From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2024-04-17T18:54:03+00:00
Subject: [ruby-core:117574] [Ruby master Feature#20335] `Thread.each_caller_location` should accept the same arguments as `caller` and `caller_locations`

Issue #20335 has been updated by Eregon (Benoit Daloze).


@byroot It's both, but for TruffleRuby I'm pretty sure the first matters much more.
These few allocations are no big deal on the JVM, so I would expect similar on JRuby.
Walking the stack is also obviously slower with a deeper stack (e.g. Rails), while the object allocations are pretty obvious and simply the number of times the block yielded before the user `break`s/`return`s.

I also don't see any valid use case for `Thread.each_caller_location` with a Range with negative begin or end, so that's why I think it's better to prevent it altogether instead of making it a performance trap (i.e. it's `O(stack depth)` instead of the expected `O(number of locations yielded)`).
(the only way to make that fast would be to maintain a stack depth field in every frame, but that's overhead in time and memory for every call just for this feature, which seems clearly unreasonable).

----------------------------------------
Feature #20335: `Thread.each_caller_location` should accept the same arguments as `caller` and `caller_locations`
https://bugs.ruby-lang.org/issues/20335#change-107974

* Author: byroot (Jean Boussier)
* Status: Closed
----------------------------------------
`Thread.each_caller_location` was added to Ruby 3.2 as part of [Feature #16663] and is a very useful API for emitting warnings with a proper source location and similar use cases.

However in many of the cases where I used it, or seen it used, it was needed to skip the first, or a couple frames:

Examples:

Sorbet: https://github.com/Shopify/sorbet/blob/b27a14c247ace7cabdf0f348bfb11fdf0b7e9ab4/gems/sorbet-runtime/lib/types/private/caller_utils.rb#L6-L18

```ruby
    def self.find_caller
      skiped_first = false
      Thread.each_caller_location do |loc|
        unless skiped_first
          skiped_first = true
          next
        end

        next if loc.path&.start_with?("<internal:")

        return loc if yield(loc)
      end
      nil
    end
```

@fxn 's PR: https://github.com/ruby/ruby/blob/9c2e686719a5a4df5ea0b8a3b6a373ca6003c229/lib/bundled_gems.rb#L140-L146

```ruby
      frames_to_skip = 2
      location = nil
      Thread.each_caller_location do |cl|
        if frames_to_skip >= 1
          frames_to_skip -= 1
          next
        end
      # snipp...

```

### Proposal

I think it would be very useful if `Thread.each_caller_location` accepted the same arguments as `caller` and `caller_locations`:

```ruby
#each_caller_location(start = 1, length = nil)
#each_caller_location(range)
```

@jeremyevans0 what do you think?





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