Determine call type based on LanguageItems

Also handles `FnMut` and `FnOnce` now

crates/flowistry/src/pdg/construct.rs

@@ -632,30 +632,20 @@ impl<'tcx> GraphConstructor<'tcx> {
       }
     }
 
-    enum CallKind {
-      /// A standard function call like `f(x)`.
-      Direct,
-      /// A call to a function variable, like `fn foo(f: impl Fn()) { f() }`
-      Indirect,
-      /// A poll to an async function, like `f.await`.
-      AsyncPoll,
-    }
-    // Determine the type of call-site.
-    let (call_kind, args) = match tcx.def_path_str(called_def_id).as_str() {
-      "std::ops::Fn::call" => (CallKind::Indirect, args),
-      "std::future::Future::poll" => {
-        let args = self.find_async_args(args)?;
-        (CallKind::AsyncPoll, args)
-      }
-      def_path => {
-        if resolved_def_id.is_local() {
-          (CallKind::Direct, args)
-        } else {
-          trace!("  Bailing because func is non-local: `{def_path}`");
-          return None;
-        }
-      }
+    let Some(call_kind) = CallKind::classify(tcx, called_def_id) else {
+      trace!(
+        "  Bailing because func is non-local: `{}`",
+        tcx.def_path_str(called_def_id)
+      );
+      return None;
+    };
+
+    let args = if call_kind == CallKind::AsyncPoll {
+      self.find_async_args(args)?
+    } else {
+      args
     };
+
     trace!("  Handling call!");
 
     // A helper to translate an argument (or return) in the child into a place in the parent.
@@ -1011,6 +1001,35 @@ impl<'tcx> GraphConstructor<'tcx> {
   }
 }
 
+#[derive(PartialEq, Eq)]
+enum CallKind {
+  /// A standard function call like `f(x)`.
+  Direct,
+  /// A call to a function variable, like `fn foo(f: impl Fn()) { f() }`
+  Indirect,
+  /// A poll to an async function, like `f.await`.
+  AsyncPoll,
+}
+
+impl CallKind {
+  /// Determine the type of call-site.
+  fn classify(tcx: TyCtxt, def_id: DefId) -> Option<Self> {
+    let lang_items = tcx.lang_items();
+    if lang_items.future_poll_fn() == Some(def_id) {
+      return Some(Self::AsyncPoll);
+    }
+    let my_impl = tcx.impl_of_method(def_id)?;
+    let my_trait = tcx.trait_id_of_impl(my_impl)?;
+    if Some(my_trait) == lang_items.fn_trait()
+      || Some(my_trait) == lang_items.fn_mut_trait()
+      || Some(my_trait) == lang_items.fn_once_trait()
+    {
+      return Some(Self::Indirect);
+    }
+    def_id.is_local().then_some(Self::Direct)
+  }
+}
+
 struct DfAnalysis<'a, 'tcx>(&'a GraphConstructor<'tcx>);
 
 impl<'tcx> df::AnalysisDomain<'tcx> for DfAnalysis<'_, 'tcx> {