--format of experimental:function-signature violates max-line-length

[pkubowicz]

Expected Behavior

• calling --format with experimental:function-signature enabled does not change the code at all if whole function definition does not fit into line length
• experimental:function-signature does not report an error if a function expression is in multiple lines that cannot be safely joined
• generally, calling --format of experimental:function-signature should not introduce new rule violations as it happens in the example below

Observed Behavior

gradle lintKotlin

> Task :lintKotlinMain FAILED
src/main/kotlin/com/example/FunctionSignature.kt:4:91: Lint error > [experimental:function-signature] First line of body expression fits on same line as function signature

gradle formatKotlin

> Task :formatKotlinMain
src/main/kotlin/com/example/FunctionSignature.kt:4:1: Format could not fix > [max-line-length] Exceeded max line length (100)
src/main/kotlin/com/example/FunctionSignature.kt:5:1: Format could not fix > [experimental:function-signature] Newline expected before expression body
src/main/kotlin/com/example/FunctionSignature.kt: Format fixed

Steps to Reproduce

Original file:

package com.example

class FunctionSignature {
    fun isSplitIntoMultipleLinesToFitIntoLineLengthLimit(param1: String, param2: String) =
        param1 + param2 + param1
}

.editorconfig:

[*.{kt,kts}]
max_line_length=100

Run ktlint --format.

File produced by ktlint (incorrect):

package com.example

class FunctionSignature {
    fun isSplitIntoMultipleLinesToFitIntoLineLengthLimit(param1: String, param2: String) = param1 + param2 + param1
}

Your Environment

• Version of ktlint used: 0.46.1 (via kotlinter 3.11.1)
• Gradle 7.4.2

[paul-dingemans]

Output below is not produced by ktlint but the kotlinter gradle plugin that you are using.

gradle lintKotlin

> Task :lintKotlinMain FAILED
src/main/kotlin/com/example/FunctionSignature.kt:4:91: Lint error > [experimental:function-signature] First line of body expression fits on same line as function signature

gradle formatKotlin

> Task :formatKotlinMain
src/main/kotlin/com/example/FunctionSignature.kt:4:1: Format could not fix > [max-line-length] Exceeded max line length (100)
src/main/kotlin/com/example/FunctionSignature.kt:5:1: Format could not fix > [experimental:function-signature] Newline expected before expression body
src/main/kotlin/com/example/FunctionSignature.kt: Format fixed

When running with the CLI you have to invoke command to enable the experimental rule:

ktlint --experimental -F

This results in output:

package com.example

class FunctionSignature {
    fun isSplitIntoMultipleLinesToFitIntoLineLengthLimit(param1: String, param2: String) =
        param1 + param2 + param1
}

Please check the configuration of the kotlinter plugin that it runs the experimental rules as well.

[pkubowicz]

Output below is not produced by ktlint

The point of this bug is not that the output looks ugly, the point is what ktlint auto-correction function does with Kotlin sources. This does not depend on the way you call ktlint.

you have to invoke command to enable the experimental rule

I don't want to invoke ktlint from the command line, or download it manually. Are there any people except for its maintainers who do such things?

But sure, let's waste some more time. Here is the output from my console.

pkubowicz:~/devel/bugs/ktlint-paren(main)% ./ktlint-0-46-1          
pkubowicz:~/devel/bugs/ktlint-paren(main)% ./ktlint-0-46-1 --experimental
/home/pkubowicz/devel/bugs/ktlint-paren/src/main/kotlin/com/example/FunctionSignature.kt:4:91: First line of body expression fits on same line as function signature (experimental:function-signature)
pkubowicz:~/devel/bugs/ktlint-paren(main)% ./ktlint-0-46-1 --experimental -F
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.jetbrains.kotlin.com.intellij.util.ReflectionUtil (file:/home/pkubowicz/devel/bugs/ktlint-paren/ktlint-0-46-1) to field java.lang.Throwable.backtrace
WARNING: Please consider reporting this to the maintainers of org.jetbrains.kotlin.com.intellij.util.ReflectionUtil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
/home/pkubowicz/devel/bugs/ktlint-paren/src/main/kotlin/com/example/FunctionSignature.kt:4:1: Exceeded max line length (100) (cannot be auto-corrected) (max-line-length)
/home/pkubowicz/devel/bugs/ktlint-paren/src/main/kotlin/com/example/FunctionSignature.kt:5:1: Newline expected before expression body (experimental:function-signature)
pkubowicz:~/devel/bugs/ktlint-paren(main)U% git di
diff --git a/src/main/kotlin/com/example/FunctionSignature.kt b/src/main/kotlin/com/example/FunctionSignature.kt
index ecf379f..4a695d5 100644
--- a/src/main/kotlin/com/example/FunctionSignature.kt
+++ b/src/main/kotlin/com/example/FunctionSignature.kt
@@ -1,6 +1,5 @@
 package com.example
 
 class FunctionSignature {
-    fun isSplitIntoMultipleLinesToFitIntoLineLengthLimit(param1: String, param2: String) =
-        param1 + param2 + param1
+    fun isSplitIntoMultipleLinesToFitIntoLineLengthLimit(param1: String, param2: String) = param1 + param2 + param1
 }
pkubowicz:~/devel/bugs/ktlint-paren(main)U% ./ktlint-0-46-1                  
/home/pkubowicz/devel/bugs/ktlint-paren/src/main/kotlin/com/example/FunctionSignature.kt:4:1: Exceeded max line length (100) (cannot be auto-corrected) (max-line-length)
pkubowicz:~/devel/bugs/ktlint-paren(main)U% ./ktlint-0-46-1 --version
0.46.1

[paul-dingemans]

Ok, the problem is that with each invocation of ktlint --experimental -F the error alternates between:

First line of body expression fits on same line as function signature (experimental:function-signature)

and

Newline expected before expression body (experimental:function-signature)

I would have expected that neither of them were reported as it is an error which is autocorrected and such errors are not reported when running with -F. Most likely the autocorrected error results in a new violation which is only seen at the next invocation.

For now, you can disable the entire rule or set following in the .editorconfig:

ktlint_function_signature_body_expression_wrapping = always