From: "Dan0042 (Daniel DeLorme)" <noreply@...>
Date: 2022-01-31T16:09:07+00:00
Subject: [ruby-core:107394] [Ruby master Feature#18370] Call Exception#full_message to print exceptions reaching the top-level

Issue #18370 has been updated by Dan0042 (Daniel DeLorme).


Would it be feasible for #full_message to accept a String/IO argument to which it writes the parts of the message? So the error printer could call `err.full_message(output_to: $stderr)` in order to avoid buffering.


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Feature #18370: Call Exception#full_message to print exceptions reaching the top-level
https://bugs.ruby-lang.org/issues/18370#change-96296

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
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Extracted from https://bugs.ruby-lang.org/issues/18296#note-6.

I think this a clear gain to improve consistency in how exceptions are shown, and it also makes it easier to evolve exception formatting in the future.

It would also solve https://bugs.ruby-lang.org/issues/18367.

https://bugs.ruby-lang.org/issues/18296#note-7 has more specifics, I'll copy here for convenience:

mame (Yusuke Endoh) wrote in #note-6:
> Does this proposal include that the ruby interpreter should use `#full_message` to show the error information? This is an incompatibility, is it acceptable?

Yes, let's fix that.
I don't think there is much if any compatibility issue here.
The output of the uncaught exception handler is already the same as the default Exception#full_message AFAIK, let's actually call it.
TruffleRuby already calls `exc.full_message` for the uncaught exception handler.

If the custom `exc.full_message` raises an exception, then it's best to report that exception *and* the original exception using the default `Exception#full_message` (written in C).
This is the current TruffleRuby output for that case and I think it's clear:
```
$ ruby -e 'class Foo < Exception; def full_message(**); raise "bar"; end; end; raise Foo, "message"'
Error while formatting Ruby exception:
-e:1:in `full_message': bar (RuntimeError)
	from <internal:core> core/truffle/exception_operations.rb:183:in `get_formatted_backtrace'
Original Ruby exception:
-e:1:in `<main>': message (Foo)
```



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