[ASTMatchers] Fixed CastKind being parsed incorrectly for dynamic matchers

[njames93]

Summary

Requires hasCastKind arguments to have CK_ prefixed to bring it in line with the documentation and other matchers that take enumerations.

[njames93]

• Added support for giving suggestions on invalid inputs

[njames93]

Fixed up documentation for CastKind matcher.

[aaron.ballman]

Can you also add some unit tests to the dynamic matcher tests?

[njames93]

Added unit test for matcher

[aaron.ballman]

LGTM!

clang/lib/ASTMatchers/Dynamic/Marshallers.h

public:
 
   static llvm::Optional<std::string> getBestGuess(const VariantValue &Value);
 };
 
 template <> struct ArgTypeTraits<CastKind> {
 private:
   static Optional<CastKind> getCastKind(llvm::StringRef AttrKind) {
     return llvm::StringSwitch<Optional<CastKind>>(AttrKind)
-#define CAST_OPERATION(Name) .Case( #Name, CK_##Name)
+#define CAST_OPERATION(Name) .Case("CK_" #Name, CK_##Name)
 #include "clang/AST/OperationKinds.def"
         .Default(llvm::None);
   }
 
 public:
   static bool is(const VariantValue &Value) {
     return Value.isString() && getCastKind(Value.getString());
   }

clang/lib/ASTMatchers/Dynamic/Marshallers.cpp

return ::getBestGuess(Value.getString(), llvm::makeArrayRef(Allowed),
                           "attr::");
   return llvm::None;
 }
 
 llvm::Optional<std::string>
 clang::ast_matchers::dynamic::internal::ArgTypeTraits<
     clang::CastKind>::getBestGuess(const VariantValue &Value) {
   static constexpr llvm::StringRef Allowed[] = {
-#define CAST_OPERATION(Name) #Name,
+#define CAST_OPERATION(Name) "CK_" #Name,
 #include "clang/AST/OperationKinds.def"
   };
   if (Value.isString())
-    return ::getBestGuess(Value.getString(), llvm::makeArrayRef(Allowed));
+    return ::getBestGuess(Value.getString(), llvm::makeArrayRef(Allowed),
+                          "CK_");
   return llvm::None;
 }
 
 llvm::Optional<std::string>
 clang::ast_matchers::dynamic::internal::ArgTypeTraits<
     clang::OpenMPClauseKind>::getBestGuess(const VariantValue &Value) {
   static constexpr llvm::StringRef Allowed[] = {
 #define OMP_CLAUSE_CLASS(Enum, Str, Class) #Enum,
 #include "llvm/Frontend/OpenMP/OMPKinds.def"
   };
   if (Value.isString())
     return ::getBestGuess(Value.getString(), llvm::makeArrayRef(Allowed),
                           "OMPC_");
   return llvm::None;
 }