RouteReuseStrategy.retrieve() gets called twice in a row

[sliekens]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

The routeReuseStrategy.retrieve(curr.value) is called twice in a row when creating the router state.

angular/packages/router/src/create_router_state.ts

Lines 32 to 44 in c8a1a14

	// retrieve an activated route that is used to be displayed, but is not currently displayed
	} else if (routeReuseStrategy.retrieve(curr.value)) {
	const tree: TreeNode<ActivatedRoute> =
	(<DetachedRouteHandleInternal>routeReuseStrategy.retrieve(curr.value)).route;
	setFutureSnapshotsOfActivatedRoutes(curr, tree);
	return tree;
	} else {
	const value = createActivatedRoute(curr.value);
	const children = curr.children.map(c => createNode(routeReuseStrategy, c));
	return new TreeNode<ActivatedRoute>(value, children);
	}
	}

Expected behavior

Call retrieve once and reuse the return value.

} else {
    // retrieve an activated route that is used to be displayed, but is not currently displayed
    const detachedHandle: DetachedRouteHandleInternal = routeReuseStrategy.retrieve(curr.value);
    if (detachedHandle) {
        const tree: TreeNode<ActivatedRoute> = detachedHandle.route;
        setFutureSnapshotsOfActivatedRoutes(curr, tree);
        return tree;

    } else {
        const value = createActivatedRoute(curr.value);
        const children = curr.children.map(c => createNode(routeReuseStrategy, c));
        return new TreeNode<ActivatedRoute>(value, children);
    }
}

What is the motivation / use case for changing the behavior?

The current behavior confuses me as an implementer of the RouteReuseStrategy interface.

Environment

Angular version: 2.3+

[jasonaden]

Thanks for the issue (and the PR). I will review in the near future so we can get this merged.

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