Error if virtual interface assignment has a config rule applied

include/slang/ast/symbols/CompilationUnitSymbols.h

@@ -261,6 +261,9 @@ struct SLANG_EXPORT ResolvedConfig {
     /// A list of libraries to use to look up definitions.
     std::span<const SourceLibrary* const> liblist;
 
+    /// The original rule that led to this resolved configuration.
+    const ConfigRule* configRule = nullptr;
+
     ResolvedConfig(const ConfigBlockSymbol& useConfig, const InstanceSymbol& rootInstance);
 };
 

scripts/diagnostics.txt

@@ -743,6 +743,7 @@ error InvalidExtendsDefault "constructor must use 'default' in its argument list
 error NonblockingDynamicAssign "nonblocking assignments to elements of dynamically sized arrays are not allowed"
 error VoidAssignment "expression of type 'void' cannot be used in assignments"
 error VirtualIfaceDefparam "interface instance cannot be assigned to a virtual interface because it is the target of a defparam or bind directive"
+error VirtualIfaceConfigRule "interface instance cannot be assigned to a virtual interface because it is the target of config rule"
 error MultipleDefaultDistWeight "'default' cannot be used more than once in dist item list"
 error DistRealRangeWeight "'dist' for a range of real values must include an explicit weight and must use the ':/' operator"
 warning ignored-slice IgnoredSlice "slice size ignored for left-to-right streaming operator"

source/ast/Expression.cpp

@@ -1459,6 +1459,16 @@ Expression* Expression::tryBindInterfaceRef(const ASTContext& context,
             diag.addNote(diag::NoteDeclarationHere, source->sourceRange());
     }
 
+    if (iface->parentInstance && iface->parentInstance->resolvedConfig) {
+        auto& diag = context.addDiag(diag::VirtualIfaceConfigRule, sourceRange);
+
+        auto rc = iface->parentInstance->resolvedConfig;
+        if (rc->configRule)
+            diag.addNote(diag::NoteConfigRule, rc->configRule->syntax->sourceRange());
+        else
+            diag.addNote(diag::NoteConfigRule, rc->useConfig.location);
+    }
+
     if (!arrayModportName.empty()) {
         if (modport) {
             // If we connected via an interface port that itself has a modport restriction,

source/ast/symbols/InstanceSymbols.cpp

@@ -425,6 +425,8 @@ InstanceSymbol& InstanceSymbol::createDefault(Compilation& comp, const Definitio
 
     if (configBlock) {
         auto rc = comp.emplace<ResolvedConfig>(*configBlock, result);
+        rc->configRule = configRule;
+
         if (configRule) {
             configRule->isUsed = true;
             if (configRule->liblist)
@@ -669,6 +671,8 @@ void InstanceSymbol::fromSyntax(Compilation& comp, const HierarchyInstantiationS
         if (confRule) {
             SLANG_ASSERT(resolvedConfig);
             auto rc = comp.emplace<ResolvedConfig>(*resolvedConfig);
+            rc->configRule = confRule;
+
             confRule->isUsed = true;
             if (confRule->liblist)
                 rc->liblist = *confRule->liblist;

tests/unittests/ast/ConfigTests.cpp

@@ -1243,3 +1243,30 @@ endmodule : cmp
         NO_COMPILATION_ERRORS;
     }
 }
+
+TEST_CASE("Configs with virtual interfaces") {
+    auto tree = SyntaxTree::fromText(R"(
+config cfg1;
+    design top;
+    instance top.i use J;
+    cell I use J;
+endconfig
+
+interface J;
+endinterface
+
+module top;
+    I i();
+    virtual I vi = i;
+endmodule
+)");
+    CompilationOptions options;
+    options.topModules.emplace("cfg1");
+
+    Compilation compilation(options);
+    compilation.addSyntaxTree(tree);
+
+    auto& diags = compilation.getAllDiagnostics();
+    REQUIRE(diags.size() == 1);
+    CHECK(diags[0].code == diag::VirtualIfaceConfigRule);
+}