Auto-formatting redundant curly braces in specific string template fails to compile

[axemorgan]

Expected Behavior

After formatting the following code (which does compile), the result should also compile.
Input (Bug.kt):

fun main() {
    println("This is: ${null}")
}

ktlint output:

fun main() {
    println("This is: $null")
}

Observed Behavior

Compilation of the formatted code fails with this error:

Bug.kt:2:25: error: keyword cannot be used as a reference

Steps to Reproduce

1. Format the input file using ktlint -F Bug.kt
2. Compile it: kotlinc Bug.kt
3. Compilation fails

Your Environment

• ktlint: 0.37.2
• kotlinc: kotlinc-jvm 1.4.0 (JRE 13.0.1+9)

Note: I don't think it's particularly useful to use ${null} in a string template, I just ran across this while formatting a large project. 😅

[romtsn]

I'm wondering if there are any other keywords that can be used in the string template?

[axemorgan]

I tried a few keywords from this list, and the same problem occurs for true and false. Those two and null seem to be the only keywords I can find that are valid expressions by themselves, otherwise "${keyword}" isn't valid code.

[romtsn]

Thanks for checking 👍