[ruby-core:101900] [Ruby master Feature#10499] Eliminate implicit magic in Proc.new and Kernel#proc

Issue #10499 has been updated by dazuma (Daniel Azuma).


Was this change implemented in Ruby 3.0.0?

It looks to me like it was. (And this is causing test failures on libraries that depend on this behavior.)

Ruby 2.7.2:

```
def foo
  Proc.new
end

foo          # => ArgumentError
foo { :hi }  # => Proc
```

Ruby 3.0.0:

```
def foo
  Proc.new
end

foo          # => ArgumentError
foo { :hi }  # => ArgumentError
```

----------------------------------------
Feature #10499: Eliminate implicit magic in Proc.new and Kernel#proc
https://bugs.ruby-lang.org/issues/10499#change-89741

* Author: headius (Charles Nutter)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
----------------------------------------
Proc.new and Kernel#proc have a little known feature: if called without a block, they capture whatever block was passed to the current method.

I propose that this feature should be removed, finally, since it:

* Doesn't enhance readability (where is this block coming from?)
* Doesn't reflect any other behavior in Ruby
* Can lead to bugs (call either without a block accidentally and you aren't sure what you'll get)

I believe this was an implementation artifact in MRI, since the most recently-pushed block would still be on global stacks, which is where the logic for proc and Proc.new looked for it.

All argument syntaxes now support &block, which I believe is the correct way to clearly, explicitly capture the incoming block into an object.

Thoughts?



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