implement brush cost gauges

they're a little ugly at the moment, and can be a little useless for most simple brushes, but whatever we'll make them better later

crates/haku-wasm/src/lib.rs

@@ -279,11 +279,24 @@ extern "C" fn haku_status_string(code: StatusCode) -> *const i8 {
     .as_ptr()
 }
 
+#[derive(Debug)]
+struct CompileStats {
+    ast_size: usize,
+}
+
+#[derive(Debug)]
+struct RunnableBrush {
+    chunk_id: ChunkId,
+    closure_spec: ClosureSpec,
+
+    compile_stats: CompileStats,
+}
+
 #[derive(Debug, Default)]
 enum BrushState {
     #[default]
     Default,
-    Ready(ChunkId, ClosureSpec),
+    Ready(RunnableBrush),
 }
 
 #[derive(Debug, Default)]
@@ -431,7 +444,13 @@ unsafe extern "C" fn haku_compile_brush(
         Ok(chunk_id) => chunk_id,
         Err(_) => return StatusCode::TooManyChunks,
     };
-    brush.state = BrushState::Ready(chunk_id, closure_spec);
+    brush.state = BrushState::Ready(RunnableBrush {
+        chunk_id,
+        closure_spec,
+        compile_stats: CompileStats {
+            ast_size: ast.len(),
+        },
+    });
 
     info!("brush compiled into {chunk_id:?}");
 
@@ -470,7 +489,7 @@ unsafe extern "C" fn haku_begin_brush(instance: *mut Instance, brush: *const Bru
     let instance = &mut *instance;
     let brush = &*brush;
 
-    let BrushState::Ready(chunk_id, closure_spec) = brush.state else {
+    let BrushState::Ready(runnable) = &brush.state else {
         panic!("brush is not compiled and ready to be used");
     };
 
@@ -479,10 +498,10 @@ unsafe extern "C" fn haku_begin_brush(instance: *mut Instance, brush: *const Bru
     instance.reset_exception();
     instance.trampoline = None;
 
-    let Ok(closure_id) = instance
-        .vm
-        .create_ref(Ref::Closure(Closure::chunk(chunk_id, closure_spec)))
-    else {
+    let Ok(closure_id) = instance.vm.create_ref(Ref::Closure(Closure::chunk(
+        runnable.chunk_id,
+        runnable.closure_spec,
+    ))) else {
         return StatusCode::OutOfRefSlots;
     };
 
@@ -574,3 +593,26 @@ unsafe extern "C" fn haku_cont_dotter(
         )
     })
 }
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn haku_stat_ast_size(brush: *const Brush) -> usize {
+    match &(*brush).state {
+        BrushState::Default => 0,
+        BrushState::Ready(runnable) => runnable.compile_stats.ast_size,
+    }
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn haku_stat_num_refs(instance: *const Instance) -> usize {
+    (*instance).vm.num_refs()
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn haku_stat_remaining_fuel(instance: *const Instance) -> usize {
+    (*instance).vm.remaining_fuel()
+}
+
+#[unsafe(no_mangle)]
+unsafe extern "C" fn haku_stat_remaining_memory(instance: *const Instance) -> usize {
+    (*instance).vm.remaining_memory()
+}