Ktlint 3 does not recognize a lower-case letter starting the function "approxE^X"

[binkley]

Expected Behavior

Ktlint should not be concerned with a function named "approxE^X". It starts with a lower-case letter contrary to the below error message. Perhaps it violates "camel case" because of non-alphabetic characters.

However I get this ERROR in a Maven build:

[ERROR] src/main/kotlin/demo/KotlinMain.kt:206:9: Function name should start with a lowercase letter (except factory methods) and use camel case (standard:function-naming)

for https://github.com/binkley/kotlin-rational/blob/9706d9763236a9adda4454d46590431383ad650e/src/main/kotlin/demo/KotlinMain.kt#L206. The function is:

fun `approxE^X`(exponent: FloatingBigRational, limit: Int = 5) {
    println(
       (0..limit).map {
            e(exponent, it)
        }.joinToString(prefix = "APPROX E^$exponent -> ") {
            it.toString()
        }
    )
}

Observed Behavior

Instructions ask for --log-level=debug, however that is a syntax error. I assume you meant -X or --debug. Output for the Ktlint sections from my Maven build:

[DEBUG] Configuration: <?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <android default-value="false">${ktlint.android}</android>
  <basedir default-value="${project.basedir}"/>
  <experimental default-value="false">${ktlint.experimental}</experimental>
  <includeScripts default-value="true">${ktlint.includeScripts}</includeScripts>
  <includeSources default-value="true">${ktlint.includeSources}</includeSources>
  <includeTestSources default-value="true">${ktlint.includeTestSources}</includeTestSources>
  <packaging default-value="${project.packaging}"/>
  <scriptRoots default-value="${project.basedir.path}">${ktlint.scriptRoots}</scriptRoots>
  <scriptsIncludes default-value="*.kts"/>
  <skip default-value="false">${ktlint.skip}</skip>
  <sourceRoots default-value="${project.compileSourceRoots}"/>
  <sourcesIncludes default-value="**/*.kt"/>
  <testSourceRoots default-value="${project.testCompileSourceRoots}"/>
  <testSourcesIncludes default-value="**/*.kt"/>
</configuration>

[DEBUG] Goal:          com.github.gantsign.maven:ktlint-maven-plugin:3.0.0:check (default)
[DEBUG] Style:         Regular
[DEBUG] Configuration: <?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <android default-value="false">${ktlint.android}</android>
  <basedir default-value="${project.basedir}"/>
  <experimental default-value="false">${ktlint.experimental}</experimental>
  <failOnViolation default-value="true">${ktlint.failOnViolation}</failOnViolation>
  <includeScripts default-value="true">${ktlint.includeScripts}</includeScripts>
  <includeSources default-value="true">${ktlint.includeSources}</includeSources>
  <includeTestSources default-value="true">${ktlint.includeTestSources}</includeTestSources>
  <packaging default-value="${project.packaging}"/>
  <scriptRoots default-value="${project.basedir.path}">${ktlint.scriptRoots}</scriptRoots>
  <scriptsIncludes default-value="*.kts"/>
  <skip default-value="false">${ktlint.skip}</skip>
  <sourceRoots default-value="${project.compileSourceRoots}"/>
  <sourcesIncludes default-value="**/*.kt"/>
  <testSourceRoots default-value="${project.testCompileSourceRoots}"/>
  <testSourcesIncludes default-value="**/*.kt"/>
  <verbose default-value="false">true</verbose>
</configuration>

Here's where it gets ugly, and I'm only showing output for the file where the issue cropped up:

