Consider this task:

```ruby
task :t, [:arg] do |task, arg: 'default_value'|
  emotion = "\e[32m^_^\e[0m"
  emotion = "\e[31mt.t\e[0m" if ARGV[0] =~ /t\[(.*)\]$/ && $1 != arg
  puts "task #{task.name.inspect} got #{arg.inspect} #{emotion}"
end
```

Run this on your machine right now, you'll see the task is in tears.
But this commit turns tearful eyes into smiling ones, observe:

```sh
$ rake t
task "t" got "default_value" ^_^
$ rake t[custom_value]
task "t" got "default_value" t.t

$ ruby -Ilib exe/rake t
task "t" got "default_value" ^_^
$ ruby -Ilib exe/rake t[custom_value]
task "t" got "custom_value" ^_^
```

It accomplishes this by always invoking the action in the same way.
Previously, Rake invoke the action with different argument structures based the arity
https://github.com/ruby/rake/blob/59856100815b841624269f817c815f54921bf321/lib/rake/task.rb#L251-L256

```ruby
case act.arity
when 1
  act.call(self)
else
  act.call(self, args)
end
```

I assume it's expecting one of these:

```ruby
proc { |task| }.arity           # => 1
proc { |task, options| }.arity  # => 2
```

However this leads numerous task signatures to be invoked incorrectly.
Eg, consider the case of our tearful task above, here is why it cries.

```ruby
proc { |task, arg: 'default_value'| }.arity # => 1
```

The solution is nice and easy: always invoke the block the same way.
Why was this ever a thing at all, then?
Looks like it was added in 2007 about a month after Ruby 1.8.6 was released.
ruby@925fbb8
Probably something was just different back then, eg the difference
between lambdas and procs was whether you did `prc.call` or `prc.yield`
https://github.com/ruby/ruby/blob/9b383bd/eval.c#L8356-L8415

https://ci.appveyor.com/project/ruby/rake/build/1.0.301