make REPL ast transforms instance-specific (#34626)

stdlib/REPL/src/REPL.jl

@@ -66,20 +66,28 @@ mutable struct REPLBackend
  response_channel::Channel
  "flag indicating the state of this backend"
  in_eval::Bool
+ "transformation functions to apply before evaluating expressions"
+ ast_transforms::Vector{Any}
  "current backend task"
  backend_task::Task
 
- REPLBackend(repl_channel, response_channel, in_eval) =
- new(repl_channel, response_channel, in_eval)
+ REPLBackend(repl_channel, response_channel, in_eval, ast_transforms=copy(repl_ast_transforms)) =
+ new(repl_channel, response_channel, in_eval, ast_transforms)
 end
 
-function softscope!(ex)
+"""
+ softscope(ex)
+
+Return a modified version of the parsed expression `ex` that uses
+the REPL's "soft" scoping rules for global syntax blocks.
+"""
+function softscope(@nospecialize ex)
  if ex isa Expr
  h = ex.head
  if h === :toplevel
- for i = 1:length(ex.args)
-  ex.args[i] = softscope!(ex.args[i])
- end
+ ex′ = Expr(h)
+ map!(softscope, resize!(ex′.args, length(ex.args)), ex.args)
+ return ex′
  elseif h in (:meta, :import, :using, :export, :module, :error, :incomplete, :thunk)
  return ex
  else
@@ -89,7 +97,10 @@ function softscope!(ex)
  return ex
 end
 
-const repl_ast_transforms = Any[softscope!]
+# Temporary alias until Documenter updates
+const softscope! = softscope
+
+const repl_ast_transforms = Any[softscope] # defaults for new REPL backends
 
 function eval_user_input(@nospecialize(ast), backend::REPLBackend)
  lasterr = nothing
@@ -101,7 +112,7 @@ function eval_user_input(@nospecialize(ast), backend::REPLBackend)
  put!(backend.response_channel, (lasterr,true))
  else
  backend.in_eval = true
- for xf in repl_ast_transforms
+ for xf in backend.ast_transforms
  ast = xf(ast)
  end
  value = Core.eval(Main, ast)