[feature][@CheckReturnValue] Make @CheckReturnValue opt-in rather than opt-out to avoid breaking existing tests.

src/core/lombok/CheckReturnValue.java

@@ -35,7 +35,7 @@ import java.lang.annotation.Target;
  * Static analysis tools (Error Prone, IntelliJ, SpotBugs) recognize {@code @CheckReturnValue}
  * by simple class name, regardless of package, and will warn when the return value is discarded.
  * <p>
- * If you want to opt out, you can add {@code lombok.addCheckReturnValueAnnotation = false} to
+ * If you want to opt in, you can add {@code lombok.addCheckReturnValueAnnotation = true} to
  * {@code lombok.config}.
  */
 @Target({ElementType.METHOD})

src/core/lombok/ConfigurationKeys.java

@@ -96,7 +96,7 @@ public class ConfigurationKeys {
 	 * If {@code true}, lombok generates {@code @lombok.CheckReturnValue} on generated methods where the return value should not be ignored,
 	 * such as {@code @With} methods and {@code @Builder}'s {@code build()} method.
 	 */
-	public static final ConfigurationKey<Boolean> ADD_CHECK_RETURN_VALUE_ANNOTATIONS = new ConfigurationKey<Boolean>("lombok.addCheckReturnValueAnnotation", "Generate @lombok.CheckReturnValue on generated methods where the return value should not be ignored (default: true).") {};
+	public static final ConfigurationKey<Boolean> ADD_CHECK_RETURN_VALUE_ANNOTATIONS = new ConfigurationKey<Boolean>("lombok.addCheckReturnValueAnnotation", "Generate @lombok.CheckReturnValue on generated methods where the return value should not be ignored (default: false).") {};
 
 	/**
 	 * lombok configuration: {@code lombok.extern.findbugs.addSuppressFBWarnings} = {@code true} | {@code false}.

src/core/lombok/eclipse/handlers/EclipseHandlerUtil.java

@@ -2128,7 +2128,7 @@ public class EclipseHandlerUtil {
 	}
 	
 	public static Annotation[] addCheckReturnValue(EclipseNode node, ASTNode source, Annotation[] originalAnnotationArray) {
-		if (Boolean.FALSE.equals(node.getAst().readConfiguration(ConfigurationKeys.ADD_CHECK_RETURN_VALUE_ANNOTATIONS))) return originalAnnotationArray;
+		if (!Boolean.TRUE.equals(node.getAst().readConfiguration(ConfigurationKeys.ADD_CHECK_RETURN_VALUE_ANNOTATIONS))) return originalAnnotationArray;
 		return addAnnotation(source, originalAnnotationArray, LOMBOK_CHECK_RETURN_VALUE);
 	}
 

src/core/lombok/javac/handlers/JavacHandlerUtil.java

@@ -1555,7 +1555,7 @@ public class JavacHandlerUtil {
 	}
 	
 	public static void addCheckReturnValue(JCModifiers mods, JavacNode node, JavacNode source) {
-		if (Boolean.FALSE.equals(node.getAst().readConfiguration(ConfigurationKeys.ADD_CHECK_RETURN_VALUE_ANNOTATIONS))) return;
+		if (!Boolean.TRUE.equals(node.getAst().readConfiguration(ConfigurationKeys.ADD_CHECK_RETURN_VALUE_ANNOTATIONS))) return;
 		addAnnotation(mods, node, source, "lombok.CheckReturnValue", null);
 	}
 

test/transform/resource/before/CheckReturnValueBuilder.java

@@ -1,3 +1,4 @@
+//CONF: lombok.addCheckReturnValueAnnotation = true
 @lombok.Builder
 class CheckReturnValueBuilder {
 	private final int x;

test/transform/resource/before/CheckReturnValueWith.java

@@ -1,3 +1,4 @@
+//CONF: lombok.addCheckReturnValueAnnotation = true
 import lombok.With;
 class CheckReturnValueWith {
 	@With final int x;