Fix corner case of pos cell with input and output being same width

backends/functional/smtlib.cc

@@ -277,7 +277,7 @@ struct SmtModule {
   SmtModule(const std::string &module_name, FunctionalIR ir) : name(module_name), ir(std::move(ir)) {}
 
   void write(std::ostream &out)
-  {
+  {    
     const bool stateful = ir.state().size() != 0;
     SmtWriter writer(out);
 
@@ -371,6 +371,8 @@ struct SmtModule {
     for (size_t i = 0; i < ir.size() - ir.inputs().size(); ++i) {
       writer.print(" )"); // Closing each node
     }
+    if (ir.size() == ir.inputs().size())
+      writer.print(" )"); // Corner case
 
     writer.print(" )"); // Closing inputs let statement
     writer.print(")\n"); // Closing step function

tests/functional/single_cells/rtlil/test_cell_pos_00001.il

@@ -0,0 +1,13 @@
+# Generated by Yosys 0.40+7 (git sha1 d8b5b90e7, g++ 13.2.0 -Og -fPIC)
+autoidx 1
+module \gold
+  wire width 6 input 1 \A
+  wire width 6 output 2 \Y
+  cell $pos \UUT
+    parameter \A_SIGNED 0
+    parameter \A_WIDTH 6
+    parameter \Y_WIDTH 6
+    connect \A \A
+    connect \Y \Y
+  end
+end