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

15 files changed, 108 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 68411d6..a8dcb4b 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -195,6 +195,9 @@ add_RunCMake_test(LinkStatic)
 if(CMAKE_CXX_COMPILER_ID MATCHES "^(Cray|PGI|XL|XLClang)$")
   add_RunCMake_test(MetaCompileFeatures)
 endif()
+if(MSVC)
+  add_RunCMake_test(MSVCRuntimeLibrary)
+endif()
 add_RunCMake_test(ObjectLibrary)
 add_RunCMake_test(ParseImplicitIncludeInfo)
 if(UNIX AND CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG AND CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW-result.txt b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW-stderr.txt b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW-stderr.txt
new file mode 100644
index 0000000..803058d
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW-stderr.txt
@@ -0,0 +1,2 @@
+^CMake Error in CMakeLists.txt:
+  MSVC_RUNTIME_LIBRARY value 'BogusValue' not known for this C compiler.$
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW.cmake b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW.cmake
new file mode 100644
index 0000000..c3ea2fd
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-NEW.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0091 NEW)
+include(CMP0091-common.cmake)
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-OLD.cmake b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-OLD.cmake
new file mode 100644
index 0000000..734cc9f
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-OLD.cmake
@@ -0,0 +1,2 @@
+cmake_policy(SET CMP0091 OLD)
+include(CMP0091-common.cmake)
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-WARN.cmake b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-WARN.cmake
new file mode 100644
index 0000000..26f86a0
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-WARN.cmake
@@ -0,0 +1,2 @@
+
+include(CMP0091-common.cmake)
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-common.cmake b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-common.cmake
new file mode 100644
index 0000000..7827d2a
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMP0091-common.cmake
@@ -0,0 +1,37 @@
+enable_language(C)
+
+cmake_policy(GET CMP0091 cmp0091)
+if(cmp0091 STREQUAL "NEW")
+  if(NOT CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT)
+    message(SEND_ERROR "CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT not set under NEW behavior")
+  endif()
+else()
+  if(CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT)
+    message(SEND_ERROR "CMAKE_MSVC_RUNTIME_LIBRARY_DEFAULT is set under OLD behavior")
+  endif()
+endif()
+
+if(CMAKE_C_COMPILER_ID STREQUAL "MSVC")
+  if(CMAKE_C_FLAGS_DEBUG MATCHES "[/-]MDd( |$)")
+    set(have_MDd 1)
+  else()
+    set(have_MDd 0)
+  endif()
+  if(CMAKE_C_FLAGS_RELEASE MATCHES "[/-]MD( |$)")
+    set(have_MD 1)
+  else()
+    set(have_MD 0)
+  endif()
+  if(cmp0091 STREQUAL "NEW")
+    if(have_MDd OR have_MD)
+      message(SEND_ERROR "Have a -MD* flag under NEW behavior.")
+    endif()
+  else()
+    if(NOT (have_MDd AND have_MD))
+      message(SEND_ERROR "Do not have -MD* flags under OLD behavior.")
+    endif()
+  endif()
+endif()
+
+set(CMAKE_MSVC_RUNTIME_LIBRARY BogusValue)
+add_library(foo empty.c)
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/CMakeLists.txt b/Tests/RunCMake/MSVCRuntimeLibrary/CMakeLists.txt
new file mode 100644
index 0000000..3e470a2
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/CMakeLists.txt
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.14)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/RunCMakeTest.cmake b/Tests/RunCMake/MSVCRuntimeLibrary/RunCMakeTest.cmake
new file mode 100644
index 0000000..fad18da
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/RunCMakeTest.cmake
@@ -0,0 +1,5 @@
+include(RunCMake)
+
+run_cmake(CMP0091-WARN)
+run_cmake(CMP0091-OLD)
+run_cmake(CMP0091-NEW)
diff --git a/Tests/RunCMake/MSVCRuntimeLibrary/empty.c b/Tests/RunCMake/MSVCRuntimeLibrary/empty.c
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/Tests/RunCMake/MSVCRuntimeLibrary/empty.c
diff --git a/Tests/RunCMake/VS10Project/RunCMakeTest.cmake b/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
index df253a9..988312b 100644
--- a/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
+++ b/Tests/RunCMake/VS10Project/RunCMakeTest.cmake
@@ -2,6 +2,7 @@ include(RunCMake)
 
