Revisit nullability annotations

This commit introduces the following changes.

1) It adds a new Spring @NonNull annotation which allows to apply
@NonNullApi semantic on a specific element, like @Nullable does.
Combined with @Nullable, it allows partial null-safety support when
package granularity is too broad.

2) @Nullable and @NonNull can apply to ElementType.TYPE_USE in order
to be used on generic type arguments (SPR-15942).

3) Annotations does not apply to ElementType.TYPE_PARAMETER anymore
since it is not supported yet (applicability for such use case is
controversial and need to be discussed).

4) @NonNullApi does not apply to ElementType.FIELD anymore since in a
lot of use cases (private, protected) it is not part for the public API
+ its usage should remain opt-in. A dedicated @NonNullFields annotation
has been added in order to set fields default to non-nullable.

5) Updated Javadoc and reference documentation.

Issue: SPR-15756

spring-test/src/main/java/org/springframework/mock/env/package-info.java

@@ -8,6 +8,8 @@
  * unit tests for code that depends on environment-specific properties.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.env;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/http/client/package-info.java

@@ -4,6 +4,8 @@
  * {@code MockClientHttpResponse}.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.http.client;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/http/client/reactive/package-info.java

@@ -2,6 +2,8 @@
  * Mock implementations of reactive HTTP client contracts.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.http.client.reactive;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/http/package-info.java

@@ -4,6 +4,8 @@
  * {@code MockHttpOutputMessage}.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.http;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/http/server/reactive/package-info.java

@@ -2,6 +2,8 @@
  * Mock implementations of reactive HTTP server contracts.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.http.server.reactive;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/jndi/package-info.java

@@ -7,6 +7,8 @@
  * configuration can be reused without changes.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.jndi;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/web/package-info.java

@@ -10,6 +10,8 @@
  * (<a href="http://www.mockobjects.com">MockObjects</a>).
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.web;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/mock/web/reactive/function/server/package-info.java

@@ -5,6 +5,8 @@
  *
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.mock.web.reactive.function.server;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/annotation/package-info.java

@@ -2,6 +2,8 @@
  * Support classes for annotation-driven tests.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.annotation;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/cache/package-info.java

@@ -2,6 +2,8 @@
  * Support for context caching within the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.cache;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/jdbc/package-info.java

@@ -3,6 +3,8 @@
  * including support for declarative SQL script execution via {@code @Sql}.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.jdbc;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/junit/jupiter/package-info.java

@@ -3,6 +3,8 @@
  * with the JUnit Jupiter extension model in JUnit 5.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.junit.jupiter;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/junit/jupiter/web/package-info.java

@@ -3,6 +3,8 @@
  * with the JUnit Jupiter extension model in JUnit 5.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.junit.jupiter.web;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/junit4/package-info.java

@@ -3,6 +3,8 @@
  * with JUnit 4.12 or higher.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.junit4;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/junit4/rules/package-info.java

@@ -2,6 +2,8 @@
  * Custom JUnit {@code Rules} used in the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.junit4.rules;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/junit4/statements/package-info.java

@@ -2,6 +2,8 @@
  * Custom JUnit {@code Statements} used in the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.junit4.statements;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/package-info.java

@@ -12,6 +12,8 @@
  * management with default rollback semantics.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/support/package-info.java

@@ -2,6 +2,8 @@
  * Support classes for the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.support;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/testng/package-info.java

@@ -3,6 +3,8 @@
  * tests run with TestNG and the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.testng;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/transaction/package-info.java

@@ -2,6 +2,8 @@
  * Transactional support classes for the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.transaction;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/util/package-info.java

@@ -2,6 +2,8 @@
  * Common utilities used within the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.util;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/web/package-info.java

@@ -2,6 +2,8 @@
  * Web support classes for the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.web;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/context/web/socket/package-info.java

@@ -2,6 +2,8 @@
  * WebSocket support classes for the <em>Spring TestContext Framework</em>.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.context.web.socket;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/jdbc/package-info.java

@@ -2,6 +2,8 @@
  * Support classes for tests based on JDBC.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.jdbc;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/util/package-info.java

@@ -2,6 +2,8 @@
  * General utility classes for use in unit and integration tests.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.util;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/client/match/package-info.java

@@ -5,6 +5,8 @@
  * to gain access to instances of those implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.client.match;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/client/package-info.java

@@ -3,6 +3,8 @@
  * @see org.springframework.test.web.client.MockRestServiceServer
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.client;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/client/response/package-info.java

@@ -5,6 +5,8 @@
  * to gain access to instances of those implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.client.response;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/reactive/server/package-info.java

@@ -3,6 +3,8 @@
  * {@link org.springframework.test.web.reactive.server.WebTestClient}.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.reactive.server;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/package-info.java

@@ -4,6 +4,8 @@
  * @see org.springframework.test.web.servlet.MockMvc
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.servlet.htmlunit;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/webdriver/package-info.java

@@ -5,6 +5,8 @@
  * @see org.openqa.selenium.htmlunit.HtmlUnitDriver
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.servlet.htmlunit.webdriver;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/servlet/package-info.java

@@ -3,6 +3,8 @@
  * @see org.springframework.test.web.servlet.MockMvc
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.servlet;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/servlet/request/package-info.java

@@ -5,6 +5,8 @@
  * to gain access to instances of those implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.servlet.request;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/servlet/result/package-info.java

@@ -5,6 +5,8 @@
  * to access instances of those implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.servlet.result;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-test/src/main/java/org/springframework/test/web/servlet/setup/package-info.java

@@ -4,6 +4,8 @@
  * to access to instances of those implementations.
  */
 @NonNullApi
+@NonNullFields
 package org.springframework.test.web.servlet.setup;
 
 import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;