[Test] Add regression test for KT-66336

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -18969,6 +18969,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
           KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/forks"), Pattern.compile("^(.+)\\.(kt|kts)$"), Pattern.compile("^(.+)\\.(reversed|fir|ll)\\.kts?$"), true);
         }
 
+        @Test
+        @TestMetadata("forkInWhen.kt")
+        public void testForkInWhen() {
+          runTest("compiler/testData/diagnostics/tests/inference/forks/forkInWhen.kt");
+        }
+
         @Test
         @TestMetadata("nestedCallVariableFixation.kt")
         public void testNestedCallVariableFixation() {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -18969,6 +18969,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
           KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/forks"), Pattern.compile("^(.+)\\.(kt|kts)$"), Pattern.compile("^(.+)\\.(reversed|fir|ll)\\.kts?$"), true);
         }
 
+        @Test
+        @TestMetadata("forkInWhen.kt")
+        public void testForkInWhen() {
+          runTest("compiler/testData/diagnostics/tests/inference/forks/forkInWhen.kt");
+        }
+
         @Test
         @TestMetadata("nestedCallVariableFixation.kt")
         public void testNestedCallVariableFixation() {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -18963,6 +18963,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
           KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/forks"), Pattern.compile("^(.+)\\.kt$"), Pattern.compile("^(.+)\\.(reversed|fir|ll)\\.kts?$"), true, "multiplatform");
         }
 
+        @Test
+        @TestMetadata("forkInWhen.kt")
+        public void testForkInWhen() {
+          runTest("compiler/testData/diagnostics/tests/inference/forks/forkInWhen.kt");
+        }
+
         @Test
         @TestMetadata("nestedCallVariableFixation.kt")
         public void testNestedCallVariableFixation() {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -18969,6 +18969,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
           KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/forks"), Pattern.compile("^(.*)\\.kts?$"), Pattern.compile("^(.+)\\.(reversed|fir|ll)\\.kts?$"), true, "multiplatform");
         }
 
+        @Test
+        @TestMetadata("forkInWhen.kt")
+        public void testForkInWhen() {
+          runTest("compiler/testData/diagnostics/tests/inference/forks/forkInWhen.kt");
+        }
+
         @Test
         @TestMetadata("nestedCallVariableFixation.kt")
         public void testNestedCallVariableFixation() {

compiler/testData/diagnostics/tests/inference/forks/forkInWhen.kt

@@ -0,0 +1,20 @@
+// FIR_IDENTICAL
+// ISSUE: KT-66336
+
+interface A : Comparable<A>
+interface B : Comparable<B>
+
+open class Base<T>
+class Derived<T : Comparable<T>, in S : T?>(expr: Base<in S>) : Base<T?>()
+
+fun call(f: (String) -> Base<*>? = { null }) {}
+
+fun test(b: Base<B>) {
+    call {
+        when (it) {
+            "a" -> b
+            "b" -> Derived(Base<A>())
+            else -> null
+        }
+    }
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -18969,6 +18969,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
           KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/inference/forks"), Pattern.compile("^(.*)\\.kts?$"), Pattern.compile("^(.+)\\.(reversed|fir|ll)\\.kts?$"), true);
         }
 
+        @Test
+        @TestMetadata("forkInWhen.kt")
+        public void testForkInWhen() {
+          runTest("compiler/testData/diagnostics/tests/inference/forks/forkInWhen.kt");
+        }
+
         @Test
         @TestMetadata("nestedCallVariableFixation.kt")
         public void testNestedCallVariableFixation() {