ghc/cygwin filename resolution issue.

Simon Peyton-Jones
Mon, 3 Feb 2003 14:21:57 -0000

Thank you Claus!  I've incorporated your section exactly as written.
It'll be in the next release of GHC.


| -----Original Message-----
| From: Claus Reinke []
| Sent: 31 January 2003 00:40
| To:
| Subject: Re: ghc/cygwin filename resolution issue.
| >As Simon M says, if you (or anyone else) felt able to write up a
| >standalone summary of what the problem is, and what the solution is,
I'd love
| >to add it to the GHC FAQ or documentation somewhere.
| Following the worse-is-better approach, here's some text for others
| to fiddle with (I'd recommend to keep the result in the GHC FAQ
| proper, possibly with a link from the building guide, if necessary).
| I've omitted the build-ghc-with-cygwin option, lest readers in search
| or solutions rush of to cause themselves even more problems;-).
| Cheers,
| Claus
| Using GHC (and other GHC-compiled executables )with cygwin
| =
| [background]
| The cygwin tools aim to provide a unix-style API on top of the windows
| libraries, to facilitate ports of unix software to windows. To this
end, they
| introduce a unix-style directory hierarchy under some root directory
| (typically / is C:\cygwin\). Moreover, everything built against the
| API (including the cygwin tools and programs compiled with cygwin's
| ghc) will see / as the root of their file system, happily pretending
to work
| in a typical unix environment, and finding things like /bin and
| without ever explicitly bothering with their actual location on the
| system (probably C:\cygwin\bin and C:\cygwin\usr\include).
| [the problem]
| GHC, by default, no longer depends on cygwin, but is a native windows
| program. It is built using mingw, and it uses mingw's ghc while
| your Haskell sources (even if you call it from cygwin's bash), but
| matters here is that - just like any other normal windows program -
| GHC nor the executables it produces are aware of cygwin's pretended
| unix hierarchy. GHC will happily accept either '/' or '\' as path
| but it won't know where to find /home/joe/Main.hs or /bin/bash or the
| like. This causes all kinds of fun when GHC is used from within
| bash, or in make-sessions running under cygwin.
| [things to do]
| 0) don't panic!
| 1) don't use absolute paths in make, configure & co if there is any
|   that those might be passed to GHC (or to GHC-compiled programs).
|   paths are fine because cygwin tools are happy with them and GHC
|   '/' as path-separator. And relative paths don't depend on where
|   root directory is located, or on which partition or network drive
your source
|   tree happens to reside, as long as you 'cd' there first.
| 2) if you have to use absolute paths (beware of the innocent-looking
|   ROOT=3D`pwd` in makefile hierarchies or configure scripts), cygwin
|   a tool called 'cygpath' that can convert cygwin's unix-style paths
to their
|   actual windows-style counterparts. Many cygwin tools actually accept
|   absolute windows-style paths (remember, though, that you either need
|   to escape '\' or convert '\' to '/'), so you should be fine just
using those
|   everywhere. If you need to use tools that do some kind of
|   that depends on unix-style paths (one fun example is trying to
interpret ':'
|   as a separator in path lists..), you can still try to convert paths
|   cygpath just before they are passed to GHC&friends.
| 3) if you don't have cygpath, you probably don't have cygwin and hence
|   no problems with it.. unless you want to write one build process for
|   platforms. Again, relative paths are your friend, but if you have to
|   absolute paths, and don't want to use different tools on different
|   you can simply write a short Haskell program to print the current
|    (thanks to George Russell for this idea): compiled with GHC, this
will give
|   you the view of the file system that GHC depends on (which will
|   depending on whether GHC is compiled with cygwin's gcc or mingw's
|   gcc or on a real unix system..) - that little program can also deal
|   escaping '\' in paths. Apart from the banner and the startup time,
|   something like this would also do:
|   $ echo "Directory.getCurrentDirectory >>=3D putStrLn . init . tail .
show " | ghci
| 4) panic now.
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