Make worker timeouts a bit more strongly typed

This tidies things up in general, but also prepares the way for the next
commit in particular.

src/libstore/build/derivation-building-goal.cc

@@ -71,12 +71,12 @@ void DerivationBuildingGoal::killChild()
 #endif
 }
 
-void DerivationBuildingGoal::timedOut(Error && ex)
+void DerivationBuildingGoal::timedOut(TimedOut && ex)
 {
     killChild();
     // We're not inside a coroutine, hence we can't use co_return here.
     // Thus we ignore the return value.
-    [[maybe_unused]] Done _ = doneFailure({BuildResult::Failure::TimedOut, std::move(ex)});
+    [[maybe_unused]] Done _ = doneFailure(std::move(ex));
 }
 
 std::string showKnownOutputs(const StoreDirConfig & store, const Derivation & drv)

src/libstore/build/goal.cc

@@ -4,6 +4,12 @@
 
 namespace nix {
 
+TimedOut::TimedOut(time_t maxDuration)
+    : BuildError(BuildResult::Failure::TimedOut, "timed out after %1% seconds", maxDuration)
+    , maxDuration(maxDuration)
+{
+}
+
 using Co = nix::Goal::Co;
 using promise_type = nix::Goal::promise_type;
 using handle_type = nix::Goal::handle_type;

src/libstore/build/worker.cc

@@ -479,14 +479,13 @@ void Worker::waitForInput()
 
         if (goal->exitCode == Goal::ecBusy && 0 != settings.maxSilentTime && j->respectTimeouts
             && after - j->lastOutput >= std::chrono::seconds(settings.maxSilentTime)) {
-            goal->timedOut(
-                Error("%1% timed out after %2% seconds of silence", goal->getName(), settings.maxSilentTime));
+            goal->timedOut(TimedOut(settings.maxSilentTime));
         }
 
         else if (
             goal->exitCode == Goal::ecBusy && 0 != settings.buildTimeout && j->respectTimeouts
             && after - j->timeStarted >= std::chrono::seconds(settings.buildTimeout)) {
-            goal->timedOut(Error("%1% timed out after %2% seconds", goal->getName(), settings.buildTimeout));
+            goal->timedOut(TimedOut(settings.buildTimeout));
         }
     }
 

src/libstore/include/nix/store/build/derivation-building-goal.hh

@@ -100,7 +100,7 @@ private:
 
     std::map<ActivityId, Activity> builderActivities;
 
-    void timedOut(Error && ex) override;
+    void timedOut(TimedOut && ex) override;
 
     std::string key() override;
 

src/libstore/include/nix/store/build/derivation-goal.hh

@@ -52,7 +52,7 @@ struct DerivationGoal : public Goal
         bool storeDerivation);
     ~DerivationGoal() = default;
 
-    void timedOut(Error && ex) override
+    void timedOut(TimedOut && ex) override
     {
         unreachable();
     };

src/libstore/include/nix/store/build/derivation-resolution-goal.hh

@@ -43,7 +43,7 @@ struct DerivationResolutionGoal : public Goal
      */
     std::unique_ptr<std::pair<StorePath, BasicDerivation>> resolvedDrv;
 
-    void timedOut(Error && ex) override {}
+    void timedOut(TimedOut && ex) override {}
 
 private:
 

src/libstore/include/nix/store/build/derivation-trampoline-goal.hh

@@ -109,7 +109,7 @@ struct DerivationTrampolineGoal : public Goal
 
     virtual ~DerivationTrampolineGoal();
 
-    void timedOut(Error && ex) override {}
+    void timedOut(TimedOut && ex) override {}
 
     std::string key() override;
 

src/libstore/include/nix/store/build/drv-output-substitution-goal.hh

@@ -33,7 +33,7 @@ public:
 
     Co init();
 
-    void timedOut(Error && ex) override
+    void timedOut(TimedOut && ex) override
     {
         unreachable();
     };

src/libstore/include/nix/store/build/goal.hh

@@ -8,6 +8,13 @@
 
 namespace nix {
 
+struct TimedOut : BuildError
+{
+    time_t maxDuration;
+
+    TimedOut(time_t maxDuration);
+};
+
 /**
  * Forward definition.
  */
@@ -454,7 +461,7 @@ public:
      * get rid of any running child processes that are being monitored
      * by the worker (important!), etc.
      */
-    virtual void timedOut(Error && ex) = 0;
+    virtual void timedOut(TimedOut && ex) = 0;
 
     /**
      * Used for comparisons. The order matters a bit for scheduling. We

src/libstore/include/nix/store/build/substitution-goal.hh

@@ -53,7 +53,7 @@ public:
         std::optional<ContentAddress> ca = std::nullopt);
     ~PathSubstitutionGoal();
 
-    void timedOut(Error && ex) override
+    void timedOut(TimedOut && ex) override
     {
         unreachable();
     };