handle DualOnly ret more reliably (#113)

compiler/rustc_builtin_macros/src/autodiff.rs

@@ -461,12 +461,20 @@ fn gen_enzyme_body(
         };
     }
 
-    let ret_tuple: P<ast::Expr> = ecx.expr_tuple(span, exprs);
-    let ret = ecx.expr_call(new_decl_span, blackbox_call_expr.clone(), thin_vec![ret_tuple]);
-    if d_sig.decl.output.has_ret() {
-        // If we return (), we don't have to match the return type.
-        body.stmts.push(ecx.stmt_expr(ret));
+    let ret : P<ast::Expr>;
+    if exprs.len() > 1 {
+        let ret_tuple: P<ast::Expr> = ecx.expr_tuple(span, exprs);
+        ret = ecx.expr_call(new_decl_span, blackbox_call_expr.clone(), thin_vec![ret_tuple]);
+    } else if exprs.len() == 1 {
+        let ret_scal = exprs.pop().unwrap();
+        ret = ecx.expr_call(new_decl_span, blackbox_call_expr.clone(), thin_vec![ret_scal]);
+    } else {
+        assert!(!d_sig.decl.output.has_ret());
+        // We don't have to match the return type.
+        return body;
     }
+    assert!(d_sig.decl.output.has_ret());
+    body.stmts.push(ecx.stmt_expr(ret));
 
     body
 }

compiler/rustc_middle/src/ty/mod.rs

@@ -2762,6 +2762,7 @@ pub fn fnc_typetrees<'tcx>(tcx: TyCtxt<'tcx>, fn_ty: Ty<'tcx>, da: &mut Vec<Diff
         // We care about safety checks, if an argument get's duplicated and we write into the
         // shadow. That's equivalent to Duplicated or DuplicatedOnly.
         let safety = if !da.is_empty() {
+            assert!(da.len() == x.inputs().len(), "{:?} != {:?}", da.len(), x.inputs().len());
             // If we have Activities, we also have spans
             assert!(span.is_some());
             match da[i] {