libstore: merge ContinueImmediately and StillAlive

nothing needs to signal being still active but not actively pollable,
only that immediate polling for the next goal work phase is in order.

Change-Id: Ia43c1015e94ba4f5f6b9cb92943da608c4a01555

src/libstore/build/derivation-goal.cc

@@ -1751,7 +1751,7 @@ DerivationGoal::continueOrError(kj::Promise<Outcome<void, Goal::Finished>> p)
 {
     return p.then([](auto r) -> Result<WorkResult> {
         if (r.has_value()) {
-            return ContinueImmediately{};
+            return StillAlive{};
         } else if (r.has_error()) {
             return r.assume_error();
         } else {

src/libstore/build/drv-output-substitution-goal.cc

@@ -86,7 +86,7 @@ try {
         });
 
     state = &DrvOutputSubstitutionGoal::realisationFetched;
-    return pipe.promise.then([]() -> Result<WorkResult> { return ContinueImmediately{}; });
+    return pipe.promise.then([]() -> Result<WorkResult> { return StillAlive{}; });
 } catch (...) {
     return {std::current_exception()};
 }

src/libstore/build/goal.cc

@@ -17,7 +17,7 @@ try {
     /* If we are polling goals that are waiting for a lock, then wake
        up after a few seconds at most. */
     co_await worker.aio.provider->getTimer().afterDelay(settings.pollInterval.get() * kj::SECONDS);
-    co_return ContinueImmediately{};
+    co_return StillAlive{};
 } catch (...) {
     co_return std::current_exception();
 }
@@ -45,11 +45,11 @@ try {
         waiteeDone(dep);
 
         if (dep->exitCode == ecFailed && !settings.keepGoing) {
-            co_return result::success(ContinueImmediately{});
+            co_return result::success(StillAlive{});
         }
     }
 
-    co_return result::success(ContinueImmediately{});
+    co_return result::success(StillAlive{});
 } catch (...) {
     co_return result::failure(std::current_exception());
 }

src/libstore/build/goal.hh

@@ -103,7 +103,6 @@ public:
     struct Finished;
 
     struct [[nodiscard]] StillAlive {};
-    struct [[nodiscard]] ContinueImmediately {};
     struct [[nodiscard]] Finished {
         ExitCode exitCode;
         BuildResult result;
@@ -116,7 +115,6 @@ public:
 
     struct [[nodiscard]] WorkResult : std::variant<
                                           StillAlive,
-                                          ContinueImmediately,
                                           Finished>
     {
         WorkResult() = delete;

src/libstore/build/substitution-goal.cc

@@ -240,7 +240,7 @@ try {
     });
 
     state = &PathSubstitutionGoal::finished;
-    return pipe.promise.then([]() -> Result<WorkResult> { return ContinueImmediately{}; });
+    return pipe.promise.then([]() -> Result<WorkResult> { return StillAlive{}; });
 } catch (...) {
     return {std::current_exception()};
 }

src/libstore/build/worker.cc

@@ -212,8 +212,7 @@ void Worker::handleWorkResult(GoalPtr goal, Goal::WorkResult how)
 {
     std::visit(
         overloaded{
-            [&](Goal::StillAlive) {},
-            [&](Goal::ContinueImmediately) { wakeUp(goal); },
+            [&](Goal::StillAlive) { wakeUp(goal); },
             [&](Goal::Finished & f) { goalFinished(goal, f); },
         },
         how