Add error on gate primitive connection width mismatch

src/V3Width.cpp

@@ -6085,18 +6085,25 @@ class WidthVisitor final : public VNVisitor {
             userIterateAndNext(nodep->exprp(), WidthVP{CONTEXT_DET, PRELIM}.p());
             nodep->dtypeFrom(nodep->rangep());
             // Very much like like an pin
-            const AstNodeDType* const conDTypep = nodep->exprp()->dtypep();
+            const AstNodeDType* const pinDTypep = nodep->exprp()->dtypep();
             const int numInsts = nodep->rangep()->elementsConst();
             const int modwidth = numInsts;
-            const int conwidth = conDTypep->width();
-            if (conwidth == 1 && modwidth > 1) {  // Multiple connections
-                AstNodeDType* const subDTypep = nodep->findLogicDType(1, 1, conDTypep->numeric());
+            const int pinwidth = pinDTypep->width();
+            if (pinwidth == 1 && modwidth > 1) {  // Multiple connections
+                AstNodeDType* const subDTypep = nodep->findLogicDType(1, 1, pinDTypep->numeric());
                 userIterateAndNext(nodep->exprp(), WidthVP{subDTypep, FINAL}.p());
                 AstNode* const newp
                     = new AstReplicate{nodep->fileline(), nodep->exprp()->unlinkFrBack(),
                                        static_cast<uint32_t>(numInsts)};
                 nodep->replaceWith(newp);
             } else {
+                if (pinwidth != modwidth) {  // && is not generic interconnect (when supported)
+                    nodep->exprp()->v3error("Gate primitive connection expects "
+                                            << modwidth << " bits "
+                                            << ((modwidth != 1) ? "or 1 bit "s : ""s)
+                                            << "on the gate port, but the connection generates "
+                                            << pinwidth << " bits (IEEE 1800-2023 28.3.6)");
+                }
                 // Eliminating so pass down all of vup
                 userIterateAndNext(nodep->exprp(), m_vup);
                 nodep->replaceWith(nodep->exprp()->unlinkFrBack());

test_regress/t/t_gate_width_bad.out

@@ -0,0 +1,14 @@
+%Error: t/t_gate_width_bad.v:14:26: Gate primitive connection expects 1 bits on the gate port, but the connection generates 2 bits (IEEE 1800-2023 28.3.6)
+                                  : ... note: In instance 't'
+   14 |   buf buf2[0:0] (out[1], 2'b01);   
+      |                          ^~~~~
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+%Error: t/t_gate_width_bad.v:15:28: Gate primitive connection expects 1 bits on the gate port, but the connection generates 2 bits (IEEE 1800-2023 28.3.6)
+                                  : ... note: In instance 't'
+   15 |   buf buf3[0:0] (out[2], in[1:0]);   
+      |                            ^
+%Error: t/t_gate_width_bad.v:16:28: Gate primitive connection expects 4 bits or 1 bit on the gate port, but the connection generates 2 bits (IEEE 1800-2023 28.3.6)
+                                  : ... note: In instance 't'
+   16 |   buf buf4[3:0] (out[2], in[1:0]);   
+      |                            ^
+%Error: Exiting due to

test_regress/t/t_gate_width_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()

test_regress/t/t_gate_width_bad.v

@@ -0,0 +1,20 @@
+// 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;
+
+  reg [1:0] in;
+  wire [2:0] out;
+
+  // verilator lint_off WIDTH
+  buf buf1 (out[0], 1);  // <--- BAD wrong connection width
+  buf buf2[0:0] (out[1], 2'b01);  // <--- BAD wrong connection width
+  buf buf3[0:0] (out[2], in[1:0]);  // <--- BAD wrong connection width
+  buf buf4[3:0] (out[2], in[1:0]);  // <--- BAD wrong connection width
+
+  initial $stop;
+
+endmodule