"stack setup" for GHCJS doesn't work on windows due to long paths

[mgsloan]

stack setup ought to work with GHCJS + windows now, but I'm running into issues due to long paths. In particularly, it fails during the install step with Setup.hs: does not exist, as it can't move C:\Users\Sloan\AppData\Local\Programs\stack\i386-windows\ghcjs-0.1.0.20150924_ghc-7.10.2\src\.stack-work\install\i386-windows\lts-3.6\7.10.2\lib\i386-windows-ghc-7.10.2\ghcjs-0.1.0.20150924-3v8gJrjhwSs4MId7xBHavX\libHSghcjs-0.1.0.20150924-3v8gJrjhwSs4MId7xBHavX.a to a different location.

What can we do to resolve this?

Maybe place the ghcjs source files relative STACK_ROOT? Then, if they take the suggestion to use the short one, maybe the paths will be short enough... (Though it's only C:\Users\Sloan\AppData\Local\Programs\stack\i386-windows\ vs C:\stack_root\programs...).

[snoyberg]

We probably need to replicate some of the functionality in #1027 for snapshot databases.

[mantkiew]

I am getting a different error for ghcjs installation on Windows (10, 64bit):

PS C:\projects> stack setup ghcjs-0.1.0_ghc-7.10.2
Preparing to install GHCJS to an isolated location.
This will not interfere with any system-level installation.
No sha1 found in metadata, download hash won't be checked.
Downloaded ghcjs-0.1.0.20150924_ghc-7.10.2.
Already downloaded.
Already downloaded.
CreateDirectory "C:\\Users\\<user>\\AppData\\Local\\Programs\\stack\\i386-windows\\ghcjs-0.1.0.20150924_ghc-7.10.2\\src-tmp4796": does not exist (The system cannot find the path specified.)

This path does not seem to be exceeding the 260 characters limit (it's 120 long); however, why does it have \\ instead of \?