VS: Use StdOutEncoding for VS 16.7 Preview 3 and above

VS 16.6 added a `StdOutEncoding` setting for custom commands to tell
MSBuild that the output is encoded as UTF-8.  In commit bc877a7e94 (Add
support to indicate UTF-8 custom command pipe output encoding,
2020-04-08) CMake learned to add the setting in anticipation of the VS
16.6 release.  However, when 16.6 was released it had a bug in the
implementation of custom tasks with StdOutEncoding enabled that was
exposed by our test suite.  In commit 5058fb5401 (VS: Drop
StdOutEncoding with VS 16.6 pending investigation, 2020-05-29) we
disabled the setting pending investigation.

The problem is fixed in VS 16.7 Preview 3, so restore use of the
setting when a VS instance of at least that version is detected.

Fixes: #20769

4 files changed, 24 insertions, 5 deletions

diff --git a/Source/cmGlobalVisualStudio10Generator.h b/Source/cmGlobalVisualStudio10Generator.h
index f659ff3..b8c18b4 100644
--- a/Source/cmGlobalVisualStudio10Generator.h
+++ b/Source/cmGlobalVisualStudio10Generator.h
@@ -121,6 +121,8 @@ public:
 
   bool IsIPOSupported() const override { return true; }
 
+  virtual bool IsStdOutEncodingSupported() const { return false; }
+
   static std::string GetInstalledNsightTegraVersion();
 
   /** Return the first two components of CMAKE_SYSTEM_VERSION.  */
diff --git a/Source/cmGlobalVisualStudioVersionedGenerator.cxx b/Source/cmGlobalVisualStudioVersionedGenerator.cxx
index d44433b..605dc8b 100644
--- a/Source/cmGlobalVisualStudioVersionedGenerator.cxx
+++ b/Source/cmGlobalVisualStudioVersionedGenerator.cxx
@@ -393,6 +393,21 @@ bool cmGlobalVisualStudioVersionedGenerator::IsDefaultToolset(
   return false;
 }
 
+bool cmGlobalVisualStudioVersionedGenerator::IsStdOutEncodingSupported() const
+{
+  // Supported from Visual Studio 16.7 Preview 3.
+  if (this->Version > cmGlobalVisualStudioGenerator::VSVersion::VS16) {
+    return true;
+  }
+  if (this->Version < cmGlobalVisualStudioGenerator::VSVersion::VS16) {
+    return false;
+  }
+  unsigned long long const vsInstanceVersion16_7_P2 = 4503631666610212;
+  unsigned long long vsInstanceVersion;
+  return (this->GetVSInstanceVersion(vsInstanceVersion) &&
+          vsInstanceVersion > vsInstanceVersion16_7_P2);
+}
+
 std::string cmGlobalVisualStudioVersionedGenerator::GetAuxiliaryToolset() const
 {
   const char* version = this->GetPlatformToolsetVersion();
diff --git a/Source/cmGlobalVisualStudioVersionedGenerator.h b/Source/cmGlobalVisualStudioVersionedGenerator.h
index bcf8546..cbd3ba7 100644
--- a/Source/cmGlobalVisualStudioVersionedGenerator.h
+++ b/Source/cmGlobalVisualStudioVersionedGenerator.h
@@ -34,6 +34,8 @@ public:
   bool IsDefaultToolset(const std::string& version) const override;
   std::string GetAuxiliaryToolset() const override;
 
+  bool IsStdOutEncodingSupported() const override;
+
 protected:
   cmGlobalVisualStudioVersionedGenerator(
     VSVersion version, cmake* cm, const std::string& name,
diff --git a/Source/cmVisualStudio10TargetGenerator.cxx b/Source/cmVisualStudio10TargetGenerator.cxx
index 8cb933b..97c4c85 100644
--- a/Source/cmVisualStudio10TargetGenerator.cxx
+++ b/Source/cmVisualStudio10TargetGenerator.cxx
@@ -19,6 +19,7 @@
 #include "cmGeneratorExpression.h"
 #include "cmGeneratorTarget.h"
 #include "cmGlobalVisualStudio10Generator.h"
+#include "cmGlobalVisualStudioVersionedGenerator.h"
 #include "cmLinkLineDeviceComputer.h"
 #include "cmLocalVisualStudio10Generator.h"
 #include "cmMakefile.h"
@@ -4951,10 +4952,9 @@ std::string cmVisualStudio10TargetGenerator::GetCMakeFilePath(
   return path;
 }
 
-void cmVisualStudio10TargetGenerator::WriteStdOutEncodingUtf8(Elem& /* e1 */)
+void cmVisualStudio10TargetGenerator::WriteStdOutEncodingUtf8(Elem& e1)
 {
-  // FIXME: As of VS 16.6.0, this breaks custom commands with symbolic outputs.
-  // See https://gitlab.kitware.com/cmake/cmake/-/issues/20769 for details.
-  // Disable it for now.
-  // e1.Element("StdOutEncoding", "UTF-8");
+  if (this->GlobalGenerator->IsStdOutEncodingSupported()) {
+    e1.Element("StdOutEncoding", "UTF-8");
+  }
 }