Added Optional emptiness handler

nullaway/src/main/java/com/uber/nullaway/handlers/Handlers.java

@@ -50,6 +50,7 @@ public static Handler buildDefault(Config config) {
     handlerListBuilder.add(new RxNullabilityPropagator());
     handlerListBuilder.add(new ContractHandler());
     handlerListBuilder.add(new ApacheThriftIsSetHandler());
+    handlerListBuilder.add(new OptionalEmptinessHandler());
     return new CompositeHandler(handlerListBuilder.build());
   }
 

nullaway/src/main/java/com/uber/nullaway/handlers/OptionalEmptinessHandler.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2018 Uber Technologies, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.uber.nullaway.handlers;
+
+import com.google.common.base.Preconditions;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.util.ASTHelpers;
+import com.sun.source.tree.ClassTree;
+import com.sun.source.tree.ExpressionTree;
+import com.sun.source.tree.Tree;
+import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.code.Types;
+import com.sun.tools.javac.util.Context;
+import com.uber.nullaway.NullAway;
+import com.uber.nullaway.Nullness;
+import com.uber.nullaway.dataflow.AccessPath;
+import com.uber.nullaway.dataflow.AccessPathNullnessPropagation;
+import java.util.Optional;
+import javax.annotation.Nullable;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
+import org.checkerframework.dataflow.cfg.node.MethodInvocationNode;
+import org.checkerframework.dataflow.cfg.node.Node;
+
+/**
+ * Handler to better handle {@code isPresent()} methods in code generated for Optionals. With this
+ * handler, we learn appropriate Emptiness facts about the relevant property from these calls.
+ */
+public class OptionalEmptinessHandler extends BaseNoOpHandler {
+
+  private static String OPTIONAL_PATH = "java.util.Optional";
+
+  @Nullable private Optional<Type> optionalType;
+
+  @Override
+  public boolean onOverrideMayBeNullExpr(
+      NullAway analysis, ExpressionTree expr, VisitorState state, boolean exprMayBeNull) {
+    if (expr.getKind() == Tree.Kind.METHOD_INVOCATION
+        && optionalIsGetCall((Symbol.MethodSymbol) ASTHelpers.getSymbol(expr), state.getTypes())) {
+      return true;
+    }
+    return exprMayBeNull;
+  }
+
+  @Override
+  public void onMatchTopLevelClass(
+      NullAway analysis, ClassTree tree, VisitorState state, Symbol.ClassSymbol classSymbol) {
+    if (optionalType == null) {
+      optionalType =
+          Optional.ofNullable(state.getTypeFromString(OPTIONAL_PATH))
+              .map(state.getTypes()::erasure);
+    }
+  }
+
+  @Override
+  public NullnessHint onDataflowVisitMethodInvocation(
+      MethodInvocationNode node,
+      Types types,
+      Context context,
+      AccessPathNullnessPropagation.SubNodeValues inputs,
+      AccessPathNullnessPropagation.Updates thenUpdates,
+      AccessPathNullnessPropagation.Updates elseUpdates,
+      AccessPathNullnessPropagation.Updates bothUpdates) {
+    Symbol.MethodSymbol symbol = ASTHelpers.getSymbol(node.getTree());
+
+    if (optionalIsGetCall(symbol, types)) {
+      return NullnessHint.HINT_NULLABLE;
+    } else if (optionalIsPresentCall(symbol, types)) {
+      Element getter = null;
+      Node base = node.getTarget().getReceiver();
+      for (Symbol elem : symbol.owner.getEnclosedElements()) {
+        if (elem.getKind().equals(ElementKind.METHOD)
+            && elem.getSimpleName().toString().equals("get")) {
+          getter = elem;
+        }
+      }
+      updateNonNullAPsForElement(thenUpdates, getter, base);
+    }
+    return NullnessHint.UNKNOWN;
+  }
+
+  private void updateNonNullAPsForElement(
+      AccessPathNullnessPropagation.Updates updates, @Nullable Element elem, Node base) {
+    if (elem != null) {
+      AccessPath ap = AccessPath.fromBaseAndElement(base, elem);
+      if (ap != null) {
+        updates.set(ap, Nullness.NONNULL);
+      }
+    }
+  }
+
+  private boolean optionalIsPresentCall(Symbol.MethodSymbol symbol, Types types) {
+    Preconditions.checkNotNull(optionalType);
+    // noinspection ConstantConditions
+    return optionalType.isPresent()
+        && symbol.getSimpleName().toString().equals("isPresent")
+        && symbol.getParameters().length() == 0
+        && types.isSubtype(symbol.owner.type, optionalType.get());
+  }
+
+  private boolean optionalIsGetCall(Symbol.MethodSymbol symbol, Types types) {
+    Preconditions.checkNotNull(optionalType);
+    // noinspection ConstantConditions
+    return optionalType.isPresent()
+        && symbol.getSimpleName().toString().equals("get")
+        && symbol.getParameters().length() == 0
+        && types.isSubtype(symbol.owner.type, optionalType.get());
+  }
+}

nullaway/src/test/java/com/uber/nullaway/NullAwayTest.java

@@ -1175,6 +1175,44 @@ public void lambdaPlusRestrictiveNegative() {
         .doTest();
   }
 
+  @Test
+  public void OptionalEmptinessHandlerTest() {
+    compilationHelper
+        .setArgs(
+            Arrays.asList(
+                "-d",
+                temporaryFolder.getRoot().getAbsolutePath(),
+                "-XepOpt:NullAway:AnnotatedPackages=com.uber",
+                "-XepOpt:NullAway:UnannotatedSubPackages=com.uber.lib.unannotated"))
+        .addSourceLines(
+            "TestNegative.java",
+            "package com.uber;",
+            "import java.util.Optional;",
+            "import javax.annotation.Nullable;",
+            "public class TestNegative {",
+            "  void foo() {",
+            "    Optional<Object> a = Optional.of(null);",
+            "      // no error since a.isPresent() is called",
+            "      if(a.isPresent()){",
+            "         a.get().toString();",
+            "       }",
+            "  }",
+            "}")
+        .addSourceLines(
+            "TestPositive.java",
+            "package com.uber;",
+            "import java.util.Optional;",
+            "import javax.annotation.Nullable;",
+            "public class TestPositive {",
+            "  void foo() {",
+            "    Optional<Object> a = Optional.of(null);",
+            "    // BUG: Diagnostic contains: dereferenced expression a.get() is @Nullable",
+            "    a.get().toString();",
+            "  }",
+            "}")
+        .doTest();
+  }
+
   @Test
   public void testCastToNonNull() {
     compilationHelper