add test for non-opt cases; fix bug

Author: crusso

packages/candid/src/idl.test.ts

@@ -749,7 +749,6 @@ test('IDL opt edge cases', () => {
     // Motoko: {a = #x } : {a : {#x;#y}}
     'opt expected type non-opt on wire',
   );
-  /*
   testDecode(
     IDL.Record({a: IDL.Opt(IDL.Variant({ x: IDL.Null, y: IDL.Null }))}),
     {a: [{x: null}]},
@@ -764,5 +763,4 @@ test('IDL opt edge cases', () => {
     // Motoko: {a = #z } : {a : {#x;#y;#z}}
     'opt expected, wire type non-opt, extended, with unexpected tag - defaulting',
   );
-  */
 });

packages/candid/src/idl.ts

@@ -950,13 +950,13 @@ export class OptClass<T> extends ConstructType<[T] | []> {
       // try constituent type
       const checkpoint = b.save();
       try {
-        const v = this._type.decodeValue(b, wireType)
+        const v = this._type.decodeValue(b, t)
         return [v];
       } catch (e : any) {
         // decoding failed, but this is opt, so return "null", i.e. []
         b.restore(checkpoint);
         // skip value at wire type (to advance b)
-        const skipped = wireType.decodeValue(b, wireType)
+        const skipped = wireType.decodeValue(b, t)
         // return "null"
         return [];
       }