Fix constant name of `Ractor::IsolationError` message

`dest` of `const_decl_path` is `NODE_COLON2` or `NODE_COLON3` in some cases.
For example, `B::C ||= [“Not ” + “shareable”]` passes `NODE_COLON2`
and `::C ||= [“Not ” + “shareable”]` passes `NODE_COLON3`.
This commit fixes `Ractor::IsolationError` message for such case.

```
# shareable_constant_value: literal
::C ||= ["Not " + "shareable"]

# Before
# => cannot assign unshareable object to C (Ractor::IsolationError)

# After
# => cannot assign unshareable object to ::C (Ractor::IsolationError)
```

1 files changed, 31 insertions, 12 deletions

diff --git a/ruby_parser.c b/ruby_parser.c
index c48f563744..7061f2be5b 100644
--- a/ruby_parser.c
+++ b/ruby_parser.c
@@ -1045,22 +1045,40 @@ VALUE
 rb_node_const_decl_val(const NODE *node)
 {
     VALUE path;
-    if (RNODE_CDECL(node)->nd_vid) {
-        path = rb_id2str(RNODE_CDECL(node)->nd_vid);
+    switch (nd_type(node)) {
+      case NODE_CDECL:
+        if (RNODE_CDECL(node)->nd_vid) {
+            path = rb_id2str(RNODE_CDECL(node)->nd_vid);
+            goto end;
+        }
+        else {
+            node = RNODE_CDECL(node)->nd_else;
+        }
+        break;
+      case NODE_COLON2:
+        break;
+      case NODE_COLON3:
+        // ::Const
+        path = rb_str_new_cstr("::");
+        rb_str_append(path, rb_id2str(RNODE_COLON3(node)->nd_mid));
+        goto end;
+      default:
+        rb_bug("unexpected node: %s", ruby_node_name(nd_type(node)));
+        UNREACHABLE_RETURN(0);
     }
-    else {
-        NODE *n = RNODE_CDECL(node)->nd_else;
-        path = rb_ary_new();
-        for (; n && nd_type_p(n, NODE_COLON2); n = RNODE_COLON2(n)->nd_head) {
-            rb_ary_push(path, rb_id2str(RNODE_COLON2(n)->nd_mid));
+
+    path = rb_ary_new();
+    if (node) {
+        for (; node && nd_type_p(node, NODE_COLON2); node = RNODE_COLON2(node)->nd_head) {
+            rb_ary_push(path, rb_id2str(RNODE_COLON2(node)->nd_mid));
         }
-        if (n && nd_type_p(n, NODE_CONST)) {
+        if (node && nd_type_p(node, NODE_CONST)) {
             // Const::Name
-            rb_ary_push(path, rb_id2str(RNODE_CONST(n)->nd_vid));
+            rb_ary_push(path, rb_id2str(RNODE_CONST(node)->nd_vid));
         }
-        else if (n && nd_type_p(n, NODE_COLON3)) {
+        else if (node && nd_type_p(node, NODE_COLON3)) {
             // ::Const::Name
-            rb_ary_push(path, rb_id2str(RNODE_COLON3(n)->nd_mid));
+            rb_ary_push(path, rb_id2str(RNODE_COLON3(node)->nd_mid));
             rb_ary_push(path, rb_str_new(0, 0));
         }
         else {
@@ -1068,7 +1086,8 @@ rb_node_const_decl_val(const NODE *node)
             rb_ary_push(path, rb_str_new_cstr("..."));
         }
         path = rb_ary_join(rb_ary_reverse(path), rb_str_new_cstr("::"));
-        path = rb_fstring(path);
     }
+  end:
+    path = rb_fstring(path);
     return path;
 }