[FIR] Properly reports about conflicts in MPP setup

Checker for conflicting declarations will now check for the following
  scenarios too
- two expect declarations in different modules
- actual and non-expect declarations in different modules

^KT-63826 Fixed

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

@@ -25332,6 +25332,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
         runTest("compiler/testData/diagnostics/tests/multiplatform/optionalExpectationDiagnostics.kt");
       }
 
+      @Test
+      @TestMetadata("platformRedeclarationOfExpect.kt")
+      public void testPlatformRedeclarationOfExpect() {
+        runTest("compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.kt");
+      }
+
       @Test
       @TestMetadata("privateTopLevelDeclarations.kt")
       public void testPrivateTopLevelDeclarations() {

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

@@ -25332,6 +25332,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
         runTest("compiler/testData/diagnostics/tests/multiplatform/optionalExpectationDiagnostics.kt");
       }
 
+      @Test
+      @TestMetadata("platformRedeclarationOfExpect.kt")
+      public void testPlatformRedeclarationOfExpect() {
+        runTest("compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.kt");
+      }
+
       @Test
       @TestMetadata("privateTopLevelDeclarations.kt")
       public void testPrivateTopLevelDeclarations() {

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

@@ -349,6 +349,12 @@ public class FirOldFrontendMPPDiagnosticsWithLightTreeTestGenerated extends Abst
     runTest("compiler/testData/diagnostics/tests/multiplatform/optionalExpectationDiagnostics.kt");
   }
 
+  @Test
+  @TestMetadata("platformRedeclarationOfExpect.kt")
+  public void testPlatformRedeclarationOfExpect() {
+    runTest("compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.kt");
+  }
+
   @Test
   @TestMetadata("privateTopLevelDeclarations.kt")
   public void testPrivateTopLevelDeclarations() {

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

@@ -349,6 +349,12 @@ public class FirOldFrontendMPPDiagnosticsWithPsiTestGenerated extends AbstractFi
     runTest("compiler/testData/diagnostics/tests/multiplatform/optionalExpectationDiagnostics.kt");
   }
 
+  @Test
+  @TestMetadata("platformRedeclarationOfExpect.kt")
+  public void testPlatformRedeclarationOfExpect() {
+    runTest("compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.kt");
+  }
+
   @Test
   @TestMetadata("privateTopLevelDeclarations.kt")
   public void testPrivateTopLevelDeclarations() {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/FirConflictsHelpers.kt

@@ -92,10 +92,19 @@ private val FirBasedSymbol<*>.resolvedStatus
         else -> null
     }
 
-internal fun isExpectAndActual(declaration1: FirBasedSymbol<*>, declaration2: FirBasedSymbol<*>): Boolean {
-    val status1 = declaration1.resolvedStatus ?: return false
-    val status2 = declaration2.resolvedStatus ?: return false
-    return (status1.isExpect && status2.isActual) || (status1.isActual && status2.isExpect)
+internal fun isExpectAndNonExpect(first: FirBasedSymbol<*>, second: FirBasedSymbol<*>): Boolean {
+    val firstIsExpect = first.resolvedStatus?.isExpect == true
+    val secondIsExpect = second.resolvedStatus?.isExpect == true
+    /*
+     * this `xor` is equivalent to the following check:
+     * when {
+     *    !firstIsExpect && secondIsExpect -> true
+     *    firstIsExpect && !secondIsExpect -> true
+     *    else -> false
+     * }
+     */
+
+    return firstIsExpect xor secondIsExpect
 }
 
 private class DeclarationBuckets {
@@ -438,9 +447,15 @@ private fun FirClassLikeSymbol<*>.expandedClassWithConstructorsScope(context: Ch
     }
 }
 
