Never import object descriptors, for they may overwrite corresponding vals

compiler/frontend/src/org/jetbrains/jet/lang/resolve/Importer.java

@@ -148,6 +148,7 @@ public interface Importer {
 
         @Override
         public void addAliasImport(@NotNull DeclarationDescriptor descriptor, @NotNull Name aliasName) {
+            assert !DescriptorUtils.isObject(descriptor) : "Never import objects: " + descriptor;
             imports.add(new AliasImportEntry(descriptor, aliasName));
         }
 

compiler/frontend/src/org/jetbrains/jet/lang/resolve/QualifiedExpressionResolver.java

@@ -104,7 +104,9 @@ public class QualifiedExpressionResolver {
         }
 
         for (DeclarationDescriptor descriptor : descriptors) {
-            importer.addAliasImport(descriptor, aliasName);
+            if (!DescriptorUtils.isObject(descriptor)) {
+                importer.addAliasImport(descriptor, aliasName);
+            }
         }
 
         return descriptors;

compiler/testData/diagnostics/tests/scopes/ImportObjectAndUseAsSupertype.kt

@@ -0,0 +1,19 @@
+// FILE: a.kt
+
+package foo
+
+object Bar {
+    fun bar() {}
+}
+
+// FILE: b.kt
+
+package baz
+
+import foo.Bar
+
+class C: <!UNRESOLVED_REFERENCE!>Bar<!>
+
+fun test() {
+    Bar.bar()
+}

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

@@ -5419,6 +5419,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/scopes/ImportFromCurrentWithDifferentName.kt");
             }
             
+            @TestMetadata("ImportObjectAndUseAsSupertype.kt")
+            public void testImportObjectAndUseAsSupertype() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/scopes/ImportObjectAndUseAsSupertype.kt");
+            }
+            
             @TestMetadata("ImportObjectHidesCurrentPackage.kt")
             public void testImportObjectHidesCurrentPackage() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/scopes/ImportObjectHidesCurrentPackage.kt");

core/descriptors/src/org/jetbrains/jet/lang/resolve/scopes/WritableScopeWithImports.java

@@ -22,6 +22,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.TestOnly;
 import org.jetbrains.jet.lang.descriptors.*;
+import org.jetbrains.jet.lang.resolve.DescriptorUtils;
 import org.jetbrains.jet.lang.resolve.name.Name;
 import org.jetbrains.jet.utils.Printer;
 
@@ -215,6 +216,10 @@ public abstract class WritableScopeWithImports extends JetScopeAdapter implement
     public void importClassifierAlias(@NotNull Name importedClassifierName, @NotNull ClassifierDescriptor classifierDescriptor) {
         checkMayWrite();
 
+        if (DescriptorUtils.isObject(classifierDescriptor)) {
+            throw new IllegalStateException("must not be object: " + classifierDescriptor);
+        }
+
         getCurrentIndividualImportScope().addClassifierAlias(importedClassifierName, classifierDescriptor);
     }