Report unclocked concurrent assertion as an error

src/V3AssertPre.cpp

@@ -91,7 +91,8 @@ private:
             fromAlways = true;
         }
         if (!senip) {
-            nodep->v3warn(E_UNSUPPORTED, "Unsupported: Unclocked assertion");
+            nodep->v3error("Concurrent assertion has no clock; provide a clocking event, a default"
+                           " clocking, or a clocked procedural context (IEEE 1800-2023 16.16)");
             newp = new AstSenTree{nodep->fileline(), nullptr};
         } else {
             if (cassertp && fromAlways) cassertp->senFromAlways(true);

test_regress/t/t_assert_unclocked_bad.out

@@ -0,0 +1,18 @@
+%Error: t/t_assert_unclocked_bad.v:9:3: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
+                                      : ... note: In instance 't'
+    9 |   assert property (a);
+      |   ^~~~~~
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+%Error: t/t_assert_unclocked_bad.v:10:22: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
+                                        : ... note: In instance 't'
+   10 |   assert property (a |=> b);
+      |                      ^~~
+%Error: t/t_assert_unclocked_bad.v:10:3: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
+                                       : ... note: In instance 't'
+   10 |   assert property (a |=> b);
+      |   ^~~~~~
+%Error: t/t_assert_unclocked_bad.v:11:3: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
+                                       : ... note: In instance 't'
+   11 |   cover property (a);
+      |   ^~~~~
+%Error: Exiting due to

test_regress/t/t_assert_unclocked_bad.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+
+test.lint(expect_filename=test.golden_filename, fails=True)
+
+test.passes()

test_regress/t/t_assert_unclocked_bad.v

@@ -0,0 +1,12 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2026 PlanV GmbH
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+  logic a, b;
+  assert property (a);
+  assert property (a |=> b);
+  cover property (a);
+endmodule

test_regress/t/t_property_pexpr_unsup.out

@@ -1,26 +1,26 @@
-%Error-UNSUPPORTED: t/t_property_pexpr_unsup.v:115:21: Unsupported: Unclocked assertion
+%Error: t/t_property_pexpr_unsup.v:115:21: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                     : ... note: In instance 't'
+                                         : ... note: In instance 't'
   115 |   assert property ((s_eventually a) implies (s_eventually a));
       |                     ^~~~~~~~~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
-%Error-UNSUPPORTED: t/t_property_pexpr_unsup.v:115:46: Unsupported: Unclocked assertion
+%Error: t/t_property_pexpr_unsup.v:115:46: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                     : ... note: In instance 't'
+                                         : ... note: In instance 't'
   115 |   assert property ((s_eventually a) implies (s_eventually a));
       |                                              ^~~~~~~~~~~~
-%Error-UNSUPPORTED: t/t_property_pexpr_unsup.v:115:3: Unsupported: Unclocked assertion
+%Error: t/t_property_pexpr_unsup.v:115:3: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                    : ... note: In instance 't'
+                                        : ... note: In instance 't'
   115 |   assert property ((s_eventually a) implies (s_eventually a));
       |   ^~~~~~
-%Error-UNSUPPORTED: t/t_property_pexpr_unsup.v:117:21: Unsupported: Unclocked assertion
+%Error: t/t_property_pexpr_unsup.v:117:21: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                     : ... note: In instance 't'
+                                         : ... note: In instance 't'
   117 |   assert property ((s_eventually a) iff (s_eventually a));
       |                     ^~~~~~~~~~~~
-%Error-UNSUPPORTED: t/t_property_pexpr_unsup.v:117:42: Unsupported: Unclocked assertion
+%Error: t/t_property_pexpr_unsup.v:117:42: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                     : ... note: In instance 't'
+                                         : ... note: In instance 't'
   117 |   assert property ((s_eventually a) iff (s_eventually a));
       |                                          ^~~~~~~~~~~~
-%Error-UNSUPPORTED: t/t_property_pexpr_unsup.v:117:3: Unsupported: Unclocked assertion
+%Error: t/t_property_pexpr_unsup.v:117:3: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                    : ... note: In instance 't'
+                                        : ... note: In instance 't'
   117 |   assert property ((s_eventually a) iff (s_eventually a));
       |   ^~~~~~
 %Error: Exiting due to

