[GHC] #7415: Add more error code support to GHC.Windows (patch)

[GHC]

#7415: Add more error code support to GHC.Windows (patch)
----------------------------+-----------------------------------------------
Reporter:  joeyadams        |          Owner:                  
    Type:  feature request  |         Status:  new             
Priority:  normal           |      Component:  libraries/base  
 Version:  7.6.1            |       Keywords:                  
      Os:  Windows          |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown     |      Blockedby:                  
Blocking:  7353             |        Related:                  
----------------------------+-----------------------------------------------
 This patch adds some infrastructure for the
 [http://hackage.haskell.org/trac/ghc/ticket/7353 Windows I/O manager]
 currently in progress.  It organizes `GHC.Windows` a little, and adds some
 things:

  * A `LPWSTR` type alias.  I'm not a Windows expert, but I think we should
 avoid [http://msdn.microsoft.com/en-
 us/library/windows/desktop/aa383751%28v=vs.85%29.aspx#lptstr LPTSTR] in
 our FFI declarations.  It depends on whether or not the `UNICODE` macro is
 defined—a notion that makes little sense in a Haskell program.  Using
 `LPWSTR` makes our intention clearer.

  I left `LPTSTR` in for compatibility.  Should we DEPRECATE it?

  * `c_maperrno_func`.  The existing `c_maperrno` calls `GetLastError`,
 converts the result, then sets `errno`.  `c_maperrno_func` exposes the
 conversion as a pure function.

  This helps eliminate a caveat in
 [http://www.haskell.org/ghc/docs/latest/html/libraries/Win32/System-
 Win32-Types.html#v:failWith failWith], which expects `GetLastError` to
 return the error passed to `failWith`.  This is not the case, for example,
 when throwing the error in another thread.

  * `failWith`, `failIf`, ...  error guards from
 [http://www.haskell.org/ghc/docs/latest/html/libraries/Win32/System-
 Win32-Types.html System.Win32.Types].

  * `ErrCode`, `getLastError`, `getErrorMessage`, `errCodeToIOError`: Lets
 you work with the system error code more directly.

  * `iNVALID_HANDLE_VALUE`

 Behavior change: `throwGetLastError` now attaches the system error
 message, making it (almost) equivalent to
 [http://www.haskell.org/ghc/docs/latest/html/libraries/Win32/System-
 Win32-Types.html#v:errorWin errorWin] from `System.Win32.Types`.
 Moreover, it no longer has the side effect of setting `errno`, thanks to
 `c_maperrno_func`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7415>
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