Error with optional argument in anonymous function defined in macro

[zsunberg]

In Julia 1.5.0 beta 1, the following fails:

macro m()
    :((a, b=1) -> a*b)
end
@m()(1)

with

ERROR: UndefVarError: b not defined
Stacktrace:
 [1] (::var"#1#2")(::Int64, ::Int64) at ./REPL[1]:3 (repeats 2 times)
 [2] top-level scope at REPL[1]:3

The reason I want to do this is here: https://github.com/JuliaPOMDP/POMDPs.jl/blob/609fe87094d4b1b01993deb0514565450266547f/src/generative.jl#L189. A workaround is to name the function.

[zsunberg]

Success/failure in julia versions:

• 1.0.3: success
• 1.1.0: success
• 1.2.0: fail
• 1.4.1: fail

[simeonschaub]

That's definitely a bug with macro hygiene:

julia> @macroexpand @m
:((var"#14#a", b = 1)->begin
          #= REPL[1]:2 =#
          var"#14#a" * Main.b
      end)

Seems like hygiene is not aware of the optional argument b and so the b in the function body is interpreted as a global.