Add support for the debug runtime in MSVC builds.

We can force the linker to choose the debug runtime, which is necessary
to override rusts libc, which by default wants to link to the release
runtime, even in debug mode.

With this patch CMake will override this behavior and use the debug
runtime if appropriate.
This is very important, as all parts of the program must agree on the runtime!
As Qt in Debug mode uses the debug runtime in their DLLs, we may
encounter undefined behavior otherwise.

Author: LeonMatthesKDAB

cmake/CxxQt.cmake

@@ -45,24 +45,6 @@ function(cxx_qt_import_crate)
     message(VERBOSE "CXX_QT_QT_MODULES: ${IMPORT_CRATE_QT_MODULES}")
   endif()
 
-  if ((NOT CXX_QT_SUPPRESS_MSVC_RUNTIME_WARNING)
-      AND (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
-      AND (CMAKE_BUILD_TYPE STREQUAL "Debug")
-      AND (NOT (CMAKE_MSVC_RUNTIME_LIBRARY STREQUAL "MultiThreadedDLL")))
-    message(WARNING
-      " CXX-Qt Warning: CMAKE_MSVC_RUNTIME_LIBRARY not set in MSVC Debug build!\n \n"
-      " To fix this, set CMAKE_MSVC_RUNTIME_LIBRARY=\"MultiThreadedDLL\" when configuring.\n \n"
-      " When building with MSVC in Debug, the CMAKE_MSVC_RUNTIME_LIBRARY variable should be set to \"MultiThreadedDLL\"\n"
-      " This needs to be done before configuring any target that links to a Rust target.\n"
-      " Otherwise, you may encounter linker errors when linking to Rust targets, like:\n \n"
-      " error LNK2038: mismatch detected for '_ITERATOR_DEBUG_LEVEL': value '0' doesn't match value '2' in ...\n \n"
-      " See also:\n"
-      " https://github.com/corrosion-rs/corrosion/blob/master/doc/src/common_issues.md#linking-debug-cc-libraries-into-rust-fails-on-windows-msvc-targets\n"
-      " and: https://github.com/KDAB/cxx-qt/pull/683\n \n"
-      " To suppress this warning set CXX_QT_SUPPRESS_MSVC_RUNTIME_WARNING to ON"
-      )
-  endif()
-
   foreach(CRATE ${__cxx_qt_imported_crates})
     # Join modules by a comma so that we can pass easily via an env variable
     #
@@ -128,8 +110,34 @@ function(cxx_qt_import_crate)
     # This can cause CMake to emit the wrong link order, with Qt before the static library, which then fails to build with ld.bfd
     # https://stackoverflow.com/questions/51333069/how-do-the-library-selection-rules-differ-between-gold-and-the-standard-bfd-li
     target_link_libraries(${CRATE}-static INTERFACE ${IMPORT_CRATE_QT_MODULES})
+
+    if ((CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+      AND (CMAKE_BUILD_TYPE STREQUAL "Debug")
+      AND (NOT (CMAKE_MSVC_RUNTIME_LIBRARY STREQUAL "MultiThreadedDLL")))
+      # MSVC(Debug): Tell the linker not to link to the MultiThreadedDLL runtime and use the Debug version instead
+      # This is a new workaround for this issue:
+      # https://corrosion-rs.github.io/corrosion/common_issues.html#linking-debug-cc-libraries-into-rust-fails-on-windows-msvc-targets
+      # As outlined in this comment:
+      # https://github.com/rust-lang/rust/issues/39016#issuecomment-2521395154
+      target_link_options(${CRATE}-static INTERFACE  /NODEFAULTLIB:msvcrt /DEFAULTLIB:msvcrtd)
+    endif()
   endforeach()
 
+  if((NOT CXX_QT_SUPPRESS_MSVC_RUNTIME_WARNING)
+    AND (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+    AND (CMAKE_BUILD_TYPE STREQUAL "Debug")
+    AND (CMAKE_MSVC_RUNTIME_LIBRARY STREQUAL "MultiThreadedDLL"))
+    message(WARNING
+      " CXX-Qt Warning: CMAKE_MSVC_RUNTIME_LIBRARY should no longer be set in MSVC Debug build!\n \n"
+      " In previous versions of CXX-Qt it was necessary to set CMAKE_MSVC_RUNTIME_LIBRARY=\"MultiThreadedDLL\".\n"
+      " Starting with CXX-Qt 0.7.2, this has been fixed and is no longer necessary or recommended.\n \n"
+
+      " See also:\n"
+      " https://github.com/KDAB/cxx-qt/issues/1234\n \n"
+      " To suppress this warning set CXX_QT_SUPPRESS_MSVC_RUNTIME_WARNING to ON"
+      )
+  endif()
+
 endfunction()