[WIP] find* bounds checking

[goretkin]

Attempt to [identify and] fix #36938

(dovetails with #36965) (already merged)

[vtjnash]

rebase, for a new CI run?

[goretkin]

I rebased.

[KristofferC]

Shouldn't these use @test_broken with the correct answer then?

[vtjnash]

Looks like all lines with 👎 are currently throwing a BoundsError so this PR is failing CI

[goretkin]

I've lost track of what needs to happen here. I think my goal was to write tests that should pass, but I don't remember if the current (inconsistent) behavior can be fixed before Julia 2.0, e.g.:

julia> findfirst(fill(true, (0,)))

julia> findfirst(fill(true, (1, 0)))

julia> findfirst(fill(true, (0, 1)))

julia> findfirst(fill(true, (2, 0)))

julia> findfirst(fill(true, (0, 2)))
ERROR: BoundsError: attempt to access 0×2 Matrix{Bool} at index [1, 1]

Obviously failing CI does not help.

I've long wanted a macro like the one below, then I could write these as @test_broken:

julia> macro error_as_value(ex)
           quote
               try
                   return Some($(ex))
               catch e
                   return e
               end
           end
       end
@error_as_value (macro with 1 method)

julia> @error_as_value sqrt(4)
Some(2.0)

julia> @error_as_value sqrt(-4)
DomainError(-4.0, "sqrt will only return a complex result if called with a complex argument. Try sqrt(Complex(x)).")

What do people think of that idea? Ideas for a better name?