Polyglot unable to evaluate python dictionary objects

[AigarsS]

I tried using truffleruby 24.0.1 with python, but it fails evaluating python's dictionary, it works fine for arrays.

:~$ ruby -v
truffleruby 24.0.1, like ruby 3.2.2, GraalVM CE JVM [x86_64-linux]
:~$ ruby --polyglot
[ruby] WARNING: truffleruby starts IRB when stdin is a TTY instead of reading from stdin, use '-' to read from stdin
irb(main):001:0> Polyglot.eval('python', '{"key1": "value1"}')
[ruby] WARNING StackOverflowError
[ruby] WARNING StackOverflowError                         
<internal:core> core/truffle/polyglot.rb:351:in `each': stack level too deep (SystemStackError)
        from com.oracle.truffle.api.strings.TStringOps.runCalcStringAttributesLatin1(TStringOps.java:1295)
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
        from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	... 885 levels...
irb(main):002:0> Polyglot.eval('python', '["key1", "value1"]')
=> #<Polyglot::ForeignArray[Python] list:0x4ff ["key1", "value1"]>

[eregon]

Thanks for the report, it seems an issue of inspect for foreign objects.
Using to_s via e.g. puts works fine and prints #<Polyglot::ForeignHashIterable[Python] {'key1': 'value1'}>.

Running it outside of IRB gives a clearer error:

p :START
h = Polyglot.eval("python", '{"key1": "value1"}')
p :OK
p h

$ truffleruby-polyglot-get python
$ ruby --polyglot pyinterop.rb
:START
:OK
[ruby] WARNING StackOverflowError
[ruby] WARNING StackOverflowError
<internal:core> core/truffle/polyglot.rb:351:in `each': stack level too deep (SystemStackError)
	from java.nio.CharBuffer.<init>(CharBuffer.java:319)
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	...
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:355:in `each'
	from <internal:core> core/truffle/polyglot.rb:99:in `each'
	from <internal:core> core/enumerable.rb:108:in `map'
	from <internal:core> core/truffle/interop_operations.rb:97:in `foreign_inspect_nonrecursive'
	from <internal:core> core/truffle/polyglot.rb:468:in `block in inspect'
	from <internal:core> core/truffle/thread_operations.rb:75:in `detect_recursion'
	from <internal:core> core/truffle/polyglot.rb:467:in `inspect'
	from <internal:core> core/post.rb:80:in `block in p'
	from <internal:core> core/post.rb:80:in `each'
	from <internal:core> core/post.rb:80:in `p'
	from pyinterop.rb:4:in `<main>'

[eregon]

We can see better what's going on with:

h = Polyglot.eval("python", '{"key1": "value1"}')
puts h
p h.class.ancestors

iterator = Truffle::Interop.hash_entries_iterator(h)
p iterator.class.ancestors

iterator2 = Truffle::Interop.iterator(iterator)
p iterator.equal?(iterator2)

p iterator.method(:each)

# p h

which gives

#<Polyglot::ForeignHashIterable[Python] {'key1': 'value1'}>
[Polyglot::ForeignHashIterable, Polyglot::HashTrait, Polyglot::IterableTrait, Enumerable, Polyglot::ForeignObject, Polyglot::ObjectTrait, Object, Kernel, BasicObject]
[Polyglot::ForeignIterableIterator, Polyglot::IterableTrait, Polyglot::IteratorTrait, Enumerable, Polyglot::ForeignObject, Polyglot::ObjectTrait, Object, Kernel, BasicObject]
true
#<Method: Polyglot::ForeignIterableIterator(Polyglot::IterableTrait)#each(&block) <internal:core> core/truffle/polyglot.rb:351>

The hash_entries_iterator has both the Iterator and Iterable traits.
Both of these traits define each, but unfortunately the order is wrong and IterableTrait wins, and that one ends up calling each on Truffle::Interop.iterator(self):

truffleruby/src/main/ruby/truffleruby/core/truffle/polyglot.rb

Lines 355 to 356 in a9674ee

	iterator = Truffle::Interop.iterator(self)
	iterator.each(&block)

But Truffle::Interop.iterator(self) is the same object in this case since it's both iterable and iterator.
So IteratorTrait#each must be before iterable in the ancestors to fix this.

[eregon]

Fix in #3634