World age error when displaying PNG images

[cormullion]

In a new Jupyter Notebook, I do this:

using FileIO; display("image/png", FileIO.load("/tmp/image.png"))

and get this error:

MethodError: no method matching show(::IOContext{Base64EncodePipe}, ::MIME{Symbol("image/png")}, 
::Array{ColorTypes.RGB4{FixedPointNumbers.Normed{UInt8,8}},2})

The applicable method may be too new: running in world age 21815, while current
world is 21860.  Closest candidates are: show(::IO,
::MIME{Symbol("image/png")}, ::AbstractArray{C<:ColorTypes.Colorant,2};
minpixels, maxpixels, mapi) where C<:ColorTypes.Colorant at
/Users/me/.julia/v0.6/Images/src/showmime.jl:23 (method too new to be called
from this world context.) show(::IO, ::MIME{Symbol("text/csv")}, ::Any) at
datafmt.jl:707 show(::IO, ::MIME{Symbol("text/tab-separated-values")}, ::Any)
at datafmt.jl:708 ...

Stacktrace: [1] limitstringmime(::MIME{Symbol("image/png")},
::Array{ColorTypes.RGB4{FixedPointNumbers.Normed{UInt8,8}},2}) at
/Users/me/.julia/v0.6/IJulia/src/inline.jl:31 [2]
display(::IJulia.InlineDisplay, ::MIME{Symbol("image/png")},
::Array{ColorTypes.RGB4{FixedPointNumbers.Normed{UInt8,8}},2}) at
/Users/me/.julia/v0.6/IJulia/src/inline.jl:41 [3]
display(::MIME{Symbol("image/png")},
::Array{ColorTypes.RGB4{FixedPointNumbers.Normed{UInt8,8}},2}) at
./multimedia.jl:208 [4] display(::String,
::Array{ColorTypes.RGB4{FixedPointNumbers.Normed{UInt8,8}},2}) at
./multimedia.jl:126 [5] include_string(::String, ::String) at ./loading.jl:515

But then when I evaluate the cell again, it works correctly; so it only generates this error the first time it runs in a notebook.

I don't really understand 'world age errors'... :(

Julia v0.6, IJulia.jl 1.6.2

[KristofferC]

I think the problem is that FileIO will load Images, but we will not hit top level scope until the call to display is executed so the world age haven't updated.

I think we can either add some invokelatest in IJulia like:

diff --git a/src/inline.jl b/src/inline.jl
index 2e82131..7cc1ee3 100644
--- a/src/inline.jl
+++ b/src/inline.jl
@@ -21,14 +21,14 @@ function limitstringmime(mime::MIME, x)
         if israwtext(mime, x)
             return String(x)
         else
-            show(IOContext(buf, :limit=>true), mime, x)
+            Base.invokelatest(show, IOContext(buf, :limit=>true), mime, x)
         end
     else
         b64 = Base64EncodePipe(buf)
         if isa(x, Vector{UInt8})
             write(b64, x) # x assumed to be raw binary data
         else
-            show(IOContext(b64, :limit=>true), mime, x)
+            Base.invokelatest(show, IOContext(b64, :limit=>true), mime, x)
         end
         close(b64)
     end

or document this somehow.

[cormullion]

Interesting. It would be nice to have it fixed in IJulia, of course! Although I'm happy to insert some (similar?) fix into Luxor.preview() if not...

[KristofferC]

You could try change e.g: https://github.com/JuliaGraphics/Luxor.jl/blob/2fec4728ef3750ba203bda0d2eb0afff4626c5a3/src/Luxor.jl#L338

to

Base.invokelatest(display, "image/png", load(currentdrawing.filename))

and see if it works.

[stevengj]

Seems similar to JuliaIO/FileIO.jl#142 ... it seems like there is a fundamental difficulty (not IJulia-specific) with how FileIO loads modules on-demand in the context of a single eval.

[cormullion]

@KristofferC That (Luxor) fix seems to work fine! It's not time critical, so I can't see any drawbacks. Thanks! I'll leave this issue open.

[stevengj]

It's not an IJulia-specific issue; the same thing would presumably happen in the REPL if you have a display backend capable of showing image/png.