From 542ffcca608328df308c109f30e7d46b201c2a6a Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Wed, 17 Sep 2025 20:42:51 -0400
Subject: [PATCH] Prevent internal error on pattern mismatch

---
 src/V3Width.cpp                               |  2 +-
 test_regress/t/t_array_pattern_scalar_bad.out |  6 ++++++
 test_regress/t/t_array_pattern_scalar_bad.py  | 16 ++++++++++++++++
 test_regress/t/t_array_pattern_scalar_bad.v   | 12 ++++++++++++
 4 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 test_regress/t/t_array_pattern_scalar_bad.out
 create mode 100755 test_regress/t/t_array_pattern_scalar_bad.py
 create mode 100644 test_regress/t/t_array_pattern_scalar_bad.v

diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index 8a768e879..35f321208 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -4764,7 +4764,7 @@ class WidthVisitor final : public VNVisitor {
                     E_UNSUPPORTED,
                     "Unsupported: Assignment pattern applies against non struct/union data type: "
                         << dtypep->prettyDTypeNameQ());
-                nodep->unlinkFrBack();
+                nodep->replaceWith(new AstConst{nodep->fileline(), AstConst::BitFalse{}});
             }
 
             // Done with the Pattern
diff --git a/test_regress/t/t_array_pattern_scalar_bad.out b/test_regress/t/t_array_pattern_scalar_bad.out
new file mode 100644
index 000000000..093130bff
--- /dev/null
+++ b/test_regress/t/t_array_pattern_scalar_bad.out
@@ -0,0 +1,6 @@
+%Error-UNSUPPORTED: t/t_array_pattern_scalar_bad.v:9:13: Unsupported: Assignment pattern applies against non struct/union data type: 'bit'
+                                                       : ... note: In instance 't'
+    9 |   bit bad = '{1'b1};   
+      |             ^~
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: Exiting due to
diff --git a/test_regress/t/t_array_pattern_scalar_bad.py b/test_regress/t/t_array_pattern_scalar_bad.py
new file mode 100755
index 000000000..55203b6c9
--- /dev/null
+++ b/test_regress/t/t_array_pattern_scalar_bad.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 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
+
+import vltest_bootstrap
+
+test.scenarios('linter')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()
diff --git a/test_regress/t/t_array_pattern_scalar_bad.v b/test_regress/t/t_array_pattern_scalar_bad.v
new file mode 100644
index 000000000..03415c521
--- /dev/null
+++ b/test_regress/t/t_array_pattern_scalar_bad.v
@@ -0,0 +1,12 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+
+  bit bad = '{1'b1};  // <--- BAD: Can't assign pattern to scalar
+
+  initial $stop;
+endmodule