[GHC] #12674: GHC doesn't handle ./ prefixed paths correctly

[GHC]

#12674: GHC doesn't handle ./ prefixed paths correctly
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        Reporter:  dobenour          |                Owner:  RolandSenn
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Driver            |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RolandSenn):

 == The Problem

 I have looked into this and found the following:

 Assume we use:


 {{{
      ghc ./-Module.hs
 }}}


 In the module ''ghc/Main.hs'' we have the following code in the function
 ''main' '' :


 {{{
   let
      -- To simplify the handling of filepaths, we normalise all filepaths
 right
      -- away - e.g., for win32 platforms, backslashes are converted
      -- into forward slashes.
     normal_fileish_paths = map (normalise . unLoc) fileish_args
     (srcs, objs)         = partition_args normal_fileish_paths [] []

          <-- --- some lines dropped --- -->

         ---------------- Final sanity checking -----------
   liftIO $ checkOptions postLoadMode dflags6 srcs objs


 }}}



 In the ''normalise'' function the FilePath **./-Module.hs** get normalised
 to **-Module.hs**.
 Then the ''checkOptions'' function reports an error, because
 ''-Module.hs'' is not a valid flag
 and processing stops!

 I see two possible solutions to fix this:


 == The hacky solution:
 We send non-normalised filenames to the ''checkOptions'' function. Then
 the processing continues.
 But we get problems, when we send the ''-Module.hs'' file to the
 preprocessor or the
 ''-Module.o'' file to the linker. At these locations (and maybe at some
 more) we have to
 prepend the ./ to the module name again, but only if it starts with a
 hyphen.


 == The radical solution:
 We extend the function
 ''library/filepath/System/FilePath/Internal/normalise''
 so it works the following way:
      **./Module.hs**   is normalised to **Module.hs** (as it does now)

      **./-Module.hs**  is not normalised and remains **./-Module.hs**
 (this is new!!)
 This change in the library is a little bit more dangerous.

 With both solutions, only users with filenames starting with a hyphen
 should be affected.

 Please advice!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12674#comment:4>
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