true === nothing when expanding macro.

[thautwarm]

This was detected when I tried to test my project MLStyle with JuliaPro 1.0.1.1 on Windows 10(64 bit), and a very ridiculous bug showed up at that time.
After that I made efforts to reproduce it without codes that depends MLStyle .
I simplify it to quite a simple case:

A = 1
B = 2

code = """
begin
    begin
        let test = x
            begin
                begin
                    let test = let
                                begin
                                    if test == 1
                                        begin
                                            println("shouldn't be nothing!")
                                            y !== 1
                                        end
                                    else
                                        nothing
                                    end
                                end
                            end

                        println("test = ", test, " => ", " `test === nothing` = ", test === nothing)
                        # true, true !!!!!!
                        if test === nothing
                            begin
                                @error "unexpected"
                            end
                        else
                            test
                        end
                    end
                end
            end
        end
    end
end
"""
ast = Meta.parse(code)

macro apply(ast)
     ast = eval(ast)
     esc(:($ast))
end

function g()
    x = 1
    y = 2
    @apply ast
end
g()

output log:

julia> include("temp/b.jl")
shouldn't be nothing!
test = true =>  `test === nothing` = true
┌ Error: unexpected
└ @ Main none:23

P.S: Only when it's inside a function, true === nothing error occurs in macro expanding, and no macro expanding works well, too.

[KristofferC]

FWIW, seems a bit similar to #29253 but that was only on master I think.

[KristofferC]

Good MWE makes for fast fixes :)