[Universal parser] Decouple IMEMO from rb_ast_t

This patch removes the `VALUE flags` member from the `rb_ast_t` structure making `rb_ast_t` no longer an IMEMO object.

## Background

We are trying to make the Ruby parser generated from parse.y a universal parser that can be used by other implementations such as mruby.
To achieve this, it is necessary to exclude VALUE and IMEMO from parse.y, AST, and NODE.

## Summary (file by file)

- `rubyparser.h`
  - Remove the `VALUE flags` member from `rb_ast_t`
- `ruby_parser.c` and `internal/ruby_parser.h`
  - Use TypedData_Make_Struct VALUE which wraps `rb_ast_t` `in ast_alloc()` so that GC can manage it
    - You can retrieve `rb_ast_t` from the VALUE by `rb_ruby_ast_data_get()`
  - Change the return type of `rb_parser_compile_XXXX()` functions from `rb_ast_t *` to `VALUE`
  - rb_ruby_ast_new() which internally `calls ast_alloc()` is to create VALUE vast outside ruby_parser.c
- `iseq.c` and `vm_core.h`
  - Amend the first parameter of `rb_iseq_new_XXXX()` functions from `rb_ast_body_t *` to `VALUE`
  - This keeps the VALUE of AST on the machine stack to prevent being removed by GC
- `ast.c`
  - Almost all change is replacement `rb_ast_t *ast` with `VALUE vast` (sorry for the big diff)
  - Fix `node_memsize()`
    - Now it includes `rb_ast_local_table_link`, `tokens` and script_lines
- `compile.c`, `load.c`, `node.c`, `parse.y`, `proc.c`, `ruby.c`, `template/prelude.c.tmpl`, `vm.c` and `vm_eval.c`
  - Follow-up due to the above changes
- `imemo.{c|h}`
  - If an object with `imemo_ast` appears, considers it a bug

Co-authored-by: Nobuyoshi Nakada <[email protected]>

1 files changed, 3 insertions, 4 deletions

diff --git a/imemo.c b/imemo.c
index 3ecee05652..1face1ce4e 100644
--- a/imemo.c
+++ b/imemo.c
@@ -130,7 +130,7 @@ rb_imemo_memsize(VALUE obj)
     size_t size = 0;
     switch (imemo_type(obj)) {
       case imemo_ast:
-        size += rb_ast_memsize((rb_ast_t *)obj);
+        rb_bug("imemo_ast is obsolete");
 
         break;
       case imemo_callcache:
@@ -273,7 +273,7 @@ rb_imemo_mark_and_move(VALUE obj, bool reference_updating)
 {
     switch (imemo_type(obj)) {
       case imemo_ast:
-        // TODO: Make AST decoupled from IMEMO
+        rb_bug("imemo_ast is obsolete");
 
         break;
       case imemo_callcache: {
@@ -513,8 +513,7 @@ rb_imemo_free(VALUE obj)
 {
     switch (imemo_type(obj)) {
       case imemo_ast:
-        rb_ast_free((rb_ast_t *)obj);
-        RB_DEBUG_COUNTER_INC(obj_imemo_ast);
+        rb_bug("imemo_ast is obsolete");
 
         break;
       case imemo_callcache: