Some recipes fail when plotting empty vectors about makie.jl HOT 3 OPEN

Most plotting functions should handle empty vectors. I can't formulate a perfect rule but usually if you can draw zero or more of something, then this should work for zero. But if there's some data transformation inherent to a recipe which just doesn't make sense for zero elements, then this should fail. Like sum(Float64[]) returns 0 but mean(Float64[]) returns NaN because you can't divide by zero.

Often, problems with zero elements will stem from type instabilities breaking subsequent dispatches. For example, a vector will be assembled given the input data and this ends up Any[] for the zero-element case because it couldn't be inferred what element type it should be. Then any following dispatch will probably fail if it expected Point2f or so. These are often reasonably easy to fix by type-constraining the relevant containers.

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@jkrumbiegel Yes, that is why I explicitely called concretely typed empty vectors, that avoids the dispatch problem I guess, at least partially.

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Right but this is not just about the input types, the recipes themselves will sometimes do type-unstable transformations. But those can be fixed one by one. We should definitely increase the test coverage for empty recipes. If you want to tackle that, it would already be very helpful to assess which empty cases are already tested, and which aren't, and then adding tests (that are failing) for the missing cases. Then somebody else can go in and fix those.

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