KT-3301 Inference with several supertypes fails

#KT-3301 fixed

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/ConstraintsUtil.java

@@ -33,6 +33,12 @@ public class ConstraintsUtil {
     public static Set<JetType> getValues(@Nullable TypeConstraints typeConstraints) {
         Set<JetType> values = Sets.newLinkedHashSet();
         if (typeConstraints != null && !typeConstraints.isEmpty()) {
+            if (typeConstraints.getExactBounds().size() == 1) {
+                if (verifyOneExactBound(typeConstraints)) {
+                    JetType exactBound = typeConstraints.getExactBounds().iterator().next();
+                    return Collections.singleton(exactBound);
+                }
+            }
             values.addAll(typeConstraints.getExactBounds());
             if (!typeConstraints.getLowerBounds().isEmpty()) {
                 JetType superTypeOfLowerBounds = CommonSupertypes.commonSupertype(typeConstraints.getLowerBounds());
@@ -63,6 +69,21 @@ public class ConstraintsUtil {
         return values;
     }
 
+    private static boolean verifyOneExactBound(@NotNull TypeConstraints typeConstraints) {
+        JetType exactBound = typeConstraints.getExactBounds().iterator().next();
+        for (JetType lowerBound : typeConstraints.getLowerBounds()) {
+            if (!JetTypeChecker.INSTANCE.isSubtypeOf(lowerBound, exactBound)) {
+                return false;
+            }
+        }
+        for (JetType upperBound : typeConstraints.getUpperBounds()) {
+            if (!JetTypeChecker.INSTANCE.isSubtypeOf(exactBound, upperBound)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     @Nullable
     public static JetType getValue(@Nullable TypeConstraints typeConstraints) {
         //todo all checks

compiler/testData/diagnostics/tests/inference/regressions/kt3301.kt

@@ -0,0 +1,20 @@
+//KT-3301 Inference with several supertypes fails
+
+package arrays
+
+trait A
+trait B
+
+object CAB : A, B
+object DAB : A, B
+
+fun m(<!UNUSED_PARAMETER!>args<!> : Array<A>) {
+
+}
+
+fun test122() {
+    m(array(CAB, DAB)) // Wrong error here: Array<Any> is inferred while expected Array<A> is satisfied
+}
+
+//from library
+fun array<T>(vararg <!UNUSED_PARAMETER!>t<!>: T): Array<T> {<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>

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

@@ -2294,6 +2294,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                     doTest("compiler/testData/diagnostics/tests/inference/regressions/kt3174.kt");
                 }
                 
+                @TestMetadata("kt3301.kt")
+                public void testKt3301() throws Exception {
+                    doTest("compiler/testData/diagnostics/tests/inference/regressions/kt3301.kt");
+                }
+                
                 @TestMetadata("kt702.kt")
                 public void testKt702() throws Exception {
                     doTest("compiler/testData/diagnostics/tests/inference/regressions/kt702.kt");