Make `RubyVM::AST.of` return a parent node of NODE_SCOPE

This change makes `RubyVM::AST.of` and `.node_id_for_backtrace_location`
return a parent node of NODE_SCOPE (such as NODE_DEFN) instead of the
NODE_SCOPE node itself.
(In future, we may remove NODE_SCOPE, which is a bit hacky AST node.)

This is preparation for [Feature #21543].

6 files changed, 47 insertions, 23 deletions

diff --git a/compile.c b/compile.c
index 92c5d6dc9e..0ef0d1b31a 100644
--- a/compile.c
+++ b/compile.c
@@ -9221,6 +9221,7 @@ compile_builtin_mandatory_only_method(rb_iseq_t *iseq, const NODE *node, const N
     rb_node_init(RNODE(&scope_node), NODE_SCOPE);
     scope_node.nd_tbl = tbl;
     scope_node.nd_body = mandatory_node(iseq, node);
+    scope_node.nd_parent = NULL;
     scope_node.nd_args = &args_node;
 
     VALUE ast_value = rb_ruby_ast_new(RNODE(&scope_node));
diff --git a/iseq.c b/iseq.c
index ac59429901..33b37bade5 100644
--- a/iseq.c
+++ b/iseq.c
@@ -634,6 +634,18 @@ new_arena(void)
     return new_arena;
 }
 
+static int
+prepare_node_id(const NODE *node)
+{
+    if (!node) return -1;
+
+    if (nd_type(node) == NODE_SCOPE && RNODE_SCOPE(node)->nd_parent) {
+        return nd_node_id(RNODE_SCOPE(node)->nd_parent);
+    }
+
+    return nd_node_id(node);
+}
+
 static VALUE
 prepare_iseq_build(rb_iseq_t *iseq,
                    VALUE name, VALUE path, VALUE realpath, int first_lineno, const rb_code_location_t *code_location, const int node_id,
@@ -1031,7 +1043,7 @@ rb_iseq_new_with_opt(VALUE ast_value, VALUE name, VALUE path, VALUE realpath,
         script_lines = ISEQ_BODY(parent)->variable.script_lines;
     }
 
-    prepare_iseq_build(iseq, name, path, realpath, first_lineno, node ? &node->nd_loc : NULL, node ? nd_node_id(node) : -1,
+    prepare_iseq_build(iseq, name, path, realpath, first_lineno, node ? &node->nd_loc : NULL, prepare_node_id(node),
                        parent, isolated_depth, type, script_lines, option);
 
     rb_iseq_compile_node(iseq, node);
diff --git a/parse.y b/parse.y
index c0f46a395f..765b4bdfd0 100644
--- a/parse.y
+++ b/parse.y
@@ -1061,8 +1061,8 @@ rb_discard_node(struct parser_params *p, NODE *n)
     rb_ast_delete_node(p->ast, n);
 }
 
-static rb_node_scope_t *rb_node_scope_new(struct parser_params *p, rb_node_args_t *nd_args, NODE *nd_body, const YYLTYPE *loc);
-static rb_node_scope_t *rb_node_scope_new2(struct parser_params *p, rb_ast_id_table_t *nd_tbl, rb_node_args_t *nd_args, NODE *nd_body, const YYLTYPE *loc);
+static rb_node_scope_t *rb_node_scope_new(struct parser_params *p, rb_node_args_t *nd_args, NODE *nd_body, NODE *nd_parent, const YYLTYPE *loc);
+static rb_node_scope_t *rb_node_scope_new2(struct parser_params *p, rb_ast_id_table_t *nd_tbl, rb_node_args_t *nd_args, NODE *nd_body, NODE *nd_parent, const YYLTYPE *loc);
 static rb_node_block_t *rb_node_block_new(struct parser_params *p, NODE *nd_head, const YYLTYPE *loc);
 static rb_node_if_t *rb_node_if_new(struct parser_params *p, NODE *nd_cond, NODE *nd_body, NODE *nd_else, const YYLTYPE *loc, const YYLTYPE* if_keyword_loc, const YYLTYPE* then_keyword_loc, const YYLTYPE* end_keyword_loc);
 static rb_node_unless_t *rb_node_unless_new(struct parser_params *p, NODE *nd_cond, NODE *nd_body, NODE *nd_else, const YYLTYPE *loc, const YYLTYPE *keyword_loc, const YYLTYPE *then_keyword_loc, const YYLTYPE *end_keyword_loc);
@@ -1169,8 +1169,8 @@ static rb_node_line_t *rb_node_line_new(struct parser_params *p, const YYLTYPE *
 static rb_node_file_t *rb_node_file_new(struct parser_params *p, VALUE str, const YYLTYPE *loc);
 static rb_node_error_t *rb_node_error_new(struct parser_params *p, const YYLTYPE *loc);
 
