Fix generated C++ bounded waits

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 ## Unreleased
 
+- Fix generated C++ bounded-wait RPCs so each promise yields exactly one
+  future, reused for both the timeout wait and the result read. Void RPCs now
+  also fulfill their promise after decoding a successful response; previously
+  non-Void calls threw `future_already_retrieved` and Void calls always timed
+  out even when the backend had completed.
+
 - Add executable product acceptance contracts. `raco rivet acceptance
   --json` validates `rivet-acceptance.rktd`, rejects missing kind/platform
   coverage, launches each current-platform suite as an executable plus argv

platform/linux/host/GeneratedBackend.hpp

@@ -75,6 +75,7 @@ class API {
   std::optional<std::string> greet_within(
       std::string name, std::chrono::milliseconds rivet_timeout) {
     auto rivet_done = std::make_shared<std::promise<std::string>>();
+    auto rivet_future = rivet_done->get_future();
     auto rivet_id = backend_.request_async(
         "greet", rivet::linux_runtime::Value::List{rivet::Value(std::move(name))},
         [rivet_done](rivet::linux_runtime::CallResult call) mutable {
@@ -85,17 +86,18 @@ class API {
             rivet_done->set_value(*result.value);
           }
         });
-    if (rivet_done->get_future().wait_for(rivet_timeout) !=
+    if (rivet_future.wait_for(rivet_timeout) !=
         std::future_status::ready) {
       backend_.cancel(rivet_id);
       return std::nullopt;
     }
-    return rivet_done->get_future().get();
+    return rivet_future.get();
   }
 
   std::optional<std::int64_t> increment_within(
       std::int64_t value, std::chrono::milliseconds rivet_timeout) {
     auto rivet_done = std::make_shared<std::promise<std::int64_t>>();
+    auto rivet_future = rivet_done->get_future();
     auto rivet_id = backend_.request_async(
         "increment", rivet::linux_runtime::Value::List{rivet::Value(value)},
         [rivet_done](rivet::linux_runtime::CallResult call) mutable {
@@ -106,12 +108,12 @@ class API {
             rivet_done->set_value(*result.value);
           }
         });
-    if (rivet_done->get_future().wait_for(rivet_timeout) !=
+    if (rivet_future.wait_for(rivet_timeout) !=
         std::future_status::ready) {
       backend_.cancel(rivet_id);
       return std::nullopt;
     }
-    return rivet_done->get_future().get();
+    return rivet_future.get();
   }
 
   // State accessors: completion callbacks run on the backend reader thread

platform/windows/host/GeneratedBackend.hpp

@@ -75,6 +75,7 @@ class API {
   std::optional<std::string> greet_within(
       std::string name, std::chrono::milliseconds rivet_timeout) {
     auto rivet_done = std::make_shared<std::promise<std::string>>();
+    auto rivet_future = rivet_done->get_future();
     auto rivet_id = backend_.request_async(
         "greet", rivet::windows::Value::List{rivet::Value(std::move(name))},
         [rivet_done](rivet::windows::CallResult call) mutable {
@@ -85,17 +86,18 @@ class API {
             rivet_done->set_value(*result.value);
           }
         });
-    if (rivet_done->get_future().wait_for(rivet_timeout) !=
+    if (rivet_future.wait_for(rivet_timeout) !=
         std::future_status::ready) {
       backend_.cancel(rivet_id);
       return std::nullopt;
     }
-    return rivet_done->get_future().get();
+    return rivet_future.get();
   }
 
   std::optional<std::int64_t> increment_within(
       std::int64_t value, std::chrono::milliseconds rivet_timeout) {
     auto rivet_done = std::make_shared<std::promise<std::int64_t>>();
+    auto rivet_future = rivet_done->get_future();
     auto rivet_id = backend_.request_async(
         "increment", rivet::windows::Value::List{rivet::Value(value)},
         [rivet_done](rivet::windows::CallResult call) mutable {
@@ -106,12 +108,12 @@ class API {
             rivet_done->set_value(*result.value);
           }
         });
-    if (rivet_done->get_future().wait_for(rivet_timeout) !=
+    if (rivet_future.wait_for(rivet_timeout) !=
         std::future_status::ready) {
       backend_.cancel(rivet_id);
       return std::nullopt;
     }
-    return rivet_done->get_future().get();
+    return rivet_future.get();
   }
 
   // State accessors: completion callbacks run on the backend reader thread

rivet-cli/codegen/cpp.rkt

@@ -158,7 +158,8 @@
 (define (cpp-promise-handler result-type backend-namespace)
   (define settle
     (if (eq? result-type 'Void)
-        (format "detail::decode_~a(*rivet_result.value);" (type-key result-type))
+        (format "detail::decode_~a(*rivet_result.value); rivet_done->set_value();"
+                (type-key result-type))
         (format "rivet_done->set_value(detail::decode_~a(*rivet_result.value));"
                 (type-key result-type))))
   (format
@@ -186,16 +187,16 @@
   (define timed-out-return (if void? "false" "std::nullopt"))
   (define final-get
     (if void?
-        "rivet_done->get_future().get(); return true;"
-        "return rivet_done->get_future().get();"))
+        "rivet_future.get(); return true;"
+        "return rivet_future.get();"))
   ;; A zero-argument RPC has no parameter list; the timeout must not follow
   ;; a stray comma.
   (define within-params
     (if (string=? params "")
         "std::chrono::milliseconds rivet_timeout"
         (format "~a, std::chrono::milliseconds rivet_timeout" params)))
   (format
-   "  ~a ~a_within(~a) { auto rivet_done = std::make_shared<std::promise<~a>>(); auto rivet_id = backend_.request_async(~a, rivet::Value::List{~a}, ~a); if (rivet_done->get_future().wait_for(rivet_timeout) != std::future_status::ready) { backend_.cancel(rivet_id); return ~a; } ~a }\n"
+   "  ~a ~a_within(~a) { auto rivet_done = std::make_shared<std::promise<~a>>(); auto rivet_future = rivet_done->get_future(); auto rivet_id = backend_.request_async(~a, rivet::Value::List{~a}, ~a); if (rivet_future.wait_for(rivet_timeout) != std::future_status::ready) { backend_.cancel(rivet_id); return ~a; } ~a }\n"
    return-type
    (cpp-id (schema-rpc-name info))
    within-params

rivet/tests/codegen.rkt

@@ -194,6 +194,18 @@ RKT
     (check-true (string-contains? cpp "bool log_line_within(std::string message, std::chrono::milliseconds rivet_timeout)"))
     (check-true (string-contains? cpp "backend_.cancel(rivet_id); return false;"))
     (check-true (string-contains? cpp "rivet_done->set_value(detail::decode_Int64(*rivet_result.value));"))
+    (check-true
+     (string-contains? cpp
+                       "auto rivet_future = rivet_done->get_future();"))
+    (check-true
+     (string-contains? cpp
+                       "rivet_future.wait_for(rivet_timeout)"))
+    (check-true (string-contains? cpp "return rivet_future.get();"))
+    (check-false
+     (string-contains? cpp "rivet_done->get_future().wait_for"))
+    (check-true
+     (string-contains? cpp
+                       "detail::decode_Void(*rivet_result.value); rivet_done->set_value();"))
     ;; A Void async handler must not assign into Result<void>, which has no
     ;; value member — the decode only validates arrival.
     (check-false (string-contains? cpp "result.value = detail::decode_void"))