[ruby-core:68021] [ruby-trunk - Bug #10561] Improve function of Thread::Backtrace::Location #path and #absolute_path

Issue #10561 has been updated by Benoit Daloze.


Nobuyoshi Nakada wrote:
> The result of `#path` equals to `__FILE__` in the script file.
> It's expanded in `require`d libraries, but not in main scripts.

There is only one main script (the file passed to the ruby executable) in a given execution, right?

Yorick: so #path is #absolute_path except for the main script, so it is similar to the formatting of usual exceptions backtraces:

    $ echo "raise" > tmp.rb
    $ ruby tmp.rb 
    tmp.rb:1:in `<main>': unhandled exception

Here tmp.rb is main script.

    $ echo "require_relative 'tmp'" > tmp2.rb
    $ ruby tmp2.rb    
    /home/eregon/code/tmp.rb:1:in `<top (required)>': unhandled exception
	from tmp2.rb:1:in `require_relative'
	from tmp2.rb:1:in `<main>'

Here tmp2.rb is the main script but tmp.rb becomes a "required library" so full path is shown.

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Bug #10561: Improve function of Thread::Backtrace::Location #path and #absolute_path
https://bugs.ruby-lang.org/issues/10561#change-51408

* Author: Sam Saffron
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: 2.2.0
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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I was working on this issue in Rails and hit an area where Backtrace Location can be improved

https://github.com/rails/rails/pull/17782


1. It is undefined in the documentation how #absolute_path should operate when #path is invalid (in case of instance eval)
2. There are a few conditions where #path and #absolute_path can return nil, this forces extra protection code when parsing paths to check for nil. (for example getting filename)  

Suggestions:

1. Instead of returning Qnil from location_path and location_absolute_path on invalid conditions, return the string "(unknown)" which is easier to parse and sticks out better in a big backtrace. There is precedent here with the string "(eval)"
2. If path is invalid have absolute_path return "(unknown)", define that in the documentation
3. (possible) add an additional method on caller_location called #filename so people stop parsing filename from #path and #absolute_path
4. Evaluate if it makes sense to have #path and #absolute_path in the API as both methods can return full paths so the semantic difference is subtle. 



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