Extend is_fn_call to find assoc reft bodies for FnOnce::call_once, FnMut::call_mut

crates/flux-middle/src/global_env.rs

@@ -497,12 +497,22 @@ impl<'genv, 'tcx> GlobalEnv<'genv, 'tcx> {
             == def_id
     }
 
-    /// Returns whether `def_id` is the `call` method in the `Fn` trait.
+    /// Returns whether `def_id` is the `call` method in the `Fn` trait,
+    /// the `call_mut` method in the `FnMut` trait,
+    /// or the `call_once` method in the `FnOnce` trait.
     pub fn is_fn_call(&self, def_id: DefId) -> bool {
+        let methods_and_names = [
+            (LangItem::Fn, sym::call),
+            (LangItem::FnMut, sym::call_mut),
+            (LangItem::FnOnce, sym::call_once),
+        ];
         let tcx = self.tcx();
         let Some(assoc_item) = tcx.opt_associated_item(def_id) else { return false };
         let Some(trait_id) = assoc_item.trait_container(tcx) else { return false };
-        assoc_item.name() == sym::call && tcx.is_lang_item(trait_id, LangItem::Fn)
+
+        methods_and_names.iter().any(|(lang_item, method_name)| {
+            assoc_item.name() == *method_name && tcx.is_lang_item(trait_id, *lang_item)
+        })
     }
 
     /// Iterator over all local def ids that are not a extern spec

tests/tests/pos/surface/no_panic06.rs

@@ -0,0 +1,17 @@
+#[flux::sig(fn(f: F) -> i32)]
+#[flux::no_panic_if(F::no_panic())]
+fn foo<F: Fn(i32) -> i32>(f: F) -> i32 {
+    f(3)
+}
+
+#[flux::sig(fn(f: F) -> i32)]
+#[flux::no_panic_if(F::no_panic())]
+fn foo2<F: FnOnce(i32) -> i32>(f: F) -> i32 {
+    f(3)
+}
+
+#[flux::sig(fn(f: F) -> i32)]
+#[flux::no_panic_if(F::no_panic())]
+fn foo3<F: FnMut(i32) -> i32>(mut f: F) -> i32 {
+    f(3)
+}