Unify FastLocals and BoxVec stack into LocalsPlus

Replace separate FastLocals (Box<[Option<PyObjectRef>]>) and BoxVec<Option<PyStackRef>> with a single LocalsPlus struct that stores both in a contiguous Box<[usize]> array. The first nlocalsplus slots are fastlocals and the rest is the evaluation stack. Typed access is provided through transmute-based methods. Remove BoxVec import from frame.rs.
RustPython · youknowone · Mar 4, 2026 · Mar 3, 2026 · Mar 3, 2026 · Mar 3, 2026
commit e286597ac2e99f7de68fb0b3cc09bd810c05ef09
diff --git a/crates/vm/src/builtins/frame.rs b/crates/vm/src/builtins/frame.rs
@@ -692,7 +692,7 @@ impl Py<Frame> {
         // Clear fastlocals
         // SAFETY: Frame is not executing (detached or stopped).
         {
-            let fastlocals = unsafe { self.fastlocals.borrow_mut() };
+            let fastlocals = unsafe { self.fastlocals_mut() };
             for slot in fastlocals.iter_mut() {
                 *slot = None;
             }

diff --git a/crates/vm/src/builtins/function.rs b/crates/vm/src/builtins/function.rs
@@ -236,7 +236,7 @@ impl PyFunction {
         // https://github.com/python/cpython/blob/main/Python/ceval.c#L3681
 
         // SAFETY: Frame was just created and not yet executing.
-        let fastlocals = unsafe { frame.fastlocals.borrow_mut() };
+        let fastlocals = unsafe { frame.fastlocals_mut() };
 
         let mut args_iter = func_args.args.into_iter();
 
@@ -671,15 +671,15 @@ impl Py<PyFunction> {
 
         // Move args directly into fastlocals (no clone/refcount needed)
         {
-            let fastlocals = unsafe { frame.fastlocals.borrow_mut() };
+            let fastlocals = unsafe { frame.fastlocals_mut() };
             for (slot, arg) in fastlocals.iter_mut().zip(args.drain(..)) {
                 *slot = Some(arg);
             }
         }
 
         // Handle cell2arg
         if let Some(cell2arg) = code.cell2arg.as_deref() {
-            let fastlocals = unsafe { frame.fastlocals.borrow_mut() };
+            let fastlocals = unsafe { frame.fastlocals_mut() };
             for (cell_idx, arg_idx) in cell2arg.iter().enumerate().filter(|(_, i)| **i != -1) {
                 let x = fastlocals[*arg_idx as usize].take();
                 frame.set_cell_contents(cell_idx, x);

diff --git a/crates/vm/src/builtins/super.rs b/crates/vm/src/builtins/super.rs
@@ -86,7 +86,7 @@ impl Initializer for PySuper {
                 return Err(vm.new_runtime_error("super(): no arguments"));
             }
             // SAFETY: Frame is current and not concurrently mutated.
-            let obj = unsafe { frame.fastlocals.borrow() }[0]
+            let obj = unsafe { frame.fastlocals() }[0]
                 .clone()
                 .or_else(|| {
                     if let Some(cell2arg) = frame.code.cell2arg.as_deref() {