From 728ddf33310300b060367edb38ed5ec6bfc911a8 Mon Sep 17 00:00:00 2001
From: Yilou Wang <wangyilou123@gmail.com>
Date: Wed, 25 Mar 2026 12:16:52 +0100
Subject: [PATCH] Fix modport selection of virtual interface handle (#7321)

---
 src/V3Width.cpp                               |  17 +++
 .../t/t_interface_virtual_modport_sel.py      |  18 +++
 .../t/t_interface_virtual_modport_sel.v       | 107 ++++++++++++++++++
 3 files changed, 142 insertions(+)
 create mode 100755 test_regress/t/t_interface_virtual_modport_sel.py
 create mode 100644 test_regress/t/t_interface_virtual_modport_sel.v

diff --git a/src/V3Width.cpp b/src/V3Width.cpp
index eec39fe8a..d34252725 100644
--- a/src/V3Width.cpp
+++ b/src/V3Width.cpp
@@ -3522,6 +3522,23 @@ class WidthVisitor final : public VNVisitor {
                     nodep->didWidth(true);
                     return;
                 }
+                if (AstModport* const modportp = VN_CAST(foundp, Modport)) {
+                    // Modport selection (e.g. vif.passive_mp) is compile-time
+                    // type narrowing: replace MemberSel with fromp re-typed.
+                    AstIfaceRefDType* const newDtypep = new AstIfaceRefDType{
+                        nodep->fileline(), nodep->fileline(), adtypep->cellName(),
+                        adtypep->ifaceName(), modportp->name()};
+                    newDtypep->ifacep(adtypep->ifacep());
+                    newDtypep->cellp(adtypep->cellp());
+                    newDtypep->modportp(modportp);
+                    newDtypep->isVirtual(adtypep->isVirtual());
+                    v3Global.rootp()->typeTablep()->addTypesp(newDtypep);
+                    AstNodeExpr* const fromp = nodep->fromp()->unlinkFrBack();
+                    fromp->dtypep(newDtypep);
+                    nodep->replaceWith(fromp);
+                    VL_DO_DANGLING(pushDeletep(nodep), nodep);
+                    return;
+                }
                 UINFO(1, "found object " << foundp);
                 nodep->v3fatalSrc("MemberSel of non-variable\n"
                                   << nodep->warnContextPrimary() << '\n'
diff --git a/test_regress/t/t_interface_virtual_modport_sel.py b/test_regress/t/t_interface_virtual_modport_sel.py
new file mode 100755
index 000000000..664e902bf
--- /dev/null
+++ b/test_regress/t/t_interface_virtual_modport_sel.py
@@ -0,0 +1,18 @@
+#!/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('simulator')
+
+test.compile(verilator_flags2=["--binary", "--timing"])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_interface_virtual_modport_sel.v b/test_regress/t/t_interface_virtual_modport_sel.v
new file mode 100644
index 000000000..187dbc0f4
--- /dev/null
+++ b/test_regress/t/t_interface_virtual_modport_sel.v
@@ -0,0 +1,107 @@
+// 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
+
+// verilog_format: off
+`define stop $stop
+`define checkh(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0x exp=%0x (%s !== %s)\n", `__FILE__,`__LINE__, (gotv), (expv), `"gotv`", `"expv`"); `stop; end while(0);
+// verilog_format: on
+
+// Modport selection on virtual interface handles:
+//   vif.modport_name   (direct)
+//   obj.vif.modport_name  (chained through class member)
+
+interface my_if (input logic clk);
+  logic [7:0] data;
+
+  clocking mon_cb @(posedge clk);
+    input data;
+  endclocking
+
+  modport passive_mp (clocking mon_cb);
+  modport active_mp (output data);
+  modport signal_mp (input data);
+endinterface
+
+class Context;
+  virtual my_if vif;
+endclass
+
+class Monitor;
+  virtual my_if.passive_mp mp;
+
+  function void connect_chain(Context cntxt);
+    mp = cntxt.vif.passive_mp;
+  endfunction
+
+  function void connect_tmp(Context cntxt);
+    automatic virtual my_if tmp = cntxt.vif;
+    mp = tmp.passive_mp;
+  endfunction
+endclass
+
+class Driver;
+  virtual my_if.active_mp drv;
+
+  function void connect(Context cntxt);
+    drv = cntxt.vif.active_mp;
+  endfunction
+
+  task drive(input logic [7:0] val);
+    drv.data = val;
+  endtask
+endclass
+
+class Reader;
+  virtual my_if.signal_mp sig;
+
+  function void connect(Context cntxt);
+    sig = cntxt.vif.signal_mp;
+  endfunction
+endclass
+
+module t;
+  logic clk = 0;
+  always #5 clk = ~clk;
+  my_if vif (.clk(clk));
+
+  initial begin
+    automatic Context c = new;
+    automatic Monitor m1 = new;
+    automatic Monitor m2 = new;
+    automatic Driver d = new;
+    automatic Reader r = new;
+    c.vif = vif;
+
+    // Connect via chain and tmp paths
+    m1.connect_chain(c);
+    m2.connect_tmp(c);
+    d.connect(c);
+    r.connect(c);
+
+    // Drive data through active_mp, read through passive_mp and signal_mp
+    d.drive(8'hAB);
+    @(posedge clk);
+    @(posedge clk);
+
+    // Verify clocking-block modport (m1 = chain, m2 = tmp)
+    `checkh(m1.mp.mon_cb.data, 8'hAB);
+    `checkh(m2.mp.mon_cb.data, 8'hAB);
+
+    // Verify signal modport (no clocking block)
+    `checkh(r.sig.data, 8'hAB);
+
+    // Drive new value, verify update propagates
+    d.drive(8'hCD);
+    @(posedge clk);
+    @(posedge clk);
+
+    `checkh(m1.mp.mon_cb.data, 8'hCD);
+    `checkh(r.sig.data, 8'hCD);
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule