getShortPathName returns invalid response in Cygwin

[NovaDenizen]

I installed Haskell Platform 8.0.1 into C:\HPlat, so gcc is at "c:\HPlat\8.0.1\mingw\bin\gcc.exe"

$ uname -a
CYGWIN_NT-6.0 myhostnameI 2.5.2(0.297/5/3) 2016-06-23 14:29 x86_64 Cygwin

$ cygpath -d "c:\\HPlat\\8.0.1\\mingw\\bin\\gcc.exe"
C:\HPlat\80227D~1.1\mingw\bin\gcc.exe

$ cygpath -l -w 'C:\HPlat\80227D~1.1\mingw\bin\gcc.exe'
C:\HPlat\8.0.1\mingw\bin\gcc.exe

$ cd ~/dl/Cabal-1.24.0.0/
$ stack repl
...much deleted...
...stribution.Version Language.Haskell.Extension> getShortPathName "c:\\HPlat\\8.0.1\\mingw\\bin\\gcc.exe"
"c:\\HPlat\\80227D~1.1"
...stribution.Version Language.Haskell.Extension>:q

$ cmd /version
Microsoft Windows [Version 6.0.6002]
Copyright (c) 2006 Microsoft Corporation.  All rights reserved.

[ezyang]

CC @23Skidoo who wrote this code.

Since cygpath computes short path correctly, we can look at its source code to see how to do it properly http://cygwin-ports.sourceforge.net/scan-build/utils/report-MWMmDX.html

From GetShortPath docs:

The path that the lpszLongPath parameter specifies does not have to be a full or long path. The short form can be longer than the specified path.

So I guess the problem is that the sample path above shortens to something longer, violating the assumption our code makes (which allocates a buffer based on the length of the input path + 1).

[NovaDenizen]

Found the way to fix it from here

Passing NULL for this parameter and zero for cchBuffer will always return the required buffer size for a specified lpszLongPath.

[NovaDenizen]

#3487 seems related too.

[ezyang]

Thanks, I think it is indeed this bug!

[ezyang]

I would close this but if we do a point release for 1.24.0.1 we should put this patch in.

[23Skidoo]

Already cherry-picked into 1.24, so closing.