[ruby-core:75959] [Ruby trunk Feature#12482] ArgumentError.new(nil) should give a better description

Issue #12482 has been updated by Nobuyoshi Nakada.

Tracker changed from Bug to Feature
Description updated

It breaks ruby/spec.

https://github.com/ruby/ruby/compare/trunk...nobu:feature/12482-Exception-nil-mesg

```diff
diff --git i/core/marshal/dump_spec.rb w/core/marshal/dump_spec.rb
index 88ff871..64bf49b 100644
--- i/core/marshal/dump_spec.rb
+++ w/core/marshal/dump_spec.rb
@@ -470,17 +470,17 @@ describe "Marshal.dump" do
 
   describe "with an Exception" do
     it "dumps an empty Exception" do
-      Marshal.dump(Exception.new).should == "\x04\bo:\x0EException\a:\tmesg0:\abt0"
+      Marshal.dump(Exception.new).should_not =~ /mesg(?!0)/
     end
 
     it "dumps the message for the exception" do
-      Marshal.dump(Exception.new("foo")).should == "\x04\bo:\x0EException\a:\tmesgI\"\bfoo\x06:\x06EF:\abt0"
+      Marshal.dump(Exception.new("foo")).should =~ /foo/
     end
 
     it "contains the filename in the backtrace" do
       obj = Exception.new("foo")
       obj.set_backtrace(["foo/bar.rb:10"])
-      Marshal.dump(obj).should == "\x04\bo:\x0EException\a:\tmesgI\"\bfoo\x06:\x06EF:\abt[\x06I\"\x12foo/bar.rb:10\x06;\aF"
+      Marshal.dump(obj).should =~ /foo\/bar.rb:10/
     end
   end
 
diff --git i/core/marshal/shared/load.rb w/core/marshal/shared/load.rb
index 8bf5f33..5a92437 100644
--- i/core/marshal/shared/load.rb
+++ w/core/marshal/shared/load.rb
@@ -441,10 +441,7 @@ describe :marshal_load, shared: true do
   describe "for an Exception" do
     it "loads a marshalled exception with no message" do
       obj = Exception.new
-      loaded = Marshal.send(@method, "\004\bo:\016Exception\a:\abt0:\tmesg0")
-      loaded.message.should == obj.message
-      loaded.backtrace.should == obj.backtrace
-      loaded = Marshal.send(@method, "\x04\bo:\x0EException\a:\tmesg0:\abt0")
+      loaded = Marshal.send(@method, "\004\bo:\016Exception\6:\abt0")
       loaded.message.should == obj.message
       loaded.backtrace.should == obj.backtrace
     end
```

----------------------------------------
Feature #12482: ArgumentError.new(nil) should give a better description
https://bugs.ruby-lang.org/issues/12482#change-59152

* Author: Eike Dierks
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
Currently:

~~~ruby
ArgumentError.new(nil)  =>  #<ArgumentError: ArgumentError>
ArgumentError.new(nil).to_s => "ArgumentError"
ArgumentError.new(nil).inspect => "#<ArgumentError: ArgumentError>"

~~~

I want to suggest to change this to "ArgumentError(nil)" instead.

Rational:

For testing arguments, I frequently use:

~~~ruby
raise ArgumentError.new(arg) unless ExpectedClass === arg
~~~

However when arg is nil, this raises "ArgumentError" while raising "ArgumentError(nil)" would be much nicer.

This would differentiate between `ArgumentError.new()` and `ArgumentError.new(nil)`

Suggested changes

It looks like `ArgumentError#initialize` inherits Exception#initialize

I'd like to suggest to differentiate between Exception.new() and Exception.new(nil)

~~~ruby
def Exception.new(msg = :__Exception_msg_arg_undefined___)
  case arg
  when :__Exception_msg_arg_undefined___
    # msg = "ClassName"
  when nil
    # msg = "ClassName(nil)" 
  end
~~~

Impact

I believe this should not break existing code as no code should rely on the string returned.
















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