Do not attempt to re-hover on exiting subplots

[etpinard]

hopefully fixes #4157 and related Cannot read _subplot of undefined issues.

@plotly/plotly_js this bug has been plaguing dash users for some times now (see https://community.plot.ly/t/dash-app-with-js-clientside-callback-sometimes-crashes/29599/5 for a reproducible case).

[etpinard]

To include in v1.50.1

[archmoj]

Looks pretty good to me.
💃
@etpinard I only have one question.
Please find my comment below.

[alexcjohnson]

Nice 🎉 presumably this works for disappearing non-cartesian subplots as well as cartesian?

[etpinard]

presumably this works for disappearing non-cartesian subplots as well as cartesian?

Presumably, we shouldn't be calling Plots.rehover on non-cartesian subplots ... but hold on looks like mapbox subplots define a _rehover function too:

Thanks for the tip!

I'll double-check if something similar happens to mapbox subplots before merging this PR.

[alexcjohnson]

Presumably, we shouldn't be calling Plots.rehover on non-cartesian subplots

that's not the implication of these comments... anyway regardless of the eventual fix, the test is pretty clear, hover on a subplot of each type while it disappears. Seems a bit overkill for a very simple fix though, also I've never seen users complaining about this with anything but cartesian. But it would be nice to have at least manually tested that this works.

plotly.js/src/components/fx/hover.js

Lines 227 to 241 in 25fe1c9

	// 'cartesian' case
	var plotObj = plots[spId];
	if(plotObj) {
	supportsCompare = true;
	// TODO make sure that fullLayout_plots axis refs
	// get updated properly so that we don't have
	// to use Axes.getFromId in general.
	xaArray[i] = Axes.getFromId(gd, plotObj.xaxis._id);
	yaArray[i] = Axes.getFromId(gd, plotObj.yaxis._id);
	continue;
	}
	// other subplot types

[etpinard]

@archmoj this PR is ready for a 2nd round of review.

[etpinard]

gd._fullLayout._plots[/* subplot id */].(x|y).axis is now always filled in properly thanks for Plots.linkSubplots called during Plots.supplyDefaults.

That TODO comment above was over three years old.

[archmoj]

Excellent.
💃 💃