From: "mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date: 2023-03-07T14:31:21+00:00
Subject: [ruby-core:112719] [Ruby master Feature#19452] `Thread::Backtrace::Location` should have column information if possible.

Issue #19452 has been updated by mame (Yusuke Endoh).


@eregon Thank you for your comment.

Eregon (Benoit Daloze) wrote in #note-5:
> That would avoid the need to reparse, at the cost of having to store 2 extra uint32 "byte offsets" per call node.

I think there is a confusion of what the word "reparse" means here.

1. When CRuby compiles a AST to a bytecode, it copies just node_id and lineno to each instruction but discards the column information. (@ko1 is not willing to copy column information due to memory consumption concerns.) So `RubyVM::AST.of` needs to "reparse" the whole source code to recover the whole AST.
2. CRuby's `RubyVM::AST` does not keep the column information of the method name because it converts the name to a symbol. It needs to "reparse" (or "re-tokenize"?) the code to identify where the method name is.

Here I am talking about 1, which will not change even if YARP is introduced. If YARP's AST keeps the method name column information, 2 will be unnecessary, which is good.

> I like the proposed API because it's straightforward.
> I think it's also enough to identity which call it is, e.g. for `foo(1).bar(2).baz(3)`, i.e. it's always the rightmost call inside `first_column...last_columns`.
> But that's indeed not as clear or obvious as underlining the operator + method name alone.

This is somewhat a matter of taste, but since this is a user interface, I believe it is important to provide pinpoint information at a glance. So I think it is worthwhile to elaborate it, even if it is somewhat tedious.

----------------------------------------
Feature #19452: `Thread::Backtrace::Location` should have column information if possible.
https://bugs.ruby-lang.org/issues/19452#change-102175

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
I discussed this with @mame and it would be pretty useful if we could also get the column information from exception backtrace location, even if it was slow.

A POC:

```ruby
class Thread::Backtrace::Location
  if defined?(RubyVM::AbstractSyntaxTree)
    def first_column
      RubyVM::AbstractSyntaxTree.of(self, keep_script_lines: true).first_column
    end
  else
    def first_column
      raise NotImplementedError
    end
  end
end
```

It would be good to have a standard interface, so we follow the same interface as https://bugs.ruby-lang.org/issues/19451 and vice versa where it makes sense. I'll investigate it.



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