[ruby-core:121122] [Ruby master Misc#20968] `Array#fetch_values` unexpected method name in stack trace

Issue #20968 has been updated by Eregon (Benoit Daloze).


Another way to look at it is if `Array#fetch_values` was defined by a gem (e.g. by `activesupport`), then everyone would expect:
```
<internal:array>:211:in 'Array#fetch': index 42 outside of array bounds: -1...1 (IndexError)
        from /path/to/activesupport/some/file.rb:211:in 'block in Array#fetch_values'
        from /path/to/activesupport/some/file.rb:211:in 'Array#map!'
        from /path/to/activesupport/some/file.rb:211:in 'Array#fetch_values'
        from -e:1:in '<main>'
```

So the fact it's `<internal:array>:211` instead of `/path/to/activesupport/some/file.rb:211` in the description seems a very small expected difference, it's just defined "in a core library Ruby file" vs "in a gem Ruby file".

I think this argument is strong enough on its own to not change stacktraces until a concrete problem is reported with the current core library stacktraces.

---

Maybe the core library Ruby paths could be a bit nicer like `<internal:/path/to/array.rb>:211` then potentially editors could just open that.
It would be pretty cool if users could just see the implementation of some core library methods defined in Ruby.
FWIW TruffleRuby uses `<internal:core> core/array.rb:211` which I think is nice and clear:
```
$ ruby -e '1.tap { raise "foo" }'
-e:1:in `block in <main>': foo (RuntimeError)
	from <internal:core> core/kernel.rb:520:in `tap'
	from -e:1:in `<main>'
```

We could ship these core files with CRuby to make it easier to understand what's going on.
We'd add a comment on top of the file explaining modifying the file would have no effect as the source is not used, only its bytecode.

----------------------------------------
Misc #20968: `Array#fetch_values` unexpected method name in stack trace
https://bugs.ruby-lang.org/issues/20968#change-112044

* Author: koic (Koichi ITO)
* Status: Open
----------------------------------------

It seems that the current Ruby implementation is displaying unexpected method name in stack trace.

## Expected

Similar to `Hash#fetch_values`, the method name `Array#fetch_values` is expected to be displayed in the stack trace.

```console
$ ruby -e '{k: 42}.fetch_values(:unknown)'
-e:1:in 'Hash#fetch_values': key not found: :unknown (KeyError)
        from -e:1:in '<main>'

$ ruby -e '[1].fetch_values(42)'
-e:1:in 'Array#fetch_values': index 42 outside of array bounds: -1...1 (IndexError)
        from -e:1:in '<main>'
```


## Actual

The stack trace displays the `Array#fetch` method, which user is not aware of, along with the `<internal.array>` stack trace.

```console
$ ruby -e '[1].fetch_values(42)'
<internal:array>:211:in 'Array#fetch': index 42 outside of array bounds: -1...1 (IndexError)
        from <internal:array>:211:in 'block in Array#fetch_values'
        from <internal:array>:211:in 'Array#map!'
        from <internal:array>:211:in 'Array#fetch_values'
        from -e:1:in '<main>'
```


It likely requires an approach such as implementing it in C, as suggested in https://github.com/ruby/ruby/pull/11555.



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