[ruby/prism] Convert start line to signed integers

Ruby allows for 0 or negative line start, this is often used
with `eval` calls to get a correct offset when prefixing a snippet.

e.g.

```ruby
caller = caller_locations(1, 1).first
class_eval <<~RUBY, caller.path, caller.line - 2
  # frozen_string_literal: true
  def some_method
    #{caller_provided_code_snippet}
  end
RUBY
```

https://github.com/ruby/prism/commit/0d14ed1452

1 files changed, 16 insertions, 0 deletions

diff --git a/test/prism/parse_test.rb b/test/prism/parse_test.rb
index 6bd7a5d2a1..2feb15b48b 100644
--- a/test/prism/parse_test.rb
+++ b/test/prism/parse_test.rb
@@ -46,6 +46,22 @@ module Prism
       assert_equal filepath, find_source_file_node(result.value).filepath
     end
 
+    def test_parse_takes_line
+      line = 4
+      result = Prism.parse("def foo\n __FILE__\nend", line: line)
+
+      assert_equal line, result.value.location.start_line
+      assert_equal line + 1, find_source_file_node(result.value).location.start_line
+    end
+
+    def test_parse_takes_negative_lines
+      line = -2
+      result = Prism.parse("def foo\n __FILE__\nend", line: line)
+
+      assert_equal line, result.value.location.start_line
+      assert_equal line + 1, find_source_file_node(result.value).location.start_line
+    end
+
     def test_parse_lex
       node, tokens = Prism.parse_lex("def foo; end").value