Using v6.e.PREVIEW + Data::Generators fails

[rcmlz]

Running

use v6.e.PREVIEW;
use Data::Generators;

fails with

Incompatible MROs in P6opaque rebless for types Perl6::Metamodel::ClassHOW+{<anon>}+{<anon>} and Perl6::Metamodel::ClassHOW+{<anon>}

I am not sure what the root cause of this error is.

raku --version
Welcome to Rakudo™ Star v2025.01.
Implementing the Raku® Programming Language v6.d.
Built on MoarVM version 2025.01.

Note: I like to use the new String.nomark to convert characters, thats why the use v6.e.PREVIEW

[2colours]

Not to sound too arrogant but I think this kind of issue is beyond what a mere user could/would want to deal with; I myself have spent some time with Rakudo core and this seems too obscure for me.

This distribution declares v6.d version context. To my understanding, the way Rakudo handles different language versions - for the core at least, which is still a rather high-level part of the compiler - is that it has different layers that wrap around each other. Inside the 6.e layer, there is a 6.d layer and within that a 6.c layer. Without any inspection, all I can guess is that a symbol resolves differently within the 6.d layer and the 6.e layer.

[2colours]

After some investigation, I could narrow the problem down to this call in v6.e context. The irony is that if I declare this file with use v6.e.PREVIEW, I can prevent the crash. (Didn't test the behavior, it's more about the debugging insights.)

The annoying thing is that the error is not raised during the function call but some point afterwards. The issue doesn't happen when using the default new method. I'm not sure what the right behavior is here - it's plain to see that this file is invoked with different version contexts either way - but whether that part is the problem or the problem is somewhere around bless, I have no idea.

It would be good to escalate this issue.