gcanti#434 Handle missing properties correctly

A property can only be missing if the property is optional.
Properties with types that accept undefined values must
always be present unless they are optional properties.

src/index.ts

@@ -798,7 +798,7 @@ export const type = <P extends Props>(props: P, name: string = getInterfaceTypeN
       if (UnknownRecord.is(u)) {
         for (let i = 0; i < len; i++) {
           const k = keys[i]
-          if (!types[i].is(u[k])) {
+          if (!(k in u) || !types[i].is(u[k])) {
             return false
           }
         }
@@ -814,12 +814,15 @@ export const type = <P extends Props>(props: P, name: string = getInterfaceTypeN
           const k = keys[i]
           const ak = a[k]
           const type = types[i]
-          const result = type.validate(ak, appendContext(c, k, type, ak))
+          const result =
+            ak === undefined && !(k in a)
+              ? failure(ak, appendContext(c, k, type, ak))
+              : type.validate(ak, appendContext(c, k, type, ak))
           if (isLeft(result)) {
             pushAll(errors, result.left)
           } else {
             const vak = result.right
-            if (vak !== ak || (vak === undefined && !hasOwnProperty.call(a, k))) {
+            if (vak !== ak || (vak === undefined && !(k in a))) {
               /* istanbul ignore next */
               if (a === o) {
                 a = { ...o }

test/exact.ts

@@ -64,7 +64,7 @@ describe('exact', () => {
 
     it('should succeed validating an undefined field', () => {
       const T = t.exact(t.type({ foo: t.string, bar: t.union([t.string, t.undefined]) }))
-      assertSuccess(T.decode({ foo: 'foo' }))
+      assertSuccess(T.decode({ foo: 'foo', bar: undefined }))
     })
 
     it('should return the same reference if validation succeeded', () => {

test/recursion.ts

@@ -73,9 +73,13 @@ describe('recursion', () => {
 
     it('should fail validating an invalid value', () => {
       assertFailure(T, 1, ['Invalid value 1 supplied to : T'])
-      assertFailure(T, {}, ['Invalid value undefined supplied to : T/a: number'])
+      assertFailure(T, {}, [
+        'Invalid value undefined supplied to : T/a: number',
+        'Invalid value undefined supplied to : T/b: (T | undefined | null)'
+      ])
       assertFailure(T, { a: 1, b: {} }, [
         'Invalid value undefined supplied to : T/b: (T | undefined | null)/0: T/a: number',
+        'Invalid value undefined supplied to : T/b: (T | undefined | null)/0: T/b: (T | undefined | null)',
         'Invalid value {} supplied to : T/b: (T | undefined | null)/1: undefined',
         'Invalid value {} supplied to : T/b: (T | undefined | null)/2: null'
       ])

test/strict.ts

@@ -30,7 +30,7 @@ describe('strict', () => {
       assert.strictEqual(T.is(undefined), false)
     })
 
-    it('#423', () => {
+    it('should allow properties to be satisified by getters - #423', () => {
       class A {
         get a() {
           return 'a'
@@ -52,7 +52,7 @@ describe('strict', () => {
 
     it('should succeed validating an undefined field', () => {
       const T = t.strict({ foo: t.string, bar: t.union([t.string, t.undefined]) })
-      assertSuccess(T.decode({ foo: 'foo' }))
+      assertSuccess(T.decode({ foo: 'foo', bar: undefined }))
     })
 
     it('should return the same reference if validation succeeded', () => {