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diff --git a/popperjs/package/lib/utils/detectOverflow.js.flow b/popperjs/package/lib/utils/detectOverflow.js.flow
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+// @flow
+import type { State, SideObject, Padding } from '../types';
+import type { Placement, Boundary, RootBoundary, Context } from '../enums';
+import getClippingRect from '../dom-utils/getClippingRect';
+import getDocumentElement from '../dom-utils/getDocumentElement';
+import getBoundingClientRect from '../dom-utils/getBoundingClientRect';
+import computeOffsets from './computeOffsets';
+import rectToClientRect from './rectToClientRect';
+import {
+  clippingParents,
+  reference,
+  popper,
+  bottom,
+  top,
+  right,
+  basePlacements,
+  viewport,
+} from '../enums';
+import { isElement } from '../dom-utils/instanceOf';
+import mergePaddingObject from './mergePaddingObject';
+import expandToHashMap from './expandToHashMap';
+
+// eslint-disable-next-line import/no-unused-modules
+export type Options = {
+  placement: Placement,
+  boundary: Boundary,
+  rootBoundary: RootBoundary,
+  elementContext: Context,
+  altBoundary: boolean,
+  padding: Padding,
+};
+
+export default function detectOverflow(
+  state: State,
+  options: $Shape<Options> = {}
+): SideObject {
+  const {
+    placement = state.placement,
+    boundary = clippingParents,
+    rootBoundary = viewport,
+    elementContext = popper,
+    altBoundary = false,
+    padding = 0,
+  } = options;
+
+  const paddingObject = mergePaddingObject(
+    typeof padding !== 'number'
+      ? padding
+      : expandToHashMap(padding, basePlacements)
+  );
+
+  const altContext = elementContext === popper ? reference : popper;
+
+  const popperRect = state.rects.popper;
+  const element = state.elements[altBoundary ? altContext : elementContext];
+
+  const clippingClientRect = getClippingRect(
+    isElement(element)
+      ? element
+      : element.contextElement || getDocumentElement(state.elements.popper),
+    boundary,
+    rootBoundary
+  );
+
+  const referenceClientRect = getBoundingClientRect(state.elements.reference);
+
+  const popperOffsets = computeOffsets({
+    reference: referenceClientRect,
+    element: popperRect,
+    strategy: 'absolute',
+    placement,
+  });
+
+  const popperClientRect = rectToClientRect({
+    ...popperRect,
+    ...popperOffsets,
+  });
+
+  const elementClientRect =
+    elementContext === popper ? popperClientRect : referenceClientRect;
+
+  // positive = overflowing the clipping rect
+  // 0 or negative = within the clipping rect
+  const overflowOffsets = {
+    top: clippingClientRect.top - elementClientRect.top + paddingObject.top,
+    bottom:
+      elementClientRect.bottom -
+      clippingClientRect.bottom +
+      paddingObject.bottom,
+    left: clippingClientRect.left - elementClientRect.left + paddingObject.left,
+    right:
+      elementClientRect.right - clippingClientRect.right + paddingObject.right,
+  };
+
+  const offsetData = state.modifiersData.offset;
+
+  // Offsets can be applied only to the popper element
+  if (elementContext === popper && offsetData) {
+    const offset = offsetData[placement];
+
+    Object.keys(overflowOffsets).forEach((key) => {
+      const multiply = [right, bottom].indexOf(key) >= 0 ? 1 : -1;
+      const axis = [top, bottom].indexOf(key) >= 0 ? 'y' : 'x';
+      overflowOffsets[key] += offset[axis] * multiply;
+    });
+  }
+
+  return overflowOffsets;
+}