document REPL `ast_transforms`

[stevengj]

Julia 1.5 includes a REPL ast_transforms variable initially added for the softscope transformation (#33864) but expanded for use by other packages (#34626, #34778), that is starting to be used by other packages. It is currently being used by Revise (timholy/Revise.jl#425), support will probably be added soon in IJulia (for the REPL.repl_ast_transforms defaults), and it might be used in the future by things like OhMyREPL.

We might consider documenting it somewhere. Maybe adding a slightly higher-level API, e.g.

REPL.current_ast_transforms() = isdefined(Base, :active_repl_backend) ? Base.active_repl_backend.ast_transforms : REPL.repl_ast_transforms

[stevengj]

Or maybe it should be part of repl.options (the REPL.Options struct)?

[rfourquet]

Maybe adding a slightly higher-level API, e.g.

REPL.current_ast_transforms() = isdefined(Base, :active_repl_backend) ? Base.active_repl_backend.ast_transforms : REPL.repl_ast_transforms

FWIW, this is almost exactly what SafeREPL uses.

[stevengj]

Note that there is the undocumented function REPL.Numbered.__current_ast_transforms():

julia/stdlib/REPL/src/REPL.jl

Line 1786 in 39f2ad1

__current_ast_transforms() = Base.active_repl_backend !== nothing ? Base.active_repl_backend.ast_transforms : REPL.repl_ast_transforms