Always acknowledge restrictive annotations in JSpecify mode (#1144)

Previously, we neglected to acknowledge explicit `@Nullable` return
types and `@NonNull` parameter types in `@NullUnmarked` code unless the
`AcknowledgeRestrictiveAnnotations` setting was passed. But, the
JSpecify spec requires acknowledging restrictive annotations in
`@NullUnmarked` code. So now, in JSpecify mode, we always acknowledge
restrictive annotations.

Note that in JSpecify mode, this change will also impact handling of
other "unannotated" code that is not explicitly annotated
`@NullUnmarked`. But, as discussed in #978, we want to switch to
acknowledging restrictive annotations by default anyway. It seems
reasonable to go ahead and make this change in JSpecify mode, to ensure
greater spec compliance.

Author: msridhar

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

@@ -46,7 +46,11 @@ public static Handler buildDefault(Config config) {
     ImmutableList.Builder<Handler> handlerListBuilder = ImmutableList.builder();
     MethodNameUtil methodNameUtil = new MethodNameUtil();
 
-    if (config.acknowledgeRestrictiveAnnotations()) {
+    // Acknowledge restrictive annotations if in JSpecify mode or if the user has explicitly
+    // requested it
+    boolean acknowledgeRestrictive =
+        config.acknowledgeRestrictiveAnnotations() || config.isJSpecifyMode();
+    if (acknowledgeRestrictive) {
       // This runs before LibraryModelsHandler, so that library models can override third-party
       // bytecode annotations
       handlerListBuilder.add(new RestrictiveAnnotationHandler(config));

nullaway/src/test/java/com/uber/nullaway/jspecify/NullMarkednessTests.java

@@ -866,6 +866,68 @@ public void nullUnmarkedMethodLevel() {
         .doTest();
   }
 
+  @Test
+  public void nullUnmarkedMethodWithNonNullParamJSpecifyMode() {
+    makeTestHelperWithArgs(
+            Arrays.asList(
+                "-d",
+                temporaryFolder.getRoot().getAbsolutePath(),
+                "-XepOpt:NullAway:OnlyNullMarked=true",
+                "-XepOpt:NullAway:JSpecifyMode=true"))
+        .addSourceLines(
+            "Foo.java",
+            "package com.uber;",
+            "import org.jspecify.annotations.NullUnmarked;",
+            "import org.jspecify.annotations.NullMarked;",
+            "import org.jspecify.annotations.NonNull;",
+            "@NullMarked",
+            "public class Foo {",
+            "  @NullUnmarked",
+            "  public static void callee(@NonNull Object o) {",
+            "  }",
+            "  @NullUnmarked",
+            "  public static void callee2(Object o) {",
+            "  }",
+            "  public static void caller() {",
+            "    // Error due to explicit @NonNull annotation",
+            "    // BUG: Diagnostic contains: passing @Nullable parameter",
+            "    callee(null);",
+            "    // this is fine",
+            "    callee2(null);",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void nullUnmarkedMethodWithNullableReturnJSpecifyMode() {
+    makeTestHelperWithArgs(
+            Arrays.asList(
+                "-d",
+                temporaryFolder.getRoot().getAbsolutePath(),
+                "-XepOpt:NullAway:OnlyNullMarked=true",
+                "-XepOpt:NullAway:JSpecifyMode=true"))
+        .addSourceLines(
+            "Foo.java",
+            "package com.uber;",
+            "import org.jspecify.annotations.NullUnmarked;",
+            "import org.jspecify.annotations.NullMarked;",
+            "import org.jspecify.annotations.Nullable;",
+            "@NullMarked",
+            "public class Foo {",
+            "  @NullUnmarked",
+            "  public static @Nullable String callee() {",
+            "    return null;",
+            "  }",
+            "  public static void caller() {",
+            "    // Error due to explicit @Nullable annotation",
+            "    // BUG: Diagnostic contains: dereferenced expression callee() is @Nullable",
+            "    callee().toString();",
+            "  }",
+            "}")
+        .doTest();
+  }
+
   @Test
   public void nullUnmarkedOuterMethodLevelWithLocalClass() {
     defaultCompilationHelper