Regex with single char output throws exception

[manish7-thakur]

Summary

Regex which matches a single character (e.g "^ User ([ABZ])$") leads to a CucumberExpressionException because BuiltInParameterTransformer in cucumber-expressions-java doesn't have a character transformer even though type is deciphered as char shown in the screenshot attached.

Expected Behavior

If the type is deciphered as char, BuiltInParameterTransformer should return it as char.

Given("""^User ([ABZ])$""") {
     (user: Char) =>
       setCriteria { sc =>
         sc.copy(experiments = user))
       }
   }

Current Behavior

Currently it simply throws the exception: io.cucumber.cucumberexpressions.CucumberExpressionException: ParameterType {anonymous} failed to transform [B] to char

Possible Solution

We can have a transformer for character type in BuiltInParameterTransformer

  if (Character.class.equals(toValueClass) || char.class.equals(toValueClass)) {
              return fromValue.toCharArray()[0];
          }

Steps to Reproduce (for bugs)

A simple step with Regex which matches single char can reproduce it.

Given("""^User ([ABZ])$""")

Context & Motivation

I updated cucumber version to 6.10.0 and it broke my existing test cases.

Your Environment

• Version used: cucumber-java-6.10.0
• Operating System and version: mac - bigSur
• Link to your project:
  

[manish7-thakur]

Raised a PR to fix the issue in cucmber-expressions-java. If the changes looks good, I can port the changes to Ruby, JavaScript, Go, .NET and would log the change as well.

[luke-hill]

This doesn't feel a bug in Ruby, because in ruby we just use the string type for all strings of arbitrary length. I suppose we could add it for standardisation, but it would rarely get used, because {string} and {word} are just more encompassing.

All 3 would have the same return type String class also.

I do understand the need in java for this, because (From my limited knowledge), the char type and the String type are fundamentally different taking up different amounts of memory.

Thoughts @mpkorstanje ?? Do we want to add this to other languages for standardisation? Where else would this be "active" (i.e. is Ruby the normal or the exception)

[mpkorstanje]

I don't think this affects anything but Java and Go.

[luke-hill]

Given that then, I'd err on the side of only adding it to Java and Go. As it's a reasonably small change and it's ok to have slight differences.

But then again these default ones we promote to our docs. I dunno I'm kinda on the fence as you can guess.

[mpkorstanje]

These are not parameter types. The BuiltInParameterTransformer handles conversion in the absence of a cucumber expression parameter type using the Java Types from the step definition methods parameters instead.

[aslakhellesoy]

Fixed in v12.0.1