[ruby-core:99387] [Ruby master Feature#17055] Allow suppressing uninitialized instance variable and method redefined verbose mode warnings

[kamipo@gmail.com]

Issue #17055 has been updated by kamipo (Ryuta Kamizono).


Rails also want a way to suppress method redefinition warnings.
For now it uses the alias hack.

https://github.com/rails/rails/blob/b2eb1d1c55a59fee1e6c4cba7030d8ceb524267c/activesupport/lib/active_support/core_ext/module/redefine_method.rb#L7-L13

```ruby
  def silence_redefinition_of_method(method)
    if method_defined?(method) || private_method_defined?(method)
      # This suppresses the "method redefined" warning; the self-alias
      # looks odd, but means we don't need to generate a unique name
      alias_method method, method
    end
  end
```

In Perl, it have similar lexical scope pragma `no warnings 'uninitialized'` and `no warnings 'redefine'` for that.

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Feature #17055: Allow suppressing uninitialized instance variable and method redefined verbose mode warnings
https://bugs.ruby-lang.org/issues/17055#change-86794

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
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These two verbose mode warnings are both fairly common and have good reasons why you would not want to warn about them in specific cases.  Not initializing instance variables to nil can be much better for performance, and redefining methods without removing the method first is the only safe approach in multi-threaded code.

There are reasons that you may want to issue verbose warnings by default in these cases.  For uninitialized instance variables, it helps catch typos. For method redefinition, it could alert you that a method already exists when you didn't expect it to, such as when a file is loaded multiple times when it should only be loaded once.

I propose we keep the default behavior the same, but offer the ability to opt-out of these warnings by defining methods.  For uninitialized instance variables in verbose mode, I propose we call `expected_uninitialized_instance_variable?(iv)` on the object.  If this method doesn't exist or returns false/nil, we issue the warning.  If the method exists and returns true, we suppress the warning.  Similarly, for redefined methods, we call `expected_redefined_method?(method_name)` on the class or module.  If the method doesn't exist or returns false/nil, we issue the warning.  If the method exists and returns true, we suppress the warning.

This approach allows high performance code (uninitialized instance variables) and safe code (redefining methods without removing) to work without verbose mode warnings.

I have implemented this support in a pull request: https://github.com/ruby/ruby/pull/3371



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