[Flang] Fix crash with parametrized derived types usage

flang/lib/Lower/Mangler.cpp

@@ -224,8 +224,18 @@ std::string Fortran::lower::mangle::mangleName(
       assert(paramExpr && "derived type kind param not explicit");
       std::optional<int64_t> init =
           Fortran::evaluate::ToInt64(paramValue->GetExplicit());
-      assert(init && "derived type kind param is not constant");
-      kinds.emplace_back(*init);
+      // TODO: put the assertion check back when parametrized derived types
+      // are supported:
+      // assert(init && "derived type kind param is not constant");
+      //
+      // The init parameter above will require a FoldingContext for proper
+      // expression evaluation to an integer constant, otherwise the
+      // compiler may crash here (see example in issue #127424).
+      if (!init) {
+        TODO_NOLOC("parameterized derived types");
+      } else {
+        kinds.emplace_back(*init);
+      }
     }
   }
   return fir::NameUniquer::doType(modules, procs, blockId, symbolName, kinds);

flang/test/Lower/parametrized-derived-types.f90

@@ -0,0 +1,19 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+! XFAIL: *
+program main
+  TYPE ty(k1,k2)
+     INTEGER ,KIND::k1,k2=5
+     INTEGER::arr(k1:k2)=10
+     CHARACTER(LEN=k2)::CHARACTER
+  END TYPE ty
+  TYPE,EXTENDS(ty)::ty1(k3)
+     INTEGER,KIND ::k3=4
+     TYPE(ty(2,k3+1))::cmp_ty = ty(2,k3+1)(55,'HI')
+  END TYPE ty1
+  TYPE ty2(l1, l2)
+  !ERROR: not yet implemented: parameterized derived types
+     INTEGER,LEN ::l1,l2
+     TYPE(ty1(2,5)), ALLOCATABLE::ty1_cmp(:)
+  END TYPE ty2
+  TYPE(ty2(4,8)) ::ty2_obj
+end program main