[clang] [Clang] Unify interface for accessing template arguments as written for class/variable template specializations (PR #81642)

[Krystian Stasiowski via cfe-commits]

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@@ -1455,21 +1455,17 @@ void TypePrinter::printTag(TagDecl *D, raw_ostream &OS) {
 
   // If this is a class template specialization, print the template
   // arguments.
-  if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(D)) {
-    ArrayRef<TemplateArgument> Args;
-    TypeSourceInfo *TAW = Spec->getTypeAsWritten();
-    if (!Policy.PrintCanonicalTypes && TAW) {
-      const TemplateSpecializationType *TST =
-        cast<TemplateSpecializationType>(TAW->getType());
-      Args = TST->template_arguments();
-    } else {
-      const TemplateArgumentList &TemplateArgs = Spec->getTemplateArgs();
-      Args = TemplateArgs.asArray();
-    }
+  if (auto S = dyn_cast<ClassTemplateSpecializationDecl>(D)) {
+    const TemplateParameterList *TParams =
+        S->getSpecializedTemplate()->getTemplateParameters();
+    const auto *TArgAsWritten = S->getTemplateArgsAsWritten();
     IncludeStrongLifetimeRAII Strong(Policy);
-    printTemplateArgumentList(
-        OS, Args, Policy,
-        Spec->getSpecializedTemplate()->getTemplateParameters());
+    if (TArgAsWritten && !Policy.PrintCanonicalTypes)
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sdkrystian wrote:

@erichkeane Unfortunately, this pattern occurs in separate files (`DeclPrinter.cpp` and `TypePrinter.cpp`), hence the duplication... 

https://github.com/llvm/llvm-project/pull/81642