Add empty veriuser.h for legacy compatibility.

Changes

@@ -17,6 +17,7 @@ Verilator 5.035 devel
   Those using build farms may need to now use `--output-groups 0` or otherwise.
 * Add check for `let` misused in statement context (#5733).
 * Add used language to `--preproc-resolve` output (#5795). [Kamil Rakoczy, Antmicro Ltd.]
+* Add empty veriuser.h for legacy compatibility.
 * Fix reset of automatic function variables (#5747). [Augustin Fabre]
 * Fix invalid code motion over branches (#5811) (#5814). [Geza Lore]
 * Fix sorting of wide SenItems (#5816). [Geza Lore]

include/vltstd/veriuser.h

@@ -0,0 +1,31 @@
+// -*- mode: C++; c-file-style: "cc-mode" -*-
+//*************************************************************************
+//
+// Code available from: https://verilator.org
+//
+// Copyright 2009-2025 by Wilson Snyder. This program is free software; you can
+// redistribute it and/or modify it under the terms of either the GNU
+// Lesser General Public License Version 3 or the Perl Artistic License
+// Version 2.0.
+// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+//
+//=========================================================================
+///
+/// \file
+/// \brief Verilated user tf_routines
+///
+/// This file contains routines to interface user VPI/PLI C++ code with
+/// Verilator.  Traditionally the veriuser.h code has been used for only
+/// tf_ routines, which verilator does not implement, so this file is
+/// empty.
+///
+/// User code relying on tf_ routines should migrate to VPI (vpi_user.h) or
+/// DPI (svdpi.h) routines.
+///
+/// This file is only provided for backwards compatibility for applications
+/// which include veriuser.h even though they use only vpi_ or dpi_
+/// routines.
+///
+//=========================================================================
+
+// Intentionally empty, see above.

test_regress/t/t_wrapper_legacy.cpp

@@ -19,6 +19,9 @@
 // These require the above. Comment prevents clang-format moving them
 #include "TestCheck.h"
 
+// Empty legacy file (see comments inside it)
+#include "veriuser.h"
+
 int errors = 0;
 
 vluint64_t main_time = 0;