FilePath causes problems (was: 'backslash' build problems on windows)

Twan van Laarhoven twanvl at
Tue Jan 15 18:41:56 EST 2008

Twan van Laarhoven wrote:
> I am having some problems with the latest builds of GHC on windows. For 
> some reason ghc has decided to use backslashes in filenames. This leads 
> to problems when building the stage libraries and the stage 2 compiler. 
> I run the scripts from a mingw bash shell.

After further investigation, it seems the problems are caused by using (</>) 
instead of joinFileName. These functions differ in two ways:

1. "." as a directory name is no longer ignored

    "." </> "x" == "./x"  /=  "x" == "." `joinFileName` "x"

    this (among other things) changes compiler messages:
      -[1 of 4] Compiling OverA            ( OverA.hs, OverA.o )
      -[2 of 4] Compiling OverB            ( OverB.hs, OverB.o )
      -[3 of 4] Compiling OverC            ( OverC.hs, OverC.o )
      +[1 of 4] Compiling OverA            ( .\OverA.hs, .\OverA.o )
      +[2 of 4] Compiling OverB            ( .\OverB.hs, .\OverB.o )
      +[3 of 4] Compiling OverC            ( .\OverC.hs, .\OverC.o )

2. a backslash is used on windows instead of a slash. Some things explicitly 
exect a slash to be used on windows as well:

   a. main/DriverPipeline.hs:1511:
	-- We hackily use Option instead of FileOption here, so that the file
	-- name is not back-slashed on Windows.  cpp is capable of
	-- dealing with / in filenames, so it works fine.  Furthermore
	-- if we put in backslashes, cpp outputs #line directives
	-- with *double* backslashes.   And that in turn means that
	-- our error messages get double backslashes in them.
	-- In due course we should arrange that the lexer deals
	-- with these \\ escapes properly.

   b. gnu make wants slashes, filenames containing backslashes are outputed 
through DriverMkDepend.

1 is a minor problem it just requires some test cases to be changed. On the 
other hand, adding "./" everywhere is needless clutter.

2a results in some warnings, 2b is a big problem, breaking the build on windows.

The only good solution I see is to switch back to joinFileName or an equivalent 


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