[Clang] Fix an iterator invalidation bug in concept normalization cache (#165352)

The NormalizationCache may be inserted recursively when normalizing
template arguments with non-dependent default arguments. Since the ADT
doesn't preserve iterator validity, this caused undefined behavior.

This is a regression on trunk so there is no release note.

Fixes #165238

Author: zyn0217

clang/lib/Sema/SemaConcept.cpp

@@ -2408,11 +2408,16 @@ const NormalizedConstraint *Sema::getNormalizedAssociatedConstraints(
   if (CacheEntry == NormalizationCache.end()) {
     auto *Normalized = NormalizedConstraint::fromAssociatedConstraints(
         *this, ND, AssociatedConstraints);
+    if (!Normalized) {
+      NormalizationCache.try_emplace(ConstrainedDeclOrNestedReq, nullptr);
+      return nullptr;
+    }
+    // substitute() can invalidate iterators of NormalizationCache.
+    bool Failed = SubstituteParameterMappings(*this).substitute(*Normalized);
     CacheEntry =
         NormalizationCache.try_emplace(ConstrainedDeclOrNestedReq, Normalized)
             .first;
-    if (!Normalized ||
-        SubstituteParameterMappings(*this).substitute(*Normalized))
+    if (Failed)
       return nullptr;
   }
   return CacheEntry->second;

clang/test/SemaTemplate/concepts.cpp

@@ -1632,3 +1632,29 @@ void fn3() {
 }
 
 }
+
+namespace GH165238 {
+
+namespace std {
+template <typename, typename _Tp>
+concept output_iterator = requires(_Tp __t) { __t; };
+template <typename _Out> struct basic_format_context {
+  static_assert(output_iterator<_Out, int>);
+  using char_type = _Out;
+};
+template <typename> class basic_format_parse_context;
+template <typename, typename _Context, typename _Formatter,
+          typename = basic_format_parse_context<typename _Context::char_type>>
+concept __parsable_with = requires(_Formatter __f) { __f; };
+template <typename _Tp, typename _CharT,
+          typename _Context = basic_format_context<_CharT>>
+concept __formattable_impl = __parsable_with<_Tp, _Context, _Context>;
+template <typename _Tp, typename _CharT>
+concept formattable = __formattable_impl<_Tp, _CharT>;
+} // namespace std
+struct {
+  void operator()(std::formattable<char> auto);
+} call;
+void foo() { call(""); }
+
+}