Fix `super` from aliased methods to work correctly; fix #4718

We needed to preserve the original method name somewhere. We kept it in
the `env` structure pointed from aliased methods. #1457 and #1531 tried
to address this issue. But this patch is more memory efficient.

Limitation: this fix does not support `super` from methods defined by
`define_method`. This limitation may be addressed in the future, but
it's low priority.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/class.c b/src/class.c
index 82ad3cf0a..1b0a37d05 100644
--- a/src/class.c
+++ b/src/class.c
@@ -1741,6 +1741,25 @@ mrb_alias_method(mrb_state *mrb, struct RClass *c, mrb_sym a, mrb_sym b)
 {
   mrb_method_t m = mrb_method_search(mrb, c, b);
 
+  if (!MRB_METHOD_CFUNC_P(m)) {
+    struct RProc *p = MRB_METHOD_PROC(m);
+
+    if (MRB_PROC_ENV_P(p)) {
+      MRB_PROC_ENV(p)->mid = b;
+    }
+    else {
+      struct RClass *tc = MRB_PROC_TARGET_CLASS(p);
+      struct REnv *e = (struct REnv*)mrb_obj_alloc(mrb, MRB_TT_ENV, NULL);
+
+      e->mid = b;
+      if (tc) {
+        e->c = tc;
+        mrb_field_write_barrier(mrb, (struct RBasic*)e, (struct RBasic*)tc);
+      }
+      p->e.env = e;
+      p->flags |= MRB_PROC_ENVSET;
+    }
+  }
   mrb_define_method_raw(mrb, c, a, m);
 }