documentation patch for process

[Evan Laforge]

Any interest in applying this?  I don't think I have permissions.

Or should I get permissions somehow?

On Wed, Feb 8, 2012 at 1:25 PM, Evan Laforge <qdunkan at gmail.com> wrote:
> I recently burned some time because I didn't realize that
> System.Process.createProcess doesn't report when the binary isn't
> found.  I guess I was used to that behaviour from python's subprocess
> module, which goes to some effort to report the error from the
> fork()ed child when exec() fails.  After a failed solution, I did some
> poking around in the source to see exactly what haskell's process
> does.
>
> In the interests of saving someone else that time, I submit a patch to
> process to add some documentation.  I'm not sure how to do a 'darcs
> send' with git, but here's the patch:
>
> % git log | head
> commit 5a46937961b3400fa58ccffc785d0de8c1c01d94
> Author: Evan Laforge <qdunkan at gmail.com>
> Date:   Wed Feb 8 13:25:16 2012 -0800
>
>    More detailed haddock for createProcess: document what happens if
>    the binary is not found
>
> commit c8b30a6f1d493ab724f2da05dbc49496b119a051
> Author: Simon Marlow <marlowsd at gmail.com>
> Date:   Mon Jan 16 16:25:34 2012 +0000
>
> % git diff HEAD\^
> diff --git a/System/Process.hs b/System/Process.hs
> index f3a8f9b..a372228 100644
> --- a/System/Process.hs
> +++ b/System/Process.hs
> @@ -234,9 +234,18 @@ To create a pipe from which to read the output of @ls@:
>  To also set the directory in which to run @ls@:
>
>  >   (_, Just hout, _, _) <-
> ->       createProcess (proc "ls" []){ cwd = Just "\home\bob",
> +>       createProcess (proc "ls" []){ cwd = Just "/home/bob",
>  >                                     std_out = CreatePipe }
>
> +Note that this does /not/ throw an error if the binary is not found,
> +or not executable.  Instead, the process will fail with the exit code 127.
> +But you can't rely on it failing quickly, because it may e.g. hang up
> +searching the PATH on a slow NFS mount.  Since there's no way to tell when
> +the exec() has succeeded, the only way to reliably know if the createProcess
> +failed is to 'waitForProcess'.
> +
> +If the CreateProcess record's 'cwd' directory doesn't exist, the exit code
> +will be 126.
>  -}
>  createProcess
>   :: CreateProcess
> diff --git a/System/Process/Internals.hs b/System/Process/Internals.hs
> index 11de1f4..2a6c047 100644
> --- a/System/Process/Internals.hs
> +++ b/System/Process/Internals.hs
> @@ -199,7 +199,8 @@ data CmdSpec
>   = ShellCommand String
>       -- ^ a command line to execute using the shell
>   | RawCommand FilePath [String]
> -      -- ^ the filename of an executable with a list of arguments
> +      -- ^ The filename of an executable with a list of arguments.
> +      -- The PATH is searched for the executable.
>
>  data StdStream
>   = Inherit                  -- ^ Inherit Handle from parent