Fixed finding variables from `proc` in `binding.eval` failed

Previously the following code did not produce the expected results:
```ruby
bx = binding
block = bx.eval("a = 1; proc { a }")
bx.eval("a = 2")
p block.call  # Expect 2 but return 1 due to a bug
```

The previous implementation of `Binding#eval` evaluated the code and then merged the top layer variables.
This patch will parse and expand the variable space before making a call to `eval`.
This means that the call to `Binding#eval` will do the parsing twice.

In addition, the following changes will be made:
- Make `mrb_parser_foreach_top_variable()`, `mrb_binding_extract_proc()` and `mrb_binding_extract_env()` functions private global functions.
- Remove the `posthook` argument from `mrb_exec_irep()`.
  The `posthook` argument was introduced to implement the `binding` method.
  This patch is unnecessary because it uses a different implementation method.

ref #5362
fixed #5491

1 files changed, 8 insertions, 1 deletions

diff --git a/src/proc.c b/src/proc.c
index 2717cd610..1d5a4aa76 100644
--- a/src/proc.c
+++ b/src/proc.c
@@ -417,7 +417,14 @@ mrb_proc_merge_lvar(mrb_state *mrb, mrb_irep *irep, struct REnv *env, int num, c
   mrb_sym *destlv = (mrb_sym*)irep->lv + irep->nlocals - 1 /* self */;
   mrb_value *destst = env->stack + irep->nlocals;
   memmove(destlv, lv, sizeof(mrb_sym) * num);
-  memmove(destst, stack, sizeof(mrb_value) * num);
+  if (stack) {
+    memmove(destst, stack, sizeof(mrb_value) * num);
+  }
+  else {
+    for (int i = num; i > 0; i--, destst++) {
+      *destst = mrb_nil_value();
+    }
+  }
   irep->nlocals += num;
   irep->nregs = irep->nlocals;
   MRB_ENV_SET_LEN(env, irep->nlocals);