fix(runtime): match Node fs.readFile prototype

changelog.d/8877-release-r23-node-function-prototype.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- Match Node's prototype surface for callback-style native module exports such as `fs.readFile`.

crates/perry-runtime/src/object/native_module/constructor_exports.rs

@@ -64,10 +64,6 @@ pub(crate) fn is_native_module_constructor_export(module: &str, property: &str)
         "crypto.KeyObject" => property == "from",
         "dns" | "dns/promises" => property == "getServers",
         "events" => property == "once",
-        // Node's callback-style fs helpers are callable but not constructors.
-        // Keep this exact: class exports such as ReadStream/WriteStream must
-        // still materialize a real prototype for userland subclassing.
-        "fs" => property == "readFile",
         "http" => property == "setMaxIdleHTTPParsers",
         "inspector" => matches!(property, "close" | "url"),
         "inspector.DOMStorage" => matches!(
@@ -199,8 +195,8 @@ mod tests {
     use super::is_native_module_constructor_export;
 
     #[test]
-    fn fs_read_file_is_not_a_constructor_but_stream_classes_are() {
-        assert!(!is_native_module_constructor_export("fs", "readFile"));
+    fn fs_read_file_and_stream_classes_expose_prototypes() {
+        assert!(is_native_module_constructor_export("fs", "readFile"));
         assert!(is_native_module_constructor_export("fs", "ReadStream"));
         assert!(is_native_module_constructor_export(
             "node:fs",

crates/perry/tests/issue_5268_native_ctor_prototype_undefined.rs

@@ -24,9 +24,9 @@
 //! `Object.create(undefined)` / `Object.setPrototypeOf(x, undefined)` then hit
 //! the spec TypeError. Fix: recognize constructor-cased bound-native exports
 //! (leading uppercase, not flagged non-constructable) and let the
-//! synthetic-class path materialize a stable `.prototype` object — while
-//! keeping non-constructor exports (`fs.readFile`, …) at `prototype ===
-//! undefined`, matching Node's built-in non-constructor functions.
+//! synthetic-class path materialize a stable `.prototype` object. Node also
+//! exposes a real prototype on callback-style JavaScript wrapper exports such
+//! as `fs.readFile`, despite the lower-case export name.
 
 use std::path::PathBuf;
 use std::process::Command;
@@ -97,13 +97,13 @@ const prototype: any = { child() { return null; } };
 Object.setPrototypeOf(prototype, (EventEmitter as any).prototype);
 console.log("setproto:", true);
 
-// Non-constructor native exports keep prototype === undefined (no spurious
-// synthesis), matching Node's built-in non-constructor functions.
-console.log("nonctor:", (fs as any).readFile.prototype === undefined);
+// Node's callback-style JavaScript wrapper exports also expose a prototype.
+const readFileProto = (fs as any).readFile.prototype;
+console.log("readFile:", typeof readFileProto === "object" && readFileProto !== null);
 "#,
     );
     assert_eq!(
         stdout,
-        "rs: true\nws: true\nee: true\ncreate: true\nchain: true\nsetproto: true\nnonctor: true\n"
+        "rs: true\nws: true\nee: true\ncreate: true\nchain: true\nsetproto: true\nreadFile: true\n"
     );
 }

test-files/test_issue_5268_native_ctor_prototype_undefined.ts

@@ -42,6 +42,10 @@ const prototype: any = { child() { return null; } };
 Object.setPrototypeOf(prototype, (EventEmitter as any).prototype);
 console.log("setPrototypeOf(obj, EventEmitter.prototype) ok:", true);
 
-// 4. Non-constructor native exports keep `prototype === undefined`, matching
-//    Node's built-in non-constructor functions (no spurious synthesis).
-console.log("fs.readFile.prototype is undefined:", (fs as any).readFile.prototype === undefined);
+// 4. Node also exposes a real prototype on callback-style JavaScript wrapper
+//    exports such as fs.readFile, despite the lower-case export name.
+const readFileProto = (fs as any).readFile.prototype;
+console.log(
+  "fs.readFile.prototype is object:",
+  typeof readFileProto === "object" && readFileProto !== null,
+);