fix(ast): instance cache key descends arrayed interface ports by elements

source/ast/InstanceCacheKey.cpp

@@ -38,7 +38,7 @@ InstanceCacheKey::InstanceCacheKey(const InstanceSymbol& symbol, bool& valid,
             auto [iface, modport] = conn->getIfaceConn();
             while (iface && iface->kind == SymbolKind::InstanceArray) {
                 auto& arr = iface->as<InstanceArraySymbol>();
-                if (arr.empty())
+                if (arr.elements.empty())
                     iface = nullptr;
                 else
                     iface = arr.elements[0];

tests/unittests/ast/InterfaceTests.cpp

@@ -940,3 +940,37 @@ endmodule
     REQUIRE(diags.size() == 1);
     CHECK(diags[0].code == diag::VirtualInterfaceIfaceMember);
 }
+
+TEST_CASE("Arrayed interface port cache regress -- GH #1947") {
+    // NoAck has no 'ack', so on_no_ack is in error. It is written second because that is
+    // the instance a shared body would hide.
+    auto tree = SyntaxTree::fromText(R"(
+interface HasAck;
+    logic req;
+    logic ack;
+endinterface
+
+interface NoAck;
+    logic req;
+endinterface
+
+module Reader (interface a[2]);
+    initial $display("%b", a[0].ack);
+endmodule
+
+module top;
+    HasAck has_ack [2] ();
+    NoAck no_ack [2] ();
+
+    Reader on_has_ack (.a(has_ack));
+    Reader on_no_ack (.a(no_ack));
+endmodule
+)");
+
+    Compilation compilation;
+    compilation.addSyntaxTree(tree);
+
+    auto& diags = compilation.getAllDiagnostics();
+    REQUIRE(diags.size() == 1);
+    CHECK(diags[0].code == diag::CouldNotResolveHierarchicalPath);
+}