VS: Allow CMAKE_GENERATOR_INSTANCE to specify portable instance

Previously the `CMAKE_GENERATOR_INSTANCE` value was used only to filter
the instances reported by the Visual Studio Installer tool.  If the
specified install location is not known to the VS Installer, but the
user provided a `version=` field, check for the installation directly
on disk.

Fixes: #21639, #22197

3 files changed, 40 insertions, 1 deletions

diff --git a/Source/cmGlobalVisualStudioVersionedGenerator.cxx b/Source/cmGlobalVisualStudioVersionedGenerator.cxx
index 806871d..f2ce83e 100644
--- a/Source/cmGlobalVisualStudioVersionedGenerator.cxx
+++ b/Source/cmGlobalVisualStudioVersionedGenerator.cxx
@@ -509,7 +509,7 @@ bool cmGlobalVisualStudioVersionedGenerator::SetGeneratorInstance(
           cmSystemTools::FileIsDirectory(this->GeneratorInstance)) {
         e << "\n"
              "The directory exists, but the instance is not known to the "
-             "Visual Studio Installer.";
+             "Visual Studio Installer, and no 'version=' field was given.";
       }
       mf->IssueMessage(MessageType::FATAL_ERROR, e.str());
       return false;
diff --git a/Source/cmVSSetupHelper.cxx b/Source/cmVSSetupHelper.cxx
index 39ddce3..cbd241b 100644
--- a/Source/cmVSSetupHelper.cxx
+++ b/Source/cmVSSetupHelper.cxx
@@ -2,6 +2,8 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmVSSetupHelper.h"
 
+#include <utility>
+
 #include "cmsys/Encoding.hxx"
 #include "cmsys/FStream.hxx"
 
@@ -342,6 +344,8 @@ bool cmVSSetupAPIHelper::EnumerateAndChooseVSInstance()
 
   std::string const wantVersion = std::to_string(this->Version) + '.';
 
+  bool specifiedLocationNotSpecifiedVersion = false;
+
   SmartCOMPtr<ISetupInstance> instance;
   while (SUCCEEDED(enumInstances->Next(1, &instance, NULL)) && instance) {
     SmartCOMPtr<ISetupInstance2> instance2 = NULL;
@@ -373,6 +377,7 @@ bool cmVSSetupAPIHelper::EnumerateAndChooseVSInstance()
             chosenInstanceInfo = instanceInfo;
             return true;
           }
+          specifiedLocationNotSpecifiedVersion = true;
         }
       } else if (!this->SpecifiedVSInstallVersion.empty()) {
         // We are looking for a specific version.
@@ -398,6 +403,13 @@ bool cmVSSetupAPIHelper::EnumerateAndChooseVSInstance()
     }
   }
 
+  if (!this->SpecifiedVSInstallLocation.empty() &&
+      !specifiedLocationNotSpecifiedVersion) {
+    // The VS Installer does not know about the specified location.
+    // Check for one directly on disk.
+    return this->LoadSpecifiedVSInstanceFromDisk();
+  }
+
   if (vecVSInstances.size() > 0) {
     isVSInstanceExists = true;
     int index = ChooseVSInstance(vecVSInstances);
@@ -460,6 +472,32 @@ int cmVSSetupAPIHelper::ChooseVSInstance(
   return chosenIndex;
 }
 
+bool cmVSSetupAPIHelper::LoadSpecifiedVSInstanceFromDisk()
+{
+  if (!cmSystemTools::FileIsDirectory(this->SpecifiedVSInstallLocation)) {
+    return false;
+  }
+  VSInstanceInfo vsInstanceInfo;
+  vsInstanceInfo.VSInstallLocation = this->SpecifiedVSInstallLocation;
+  // FIXME: Is there a better way to get SDK information?
+  vsInstanceInfo.IsWin10SDKInstalled = true;
+  vsInstanceInfo.IsWin81SDKInstalled = false;
+
+  if (!this->SpecifiedVSInstallVersion.empty()) {
+    // Assume the version specified by the user is correct.
+    vsInstanceInfo.Version = this->SpecifiedVSInstallVersion;
+  } else {
+    return false;
+  }
+
+  if (!LoadVSInstanceVCToolsetVersion(vsInstanceInfo)) {
+    return false;
+  }
+
+  chosenInstanceInfo = std::move(vsInstanceInfo);
+  return true;
+}
+
 bool cmVSSetupAPIHelper::Initialize()
 {
   if (initializationFailure)
diff --git a/Source/cmVSSetupHelper.h b/Source/cmVSSetupHelper.h
index d7e82d0..44c883b 100644
--- a/Source/cmVSSetupHelper.h
+++ b/Source/cmVSSetupHelper.h
@@ -117,6 +117,7 @@ private:
                                bool& bWin10SDK, bool& bWin81SDK);
   int ChooseVSInstance(const std::vector<VSInstanceInfo>& vecVSInstances);
   bool EnumerateAndChooseVSInstance();
+  bool LoadSpecifiedVSInstanceFromDisk();
 
   unsigned int Version;