[clang][TypePrinter][NFC] Factor default argument substitution logic into separate function

[Michael137]

Abandoning in favour of https://reviews.llvm.org/D141826

clang/lib/AST/TypePrinter.cpp

if (auto *TTPD = dyn_cast<TemplateTypeParmDecl>(Param)) {
     return NTTPD->hasDefaultArgument() &&
            isSubstitutedTemplateArgument(Ctx, Arg, NTTPD->getDefaultArgument(),
                                          Args, Depth);
   }
   return false;
 }
 
 template <typename TA>
-static void
-printTo(raw_ostream &OS, ArrayRef<TA> Args, const PrintingPolicy &Policy,
-        const TemplateParameterList *TPL, bool IsPack, unsigned ParmIndex) {
-  // Drop trailing template arguments that match default arguments.
-  if (TPL && Policy.SuppressDefaultTemplateArgs &&
-      !Policy.PrintCanonicalTypes && !Args.empty() && !IsPack &&
-      Args.size() <= TPL->size()) {
-    ASTContext &Ctx = TPL->getParam(0)->getASTContext();
-    llvm::SmallVector<TemplateArgument, 8> OrigArgs;
-    for (const TA &A : Args)
-      OrigArgs.push_back(getArgument(A));
-    while (!Args.empty() &&
-           isSubstitutedDefaultArgument(Ctx, getArgument(Args.back()),
-                                        TPL->getParam(Args.size() - 1),
-                                        OrigArgs, TPL->getDepth()))
-      Args = Args.drop_back();
+static ArrayRef<TA> dropDefaultedArguments(ArrayRef<TA> Args,
+                                           const PrintingPolicy &Policy,
+                                           const TemplateParameterList *TPL) {
+                                      TPL->getParam(Args.size() - 1), OrigArgs,
+                                      TPL->getDepth()))
+
+  return Args;
+}
+
+template <typename TA>
+static void
+printTo(raw_ostream &OS, ArrayRef<TA> Args, const PrintingPolicy &Policy,
+        const TemplateParameterList *TPL, bool IsPack, unsigned ParmIndex) {
+  // Drop trailing template arguments that match default arguments.
+  if (TPL && Policy.SuppressDefaultTemplateArgs &&
+      !Policy.PrintCanonicalTypes && !Args.empty() && !IsPack &&
+      Args.size() <= TPL->size()) {
+    Args = dropDefaultedArguments(Args, Policy, TPL);
   }
 
   const char *Comma = Policy.MSVCFormatting ? "," : ", ";
   if (!IsPack)
     OS << '<';
 
   bool NeedSpace = false;
   bool FirstArg = true;