Do not call C++ with positions, velocities or angular velocities that are NaNs.

geometry/r3x3_matrix_body.hpp

@@ -162,12 +162,12 @@ R3Element<Quotient<RScalar, Scalar>> R3x3Matrix<Scalar>::Solve(
         max = Abs(A(i, k));
       }
     }
-    CHECK_LE(0, r);
-    CHECK_GT(3, r);
+    CHECK_LE(0, r) << *this << " cannot pivot";
+    CHECK_GT(3, r) << *this << " cannot pivot";
     std::swap(A.rows_[k], A.rows_[r]);
     std::swap(L.rows_[k], L.rows_[r]);
     std::swap(b[k], b[r]);
-    CHECK_NE(Scalar{}, A(k, k));
+    CHECK_NE(Scalar{}, A(k, k)) << *this << " is singular";
 
     for (int j = k; j < 3; ++j) {
       Scalar U_kj = A(k, j);

journal/player_test.cpp

@@ -89,7 +89,7 @@ TEST_F(PlayerTest, DISABLED_SECULAR_Debug) {
   // An example of how journaling may be used for debugging.  You must set
   // |path| and fill the |method_in| and |method_out_return| protocol buffers.
   std::string path =
-      R"(P:\Public Mockingbird\Principia\Crashes\2507\JOURNAL.20200328-214524)";  // NOLINT
+      R"(P:\Public Mockingbird\Principia\Crashes\2530\JOURNAL.20200416-093807)";  // NOLINT
   Player player(path);
   int count = 0;
   while (player.Play(count)) {
@@ -109,7 +109,7 @@ TEST_F(PlayerTest, DISABLED_SECULAR_Debug) {
     auto* extension = method_in.MutableExtension(
         serialization::CatchUpLaggingVessels::extension);
     auto* in = extension->mutable_in();
-    in->set_plugin(2014156823824);
+    in->set_plugin(2899402431696);
   }
   serialization::Method method_out_return;
   {

ksp_plugin/part.hpp

@@ -63,6 +63,8 @@ class Part final {
 
   PartId part_id() const;
 
+  // When a part is not truthful, all its properties except for name and part_id
+  // are lies and should not be propagated to the game.
   bool truthful() const;
   void make_truthful();
 

ksp_plugin_adapter/ksp_plugin_adapter.cs

@@ -550,6 +550,24 @@ private static bool JustAboveTheGround(Vessel vessel,
     return height + vertical_speed * Δt < 0;
   }
 
+  private static bool IsNaN(Vector3d v) {
+    return double.IsNaN(v.x + v.y + v.z);
+  }
+
+  private static bool IsNaN(XYZ xyz) {
+    return double.IsNaN(xyz.x + xyz.y + xyz.z);
+  }
+
+  // It seems that parts sometimes have NaN position, velocity or angular
+  // velocity, presumably because they are being destroyed.  Just skip these
+  // unfaithful parts as if they had no rigid body.
+  private static bool PartIsFaithful(Part part) {
+    return part.rb != null &&
+           !IsNaN(part.rb.position) &&
+           !IsNaN(part.rb.velocity) &&
+           !IsNaN(part.rb.angularVelocity);
+  }
+
   private void OverrideRSASTarget(FlightCtrlState state) {
     if (override_rsas_target_ && FlightGlobals.ActiveVessel.Autopilot.Enabled) {
       FlightGlobals.ActiveVessel.Autopilot.SAS.SetTargetOrientation(
@@ -1045,7 +1063,7 @@ private System.Collections.IEnumerator WaitedForFixedUpdate() {
                                  !vessel.packed,
                                  out bool inserted);
       if (!vessel.packed) {
-        foreach (Part part in vessel.parts.Where((part) => part.rb != null)) {
+        foreach (Part part in vessel.parts.Where(PartIsFaithful)) {
           QP degrees_of_freedom;
           if (part_id_to_degrees_of_freedom_.ContainsKey(part.flightID)) {
             degrees_of_freedom = part_id_to_degrees_of_freedom_[part.flightID];
@@ -1224,10 +1242,7 @@ private System.Collections.IEnumerator WaitedForFixedUpdate() {
       if (!plugin_.HasVessel(vessel.id.ToString())) {
         continue;
       }
-      foreach (Part part in vessel.parts) {
-        if (part.rb == null) {
-          continue;
-        }
+      foreach (Part part in vessel.parts.Where(PartIsFaithful)) {
         if (main_body_change_countdown_ == 0 &&
             last_main_body_ == FlightGlobals.ActiveVessel?.mainBody) {
           plugin_.PartSetApparentRigidMotion(
@@ -1270,10 +1285,7 @@ private System.Collections.IEnumerator WaitedForFixedUpdate() {
         if (!plugin_.HasVessel(vessel.id.ToString())) {
           continue;
         }
-        foreach (Part part in vessel.parts) {
-          if (part.rb == null) {
-            continue;
-          }
+        foreach (Part part in vessel.parts.Where(PartIsFaithful)) {
           QPRW part_actual_motion =
               plugin_.PartGetActualDegreesOfFreedom(
                   part.flightID,
@@ -1463,7 +1475,7 @@ private void FashionablyLate() {
       foreach (Vessel vessel in
                FlightGlobals.Vessels.Where(v => is_manageable(v) &&
                                                 !v.packed)) {
-        foreach (Part part in vessel.parts.Where((part) => part.rb != null)) {
+        foreach (Part part in vessel.parts.Where(PartIsFaithful)) {
           if (part.torque != Vector3d.zero) {
             part_id_to_intrinsic_torque_.Add(part.flightID, part.torque);
           }
@@ -1555,7 +1567,7 @@ private void BetterLateThanNever() {
       foreach (Vessel vessel in
                FlightGlobals.Vessels.Where(v => is_manageable(v) &&
                                                 !v.packed)) {
-        foreach (Part part in vessel.parts.Where((part) => part.rb != null)) {
+        foreach (Part part in vessel.parts.Where(PartIsFaithful)) {
           // TODO(egg): use the centre of mass.
           part_id_to_degrees_of_freedom_.Add(
               part.flightID,
@@ -1651,8 +1663,7 @@ private void RenderGuidance(Vessel active_vessel) {
         Burn burn = plugin_.FlightPlanGetManoeuvre(
                         vessel_guid,
                         first_future_manœuvre_index.Value).burn;
-        if (flight_planner_.show_guidance &&
-            !double.IsNaN(guidance.x + guidance.y + guidance.z)) {
+        if (flight_planner_.show_guidance && !IsNaN(guidance)) {
           // The user wants to show the guidance node, and that node was
           // properly computed by the C++ code.
           PatchedConicSolver solver = active_vessel.patchedConicSolver;