From 37c3ff06f1d692295fa0121ca71550106d52b72f Mon Sep 17 00:00:00 2001
From: paul-dingemans <paul-dingemans@users.noreply.github.com>
Date: Mon, 11 Dec 2023 14:54:40 +0100
Subject: [PATCH] Disallow `else-if (..) <statement>` as single line construct

Closes #2420
---
 .../standard/rules/MultiLineIfElseRule.kt     |  9 ++++---
 .../standard/rules/MultiLineIfElseRuleTest.kt | 26 +++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRule.kt b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRule.kt
index 47eefde2a6..c5a1417dcc 100644
--- a/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRule.kt
+++ b/ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRule.kt
@@ -107,10 +107,13 @@ public class MultiLineIfElseRule :
                 // Allow single line if statements as long as they are really simple (e.g. do not contain newlines)
                 //    if (...) <statement> // no else statement
                 //    if (...) <statement> else <statement>
-                return
+                if (node.treeParent.treeParent.elementType == ELSE) {
+                    // Except in case nested if-else-if on single line
+                    //    if (...) <statement> else if (..) <statement>
+                } else {
+                    return
+                }
             }
-
-            Unit
         }
 
         emit(node.firstChildNode.startOffset, "Missing { ... }", true)
diff --git a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRuleTest.kt b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRuleTest.kt
index 3f973f3474..971f3c6e29 100644
--- a/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRuleTest.kt
+++ b/ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/MultiLineIfElseRuleTest.kt
@@ -678,4 +678,30 @@ class MultiLineIfElseRuleTest {
                 LintViolation(1, 53, "Missing { ... }"),
             ).isFormattedAs(formattedCode)
     }
+
+    @Test
+    fun `Issue 2420 - Given a single line else-if`() {
+        val code =
+            """
+            fun foo() {
+                if (foo) {
+                    doFoo()
+                } else if (bar) doBar()
+            }
+            """.trimIndent()
+        val formattedCode =
+            """
+            fun foo() {
+                if (foo) {
+                    doFoo()
+                } else if (bar) {
+                    doBar()
+                }
+            }
+            """.trimIndent()
+        multiLineIfElseRuleAssertThat(code)
+            .hasLintViolations(
+                LintViolation(4, 21, "Missing { ... }"),
+            ).isFormattedAs(formattedCode)
+    }
 }