[COMPILER] Compiling array within a hash

[jemmaissroff]

Minimal repro:

{[] => 1}

leads to method hash' called on hidden T_ARRAY object`

Found from: RUBY_ISEQ_DUMP_DEBUG=prism make test/coverage/test_coverage.rb

[jemmaissroff]

@tenderlove @kddnewton , this is still a bug on the latest master. I don't think #2016 fixed it.

[paracycle]

There is a similar problem that exhibits itself with a similar message, which can be reproduced by:

RubyVM::InstructionSequence.compile_prism(<<~RUBY).eval
  def foo a: [], b: []
    p a
    p b
  end
  foo(a: [Symbol])
RUBY

and it outputs:

[Symbol]
<compiled>:2:in `p': method `inspect' called on hidden T_ARRAY object (0x00000001033d4de0 flags=0xa00002807) (NotImplementedError)
        from <compiled>:2:in `foo'
        from <compiled>:4:in `<compiled>'
        from ../test.rb:39:in `eval'
        from ../test.rb:39:in `<main>'

Note that since the second optional param is not passed, it causes an error on the p b line, so this version of the error looks like a default parameter bug.

I found this by isolating it from the failure of RUBY_ISEQ_DUMP_DEBUG=prism make ../test/ostruct/test_ostruct.rb

[paracycle]

Oh I think I know what's wrong with #2016. The PR checks if element is any of the types PM_NODE_ARRAY, PM_NODE_HASH and PM_NODE_RANGE, but the element won't be any of those types for a hash, it will be PM_NODE_ASSOC.

Now, PM_NODE_ASSOC also has a static literal check of its own, but that only checks to see if the value (not the key) is an array, hash or range.

So, none of our code actually makes the PM_HASH_NODE in the above example to not be a static literal.

[paracycle]

OK, I have what I think is a fix here: #2055 and a test that passes on ruby/ruby with that change here: ruby/ruby#9215