problem with doctests for code that writes to `stdout`

[ThomasBreuer]

The following works in a Julia session (version 1.5 or 1.6 or 1.7.0-DEV), but I get the error message ERROR: IOError: stream is closed or unusable when it is run as a doctest.

julia> io = IOContext(stdout);

julia> println(io, "abc")
abc

Note that the following code works as a doctest as well as in a Julia session.

julia> println(stdout, "abc")
abc

julia> println(IOContext(stdout), "abc")
abc

(See oscar-system/Oscar.jl/pull/445 for some context. Perhaps the problem is related to issue #1245, at least the topic and the error message fit.)

[mortenpi]

You're running into this: https://github.com/JuliaDocs/IOCapture.jl/#separately-stored-stdout-or-stderr-objects

It's a limitation on how we implement the output capture. Definitely a bug, but I am not sure there's an easy fix.

[ThomasBreuer]

Thanks. I will use a workaround as long as the problem is present.

[findmyway]

I'm also getting this error when the example code involves ProgressMeter.jl.

[ericphanson]

I wonder if there's some way to use same redirected IO streams can be used for each capture invocation within a block, rather than separate streams each time[^1]. That would fix examples like

using ProgressMeter
prog = ProgressThresh(1e-5; desc="Minimizing:")
for val in exp10.(range(2, stop=-6, length=20))
    update!(prog, val)
    sleep(0.1)
end

where stderr is being captured in the prog = line, but it gets closed after the line executes, before the for-loop.

I guess a workaround in cases like that is an extra begin or let block;

using ProgressMeter
begin
    prog = ProgressThresh(1e-5; desc="Minimizing:")
    for val in exp10.(range(2, stop=-6, length=20))
        update!(prog, val)
        sleep(0.1)
    end
end

so that documenter executes the whole block within a single capture invocation.

[^1]: I'm not sure this is actually easy, since we want to close the streams to ensure we get all the outputs from that line before moving to the next one.