Crash when parallel render; not thread safe? Dies with X::HyperRace::Died in test case about raku-template-mustache

[softmoth]

It's not affecting anyone as far as I know, and I suspect it's a generic gotcha with Raku rather than an actual bug. But I've left this bug open as a warning and reminder to any future maintainer that something brittle and poorly understood may be going on. And as an invitation for anyone who knows better to proffer an improvement.

[Xliff]

Odd. I get something different:

An operation first awaited:
  in block  at t/11-iterable.t line 71
  in block <unit> at t/11-iterable.t line 38

Died with the exception:
    A worker in a parallel iteration (hyper or race) initiated here:
      in block  at /home/cbwood/.zef/store/Template-Mustache-1.2.3.tar.gz/Template-Mustache-1.2.3/lib/Template/Mustache.rakumod (Template::Mustache) line 577
      in block  at /home/cbwood/.zef/store/Template-Mustache-1.2.3.tar.gz/Template-Mustache-1.2.3/lib/Template/Mustache.rakumod (Template::Mustache) line 566
      in sub format at /home/cbwood/.zef/store/Template-Mustache-1.2.3.tar.gz/Template-Mustache-1.2.3/lib/Template/Mustache.rakumod (Template::Mustache) line 537
      in sub format at /home/cbwood/.zef/store/Template-Mustache-1.2.3.tar.gz/Template-Mustache-1.2.3/lib/Template/Mustache.rakumod (Template::Mustache) line 397
      in sub format at /home/cbwood/.zef/store/Template-Mustache-1.2.3.tar.gz/Template-Mustache-1.2.3/lib/Template/Mustache.rakumod (Template::Mustache) line 397
      in method render at /home/cbwood/.zef/store/Template-Mustache-1.2.3.tar.gz/Template-Mustache-1.2.3/lib/Template/Mustache.rakumod (Template::Mustache) line 295
      in block  at t/11-iterable.t line 57

    Died at:
        Cannot invoke object with invocation handler in this context

This is from Raku v2021.02.1-64-gbf67b1f71

[softmoth]

Yes, Xliff, I get the same error as you. I'd accidentally switched to an older Raku and forgot to switch back before reporting.

[softmoth]

This bug is triggered by calling .Str or .gist on the HyperSeq prior to calling .map. In Template::Mustache, the call to .Str is in sub resolve, and removing line 426 causes the test case to succeed.

This is a golfed down test case:

my $hyp = (gather { take $(:line("line 1")) }).hyper;

# XXX THIS TRIGGERS THE SUBSEQUENT CRASH
$hyp.Str;

my $result = $hyp.map({ .raku }).join;

put "RESULT «{$result}»";

What remains to be resolved is whether this is a bug in Template::Mustache or in Rakudo.

[softmoth]

Workaround pushed as b1fbd76. I don't know what the right solution really is, so leaving this open.

[Xliff]

Nice job, @softmoth!

[2colours]

What's the current state of the issue?