[GHC] #9056: --make paths are not deduplicated

[GHC]

#9056: --make paths are not deduplicated
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        Reporter:  evincarofautumn   |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Driver            |                 Version:  7.8.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by thomie):

 I was working on a patch for this (attached, unfinished), but now don't
 think there's actually a bug here. I find the current error message quite
 clear, and think that it can be expected from a build system or the user
 not to supply the same filename twice. Please do reopen if you disagree,
 perhaps as a feature request.

 Fwiw: gcc doesn't seem to deduplicate input filenames either, giving a
 similar error message.

 {{{
 $ cat test.c
 int main(void) {
   return 0;
   }

 $ gcc test.c test.c
 /tmp/ccL0QwIZ.o: In function `main':
 test.c:(.text+0x0): multiple definition of `main'
 /tmp/ccxMTZBK.o:test.c:(.text+0x0): first defined here
 collect2: error: ld returned 1 exit status
 }}}

 If we do want this:

 It is not as simple as just deduplicating filenames. For starters,
 comparing paths with (==) returns False for `./foo` and `foo`, so
 `System.FilePath.equalFilePaths` should be used. But what about relative
 vs absolute paths? What about `Main` and `Main.hs`, are they the same?
 What about `Main.lhs` and `Main.hs`?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9056#comment:2>
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