fix(warn): better message with no constructors props (#9241)

Co-authored-by: Siddhesh Mhadnak <siddhesh.mhadnak@outlook.com>
Co-authored-by: Eduardo San Martin Morote <posva@users.noreply.github.com>

src/core/util/props.js

@@ -122,13 +122,14 @@ function assertProp (
       type = [type]
     }
     for (let i = 0; i < type.length && !valid; i++) {
-      const assertedType = assertType(value, type[i])
+      const assertedType = assertType(value, type[i], vm)
       expectedTypes.push(assertedType.expectedType || '')
       valid = assertedType.valid
     }
   }
 
-  if (!valid) {
+  const haveExpectedTypes = expectedTypes.some(t => t)
+  if (!valid && haveExpectedTypes) {
     warn(
       getInvalidTypeMessage(name, value, expectedTypes),
       vm
@@ -148,7 +149,7 @@ function assertProp (
 
 const simpleCheckRE = /^(String|Number|Boolean|Function|Symbol)$/
 
-function assertType (value: any, type: Function): {
+function assertType (value: any, type: Function, vm: ?Component): {
   valid: boolean;
   expectedType: string;
 } {
@@ -166,7 +167,12 @@ function assertType (value: any, type: Function): {
   } else if (expectedType === 'Array') {
     valid = Array.isArray(value)
   } else {
-    valid = value instanceof type
+    try {
+      valid = value instanceof type
+    } catch (e) {
+      warn('Invalid prop type: "' + String(type) + '" is not a constructor', vm);
+      valid = false;
+    }
   }
   return {
     valid,

test/unit/features/options/props.spec.js

@@ -553,4 +553,20 @@ describe('Options props', () => {
     expect(vm.$refs.test.$props.booleanOrString).toBe(true)
     expect(vm.$refs.test.$props.stringOrBoolean).toBe('')
   })
+
+  it('should warn when a prop type is not a constructor', () => {
+    const vm = new Vue({
+      template: '<div>{{a}}</div>',
+      props: {
+        a: {
+          type: 'String',
+          default: 'test'
+        }
+      }
+    }).$mount()
+    expect(
+      'Invalid prop type: "String" is not a constructor'
+    ).toHaveBeenWarned()
+  })
+
 })