-#define NEW_SCOPE(a,b,loc) (NODE *)rb_node_scope_new(p,a,b,loc)
-#define NEW_SCOPE2(t,a,b,loc) (NODE *)rb_node_scope_new2(p,t,a,b,loc)
+#define NEW_SCOPE(a,b,c,loc) (NODE *)rb_node_scope_new(p,a,b,c,loc)
+#define NEW_SCOPE2(t,a,b,c,loc) (NODE *)rb_node_scope_new2(p,t,a,b,c,loc)
 #define NEW_BLOCK(a,loc) (NODE *)rb_node_block_new(p,a,loc)
 #define NEW_IF(c,t,e,loc,ik_loc,tk_loc,ek_loc) (NODE *)rb_node_if_new(p,c,t,e,loc,ik_loc,tk_loc,ek_loc)
 #define NEW_UNLESS(c,t,e,loc,k_loc,t_loc,e_loc) (NODE *)rb_node_unless_new(p,c,t,e,loc,k_loc,t_loc,e_loc)
@@ -1634,11 +1634,11 @@ aryptn_pre_args(struct parser_params *p, VALUE pre_arg, VALUE pre_args)
 #define KWD2EID(t, v) keyword_##t
 
 static NODE *
-new_scope_body(struct parser_params *p, rb_node_args_t *args, NODE *body, const YYLTYPE *loc)
+new_scope_body(struct parser_params *p, rb_node_args_t *args, NODE *body, NODE *parent, const YYLTYPE *loc)
 {
     body = remove_begin(body);
     reduce_nodes(p, &body);
-    NODE *n = NEW_SCOPE(args, body, loc);
+    NODE *n = NEW_SCOPE(args, body, parent, loc);
     nd_set_line(n, loc->end_pos.lineno);
     set_line_body(body, loc->beg_pos.lineno);
     return n;
@@ -2949,8 +2949,8 @@ rb_parser_ary_free(rb_parser_t *p, rb_parser_ary_t *ary)
                     {
                         endless_method_name(p, $head->nd_mid, &@head);
                         restore_defun(p, $head);
-                        $bodystmt = new_scope_body(p, $args, $bodystmt, &@$);
                         ($$ = $head->nd_def)->nd_loc = @$;
+                        $bodystmt = new_scope_body(p, $args, $bodystmt, $$, &@$);
                         RNODE_DEFN($$)->nd_defn = $bodystmt;
                     /*% ripper: bodystmt!($:bodystmt, Qnil, Qnil, Qnil) %*/
                     /*% ripper: def!($:head, $:args, $:$) %*/
@@ -2960,8 +2960,8 @@ rb_parser_ary_free(rb_parser_t *p, rb_parser_ary_t *ary)
                     {
                         endless_method_name(p, $head->nd_mid, &@head);
                         restore_defun(p, $head);
-                        $bodystmt = new_scope_body(p, $args, $bodystmt, &@$);
                         ($$ = $head->nd_def)->nd_loc = @$;
+                        $bodystmt = new_scope_body(p, $args, $bodystmt, $$, &@$);
                         RNODE_DEFS($$)->nd_defn = $bodystmt;
                     /*% ripper: bodystmt!($:bodystmt, Qnil, Qnil, Qnil) %*/
                     /*% ripper: defs!(*$:head[0..2], $:args, $:$) %*/
@@ -3176,7 +3176,7 @@ program		:  {
                             node = remove_begin(node);
                             void_expr(p, node);
                         }
-                        p->eval_tree = NEW_SCOPE(0, block_append(p, p->eval_tree, $2), &@$);
+                        p->eval_tree = NEW_SCOPE(0, block_append(p, p->eval_tree, $2), NULL, &@$);
