From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2024-03-14T14:52:08+00:00
Subject: [ruby-core:117174] [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).


I think omitting the first N frames is useful.
However I see little reason to have a `length` or `Range`, one can just `break/return` out of the `Thread.each_caller_location`, and it seems pretty rare to need that.
So I think it's best to only add `start = 1` for now.

In fact the `length` argument is already an issue for `caller_locations`: if it's too high it causes `caller_locations` to return an empty Array instead of whatever is available:
```
irb(main):001:0> caller_locations(10)
=> 
["/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb/ruby-lex.rb:248:in `catch'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb/ruby-lex.rb:248:in `each_top_level_statement'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb.rb:566:in `eval_input'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb.rb:500:in `block in run'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb.rb:499:in `catch'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb.rb:499:in `run'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/3.2.0/irb.rb:421:in `start'",
 "/home/eregon/.rubies/ruby-3.2.2/lib/ruby/gems/3.2.0/gems/irb-1.6.2/exe/irb:11:in `<top (required)>'",
 "/home/eregon/.rubies/ruby-3.2.2/bin/irb:25:in `load'",
 "/home/eregon/.rubies/ruby-3.2.2/bin/irb:25:in `<main>'"]
irb(main):002:0> caller_locations(20)
=> []
```
That implies it needs to count how many frames are available, which is inefficient.
So we certainly wouldn't want that behavior for `each_caller_location` as it would ruin a significant part of its performance advantage.
(we should probably also fix this for `caller_locations`, but that should be a separate ticket)

Similarly the Range form is also problematic as it also requires iterating all the stack to find how many frames there are to know which frames `0..-2` should use.

----------------------------------------
Feature #20335: `Thread.each_caller_location` should accept the same arguments as `caller` and `caller_locations`
https://bugs.ruby-lang.org/issues/20335#change-107264

* Author: byroot (Jean Boussier)
* Status: Open
----------------------------------------
`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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