Filter out overridden candidates before looking for most specific

This filtering will remove signature duplicates that prevent findMaximallySpecific() from finding best candidate.

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/results/ResolutionResultsHandler.java

@@ -179,24 +179,24 @@ public class ResolutionResultsHandler {
             return OverloadResolutionResultsImpl.success(candidates.iterator().next());
         }
 
-        MutableResolvedCall<D> maximallySpecific = OverloadingConflictResolver.INSTANCE.findMaximallySpecific(candidates, false);
+        Set<MutableResolvedCall<D>> noOverrides = OverrideResolver.filterOutOverridden(candidates, MAP_TO_RESULT);
+        if (noOverrides.size() == 1) {
+            return OverloadResolutionResultsImpl.success(noOverrides.iterator().next());
+        }
+
+        MutableResolvedCall<D> maximallySpecific = OverloadingConflictResolver.INSTANCE.findMaximallySpecific(noOverrides, false);
         if (maximallySpecific != null) {
             return OverloadResolutionResultsImpl.success(maximallySpecific);
         }
 
         if (discriminateGenerics) {
             MutableResolvedCall<D> maximallySpecificGenericsDiscriminated = OverloadingConflictResolver.INSTANCE.findMaximallySpecific(
-                    candidates, true);
+                    noOverrides, true);
             if (maximallySpecificGenericsDiscriminated != null) {
                 return OverloadResolutionResultsImpl.success(maximallySpecificGenericsDiscriminated);
             }
         }
 
-        Set<MutableResolvedCall<D>> noOverrides = OverrideResolver.filterOutOverridden(candidates, MAP_TO_RESULT);
-        if (noOverrides.size() == 1) {
-                return OverloadResolutionResultsImpl.success(noOverrides.iterator().next());
-        }
-
         return OverloadResolutionResultsImpl.ambiguity(noOverrides);
     }
 

compiler/testData/diagnostics/tests/multimodule/varargConflict.kt

@@ -0,0 +1,26 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
+// MODULE: m1
+// FILE: a.kt
+
+package p
+
+public fun foo(a: Int) {}
+public fun foo(vararg values: Int) {}
+
+// MODULE: m2
+// FILE: b.kt
+
+package p
+
+public fun foo(a: Int) {}
+public fun foo(vararg values: Int) {}
+
+// MODULE: m3(m1, m2)
+// FILE: c.kt
+package m
+
+import p.foo
+
+fun main() {
+    foo(12)
+}

compiler/testData/diagnostics/tests/multimodule/varargConflict.txt

@@ -0,0 +1,33 @@
+// -- Module: <m1> --
+package
+
+package p {
+    public fun foo(/*0*/ a: kotlin.Int): kotlin.Unit
+    public fun foo(/*0*/ vararg values: kotlin.Int /*kotlin.IntArray*/): kotlin.Unit
+}
+
+
+// -- Module: <m2> --
+package
+
+package p {
+    public fun foo(/*0*/ a: kotlin.Int): kotlin.Unit
+    public fun foo(/*0*/ vararg values: kotlin.Int /*kotlin.IntArray*/): kotlin.Unit
+}
+
+
+// -- Module: <m3> --
+package
+
+package m {
+    internal fun main(): kotlin.Unit
+}
+
+package p {
+    public fun foo(/*0*/ a: kotlin.Int): kotlin.Unit
+    public fun foo(/*0*/ a: kotlin.Int): kotlin.Unit
+    public fun foo(/*0*/ vararg values: kotlin.Int /*kotlin.IntArray*/): kotlin.Unit
+    public fun foo(/*0*/ vararg values: kotlin.Int /*kotlin.IntArray*/): kotlin.Unit
+}
+
+

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

@@ -8388,6 +8388,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("varargConflict.kt")
+            public void testVarargConflict() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/multimodule/varargConflict.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("compiler/testData/diagnostics/tests/multimodule/duplicateClass")
             @TestDataPath("$PROJECT_ROOT")
             @RunWith(JUnit3RunnerWithInners.class)