                     /*% ripper[final]: program!($:2) %*/
                         local_pop(p);
                     }
@@ -3375,8 +3375,9 @@ stmt		: keyword_alias fitem {SET_LEX_STATE(EXPR_FNAME|EXPR_FITEM);} fitem
                         restore_block_exit(p, $allow_exits);
                         p->ctxt = $k_END;
                         {
-                            NODE *scope = NEW_SCOPE2(0 /* tbl */, 0 /* args */, $compstmt /* body */, &@$);
+                            NODE *scope = NEW_SCOPE2(0 /* tbl */, 0 /* args */, $compstmt /* body */, NULL /* parent */, &@$);
                             $$ = NEW_POSTEXE(scope, &@$, &@1, &@3, &@5);
+                            RNODE_SCOPE(scope)->nd_parent = $$;
                         }
                     /*% ripper: END!($:compstmt) %*/
                     }
@@ -4567,9 +4568,10 @@ primary		: inline_primary
                     }
                     /* {|*internal_id| <m> = internal_id; ... } */
                     args = new_args(p, m, 0, id, 0, new_args_tail(p, 0, 0, 0, &@for_var), &@for_var);
-                    scope = NEW_SCOPE2(tbl, args, $compstmt, &@$);
+                    scope = NEW_SCOPE2(tbl, args, $compstmt, NULL, &@$);
                     YYLTYPE do_keyword_loc = $do == keyword_do_cond ? @do : NULL_LOC;
                     $$ = NEW_FOR($5, scope, &@$, &@k_for, &@keyword_in, &do_keyword_loc, &@k_end);
+                    RNODE_SCOPE(scope)->nd_parent = $$;
                     fixpos($$, $for_var);
                 /*% ripper: for!($:for_var, $:expr_value, $:compstmt) %*/
                 }
@@ -4640,8 +4642,8 @@ primary		: inline_primary
               k_end
                 {
                     restore_defun(p, $head);
-                    $bodystmt = new_scope_body(p, $args, $bodystmt, &@$);
                     ($$ = $head->nd_def)->nd_loc = @$;
+                    $bodystmt = new_scope_body(p, $args, $bodystmt, $$, &@$);
                     RNODE_DEFN($$)->nd_defn = $bodystmt;
                 /*% ripper: def!($:head, $:args, $:bodystmt) %*/
                     local_pop(p);
@@ -4655,8 +4657,8 @@ primary		: inline_primary
               k_end
                 {
                     restore_defun(p, $head);
-                    $bodystmt = new_scope_body(p, $args, $bodystmt, &@$);
                     ($$ = $head->nd_def)->nd_loc = @$;
+                    $bodystmt = new_scope_body(p, $args, $bodystmt, $$, &@$);
                     RNODE_DEFS($$)->nd_defn = $bodystmt;
                 /*% ripper: defs!(*$:head[0..2], $:args, $:bodystmt) %*/
                     local_pop(p);
@@ -11208,24 +11210,26 @@ node_newnode(struct parser_params *p, enum node_type type, size_t size, size_t a
 #define NODE_NEWNODE(node_type, type, loc) (type *)(node_newnode(p, node_type, sizeof(type), RUBY_ALIGNOF(type), loc))
 
