From 71da8212892476ae0b5bed4804417e80be7157c4 Mon Sep 17 00:00:00 2001
From: paul-dingemans <paul-dingemans@users.noreply.github.com>
Date: Sat, 16 Sep 2023 15:22:08 +0200
Subject: [PATCH] Ignore anonymous function in rule `function-naming`

Closes #2260
---
 CHANGELOG.md                                         |  1 +
 .../ruleset/standard/rules/FunctionNamingRule.kt     | 12 +++++++++++-
 .../ruleset/standard/rules/FunctionNamingRuleTest.kt | 12 ++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e846156782..b5bd8530d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ### Fixed
 
 * Fix ktlint cli parameter `--code-style` [#2238](https://github.com/pinterest/ktlint/pull/2238)
+* Ignore anonymous function in rule `function-naming` [#2260](https://github.com/pinterest/ktlint/issue/2260)
 
 ### Changed
 
diff --git a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRule.kt b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRule.kt
index d98d244d74..a1ad1baab4 100644
--- a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRule.kt
+++ b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRule.kt
@@ -1,12 +1,15 @@
 package com.pinterest.ktlint.ruleset.standard.rules
 
 import com.pinterest.ktlint.rule.engine.core.api.ElementType.FUN
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.FUN_KEYWORD
 import com.pinterest.ktlint.rule.engine.core.api.ElementType.IDENTIFIER
 import com.pinterest.ktlint.rule.engine.core.api.ElementType.IMPORT_DIRECTIVE
+import com.pinterest.ktlint.rule.engine.core.api.ElementType.VALUE_PARAMETER_LIST
 import com.pinterest.ktlint.rule.engine.core.api.RuleId
 import com.pinterest.ktlint.rule.engine.core.api.SinceKtlint
 import com.pinterest.ktlint.rule.engine.core.api.SinceKtlint.Status.EXPERIMENTAL
 import com.pinterest.ktlint.rule.engine.core.api.SinceKtlint.Status.STABLE
+import com.pinterest.ktlint.rule.engine.core.api.nextCodeSibling
 import com.pinterest.ktlint.ruleset.standard.StandardRule
 import com.pinterest.ktlint.ruleset.standard.rules.internal.regExIgnoringDiacriticsAndStrokesOnLetters
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
@@ -43,7 +46,8 @@ public class FunctionNamingRule : StandardRule("function-naming") {
             ?.takeUnless {
                 node.isFactoryMethod() ||
                     node.isTestMethod() ||
-                    node.hasValidFunctionName()
+                    node.hasValidFunctionName() ||
+                    node.isAnonymousFunction()
             }?.let {
                 val identifierOffset =
                     node
@@ -76,6 +80,12 @@ public class FunctionNamingRule : StandardRule("function-naming") {
             .orEmpty()
             .matches(VALID_FUNCTION_NAME_REGEXP)
 
+    private fun ASTNode.isAnonymousFunction() =
+        VALUE_PARAMETER_LIST ==
+            findChildByType(FUN_KEYWORD)
+                ?.nextCodeSibling()
+                ?.elementType
+
     private companion object {
         val VALID_FUNCTION_NAME_REGEXP = "[a-z][A-Za-z\\d]*".regExIgnoringDiacriticsAndStrokesOnLetters()
         val VALID_TEST_FUNCTION_NAME_REGEXP = "(`.*`)|([a-z][A-Za-z\\d_]*)".regExIgnoringDiacriticsAndStrokesOnLetters()
diff --git a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRuleTest.kt b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRuleTest.kt
index 6f8116f8b9..34ab7fb691 100644
--- a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRuleTest.kt
+++ b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/FunctionNamingRuleTest.kt
@@ -170,4 +170,16 @@ class FunctionNamingRuleTest {
             """.trimIndent()
         functionNamingRuleAssertThat(code).hasNoLintViolations()
     }
+
+    @Test
+    fun `Issue 2260 - Given an anonymous function in a property assignment`() {
+        val code =
+            """
+            val foo =
+                fun(): String {
+                    return "foo"
+                }
+            """.trimIndent()
+        functionNamingRuleAssertThat(code).hasNoLintViolations()
+    }
 }