[Haskell-cafe] Cabal install on Windows 7

[Regis Saint-Paul]

> > - use windows API for requesting elevation during the process (ugly)
> 
> If it really has to be done, then this seems like the best approach. In
> principle there's no problem with calling funky win32 functions in
> Cabal, it's mostly a matter of working out what bahaviour we want and
> what UAC lets us do.

To achieve this, a candidate solution would be: 
- to have a separate executable with a manifest indicating that
administrator privilege are needed (and, ideally, signed) and able to
perform the tasks necessitating elevation
- from cabal, to run this separate process (calling shellexecute) exactly at
the point when elevation is needed 
- alternatively, it might be possible to try the operation, catch the
exception that would happen if it fails, and call the separate process in
this case (see:
http://stackoverflow.com/questions/17533/request-vista-uac-elevation-if-path
-is-protected#17544)

The advantage is that, with this solution, users only use "cabal" and the
elevation is performed when needed.
 
By contrast, the other suggested solution of having two executables
(cabal-user and cabal-global) leaves the choice of elevating cabal to the
user and only needs to modify the build process (no code changed in cabal).
Its drawback is that elevation will be requested even when unnecessary every
time cabal-global is launched. 

So a first task would be to identify the cases where cabal needs to run with
elevated rights and the task to perform in that case. 
- Is cabal going to be modified to use AppData for library install? 
- If this is the case, then writing in protected folders would be only for
binary install (with cabal install). Are there other cases?
- If this is not the case, then writing in protected folder is for all
package install when in global mode...other cases? 
- Am I missing operations where cabal would need admin privileges? For
instance, may cabal need to modify some environment variable? 

Cheers,
Regis