[ruby-core:71648] [Ruby trunk - Feature #11181] Add a line directive to Ruby

Issue #11181 has been updated by Martin D端rst.

Assignee changed from ruby-core to Yukihiro Matsumoto

I have changed the assignee from ruby-core (all committers) to Matz to make sure this doesn't show up in everybody's todo list.

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Feature #11181: Add a line directive to Ruby
https://bugs.ruby-lang.org/issues/11181#change-55051

* Author: Allen Morris
* Status: Open
* Priority: Normal
* Assignee: Yukihiro Matsumoto
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Add a __line directive__ to Ruby

```
  #line {nn} ["filename"]
```

This is done by creating a array of filenames and using the upper bits of the line_number to determine the current filename.  The original filename is in position 0.

An extra node is added by the parser that informs the compiler of the filenames so the backtrace code can also use the correct file names.

The __\_\_LINE____ and __\_\_FILE____ _constants_ are updated and compile time warnings are also effected.

There is a pull request at https://github.com/ruby/ruby/pull/911

The patch does not have any affect on current programs unless a line matching '#\s*line \d+(\s+"(.*)")?\s*$' is found in the ruby source code. 


More tests need to be written before this change sould be applied.

Use case:

This is helpful for debugging any generated code but is particularlly helpful for literate programming using Noweb.



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