Make it possible to include nonlinear.h when no external libs are enabled

The file nonlinear.h can not be included when none of SUNDIALS,
TRILINOS, or PETSC are enabled. Fix this.

diff --git a/include/deal.II/numerics/nonlinear.h b/include/deal.II/numerics/nonlinear.h
index bde8ee41b6a90616cf68a5a758013ced3b228e4a..712db8b5c7c277b4ccf472ee823c1e76625460db 100644 (file)
--- a/include/deal.II/numerics/nonlinear.h
+++ b/include/deal.II/numerics/nonlinear.h
@@ -689,15 +689,15 @@ NonlinearSolverSelector<VectorType>::solve(
     }
   else
     {
-      const std::string solvers =
+      const std::string solvers = ""
 #ifdef DEAL_II_WITH_SUNDIALS
-        "kinsol\n"
+                                  "kinsol\n"
 #endif
 #ifdef DEAL_II_TRILINOS_WITH_NOX
-        "NOX\n"
+                                  "NOX\n"
 #endif
 #ifdef DEAL_II_WITH_PETSC
-        "SNES\n"
+                                  "SNES\n"
 #endif
         ;
 

diff --git a/tests/numerics/nonlinear_solver_selector_04.cc b/tests/numerics/nonlinear_solver_selector_04.cc
new file mode 100644 (file)
index 0000000..2ce8c47
--- /dev/null
+++ b/tests/numerics/nonlinear_solver_selector_04.cc
@@ -0,0 +1,37 @@
+// ------------------------------------------------------------------------
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// Copyright (C) 2022 - 2024 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// Part of the source code is dual licensed under Apache-2.0 WITH
+// LLVM-exception OR LGPL-2.1-or-later. Detailed license information
+// governing the source code and code contributions can be found in
+// LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
+//
+// ------------------------------------------------------------------------
+
+
+
+// Tests that nonlinear.h can be included and that an object of
+// NonlinearSolverSelector can be created, even when none of SUNDIALS,
+// TRILINOS, or PETSC are enabled. Test added to trigger the bug, that this was
+// not possibles.
+
+#include <deal.II/base/function.h>
+
+#include <deal.II/numerics/nonlinear.h>
+
+#include "../tests.h"
+
+
+int
+main()
+{
+  initlog();
+
+  NonlinearSolverSelector solver;
+
+  deallog << "OK" << std::endl;
+}

diff --git a/tests/numerics/nonlinear_solver_selector_04.output b/tests/numerics/nonlinear_solver_selector_04.output
new file mode 100644 (file)
index 0000000..0fd8fc1
--- /dev/null
+++ b/tests/numerics/nonlinear_solver_selector_04.output
@@ -0,0 +1,2 @@
+
+DEAL::OK