Windows: Prevent auto exports to be regenerated on every build

Check modified time stamps of input files against an existing exports file
before generating the auto exports.

Fixes: #19650

2 files changed, 34 insertions, 3 deletions

diff --git a/Tests/RunCMake/AutoExportDll/RunCMakeTest.cmake b/Tests/RunCMake/AutoExportDll/RunCMakeTest.cmake
index 27a609d..6c9be4b 100644
--- a/Tests/RunCMake/AutoExportDll/RunCMakeTest.cmake
+++ b/Tests/RunCMake/AutoExportDll/RunCMakeTest.cmake
@@ -7,9 +7,13 @@ file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
 run_cmake(AutoExport)
 unset(RunCMake_TEST_OPTIONS)
 # don't run this test on Watcom or Borland make as it is not supported
-if("${RunCMake_GENERATOR}" MATCHES "Watcom WMake|Borland Makefiles")
+if(RunCMake_GENERATOR MATCHES "Watcom WMake|Borland Makefiles")
   return()
 endif()
+if(RunCMake_GENERATOR MATCHES "Ninja|Visual Studio" AND
+   CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+  set(EXPORTS TRUE)
+endif()
 # we build debug so the say.exe will be found in Debug/say.exe for
 # Visual Studio generators
 if(RunCMake_GENERATOR_IS_MULTI_CONFIG)
@@ -18,9 +22,36 @@ endif()
 # build AutoExport
 run_cmake_command(AutoExportBuild ${CMAKE_COMMAND} --build
   ${RunCMake_TEST_BINARY_DIR} --config Debug --clean-first)
+# save the current timestamp of exports.def
+if(EXPORTS)
+  set(EXPORTS_DEF "${RunCMake_TEST_BINARY_DIR}/say.dir/${INTDIR}exports.def")
+  if(NOT EXISTS "${EXPORTS_DEF}")
+    set(EXPORTS_DEF
+      "${RunCMake_TEST_BINARY_DIR}/CMakeFiles/say.dir/${INTDIR}exports.def")
+  endif()
+  file(TIMESTAMP "${EXPORTS_DEF}" timestamp)
+  if(NOT timestamp)
+    message(SEND_ERROR "Could not get timestamp for \"${EXPORTS_DEF}\"")
+  endif()
+endif()
 # run the executable that uses symbols from the dll
 if(WIN32)
   set(EXE_EXT ".exe")
 endif()
 run_cmake_command(AutoExportRun
-  ${RunCMake_BINARY_DIR}/AutoExport-build/bin/${INTDIR}say${EXE_EXT})
+  ${RunCMake_TEST_BINARY_DIR}/bin/${INTDIR}say${EXE_EXT})
+# build AutoExport again without modification
+run_cmake_command(AutoExportBuildAgain ${CMAKE_COMMAND} --build
+  ${RunCMake_TEST_BINARY_DIR} --config Debug)
+# compare timestamps of exports.def to make sure it has not been updated
+if(EXPORTS)
+  file(TIMESTAMP "${EXPORTS_DEF}" timestamp_after)
+  if(NOT timestamp_after)
+    message(SEND_ERROR "Could not get timestamp for \"${EXPORTS_DEF}\"")
+  endif()
+  if (timestamp_after STREQUAL timestamp)
+    message(STATUS "AutoExportTimeStamp - PASSED")
+  else()
+    message(SEND_ERROR "\"${EXPORTS_DEF}\" has been updated.")
+  endif()
+endif()
diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 8fd5234..c663484 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -543,7 +543,7 @@ set(cpack_tests
 add_RunCMake_test_group(CPack "${cpack_tests}")
 # add a test to make sure symbols are exported from a shared library
 # for MSVC compilers CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS property is used
-add_RunCMake_test(AutoExportDll)
+add_RunCMake_test(AutoExportDll -DCMAKE_CXX_COMPILER_ID=${CMAKE_CXX_COMPILER_ID})
 
 add_RunCMake_test(AndroidMK)