find that out, it would help if you could test with a version before 3b943782768260d4422933f4e2e71be40429c570 with manual precompilation
<masak> how do I do manual precompilation?
<nine> masak​: perl6 --target=mbc --output Foo.moarvm Foo.pm
<masak> nine​: do I need to put the Foo.moarvm anywhere in particular for it to be picked up?
<nine> masak​: the old implementation just looked alongside the .pm6 file

...

<masak> good news! it works on the commit before, with manual precompilation \o/
<masak> so it's *not* an ancient error surfacing only now
<timotimo> good!
<masak> which means I should keep investigating 8728828...
<nine> masak​: why is that good news? Now I have to fix it ;)
<masak> nine​: hm. I may have spoken too soon.
<masak> nine​: I just went one commit back, not to before 3b943782
<masak> nine​: trying from that one.
<masak> nine​: ok, now it's conclusive. building off 3b943782^, with modules precompiled, everything works fine.
* masak adds this to the ticket

From @masak

<nine> masak​: I still doubt it's actually 8728828 that's to blame. Between 3b943782 and 8728828 there's a lot of refactoring, especially some changes touching the handling of global merging. Might be a good idea to bisect that (with manual precompilation in every step)
<masak> nine​: will do.

[...]

<masak> nine​: the results are in. a bisect of 3b943782^..87288285f, with precompilation at every step, turned up 87288285f as the first bad commit.

From @masak

On Sat Dec 05 16​:37​:23 2015, masak wrote​:

$ perl6 --version
This is rakudo version 2015.11-379-gfdec627 built on MoarVM version
2015.11-34-gc3eea17 implementing Perl v6.b.

$ cat foo.t
use B;

say X​::Y​::B;

$ cat bar.t
use B;
use C;

say X​::Y​::B;

$ cat lib/B.pm
class X​::Y​::B {}

$ cat lib/C.pm
class X​::Y​::C {}

$ perl6 foo.t
(B)

$ perl6 bar.t
Could not find symbol '&B'
in block <unit> at bar.t​:4

Actually thrown at​:
in block <unit> at bar.t​:4

I can no longer reproduce this bug, so I assume it's been fixed. Resolving the ticket.

@masak - Status changed from 'new' to 'resolved'