don't report autocast on left expression in equality

if it was checked for not-null beforehand

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/BasicExpressionTypingVisitor.java

@@ -867,7 +867,7 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
             JetBinaryExpression expression,
             ExpressionTypingContext context,
             JetSimpleNameExpression operationSign,
-            JetExpression left,
+            final JetExpression left,
             final JetExpression right
     ) {
         DataFlowInfo dataFlowInfo = context.dataFlowInfo;
@@ -892,7 +892,16 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
             traceInterpretingRightAsNullableAny.commit(new TraceEntryFilter() {
                 @Override
                 public boolean accept(@Nullable WritableSlice<?, ?> slice, Object key) {
-                    return !(key == right && (slice == EXPRESSION_TYPE || slice == PROCESSED));
+
+                    // the type of the right expression isn't 'Any?' actually
+                    if (key == right && (slice == EXPRESSION_TYPE || slice == PROCESSED)) return false;
+
+                    // a hack due to KT-678
+                    // without this line an autocast is reported on the receiver (if it was previously checked for not-null)
+                    // with not-null check the resolution result changes from 'fun Any?.equals' to 'equals' member
+                    if (key == left && slice == AUTOCAST) return false;
+
+                    return true;
                 }
             }, true);
             dataFlowInfo = facade.getTypeInfo(right, contextWithDataFlow).getDataFlowInfo();

compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/equalityUnderNotNullCheck.kt

@@ -0,0 +1,5 @@
+fun test(a: Any?) {
+    if (a is String) {
+        a == ""
+    }
+}

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

@@ -4577,6 +4577,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/AssertNotNull.kt");
             }
             
+            @TestMetadata("equalityUnderNotNullCheck.kt")
+            public void testEqualityUnderNotNullCheck() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/equalityUnderNotNullCheck.kt");
+            }
+            
             @TestMetadata("funcLiteralArgsInsideAmbiguity.kt")
             public void testFuncLiteralArgsInsideAmbiguity() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/nullabilityAndAutoCasts/funcLiteralArgsInsideAmbiguity.kt");