[Clang][Concepts] Avoid substituting into constraints for invalid Tem…

…plateDecls (#75697)

Fixes #73885.

Substituting into constraints for invalid TemplateDecls might still
yield dependent expressions and end up crashing later in evaluation.

clang/docs/ReleaseNotes.rst

@@ -1042,6 +1042,7 @@ Bug Fixes to C++ Support
 - Fixed failed assertion when resolving context of defaulted comparison method outside of struct. (#GH96043).
 - Clang now diagnoses explicit object parameters in member pointers and other contexts where they should not appear.
   Fixes (#GH85992).
+- Fixed a crash-on-invalid bug involving extraneous template parameter with concept substitution. (#GH73885)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaConcept.cpp

@@ -625,6 +625,12 @@ bool Sema::CheckConstraintSatisfaction(
         *this, nullptr, ConstraintExprs, ConvertedConstraints,
         TemplateArgsLists, TemplateIDRange, OutSatisfaction);
   }
+  // Invalid templates could make their way here. Substituting them could result
+  // in dependent expressions.
+  if (Template->isInvalidDecl()) {
+    OutSatisfaction.IsSatisfied = false;
+    return true;
+  }
 
   // A list of the template argument list flattened in a predictible manner for
   // the purposes of caching. The ConstraintSatisfaction type is in AST so it

clang/test/SemaTemplate/instantiate-requires-expr.cpp

@@ -227,3 +227,13 @@ struct r6 {};
 
 using r6i = r6<int>;
 // expected-error@-1 {{constraints not satisfied for class template 'r6' [with T = int]}}
+
+namespace GH73885 {
+
+template <class> // expected-error {{extraneous}}
+template <class T> requires(T{})
+constexpr bool e_v = true;
+
+static_assert(e_v<bool>);
+
+} // namespace GH73885