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

[GHC]

#16167: -ddump-json output empty with runghc
-------------------------------------+-------------------------------------
        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 mpickering):

 With 8.6.2,

 {{{
 > ghc f.hs -fforce-recomp  -ddump-json
 {"span": null,"doc": "Loaded package environment from /root/sql-
 haskell/.ghc.environment.x86_64-linux-8.6.2","severity":
 "SevInfo","reason": null}
 {"span": {"file": "f.hs","startLine": 1,"startCol": 8,"endLine":
 1,"endCol": 9},"doc": "parse error on input \u2018f\u2019","severity":
 "SevError","reason": null}
 }}}

 {{{
 > runghc f.hs  -fforce-recomp  -ddump-json
 Loaded package environment from /root/sql-
 haskell/.ghc.environment.x86_64-linux-8.6.2

 f.hs:1:8: error: parse error on input ‘f’
   |
 1 | module f
   |
 }}}

 I'm not sure why `runghc` behaves differently.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16167#comment:3>
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