[GHC] #9403: Make --show-iface more human readable

[GHC]

#9403: Make --show-iface more human readable
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       Reporter:  ezyang             |                   Owner:  ezyang
           Type:  task               |                  Status:  new
       Priority:  low                |               Milestone:
      Component:  Compiler           |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:  Other
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
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 Right now --show-iface is not particularly interpretable, even if you are
 looking at the Outputable instance for `ModIface`. The problem seems to be
 the output for `mi_deps`, `mi_usages`, `mi_decls`, `mi_insts`,
 `mi_fam_insts` and `mi_rules` is not clearly delimited, making it unclear
 (for example) what `import  -/  base:Prelude HASH` refers to unless you
 already happen to know that this must be from `mi_usages`.

 It should be relatively easy to improve this, but I want to make sure
 people who rely on this output aren't blindsided by the changes.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9403>
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