VS: Allow toolset version selection to specify default toolset

Teach the feature added by commit v3.12.0-rc1~38^2 (VS: Add option to
select the version of the toolset used by VS 2017, 2018-05-19) to accept
the default toolset version in addition to older versions.  If the
default toolset version is supplied, simply clear it so the default will
be used.

Fixes: #18107

1 files changed, 21 insertions, 0 deletions

diff --git a/Source/cmGlobalVisualStudio15Generator.cxx b/Source/cmGlobalVisualStudio15Generator.cxx
index 6af5793..9983a43 100644
--- a/Source/cmGlobalVisualStudio15Generator.cxx
+++ b/Source/cmGlobalVisualStudio15Generator.cxx
@@ -158,6 +158,27 @@ bool cmGlobalVisualStudio15Generator::GetVSInstance(std::string& dir) const
   return vsSetupAPIHelper.GetVSInstanceInfo(dir);
 }
 
+bool cmGlobalVisualStudio15Generator::IsDefaultToolset(
+  const std::string& version) const
+{
+  if (version.empty()) {
+    return true;
+  }
+
+  std::string vcToolsetVersion;
+  if (this->vsSetupAPIHelper.GetVCToolsetVersion(vcToolsetVersion)) {
+
+    cmsys::RegularExpression regex("[0-9][0-9]\\.[0-9]+");
+    if (regex.find(version) && regex.find(vcToolsetVersion)) {
+      const auto majorMinorEnd = vcToolsetVersion.find('.', 3);
+      const auto majorMinor = vcToolsetVersion.substr(0, majorMinorEnd);
+      return version == majorMinor;
+    }
+  }
+
+  return false;
+}
+
 std::string cmGlobalVisualStudio15Generator::GetAuxiliaryToolset() const
 {
   const char* version = this->GetPlatformToolsetVersion();