Support unassigned virtual interfaces (#5265) (#6245)

src/V3LinkDot.cpp

@@ -516,30 +516,39 @@ public:
                 } else {
                     ifacerefp->v3fatalSrc("Unlinked interface");
                 }
-            } else if (ifacerefp->ifaceViaCellp()->dead()) {
-                if (varp->isIfaceRef()) {
-                    if (forPrimary() && !varp->isIfaceParent()
-                        && !v3Global.opt.topIfacesSupported()) {
-                        // Only AstIfaceRefDType's at this point correspond to ports;
-                        // haven't made additional ones for interconnect yet, so assert is simple
-                        // What breaks later is we don't have a Scope/Cell representing
-                        // the interface to attach to
-                        varp->v3warn(E_UNSUPPORTED,
-                                     "Unsupported: Interfaced port on top level module");
-                    }
-                    ifacerefp->v3error("Parent instance's interface is not found: "
-                                       << AstNode::prettyNameQ(ifacerefp->ifaceName()) << '\n'
-                                       << ifacerefp->warnMore()
-                                       << "... Perhaps intended an interface instantiation but "
-                                          "are missing parenthesis (IEEE 1800-2023 25.3)?");
-                } else {
-                    ifacerefp->v3warn(
-                        E_UNSUPPORTED,
-                        "Unsupported: virtual interface never assigned any actual interface");
-                    varp->dtypep(ifacerefp->findCHandleDType());
-                    VL_DO_DANGLING(ifacerefp->unlinkFrBack()->deleteTree(), ifacerefp);
+            } else if (ifacerefp->ifaceViaCellp()->dead() && varp->isIfaceRef()) {
+                if (forPrimary() && !varp->isIfaceParent() && !v3Global.opt.topIfacesSupported()) {
+                    // Only AstIfaceRefDType's at this point correspond to ports;
+                    // haven't made additional ones for interconnect yet, so assert is simple
+                    // What breaks later is we don't have a Scope/Cell representing
+                    // the interface to attach to
+                    varp->v3warn(E_UNSUPPORTED,
+                                 "Unsupported: Interfaced port on top level module");
                 }
+                ifacerefp->v3error("Parent instance's interface is not found: "
+                                   << AstNode::prettyNameQ(ifacerefp->ifaceName()) << '\n'
+                                   << ifacerefp->warnMore()
+                                   << "... Perhaps intended an interface instantiation but "
+                                      "are missing parenthesis (IEEE 1800-2023 25.3)?");
                 continue;
+            } else if (ifacerefp->ifaceViaCellp()->dead()
+                       || !existsNodeSym(ifacerefp->ifaceViaCellp())) {
+                // virtual interface never assigned any actual interface
+                ifacerefp->ifacep()->dead(false);
+                varp->dtypep(ifacerefp->dtypep());
+                // Create dummy cell to keep the virtual interface alive
+                // (later stages assume that non-dead interface has associated cell)
+                AstCell* const ifacecellp
+                    = new AstCell{ifacerefp->ifacep()->fileline(),
+                                  ifacerefp->ifacep()->fileline(),
+                                  ifacerefp->ifacep()->name() + "__02E" + varp->name(),
+                                  ifacerefp->ifaceName(),
+                                  nullptr,
+                                  nullptr,
+                                  nullptr};
+                ifacecellp->modp(ifacerefp->ifacep());
+                VSymEnt* const symp = new VSymEnt{&m_syms, ifacecellp};
+                ifacerefp->ifacep()->user1p(symp);
             }
             VSymEnt* const ifaceSymp = getNodeSym(ifacerefp->ifaceViaCellp());
             VSymEnt* ifOrPortSymp = ifaceSymp;
@@ -2787,7 +2796,7 @@ class LinkDotResolveVisitor final : public VNVisitor {
     void visit(AstTypeTable*) override {}
     void visit(AstConstPool*) override {}
     void visit(AstNodeModule* nodep) override {
-        if (nodep->dead()) return;
+        if (nodep->dead() || !m_statep->existsNodeSym(nodep)) return;
         LINKDOT_VISIT_START();
         UINFO(8, indent() << "visit " << nodep);
         checkNoDot(nodep);

test_regress/t/t_interface_virtual_unused.py

@@ -9,8 +9,10 @@
 
 import vltest_bootstrap
 
-test.scenarios('linter')
+test.scenarios('simulator')
 
-test.lint(fails=True, expect_filename=test.golden_filename)
+test.compile()
+
+test.execute()
 
 test.passes()

test_regress/t/t_interface_virtual_unused_bad.out

@@ -1,5 +0,0 @@
-%Error-UNSUPPORTED: t/t_interface_virtual_unused_bad.v:14:12: Unsupported: virtual interface never assigned any actual interface
-   14 |    virtual QBus q8;
-      |            ^~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
-%Error: Exiting due to