No, I meant this suggestion....
But there's a check box that allows the user to determine whether or not the extension should be auto-generated. If (s)he checks the box and types "App.Plugin" then (s)he'll get "App.Plugin.dll". If (s)he doesn't check the box there should be an assumption that the typed extension (if there is one) is the intended extension.
If the user types in "foo.dll" amd also checks the box, no further extension would be added (to the dll) because the functionality should be intelligent enough to realise that the extension is already the one that would have been auto-generated. This is the same scenario as if the user had only typed in "foo" (I think... it's quite some time since I looked at what happens if no extension is given but the box is also left unchecked. I might be wrong about that). However, whether I'm right or wrong about the dll naming, any associated files would be called "foo.lib", "foo.def", foo.a" or whatever is appropriate.
However, if the user types in "foo.plugin" and selects auto-generation for the extension, the resulting libraries will be "foo.plugin.dll", "foo.plugin.lib", "foo.plugin.def", "foo.plugin.a" or whatever.
Final scenario - if the user types in "foo.plugin" but doesn't select auto-generation (for the extension) the resulting libraries will be "foo.plugin", "foo.lib", "foo.def", "foo.a" etc.
Hope that makes sense.