Custom Rule for ktlint

customRule.kt

class CustomRuleSetProvider : RuleSetProvider {
    override fun get() = RuleSet("rules",
        NoInternalImportRule(),
        NoVarRule()
    )
}

class NoInternalImportRule : Rule("no-internal-import") {
    override fun visit(
        node: ASTNode, autoCorrect: Boolean,
        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
    ) {
        if (node.elementType == KtStubElementTypes.IMPORT_DIRECTIVE) {
            val importDirective = node.psi as KtImportDirective
            val path = importDirective.importPath?.pathStr
            if (path?.contains("internal") == true) {
                emit(node.startOffset, "Importing '$path' which is an internal import.", false)
            }
        }
    }
}

class NoVarRule : Rule("no-var") {

    override fun visit(
        node: ASTNode,
        autoCorrect: Boolean,
        emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit
    ) {
        if (node.elementType == VAR_KEYWORD) {
            emit(node.startOffset, "😱 Unexpected var, use val instead 🏄‍", false)
        }
    }
}