VS: Teach VS 2019 generator to select host tools matching host arch

This generator is new so we can introduce the long-desired behavior
of selecting ``host=x64`` tools by default on x64 hosts.

Help/generator/Visual Studio 16 2019.rst

@@ -47,6 +47,7 @@ default.  The :variable:`CMAKE_GENERATOR_TOOLSET` option may be set, perhaps
 via the :manual:`cmake(1)` ``-T`` option, to specify another toolset.
 
 .. |VS_TOOLSET_HOST_ARCH_DEFAULT| replace::
-   By default this generator uses the 32-bit variant even on a 64-bit host.
+   By default this generator uses the 64-bit variant on x64 hosts and
+   the 32-bit variant otherwise.
 
 .. include:: VS_TOOLSET_HOST_ARCH.txt

Help/release/dev/vs2019.rst

@@ -10,4 +10,5 @@ vs2019
   in the generator name.  Instead :variable:`CMAKE_GENERATOR_PLATFORM`
   must be used, e.g. through the ``-A`` command-line option.  Furthermore,
   the default target platform (architecture) is now based on the *host*
-  platform.
+  platform.  The VS host toolset selection is now based on the host
+  architecture as well.

Source/cmGlobalVisualStudio10Generator.cxx

@@ -606,11 +606,27 @@ cmGlobalVisualStudio10Generator::GetPlatformToolsetVersionString() const
 
 const char*
 cmGlobalVisualStudio10Generator::GetPlatformToolsetHostArchitecture() const
+{
+  std::string const& hostArch =
+    this->GetPlatformToolsetHostArchitectureString();
+  if (hostArch.empty()) {
+    return nullptr;
+  }
+  return hostArch.c_str();
+}
+
+std::string const&
+cmGlobalVisualStudio10Generator::GetPlatformToolsetHostArchitectureString()
+  const
 {
   if (!this->GeneratorToolsetHostArchitecture.empty()) {
-    return this->GeneratorToolsetHostArchitecture.c_str();
+    return this->GeneratorToolsetHostArchitecture;
   }
-  return nullptr;
+  if (!this->DefaultPlatformToolsetHostArchitecture.empty()) {
+    return this->DefaultPlatformToolsetHostArchitecture;
+  }
+  static std::string const empty;
+  return empty;
 }
 
 const char* cmGlobalVisualStudio10Generator::GetPlatformToolsetCuda() const

Source/cmGlobalVisualStudio10Generator.h

@@ -58,6 +58,7 @@ public:
 
   /** The toolset host architecture name (e.g. x64 for 64-bit host tools).  */
   const char* GetPlatformToolsetHostArchitecture() const;
+  std::string const& GetPlatformToolsetHostArchitectureString() const;
 
   /** The cuda toolset version.  */
   const char* GetPlatformToolsetCuda() const;
@@ -152,6 +153,7 @@ protected:
   std::string GeneratorToolsetHostArchitecture;
   std::string GeneratorToolsetCuda;
   std::string DefaultPlatformToolset;
+  std::string DefaultPlatformToolsetHostArchitecture;
   std::string WindowsTargetPlatformVersion;
   std::string SystemName;
   std::string SystemVersion;

Source/cmGlobalVisualStudioVersionedGenerator.cxx

@@ -11,10 +11,13 @@
 
 #if defined(_M_ARM64)
 #  define HOST_PLATFORM_NAME "ARM64"
+#  define HOST_TOOLS_ARCH ""
 #elif defined(_M_ARM)
 #  define HOST_PLATFORM_NAME "ARM"
+#  define HOST_TOOLS_ARCH ""
 #elif defined(_M_IA64)
 #  define HOST_PLATFORM_NAME "Itanium"
+#  define HOST_TOOLS_ARCH ""
 #else
 #  include "cmsys/SystemInformation.hxx"
 #endif
@@ -33,6 +36,20 @@ static std::string VSHostPlatformName()
 #endif
 }
 
+static std::string VSHostArchitecture()
+{
+#ifdef HOST_TOOLS_ARCH
+  return HOST_TOOLS_ARCH;
+#else
+  cmsys::SystemInformation info;
+  if (info.Is64Bits()) {
+    return "x64";
+  } else {
+    return "x86";
+  }
+#endif
+}
+
 static unsigned int VSVersionToMajor(
   cmGlobalVisualStudioGenerator::VSVersion v)
 {
@@ -262,6 +279,7 @@ cmGlobalVisualStudioVersionedGenerator::cmGlobalVisualStudioVersionedGenerator(
   this->DefaultLinkFlagTableName = VSVersionToToolset(this->Version);
   if (this->Version >= cmGlobalVisualStudioGenerator::VS16) {
     this->DefaultPlatformName = VSHostPlatformName();
+    this->DefaultPlatformToolsetHostArchitecture = VSHostArchitecture();
   }
 }
 

Tests/RunCMake/GeneratorToolset/TestToolsetHostArchNone-stdout.txt

@@ -1,2 +1,2 @@
 -- CMAKE_VS_PLATFORM_TOOLSET='Test Toolset'
--- CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE=''
+-- CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE='.*'

Tests/RunCMake/GeneratorToolset/TestToolsetHostArchNone.cmake

@@ -1,2 +1,15 @@
 message(STATUS "CMAKE_VS_PLATFORM_TOOLSET='${CMAKE_VS_PLATFORM_TOOLSET}'")
 message(STATUS "CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE='${CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE}'")
+
+if(CMAKE_GENERATOR MATCHES "Visual Studio 1[6]")
+  cmake_host_system_information(RESULT is_64_bit QUERY IS_64BIT)
+  if(is_64_bit)
+    if(NOT "${CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE}" STREQUAL "x64")
+      message(FATAL_ERROR "CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE is not 'x64' as expected.")
+    endif()
+  endif()
+else()
+  if(NOT "${CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE}" STREQUAL "")
+    message(FATAL_ERROR "CMAKE_VS_PLATFORM_TOOLSET_HOST_ARCHITECTURE is not empty as expected.")
+  endif()
+endif()