Splat block arguments not producing a tuple

[icy-arctic-fox]

When using a splat for block arguments with Proc.new, a tuple isn't created. Just the first block argument is assigned.

For example:

add = Proc(Int32, Int32, Int32).new do |*args|
  args.sum
end
puts add.call(1, 2)

results in:

Error: undefined method 'sum' for Int32

Only the first argument is picked up and assigned to args. It is not a tuple.

A more practical example is wrapping a proc where the arguments are unknown.

def wrap(proc : P) : P forall P
  P.new do |*args|
    puts "Before"
    value = proc.call(*args)
    puts "After"
    value
  end
end

proc = ->(x : Int32) { puts x }
wrapped = wrap(proc)
wrapped.call(42)

produces:

Error: argument to splat must be a tuple, not Int32

I've tried this in Crystal 1.14 and 1.15.

Related: #10242
There's something specific about Proc.new that causes this to fail.

[straight-shoota]

Proc.new isn't anything special, it just captures a block.

Reduced:

def capture(&block : Proc(Int32, Int32, Int32))
  block
end

capture do |*args|
  args.sum # Error: undefined method 'sum' for Int32
end

It seems the parser completely ignores the *. This should rather be a parser error.
Or it should work as expected, which I believe would be feasible.