Better error message for validation

[mslinn]

Discussed in #183

^{Originally posted by mslinn May 10, 2022}
I want to verify that the provided answer is within the range of allowable string lengths (min..max).

Attempt 1

value = @prompt.ask(msg, value: value) do |q|
  q.required true
  q.validate ->(v) { return v.length >= min && v.length <= max }
end

When the input is not within the range of min characters to max characters in length, the error message is: The answer is invalid (must match #<Proc:0x00007f395836e410 /jekyll-new_post/lib/jekyll/new_post.rb:131 (lambda)>). That is a not a user-friendly error message.

Attempt 2

I was unable to access the current answer while preparing q.messages[:valid?]:

value = @prompt.ask(msg, value: value) do |q|
  q.required true
  q.messages[:valid?] = check_length(min, max, ????) # Is there some way to pass the current answer to `check_length`?
  q.validate ->(v) { return v.length >= min && v.length <= max }
end

def check_length(min, max, string)
  length = string.length
  if length < min
    "#{min - length} characters too short, please edit"
  elsif length > max
    "#{length - max} characters too long, please edit"
  else
    "#{length} characters, excellent!"
  end
end

Is there some way to use q.messages[:valid] so that a better error message can be provided? If not, is there a way to invoke q.validate to avoid the user-unfriendly message shown?

Attempt 3

I tried validating using this regex:

q.validate(/\A.{#{min},#{max}}\Z/)

This validation works, but the error message is not user-friendly:

Your answer is invalid (must match /\A.{30,60}\Z/)

Attempt 4

Next, I tried a lambda:

    error_msg = lambda do |val|
      puts val.red
      case val.length
      when proc { |n| n < min }
        "Only #{val.length} characters provided, need at least #{min}"
      when proc { |n| n > max }
        "#{val.length} characters provided, maximum allowable is #{max}"
      else
        ''
      end
    end
    value = @prompt.ask(msg, value: value) do |q|
      q.required true
      q.validate(/\A.{#{min},#{max}}\Z/, error_msg.call('%{value}'))
    end

... but the screen would tear up for input that was too long, and '%{value}' was not expanded.