ctest_configure: Propagate CTEST_USE_LAUNCHERS from caller to project

If `CTEST_USE_LAUNCHERS` is `TRUE` in a CTest script then the
`ctest_configure` command will add `-DCTEST_USE_LAUNCHERS:BOOL=TRUE` to
the cmake command used to configure the project.  This allows a project
to only set `CTEST_USE_LAUNCHERS` in a ctest script and have launchers
work.

Modules/CTestUseLaunchers.cmake

@@ -24,7 +24,9 @@
 # include(CTestUseLaunchers), it will use the value of the ENV variable
 # to initialize a CTEST_USE_LAUNCHERS cache variable.  This cache
 # variable initialization only occurs if CTEST_USE_LAUNCHERS is not
-# already defined.
+# already defined. If CTEST_USE_LAUNCHERS is on in a ctest -S script
+# the ctest_configure command will add -DCTEST_USE_LAUNCHERS:BOOL=TRUE
+# to the cmake command used to configure the project.
 
 if(NOT DEFINED CTEST_USE_LAUNCHERS AND DEFINED ENV{CTEST_USE_LAUNCHERS_DEFAULT})
   set(CTEST_USE_LAUNCHERS "$ENV{CTEST_USE_LAUNCHERS_DEFAULT}"

Source/CTest/cmCTestConfigureCommand.cxx

@@ -102,6 +102,10 @@ cmCTestGenericHandler* cmCTestConfigureCommand::InitializeHandler()
         cmakeConfigureCommand += "\"";
       }
 
+      if (this->Makefile->IsOn("CTEST_USE_LAUNCHERS")) {
+        cmakeConfigureCommand += " \"-DCTEST_USE_LAUNCHERS:BOOL=TRUE\"";
+      }
+
       cmakeConfigureCommand += " \"-G";
       cmakeConfigureCommand += cmakeGeneratorName;
       cmakeConfigureCommand += "\"";

Tests/RunCMake/ctest_build/CMakeLists.txt.in

@@ -1,4 +1,5 @@
 cmake_minimum_required(VERSION 3.1)
+@CASE_CMAKELISTS_PREFIX_CODE@
 project(CTestBuild@CASE_NAME@ NONE)
 include(CTest)
 add_test(NAME RunCMakeVersion COMMAND "${CMAKE_COMMAND}" --version)

Tests/RunCMake/ctest_build/RunCMakeTest.cmake

@@ -12,6 +12,11 @@ run_ctest_build(BuildQuiet QUIET)
 function(run_BuildFailure)
   set(CASE_CMAKELISTS_SUFFIX_CODE [[
 add_custom_target(BuildFailure ALL COMMAND command-does-not-exist)
+]])
+  set(CASE_CMAKELISTS_PREFIX_CODE [[
+if(NOT CTEST_USE_LAUNCHERS)
+  message(FATAL_ERROR "CTEST_USE_LAUNCHERS not set")
+endif()
 ]])
   set(CASE_TEST_PREFIX_CODE [[
 cmake_policy(SET CMP0061 NEW)

Tests/RunCMake/ctest_build/test.cmake.in

@@ -9,6 +9,7 @@ set(CTEST_CMAKE_GENERATOR               "@RunCMake_GENERATOR@")
 set(CTEST_CMAKE_GENERATOR_PLATFORM      "@RunCMake_GENERATOR_PLATFORM@")
 set(CTEST_CMAKE_GENERATOR_TOOLSET       "@RunCMake_GENERATOR_TOOLSET@")
 set(CTEST_BUILD_CONFIGURATION           "$ENV{CMAKE_CONFIG_TYPE}")
+set(CTEST_USE_LAUNCHERS                 TRUE)
 
 set(ctest_build_args "@CASE_CTEST_BUILD_ARGS@")
 ctest_start(Experimental)