[FIR] Report redeclaration across KMP source sets

^KT-57585 Fixed

Related tests:
- MultiPlatformIntegrationTestGenerated.testSimpleNoImplKeywordOnTopLevelFunction
- MultiPlatformIntegrationTestGenerated.testWeakIncompatibilityWithoutActualModifier
- FirPsiJsKlibDiagnosticsTestGenerated.testSignatureClash_MPP
- LLFirPreresolvedReversedDiagnosticCompilerFirTestDataTestGenerated$ResolveWithStdlib$MultiModule.testFakeOverrides
- DiagnosticCompilerTestFE10TestdataTestGenerated$Tests$Multiplatform:
- LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated$Tests$Multiplatform
- FirOldFrontendMPPDiagnosticsWithPsiTestGenerated
- FirOldFrontendMPPDiagnosticsWithLightTreeTestGenerated
- FirLibraryModuleDeclarationResolveTestGenerated.testDataClass
- org.jetbrains.kotlin.idea.k2.highlighting.K2HighlightingMetaInfoTestGenerated$Diagnostics.testDataClassFromLibrary
- org.jetbrains.fir.uast.test.FirLightClassBehaviorTest.testContainingFile
- org.jetbrains.fir.uast.test.FirLightClassBehaviorTest.testAnnotationParameterReference
- org.jetbrains.uast.test.kotlin.org.jetbrains.uast.test.kotlin.comparison.FE1LightClassBehaviorTest.testContainingFile

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

@@ -1740,6 +1740,18 @@ public class FirOldFrontendMPPDiagnosticsWithLightTreeTestGenerated extends Abst
       runTest("compiler/testData/diagnostics/tests/multiplatform/hmpp/ambiguousActuals.kt");
     }
 
+    @Test
+    @TestMetadata("hmppRedeclaration.kt")
+    public void testHmppRedeclaration() {
+      runTest("compiler/testData/diagnostics/tests/multiplatform/hmpp/hmppRedeclaration.kt");
+    }
+
+    @Test
+    @TestMetadata("hmppRedeclarationWithExpectActualPair.kt")
+    public void testHmppRedeclarationWithExpectActualPair() {
+      runTest("compiler/testData/diagnostics/tests/multiplatform/hmpp/hmppRedeclarationWithExpectActualPair.kt");
+    }
+
     @Test
     @TestMetadata("intermediateActualHasAdditionalSupertypes.kt")
     public void testIntermediateActualHasAdditionalSupertypes() {

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

@@ -1740,6 +1740,18 @@ public class FirOldFrontendMPPDiagnosticsWithPsiTestGenerated extends AbstractFi
       runTest("compiler/testData/diagnostics/tests/multiplatform/hmpp/ambiguousActuals.kt");
     }
 
+    @Test
+    @TestMetadata("hmppRedeclaration.kt")
+    public void testHmppRedeclaration() {
+      runTest("compiler/testData/diagnostics/tests/multiplatform/hmpp/hmppRedeclaration.kt");
+    }
+
+    @Test
+    @TestMetadata("hmppRedeclarationWithExpectActualPair.kt")
+    public void testHmppRedeclarationWithExpectActualPair() {
+      runTest("compiler/testData/diagnostics/tests/multiplatform/hmpp/hmppRedeclarationWithExpectActualPair.kt");
+    }
+
     @Test
     @TestMetadata("intermediateActualHasAdditionalSupertypes.kt")
     public void testIntermediateActualHasAdditionalSupertypes() {

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

@@ -16,7 +16,6 @@ import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirNameConflictsTr
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.isEffectivelyFinal
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.*
-import org.jetbrains.kotlin.fir.declarations.FirValueParameter
 import org.jetbrains.kotlin.fir.declarations.impl.FirResolvedDeclarationStatusImpl.Companion.DEFAULT_STATUS_FOR_STATUSLESS_DECLARATIONS
 import org.jetbrains.kotlin.fir.declarations.impl.FirResolvedDeclarationStatusImpl.Companion.DEFAULT_STATUS_FOR_SUSPEND_MAIN_FUNCTION
 import org.jetbrains.kotlin.fir.declarations.impl.modifiersRepresentation
@@ -439,6 +438,10 @@ 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 FirDeclarationCollector<FirBasedSymbol<*>>.collectTopLevelConflict(
     declaration: FirBasedSymbol<*>,
     declarationPresentation: String,
@@ -448,7 +451,11 @@ private fun FirDeclarationCollector<FirBasedSymbol<*>>.collectTopLevelConflict(
     conflictingFile: FirFile? = null,
 ) {
     conflictingSymbol.lazyResolveToPhase(FirResolvePhase.STATUS)
-    if (conflictingSymbol == declaration || declaration.moduleData != conflictingSymbol.moduleData) return
+    if (conflictingSymbol == declaration) return
+    if (
+        declaration.moduleData != conflictingSymbol.moduleData &&
+        !shouldCheckForMultiplatformRedeclaration(declaration, conflictingSymbol)
+    ) return
     val actualConflictingPresentation = conflictingPresentation ?: FirRedeclarationPresenter.represent(conflictingSymbol)
     if (actualConflictingPresentation != declarationPresentation) return
     val actualConflictingFile =