 static rb_node_scope_t *
-rb_node_scope_new(struct parser_params *p, rb_node_args_t *nd_args, NODE *nd_body, const YYLTYPE *loc)
+rb_node_scope_new(struct parser_params *p, rb_node_args_t *nd_args, NODE *nd_body, NODE *nd_parent, const YYLTYPE *loc)
 {
     rb_ast_id_table_t *nd_tbl;
     nd_tbl = local_tbl(p);
     rb_node_scope_t *n = NODE_NEWNODE(NODE_SCOPE, rb_node_scope_t, loc);
     n->nd_tbl = nd_tbl;
     n->nd_body = nd_body;
+    n->nd_parent = nd_parent;
     n->nd_args = nd_args;
 
     return n;
 }
 
 static rb_node_scope_t *
-rb_node_scope_new2(struct parser_params *p, rb_ast_id_table_t *nd_tbl, rb_node_args_t *nd_args, NODE *nd_body, const YYLTYPE *loc)
+rb_node_scope_new2(struct parser_params *p, rb_ast_id_table_t *nd_tbl, rb_node_args_t *nd_args, NODE *nd_body, NODE *nd_parent, const YYLTYPE *loc)
 {
     rb_node_scope_t *n = NODE_NEWNODE(NODE_SCOPE, rb_node_scope_t, loc);
     n->nd_tbl = nd_tbl;
     n->nd_body = nd_body;
+    n->nd_parent = nd_parent;
     n->nd_args = nd_args;
 
     return n;
@@ -11413,8 +11417,9 @@ static rb_node_class_t *
 rb_node_class_new(struct parser_params *p, NODE *nd_cpath, NODE *nd_body, NODE *nd_super, const YYLTYPE *loc, const YYLTYPE *class_keyword_loc, const YYLTYPE *inheritance_operator_loc, const YYLTYPE *end_keyword_loc)
 {
     /* Keep the order of node creation */
-    NODE *scope = NEW_SCOPE(0, nd_body, loc);
+    NODE *scope = NEW_SCOPE(0, nd_body, NULL, loc);
     rb_node_class_t *n = NODE_NEWNODE(NODE_CLASS, rb_node_class_t, loc);
+    RNODE_SCOPE(scope)->nd_parent = &n->node;
     n->nd_cpath = nd_cpath;
     n->nd_body = scope;
     n->nd_super = nd_super;
@@ -11429,8 +11434,9 @@ static rb_node_sclass_t *
 rb_node_sclass_new(struct parser_params *p, NODE *nd_recv, NODE *nd_body, const YYLTYPE *loc)
 {
     /* Keep the order of node creation */
-    NODE *scope = NEW_SCOPE(0, nd_body, loc);
+    NODE *scope = NEW_SCOPE(0, nd_body, NULL, loc);
     rb_node_sclass_t *n = NODE_NEWNODE(NODE_SCLASS, rb_node_sclass_t, loc);
+    RNODE_SCOPE(scope)->nd_parent = &n->node;
     n->nd_recv = nd_recv;
     n->nd_body = scope;
 
@@ -11441,8 +11447,9 @@ static rb_node_module_t *
 rb_node_module_new(struct parser_params *p, NODE *nd_cpath, NODE *nd_body, const YYLTYPE *loc, const YYLTYPE *module_keyword_loc, const YYLTYPE *end_keyword_loc)
 {
     /* Keep the order of node creation */
-    NODE *scope = NEW_SCOPE(0, nd_body, loc);
+    NODE *scope = NEW_SCOPE(0, nd_body, NULL, loc);
     rb_node_module_t *n = NODE_NEWNODE(NODE_MODULE, rb_node_module_t, loc);
+    RNODE_SCOPE(scope)->nd_parent = &n->node;
     n->nd_cpath = nd_cpath;
     n->nd_body = scope;
     n->module_keyword_loc = *module_keyword_loc;
@@ -11455,8 +11462,9 @@ static rb_node_iter_t *
 rb_node_iter_new(struct parser_params *p, rb_node_args_t *nd_args, NODE *nd_body, const YYLTYPE *loc)
 {
     /* Keep the order of node creation */
-    NODE *scope = NEW_SCOPE(nd_args, nd_body, loc);
+    NODE *scope = NEW_SCOPE(nd_args, nd_body, NULL, loc);
     rb_node_iter_t *n = NODE_NEWNODE(NODE_ITER, rb_node_iter_t, loc);
+    RNODE_SCOPE(scope)->nd_parent = &n->node;
     n->nd_body = scope;
     n->nd_iter = 0;
 
