add test; fix checkType bug (replace by normalization)

Author: crusso

packages/candid/src/idl.test.ts

@@ -759,8 +759,8 @@ test('IDL opt edge cases', () => {
   testDecode(
     IDL.Record({a: IDL.Opt(IDL.Variant({ x: IDL.Null, y: IDL.Null }))}),
     {a: []},
-    `4449444c026c0161016b03787f797f7a7f010002`,
-    // Motoko: {a = #z } : {a : {#x;#y;#z}}
-    'opt expected, wire type non-opt, extended, with unexpected tag - defaulting',
+    `4449444c016c01617d010001`,
+    // Motoko: {a = 1} : {a : Nat}
+    'opt expected, wire type non-opt, other type - defaulting',
   );
 });

packages/candid/src/idl.ts

@@ -215,6 +215,7 @@ export abstract class Type<T = any> {
   public abstract encodeType(typeTable: TypeTable): ArrayBuffer;
 
   public abstract checkType(t: Type): Type;
+
   public abstract decodeValue(x: Pipe, t: Type): T;
 
   protected abstract _buildTypeTableImpl(typeTable: TypeTable): void;
@@ -227,6 +228,7 @@ export abstract class PrimitiveType<T = any> extends Type<T> {
     }
     return t;
   }
+
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
   public _buildTypeTableImpl(typeTable: TypeTable): void {
     // No type table encoding for Primitive types.
@@ -920,7 +922,9 @@ export class OptClass<T> extends ConstructType<[T] | []> {
     if (t instanceof ReservedClass) {
       return []
     }
-    const wireType = this.checkType(t);
+
+    const wireType = (t instanceof RecClass) ? t.getType() : t;
+
     if (wireType instanceof OptClass) {
       switch (safeReadUint8(b)) {
         case 0: