fail should accept boolean

types/yargs/index.d.ts

@@ -333,7 +333,7 @@ declare namespace yargs {
          * Method to execute when a failure occurs, rather than printing the failure message.
          * @param func Is called with the failure message that would have been printed, the Error instance originally thrown and yargs state when the failure occurred.
          */
-        fail(func: (msg: string, err: Error, yargs: Argv<T>) => any): Argv<T>;
+        fail(func: ((msg: string, err: Error, yargs: Argv<T>) => any) | boolean): Argv<T>;
 
         /**
          * Allows to programmatically get completion choices for any line.

types/yargs/yargs-tests.ts

@@ -660,6 +660,12 @@ function Argv$fail() {
             process.exit(1);
         })
         .argv;
+
+    // Providing false as a value for fn can be used to prevent yargs from
+    // exiting and printing a failure message
+    const ya2 = yargs
+        .fail(false)
+        .argv;
 }
 
 function Argv$implies() {