Zoom event listeners are passed an incorrect sourceEvent if a programmatic zoom occurs during a user zoom gesture

[yurivish]

Programmatic zoom intiated while the user is making a gesture causes the zoom callback to be invoked with the sourceEvent from the preceding user action, rather than an undefined sourceEvent.

I think this is because there is an active Gesture on the element and the following line does not update the event to null or undefined:

d3-zoom/src/zoom.js

Line 192 in 23016d4

if (event) this.sourceEvent = event;

which is called indirectly from

https://github.com/d3/d3-zoom/blob/main/src/zoom.js#L85

with an undefined event.

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Example: https://observablehq.com/d/11402b3301150892 (see console for stack overflow)

The example notebook tries to perform a programmatic zoom once for every user-initiated zoom, but because the programmatic zoomed callback is invoked with a trusted sourceEvent, this results in infinite recursion.

First noticed here (which now implements a workaround)