@@ -11467,9 +11475,10 @@ static rb_node_lambda_t *
 rb_node_lambda_new(struct parser_params *p, rb_node_args_t *nd_args, NODE *nd_body, const YYLTYPE *loc, const YYLTYPE *operator_loc, const YYLTYPE *opening_loc, const YYLTYPE *closing_loc)
 {
     /* Keep the order of node creation */
-    NODE *scope = NEW_SCOPE(nd_args, nd_body, loc);
+    NODE *scope = NEW_SCOPE(nd_args, nd_body, NULL, loc);
     YYLTYPE lambda_loc = code_loc_gen(operator_loc, closing_loc);
     rb_node_lambda_t *n = NODE_NEWNODE(NODE_LAMBDA, rb_node_lambda_t, &lambda_loc);
+    RNODE_SCOPE(scope)->nd_parent = &n->node;
     n->nd_body = scope;
     n->operator_loc = *operator_loc;
     n->opening_loc = *opening_loc;
diff --git a/rubyparser.h b/rubyparser.h
index cc63efd3f8..4ab2480b7d 100644
--- a/rubyparser.h
+++ b/rubyparser.h
@@ -248,6 +248,7 @@ typedef struct RNode_SCOPE {
 
     rb_ast_id_table_t *nd_tbl;
     struct RNode *nd_body;
+    struct RNode *nd_parent;
     struct RNode_ARGS *nd_args;
 } rb_node_scope_t;
 
diff --git a/test/ruby/test_ast.rb b/test/ruby/test_ast.rb
index 9a7d75c270..f5c4b8d6b9 100644
--- a/test/ruby/test_ast.rb
+++ b/test/ruby/test_ast.rb
@@ -801,7 +801,7 @@ dummy
     node_proc = RubyVM::AbstractSyntaxTree.of(proc, keep_script_lines: true)
     node_method = RubyVM::AbstractSyntaxTree.of(method, keep_script_lines: true)
 
-    assert_equal("{ 1 + 2 }", node_proc.source)
+    assert_equal("Proc.new { 1 + 2 }", node_proc.source)
     assert_equal("def test_keep_script_lines_for_of\n", node_method.source.lines.first)
   end
 
@@ -878,7 +878,7 @@ dummy
     omit if ParserSupport.prism_enabled? || ParserSupport.prism_enabled_in_subprocess?
 
     assert_in_out_err(["-e", "def foo; end; pp RubyVM::AbstractSyntaxTree.of(method(:foo)).type"],
-                      "", [":SCOPE"], [])
+                      "", [":DEFN"], [])
   end
 
   def test_error_tolerant
diff --git a/vm.c b/vm.c
index 479b3be94f..60c26cf018 100644
--- a/vm.c
+++ b/vm.c
@@ -1541,6 +1541,7 @@ rb_binding_add_dynavars(VALUE bindval, rb_binding_t *bind, int dyncount, const I
     rb_node_init(RNODE(&tmp_node), NODE_SCOPE);
     tmp_node.nd_tbl = dyns;
     tmp_node.nd_body = 0;
+    tmp_node.nd_parent = NULL;
     tmp_node.nd_args = 0;
 
     VALUE ast_value = rb_ruby_ast_new(RNODE(&tmp_node));