[FIR] Fix IncDecOperatorsInExpectClass for FIR, add multi-module test

- `IncDecOperatorsInExpectClass.kt` should produce an
  `ACTUAL_WITHOUT_EXPECT` in K2 (see KT-55177). This went unnoticed
  because of KT-55570.
- A similar multi-module test for K1 and K2 has been added, called:
  `multiplatform/incDecOperatorsInExpectClass.kt`.

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -21356,6 +21356,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                 runTest("compiler/testData/diagnostics/tests/multiplatform/implFakeOverride.kt");
             }
 
+            @Test
+            @TestMetadata("incDecOperatorsInExpectClass.kt")
+            public void testIncDecOperatorsInExpectClass() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.kt");
+            }
+
             @Test
             @TestMetadata("incompatibles.kt")
             public void testIncompatibles() throws Exception {

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

@@ -21362,6 +21362,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                 runTest("compiler/testData/diagnostics/tests/multiplatform/implFakeOverride.kt");
             }
 
+            @Test
+            @TestMetadata("incDecOperatorsInExpectClass.kt")
+            public void testIncDecOperatorsInExpectClass() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.kt");
+            }
+
             @Test
             @TestMetadata("incompatibles.kt")
             public void testIncompatibles() throws Exception {

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

@@ -21356,6 +21356,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                 runTest("compiler/testData/diagnostics/tests/multiplatform/implFakeOverride.kt");
             }
 
+            @Test
+            @TestMetadata("incDecOperatorsInExpectClass.kt")
+            public void testIncDecOperatorsInExpectClass() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.kt");
+            }
+
             @Test
             @TestMetadata("incompatibles.kt")
             public void testIncompatibles() throws Exception {

compiler/testData/diagnostics/tests/IncDecOperatorsInExpectClass.fir.kt

@@ -0,0 +1,13 @@
+// In FIR, declaring the same `expect` and `actual` classes in one compiler module is not possible (see KT-55177). Hence the `.fir.kt` test
+// expects a diagnostic here. The multi-module test corresponding to this test is called: `multiplatform/incDecOperatorsInExpectClass.kt`.
+
+// !LANGUAGE: +MultiPlatformProjects
+// SKIP_TXT
+// Issue: KT-49714
+
+expect class Counter {
+    operator fun inc(): Counter
+    operator fun dec(): Counter
+}
+
+<!ACTUAL_WITHOUT_EXPECT!>actual typealias Counter = Int<!>

compiler/testData/diagnostics/tests/IncDecOperatorsInExpectClass.kt

@@ -1,4 +1,6 @@
-// FIR_IDENTICAL
+// In FIR, declaring the same `expect` and `actual` classes in one compiler module is not possible (see KT-55177). Hence the `.fir.kt` test
+// expects a diagnostic here. The multi-module test corresponding to this test is called: `multiplatform/incDecOperatorsInExpectClass.kt`.
+
 // !LANGUAGE: +MultiPlatformProjects
 // SKIP_TXT
 // Issue: KT-49714

compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// Issue: KT-49714
+
+// MODULE: common
+// TARGET_PLATFORM: Common
+expect class Counter {
+    operator fun inc(): Counter
+    operator fun dec(): Counter
+}
+
+// MODULE: main()()(common)
+actual typealias Counter = Int

compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.txt

@@ -0,0 +1,15 @@
+// -- Module: <common> --
+package
+
+public final expect class Counter {
+    public final expect operator fun dec(): Counter
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final expect operator fun inc(): Counter
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+// -- Module: <main> --
+package
+
+public actual typealias Counter = kotlin.Int

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

@@ -21362,6 +21362,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/multiplatform/implFakeOverride.kt");
             }
 
+            @Test
+            @TestMetadata("incDecOperatorsInExpectClass.kt")
+            public void testIncDecOperatorsInExpectClass() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/multiplatform/incDecOperatorsInExpectClass.kt");
+            }
+
             @Test
             @TestMetadata("incompatibles.kt")
             public void testIncompatibles() throws Exception {