[ruby-core:120079] [Ruby master Bug#20916] Prism compiler should support ** in Ractor constant

Issue #20916 has been updated by kddnewton (Kevin Newton).


I'm fine supporting this, but I'm not sure what the behavior should be since the current compiler just segfaults. What is the behavior if the value being splatted isn't an empty hash?

----------------------------------------
Bug #20916: Prism compiler should support ** in Ractor constant
https://bugs.ruby-lang.org/issues/20916#change-110822

* Author: mame (Yusuke Endoh)
* Status: Open
* Assignee: prism
* ruby -v: ruby 3.4.0dev (2024-11-28T02:34:20Z avoid-uninitialize.. 79ae6e72c8) +PRISM [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
The Prism compiler raises an exception against the following code.

```
$ ./miniruby -e '# shareable_constant_value: experimental_everything
C = { **{ } }'
-e:2: Ractor constant writes do not support **
-e: node type  not implemented (NotImplementedError)
```

But the traditional compiler support it, and @ko1 said it should be supported.

Also, I feel that this error message `node type  not implemented` is a sign of a worse problem. Actually, valgrind reports `Conditional jump or move depends on uninitialised value(s)`against the Prism compiler. An assertion failure is also reported.

```
$ valgrind ./miniruby -e '# shareable_constant_value: experimental_everything
C = { **{ } }'
==49978== Memcheck, a memory error detector
==49978== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==49978== Using Valgrind-3.22.0 and LibVEX; rerun with -h for copyright info
==49978== Command: ./miniruby -e #\ shareable_constant_value:\ experimental_everything_C\ =\ {\ **{\ }\ }
==49978==
==49978== Warning: set address range perms: large range [0x64e0000, 0x1e4e0000) (defined)
-e:2: Ractor constant writes do not support **
==49978== Conditional jump or move depends on uninitialised value(s)
==49978==    at 0x4BB42A: pm_newline_list_line (pm_newline_list.c:63)
==49978==    by 0x1E718A: pm_compile_shareable_constant_value (prism_compile.c:5280)
==49978==    by 0x1E7243: pm_compile_shareable_constant_value (prism_compile.c:5318)
==49978==    by 0x1E8DC1: pm_compile_constant_write_node.isra.0 (prism_compile.c:5372)
==49978==    by 0x1DCB2F: pm_compile_node (prism_compile.c:9823)
==49978==    by 0x1DC9C8: pm_compile_node (prism_compile.c:9934)
==49978==    by 0x1F3AC9: pm_compile_scope_node.isra.0 (prism_compile.c:6603)
==49978==    by 0x1DA66A: pm_compile_node (prism_compile.c:9805)
==49978==    by 0x1F61A7: pm_iseq_compile_node (prism_compile.c:10109)
==49978==    by 0x2A5303: pm_iseq_new_with_opt_try (iseq.c:1027)
==49978==    by 0x23DFF2: rb_protect (eval.c:1033)
==49978==    by 0x2AB198: pm_iseq_new_with_opt (iseq.c:1080)
==49978==
miniruby: prism/util/pm_newline_list.c:63: pm_newline_list_line: Assertion `cursor >= list->start' failed.
==49978==
==49978== Process terminating with default action of signal 6 (SIGABRT)
==49978==    at 0x4AFAB1C: __pthread_kill_implementation (pthread_kill.c:44)
==49978==    by 0x4AFAB1C: __pthread_kill_internal (pthread_kill.c:78)
==49978==    by 0x4AFAB1C: pthread_kill@@GLIBC_2.34 (pthread_kill.c:89)
==49978==    by 0x4AA126D: raise (raise.c:26)
==49978==    by 0x4A848FE: abort (abort.c:79)
==49978==    by 0x4A8481A: __assert_fail_base.cold (assert.c:94)
==49978==    by 0x4A97506: __assert_fail (assert.c:103)
==49978==    by 0x4BB49B: pm_newline_list_line (pm_newline_list.c:63)
==49978==    by 0x1E718A: pm_compile_shareable_constant_value (prism_compile.c:5280)
==49978==    by 0x1E7243: pm_compile_shareable_constant_value (prism_compile.c:5318)
==49978==    by 0x1E8DC1: pm_compile_constant_write_node.isra.0 (prism_compile.c:5372)
==49978==    by 0x1DCB2F: pm_compile_node (prism_compile.c:9823)
==49978==    by 0x1DC9C8: pm_compile_node (prism_compile.c:9934)
==49978==    by 0x1F3AC9: pm_compile_scope_node.isra.0 (prism_compile.c:6603)
==49978==
==49978== HEAP SUMMARY:
==49978==     in use at exit: 2,645,494 bytes in 10,084 blocks
==49978==   total heap usage: 36,662 allocs, 26,578 frees, 6,066,537 bytes allocated
==49978==
==49978== LEAK SUMMARY:
==49978==    definitely lost: 0 bytes in 0 blocks
==49978==    indirectly lost: 0 bytes in 0 blocks
==49978==      possibly lost: 1,050,576 bytes in 4 blocks
==49978==    still reachable: 1,594,918 bytes in 10,080 blocks
==49978==         suppressed: 0 bytes in 0 blocks
==49978== Rerun with --leak-check=full to see details of leaked memory
==49978==
==49978== Use --track-origins=yes to see where uninitialised values come from
==49978== For lists of detected and suppressed errors, rerun with: -s
==49978== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Aborted (core dumped)
```



-- 
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