+Note [Splices]
+~~~~~~~~~~~~~~
+Consider
+ f = ...
+ h = ...$(thing "f")...
+
+The splice can expand into literally anything, so when we do dependency
+analysis we must assume that it might mention 'f'. So we simply treat
+all locally-defined names as mentioned by any splice. This is terribly
+brutal, but I don't see what else to do. For example, it'll mean
+that every locally-defined thing will appear to be used, so no unused-binding
+warnings. But if we miss the dependency, then we might typecheck 'h' before 'f',
+and that will crash the type checker because 'f' isn't in scope.
+
+Currently, I'm not treating a splice as also mentioning every import,
+which is a bit inconsistent -- but there are a lot of them. We might
+thereby get some bogus unused-import warnings, but we won't crash the
+type checker. Not very satisfactory really.
+