Issue #14183 has been reported by mame (Yusuke Endoh).

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Bug #14183: "Real" keyword argument
https://bugs.ruby-lang.org/issues/14183

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: Next Major
* ruby -v: 
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN
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In RubyWorld Conference 2017 and RubyConf 2017, Matz officially said that Ruby 3.0 will have "real" keyword arguments.  AFAIK there is no ticket about it, so I'm creating this (based on my understanding).

In Ruby 2, the keyword argument is a normal argument that is a Hash object (whose keys are all symbols) and is passed as the last argument.  This design is chosen because of compatibility, but it is fairly complex, and has been a source of many corner cases where the behavior is not intuitive.  (Some related tickets: #8040, #8316, #9898, #10856, #11236, #11967, #12104, #12717, #12821, #13336, #13647, #14130)

In Ruby 3, a keyword argument will be completely separated from normal arguments.  (Like a block parameter that is also completely separated from normal arguments.)
This change will break compatibility; if you want to pass or accept keyword argument, you always need to use bare `sym: val` or double-splat `**` syntax:

```
# The following calls pass keyword arguments
foo(..., key: val)
foo(..., **hsh)
foo(..., key: val, **hsh)

# The following calls pass **normal** arguments
foo(..., {key: val})
foo(..., hsh)
foo(..., {key: val, **hsh})

# The following method definitions accept keyword argument
def foo(..., key: val)
end
def foo(..., **hsh)
end

# The following method definitions accept **normal** argument
def foo(..., hsh)
end
```

I think here is a transition path:

* Ruby 2.6 (or 2.7?) will output a warning when a normal argument is interpreted as keyword argument, or vice versa.
* Ruby 3.0 will use the new semantics.



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