Fix world age errors with show(eval_result) (#27)

We use `show` to format the user's evaluation result, but this is done
from outside of `eval` so we need to ensure it's running in the latest
world.

Project.toml

@@ -1,7 +1,7 @@
 name = "RemoteREPL"
 uuid = "1bd9f7bb-701c-4338-bec7-ac987af7c555"
 authors = ["Chris Foster <[email protected]> and contributors"]
-version = "0.2.9"
+version = "0.2.10"
 
 [deps]
 Logging = "56ddb016-857b-54e1-b83d-db4d58db5568"

src/server.jl

@@ -45,7 +45,10 @@ function eval_message(display_properties, messageid, messagebody)
                     expr = preprocess_expression!(messagebody, io)
                     result = Main.eval(expr)
                     if messageid === :eval && !isnothing(result)
-                        show(io, MIME"text/plain"(), result)
+                        # We require invokelatest here in case the user
+                        # modifies any method tables after starting the session,
+                        # which change methods of `show`
+                        Base.invokelatest(show, io, MIME"text/plain"(), result)
                     end
                 end
             end
@@ -55,7 +58,7 @@ function eval_message(display_properties, messageid, messagebody)
         elseif messageid === :help
             resultstr = sprint_ctx(display_properties[]) do io
                 md = Main.eval(REPL.helpmode(io, messagebody))
-                show(io, MIME"text/plain"(), md)
+                Base.invokelatest(show, io, MIME"text/plain"(), md)
             end
             return (:help_result, resultstr)
         elseif messageid === :display_properties
@@ -73,7 +76,7 @@ function eval_message(display_properties, messageid, messagebody)
         end
     catch _
         resultstr = sprint_ctx(display_properties[]) do io
-            Base.display_error(io, Base.catch_stack())
+            Base.invokelatest(Base.display_error, io, Base.catch_stack())
         end
         return (:error, resultstr)
     end

test/runtests.jl

@@ -141,6 +141,24 @@ try
     # Special case handling of stdout
     @test runcommand("println(@remote(stdout), \"hi\")") == "hi\n"
 
+    # Issue #26: world age errors showing output
+    @test runcommand("""
+        struct A
+        end
+
+        Base.show(io::IO, a::A) = print(io, "Surprise")
+
+        A()
+        """) == "Surprise"
+    @test occursin("Surprise", runcommand("""
+        struct MyExc <: Exception
+        end
+
+        Base.showerror(io::IO, e::MyExc) = print(io, "Surprise")
+
+        throw(MyExc())
+        """))
+
     # Execute a single command on a separate connection
     @test (RemoteREPL.remote_eval(test_interface, test_port, "asdf")::Text).content == "42"