[REPL] fix type confusion resulting in nonsensical errors (#58414)

Author: vtjnash

stdlib/REPL/src/REPL.jl

@@ -452,8 +452,8 @@ function repl_backend_loop(backend::REPLBackend, get_module::Function)
             try
                 ret = f()
                 put!(backend.response_channel, Pair{Any, Bool}(ret, false))
-            catch err
-                put!(backend.response_channel, Pair{Any, Bool}(err, true))
+            catch
+                put!(backend.response_channel, Pair{Any, Bool}(current_exceptions(), true))
             end
         else
             ast = ast_or_func
@@ -594,11 +594,11 @@ function print_response(errio::IO, response, backend::Union{REPLBackendRef,Nothi
                 if val !== nothing && show_value
                     val2, iserr = if specialdisplay === nothing
                         # display calls may require being run on the main thread
-                        eval_with_backend(backend) do
+                        call_on_backend(backend) do
                             Base.invokelatest(display, val)
                         end
                     else
-                        eval_with_backend(backend) do
+                        call_on_backend(backend) do
                             Base.invokelatest(display, specialdisplay, val)
                         end
                     end
@@ -715,7 +715,7 @@ function run_frontend(repl::BasicREPL, backend::REPLBackendRef)
             (isa(ast,Expr) && ast.head === :incomplete) || break
         end
         if !isempty(line)
-            response = eval_with_backend(ast, backend)
+            response = eval_on_backend(ast, backend)
             print_response(repl, response, !ends_with_semicolon(line), false)
         end
         write(repl.terminal, '\n')
@@ -1166,21 +1166,23 @@ find_hist_file() = get(ENV, "JULIA_HISTORY",
 backend(r::AbstractREPL) = hasproperty(r, :backendref) ? r.backendref : nothing
 
 
-function eval_with_backend(ast::Expr, backend::REPLBackendRef)
+function eval_on_backend(ast, backend::REPLBackendRef)
     put!(backend.repl_channel, (ast, 1)) # (f, show_value)
     return take!(backend.response_channel) # (val, iserr)
 end
-function eval_with_backend(f, backend::REPLBackendRef)
+function call_on_backend(f, backend::REPLBackendRef)
+    applicable(f) || error("internal error: f is not callable")
     put!(backend.repl_channel, (f, 2)) # (f, show_value) 2 indicates function (rather than ast)
     return take!(backend.response_channel) # (val, iserr)
 end
 # if no backend just eval (used by tests)
-function eval_with_backend(f, backend::Nothing)
+eval_on_backend(ast, backend::Nothing) = error("no backend for eval ast")
+function call_on_backend(f, backend::Nothing)
     try
         ret = f()
         return (ret, false) # (val, iserr)
-    catch err
-        return (err, true)
+    catch
+        return (current_exceptions(), true)
     end
 end
 
@@ -1196,7 +1198,7 @@ function respond(f, repl, main; pass_empty::Bool = false, suppress_on_semicolon:
             local response
             try
                 ast = Base.invokelatest(f, line)
-                response = eval_with_backend(ast, backend(repl))
+                response = eval_on_backend(ast, backend(repl))
             catch
                 response = Pair{Any, Bool}(current_exceptions(), true)
             end
@@ -1803,7 +1805,7 @@ function run_frontend(repl::StreamREPL, backend::REPLBackendRef)
             if have_color
                 print(repl.stream, Base.color_normal)
             end
-            response = eval_with_backend(ast, backend)
+            response = eval_on_backend(ast, backend)
             print_response(repl, response, !ends_with_semicolon(line), have_color)
         end
     end