MSVC: Add abstraction for runtime library selection

Replace our hard-coded defaults for `/MD` and `/MDd` with a first-class
abstraction to select the runtime library from an enumeration of logical
names.  We've long hesitated to do this because the idea of "runtime
library selection" touches on related concepts on several platforms.
Avoid that scope creep by simply defining an abstraction that applies
only when targeting the MSVC ABI on Windows.

Removing the old default flags requires a policy because existing
projects may rely on string processing to edit them and choose a runtime
library under the old behavior.  Add policy CMP0091 to provide
compatibility.

Fixes: #19108

2 files changed, 58 insertions, 10 deletions

diff --git a/Modules/Platform/Windows-Intel-Fortran.cmake b/Modules/Platform/Windows-Intel-Fortran.cmake
index 3981a09..f00a8e4 100644
--- a/Modules/Platform/Windows-Intel-Fortran.cmake
+++ b/Modules/Platform/Windows-Intel-Fortran.cmake
@@ -4,8 +4,34 @@ set(_COMPILE_Fortran " /fpp")
 set(CMAKE_Fortran_MODDIR_FLAG "-module:")
 set(CMAKE_Fortran_STANDARD_LIBRARIES_INIT "user32.lib")
 __windows_compiler_intel(Fortran)
-string(APPEND CMAKE_Fortran_FLAGS_INIT " /W1 /nologo /fpp /libs:dll /threads")
-string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " /Od /debug:full /dbglibs")
+if(CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT)
+  set(_LIBSDLL "")
+  set(_DBGLIBS "")
+  set(_THREADS "")
+else()
+  set(_LIBSDLL " /libs:dll")
+  set(_DBGLIBS " /dbglibs")
+  set(_THREADS " /threads")
+endif()
+string(APPEND CMAKE_Fortran_FLAGS_INIT " /W1 /nologo /fpp${_LIBSDLL}${_THREADS}")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " /Od /debug:full${_DBGLIBS}")
 string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " /O1 /DNDEBUG")
 string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " /O2 /DNDEBUG")
 string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " /O2 /debug:full /DNDEBUG")
+unset(_LIBSDLL)
+unset(_DBGLIBS)
+unset(_THREADS)
+
+set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreaded         -threads -libs:static)
+set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreadedDLL      -threads -libs:dll)
+set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreadedDebug    -threads -libs:static -dbglibs)
+set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreadedDebugDLL -threads -libs:dll    -dbglibs)
+
+# Intel Fortran for Windows supports single-threaded RTL but it is
+# not implemented by the Visual Studio integration.
+if(NOT CMAKE_GENERATOR MATCHES "Visual Studio")
+  set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_SingleThreaded                 -libs:static)
+  set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_SingleThreadedDLL              -libs:dll)
+  set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_SingleThreadedDebug            -libs:static -dbglibs)
+  set(CMAKE_Fortran_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_SingleThreadedDebugDLL         -libs:dll    -dbglibs)
+endif()
diff --git a/Modules/Platform/Windows-MSVC.cmake b/Modules/Platform/Windows-MSVC.cmake
index df3bd1e..4279a74 100644
--- a/Modules/Platform/Windows-MSVC.cmake
+++ b/Modules/Platform/Windows-MSVC.cmake
@@ -298,6 +298,14 @@ endforeach()
 string(APPEND CMAKE_STATIC_LINKER_FLAGS_INIT " ${_MACHINE_ARCH_FLAG}")
 unset(_MACHINE_ARCH_FLAG)
 
+cmake_policy(GET CMP0091 __WINDOWS_MSVC_CMP0091)
+if(__WINDOWS_MSVC_CMP0091 STREQUAL "NEW")
+  set(CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT "MultiThreaded$<$<CONFIG:Debug>:Debug>DLL")
+else()
+  set(CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT "")
+endif()
+unset(__WINDOWS_MSVC_CMP0091)
+
 macro(__windows_compiler_msvc lang)
   if(NOT MSVC_VERSION LESS 1400)
     # for 2005 make sure the manifest is put in the dll with mt
@@ -351,21 +359,35 @@ macro(__windows_compiler_msvc lang)
 
   if("x${lang}" STREQUAL "xC" OR
       "x${lang}" STREQUAL "xCXX")
+    if(CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT)
+      set(_MDd "")
+      set(_MD "")
+    else()
+      set(_MDd " /MDd")
+      set(_MD " /MD")
+    endif()
     if(CMAKE_VS_PLATFORM_TOOLSET MATCHES "v[0-9]+_clang_.*")
       # note: MSVC 14 2015 Update 1 sets -fno-ms-compatibility by default, but this does not allow one to compile many projects
       # that include MS's own headers. CMake itself is affected project too.
       string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} -fms-extensions -fms-compatibility -D_WINDOWS -Wall${_FLAGS_${lang}}")
-      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " /MDd -gline-tables-only -fno-inline -O0 ${_RTC1}")
-      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " /MD -O2 -DNDEBUG")
-      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " /MD -gline-tables-only -O2 -fno-inline -DNDEBUG")
-      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " /MD -DNDEBUG") # TODO: Add '-Os' once VS generator maps it properly for Clang
+      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT "${_MDd} -gline-tables-only -fno-inline -O0 ${_RTC1}")
+      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT "${_MD} -O2 -DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "${_MD} -gline-tables-only -O2 -fno-inline -DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "${_MD} -DNDEBUG") # TODO: Add '-Os' once VS generator maps it properly for Clang
     else()
       string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} /D_WINDOWS /W3${_FLAGS_${lang}}")
-      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " /MDd /Zi /Ob0 /Od ${_RTC1}")
-      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " /MD /O2 /Ob2 /DNDEBUG")
-      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " /MD /Zi /O2 /Ob1 /DNDEBUG")
-      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " /MD /O1 /Ob1 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT "${_MDd} /Zi /Ob0 /Od ${_RTC1}")
+      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT "${_MD} /O2 /Ob2 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "${_MD} /Zi /O2 /Ob1 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "${_MD} /O1 /Ob1 /DNDEBUG")
     endif()
+    unset(_MDd)
+    unset(_MD)
+
+    set(CMAKE_${lang}_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreaded         -MT)
+    set(CMAKE_${lang}_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreadedDLL      -MD)
+    set(CMAKE_${lang}_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreadedDebug    -MTd)
+    set(CMAKE_${lang}_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY_MultiThreadedDebugDLL -MDd)
   endif()
   set(CMAKE_${lang}_LINKER_SUPPORTS_PDB ON)
   set(CMAKE_NINJA_DEPTYPE_${lang} msvc)