cmSystemTools::RunSingleCommand(): Pass stdin to child process

Fixes: #25383

Source/cmSystemTools.cxx

@@ -576,7 +576,9 @@ bool cmSystemTools::RunSingleCommand(std::vector<std::string> const& command,
                                      cmDuration timeout, Encoding encoding)
 {
   cmUVProcessChainBuilder builder;
-  builder.AddCommand(command);
+  builder
+    .SetExternalStream(cmUVProcessChainBuilder::Stream_INPUT, cm_fileno(stdin))
+    .AddCommand(command);
   if (dir) {
     builder.SetWorkingDirectory(dir);
   }

Tests/RunCMake/CMakeLists.txt

@@ -827,7 +827,8 @@ endif()
 add_executable(pseudo_llvm-rc pseudo_llvm-rc.c)
 add_RunCMake_test(CommandLine -DLLVM_RC=$<TARGET_FILE:pseudo_llvm-rc> -DCMAKE_SYSTEM_NAME=${CMAKE_SYSTEM_NAME}
                   -DCYGWIN=${CYGWIN} -DMSYS=${MSYS} -DPython_EXECUTABLE=${Python_EXECUTABLE}
-                  -DEXIT_CODE_EXE=$<TARGET_FILE:exit_code>)
+                  -DEXIT_CODE_EXE=$<TARGET_FILE:exit_code>
+                  -DPRINT_STDIN_EXE=$<TARGET_FILE:print_stdin>)
 add_RunCMake_test(CommandLineTar)
 
 if(CMAKE_PLATFORM_NO_VERSIONED_SONAME OR (NOT CMAKE_SHARED_LIBRARY_SONAME_FLAG AND NOT CMAKE_SHARED_LIBRARY_SONAME_C_FLAG))

Tests/RunCMake/CommandLine/E_env-stdin-stdout.txt

@@ -0,0 +1 @@
+^Hello world$

Tests/RunCMake/CommandLine/E_env-stdin.cmake

@@ -0,0 +1,4 @@
+execute_process(
+  COMMAND ${CMAKE_COMMAND} -E echo "Hello world"
+  COMMAND ${CMAKE_COMMAND} -E env ${PRINT_STDIN_EXE}
+  )

Tests/RunCMake/CommandLine/RunCMakeTest.cmake

@@ -791,6 +791,7 @@ run_cmake_command(E_env-no-command1 ${CMAKE_COMMAND} -E env TEST_ENV=1)
 run_cmake_command(E_env-bad-arg1 ${CMAKE_COMMAND} -E env -bad-arg1)
 run_cmake_command(E_env-set   ${CMAKE_COMMAND} -E env TEST_ENV=1 ${CMAKE_COMMAND} -P ${RunCMake_SOURCE_DIR}/E_env-set.cmake)
 run_cmake_command(E_env-unset ${CMAKE_COMMAND} -E env TEST_ENV=1 ${CMAKE_COMMAND} -E env --unset=TEST_ENV ${CMAKE_COMMAND} -P ${RunCMake_SOURCE_DIR}/E_env-unset.cmake)
+run_cmake_command(E_env-stdin ${CMAKE_COMMAND} -DPRINT_STDIN_EXE=${PRINT_STDIN_EXE} -P ${RunCMake_SOURCE_DIR}/E_env-stdin.cmake)
 
 # To test whether the double dash (--) works for the env command, we need a command that e.g. contains an equals sign (=)
 # and would normally be interpreted as an NAME=VALUE environment variable.