Exit when calling root command with unrecognized option

core/rint/src/TRint.cxx

@@ -41,7 +41,7 @@
 #include "TTabCom.h"
 #include <cstdlib>
 #include <algorithm>
-
+#include <iostream>
 #include "Getline.h"
 #include "strlcpy.h"
 #include "snprintf.h"
@@ -146,6 +146,16 @@ TRint::TRint(const char *appClassName, Int_t *argc, char **argv, void *options,
    TApplication(appClassName, argc, argv, options, numOptions),
    fCaughtSignal(-1)
 {
+
+   if (*argc > 1) {
+      // Early exit if there are remaining unrecognized options
+      for (auto n = 1; n < *argc; n++) {
+         std::cerr << "root: unrecognized option '" << argv[n] << "'\n";
+      }
+      std::cerr << "Try 'root --help' for more information.\n";
+      TApplication::Terminate(0);
+   }
+
    fNcmd          = 0;
    fDefaultPrompt = "root [%d] ";
    fInterrupt     = kFALSE;

core/rint/test/CMakeLists.txt

@@ -5,3 +5,5 @@
 # For the list of contributors see $ROOTSYS/README/CREDITS.
 
 ROOT_ADD_GTEST(TTabComTests TTabComTests.cxx LIBRARIES Rint)
+ROOT_ADD_GTEST(TRintTests TRintTests.cxx LIBRARIES Rint)
+

core/rint/test/TRintTests.cxx

@@ -0,0 +1,43 @@
+#include <iostream>
+#include <string>
+
+#include "gtest/gtest.h"
+
+#include "TRint.h"
+
+using testing::internal::CaptureStderr;
+using testing::internal::GetCapturedStderr;
+
+TEST(TRint, UnrecognizedOptions)
+{
+   // Create array of options.
+   // We need to create it as a dynamic array for the following reasons:
+   // - TRint constructor accepts a char** so we construct directly that type
+   // - TRint will modify this array, removing recognized options and leaving
+   //   only unrecognized ones, so we can't create an std::vector and pass its
+   //   data to TRint directly.
+   int argc{4};
+   char **argv = new char *[argc];
+   argv[0] = const_cast<char *>("-q");
+   argv[1] = const_cast<char *>("-z");
+   argv[2] = const_cast<char *>("--nonexistingoption");
+   argv[3] = const_cast<char *>("-b");
+
+   CaptureStderr();
+   // Unrecognized options will be printed to stderr
+   TRint app{"App", &argc, argv};
+   std::string trinterr = GetCapturedStderr();
+
+   const std::string expected{"root: unrecognized option '-z'\n"
+                              "root: unrecognized option '--nonexistingoption'\n"
+                              "Try 'root --help' for more information.\n"};
+
+   EXPECT_EQ(trinterr, expected);
+
+   // Properly delete the array
+   for (int i = 0; i < argc; i++) {
+      delete[] argv[i];
+   }
+   delete[] argv;
+   argv = nullptr;
+}