Treat parameter of generated Record.equals() methods as @Nullable

jdk17-unit-tests/src/test/java/com/uber/nullaway/jdk17/NullAwayRecordTests.java

@@ -178,4 +178,36 @@ public void testLocalRecord() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void recordEqualsNull() {
+    defaultCompilationHelper
+        .addSourceLines(
+            "Records.java",
+            "package com.uber;",
+            "import javax.annotation.Nullable;",
+            "class Records {",
+            "  public void recordEqualsNull() {",
+            "    record Rec() {",
+            "      void print(Object o) { System.out.println(o.toString()); }",
+            "      void equals(Integer i1, Integer i2) { }",
+            "      boolean equals(String i1, String i2) { return false; }",
+            "      boolean equals(Long l1) { return false; }",
+            "    }",
+            "    Object o = null;",
+            "    // null can be passed to the generated equals() method taking an Object parameter",
+            "    new Rec().equals(o);",
+            "    // BUG: Diagnostic contains: passing @Nullable parameter 'null'",
+            "    new Rec().print(null);",
+            "    // BUG: Diagnostic contains: passing @Nullable parameter 'null'",
+            "    new Rec().equals(null, Integer.valueOf(100));",
+            "    // BUG: Diagnostic contains: passing @Nullable parameter 'null'",
+            "    new Rec().equals(\"hello\", null);",
+            "    Long l = null;",
+            "    // BUG: Diagnostic contains: passing @Nullable parameter 'l'",
+            "    new Rec().equals(l);",
+            "  }",
+            "}")
+        .doTest();
+  }
 }

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

@@ -19,6 +19,8 @@
 package com.uber.nullaway;
 
 import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.Type;
+import com.sun.tools.javac.util.List;
 import java.util.stream.Stream;
 import javax.lang.model.element.AnnotationMirror;
 import org.checkerframework.nullaway.dataflow.analysis.AbstractValue;
@@ -210,10 +212,36 @@ public static boolean hasNullableAnnotation(Symbol symbol, Config config) {
    */
   public static boolean paramHasNullableAnnotation(
       Symbol.MethodSymbol symbol, int paramInd, Config config) {
+    // We treat the (generated) equals() method of record types to have a @Nullable parameter, as
+    // the generated implementation handles null (as required by the contract of Object.equals())
+    if (isRecordEqualsParam(symbol, paramInd)) {
+      return true;
+    }
     return hasNullableAnnotation(
         NullabilityUtil.getAllAnnotationsForParameter(symbol, paramInd), config);
   }
 
+  private static boolean isRecordEqualsParam(Symbol.MethodSymbol symbol, int paramInd) {
+    // Here we compare with toString() to preserve compatibility with JDK 11 (records only
+    // introduced in JDK 16)
+    if (!symbol.owner.getKind().toString().equals("RECORD")) {
+      return false;
+    }
+    if (!symbol.getSimpleName().contentEquals("equals")) {
+      return false;
+    }
+    // Check for a boolean return type and a single parameter of type java.lang.Object
+    Type type = symbol.type;
+    List<Type> parameterTypes = type.getParameterTypes();
+    if (!(type.getReturnType().toString().equals("boolean")
+        && parameterTypes != null
+        && parameterTypes.size() == 1
+        && parameterTypes.get(0).toString().equals("java.lang.Object"))) {
+      return false;
+    }
+    return paramInd == 0;
+  }
+
   /**
    * Does the parameter of {@code symbol} at {@code paramInd} have a {@code @NonNull} declaration or
    * type-use annotation? This method works for methods defined in either source or class files.