## Summary

This `Lint/ErbNewArguments` cop emulates the following
Ruby warnings in Ruby 2.6.

```console
% cat example.rb
ERB.new('hi', nil, '-', '@output_buffer')
% ruby -vrerb example.rb
ruby 2.6.0dev (2018-04-08 trunk 63120) [x86_64-darwin17]
example.rb:1: warning: Passing safe_level with the 2nd argument of
ERB.new is deprecated. Do not use it, and specify other arguments as
keyword arguments.
example.rb:1: warning: Passing trim_mode with the 3rd argument of
ERB.new is deprecated. Use keyword argument like ERB.new(str, trim_mode:
...) instead.
example.rb:1: warning: Passing eoutvar with the 4th argument of ERB.new
is deprecated. Use keyword argument like ERB.new(str, eoutvar: ...) instead.
```

The interface of `ERB.new` will change from Ruby 2.6.

> Add :trim_mode and :eoutvar keyword arguments to ERB.new.
> Now non-keyword arguments other than first one are softly deprecated
> and will be removed when Ruby 2.5 becomes EOL. [Feature rubocop#14256]

https://github.com/ruby/ruby/blob/2311087b685e8dc0f21f4a89875f25c22f5c39a9/NEWS#stdlib-updates-outstanding-ones-only

Now non-keyword arguments other than first one are softly deprecated
and will be removed when Ruby 2.5 becomes EOL.
`ERB.new` with non-keyword arguments is deprecated since ERB 2.2.0.
Use `:trim_mode` and `:eoutvar` keyword arguments to `ERB.new`.
This cop identifies places where `ERB.new(str, trim_mode, eoutvar)`
can be replaced by `ERB.new(str, :trim_mode: trim_mode, eoutvar: eoutvar)`.

This cop does not have autocorrect because uses of `ERB.new`
depends on existing algorithm and code.

## Examples

```ruby
# Target codes supports Ruby 2.6 and higher only

# bad
ERB.new(str, nil, '-')

# Target codes supports Ruby 2.5 and lower only

# good
ERB.new(str, trim_mode: nil, eoutvar: '-')

# Target codes supports Ruby 2.6, 2.5 and lower
# bad
ERB.new(str, nil, '-')

# good
# Ruby standard library style
# ruby/ruby@3406c5d
if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
  ERB.new(str, trim_mode: nil, eoutvar: '-')
else
  ERB.new(str, nil, '-')
end

# good
# Use `RUBY_VERSION` style
if RUBY_VERSION >= '2.6'
  ERB.new(str, trim_mode: nil, eoutvar: '-')
else
  ERB.new(str, nil, '-')
end
```