Fixed some minor type issues

src/types/utility-types/identifier.ts

@@ -35,7 +35,7 @@ export class IdentifierType<T> extends Type<T, T> {
     }
 
     describe() {
-        return `identifier(${this.identifierType})`
+        return `identifier(${this.identifierType.describe()})`
     }
 
     isValidSnapshot(value: any, context: IContext): IValidationResult {

src/types/utility-types/reference.ts

@@ -92,13 +92,11 @@ export class ReferenceType<T> extends Type<ReferenceSnapshot, T> {
     }
 }
 
-// TODO: fix, references are not mentioned in type.describe...
 // TODO support get / set
-export function reference<T>(factory: IType<any, T>): IType<{ $ref: string }, T | null>;
+export function reference<T>(factory: IType<any, T>): IType<string | number, T>
 export function reference<T>(factory: IType<any, T>): any {
     if (arguments.length === 2 && typeof arguments[1] === "string")
         fail("References with base path are no longer supported. Please remove the base path.")
-    // FIXME: IType return type is inconsistent with what is actually returned, however, results in the best type-inference results for objects...
     return new ReferenceType(factory)
 }
 

test/reference.ts

@@ -76,7 +76,7 @@ test("identifiers are required", (t) => {
 
     t.throws(() => Todo.create(),
         "[mobx-state-tree] Error while converting `{}` to `AnonymousModel`:\n" +
-        "at path \"/id\" value `undefined` is not assignable to type: `identifier(string)`, expected an instance of `identifier(string)` or a snapshot like `identifier([object Object])` instead."
+        "at path \"/id\" value `undefined` is not assignable to type: `identifier(string)`, expected an instance of `identifier(string)` or a snapshot like `identifier(string)` instead."
     )
 })
 
@@ -89,9 +89,9 @@ test("identifiers cannot be modified", (t) => {
     unprotect(todo)
 
     t.throws(() => todo.id = "stuff", "[mobx-state-tree] Tried to change identifier from 'x' to 'stuff'. Changing identifiers is not allowed.")
-    t.throws(() => applySnapshot(todo, {}),
-        "[mobx-state-tree] Error while converting `{}` to `AnonymousModel`:\n" +
-        "at path \"/id\" value `undefined` is not assignable to type: `identifier(string)`, expected an instance of `identifier(string)` or a snapshot like `identifier([object Object])` instead.")
+    t.throws(() => applySnapshot(todo, { id: "stuff" }),
+        "[mobx-state-tree] Tried to change identifier from 'x' to 'stuff'. Changing identifiers is not allowed."
+     )
 })
 
 test("it should resolve refs during creation, when using path", t => {
@@ -514,7 +514,20 @@ test("References are non-nullable by default", t => {
     store.maybeRef = null
     t.is(store.maybeRef, null)
     t.throws(
-        () => store.ref = null,
+        () => store.ref = null as any,
         "[mobx-state-tree] Error while converting `null` to `reference(AnonymousModel)`:\nvalue `null` is not assignable to type: `reference(AnonymousModel)` (Value '`null`' is not a valid reference. Expected a string or number.), expected an instance of `reference(AnonymousModel)` or a snapshot like `reference(AnonymousModel)` instead."
     )
+})
+
+test("References are described properly", t => {
+    const Todo = types.model({
+        id: types.identifier(types.number)
+    })
+    const Store = types.model({
+        todo: types.maybe(Todo),
+        ref: types.reference(Todo),
+        maybeRef: types.maybe(types.reference(Todo))
+    })
+
+    t.is(Store.describe(), "{ todo: ({ id: identifier(number) } | null?); ref: reference(AnonymousModel); maybeRef: (reference(AnonymousModel) | null?) }")
 })