scoping/escaping bug in @cfunction

[stevengj]

The Compat.@cfunction macro (#553) seems to have an escaping or scoping bug of some kind that prevents it from being used in a function. For example:

julia> using Compat

julia> foo(x) = x+1
foo (generic function with 1 method)

julia> bar() = @cfunction(foo, Int, (Int,))
bar (generic function with 1 method)

julia> bar()
ERROR: UndefVarError: foo not defined
Stacktrace:
 [1] bar() at ./REPL[3]:1

julia> baz() = cfunction(foo, Int, Tuple{Int})
baz (generic function with 1 method)

julia> baz()
Ptr{Void} @0x0000000121a79f50

cc @ararslan .

[stevengj]

It seems to be an escaping bug. Adding an esc call fixes the problem:

@static if !isdefined(Base, Symbol("@cfunction"))
    macro cfunction(f, rt, tup)
        :(Base.cfunction($(esc(f)), $rt, Tuple{$tup...}))
    end
    export @cfunction
end

I don't really understand why the esc is needed here since the first argument of cfunction is not being written to, but maybe cfunction is magic in some way?

[stevengj]

Looks like the other arguments need to be escaped too: :(Base.cfunction($(esc(f)), $(esc(rt)), Tuple{$(esc(tup))...}))

[yuyichao]

esc is needed for ALL user inputs, doesn't matter if they are written to or not. Unescaped symbols will always be interpreted as belonging to the scope of the macro. Ones that are written to will be interpreted as local variable of the macro and symbols that are not written to will be interpreted as global variable in the scope of the macro.