cmake: Stop parsing after `--` when detecting script mode

Fixes #24220

Source/cmakemain.cxx

@@ -311,6 +311,11 @@ int do_cmake(int ac, char const* const* av)
         }
         return 1; // failed to parse
       }
+      // Only in script mode do we stop parsing instead
+      // of preferring the last mode flag provided
+      if (arg == "--" && workingMode == cmake::SCRIPT_MODE) {
+        break;
+      }
     }
     if (!matched) {
       parsedArgs.emplace_back(av[i]);

Tests/RunCMake/CommandLine/P_P_in_arbitrary_args-stdout.txt

@@ -0,0 +1,10 @@
+^-- CMAKE_ARGC='6'
+-- CMAKE_ARGV1='-P'
+-- CMAKE_ARGV2='[^']*/Tests/RunCMake/CommandLine/P_arbitrary_args.cmake'
+-- CMAKE_ARGV3='--'
+-- CMAKE_ARGV4='-P'
+-- CMAKE_ARGV5='[^']*/Tests/RunCMake/CommandLine/non_existing.cmake'
+-- CMAKE_ARGV6=''
+-- CMAKE_ARGV7=''
+-- CMAKE_ARGV8=''
+-- CMAKE_ARGV9=''$

Tests/RunCMake/CommandLine/RunCMakeTest.cmake

@@ -54,6 +54,7 @@ run_cmake_command(P_no-arg ${CMAKE_COMMAND} -P)
 run_cmake_command(P_no-file ${CMAKE_COMMAND} -P nosuchscriptfile.cmake)
 run_cmake_command(P_args ${CMAKE_COMMAND} -P "${RunCMake_SOURCE_DIR}/P_args.cmake" relative/path "${RunCMake_SOURCE_DIR}")
 run_cmake_command(P_arbitrary_args ${CMAKE_COMMAND} -P "${RunCMake_SOURCE_DIR}/P_arbitrary_args.cmake" -- -DFOO -S -B --fresh --version)
+run_cmake_command(P_P_in_arbitrary_args ${CMAKE_COMMAND} -P "${RunCMake_SOURCE_DIR}/P_arbitrary_args.cmake" -- -P "${RunCMake_SOURCE_DIR}/non_existing.cmake")
 run_cmake_command(P_fresh ${CMAKE_COMMAND} -P "${RunCMake_SOURCE_DIR}/P_fresh.cmake" --fresh)
 
 run_cmake_command(build-no-dir