[clang] missing outer template levels when checking template constraints

[Lancern]

Summary

When checking constraint satisfaction on template arguments, the outer
template levels are not added to MultiLevelTemplateArgumentList.

Fix bugs https://github.com/llvm/llvm-project/issues/50845

[Lancern]

Fix some regression issues

[erichkeane]

So I don't think this is the right fix for this... But I DID check and see that the test case seems to be fixed here: https://reviews.llvm.org/D126907 , which does a lot of rework for this sort of thing.

That patch is expected to be complete/ready for submission in the 'near future', but I'm still working through 1 more issue.

clang/lib/Sema/SemaConcept.cpp

static bool CheckConstraintSatisfaction(Sema &S, const NamedDecl *Template,
   Sema::InstantiatingTemplate Inst(S, TemplateIDRange.getBegin(),
       Sema::InstantiatingTemplate::ConstraintsCheck{},
       const_cast<NamedDecl *>(Template), TemplateArgs, TemplateIDRange);
   if (Inst.isInvalid())
     return true;
 
   MultiLevelTemplateArgumentList MLTAL;
   MLTAL.addOuterTemplateArguments(TemplateArgs);
+  if (const TypeAliasTemplateDecl *AliasTemplate =
+          dyn_cast_or_null<TypeAliasTemplateDecl>(Template)) {
+    MLTAL.addOuterRetainedLevels(AliasTemplate->getTemplateDepth());
+  }
 
   for (const Expr *ConstraintExpr : ConstraintExprs) {
     if (calculateConstraintSatisfaction(S, Template, TemplateArgs,
                                         TemplateIDRange.getBegin(), MLTAL,
                                         ConstraintExpr, Satisfaction))
       return true;
     if (!Satisfaction.IsSatisfied)
       // [temp.constr.op] p2

clang/test/SemaCXX/template-member-alias-constraint.cpp

+// RUN: %clang_cc1 %s -std=c++20 -fsyntax-only -verify
+
+template <typename T>
+concept Foo = true;
+
+template <typename T, typename U>
+struct Bar {};
+
+template <typename T>
+struct Baz {
+  template <Foo U>
+  using BazBar = Bar<T, U>;
+
+  using BazBarInt = BazBar<int>; // expected-no-diagnostics
+};
+
+template <typename urng_t>
+struct contiguous_range {
+  template <bool const_range>
+    requires(const_range == false)
+  using basic_iterator = int;
+
+  auto begin() {
+    return basic_iterator<false>{}; // expected-no-diagnostics
+  }
+};