Doctest failures on julia 0.6 related to world age counter

[ajkeller34]

I'm encountering a doctest failure on Julia 0.6.0-dev (built yesterday) which is related to the newly-implemented world age counter (JuliaLang/julia#17057). I've made a minimal example in a mockup package that I'll call DocumenterTest. Here's the code:

module DocumenterTest

immutable TestType{T} end

function _show end
Base.show(io::IO, t::TestType) = _show(io, t)

macro define_show_and_make_object(x, y)
    z = Expr(:quote, x)
    esc(quote
        DocumenterTest._show(io::IO, t::DocumenterTest.TestType{$z}) = print(io, $y)
        const $x = DocumenterTest.TestType{$z}()
    end)
end

end # module

At the REPL you may try using the macro, which defines a method for show and makes an object:

julia> DocumenterTest.@define_show_and_make_object q "abcd"
abcd

julia> q
abcd

julia> DocumenterTest.TestType{:q}()
abcd

Now suppose we open a new Julia session. If we try to run Documenter with the following markdown file, the doctest will error (pretend I used three backticks, I'm not sure how to get the formatting right here):

``@meta
DocTestSetup = quote
    using DocumenterTest
end
``

``jldoctest
julia> DocumenterTest.@define_show_and_make_object q "abcd"
abcd
``

The output from the doctest is the following error instead of "abcd":

MethodError: no method matching _show(::IOContext{Base.AbstractIOBuffer{Array{UInt8,1}}}, ::DocumenterTest.TestType{:q})
The applicable method may be too new: running in world age 20490, while current world is 20492.
Closest candidates are:
  _show(::IO, ::DocumenterTest.TestType{:q}) at /Users/ajkeller/.julia/v0.6/DocumenterTest/src/DocumenterTest.jl:12 (method too new to be called from this world context.)

[MichaelHatherly]

If it's specific to show-related code then perhaps just needs something like

diff --git a/src/DocChecks.jl b/src/DocChecks.jl
index 7d229d6..5cb9674 100644
--- a/src/DocChecks.jl
+++ b/src/DocChecks.jl
@@ -271,7 +271,7 @@ end

 function result_to_string(buf, value)
     dis = text_display(buf)
-    value === nothing || display(dis, value)
+    value === nothing || eval(Expr(:call, display, dis, value))
     sanitise(buf)
 end

perhaps. Does that help at all?

[ajkeller34]

Yes, that seems to solve both my test case and my problem-in-the-wild. Thank you!

[MichaelHatherly]

Fix will be part of 0.8.9 to be tagged shortly.