 run_cmake(VsCSharpCompilerOpts)
 run_cmake(ExplicitCMakeLists)
+run_cmake(RuntimeLibrary)
 run_cmake(SourceGroupCMakeLists)
 
 run_cmake(VsConfigurationType)
diff --git a/Tests/RunCMake/VS10Project/RuntimeLibrary-check.cmake b/Tests/RunCMake/VS10Project/RuntimeLibrary-check.cmake
new file mode 100644
index 0000000..6b43d47
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/RuntimeLibrary-check.cmake
@@ -0,0 +1,34 @@
+macro(RuntimeLibrary_check tgt rtl_expect)
+  set(vcProjectFile "${RunCMake_TEST_BINARY_DIR}/${tgt}.vcxproj")
+  if(NOT EXISTS "${vcProjectFile}")
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not exist.")
+    return()
+  endif()
+
+  set(HAVE_Runtimelibrary 0)
+
+  file(STRINGS "${vcProjectFile}" lines)
+  foreach(line IN LISTS lines)
+    if(line MATCHES "^ *<RuntimeLibrary>([^<>]+)</RuntimeLibrary>")
+      set(rtl_actual "${CMAKE_MATCH_1}")
+      if(NOT "${rtl_actual}" STREQUAL "${rtl_expect}")
+        set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj has RuntimeLibrary '${rtl_actual}', not '${rtl_expect}'.")
+        return()
+      endif()
+      set(HAVE_Runtimelibrary 1)
+      break()
+    endif()
+  endforeach()
+
+  if(NOT HAVE_Runtimelibrary)
+    set(RunCMake_TEST_FAILED "Project file ${tgt}.vcxproj does not have a RuntimeLibrary field.")
+    return()
+  endif()
+endmacro()
+
+RuntimeLibrary_check(default-C MultiThreadedDebugDLL)
+RuntimeLibrary_check(default-CXX MultiThreadedDebugDLL)
+RuntimeLibrary_check(MTd-C MultiThreadedDebug)
+RuntimeLibrary_check(MTd-CXX MultiThreadedDebug)
+RuntimeLibrary_check(MT-C MultiThreaded)
+RuntimeLibrary_check(MT-CXX MultiThreaded)
diff --git a/Tests/RunCMake/VS10Project/RuntimeLibrary.cmake b/Tests/RunCMake/VS10Project/RuntimeLibrary.cmake
new file mode 100644
index 0000000..6c77a25
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/RuntimeLibrary.cmake
@@ -0,0 +1,16 @@
+set(CMAKE_CONFIGURATION_TYPES Debug)
+cmake_policy(SET CMP0091 NEW)
+enable_language(C)
+enable_language(CXX)
+
+add_library(default-C empty.c)
+add_library(default-CXX empty.cxx)
+
+set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreadedDebug")
+add_library(MTd-C empty.c)
+add_library(MTd-CXX empty.cxx)
+
+add_library(MT-C empty.c)
+set_property(TARGET MT-C PROPERTY MSVC_RUNTIME_LIBRARY "MultiThreaded")
+add_library(MT-CXX empty.cxx)
+set_property(TARGET MT-CXX PROPERTY MSVC_RUNTIME_LIBRARY "MultiThreaded")
diff --git a/Tests/RunCMake/VS10Project/empty.c b/Tests/RunCMake/VS10Project/empty.c
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/empty.c
diff --git a/Tests/RunCMake/VS10Project/empty.cxx b/Tests/RunCMake/VS10Project/empty.cxx
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/Tests/RunCMake/VS10Project/empty.cxx