fix: support default functions which return undefined

Author: wesleytodd

index.js

@@ -211,11 +211,27 @@ module.exports = function (opts = {}) {
       }
 
       // Handle default as functions, augment with entire options
-      const __default = typeof defaults[key] !== 'undefined' ? defaults[key] : prompt.default
+      const defaultFromRoot = typeof prompt.default === 'undefined'
+      const __default = !defaultFromRoot ? prompt.default : defaults[key]
       let _default = __default
       if (typeof _default === 'function') {
         _default = (ans) => {
-          return __default(ans, values(ans))
+          let ret = __default(ans, values(ans))
+          if (ret && typeof ret.then === 'function') {
+            // Resolve promise
+            ret = ret.then((val) => {
+              // If the default came from the root of the options object,
+              // ensure we assign it so undefined's are preserved
+              if (val === undefined && defaultFromRoot) {
+                defaults[key] = val
+              }
+              return val
+            })
+          } else if (ret === undefined && defaultFromRoot) {
+            // See above on undefineds from the root options object
+            defaults[key] = ret
+          }
+          return ret
         }
       }
 

test/index.js

@@ -289,4 +289,30 @@ suite(pkg.name, () => {
       baz: 'baz'
     })
   })
+
+  test('default functions which return undefined', async () => {
+    const opts = opta({
+      options: {
+        foo: {
+          default: () => undefined
+        },
+        bar: {
+          default: async () => undefined
+        }
+      },
+      promptModule: () => {
+        return async (prompts) => {
+          return {
+            foo: prompts[0].default(),
+            bar: await prompts[1].default()
+          }
+        }
+      }
+    })
+
+    await opts.prompt()()
+    const o = opts.values()
+    assert.strictEqual(o.foo, undefined)
+    assert.strictEqual(o.bar, undefined)
+  })
 })