fix(gc): complete IMPLICIT_THIS receiver rooting (two-line save forms) (#8519)

* fix(gc): root displaced receiver in two-line IMPLICIT_THIS save/restore forms

* chore: bump version to 0.5.1515

* chore: drop the version bump and PR-key the changelog fragment

Standing instruction is no version bump for now; the maintainer bumps at
merge time. Reverts CLAUDE.md, Cargo.toml and the 76 Cargo.lock version
strings to main's 0.5.1514. Renames the fragment to match this PR number so
in-flight PRs cannot collide on the filename.

---------

Co-authored-by: Ralph Küpper <ralph@skelpo.com>

Author: proggeramlug

changelog.d/8519-implicit-this-two-line-forms.md

@@ -0,0 +1,7 @@
+**GC: complete the `IMPLICIT_THIS` receiver-rooting conversion started in #8500.**
+
+#8500 converted 22 receiver save/restore pairs that manipulated the `IMPLICIT_THIS` cell directly, rooting the displaced receiver so an evacuating collection inside the callee cannot leave the restore publishing a pre-move address. Four sites of the identical shape were missed because the save spans two lines (`let prev =` on one line, the `IMPLICIT_THIS.with(|c| c.replace(…))` on the next) and so did not match the pattern used to find the others.
+
+No behavioural test moves — these four are latent rather than currently reachable by a failing case — but leaving four instances of a shape that is known to produce a stale `this` is the kind of residue that costs a future session a week. The conversion is now exhaustive: no unrooted direct-access save/restore pair remains in `perry-runtime`.
+
+Does **not** address #8507 (`defineProperty` / `Reflect` own-key paths under forced evacuation), which is a distinct defect — verified by re-running that suite with these four converted, and again with all 135 `js_implicit_this_set(...)`-call pairs converted.

crates/perry-runtime/src/object/native_call_method.rs

@@ -1535,8 +1535,10 @@ pub unsafe extern "C-unwind" fn js_native_call_method(
                     let getter = (acc.get & crate::value::POINTER_MASK)
                         as *const crate::closure::ClosureHeader;
                     if !getter.is_null() {
-                        let prev_getter_this =
-                            IMPLICIT_THIS.with(|c| c.replace(object().to_bits()));
+                        // #8495: root the displaced receiver across the call below.
+                        let prev_getter_this_scope = crate::gc::RuntimeHandleScope::new();
+                        let prev_getter_this_h = prev_getter_this_scope
+                            .root_nanbox_u64(IMPLICIT_THIS.with(|c| c.replace(object().to_bits())));
                         let method_fn = crate::closure::js_closure_call0(getter);
                         let bound = crate::closure::clone_closure_rebind_this(
                             method_fn.to_bits(),
@@ -1553,7 +1555,7 @@ pub unsafe extern "C-unwind" fn js_native_call_method(
                             call_args.as_ptr(),
                             call_args.len(),
                         );
-                        IMPLICIT_THIS.with(|c| c.set(prev_getter_this));
+                        IMPLICIT_THIS.with(|c| c.set(prev_getter_this_h.get_nanbox_u64()));
                         return result;
                     }
                 }

crates/perry-runtime/src/object/native_call_method/handle_methods.rs

@@ -1080,8 +1080,11 @@ pub(super) unsafe fn dispatch_handle(
                                 // Mirrors `resolve_proto_chain_field_with_receiver`
                                 // (the winston `get transports()` fix).
                                 let receiver_f64 = f64::from_bits(jsval.bits());
-                                let prev_this =
-                                    IMPLICIT_THIS.with(|c| c.replace(receiver_f64.to_bits()));
+                                // #8495: root the displaced receiver across the call below.
+                                let prev_this_scope = crate::gc::RuntimeHandleScope::new();
+                                let prev_this_h = prev_this_scope.root_nanbox_u64(
+                                    IMPLICIT_THIS.with(|c| c.replace(receiver_f64.to_bits())),
+                                );
                                 let prev_override =
                                     super::super::field_get_set::accessor_receiver_override_begin(
                                         receiver_f64,
@@ -1093,7 +1096,7 @@ pub(super) unsafe fn dispatch_handle(
                                 super::super::field_get_set::accessor_receiver_override_end(
                                     prev_override,
                                 );
-                                IMPLICIT_THIS.with(|c| c.set(prev_this));
+                                IMPLICIT_THIS.with(|c| c.set(prev_this_h.get_nanbox_u64()));
                                 if !field_val.is_undefined() && !field_val.is_null() {
                                     resolved_method = Some(ResolvedMethod::ProtoClosure {
                                         field_bits: field_val.bits(),

crates/perry-runtime/src/object/native_call_method/primitive_methods.rs

@@ -97,14 +97,17 @@ pub(super) unsafe fn dispatch_primitive(
                 );
                 let prop_handle = root_scope.root_nanbox_f64(f64::from_bits(bound));
                 let args = refreshed_args();
-                let prev_this =
-                    IMPLICIT_THIS.with(|c| c.replace(object_handle.get_nanbox_f64().to_bits()));
+                // #8495: root the displaced receiver across the call below.
+                let prev_this_scope = crate::gc::RuntimeHandleScope::new();
+                let prev_this_h = prev_this_scope.root_nanbox_u64(
+                    IMPLICIT_THIS.with(|c| c.replace(object_handle.get_nanbox_f64().to_bits())),
+                );
                 let result = crate::closure::js_native_call_value(
                     prop_handle.get_nanbox_f64(),
                     args.as_ptr(),
                     args.len(),
                 );
-                IMPLICIT_THIS.with(|c| c.set(prev_this));
+                IMPLICIT_THIS.with(|c| c.set(prev_this_h.get_nanbox_u64()));
                 return Some(result);
             }
         }
@@ -528,14 +531,17 @@ pub(super) unsafe fn dispatch_primitive(
                     );
                     let prop_handle = root_scope.root_nanbox_f64(f64::from_bits(bound));
                     let args = refreshed_args();
-                    let prev_this =
-                        IMPLICIT_THIS.with(|c| c.replace(object_handle.get_nanbox_f64().to_bits()));
+                    // #8495: root the displaced receiver across the call below.
+                    let prev_this_scope = crate::gc::RuntimeHandleScope::new();
+                    let prev_this_h = prev_this_scope.root_nanbox_u64(
+                        IMPLICIT_THIS.with(|c| c.replace(object_handle.get_nanbox_f64().to_bits())),
+                    );
                     let result = crate::closure::js_native_call_value(
                         prop_handle.get_nanbox_f64(),
                         args.as_ptr(),
                         args.len(),
                     );
-                    IMPLICIT_THIS.with(|c| c.set(prev_this));
+                    IMPLICIT_THIS.with(|c| c.set(prev_this_h.get_nanbox_u64()));
                     return Some(result);
                 }
                 // Own key present but NOT callable (`re.exec = 5; re.exec()`).