Struct FrameDescriptor 

pub struct FrameDescriptor {
    pub slots: Vec<NativeKind>,
    pub return_kind: Option<NativeKind>,
}

Typed frame layout metadata.

A FrameDescriptor describes the storage layout for every local slot (parameters + locals) in a single function or top-level frame. The JIT and VM use this to allocate registers / stack space with correct widths and to skip NaN-boxing for slots whose type is statically known.

This is the canonical replacement for the loose Vec<StorageHint> arrays that were previously threaded through BytecodeProgram and Function.

Wire-format binding (ADR-006 §2.7.5.1)

FrameDescriptor is #[derive(Serialize, Deserialize)] and lives inside FunctionBlob, the content-hash unit for distributed bytecode. Per §2.7.5.1, slots: Vec<NativeKind> is post-proof — no Vec<Option<NativeKind>> wrap, no NativeKind::Unknown placeholder (both deleted by the bulldozer). By the time a FrameDescriptor reaches FunctionBlob construction, every slot’s NativeKind is proven; an unproven slot is a compile error per CLAUDE.md type-system rules.

return_kind: Option<NativeKind> is the single-slot field carrying the function’s return-value kind, or None for “no return value / kind not yet stamped”. The single-slot Option<NativeKind> shape is the §2.7.8 / Q10 cell-storage pattern (single-slot fields take Option<NativeKind>); §2.7.5.1’s “no Option<NativeKind> wrapping” rule targets the bulk slots Vec, not single-slot fields where None distinguishes “no return value” from “return value of kind X”.

Fields

slots: Vec<NativeKind>

One entry per local slot (index 0 = first param or local). Every slot’s kind is proven at FunctionBlob construction time per ADR-006 §2.7.5.1 — NativeKind::Unknown was deleted from the enum and is never re-introduced under any name.

return_kind: Option<NativeKind>

Return type kind for the function, or None for “no return value / kind not stamped”. Some(kind) means the JIT boundary ABI uses kind to unmarshal the return value from JIT-compiled code; None means the host boundary has no return-kind to unmarshal (e.g. top-level program with no terminal expression).

Implementations

impl FrameDescriptor

pub fn new() -> Self

Create an empty descriptor with no slots and an unset return kind. Callers stamp return_kind to Some(kind) once the function’s return type is proven.

pub fn from_slots(slots: Vec<NativeKind>) -> Self

Build a descriptor from an existing Vec<NativeKind> of proven slot kinds. return_kind is left None for the caller to stamp.

pub fn len(&self) -> usize

Number of slots described.

pub fn is_empty(&self) -> bool

Whether the descriptor is empty.

pub fn slot(&self, index: usize) -> Option<NativeKind>

Get the kind of a specific slot, or None for out-of-range indices. Note: a present slot always has a proven NativeKind (no Unknown sentinel post-bulldozer).

Trait Implementations

impl Clone for FrameDescriptor

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FrameDescriptor

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for FrameDescriptor

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for FrameDescriptor

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for FrameDescriptor

impl PartialEq for FrameDescriptor

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for FrameDescriptor

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for FrameDescriptor