fix KT-9733 No error shown for 2 "main" functions in the same file

#KT-9733 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/state/BuilderFactoryForDuplicateSignatureDiagnostics.kt

@@ -70,9 +70,6 @@ class BuilderFactoryForDuplicateSignatureDiagnostics(
             for (origin in data.signatureOrigins) {
                 var element = origin.element
 
-                // TODO Remove this code after dropping package facades
-                if (element is KtNamedFunction && mainFunctionDetector.isMain(element) && !element.isInsideJvmMultifileClassFile()) return
-
                 if (element == null || origin.originKind in EXTERNAL_SOURCES_KINDS) {
                     element = data.classOrigin.element
                 }

compiler/frontend/src/org/jetbrains/kotlin/resolve/OverloadResolver.java

@@ -25,10 +25,7 @@ import org.jetbrains.kotlin.diagnostics.Errors;
 import org.jetbrains.kotlin.idea.MainFunctionDetector;
 import org.jetbrains.kotlin.name.FqNameUnsafe;
 import org.jetbrains.kotlin.name.Name;
-import org.jetbrains.kotlin.psi.KtClassOrObject;
+import org.jetbrains.kotlin.psi.*;
-import org.jetbrains.kotlin.psi.KtDeclaration;
-import org.jetbrains.kotlin.psi.KtObjectDeclaration;
-import org.jetbrains.kotlin.psi.KtSecondaryConstructor;
 
 import java.util.Collection;
 import java.util.Map;
@@ -156,7 +153,7 @@ public class OverloadResolver {
     }
 
     @NotNull
-    private static Set<Pair<KtDeclaration, CallableMemberDescriptor>> findRedeclarations(@NotNull Collection<? extends CallableMemberDescriptor> members) {
+    private Set<Pair<KtDeclaration, CallableMemberDescriptor>> findRedeclarations(@NotNull Collection<? extends CallableMemberDescriptor> members) {
         Set<Pair<KtDeclaration, CallableMemberDescriptor>> redeclarations = Sets.newLinkedHashSet();
         for (CallableMemberDescriptor member : members) {
             for (CallableMemberDescriptor member2 : members) {
@@ -165,6 +162,10 @@ public class OverloadResolver {
                 }
 
                 if (!OverloadUtil.isOverloadable(member, member2) && member.getKind() != CallableMemberDescriptor.Kind.SYNTHESIZED) {
+                    if (isTopLevelMainInDifferentFiles(member, member2)) {
+                        continue;
+                    }
+
                     KtDeclaration ktDeclaration = (KtDeclaration) DescriptorToSourceUtils.descriptorToDeclaration(member);
                     if (ktDeclaration != null) {
                         redeclarations.add(Pair.create(ktDeclaration, member));
@@ -187,11 +188,19 @@ public class OverloadResolver {
                member.getContainingDeclaration().getContainingDeclaration().equals(member2.getContainingDeclaration().getContainingDeclaration());
     }
 
+    private boolean isTopLevelMainInDifferentFiles(@NotNull CallableMemberDescriptor member, @NotNull CallableMemberDescriptor member2) {
+        if (!DescriptorToSourceUtils.isTopLevelMainFunction(member, mainFunctionDetector) ||
+            !DescriptorToSourceUtils.isTopLevelMainFunction(member2, mainFunctionDetector)) {
+            return false;
+        }
+
+        return DescriptorToSourceUtils.getContainingFile(member) != DescriptorToSourceUtils.getContainingFile(member2);
+    }
+
     private void reportRedeclarations(@NotNull String functionContainer,
             @NotNull Set<Pair<KtDeclaration, CallableMemberDescriptor>> redeclarations) {
         for (Pair<KtDeclaration, CallableMemberDescriptor> redeclaration : redeclarations) {
             CallableMemberDescriptor memberDescriptor = redeclaration.getSecond();
-            if (DescriptorToSourceUtils.isTopLevelMainFunction(memberDescriptor, mainFunctionDetector)) return;
 
             KtDeclaration ktDeclaration = redeclaration.getFirst();
             if (memberDescriptor instanceof PropertyDescriptor) {

compiler/testData/diagnostics/tests/redeclarations/RedeclarationMainInFile.kt

@@ -0,0 +1,4 @@
+// KT-9733 No error shown for 2 "main" functions in the same file
+
+<!CONFLICTING_OVERLOADS!>fun main(args: Array<String>)<!> {}
+<!CONFLICTING_OVERLOADS!>fun main(args: Array<String>)<!> {}

compiler/testData/diagnostics/tests/redeclarations/RedeclarationMainInFile.txt

@@ -0,0 +1,4 @@
+package
+
+public fun main(/*0*/ args: kotlin.Array<kotlin.String>): kotlin.Unit
+public fun main(/*0*/ args: kotlin.Array<kotlin.String>): kotlin.Unit

compiler/tests/org/jetbrains/kotlin/checkers/JetDiagnosticsTestGenerated.java

@@ -11937,6 +11937,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("RedeclarationMainInFile.kt")
+            public void testRedeclarationMainInFile() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/redeclarations/RedeclarationMainInFile.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("RedeclarationMainInMultiFile.kt")
             public void testRedeclarationMainInMultiFile() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/redeclarations/RedeclarationMainInMultiFile.kt");