Separate SCRIPT_LINES__ from ast.c

This patch suggests relocating the code dealing with `SCRIPT_LINES__` from ast.c to ruby_parser.c.

## Background

- I guess `AbstractSyntaxTree.of` method used to use `SCRIPT_LINES__` internally for some reason before
- However, now it appears `SCRIPT_LINES__` is no longer used meaningfully by the method
- As evidence of this, (and as my patch shows,) removing the function call of `rb_script_lines_for()` from `ast_s_of()` does not affect the result of `test/ruby/test_ast.rb`

Given the above, I think two possibilities can be considered:

- (A) `AbstractSyntaxTree.of` has not needed `SCRIPT_LINES__` already (I pick this)
- (B) We lack a test case of `AbstractSyntaxTree.of` that needs to use `SCRIPT_LINES__`

## Besides,

The current implementation causes strange behavior:

```console
ruby -e"SCRIPT_LINES__ = {__FILE__ => []}; puts RubyVM::AbstractSyntaxTree.of(->{ 1 + 2 }, keep_script_lines: true).script_lines"
=> `-e:1:in '<main>': undefined method 'script_lines' for nil (NoMethodError)`
```

I think this is a bug because `AbstractSyntaxTree.of` is not supposed to return `nil` even in this case.
This happens due to the ast.c's dependence on `SCRIPT_LINES__`.
And at the end of the `ast_s_of()`, `node_find()` can not find the target child node obviously because it doesn't make sense to look for a corresponding node made from the parameter of `AbstractSyntaxTree.of` in the AST tree made from the value of `{__FILE__ => []}`

## Solution

Since I think it's good enough `SCRIPT_LINES__` to be only referred by ruby.c, I chose the possibility "(A)" and wrote this patch which moves `rb_script_lines_for()` from ast.c to ruby_parser.c.

So as the result:

- `ast_s_of()` function no longer look up `SCRIPT_LINES__`
- Even so, this patched code passes the existing tests
- The strange behavior above no longer happens (I also added a test for it)

Please correct me if I miss something🙏

1 files changed, 13 insertions, 0 deletions

diff --git a/test/ruby/test_ast.rb b/test/ruby/test_ast.rb
index d19bda118f..90d19c3d68 100644
--- a/test/ruby/test_ast.rb
+++ b/test/ruby/test_ast.rb
@@ -746,6 +746,19 @@ dummy
     assert_equal("def test_keep_script_lines_for_of\n", node_method.source.lines.first)
   end
 
+  def test_keep_script_lines_for_of_with_existing_SCRIPT_LINES__that_has__FILE__as_a_key
+    # This test confirms that the bug that previously occurred because of
+    # `AbstractSyntaxTree.of`s unnecessary dependence on SCRIPT_LINES__ does not reproduce.
+    # The bug occurred only if SCRIPT_LINES__ included __FILE__ as a key.
+    lines = [
+      "SCRIPT_LINES__ = {__FILE__ => []}",
+      "puts RubyVM::AbstractSyntaxTree.of(->{ 1 + 2 }, keep_script_lines: true).script_lines",
+      "p SCRIPT_LINES__"
+    ]
+    test_stdout = lines + ['{"-e"=>[]}']
+    assert_in_out_err(["-e", lines.join("\n")], "", test_stdout, [])
+  end
+
   def test_source_with_multibyte_characters
     ast = RubyVM::AbstractSyntaxTree.parse(%{a("\u00a7");b("\u00a9")}, keep_script_lines: true)
     a_fcall, b_fcall = ast.children[2].children