VS: Consolidate Windows SDK major version selection dispatch

Make logic choosing between Windows 10 SDKs and the Windows 8.1 SDK
easier to follow by consolidating it in the VS 14 generator.  The only
information we need from VS 15+ generators is whether the 8.1 SDK is
installed.

1 files changed, 20 insertions, 1 deletions

diff --git a/Source/cmGlobalVisualStudio14Generator.cxx b/Source/cmGlobalVisualStudio14Generator.cxx
index 20aa0b0..e74c211 100644
--- a/Source/cmGlobalVisualStudio14Generator.cxx
+++ b/Source/cmGlobalVisualStudio14Generator.cxx
@@ -140,9 +140,23 @@ bool cmGlobalVisualStudio14Generator::MatchesGeneratorName(
 
 bool cmGlobalVisualStudio14Generator::InitializePlatformWindows(cmMakefile* mf)
 {
-  if (cmHasLiteralPrefix(this->SystemVersion, "10.0")) {
+  // If we are targeting Windows 10+, we select a Windows 10 SDK.
+  // If no Windows 8.1 SDK is installed, which is possible with VS 2017 and
+  // higher, then we must choose a Windows 10 SDK anyway.
+  if (cmHasLiteralPrefix(this->SystemVersion, "10.0") ||
+      !this->IsWin81SDKInstalled()) {
     return this->SelectWindows10SDK(mf);
   }
+
+  // We are not targeting Windows 10+, so fall back to the Windows 8.1 SDK.
+  // For VS 2019 and above we must explicitly specify it.
+  if (this->Version >= cmGlobalVisualStudioGenerator::VSVersion::VS16 &&
+      !cmSystemTools::VersionCompareGreater(this->SystemVersion, "8.1")) {
+    this->SetWindowsTargetPlatformVersion("8.1", mf);
+    return this->VerifyNoGeneratorPlatformVersion(
+      mf, "with the Windows 8.1 SDK installed");
+  }
+
   return this->VerifyNoGeneratorPlatformVersion(mf);
 }
 
@@ -296,6 +310,11 @@ bool cmGlobalVisualStudio14Generator::IsWindowsStoreToolsetInstalled() const
                                           cmSystemTools::KeyWOW64_32);
 }
 
+bool cmGlobalVisualStudio14Generator::IsWin81SDKInstalled() const
+{
+  return true;
+}
+
 std::string cmGlobalVisualStudio14Generator::GetWindows10SDKMaxVersion(
   cmMakefile* mf) const
 {