This reverts commit 7adf89d7ad30552d7e57709d24eec266f601d38b.

	[PRISM] Handle forwarding inside eval

	Fixes [Bug #21031]

	[Bug #20992] Test for local variable name encodings

	Do not intern invalid symbols in eval parse

	When the inner code cannot represent the name of the locals in the
	outer code, do not bother putting them into the constant pool as
	they will not be referenced.

	Fixes [Bug #20992]

	Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

We need to GC guard the iseq because the code above it malloc memory which
could trigger a GC. Since we only use ISEQ_BODY, the compiler may optimize
out the iseq local variable so we need to GC guard it.

Fixes: http://ci.rvm.jp/results/trunk_asan@ruby-sp1/5484752

If we have local variables outside of the eval, the local variables names
are IDs. We convert these IDs to char * using rb_id2name. However, these
char * are actually Ruby strings, which may be embedded. This means that
it is not safe to rb_id2name and call any potential GC entrypoints because
if a GC compaction runs, the embedded string may move and the pointer will
change.

For example, if you compile with `-DRGENGC_CHECK_MODE=1`, then the following
script will crash:

    GC.auto_compact = :empty
    GC.stress = true

    o = Object.new

    eval("def o.m(k: 0) k end")

The crash message is:

    test.rb:6: [BUG] Local with constant_id 1 does not exist
    ruby 3.4.0dev (2024-12-17T18:34:57Z prism-local-compac.. 434346726c) +PRISM [arm64-darwin24]

    -- C level backtrace information -------------------------------------------
    miniruby(rb_print_backtrace+0x24) [0x10312fec4] vm_dump.c:823
    miniruby(rb_print_backtrace) (null):0
    miniruby(rb_vm_bugreport+0x2d4) [0x1031301b8] vm_dump.c:1155
    miniruby(rb_bug_without_die_internal+0xa8) [0x102dd6a94] error.c:1097
    miniruby(rb_bug+0x28) [0x102dd6b00] error.c:1115
    miniruby(pm_lookup_local_index+0xec) [0x102d61e4c] prism_compile.c:1237
    miniruby(pm_compile_node+0x45d0) [0x102d252f4] prism_compile.c:9334
    miniruby(pm_compile_node+0x1864) [0x102d22588] prism_compile.c:8650
    miniruby(pm_compile_node+0x65ec) [0x102d27310] prism_compile.c:9897
    miniruby(pm_compile_scope_node+0x3008) [0x102d77bcc] prism_compile.c:6584
    miniruby(pm_compile_node+0x5ec4) [0x102d26be8] prism_compile.c:9768
    miniruby(pm_iseq_compile_node+0xac) [0x102d20bf0] prism_compile.c:10069
    miniruby(pm_iseq_new_with_opt_try+0x2c) [0x102e7d088] iseq.c:1029
    miniruby(rb_protect+0x108) [0x102dea9bc] eval.c:1033
    miniruby(pm_iseq_new_with_opt+0x264) [0x102e7c444] iseq.c:1082
    miniruby(pm_iseq_new_eval+0xec) [0x102e7c8e0] iseq.c:961
    miniruby(pm_eval_make_iseq+0x594) [0x1031209cc] vm_eval.c:1770
    miniruby(eval_make_iseq+0x54) [0x103120068] vm_eval.c:1799

We've already computed the length of the string, so we can reuse it.

If there's a syntax error during iseq compilation then prism would leak
memory because it would not free the pm_parse_result_t.

This commit changes pm_iseq_new_with_opt to have a rb_protect to catch
when an error is raised, and return NULL and set error_state to a value
that can be raised by calling rb_jump_tag after memory has been freed.

For example:

    10.times do
      10_000.times do
        eval("/[/=~s")
      rescue SyntaxError
      end

      puts `ps -o rss= -p #{$$}`
    end

Before:

    39280
    68736
    99232
    128864
    158896
    188208
    217344
    246304
    275376
    304592

After:

    12192
    13200
    14256
    14848
    16000
    16000
    16000
    16064
    17232
    17952

Fixes [Bug #20856]

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

* Remove 1 allocation in Enumerable#each_with_index

Previously, each call to Enumerable#each_with_index allocates 2
objects, one for the counting index, the other an imemo_ifunc passed
to `self.each` as a block.

Use `struct vm_ifunc::data` to hold the counting index directly to
remove 1 allocation.

* [DOC] Brief summary for usages of `struct vm_ifunc`