implement Base.redirect_{stdout,stderr,stdin}

[rdeits]

Fixes #640. Please let me know if this isn't the appropriate solution to the problem.

[stevengj]

You are calling redirect_stdout twice...

[stevengj]

Oh, I see, you're calling the overloaded method below...

[JobJob]

Datapoint: this fixes TraceCalls in IJulia (cstjean/TraceCalls.jl#60) which makes me happy.

[stevengj]

This doesn't seem right to me. It's not returning the documented (rd, wr) pair...

[rdeits]

The documentation seems to be wrong in this case. Calling redirect_stdout(STDERR), for example, just returns STDERR. See: https://github.com/JuliaLang/julia/blob/v0.6.2/base/stream.jl#L1031

[rdeits]

JuliaLang/julia#26558

[stevengj]

I guess it's only called for restoring the original STDOUT stream in redirect_*. In that case, however, probably check that this is the case. Something like:

for s in ("stdout", "stderr", "stdin")
    f = Symbol("redirect_", s)
    S = QuoteNode(Symbol(uppercase(s)))
    @eval function Base.$f(io::IJuliaStdio)
        io[:jupyter_stream] != $s && error("expecting ", $s, " stream)
        eval(Base, Expr(:=, $S, :io))
        return io, io
    end
end

[rdeits]

Sure, we can do that. It does seem a bit odd for the return type to be inconsistent with the Base implementation of redirect_stdout(STDOUT), though, doesn't it?

[stevengj]

Oh, I didn't notice that redirect_stdout(STDOUT) returned only a single stream. That seems like a bug in base, since redirect_stdout is documented to return two streams. Ah, now I see that you filed an issue for that.

But sure, in that case do return io rather than return io, io. But we should still check that it is restoring the correct stream.

[rdeits]

Ok, done

[chethega]

Datapoint: Before this patch, I got error #640 on the following in jupyter. After this patch, the julia kernel hangs somewhere (no CPU consumption; still reacts to "restart kernel", but does not react to "interrupt kernel"). On the REPL, this works like expected.

using Suppressor
output = @capture_out begin
    println("should get captured, not printed")
end;
@show output;