Revert "clean up identifiers defined in Main (#51411)" (#51825)

This reverts commit ab94a24.

Ref
#51411 (comment)
fixes #51823

base/client.jl

@@ -261,8 +261,8 @@ function exec_options(opts)
     distributed_mode = (opts.worker == 1) || (opts.nprocs > 0) || (opts.machine_file != C_NULL)
     if distributed_mode
         let Distributed = require(PkgId(UUID((0x8ba89e20_285c_5b6f, 0x9357_94700520ee1b)), "Distributed"))
-            Core.eval(MainInclude, :(const Distributed = $Distributed))
-            Core.eval(Main, :(using Base.MainInclude.Distributed))
+            Core.eval(Main, :(const Distributed = $Distributed))
+            Core.eval(Main, :(using .Distributed))
         end
 
         invokelatest(Main.Distributed.process_opts, opts)
@@ -384,18 +384,19 @@ _atreplinit(repl) = invokelatest(__atreplinit, repl)
 
 function load_InteractiveUtils(mod::Module=Main)
     # load interactive-only libraries
-    if !isdefined(MainInclude, :InteractiveUtils)
+    if !isdefined(mod, :InteractiveUtils)
         try
             let InteractiveUtils = require(PkgId(UUID(0xb77e0a4c_d291_57a0_90e8_8db25a27a240), "InteractiveUtils"))
-                Core.eval(MainInclude, :(const InteractiveUtils = $InteractiveUtils))
+                Core.eval(mod, :(const InteractiveUtils = $InteractiveUtils))
+                Core.eval(mod, :(using .InteractiveUtils))
+                return InteractiveUtils
             end
         catch ex
             @warn "Failed to import InteractiveUtils into module $mod" exception=(ex, catch_backtrace())
-            return nothing
         end
+        return nothing
     end
-    Core.eval(mod, :(using Base.MainInclude.InteractiveUtils))
-    return MainInclude.InteractiveUtils
+    return getfield(mod, :InteractiveUtils)
 end
 
 function load_REPL()
@@ -512,6 +513,10 @@ A variable referring to the last thrown errors, automatically imported to the in
 The thrown errors are collected in a stack of exceptions.
 """
 global err = nothing
+
+# weakly exposes ans and err variables to Main
+export ans, err
+
 end
 
 """

base/sysimg.jl

@@ -4,6 +4,10 @@ Core.include(Main, "Base.jl")
 
 using .Base
 
+# Set up Main module
+using Base.MainInclude # ans, err, and sometimes Out
+import Base.MainInclude: eval, include
+
 # Ensure this file is also tracked
 pushfirst!(Base._included_files, (@__MODULE__, abspath(@__FILE__)))
 
@@ -75,10 +79,7 @@ let
     empty!(LOAD_PATH)
     Base.init_load_path() # want to be able to find external packages in userimg.jl
 
-    # Set up Main module
     ccall(:jl_clear_implicit_imports, Cvoid, (Any,), Main)
-    eval(Main, :(using Base.MainInclude: eval, include, ans, err))
-
     tot_time_userimg = @elapsed (isfile("userimg.jl") && Base.include(Main, "userimg.jl"))
 
     tot_time_base = (Base.end_base_include - Base.start_base_include) * 10.0^(-9)

stdlib/REPL/src/REPL.jl

@@ -1490,8 +1490,8 @@ function capture_result(n::Ref{Int}, @nospecialize(x))
     mod = Base.MainInclude
     if !isdefined(mod, :Out)
         @eval mod global Out
+        @eval mod export Out
         setglobal!(mod, :Out, Dict{Int, Any}())
-        @eval Main using Base.MainInclude: Out
     end
     if x !== getglobal(mod, :Out) && x !== nothing # remove this?
         getglobal(mod, :Out)[n] = x

stdlib/REPL/test/replcompletions.jl

@@ -2089,3 +2089,6 @@ let t = REPLCompletions.repl_eval_ex(:(`a b`), @__MODULE__; limit_aggressive_inf
     @test t isa Core.Const
     @test t.val == `a b`
 end
+
+# issue #51823
+@test "include" in test_complete_context("inc", Main)[1]

test/client.jl

@@ -52,3 +52,8 @@ end
         ERROR: ErrorException
         """s, err_str)
 end
+
+@testset "defining `ans` and `err`" begin
+    @test eval(:(ans = 1)) == 1
+    @test eval(:(err = 1)) == 1
+end