From: "vo.x (Vit Ondruch) via ruby-core" <ruby-core@...>
Date: 2025-11-19T11:38:27+00:00
Subject: [ruby-core:123856] [Ruby Bug#21698] Should simple ArgumentError refer to Object?

Issue #21698 has been reported by vo.x (Vit Ondruch).

----------------------------------------
Bug #21698: Should simple ArgumentError refer to Object?
https://bugs.ruby-lang.org/issues/21698

* Author: vo.x (Vit Ondruch)
* Status: Open
* ruby -v: ruby 4.0.0dev (2025-11-18 master 85abc59c32) +PRISM [x86_64-linux]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Having this simple test file:

~~~
$ cat test.rb
def foo(x, y)
end

foo(1)
~~~

This is the Ruby 3.4 behavior:

~~~
$ ruby --disable-gems test.rb 
test.rb:1:in 'foo': wrong number of arguments (given 1, expected 2) (ArgumentError)
        from test.rb:4:in '<main>'

$ ruby -v
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]
~~~

While Ruby 4.0 refers to `Object` in the backtrace:

~~~
$ ruby --disable-gems test.rb
test.rb:1:in 'Object#foo': wrong number of arguments (given 1, expected 2) (ArgumentError)
        from test.rb:4:in '<main>'

$ ruby -v
ruby 4.0.0dev (2025-11-18 master 85abc59c32) +PRISM [x86_64-linux]
~~~

While this is certainly correct, I also think it is a bit confusing, because the code does not explicitly refer to `Object`. This likely comes as a result of #21543, but I think that there the original proposal for such simple case was different.

I am also not convinced that the `did_you_mean` output really helps:

~~~
$ ruby test.rb
test.rb:1:in 'Object#foo': wrong number of arguments (given 1, expected 2) (ArgumentError)

    caller: test.rb:4
    | foo(1)
      ^^^
    callee: test.rb:1
    | def foo(x, y)
          ^^^
        from test.rb:4:in '<main>'
~~~

But maybe I should just get used to it ����

Just FTR, I have come here trying to fix the following Sass gem test suite error on Fedora:

~~~
  1) Failure:
SassScriptTest#test_shallow_argument_error_unwrapped [test/sass/script_test.rb:704]:
--- expected
+++ actual
@@ -1 +1,3 @@
-"wrong number of arguments (1 for 0) for `arg-error'"
+# encoding: ASCII-8BIT
+#    valid: true
+"wrong number of arguments (given 1, expected 0) for `arg-error'"
~~~

The problem there is that Sass is trying to parse the backtrace:

https://github.com/sass/ruby-sass/blob/7a50eae567260a23d3bbf4d5aaf1a76db43dec32/lib/sass/script/tree/funcall.rb#L303-L310

and changes like these breaks the compatibility. We already had to apply some [changes for Ruby 3.4](https://src.fedoraproject.org/rpms/rubygem-sass/blob/rawhide/f/rubygem-sass-3.7.4-Support-caller-format-change-in-ruby3.4.patch) and this is yet another breakage. This is the actual difference:

~~~
--- ruby-3.4
+++ ruby-4.0
@@ -1,3 +1,3 @@
 > e.backtrace
 => 
-["/builddir/build/BUILD/rubygem-sass-3.7.4-build/sass-3.7.4/usr/share/gems/gems/sass-3.7.4/test/sass/script_test.rb:11:in 'arg_error'",
+["/builddir/build/BUILD/rubygem-sass-3.7.4-build/sass-3.7.4/usr/share/gems/gems/sass-3.7.4/test/sass/script_test.rb:11:in 'Sass::Script::Functions::UserFunctions#arg_error'",
~~~

Contrary to my original point, in this case the backtrace might be better. Maybe this needs more polishing?



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