equals implies not-nullness of its argument (IDEA-88777, IDEA-92809, IDEA-16979)

java/java-impl/src/com/intellij/codeInspection/dataFlow/ControlFlowAnalyzer.java

@@ -701,12 +701,24 @@ class ControlFlowAnalyzer extends JavaElementVisitor {
   }
 
   private static class ApplyNotNullInstruction extends Instruction {
+    private PsiMethodCallExpression myCall;
+
+    private ApplyNotNullInstruction(PsiMethodCallExpression call) {
+      myCall = call;
+    }
+
     @Override
     public DfaInstructionState[] accept(DataFlowRunner runner, DfaMemoryState state, InstructionVisitor visitor) {
       DfaValue value = state.pop();
       DfaValueFactory factory = runner.getFactory();
-      state.applyCondition(factory.getRelationFactory().createRelation(value, factory.getConstFactory().getNull(), JavaTokenType.EQEQ, true));
-      return nextInstruction(runner, state);
+      if (state.applyCondition(
+        factory.getRelationFactory().createRelation(value, factory.getConstFactory().getNull(), JavaTokenType.EQEQ, true))) {
+        return nextInstruction(runner, state);
+      }
+      if (visitor instanceof StandardInstructionVisitor) {
+        ((StandardInstructionVisitor)visitor).skipConstantConditionReporting(myCall);
+      }
+      return DfaInstructionState.EMPTY_ARRAY;
     }
   }
 
@@ -1225,7 +1237,7 @@ class ControlFlowAnalyzer extends JavaElementVisitor {
         addInstruction(new PushInstruction(myFactory.getConstFactory().getTrue(), null));
 
         paramExprs[0].accept(this);
-        addInstruction(new ApplyNotNullInstruction());
+        addInstruction(new ApplyNotNullInstruction(expression));
       }
     }
     finally {

java/java-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java

@@ -615,7 +615,7 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
     if (dfaRight == myFactory.getConstFactory().getNull() && dfaLeft instanceof DfaVariableValue) {
       final DfaVariableState varState = getVariableState((DfaVariableValue)dfaLeft);
       if (varState.isNotNull()) return isNegated;
-      varState.setNullable(true);
+      varState.setNullable(!isNegated);
     }
 
     if (dfaLeft instanceof DfaUnknownValue || dfaRight instanceof DfaUnknownValue) return true;

java/java-impl/src/com/intellij/codeInspection/dataFlow/StandardInstructionVisitor.java

@@ -330,7 +330,7 @@ public class StandardInstructionVisitor extends InstructionVisitor {
     }
 
     if (isViaMethods(dfaLeft) || isViaMethods(dfaRight)) {
-      ContainerUtil.addIfNotNull(myNotToReportReachability, instruction.getPsiAnchor());
+      skipConstantConditionReporting(instruction.getPsiAnchor());
     }
     myCanBeNullInInstanceof.add(instruction);
 
@@ -363,6 +363,10 @@ public class StandardInstructionVisitor extends InstructionVisitor {
     return states.toArray(new DfaInstructionState[states.size()]);
   }
 
+  public void skipConstantConditionReporting(@Nullable PsiElement anchor) {
+    ContainerUtil.addIfNotNull(myNotToReportReachability, anchor);
+  }
+
   private static boolean isViaMethods(DfaValue dfa) {
     return dfa instanceof DfaVariableValue && ((DfaVariableValue)dfa).isViaMethods();
   }

java/java-impl/src/com/intellij/codeInspection/dataFlow/value/DfaRelationValue.java

@@ -51,7 +51,6 @@ public class DfaRelationValue extends DfaValue {
       myStringToObject = new HashMap<String, ArrayList<DfaRelationValue>>();
     }
 
-    @Nullable
     public DfaRelationValue createRelation(DfaValue dfaLeft, DfaValue dfaRight, IElementType relation, boolean negated) {
       if (dfaRight instanceof DfaTypeValue && INSTANCEOF_KEYWORD != relation) return null;
       if (PLUS == relation) return null;

java/java-tests/testData/inspection/dataFlow/fixture/EqualsImpliesNotNull.java

@@ -0,0 +1,24 @@
+import org.jetbrains.annotations.NotNull;
+
+class Test {
+  public static void main(String[] args) {
+    Object first = null;
+    for (int i = 0; i < 10; i++) {
+      if (!"b".equals(first)) {
+        first = "b";
+      }
+      System.out.println(first.toString());
+    }
+  }
+
+  public void buggyInspectionExample(Object parentNode) {
+    final String parentName = parentNode == null ? null : parentNode.toString();
+    if ("Topics".equals(parentName)) {
+      System.out.println(parentNode.toString());
+    } else if ("Queues".equals(parentName)) {
+      System.out.println(parentNode.toString());
+    }
+    System.out.println(<warning descr="Method invocation 'parentNode.toString()' may produce 'java.lang.NullPointerException'">parentNode.toString()</warning>);
+  }
+
+}

java/java-tests/testData/inspection/dataFlow/fixture/EqualsNotNull.java

@@ -52,8 +52,23 @@ public class Main {
       return val;
     }
     if (defVal.equals(val)) {
-      return <warning descr="Expression 'val' might evaluate to null but is returned by the method declared as @NotNull">val</warning>;
+      return val;
     }
     return defVal;
   }
+
+  @NotNull
+  private static Object test(@NotNull Object defVal, @Nullable final Object val) {
+    if (val != null) {
+      return val;
+    }
+    if (defVal == val) {
+      return val;
+    }
+    if (defVal.equals(val)) {
+      return val;
+    }
+    return defVal;
+  }
+
 }

java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionFixtureTest.java

@@ -101,5 +101,6 @@ public class DataFlowInspectionFixtureTest extends JavaCodeInsightFixtureTestCas
   public void testPreserveNullableOnUncheckedCast() throws Throwable { doTest(); }
 
   public void testPassingNullableIntoVararg() throws Throwable { doTest(); }
+  public void testEqualsImpliesNotNull() throws Throwable { doTest(); }
 
 }