Introduce package dependencies that are only used for development, eliminating "runtime-free" macro packages such as MLStyle.jl.

Suppose we have such a module:

module MyMod

using DevOnly
@devonly using MLStyle

f(x) = @match x begin
    1 => :one
    2 => :two
    _ => :other
end

end

Then we create a script by copying regenerate.jl to the root directory of the package, and run it:

> julia regenerate.jl

Then we can use MyMod without including MLStyle.jl:

Pkg.activate(".")
using MyMod

# MLStyle is not loaded!
isdefined(MyMod, :MLStyle) # => false

# but the macro works!

f(1) # :one
f(2) # :two
f(3) # :other

Change regenerate.jl, set julia_compiler to a path to an early Julia version.

julia_compiler = "/path/to/julia-1.5"

Then run regenerate.jl again.