[GHC] #16104: Plugin name lookup behavior change from GHC 8.4 series

[GHC]

#16104: Plugin name lookup behavior change from GHC 8.4 series
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        Reporter:  lerkok            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      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 michaelpj):

 I think we're also observing this.

 I think this is not the intended behaviour. Looking at the documentation
 of `thNameToGhcName` it says: "Qualified or unqualified TH names will be
 dynamically bound to names in the module being compiled, if possible." My
 interpretation of this was: if you can import the name qualified in the
 module being compiled when the core plugin triggers, then the name lookup
 should succeed. This seems to no longer be true.

 I can also confirm that adding (unused) imports for the modules whose
 names are being accessed makes the lookup work again.

 In our case the plugin *is* registered via a separate package and we're
 still seeing this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16104#comment:4>
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