Issue #14183 has been updated by jeremyevans0 (Jeremy Evans).


jeremyevans0 (Jeremy Evans) wrote:
> More work should be done if this is accepted.  Specifically, we need to decide:
> 
> * What should Method#parameters return for a method that uses `**nil`?
> * How should ripper handle for the `**nil` syntax?
> * How should RubyVM::AbstractSyntaxTree handle the `**nil` syntax?

I've updated my branch (https://github.com/jeremyevans/ruby/tree/keyword-argument-separation) to add support for the `**nil` syntax in `Method/Proc#parameters`, ripper, and `RubyVM::AbstractSyntaxTree`

`Method/Proc#parameters` uses a `:nokey` entry if the `**nil` syntax is used:

```ruby
proc{||}.parameters
# => []

proc{|**a|}.parameters
# => [[:keyrest, :a]]

proc{|**nil|}.parameters
# => [[:nokey]]
```

Ripper uses `:nil` for the keyword rest argument if the `**nil` syntax is used:

```ruby
Ripper.sexp('def a() end')
# => [:program, [[:def, [:@ident, "a", [1, 4]], [:paren, [:params, nil, nil, nil, nil, nil, nil, nil]], [:bodystmt, [[:void_stmt]], nil, nil, nil]]]]

 Ripper.sexp('def a(**b) end')
# => [:program, [[:def, [:@ident, "a", [1, 4]], [:paren, [:params, nil, nil, nil, nil, nil, [:kwrest_param, [:@ident, "b", [1, 8]]], nil]], [:bodystmt, [[:void_stmt]], nil, nil, nil]]]]

Ripper.sexp('def a(**nil) end')
# => [:program, [[:def, [:@ident, "a", [1, 4]], [:paren, [:params, nil, nil, nil, nil, nil, :nil, nil]], [:bodystmt, [[:void_stmt]], nil, nil, nil]]]]
```

`RubyVM::AbstractSyntaxTree` uses `false` instead of `nil` for the keyword and keyword rest arguments if the `**nil` syntax is used:

```ruby
node = RubyVM::AbstractSyntaxTree.parse("def a() end")
node.children.last.children.last.children[1].children
# => [0, nil, nil, nil, 0, nil, nil, nil, nil, nil]

node = RubyVM::AbstractSyntaxTree.parse("def a(**a) end")
node.children.last.children.last.children[1].children
# => [0, nil, nil, nil, 0, nil, nil, nil, #<RubyVM::AbstractSyntaxTree::Node:DVAR@1:6-1:9>, nil]

node = RubyVM::AbstractSyntaxTree.parse("def a(**nil) end")
node.children.last.children.last.children[1].children
# => [0, nil, nil, nil, 0, nil, nil, false, false, nil]
```

Hopefully these are all of the introspection methods that we need to modify to support `**nil`.  I'm not sure that these are the best ways of handling each case, but I'm open to better ideas.

----------------------------------------
Feature #14183: "Real" keyword argument
https://bugs.ruby-lang.org/issues/14183#change-77760

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: Next Major
----------------------------------------
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
```

In other words, the following programs WILL NOT work:

```
# This will cause an ArgumentError because the method foo does not accept keyword argument
def foo(a, b, c, hsh)
  p hsh[:key]
end
foo(1, 2, 3, key: 42)

# The following will work; you need to use keyword rest operator explicitly
def foo(a, b, c, **hsh)
  p hsh[:key]
end
foo(1, 2, 3, key: 42)

# This will cause an ArgumentError because the method call does not pass keyword argument
def foo(a, b, c, key: 1)
end
h = {key: 42}
foo(1, 2, 3, h)

# The following will work; you need to use keyword rest operator explicitly
def foo(a, b, c, key: 1)
end
h = {key: 42}
foo(1, 2, 3, **h)
```

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.

---Files--------------------------------
vm_args.diff (4.19 KB)
vm_args_v2.diff (4.18 KB)


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