GTK fails to precompile against master: ccall - type - typevar

[colbec]

In

Commit b46df09eb6* (2021-05-31 02:08 UTC)
Platform Info:
  OS: Linux (x86_64-suse-linux)
  CPU: Intel(R) Core(TM) i5-4460  CPU @ 3.20GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.0 (ORCJIT, haswell)

precompile of GTK, GTKReactive and ImageView all fail. Problem started about 3 days ago. Precompile is fine in Julia 1.6.1.

Assuming that GTK is the most fundamental requirement, here is the relevant error output:

ERROR: LoadError: TypeError: in ccall method definition, expected Type, got a value of type TypeVar
Stacktrace:
  [1] top-level scope
    @ ~/.julia/packages/Gtk/3TfRG/src/GLib/signals.jl:331
  [2] include(mod::Module, _path::String)
    @ Base ./Base.jl:389
  [3] include(x::String)
    @ Gtk.GLib ~/.julia/packages/Gtk/3TfRG/src/GLib/GLib.jl:1
  [4] top-level scope
    @ ~/.julia/packages/Gtk/3TfRG/src/GLib/GLib.jl:62
  [5] include(mod::Module, _path::String)
    @ Base ./Base.jl:389
  [6] include(x::String)
    @ Gtk ~/.julia/packages/Gtk/3TfRG/src/Gtk.jl:2
  [7] top-level scope
    @ ~/.julia/packages/Gtk/3TfRG/src/Gtk.jl:17
  [8] include
    @ ./Base.jl:389 [inlined]
  [9] include_package_for_output(pkg::Base.PkgId, input::String, depot_path::Vector{String}, dl_load_path::Vector{String}, load_path::Vector{String}, concrete_deps::Vector{Pair{Base.PkgId, UInt64}}, source::String)
    @ Base ./loading.jl:1232
 [10] top-level scope
    @ none:1
 [11] eval
    @ ./boot.jl:369 [inlined]
 [12] eval(x::Expr)
    @ Base.MainInclude ./client.jl:453
 [13] top-level scope
    @ none:1
in expression starting at /home/colin/.julia/packages/Gtk/3TfRG/src/GLib/signals.jl:331
in expression starting at /home/colin/.julia/packages/Gtk/3TfRG/src/GLib/GLib.jl:1
in expression starting at /home/colin/.julia/packages/Gtk/3TfRG/src/Gtk.jl:2

[gustaphe]

Can reproduce, in a fresh project with only Gtk.

julia 1.7.0-DEV.1244, Commit 8535b8c4d7
Gtk 1.1.7

[oscardssmith]

Confirming this. Any chance it can be fixed? It's breaking ProfileView.

[colbec]

I looked at this and found that a couple of functions are declared in signals.jl:

function uv_check(src::Ptr{Nothing})
    global expiration
    ex = expiration::UInt64
    if !_isempty_workqueue()
        return Int32(1)
    elseif !uv_loop_alive(Base.eventloop())
        return Int32(0)
    elseif ex == 0
        return Int32(1)
    elseif uv_pollfd.revents != 0
        return Int32(1)
    else
        now = ccall((:g_source_get_time, GLib.libglib), UInt64, (Ptr{Nothing},), src)
        return Int32(ex <= now)
    end
end
function uv_dispatch(src::Ptr{Nothing}, callback::Ptr{Nothing}, data::T) where T
    return ccall(callback, Cint, (T,), data)
end

The problem is in the uv_dispatch() function, the third argument to the ccall() function:
ccall(callback, Cint, (T,), data)
should be more like
ccall(callback, Cint, (Ptr{Nothing}), data)
and this actually works (as in passes syntax check) in the REPL, but I have no idea what that argument should really be, so cannot make a PR.

[giordano]

See JuliaLang/julia#41278

[jonathanBieler]

I'm not too sure but looking at Gtk's doc the data parameter is typed as gpointer which is an alias for void*, so I suspect Ptr{Cvoid} might be correct.

https://developer.gnome.org/glib/stable/glib-The-Main-Event-Loop.html#g-source-set-callback

Tried it but it doesn't work, no method matching unsafe_convert(::Type{Ptr{Nothing}}, ::Int64).

[jonathanBieler]

I tried to come up with a minimal example, as I understand callbacks can be any user defined function, and data can be anything as well so the situation is a bit like this :

test(x,y) = begin @show x, y ; true end

call_fun(f, data::T) where T  = ccall(f, Bool, (T,), data) # this is our uv_dispatch

funs = [@cfunction(test, Bool, (Int, Int)), @cfunction(test, Bool, (Float64, Float64))]
data = [(1,2), (1.0, 2.0)]

call_fun.(funs, data)

But this doesn't work (test prints gibberish instead of the correct values on v1.6), so something must be missing. That said if you define :

@generated function call_fun(f, data)
    :( ccall(f, Bool, ($(data),), data) )
end

Then it works (all Gtk's test pass in v1.8 with this solution). I find this a bit strange because in mind my mind the two call_fun should be equivalent. When I pass some data::T the compiler should compile a version of the function where T is the type of of data, which is what @generated does as well, but at a different stage. Obviously I don't understand everything here...

Edit : this explains why my example doesn't work : https://docs.julialang.org/en/v1/manual/calling-c-and-fortran-code/#Type-Parameters