fix: enable nested option

shapes/option.ts

@@ -3,9 +3,6 @@ import { createShape, metadata, Shape, ShapeDecodeError } from "../common/mod.ts
 export function option<SI, SO>($some: Shape<SI, SO>): Shape<SI | undefined, SO | undefined>
 export function option<SI, SO, N>($some: Shape<SI, SO>, none: N): Shape<SI | N, SO | N>
 export function option<SI, SO, N>($some: Shape<SI, SO>, none?: N): Shape<SI | N, SO | N> {
-  if ($some.metadata.some((x) => x.factory === option && x.args[1] === none)) {
-    throw new Error("Nested option shape will not roundtrip correctly")
-  }
   return createShape({
     metadata: metadata("$.option", option<SI, SO, N>, $some, ...(none === undefined ? [] : [none!]) as [N]),
     staticSize: 1 + $some.staticSize,
@@ -18,13 +15,8 @@ export function option<SI, SO, N>($some: Shape<SI, SO>, none?: N): Shape<SI | N,
       switch (buffer.array[buffer.index++]) {
         case 0:
           return none as N
-        case 1: {
-          const value = $some.subDecode(buffer)
-          if (value === none) {
-            throw new ShapeDecodeError(this, buffer, "Some(None) will not roundtrip correctly")
-          }
-          return value
-        }
+        case 1:
+          return $some.subDecode(buffer)
         default:
           throw new ShapeDecodeError(this, buffer, "Option discriminant neither 0 nor 1")
       }

shapes/test/option.test.ts

@@ -1,5 +1,6 @@
+
 import * as $ from "../../mod.ts"
-import { assertThrows, testInvalid, testShape } from "../../test-util.ts"
+import { assertEquals, testInvalid, testShape } from "../../test-util.ts"
 
 testShape($.option($.str), ["HELLO!"])
 testShape($.option($.u8), [1])
@@ -9,14 +10,74 @@ testShape($.option($.str, null), ["hi", "low", null])
 
 testInvalid($.option($.bool), [123])
 
-Deno.test("option roundtrip error", () => {
-  assertThrows(() => $.option($.option($.u8)))
-  assertThrows(() => $.option($.withMetadata($.metadata("$foo"), $.option($.u8))))
-  assertThrows(() => {
-    const $foo = $.option($.u8)
-    $foo.metadata = []
-    $.option($foo)
-      // Some(None)
-      .decode(new Uint8Array([1, 0]))
-  })
+Deno.test("nested option support", () => {
+  // Create nested option shapes
+  const $nestedOption = $.option($.option($.u8));
+  const $nestedOptionWithCustomNone = $.option($.option($.str, null), undefined);
+
+  // Test Some(Some(value))
+  const someValue = 42;
+  const encodedSomeSome = $nestedOption.encode(someValue);
+  assertEquals(encodedSomeSome[0], 1); // Outer discriminant is 1 (Some)
+  assertEquals(encodedSomeSome[1], 1); // Inner discriminant is 1 (Some)
+  assertEquals(encodedSomeSome[2], someValue); // Value is preserved
+  assertEquals($nestedOption.decode(encodedSomeSome), someValue); // Roundtrips correctly
+
+  // Test Some(None)
+  const encodedSomeNone = new Uint8Array([1, 0]); // Manually create Some(None)
+  assertEquals($nestedOption.decode(encodedSomeNone), undefined); // Decodes to undefined
+
+  // Test None
+  const encodedNone = new Uint8Array([0]); // Just outer None
+  assertEquals($nestedOption.decode(encodedNone), undefined); // Decodes to undefined
 })
+
+// Add more comprehensive tests for nested options
+Deno.test("nested option with values", () => {
+  // Test with u8
+  const $nestedU8 = $.option($.option($.u8));
+  const u8Value = 42;
+  const encodedU8 = $nestedU8.encode(u8Value);
+  assertEquals($nestedU8.decode(encodedU8), u8Value);
+
+  // Test with string
+  const $nestedStr = $.option($.option($.str));
+  const strValue = "hello";
+  const encodedStr = $nestedStr.encode(strValue);
+  assertEquals($nestedStr.decode(encodedStr), strValue);
+
+  // Test with boolean
+  const $nestedBool = $.option($.option($.bool));
+  const boolValue = true;
+  const encodedBool = $nestedBool.encode(boolValue);
+  assertEquals($nestedBool.decode(encodedBool), boolValue);
+});
+
+Deno.test("nested option with custom none values", () => {
+  // Test with custom none values
+  const $nestedCustom = $.option($.option($.str, null), undefined);
+  const strValue = "test";
+  const encodedStr = $nestedCustom.encode(strValue);
+  assertEquals($nestedCustom.decode(encodedStr), strValue);
+
+  const nullValue = null;
+  const encodedNull = $nestedCustom.encode(nullValue);
+  assertEquals($nestedCustom.decode(encodedNull), nullValue);
+
+  const undefinedValue = undefined;
+  const encodedUndefined = $nestedCustom.encode(undefinedValue);
+  assertEquals(encodedUndefined, new Uint8Array([0]));
+  assertEquals($nestedCustom.decode(encodedUndefined), undefinedValue);
+});
+
+Deno.test("deep nested option (3 levels)", () => {
+  // Test deeper nesting (3 levels)
+  const $deepNested = $.option($.option($.option($.u8)));
+  const value = 123;
+  const encoded = $deepNested.encode(value);
+  assertEquals($deepNested.decode(encoded), value);
+
+  const undefinedValue = undefined;
+  const encodedUndefined = $deepNested.encode(undefinedValue);
+  assertEquals($deepNested.decode(encodedUndefined), undefinedValue);
+});