test_regress/t/t_property_s_eventually_unsup.out

@@ -1,14 +1,15 @@
-%Error-UNSUPPORTED: t/t_property_s_eventually_unsup.v:14:20: Unsupported: Unclocked assertion
+%Error: t/t_property_s_eventually_unsup.v:14:20: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                           : ... note: In instance 't'
+                                               : ... note: In instance 't'
    14 |   assert property (s_eventually ##1 1);
       |                    ^~~~~~~~~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
-%Error-UNSUPPORTED: t/t_property_s_eventually_unsup.v:14:3: Unsupported: Unclocked assertion
+%Error: t/t_property_s_eventually_unsup.v:14:3: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                          : ... note: In instance 't'
+                                              : ... note: In instance 't'
    14 |   assert property (s_eventually ##1 1);
       |   ^~~~~~
 %Error-UNSUPPORTED: t/t_property_s_eventually_unsup.v:15:35: Unsupported: cycle delay in s_eventually
                                                            : ... note: In instance 't'
    15 |   assert property (@(negedge clk) s_eventually ##1 1);
       |                                   ^~~~~~~~~~~~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error: Exiting due to

test_regress/t/t_sequence_first_match_unsup.out

@@ -7,11 +7,10 @@
                                               : ... note: In instance 'main'
    51 |   initial p0 : assert property ((##1 1) or(##2 1) |-> x == 1);
       |                                            ^~
-%Error-UNSUPPORTED: t/t_sequence_first_match_unsup.v:51:16: Unsupported: Unclocked assertion
+%Error: t/t_sequence_first_match_unsup.v:51:16: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                          : ... note: In instance 'main'
+                                              : ... note: In instance 'main'
    51 |   initial p0 : assert property ((##1 1) or(##2 1) |-> x == 1);
       |                ^~~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error: t/t_sequence_first_match_unsup.v:54:47: Usage of cycle delays requires default clocking (IEEE 1800-2023 14.11)
                                               : ... note: In instance 'main'
    54 |   initial p1 : assert property (first_match ((##1 1) or(##2 1)) |-> x == 1);
@@ -20,24 +19,24 @@
                                               : ... note: In instance 'main'
    54 |   initial p1 : assert property (first_match ((##1 1) or(##2 1)) |-> x == 1);
       |                                                         ^~
-%Error-UNSUPPORTED: t/t_sequence_first_match_unsup.v:54:16: Unsupported: Unclocked assertion
+%Error: t/t_sequence_first_match_unsup.v:54:16: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                          : ... note: In instance 'main'
+                                              : ... note: In instance 'main'
    54 |   initial p1 : assert property (first_match ((##1 1) or(##2 1)) |-> x == 1);
       |                ^~~~~~
 %Error: t/t_sequence_first_match_unsup.v:57:38: Usage of cycle delays requires default clocking (IEEE 1800-2023 14.11)
                                               : ... note: In instance 'main'
    57 |   initial p2 : assert property (1 or ##1 1 |-> x == 0);
       |                                      ^~
-%Error-UNSUPPORTED: t/t_sequence_first_match_unsup.v:57:16: Unsupported: Unclocked assertion
+%Error: t/t_sequence_first_match_unsup.v:57:16: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                          : ... note: In instance 'main'
+                                              : ... note: In instance 'main'
    57 |   initial p2 : assert property (1 or ##1 1 |-> x == 0);
       |                ^~~~~~
 %Error: t/t_sequence_first_match_unsup.v:60:51: Usage of cycle delays requires default clocking (IEEE 1800-2023 14.11)
                                               : ... note: In instance 'main'
    60 |   initial p3 : assert property (first_match (1 or ##1 1) |-> x == 0);
       |                                                   ^~
-%Error-UNSUPPORTED: t/t_sequence_first_match_unsup.v:60:16: Unsupported: Unclocked assertion
+%Error: t/t_sequence_first_match_unsup.v:60:16: Concurrent assertion has no clock; provide a clocking event, a default clocking, or a clocked procedural context (IEEE 1800-2023 16.16)
-                                                          : ... note: In instance 'main'
+                                              : ... note: In instance 'main'
    60 |   initial p3 : assert property (first_match (1 or ##1 1) |-> x == 0);
       |                ^~~~~~
 %Error: Internal Error: t/t_sequence_first_match_unsup.v:51:34: ../V3Ast.cpp:#: AstSExpr must have non-nullptr delayp()