Tests/CXXModules: test forced rsp files with ninja

Fixes: #25367

Source/cmNinjaTargetGenerator.cxx

@@ -1257,8 +1257,6 @@ cmNinjaBuild GetScanBuildStatement(const std::string& ruleName,
 {
   cmNinjaBuild scanBuild(ruleName);
 
-  scanBuild.RspFile = "$out.rsp";
-
   if (compilePP) {
     // Move compilation dependencies to the scan/preprocessing build statement.
     std::swap(scanBuild.ExplicitDeps, objBuild.ExplicitDeps);
@@ -1299,6 +1297,7 @@ cmNinjaBuild GetScanBuildStatement(const std::string& ruleName,
   // Tell dependency scanner where to store dyndep intermediate results.
   std::string ddiFileName = cmStrCat(objectFileName, ".ddi");
   scanBuild.Variables["DYNDEP_INTERMEDIATE_FILE"] = ddiFileName;
+  scanBuild.RspFile = cmStrCat(ddiFileName, ".rsp");
 
   // Outputs of the scan/preprocessor build statement.
   if (compilePP) {

Tests/RunCMake/CXXModules/NinjaForceResponseFile-check.cmake

@@ -0,0 +1,23 @@
+if (RunCMake_GENERATOR_IS_MULTI_CONFIG)
+  set(path "${RunCMake_TEST_BINARY_DIR}/CMakeFiles/impl-Debug.ninja")
+else ()
+  set(path "${RunCMake_TEST_BINARY_DIR}/build.ninja")
+endif ()
+
+if (NOT EXISTS "${path}")
+  list(APPEND RunCMake_TEST_FAILED
+    "Failed to find `ninja` build file: '${path}'")
+endif ()
+
+file(READ "${path}" rspfiles
+  REGEX "^ *RSP_FILE =")
+
+if (rspfiles MATCHES "\\$out\\.rsp$")
+  message(FATAL_ERROR
+    "rspfiles for modules should be specified explicitly")
+elseif (NOT rspfiles MATCHES "ddi\\.rsp")
+  message(FATAL_ERROR
+    "rspfiles for scanning rules should be specified according to scan output filenames")
+endif ()
+
+string(REPLACE ";" "\n  " RunCMake_TEST_FAILED "${RunCMake_TEST_FAILED}")

Tests/RunCMake/CXXModules/NinjaForceResponseFile.cmake

@@ -0,0 +1,27 @@
+# Fake out that we have dyndep; we only need to generate, not actually build
+# here.
+set(CMAKE_CXX_SCANDEP_SOURCE "")
+
+enable_language(CXX)
+
+if (NOT CMAKE_GENERATOR MATCHES "Ninja")
+  message(FATAL_ERROR
+    "This test requires a 'Ninja' generator to be used.")
+endif ()
+
+set(CMAKE_NINJA_FORCE_RESPONSE_FILE 1)
+
+add_library(ninja-forced-response-file)
+target_sources(ninja-forced-response-file
+  PRIVATE
+    FILE_SET modules TYPE CXX_MODULES
+    BASE_DIRS
+      "${CMAKE_CURRENT_SOURCE_DIR}/sources"
+    FILES
+      sources/module.cxx
+      sources/module-part.cxx
+    FILE_SET internal_partitions TYPE CXX_MODULES FILES
+      sources/module-internal-part.cxx)
+target_compile_features(ninja-forced-response-file
+  PRIVATE
+    cxx_std_20)

Tests/RunCMake/CXXModules/RunCMakeTest.cmake

@@ -94,6 +94,7 @@ if (RunCMake_GENERATOR MATCHES "Ninja")
   run_cmake(NinjaDependInfoFileSet)
   run_cmake(NinjaDependInfoExport)
   run_cmake(NinjaDependInfoBMIInstall)
+  run_cmake(NinjaForceResponseFile) # issue#25367
 elseif (RunCMake_GENERATOR MATCHES "Visual Studio")
   run_cmake(VisualStudioNoSyntheticTargets)
 else ()