[ruby-core:109205] [Ruby master Feature#18913] Add object name to the NoMethodError error message: undefined method `_method_' for `_class_' in `_object_name_'

Issue #18913 has been updated by mame (Yusuke Endoh).


I don't understand what you mean by "object name", but did you try Ruby 3.1? It shows a code snippet that caused NameError and NoMethodError.

```
$ ruby test.rb
test.rb:5:in `<main>': undefined method `foo' for nil:NilClass (NoMethodError)

who_failed = a.foo & b.foo & c.foo
                      ^^^^

$ ruby -v
ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]
```

----------------------------------------
Feature #18913: Add object name to the NoMethodError error message: undefined method `_method_' for `_class_' in `_object_name_'
https://bugs.ruby-lang.org/issues/18913#change-98343

* Author: stillhart (Fabian Stillhart)
* Status: Open
* Priority: Normal
----------------------------------------

Hi

I think the `NoMethodError` error message is missing the object name. The object name is already present in `NameError`. Currently one needs to dig into the source code and debug it in order to find which variable or method is actually affected.

The current error message looks like this:
``` ruby
bar = nil
bar.i_wish_i_saw_the_name_bar
# (irb):00:in `<main>': undefined method `i_wish_i_saw_the_name_bar' for nil:NilClass (NoMethodError)
```

I wish that it was more like this
``` ruby
bar = nil
bar.i_wish_i_saw_the_name_bar
#(irb):00:in `<main>': undefined method `i_wish_i_saw_the_name_bar' for nil:NilClass in `bar' (NoMethodError)
#                                                                                        ^^^ It should mention the object name
```


The NameError error message supports this already, and I think it avoids a whole lot of issue tickets, stackoverflow searches and more. See NoMethodError vs NameError https://trends.google.ch/trends/explore?date=today%205-y&q=ruby%20%20NoMethodError,ruby%20NameError
``` ruby
foo
# (irb):00:in `<main>': undefined local variable or method `foo' for main:Object (NameError)
#                                                           ^^^ the object name is mentioned
```

One can always use the backtrace to find the affected line, but even that won't help in the following situation:
```ruby
a = OpenStruct.new
b = nil
c = nil
who_failed = a.foo & b.foo & c.foo
# (irb):00:in `<main>': undefined method `foo' for nil:NilClass (NoMethodError)
```

I would add the object name at the end of the exception message not to break compatibility. I hope most users use regex to match the exception message.

I don't know how to program c but I think the source is located here
https://github.com/ruby/ruby/blob/554befb/proc.c#L1959

I assume there will be some edge cases around meta programming and procs. Anyway, I think we should show them if available. I think we all spent many hours tracking down when we have a type/method mismatch, and this would have helped greatly.



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