REPL: make UndefVarError aware of imported modules (#55932)

(cherry picked from commit fbb3e11)

base/experimental.jl

@@ -319,9 +319,9 @@ function show_error_hints(io, ex, args...)
     for handler in hinters
         try
             @invokelatest handler(io, ex, args...)
-        catch err
+        catch
             tn = typeof(handler).name
-            @error "Hint-handler $handler for $(typeof(ex)) in $(tn.module) caused an error"
+            @error "Hint-handler $handler for $(typeof(ex)) in $(tn.module) caused an error" exception=current_exceptions()
         end
     end
 end

stdlib/REPL/src/REPL.jl

@@ -81,7 +81,17 @@ end
 function _UndefVarError_warnfor(io::IO, m::Module, var::Symbol)
     Base.isbindingresolved(m, var) || return false
     (Base.isexported(m, var) || Base.ispublic(m, var)) || return false
-    print(io, "\nHint: a global variable of this name also exists in $m.")
+    active_mod = Base.active_module()
+    print(io, "\nHint: ")
+    if isdefined(active_mod, Symbol(m))
+        print(io, "a global variable of this name also exists in $m.")
+    else
+        if Symbol(m) == var
+            print(io, "$m is loaded but not imported in the active module $active_mod.")
+        else
+            print(io, "a global variable of this name may be made accessible by importing $m in the current active module $active_mod")
+        end
+    end
     return true
 end