[GHC] #16167: -ddump-json output empty with runghc

[GHC]

#16167: -ddump-json output empty with runghc
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        Reporter:  shmish111         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Incorrect         |  (amd64)
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by shmish111):

 Ok, I seem to have narrowed it down to the `-e ":set prog Main.hs"` flag

 ```
 [nix-shell:~]$ ghc --version
 The Glorious Glasgow Haskell Compilation System, version 8.4.4

 [nix-shell:~]$ ghc -x hs -e ":set prog Main.hs" -ddump-json Main2.hs

 Main2.hs:4:8: error:
     • Variable not in scope: undefinedx :: IO ()
     • Perhaps you meant ‘undefined’ (imported from Prelude)
   |
 4 | main = undefinedx
   |        ^^^^^^^^^^
 []

 ```

 ```
 [nix-shell:~]$ ghc --version
 The Glorious Glasgow Haskell Compilation System, version 8.6.3

 [nix-shell:~]$ ghc -x hs -e ":set prog Main.hs" -ddump-json Main2.hs

 Main2.hs:4:8: error:
     • Variable not in scope: undefinedx :: IO ()
     • Perhaps you meant ‘undefined’ (imported from Prelude)
   |
 4 | main = undefinedx
   |        ^^^^^^^^^^

 ```

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16167#comment:4>
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