From 524ecb3df78162b85e1ec79ac4d0470ef7c0fb94 Mon Sep 17 00:00:00 2001
From: Paul Dingemans <paul-dingemans@users.noreply.github.com>
Date: Fri, 4 Oct 2024 15:58:03 +0200
Subject: [PATCH] Do not insert a trailing comma in a multiline when-entry
 containing a guard (#2825)

Closes #2817
---
 .../TrailingCommaOnDeclarationSiteRule.kt     |  9 +++++++
 .../TrailingCommaOnDeclarationSiteRuleTest.kt | 24 +++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRule.kt b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRule.kt
index c2a5a96e1c..511e412698 100644
--- a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRule.kt
+++ b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRule.kt
@@ -35,6 +35,7 @@ import com.pinterest.ktlint.rule.engine.core.util.cast
 import com.pinterest.ktlint.ruleset.standard.StandardRule
 import org.ec4j.core.model.PropertyType
 import org.ec4j.core.model.PropertyType.PropertyValueParser
+import org.jetbrains.kotlin.KtNodeTypes.WHEN_ENTRY_GUARD
 import org.jetbrains.kotlin.com.intellij.lang.ASTNode
 import org.jetbrains.kotlin.com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.com.intellij.psi.PsiWhiteSpace
@@ -257,7 +258,13 @@ public class TrailingCommaOnDeclarationSiteRule :
         val trailingCommaNode = prevLeaf?.findPreviousTrailingCommaNodeOrNull()
         val trailingCommaState =
             when {
+                hasWhenGuard() -> {
+                    // The compiler won't allow any comma in the when-entry in case it contains a guard clause
+                    TrailingCommaState.NOT_EXISTS
+                }
+
                 isMultiline(psi) -> if (trailingCommaNode != null) TrailingCommaState.EXISTS else TrailingCommaState.MISSING
+
                 else -> if (trailingCommaNode != null) TrailingCommaState.REDUNDANT else TrailingCommaState.NOT_EXISTS
             }
         when (trailingCommaState) {
@@ -425,6 +432,8 @@ public class TrailingCommaOnDeclarationSiteRule :
         return codeLeaf?.takeIf { it.elementType == COMMA }
     }
 
+    private fun ASTNode.hasWhenGuard() = elementType == WHEN_ENTRY && children().any { it.elementType == WHEN_ENTRY_GUARD }
+
     private fun containsLineBreakInLeavesRange(
         from: PsiElement,
         to: PsiElement,
diff --git a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRuleTest.kt b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRuleTest.kt
index 0c520fb513..50e3152453 100644
--- a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRuleTest.kt
+++ b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/TrailingCommaOnDeclarationSiteRuleTest.kt
@@ -1066,4 +1066,28 @@ class TrailingCommaOnDeclarationSiteRuleTest {
             .hasLintViolation(3, 13, "Missing trailing comma and newline before \"->\"")
             .isFormattedAs(formattedCode)
     }
+
+    @Test
+    fun `Issue 2817 - Given when condition with guard clause`() {
+        val code =
+            """
+            val x1 =
+                when (true) {
+                    true if foo("a") -> true
+                    else -> false
+                }
+            val x2 =
+                when (true) {
+                    true if foo(
+                        "a",
+                    )
+                    -> true
+
+                    else -> false
+                }
+            """.trimIndent()
+        trailingCommaOnDeclarationSiteRuleAssertThat(code)
+            .withEditorConfigOverride(TRAILING_COMMA_ON_DECLARATION_SITE_PROPERTY to true)
+            .hasNoLintViolations()
+    }
 }