Report why a simulation setup library cannot be loaded

This replaces the asserts in execFromPlugin by fatal messages with the reason.

- A failed dlopen of libO2G4Setup and friends stopped at assert(libHandle), without the error from dlerror().
- The message now gives the dlopen error, e.g. a missing static TLS reserve for Geant4 built with the initial-exec TLS model.
- Errors of the names that do not exist are listed only if no other error occurred.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sawenzel

Detectors/gconfig/src/SimSetup.cxx

@@ -15,11 +15,7 @@
 #include <fairlogger/Logger.h>
 #include "SetCuts.h"
 #include <dlfcn.h>
-#ifdef NDEBUG
-#undef NDEBUG
-#endif
-#include <cassert>
-#include <sstream>
+#include <string>
 
 namespace o2
 {
@@ -28,23 +24,36 @@ typedef void (*setup_fnc)();
 
 void execFromPlugin(const char* libname, const char* funcname)
 {
-  auto libHandle = dlopen(libname, RTLD_NOW);
-  // try to make the library loading a bit more portable:
+  // errors other than "not found" explain why an existing library could not be loaded
+  std::string notFound, otherErrors;
+  auto open = [&notFound, &otherErrors](const std::string& name) {
+    auto handle = dlopen(name.c_str(), RTLD_NOW);
+    if (!handle) {
+      const char* error = dlerror();
+      const std::string message = error ? error : "unknown error";
+      (message.find("No such file or directory") != std::string::npos ? notFound : otherErrors) += "\n  " + message;
+    }
+    return handle;
+  };
+  // try to make the library loading a bit more portable by also trying the *.so and *.dylib names
+  auto libHandle = open(libname);
   if (!libHandle) {
-    // try appending *.so
-    std::stringstream stream;
-    stream << libname << ".so";
-    libHandle = dlopen(stream.str().c_str(), RTLD_NOW);
+    libHandle = open(std::string(libname) + ".so");
   }
   if (!libHandle) {
-    // try appending *.dylib
-    std::stringstream stream;
-    stream << libname << ".dylib";
-    libHandle = dlopen(stream.str().c_str(), RTLD_NOW);
+    libHandle = open(std::string(libname) + ".dylib");
   }
-  assert(libHandle);
+  if (!libHandle) {
+    LOG(fatal) << "Cannot load " << libname << ":" << (otherErrors.empty() ? notFound : otherErrors);
+    return;
+  }
+  dlerror(); // clear any pending error before dlsym
   auto func = (setup_fnc)dlsym(libHandle, funcname);
-  assert(func);
+  if (!func) {
+    const char* error = dlerror();
+    LOG(fatal) << "Cannot find " << funcname << " in " << libname << ": " << (error ? error : "the symbol is null");
+    return;
+  }
   func();
 }