VS: Detect compiler component in VS 2017 instances more reliably

The `Microsoft.VisualStudio.Component.VC.Tools.x86.x64` component is
not the only way a VS instance may provide the `cl` compiler tool.
For example, VS 2017 Express Edition does not install that component.
Instead search for the tools directly on disk within an instance.

Suggested-by: Rich Chiodo <rchiodo@microsoft.com>
Fixes: #17349

Source/cmVSSetupHelper.cxx

@@ -4,6 +4,7 @@
 
 #include "cmSystemTools.h"
 #include "cmsys/Encoding.hxx"
+#include "cmsys/FStream.hxx"
 
 #ifndef VSSetupConstants
 #define VSSetupConstants
@@ -43,8 +44,6 @@ const CLSID CLSID_SetupConfiguration = {
 /* clang-format on */
 #endif
 
-const WCHAR* VCToolsetComponent =
-  L"Microsoft.VisualStudio.Component.VC.Tools.x86.x64";
 const WCHAR* Win10SDKComponent =
   L"Microsoft.VisualStudio.Component.Windows10SDK";
 const WCHAR* Win81SDKComponent =
@@ -99,11 +98,11 @@ bool cmVSSetupAPIHelper::IsWin81SDKInstalled()
 }
 
 bool cmVSSetupAPIHelper::CheckInstalledComponent(
-  SmartCOMPtr<ISetupPackageReference> package, bool& bVCToolset,
-  bool& bWin10SDK, bool& bWin81SDK)
+  SmartCOMPtr<ISetupPackageReference> package, bool& bWin10SDK,
+  bool& bWin81SDK)
 {
   bool ret = false;
-  bVCToolset = bWin10SDK = bWin81SDK = false;
+  bWin10SDK = bWin81SDK = false;
   SmartBSTR bstrId;
   if (FAILED(package->GetId(&bstrId))) {
     return ret;
@@ -116,11 +115,6 @@ bool cmVSSetupAPIHelper::CheckInstalledComponent(
 
   std::wstring id = std::wstring(bstrId);
   std::wstring type = std::wstring(bstrType);
-  if (id.compare(VCToolsetComponent) == 0 &&
-      type.compare(ComponentType) == 0) {
-    bVCToolset = true;
-    ret = true;
-  }
 
   // Checks for any version of Win10 SDK. The version is appended at the end of
   // the
@@ -144,7 +138,6 @@ bool cmVSSetupAPIHelper::CheckInstalledComponent(
 bool cmVSSetupAPIHelper::GetVSInstanceInfo(
   SmartCOMPtr<ISetupInstance2> pInstance, VSInstanceInfo& vsInstanceInfo)
 {
-  bool isVCToolSetInstalled = false;
   if (pInstance == NULL)
     return false;
 
@@ -183,6 +176,23 @@ bool cmVSSetupAPIHelper::GetVSInstanceInfo(
     }
   }
 
+  // Check if a compiler is installed with this instance.
+  {
+    std::string const vcRoot = vsInstanceInfo.GetInstallLocation();
+    std::string const vcToolsVersionFile =
+      vcRoot + "/VC/Auxiliary/Build/Microsoft.VCToolsVersion.default.txt";
+    std::string vcToolsVersion;
+    cmsys::ifstream fin(vcToolsVersionFile.c_str());
+    if (!fin || !cmSystemTools::GetLineFromStream(fin, vcToolsVersion)) {
+      return false;
+    }
+    vcToolsVersion = cmSystemTools::TrimWhitespace(vcToolsVersion);
+    std::string const vcToolsDir = vcRoot + "/VC/Tools/MSVC/" + vcToolsVersion;
+    if (!cmSystemTools::FileIsDirectory(vcToolsDir)) {
+      return false;
+    }
+  }
+
   // Reboot may have been required before the product package was registered
   // (last).
   if ((eRegistered & state) == eRegistered) {
@@ -208,12 +218,11 @@ bool cmVSSetupAPIHelper::GetVSInstanceInfo(
           package == NULL)
         continue;
 
-      bool vcToolsetInstalled = false, win10SDKInstalled = false,
-           win81SDkInstalled = false;
-      bool ret = CheckInstalledComponent(package, vcToolsetInstalled,
-                                         win10SDKInstalled, win81SDkInstalled);
+      bool win10SDKInstalled = false;
+      bool win81SDkInstalled = false;
+      bool ret =
+        CheckInstalledComponent(package, win10SDKInstalled, win81SDkInstalled);
       if (ret) {
-        isVCToolSetInstalled |= vcToolsetInstalled;
         vsInstanceInfo.IsWin10SDKInstalled |= win10SDKInstalled;
         vsInstanceInfo.IsWin81SDKInstalled |= win81SDkInstalled;
       }
@@ -222,7 +231,7 @@ bool cmVSSetupAPIHelper::GetVSInstanceInfo(
     SafeArrayDestroy(lpsaPackages);
   }
 
-  return isVCToolSetInstalled;
+  return true;
 }
 
 bool cmVSSetupAPIHelper::GetVSInstanceInfo(std::string& vsInstallLocation)

Source/cmVSSetupHelper.h

@@ -136,8 +136,7 @@ private:
   bool GetVSInstanceInfo(SmartCOMPtr<ISetupInstance2> instance2,
                          VSInstanceInfo& vsInstanceInfo);
   bool CheckInstalledComponent(SmartCOMPtr<ISetupPackageReference> package,
-                               bool& bVCToolset, bool& bWin10SDK,
-                               bool& bWin81SDK);
+                               bool& bWin10SDK, bool& bWin81SDK);
   int ChooseVSInstance(const std::vector<VSInstanceInfo>& vecVSInstances);
   bool EnumerateAndChooseVSInstance();