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, 7 insertions, 0 deletions

diff --git a/mrbgems/mruby-binding/test/binding.rb b/mrbgems/mruby-binding/test/binding.rb
index 7dd3fd1dd..296fb48d4 100644
--- a/mrbgems/mruby-binding/test/binding.rb
+++ b/mrbgems/mruby-binding/test/binding.rb
@@ -68,3 +68,10 @@ assert "Binding#eval with Binding.new via Method" do
 
   assert_true true
 end
+
+assert "access local variables into procs" do
+  bx = binding
+  block = bx.eval("a = 1; proc { a }")
+  bx.eval("a = 2")
+  assert_equal 2, block.call
+end