repl: change preview default in case of custom eval functions

Custom eval functions might have a very different behavior than the
current implementation and having a preview in such case might be
confusing. This changes the preview default to `false` in case a
custom eval function is used. It is still possible to opt into using
the previews in case that's still desirable.

PR-URL: #31259
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Anto Aravinth <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Gus Caplan <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: James M Snell <[email protected]>

doc/api/repl.md

@@ -597,8 +597,9 @@ changes:
     `SIGINT` is received, such as when `Ctrl+C` is pressed. This cannot be used
     together with a custom `eval` function. **Default:** `false`.
   * `preview` {boolean} Defines if the repl prints autocomplete and output
-    previews or not. **Default:** `true`. If `terminal` is falsy, then there are
-    no previews and the value of `preview` has no effect.
+    previews or not. **Default:** `true` with the default eval function and
+    `false` in case a custom eval function is used. If `terminal` is falsy, then
+    there are no previews and the value of `preview` has no effect.
 * Returns: {repl.REPLServer}
 
 The `repl.start()` method creates and starts a [`repl.REPLServer`][] instance.

lib/repl.js

@@ -213,8 +213,9 @@ function REPLServer(prompt,
     }
   }
 
+  // TODO(devsnek): Add a test case for custom eval functions.
   const preview = options.terminal &&
-    (options.preview !== undefined ? !!options.preview : true);
+    (options.preview !== undefined ? !!options.preview : !eval_);
 
   this.inputStream = options.input;
   this.outputStream = options.output;