haku2: add stats + fix crash w uninit vm

crates/haku2/src/lib.rs

@@ -134,9 +134,15 @@ extern "C" {
     ) -> *mut DefsC;
     fn haku2_defs_destroy(defs: *mut DefsC);
 
-    fn haku2_vm_new(s: *mut ScratchC, defs: *const DefsC, limits: *const LimitsC) -> *mut VmC;
+    fn haku2_vm_new() -> *mut VmC;
     fn haku2_vm_destroy(vm: *mut VmC);
-    fn haku2_vm_reset(vm: *mut VmC, fuel: u32);
+    fn haku2_vm_reset(
+        vm: *mut VmC,
+        s: *mut ScratchC,
+        defs: *const DefsC,
+        limits: *const LimitsC,
+        fuel: u32,
+    );
     fn haku2_vm_run_main(
         vm: *mut VmC,
         scratch: *mut ScratchC,
@@ -296,6 +302,7 @@ impl Code {
 pub struct Vm {
     scratch: Scratch,
     code: Code,
+    limits: Limits,
     inner: VmInner,
 }
 
@@ -318,15 +325,10 @@ pub struct Dotter {
 }
 
 impl Vm {
-    pub fn new(scratch: Scratch, code: Code, limits: &Limits) -> Self {
-        let raw = NonNull::new(unsafe {
-            haku2_vm_new(
-                scratch.raw.as_ptr(),
-                code.defs.raw.as_ptr(),
-                limits.raw.as_ptr(),
-            )
-        })
-        .expect("out of memory");
+    pub fn new(scratch: Scratch, code: Code, limits: Limits) -> Self {
+        // SAFETY: haku2_vm_new cannot fail.
+        // Do note that this returns an uninitialized VM, which must be reset before use.
+        let raw = NonNull::new(unsafe { haku2_vm_new() }).expect("out of memory");
         trace!("Vm::new({scratch:?}, {code:?}, {limits:?}) -> {raw:?}");
         Self {
             // SAFETY:
@@ -336,6 +338,7 @@ impl Vm {
             inner: VmInner { raw },
             scratch,
             code,
+            limits,
         }
     }
 
@@ -346,8 +349,15 @@ impl Vm {
     /// continuation being stack on top of the old one---at the expense of a stack slot.
     pub fn begin(&mut self, fuel: u32) -> Result<(), Exception> {
         trace!("Vm::begin({self:?}, {fuel})");
+        self.scratch.reset();
         let ok = unsafe {
-            haku2_vm_reset(self.inner.raw.as_ptr(), fuel);
+            haku2_vm_reset(
+                self.inner.raw.as_ptr(),
+                self.scratch.raw.as_ptr(),
+                self.code.defs.raw.as_ptr(),
+                self.limits.raw.as_ptr(),
+                fuel,
+            );
             haku2_vm_run_main(
                 self.inner.raw.as_ptr(),
                 self.scratch.raw.as_ptr(),
@@ -422,6 +432,7 @@ impl Vm {
             mut scratch,
             code: _,
             inner: _,
+            limits: _,
         } = self;
         scratch.reset();
         scratch