cmProcess: compute the timeout when needed

When a timeout is updated during runtime (e.g., via
`TIMEOUT_AFTER_MATCH`), the actual timeout needs recomputed based on
consideration of `StopTimeout` as well. Instead of using `Timeout`
directly, add a `GetComputedTimeout` method which also retrieves the
timeout reason based on which timeout is selected.

Source/CTest/cmCTestRunTest.cxx

@@ -813,9 +813,6 @@ bool cmCTestRunTest::ForkProcess()
   if (stop_time != std::chrono::system_clock::time_point()) {
     cmDuration timeUntilStop =
       (stop_time - std::chrono::system_clock::now()) % std::chrono::hours(24);
-    if (timeUntilStop < timeRemaining) {
-      timeRemaining = timeUntilStop;
-    }
     this->TestProcess->SetStopTimeout(timeUntilStop);
   }
 
@@ -825,7 +822,16 @@ bool cmCTestRunTest::ForkProcess()
   }
   if (!timeout || timeRemaining < *timeout) {
     timeout = timeRemaining;
-    this->TestProcess->SetTimeoutReason(cmProcess::TimeoutReason::StopTime);
+  }
+
+  // Inform the test process of its normal timeout
+  if (timeout) {
+    this->TestProcess->SetTimeout(*timeout);
+  }
+
+  // Ask the test process which timeout is in effect.
+  if (auto ctimeout = this->TestProcess->GetComputedTimeout()) {
+    timeout = ctimeout->Duration;
   }
 
   if (timeout) {

Source/CTest/cmProcess.cxx

@@ -158,9 +158,10 @@ bool cmProcess::StartProcess(uv_loop_t& loop, std::vector<size_t>* affinity)
 
 void cmProcess::StartTimer()
 {
-  if (this->Timeout) {
-    auto msec =
-      std::chrono::duration_cast<std::chrono::milliseconds>(*this->Timeout);
+  if (auto ctimeout = this->GetComputedTimeout()) {
+    this->TimeoutReason_ = ctimeout->Reason;
+    auto msec = std::chrono::duration_cast<std::chrono::milliseconds>(
+      ctimeout->Duration);
     this->Timer.start(&cmProcess::OnTimeoutCB,
                       static_cast<uint64_t>(msec.count()), 0,
                       cm::uv_update_time::no);
@@ -374,6 +375,24 @@ cmProcess::State cmProcess::GetProcessStatus()
   return this->ProcessState;
 }
 
+cm::optional<cmProcess::ComputedTimeout> cmProcess::GetComputedTimeout() const
+{
+  if (this->StopTimeout && this->Timeout) {
+    if (*this->StopTimeout < *this->Timeout) {
+      return ComputedTimeout{ TimeoutReason::StopTime, *this->StopTimeout };
+    }
+    return ComputedTimeout{ TimeoutReason::Normal, *this->Timeout };
+  }
+  if (this->StopTimeout) {
+    return ComputedTimeout{ TimeoutReason::StopTime, *this->StopTimeout };
+  }
+  if (this->Timeout) {
+    return ComputedTimeout{ TimeoutReason::Normal, *this->Timeout };
+  }
+
+  return cm::nullopt;
+}
+
 void cmProcess::ChangeTimeout(cmDuration t)
 {
   this->Timeout = t;

Source/CTest/cmProcess.h

@@ -49,8 +49,13 @@ public:
     Normal,
     StopTime,
   };
-  void SetTimeoutReason(TimeoutReason r) { this->TimeoutReason_ = r; }
   TimeoutReason GetTimeoutReason() const { return this->TimeoutReason_; }
+  struct ComputedTimeout
+  {
+    TimeoutReason Reason;
+    cmDuration Duration;
+  };
+  cm::optional<ComputedTimeout> GetComputedTimeout() const;
 
   enum class State
   {