error message for indexing with BitArray

[JeffFessler]

Closes #38685 by making the error message for (e.g.) ones(2,3)[trues(4,5)] more informative.

This is a WIP because I don't know how to test locally, so let's see what the CI says.

Will this change require a line in the release notes?
Seems small enough to me to be below the threshold of worth mentioning, but up to y'all...

[mbauman]

This is just changing the printing of an error message so it can be improved without warning :)

But I see I directed you to the wrong place. We don't want to add a branch here — rather, we want to change show_index(io, ::LogicalIndex) here:

julia/base/errorshow.jl

Line 34 in 49b8e61

show_index(io::IO, x::LogicalIndex) = show_index(io, x.mask)

[JeffFessler]

Thanks for the feedback. I've updated it to modify show_index now.
Again, not tested so hopefully CI works...

[mbauman]

To test it locally, you can just do:

julia> @eval Base show_index(io::IO, x::LogicalIndex) = summary(io, x.mask)
show_index (generic function with 5 methods)

julia> rand(4)[rand(Bool, 5)]
ERROR: BoundsError: attempt to access 4-element Vector{Float64} at index [5-element Vector{Bool}]
Stacktrace:
    ...

julia> rand(1, 4)[:, rand(Bool, 5)]
ERROR: BoundsError: attempt to access 1×4 Matrix{Float64} at index [1:1, 5-element Vector{Bool}]
Stacktrace:
    ...

julia> rand(1, 4)[rand(Bool, 1, 5)]
ERROR: BoundsError: attempt to access 1×4 Matrix{Float64} at index [1×5 Matrix{Bool}]
Stacktrace:
    ...

[JeffFessler]

Oh, I understand that level of testing of the tiny function change I made, but I also added a test to the test suite and I don't know how to locally check the test suite for a fork of julia that I can't compile. For a package I just run ] test MyPackage of course, but I don't know how to test all (or part) of julia Base in a local fork. Probably I need to RTFM :) Sure enough an error in the test was causing the CI to fail, so I've revised the test based on the CI output and try again!

[JeffFessler]

@mbauman, 5 commits later it finally passes the tests :)

[dkarrasch]

Tests are passing. So if you're satisfied with the result, @JeffFessler, I think we can merge.