[clang] [Clang] support friend declarations with a dependent nested-name-specifier (PR #191268)

[Matheus Izvekov via cfe-commits]

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@@ -274,6 +275,99 @@ struct AccessTarget : public AccessedEntity {
 
 }
 
+static bool CanDeduceTemplateArguments(Sema &S, TemplateParameterList *TPL,
+                                       ArrayRef<TemplateArgument> PatternArgs,
+                                       ArrayRef<TemplateArgument> Args,
+                                       SourceLocation Loc) {
+  if (PatternArgs.size() != Args.size())
+    return false;
+
+  auto Equal =
+      llvm::equal(PatternArgs, Args,
+                  [](const TemplateArgument &LHS, const TemplateArgument &RHS) {
+                    return LHS.structurallyEquals(RHS);
+                  });
+  if (Equal)
+    return true;
+
+  TemplateDeductionInfo Info(Loc);
+  SmallVector<DeducedTemplateArgument, 4> Deduced(TPL->size());
+  S.DeduceTemplateArguments(TPL, PatternArgs, Args, Info, Deduced,
+                            /*NumberOfArgumentsMustMatch=*/false);
+
+  for (const DeducedTemplateArgument &Arg : Deduced)
+    if (Arg.isNull())
+      return false;
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mizvekov wrote:

Normally you wouldn't be checking if all arguments were deduced, because they can have defaults and that's fine.

https://github.com/llvm/llvm-project/pull/191268