Bug #20939: When using the parse.y parser, it occurs argument stack underflow (-1) if there is processing after the shareable_constant_value: experimental_everything comment and `C = { **{ k: v } }`

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.4.0dev (2024-12-10T03:31:47Z master f12e2622c1) [arm64-darwin23]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[ydah (Yudai Takada)]

The following code will occurs argument stack underflow if it is a parse.y parser.

# shareable_constant_value: experimental_everything
C = { **{ k: v } }
p C

The following error message is output.

ruby 3.4.0dev (2024-12-06T03:32:20Z master 6ccaa37eb3) [arm64-darwin23]
-- raw disasm--------
   trace: 1
   0000 putspecialobject     1                                           (   2)
   0002 putobject            :k                                          (   2)
   0004 putself                                                          (   2)
   0005 opt_send_without_block <calldata:v, 0>                           (   2)
   0007 newhash              2                                           (   2)
   0009 newhash              2                                           (   2)
   0011 opt_send_without_block <calldata:make_shareable, 1>              (   2)
   0013 putspecialobject     3                                           (   2)
*  0015 setconstant          :C                                          (   2)
   trace: 1
   0017 putself                                                          (   3)
   0018 opt_getconstant_path [:C]                                        (   3)
   0020 opt_send_without_block <calldata:p, 1>                           (   3)
   0022 leave                                                            (   3)
---------------------
-e:2: argument stack underflow (-1)
-e: compile error (SyntaxError)

It does not occur in the following cases:

# shareable_constant_value: experimental_everything
C = { **{ k: v } }

C = { **{ k: v } }                           
p C

# shareable_constant_value: experimental_everything
{ **{ k: v } }
p C

# shareable_constant_value: experimental_everything
C = { **{ k: 1 } }
p C

This does not occur in Ruby 3.3:

❯ ruby --parser=parse.y -v -e '# shareable_constant_value: experimental_everything

C = { **{ foo: bar } }

p C'
ruby 3.3.6 (2024-11-05 revision 75015d4c1f) [arm64-darwin23]
-e:3:in `<main>': undefined local variable or method `bar' for main (NameError)

C = { **{ foo: bar } }
               ^^^

[tompng (tomoya ishida)]

I think the cause is same as https://bugs.ruby-lang.org/issues/20927