Marshal.dump of Rational sets ivars on array & can't be loaded in MRI

[segiddins]

❯ chruby-exec truffleruby -- ruby --debug -vwe 'p Marshal.dump Rational(1, 3)'
truffleruby 23.0.0, like ruby 3.1.3, Oracle GraalVM Native [aarch64-darwin]
"\x04\bU:\rRationalI[\ai\x06i\b\a:\x0F@numeratori\x06:\x11@denominatori\b"

❯ chruby-exec ruby-3.2.2 -- ruby --debug -vwe 'p Marshal.dump Rational(1, 3)'
ruby 3.2.2 (2023-03-30 revision e51014f9c0) [arm64-darwin22]
"\x04\bU:\rRational[\ai\x06i\b"

❯ chruby-exec ruby-3.2.2 -- ruby -vwe 'p Marshal.load("\x04\bU:\rRationalI[\ai\x06i\b\a:\x0F@numeratori\x06:\x11@denominatori\b")'
ruby 3.2.2 (2023-03-30 revision e51014f9c0) [arm64-darwin22]
<internal:marshal>:34:in `load': can't modify frozen Rational: (1/3) (FrozenError)
        from -e:1:in `<main>'

I think that omitting the ivars entirely from the dumped array (and thus not nesting under an I element) would work perfectly fine since truffleruby is able to load the more compact dumped output from MRI:

❯ chruby-exec truffleruby -- ruby -vwe 'p Marshal.load("\x04\bU:\rRational[\ai\x06i\b")'
truffleruby 23.0.0, like ruby 3.1.3, Oracle GraalVM Native [aarch64-darwin]
(1/3)

[eregon]

Thanks for the report.
Rational uses 2 ivars on TruffleRuby internally, but we should be able to match MRI's format for Marshal of Rational.
Maybe the current logic (from Rubinius) dealt with extra ivars on Rational but since Rational is frozen that shouldn't be a concern anymore.