cairo (and things it depends on) fails to install on MSYS2

[RyanGlScott]

I'm using MSYS2-x86_64-20150916 on Windows 8.1. I noticed that cairo and, by extension, anything that depends on cairo (i.e., all gtk-related packages) fails to install without some gross hacks. Here's some output to show you what's going on:

$ cabal get cairo
$ cd cairo-0.13.1.0/
$ cabal sandbox init
$ cabal install --only-dependencies
$ cabal install -j1
...
In-place registering cairo-0.13.1.0...
setup.exe:
'C:\Users\ryanscot\Documents\Software\Haskell\ghc-7.10.2\bin\ghc-pkg.exe'
exited with an error:
cairo-0.13.1.0: Warning: haddock-interfaces:
C:\Users\ryanscot\Documents\Hacking\Haskell\cairo-0.13.1.0\dist/dist-sandbox-e81b42b6\doc\html\cairo\cairo.haddock
doesn't exist or isn't a file
cairo-0.13.1.0: Warning: haddock-html:
C:\Users\ryanscot\Documents\Hacking\Haskell\cairo-0.13.1.0\dist/dist-sandbox-e81b42b6\doc\html\cairo
doesn't exist or isn't a directory
cairo-0.13.1.0: include-dirs: /mingw64/include/freetype2 is a relative path
which makes no sense (as there is nothing for it to be relative to). You can
make paths relative to the package database itself by using ${pkgroot}. (use
--force to override)
cairo-0.13.1.0: include-dirs: /mingw64/include/libpng16 is a relative path
which makes no sense (as there is nothing for it to be relative to). You can
make paths relative to the package database itself by using ${pkgroot}. (use
--force to override)
cairo-0.13.1.0: include-dirs: /mingw64/include/harfbuzz is a relative path
which makes no sense (as there is nothing for it to be relative to). You can
make paths relative to the package database itself by using ${pkgroot}. (use
--force to override)
cairo-0.13.1.0: include-dirs: /mingw64/include/glib-2.0 is a relative path
which makes no sense (as there is nothing for it to be relative to). You can
make paths relative to the package database itself by using ${pkgroot}. (use
--force to override)
cairo-0.13.1.0: include-dirs: /mingw64/lib/glib-2.0/include is a relative path
which makes no sense (as there is nothing for it to be relative to). You can
make paths relative to the package database itself by using ${pkgroot}. (use
--force to override)
Failed to install cairo-0.13.1.0
cabal.exe: Error: some packages failed to install:
cairo-0.13.1.0 failed during the building phase. The exception was:
ExitFailure 1

As the error suggests, you can fix this by running cabal install --ghc-pkg-options="--force", but that's not a very satisfying solution. Trying to install cairo with stack also yields the same error, so cabal-install isn't the culprit.

The culprit here might be MSYS2, to some degree. I installed mingw-w64-x86_64-cairo via pacman in MSYS2, and I noticed something suspicious from pkg-config:

$ pkg-config --cflags cairo
-mms-bitfields -IC:/msys64/mingw64/include/cairo -IC:/msys64/mingw64/include/pixman-1 -IC:/msys64/mingw64/include -I/mingw64/include/freetype2 -I/mingw64/include/libpng16 -I/mingw64/include/harfbuzz -I/mingw64/include/glib-2.0 -I/mingw64/lib/glib-2.0/include -IC:/msys64/mingw64/include -IC:/msys64/mingw64/include/freetype2 -IC:/msys64/mingw64/include -IC:/msys64/mingw64/include/harfbuzz -IC:/msys64/mingw64/include/glib-2.0 -IC:/msys64/mingw64/lib/glib-2.0/include -IC:/msys64/mingw64/include/libpng16

In particular, note how it passes flags like -I/mingw64/include/freetype2, since the build output was complaining about /mingw64/include/freetype2 being a relative path! (On Windows it is, anyway.) We clearly have some bad path-related interaction going on here, but I'm not sure where would be the best place to fix it.

[RyanGlScott]

It turns out this was a MSYS2 issue, not a gtk2hs one. And that MSYS2 issue now fixed! You now no longer have to use the --ghc-pkg-options="--force" hack to get cairo to install.