Conflicting imports error for imports of classes and packages

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -103,7 +103,7 @@ public interface Errors {
     DiagnosticFactory1<JetSimpleNameExpression, DeclarationDescriptor> CANNOT_BE_IMPORTED = DiagnosticFactory1.create(ERROR);
 
     DiagnosticFactory0<JetExpression> USELESS_HIDDEN_IMPORT = DiagnosticFactory0.create(WARNING);
-
+    DiagnosticFactory1<JetExpression, String> CONFLICTING_IMPORT = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory0<JetExpression> USELESS_SIMPLE_IMPORT = DiagnosticFactory0.create(WARNING);
 
     // Modifiers

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -169,6 +169,7 @@ public class DefaultErrorMessages {
         MAP.put(CANNOT_IMPORT_FROM_ELEMENT, "Cannot import from ''{0}''", NAME);
         MAP.put(CANNOT_BE_IMPORTED, "Cannot import ''{0}'', functions and properties can be imported only from packages", NAME);
         MAP.put(USELESS_HIDDEN_IMPORT, "Useless import, it is hidden further");
+        MAP.put(CONFLICTING_IMPORT, "Conflicting import, imported name ''{0}'' is ambiguous", STRING);
         MAP.put(USELESS_SIMPLE_IMPORT, "Useless import, does nothing");
         MAP.put(PLATFORM_CLASS_MAPPED_TO_KOTLIN, "This class shouldn''t be used in Kotlin. Use {0} instead.", CLASSES_OR_SEPARATED);
 

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

@@ -175,13 +175,10 @@ public class ImportsResolver {
     ) {
 
         JetExpression importedReference = importDirective.getImportedReference();
-        if (importedReference == null || resolvedTo == null) {
-            return;
-        }
+        if (importedReference == null || resolvedTo == null) return;
+
         Name aliasName = JetPsiUtil.getAliasName(importDirective);
-        if (aliasName == null) {
-            return;
-        }
+        if (aliasName == null) return;
 
         boolean uselessHiddenImport = true;
         for (DeclarationDescriptor target : resolvedTo) {
@@ -202,6 +199,23 @@ public class ImportsResolver {
         if (uselessHiddenImport) {
             trace.report(USELESS_HIDDEN_IMPORT.on(importedReference));
         }
+        else {
+            if (resolvedTo.size() == 1) {
+                DeclarationDescriptor target = resolvedTo.iterator().next();
+                if (target instanceof ClassDescriptor) {
+                    if (fileScope.getClassifier(aliasName) == null) {
+                        trace.report(CONFLICTING_IMPORT.on(importedReference, aliasName.asString()));
+                        return;
+                    }
+                }
+                else if (target instanceof PackageViewDescriptor) {
+                    if (fileScope.getPackage(aliasName) == null) {
+                        trace.report(CONFLICTING_IMPORT.on(importedReference, aliasName.asString()));
+                        return;
+                    }
+                }
+            }
+        }
 
         if (!importDirective.isAllUnder() &&
             importedReference instanceof JetSimpleNameExpression &&