fix(runtime): inherit static data fields from a parent class

crates/perry-runtime/src/object/field_get_set/get_field_by_name.rs

@@ -852,6 +852,47 @@ pub extern "C" fn js_object_get_field_by_name(
                     if let Some(v) = result {
                         return JSValue::from_bits(v.to_bits());
                     }
+                    // Static DATA fields are INHERITED by subclasses, exactly like
+                    // static methods: `class D {}; D.kind = "x"; class G extends D {}`
+                    // makes `G.kind === "x"` (the class-object proto chain
+                    // `G.__proto__ === D` carries statics). The own-field read above
+                    // only consulted `class_id`; walk the parent class_id chain here
+                    // so an inherited static field (or runtime `Parent.x = …`
+                    // assignment — both live in CLASS_DYNAMIC_PROPS) resolves. Static
+                    // METHODS are handled by `lookup_static_method_in_chain` below;
+                    // this covers the data-field case that was returning `undefined`
+                    // (Auth.js sets `SignInError.kind = "signIn"` and reads it off a
+                    // `CredentialsSignin` subclass to pick the sign-in vs error page).
+                    {
+                        let mut cid = class_id;
+                        let mut depth = 0usize;
+                        while depth < 32 {
+                            match get_parent_class_id(cid) {
+                                Some(p) if p != 0 && p != cid => {
+                                    cid = p;
+                                    depth += 1;
+                                }
+                                _ => break,
+                            }
+                            if super::super::class_registry::class_is_key_deleted(cid, name) {
+                                // A key deleted on THIS ancestor is not provided by
+                                // it, but a higher ancestor may still define it —
+                                // `delete Mid.foo` must let `Sub.foo` inherit
+                                // `Base.foo`, not resolve to undefined. Skip this
+                                // level and keep walking up (safe: `cid`/`depth`
+                                // advance at the top of every iteration).
+                                continue;
+                            }
+                            let inherited = CLASS_DYNAMIC_PROPS.with(|m| {
+                                m.borrow()
+                                    .get(&cid)
+                                    .and_then(|props| props.get(name).copied())
+                            });
+                            if let Some(v) = inherited {
+                                return JSValue::from_bits(v.to_bits());
+                            }
+                        }
+                    }
                     if super::super::class_registry::lookup_static_method_in_chain(class_id, name)
                         .is_some()
                     {

test-files/test_gap_static_field_inheritance.ts

@@ -0,0 +1,32 @@
+// A subclass inherits its parent's static DATA properties — both in-body static
+// fields and runtime `Parent.x = …` assignments — via the class-object prototype
+// chain (`Sub.__proto__ === Base`). Regression: perry inherited static METHODS
+// but returned `undefined` for inherited static data fields, so
+// `Sub.tag` / `Sub.kind` read undefined even though `Base` defined them. (Auth.js
+// sets `SignInError.kind = "signIn"` and reads it off a `CredentialsSignin`
+// subclass to choose the sign-in vs error redirect page.)
+class Base {
+  static inBody = "field";
+}
+(Base as any).external = "assigned";
+class Sub extends Base {}
+class Leaf extends Sub {}
+console.log("Sub.inBody=" + (Sub as any).inBody);
+console.log("Sub.external=" + (Sub as any).external);
+console.log("Leaf.inBody=" + (Leaf as any).inBody);
+console.log("Leaf.external=" + (Leaf as any).external);
+// own field still wins over inherited
+(Sub as any).external = "own";
+console.log("Sub.own-wins=" + (Sub as any).external);
+console.log("Base.unshadowed=" + (Base as any).external);
+
+// A key deleted on an INTERMEDIATE ancestor must not shadow a higher one:
+// `delete Mid.foo` should let `Sub.foo` inherit `Base.foo`, not resolve to
+// undefined. (The chain walk must `continue` past the deleted level, not
+// `break` out of the whole traversal.)
+class DBase { static tag = "base"; }
+class DMid extends DBase { static tag = "mid"; }
+class DSub extends DMid {}
+console.log("del-intermediate before:", (DSub as any).tag);
+delete (DMid as any).tag;
+console.log("del-intermediate after :", (DSub as any).tag);