Adjust error when having distributed MSWells without setting --allow-distributed-wells=false

Instead of throwing inside the loop over all wells, collect the findings and throw at the end. Throwing inside of the loop over all wells leads to a deadlock in some cases.

opm/simulators/wells/WellState.cpp

@@ -44,6 +44,7 @@
 #include <cassert>
 #include <initializer_list>
 #include <numeric>
+#include <optional>
 #include <set>
 #include <stdexcept>
 #include <type_traits>
@@ -669,6 +670,8 @@ void WellState<Scalar>::initWellStateMSWell(const std::vector<Well>& wells_ecl,
     const auto& pu = this->phaseUsage();
     const int np = pu.num_phases;
 
+    std::optional<std::string> distributedMSWellLocalErrorMessage;
+
     // in the init function, the well rates and perforation rates have been initialized or copied from prevState
     // what we do here, is to set the segment rates and perforation rates
     for (int w = 0; w < nw; ++w) {
@@ -716,8 +719,26 @@ void WellState<Scalar>::initWellStateMSWell(const std::vector<Well>& wells_ecl,
             }
             ws.parallel_info.get().setActiveToLocalMap(active_to_local);
 
-            if (!this->enableDistributedWells_ && static_cast<int>(ws.perf_data.size()) != n_activeperf)
-                throw std::logic_error("Distributed multi-segment wells cannot be initialized properly yet.");
+            // Check if the multi-segment well is distributed across several processes by comparing the local number
+            // of active perforations (ws.perf_data.size()) with the total number of active perforations (n_activeperf).
+            // If they differ on any rank, the well is considered distributed.
+
+            if (static_cast<int>(ws.perf_data.size()) != n_activeperf) {
+                if (!distributedMSWellLocalErrorMessage) {
+                    distributedMSWellLocalErrorMessage = ""; // First well with error: initialize the string
+                }
+
+                // Append to the existing error message for errors in further wells
+                *distributedMSWellLocalErrorMessage += fmt::format(
+                    "Distributed multi-segment well {} detected on rank {}.\n"
+                    "The number of active perforations on rank {} is {}, but the total number of active perforations is {}.\n\n",
+                    well_ecl.name(),
+                    ws.parallel_info.get().communication().rank(),
+                    ws.parallel_info.get().communication().rank(),
+                    ws.perf_data.size(),
+                    n_activeperf
+                );
+            }
 
 
             std::vector<std::vector<int>> segment_inlets(well_nseg);
@@ -809,6 +830,12 @@ void WellState<Scalar>::initWellStateMSWell(const std::vector<Well>& wells_ecl,
         }
     }
 
+    // Instead of throwing inside the loop over all wells, collect the findings and throw at the end.
+    // Throwing inside of the loop over all wells leads to a deadlock in some cases.
+
+    if (!this->enableDistributedWells_ && distributedMSWellLocalErrorMessage) {
+        throw std::logic_error(*distributedMSWellLocalErrorMessage);
+    }
 
     if (prev_well_state) {
         for (int w = 0; w < nw; ++w) {