Prepare for Nullable ASTHelpers.getSymbol (#733)

This method will return `@Nullable` in the next Error Prone release: google/error-prone#3760 This change prepares for that by adding appropriate null checks.

nullaway/src/main/java/com/uber/nullaway/NullAway.java

@@ -315,7 +315,6 @@ private boolean withinAnnotatedCode(VisitorState state) {
   }
 
   private boolean checkMarkingForPath(VisitorState state) {
-    Symbol enclosingMarkableSymbol;
     TreePath path = state.getPath();
     Tree currentTree = path.getLeaf();
     // Find the closest class or method symbol, since those are the only ones we have code
@@ -334,7 +333,10 @@ private boolean checkMarkingForPath(VisitorState state) {
       }
       currentTree = path.getLeaf();
     }
-    enclosingMarkableSymbol = ASTHelpers.getSymbol(currentTree);
+    Symbol enclosingMarkableSymbol = ASTHelpers.getSymbol(currentTree);
+    if (enclosingMarkableSymbol == null) {
+      return false;
+    }
     return !codeAnnotationInfo.isSymbolUnannotated(enclosingMarkableSymbol, config);
   }
 
@@ -2277,6 +2279,13 @@ private boolean mayBeNullExpr(VisitorState state, ExpressionTree expr) {
           return exprMayBeNull ? nullnessFromDataflow(state, expr) : false;
         }
       case METHOD_INVOCATION:
+        if (!(exprSymbol instanceof Symbol.MethodSymbol)) {
+          throw new IllegalStateException(
+              "unexpected symbol "
+                  + exprSymbol
+                  + " for method invocation "
+                  + state.getSourceForNode(expr));
+        }
         // Special case: mayBeNullMethodCall runs handler.onOverrideMayBeNullExpr before dataflow.
         return mayBeNullMethodCall(state, expr, (Symbol.MethodSymbol) exprSymbol);
       case CONDITIONAL_EXPRESSION:

nullaway/src/main/java/com/uber/nullaway/NullabilityUtil.java

@@ -330,16 +330,13 @@ private static boolean isDirectTypeUseAnnotation(Attribute.TypeCompound t) {
   /**
    * Check if a field might be null, based on the type.
    *
-   * @param symbol symbol for field; must be non-null
+   * @param symbol symbol for field
    * @param config NullAway config
    * @return true if based on the type, package, and name of the field, the analysis should assume
    *     the field might be null; false otherwise
-   * @throws NullPointerException if {@code symbol} is null
    */
   public static boolean mayBeNullFieldFromType(
       Symbol symbol, Config config, CodeAnnotationInfo codeAnnotationInfo) {
-    Preconditions.checkNotNull(
-        symbol, "mayBeNullFieldFromType should never be called with a null symbol");
     return !(symbol.getSimpleName().toString().equals("class")
             || symbol.isEnum()
             || codeAnnotationInfo.isSymbolUnannotated(symbol, config))

nullaway/src/main/java/com/uber/nullaway/dataflow/AccessPath.java

@@ -429,7 +429,8 @@ && isBoxingMethod(ASTHelpers.getSymbol(methodInvocationTree))) {
             case IDENTIFIER: // check for CONST
               // Check for a constant field (static final)
               Symbol symbol = ASTHelpers.getSymbol(tree);
-              if (symbol.getKind().equals(ElementKind.FIELD)) {
+              if (symbol instanceof Symbol.VarSymbol
+                  && symbol.getKind().equals(ElementKind.FIELD)) {
                 Symbol.VarSymbol varSymbol = (Symbol.VarSymbol) symbol;
                 // From docs: getConstantValue() returns the value of this variable if this is a
                 // static final field initialized to a compile-time constant. Returns null

nullaway/src/main/java/com/uber/nullaway/dataflow/AccessPathNullnessPropagation.java

@@ -718,7 +718,7 @@ public TransferResult<Nullness, NullnessStore> visitVariableDeclaration(
   public TransferResult<Nullness, NullnessStore> visitFieldAccess(
       FieldAccessNode fieldAccessNode, TransferInput<Nullness, NullnessStore> input) {
     ReadableUpdates updates = new ReadableUpdates();
-    Symbol symbol = ASTHelpers.getSymbol(fieldAccessNode.getTree());
+    Symbol symbol = Preconditions.checkNotNull(ASTHelpers.getSymbol(fieldAccessNode.getTree()));
     setReceiverNonnull(updates, fieldAccessNode.getReceiver(), symbol);
     Nullness nullness = NULLABLE;
     boolean fieldMayBeNull;

nullaway/src/main/java/com/uber/nullaway/fixserialization/out/ClassAndMemberInfo.java

@@ -51,13 +51,15 @@ public ClassAndMemberInfo(TreePath path) {
 
   public ClassAndMemberInfo(Tree regionTree) {
     // regionTree should either represent a field or a method
+    Symbol symbol = ASTHelpers.getSymbol(regionTree);
     if (!(regionTree instanceof MethodTree
         || (regionTree instanceof VariableTree
-            && ASTHelpers.getSymbol(regionTree).getKind().equals(ElementKind.FIELD)))) {
+            && symbol != null
+            && symbol.getKind().equals(ElementKind.FIELD)))) {
       throw new RuntimeException(
           "not expecting a region tree " + regionTree + " of type " + regionTree.getClass());
     }
-    this.member = ASTHelpers.getSymbol(regionTree);
+    this.member = symbol;
     this.clazz = ASTHelpers.enclosingClass(this.member);
   }
 

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

@@ -68,8 +68,11 @@ public void onNonNullFieldAssignment(
     if (pathToMethod == null || pathToMethod.getLeaf().getKind() != Tree.Kind.METHOD) {
       return;
     }
-    Symbol.MethodSymbol methodSymbol =
-        (Symbol.MethodSymbol) ASTHelpers.getSymbol(pathToMethod.getLeaf());
+    Symbol symbol = ASTHelpers.getSymbol(pathToMethod.getLeaf());
+    if (!(symbol instanceof Symbol.MethodSymbol)) {
+      return;
+    }
+    Symbol.MethodSymbol methodSymbol = (Symbol.MethodSymbol) symbol;
     // Check if the method and the field are in the same class.
     if (!field.enclClass().equals(methodSymbol.enclClass())) {
       // We don't want m in A.m() to be a candidate initializer for B.f unless A == B

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

@@ -94,7 +94,9 @@ public NullnessHint onDataflowVisitMethodInvocation(
       Node base = node.getTarget().getReceiver();
       // Argument list and types should be already checked by grpcIsMetadataContainsKeyCall
       Symbol keyArgSymbol = ASTHelpers.getSymbol(tree.getArguments().get(0));
-      if (getter != null && keyArgSymbol.getKind().equals(ElementKind.FIELD)) {
+      if (getter != null
+          && keyArgSymbol instanceof Symbol.VarSymbol
+          && keyArgSymbol.getKind().equals(ElementKind.FIELD)) {
         Symbol.VarSymbol varSymbol = (Symbol.VarSymbol) keyArgSymbol;
         String immutableFieldFQN =
             varSymbol.enclClass().flatName().toString() + "." + varSymbol.flatName().toString();