Add conversion operator between version::Version and clang::VersionTuple

Author: graydon

include/swift/Basic/Version.h

@@ -24,6 +24,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "clang/Basic/VersionTuple.h"
 #include <string>
 
 namespace swift {
@@ -89,6 +90,10 @@ class Version {
     return Components.empty();
   }
 
+  /// Convert to a (maximum-4-element) clang::VersionTuple, truncating
+  /// away any 5th component that might be in this version.
+  operator clang::VersionTuple() const;
+
   /// Return whether this version is a valid Swift language version number
   /// to set the compiler to using -swift-version; this is not the same as
   /// the set of Swift versions that have ever existed, just those that we

lib/Basic/Version.cpp

@@ -285,6 +285,31 @@ Version::preprocessorDefinition(StringRef macroName,
   return define;
 }
 
+Version::operator clang::VersionTuple() const
+{
+  switch (Components.size()) {
+ case 0:
+   return clang::VersionTuple();
+ case 1:
+   return clang::VersionTuple((unsigned)Components[0]);
+ case 2:
+   return clang::VersionTuple((unsigned)Components[0],
+                              (unsigned)Components[1]);
+ case 3:
+   return clang::VersionTuple((unsigned)Components[0],
+                              (unsigned)Components[1],
+                              (unsigned)Components[2]);
+ case 4:
+ case 5:
+   return clang::VersionTuple((unsigned)Components[0],
+                              (unsigned)Components[1],
+                              (unsigned)Components[2],
+                              (unsigned)Components[3]);
+ default:
+   llvm_unreachable("swift::version::Version with 6 or more components");
+  }
+}
+
 bool
 Version::isValidEffectiveLanguageVersion() const
 {