[DEBUG] Discovered RuleSetProviderV3 'RuleSetId(value=standard)'
[DEBUG] checking format: src/main/kotlin/demo/KotlinMain.kt
[DEBUG] Starting with formatting file 'KotlinMain.kt'
[DEBUG] Effective editorconfig properties for file '/home/binkley/src/kt/kotlin-rational/src/main/kotlin/demo/KotlinMain.kt':
        end_of_line: lf
        max_line_length: 80
        ktlint_code_style: intellij_idea
        ktlint_standard_discouraged-comment-location: disabled
        ktlint_standard_filename: disabled
        ktlint_standard_import-ordering: disabled
        ktlint_standard_trailing-comma-on-call-site: disabled
        ktlint_standard_trailing-comma-on-declaration-site: disabled
[DEBUG] Rule with id 'standard:argument-list-wrapping' should run after the rule with id 'standard:class-signature'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rule with id 'standard:indent' should run after the rule with id 'standard:class-signature'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rule with id 'standard:indent' should run after the rule with id 'standard:trailing-comma-on-call-site'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rule with id 'standard:indent' should run after the rule with id 'standard:trailing-comma-on-declaration-site'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rule with id 'standard:max-line-length' should run after the rule with id 'standard:trailing-comma-on-call-site'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rule with id 'standard:max-line-length' should run after the rule with id 'standard:trailing-comma-on-declaration-site'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rule with id 'standard:argument-list-wrapping' should run after the rule with id 'standard:class-signature'. However, the latter rule is not loaded and is allowed to be ignored. For best results, it is advised load the rule.
[DEBUG] Rules will be executed in order below:
           - internal:ktlint-suppression,
           - standard:annotation-spacing,
           - standard:chain-wrapping,
           - standard:class-naming,
           - standard:colon-spacing,
           - standard:comma-spacing,
           - standard:comment-spacing,
           - standard:comment-wrapping,
           - standard:context-receiver-wrapping,
           - standard:curly-spacing,
           - standard:dot-spacing,
           - standard:double-colon-spacing,
           - standard:enum-entry-name-case,
           - standard:enum-wrapping,
           - standard:final-newline,
           - standard:fun-keyword-spacing,
           - standard:function-naming,
           - standard:function-return-type-spacing,
           - standard:function-start-of-body-spacing,
           - standard:function-type-reference-spacing,
           - standard:kdoc-wrapping,
           - standard:keyword-spacing,
           - standard:modifier-list-spacing,
           - standard:modifier-order,
           - standard:multiline-if-else,
           - standard:no-blank-line-before-rbrace,
           - standard:no-blank-lines-in-chained-method-calls,
           - standard:no-consecutive-blank-lines,
           - standard:no-empty-class-body,
           - standard:no-empty-file,
           - standard:no-empty-first-line-in-method-block,
           - standard:no-line-break-after-else,
           - standard:no-line-break-before-assignment,
           - standard:no-wildcard-imports,
           - standard:nullable-type-spacing,
           - standard:op-spacing,
           - standard:package-name,
           - standard:parameter-list-spacing,
           - standard:parameter-list-wrapping,
           - standard:parameter-wrapping,
           - standard:paren-spacing,
           - standard:property-naming,
           - standard:property-wrapping,
           - standard:range-spacing,
           - standard:spacing-around-angle-brackets,
           - standard:spacing-between-declarations-with-annotations,
           - standard:spacing-between-declarations-with-comments,
           - standard:spacing-between-function-name-and-opening-parenthesis,
           - standard:statement-wrapping,
           - standard:string-template,
           - standard:type-argument-list-spacing,
           - standard:type-parameter-list-spacing,
           - standard:unary-op-spacing,
           - standard:unnecessary-parentheses-before-trailing-lambda,
           - standard:annotation,
           - standard:wrapping,
           - standard:argument-list-wrapping,
           - standard:no-semi,
           - standard:function-signature,
           - standard:indent,
           - standard:block-comment-initial-star-alignment,
           - standard:max-line-length
[DEBUG] Format could not fix > src/main/kotlin/demo/KotlinMain.kt:207:9: Function name should start with a lowercase letter (except factory methods) and use camel case

Steps to Reproduce

Latest commit to this repo is binkley/kotlin-rational@e4de9a4 where I suppressed numerous Ktlint 3.0.0 complaints.

Your Environment

• Version of ktlint used: 3.0.0
• Relevant parts of the .editorconfig settings

[**]
end_of_line = lf
max_line_length = 80

[*.{kt,kts}]
# TODO: Decide if an Android mix makes more sense
ktlint_code_style = intellij_idea
ktlint_standard_discouraged-comment-location = disabled
ktlint_standard_filename = disabled
# Oh, the irony.  IntelliJ insists on sorting java* imports last
ktlint_standard_import-ordering = disabled
ktlint_standard_trailing-comma-on-call-site = disabled
ktlint_standard_trailing-comma-on-declaration-site = disabled

• Name and version (or code for custom task) of integration used (Gradle plugin, Maven plugin, command line, custom Gradle task): Maven 3.8.4 via Maven wrapper
• Operating System and version: Linux Hobbiton 5.15.90.1-microsoft-standard-WSL2 #1 SMP Fri Jan 27 02:56:13 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux using WSL under Windows 11 Home latest

[paul-dingemans]

Your function name starts with a "`" which is not a lowercase character.

According to Kotlin Coding conventions:

In tests (and only in tests), you can use method names with spaces enclosed in backticks.

Android Kotlin style guide does not mention anything about backticks. But I think it is a commonly accepted guideline to not use method names enclosed in backticks.

[binkley]

@paul-dingemans Thanks for the helpful explanation!

I'll update my non-test code accordingly.