-private fun shouldCheckForMultiplatformRedeclaration(dependency: FirBasedSymbol<*>, dependent: FirBasedSymbol<*>): Boolean =
-    dependent.moduleData.allDependsOnDependencies.contains(dependency.moduleData) &&
-            dependency.resolvedStatus?.isExpect != true // ACTUAL_MISSING takes care of this case
+private fun shouldCheckForMultiplatformRedeclaration(dependency: FirBasedSymbol<*>, dependent: FirBasedSymbol<*>): Boolean {
+    if (dependency.moduleData !in dependent.moduleData.allDependsOnDependencies) return false
+
+    /*
+     * If one of declarations is expect and the other is not expect, ExpectActualChecker will handle this case
+     * All other cases (both are expect or both are not expect) should be reported as declarations conflict
+     */
+    return !isExpectAndNonExpect(dependency, dependent)
+}
 
 private fun FirDeclarationCollector<FirBasedSymbol<*>>.collectTopLevelConflict(
     declaration: FirBasedSymbol<*>,
@@ -503,7 +518,7 @@ private fun FirDeclarationCollector<*>.areNonConflictingCallables(
     declaration: FirBasedSymbol<*>,
     conflicting: FirBasedSymbol<*>,
 ): Boolean {
-    if (isExpectAndActual(declaration, conflicting) && declaration.moduleData != conflicting.moduleData) return true
+    if (isExpectAndNonExpect(declaration, conflicting) && declaration.moduleData != conflicting.moduleData) return true
 
     val declarationIsLowPriority = hasLowPriorityAnnotation(declaration.annotations)
     val conflictingIsLowPriority = hasLowPriorityAnnotation(conflicting.annotations)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirConflictsDeclarationChecker.kt

@@ -6,7 +6,6 @@
 package org.jetbrains.kotlin.fir.analysis.checkers.declaration
 
 import org.jetbrains.kotlin.KtFakeSourceElementKind
-import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.diagnostics.KtDiagnosticFactory1
 import org.jetbrains.kotlin.diagnostics.reportOn
@@ -123,7 +122,7 @@ object FirConflictsDeclarationChecker : FirBasicDeclarationChecker(MppCheckerKin
                 conflictingDeclaration.isPrimaryConstructor && symbols.all { it.isPrimaryConstructor }
             ) return@forEach
 
-            if (symbols.singleOrNull()?.let { isExpectAndActual(conflictingDeclaration, it) } == true) {
+            if (symbols.singleOrNull()?.let { isExpectAndNonExpect(conflictingDeclaration, it) } == true) {
                 reporter.reportOn(source, FirErrors.EXPECT_AND_ACTUAL_IN_THE_SAME_MODULE, conflictingDeclaration, context)
                 return@forEach
             }

compiler/testData/diagnostics/tests/multiplatform/expectActualMainInTheSameModuleDifferentFiles.fir.kt

@@ -1,6 +1,6 @@
 // MODULE: m1-common
 // FILE: common.kt
-expect fun <!EXPECT_AND_ACTUAL_IN_THE_SAME_MODULE!>main<!>()
+<!CONFLICTING_OVERLOADS!>expect fun main()<!>
 
 // FILE: common2.kt
 <!CONFLICTING_OVERLOADS!>actual fun <!ACTUAL_WITHOUT_EXPECT!>main<!>()<!> {}

compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.fir.kt

@@ -0,0 +1,7 @@
+// MODULE: common
+// FILE: common.kt
+expect class <!PACKAGE_OR_CLASSIFIER_REDECLARATION!>Foo<!>
+
+// MODULE: main()()(common)
+// FILE: test.kt
+expect class Foo

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

@@ -0,0 +1,7 @@
+// MODULE: common
+// FILE: common.kt
+expect class <!NO_ACTUAL_FOR_EXPECT, NO_ACTUAL_FOR_EXPECT{JVM}, PACKAGE_OR_CLASSIFIER_REDECLARATION{JVM}!>Foo<!>
+
+// MODULE: main()()(common)
+// FILE: test.kt
+expect class <!NO_ACTUAL_FOR_EXPECT, PACKAGE_OR_CLASSIFIER_REDECLARATION!>Foo<!>

compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.ll.kt

@@ -0,0 +1,7 @@
+// MODULE: common
+// FILE: common.kt
+expect class Foo
+
+// MODULE: main()()(common)
+// FILE: test.kt
+expect class Foo

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

@@ -25332,6 +25332,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
         runTest("compiler/testData/diagnostics/tests/multiplatform/optionalExpectationDiagnostics.kt");
       }
 
+      @Test
+      @TestMetadata("platformRedeclarationOfExpect.kt")
+      public void testPlatformRedeclarationOfExpect() {
+        runTest("compiler/testData/diagnostics/tests/multiplatform/platformRedeclarationOfExpect.kt");
+      }
+
       @Test
       @TestMetadata("privateTopLevelDeclarations.kt")
       public void testPrivateTopLevelDeclarations() {