vm, runtime: add slots! macro and port filter primop to typed slots

fix-runtime/src/slot.rs

@@ -0,0 +1,87 @@
+use std::marker::PhantomData;
+use std::ops::ControlFlow;
+
+use fix_bytecode::BytecodeReader;
+use gc_arena::Mutation;
+
+use crate::{Break, Forced, Machine, NixType, Step, StrictValue, Value, ValueVariant};
+
+pub trait SlotContent<'gc> {
+    type Ty: Into<Value<'gc>> + TryFrom<Value<'gc>> + 'gc;
+}
+
+impl<'gc> SlotContent<'gc> for Value<'gc> {
+    type Ty = Value<'gc>;
+}
+
+impl<'gc> SlotContent<'gc> for StrictValue<'gc> {
+    type Ty = StrictValue<'gc>;
+}
+
+impl<'gc, T> SlotContent<'gc> for T
+where
+    T: ValueVariant<'gc>,
+{
+    type Ty = T::Ty;
+}
+
+pub struct Slot<T> {
+    depth: u8,
+    _marker: PhantomData<T>,
+}
+
+impl<T> Slot<T> {
+    #[inline(always)]
+    pub const fn new(depth: u8) -> Self {
+        Self {
+            depth,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<'gc, T> Slot<T>
+where
+    T: SlotContent<'gc>,
+    <T::Ty as TryFrom<Value<'gc>>>::Error: std::fmt::Debug,
+{
+    #[inline(always)]
+    pub fn read<M: Machine<'gc>>(&self, m: &M) -> T::Ty {
+        T::Ty::try_from(m.peek(self.depth as usize)).expect("slot held a value of the wrong type")
+    }
+
+    #[inline(always)]
+    pub fn read_checked<M: Machine<'gc>>(&self, m: &M) -> Result<T::Ty, NixType> {
+        let val = m.peek(self.depth as usize);
+        T::Ty::try_from(val).map_err(|_err| val.ty())
+    }
+
+    #[inline(always)]
+    pub fn write<M: Machine<'gc>>(&self, m: &mut M, val: T::Ty) {
+        m.replace(self.depth as usize, T::Ty::into(val));
+    }
+}
+
+impl<'gc> Slot<Value<'gc>> {
+    #[inline(always)]
+    pub fn force<T: Forced<'gc>, M: Machine<'gc>>(
+        &self,
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> ControlFlow<Break, Slot<T>> {
+        T::force_and_check(m, reader, mc, self.depth as usize, reader.inst_start_pc())?;
+        ControlFlow::Continue(Slot::new(self.depth))
+    }
+
+    #[inline(always)]
+    pub fn force_to_pc<M: Machine<'gc>>(
+        &self,
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        pc: usize,
+    ) -> Step {
+        m.force_slot_to_pc(self.depth as usize, reader, mc, pc)
+    }
+}