fix: more Flow fixes

.flowconfig

@@ -9,7 +9,7 @@
 [lints]
 
 [options]
-suppress_comment=\\(.\\|\n\\)*\\$FlowExpectError
+suppress_comment=\\(.\\|\n\\)*\\$\\(FlowExpectError\\|FlowFixMe\\)
 
 [strict]
 

src/__typings__/main-test.js

@@ -5,6 +5,7 @@
 
 import React from 'react';
 import { Manager, Reference, Popper, usePopper } from '..';
+import type { Modifier, StrictModifiers } from '@popperjs/core';
 
 export const Test = () => (
   <Manager>
@@ -68,21 +69,43 @@ export const HookTest = () => {
       modifiers: [
         {
           name: 'arrow',
-          options: { element: arrowElement || undefined },
+          options: { element: arrowElement },
         },
       ],
     }
   );
 
-  usePopper(
+  usePopper(referenceElement, popperElement, {
+    modifiers: [
+      // $FlowExpectError: offset tuple accepts only numbers
+      {
+        name: 'offset',
+        options: { offset: [0, ''] },
+      },
+    ],
+  });
+
+  Number(2 + null);
+
+  type CustomModifier = $Shape<Modifier<'custom', { foo: boolean }>>;
+  usePopper<StrictModifiers | CustomModifier>(referenceElement, popperElement, {
+    modifiers: [
+      {
+        name: 'custom',
+        options: { foo: true },
+      },
+    ],
+  });
+
+  usePopper<StrictModifiers | CustomModifier>(
     referenceElement,
     popperElement,
-    // $FlowExpectError
+    // $FlowExpectError: foo should be boolean
     {
       modifiers: [
         {
-          name: 'offset',
-          options: { offset: [0, ''] },
+          name: 'custom',
+          options: { foo: 'str' },
         },
       ],
     }

src/usePopper.js

@@ -28,16 +28,16 @@ type UpdateStateModifier = Modifier<'updateState', {||}>;
 
 const EMPTY_MODIFIERS = [];
 
-export const usePopper = <
-  TModifiers: StrictModifiers | $Shape<Modifier<string, {}>>
->(
+type DefaultModifiers = StrictModifiers | $Shape<Modifier<any, any>>;
+
+export const usePopper = <Modifiers: DefaultModifiers = DefaultModifiers>(
   referenceElement: ?(Element | VirtualElement),
   popperElement: ?HTMLElement,
-  options: Options<TModifiers> = {}
+  options: Options<Modifiers> = {}
 ) => {
-  type TExtendedModifier = TModifiers | $Shape<UpdateStateModifier>;
+  type InternalModifiers = Modifiers | $Shape<UpdateStateModifier>;
 
-  const prevOptions = React.useRef<?OptionsGeneric<TExtendedModifier>>(null);
+  const prevOptions = React.useRef<?OptionsGeneric<InternalModifiers>>(null);
 
   const optionsWithDefaults = {
     onFirstUpdate: options.onFirstUpdate,
@@ -79,7 +79,7 @@ export const usePopper = <
     [setState]
   );
 
-  const popperOptions = React.useMemo<OptionsGeneric<TExtendedModifier>>(() => {
+  const popperOptions = React.useMemo<OptionsGeneric<InternalModifiers>>(() => {
     const newOptions = {
       onFirstUpdate: optionsWithDefaults.onFirstUpdate,
       placement: optionsWithDefaults.placement || 'bottom',
@@ -97,6 +97,7 @@ export const usePopper = <
     ) {
       return prevOptions.current;
     } else {
+      // $FlowFixMe: Cannot assign `newOptions` to `prevOptions.current` because  string [1] is incompatible with  string literal `updateState` [2] in property `name` of array element of property `modifiers`
       prevOptions.current = newOptions;
       return newOptions;
     }
@@ -111,15 +112,15 @@ export const usePopper = <
   const popperInstanceRef = React.useRef();
 
   const createPopper = React.useMemo<typeof defaultCreatePopper>(
-    // For some reason the two identical types don't like to be cast to one of them
-    () => (options.createPopper: any) || defaultCreatePopper,
+    // $FlowFixMe: Cannot call `React.useMemo` with function bound to `create` because  `TModifier` [1] is incompatible with  `Modifier` [2] in array element of property `modifiers` of the third argument of the return value.
+    () => options.createPopper || defaultCreatePopper,
     [options.createPopper]
   );
 
   useIsomorphicLayoutEffect(() => {
     let popperInstance = null;
     if (referenceElement != null && popperElement != null) {
-      popperInstance = createPopper<TExtendedModifier>(
+      popperInstance = createPopper<InternalModifiers>(
         referenceElement,
         popperElement,
         popperOptions