[GHC] #13054: Generating unique names with template haskell

[GHC]

#13054: Generating unique names with template haskell
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        Reporter:  tim-m89           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 I don't see how `newName` could possibly be made to work for this purpose.
 The problem is that after you splice in a Template Haskell splice (in
 `Convert`), it has to be fed back into the renamer. But `newName` is
 designed to keep the same original name (just with a different unique), so
 the renamer will rightly reject multiple top-level things named `con2Tag`,
 even if they were produced via `newName`, as there's no good way to
 disambiguate them.

 Now, you might object "but RyanGlScott, just disambiguate them by their
 uniques!" That's all well and good, but disambiguating by uniques is
 really a strategy that I can only envision working in the internals of
 GHC. The problem is that there are adversarial users who will want to
 abuse the fact that `newName` can now be used to create top-level names.
 For instance, what happens if a user tries this?

 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}

 $(splice1) -- produces top-level function named con2Tag
 $(splice2) -- produces top-level function named con2Tag

 uhOh = con2Tag
 }}}

 Here, `con2Tag` is written using surface syntax, where we don't have the
 power to refer to the unique of the particular `con2Tag` we want. The only
 sensible thing I can see doing in this situation is to error.

 To avoid this hornet's nest of tricky design questions, I propose we not
 try to retrofit the ability to create top-level names onto `newName`, but
 instead create a different function for this purpose.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13054#comment:9>
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