Add support for collecting garbage to the public API fuzzer (bytecodealliance#13457)

Author: fitzgen

crates/fuzzing/src/generators/api.rs

@@ -45,6 +45,7 @@ impl FuzzValType {
 struct Swarm {
     store_new: bool,
     store_drop: bool,
+    store_gc: bool,
     module_new: bool,
     module_drop: bool,
     instance_new: bool,
@@ -148,6 +149,9 @@ pub enum ApiCall {
     StoreDrop {
         id: usize,
     },
+    StoreGc {
+        id: usize,
+    },
     ModuleNew {
         id: usize,
         wasm: Vec<u8>,
@@ -668,6 +672,13 @@ impl<'a> Arbitrary<'a> for ApiCalls {
                     Ok(StoreDrop { id })
                 });
             }
+            if swarm.store_gc && !scope.stores.is_empty() {
+                choices.push(|input, scope| {
+                    let stores: Vec<_> = scope.stores.iter().collect();
+                    let id = **input.choose(&stores)?;
+                    Ok(StoreGc { id })
+                });
+            }
             if swarm.module_new {
                 choices.push(|input, scope| {
                     let id = scope.next_id();

crates/fuzzing/src/oracles/api.rs

@@ -65,6 +65,15 @@ pub fn make_api_calls(api: ApiCalls) {
                 stores.remove(&id);
             }
 
+            ApiCall::StoreGc { id } => {
+                log::trace!("collecting garbage in store {id}");
+                let st = match stores.get_mut(&id) {
+                    Some(s) => s,
+                    None => continue,
+                };
+                let _ = st.gc(None);
+            }
+
             ApiCall::ModuleNew { id, wasm } => {
                 log::debug!("creating module: {id}");
                 log_wasm(&wasm);