process library broken on Windows

[Michael Snoyman]

That's the goal; it's a feature that does not work on Windows, only on
non-Windows systems (setuid/setgid for a child process). For POSIX systems,
CGid is exported from base, and can be used. On Windows, the data type is
present to give the same signature, but the constructor itself is not
exported to prevent using the feature. An argument could be made for other
approaches:

1. Expose the constructor, allowing users to set a value, and that value
will be ignored
2. Make the fields themselves conditional on the OS being used

I don't think there's a strong argument in any direction for this.

On Mon, Nov 2, 2015 at 5:37 AM, Simon Peyton Jones <simonpj at microsoft.com>
wrote:

> I’m puzzled.   Internals.hs defines a newtype
>
>
>
> newtype CGid = CGid Word32
>
>
>
> A value of this type is needed to fill in the child_group field of
> CreateProcess.  If you don’t export it, you could never initialise this
> field to anything other than Nothing, so why do you have it?
>
>
>
> Looks to me as if the warning has nailed a real bug
>
>
>
> Simon
>
>
>
> *From:* michael.snoyman at gmail.com [mailto:michael.snoyman at gmail.com] *On
> Behalf Of *Michael Snoyman
> *Sent:* 02 November 2015 13:34
> *To:* Simon Peyton Jones
> *Cc:* ghc-devs at haskell.org
> *Subject:* Re: process library broken on Windows
>
>
>
> I didn't read closely enough: I see now that it's a warning, not an error.
> I initially didn't export that constructor since it's only present on
> Windows for API compatibility, but will never be used. Since this is just
> the internals module, I can export it, but my preference would in fact be
> to leave it as-is with the warning. Two alternatives:
>
>
>
> 1. Create a new hidden module that creates and exports the type
> constructor, just to hide the warning. I'm -1 on that, since that's extra
> compile time everyone has to endure just for warning avoidance.
>
> 2. base could export CGid for Windows (currently, it does not).
>
>
>
> On Mon, Nov 2, 2015 at 5:17 AM, Michael Snoyman <michael at snoyman.com>
> wrote:
>
> I'll look into this. I just made a new release of process, and was certain
> I tested on Windows, but perhaps something changed between that commit and
> release.
>
>
>
> On Mon, Nov 2, 2015 at 5:15 AM, Simon Peyton Jones <simonpj at microsoft.com>
> wrote:
>
> I’m getting this on HEAD in te ‘
>
> libraries\process\System\Process\Internals.hs:106:16: warning:
>
>     Defined but not used: data constructor ‘CGid’
>
> Indeed it looks as if CGId(..) should be exported, else createProcess is
> unusuable.  This looks like the right change.  Would someone like to check
> and make the change
>
> Simon
>
> diff --git a/System/Process/Internals.hs b/System/Process/Internals.hs
>
> index 5575ac4..3e23ad5 100644
>
> --- a/System/Process/Internals.hs
>
> +++ b/System/Process/Internals.hs
>
> @@ -37,6 +37,8 @@ module System.Process.Internals (
>
> #if !defined(mingw32_HOST_OS) && !defined(__MINGW32__)
>
>      pPrPr_disableITimers, c_execvpe,
>
>      ignoreSignal, defaultSignal,
>
> +#else
>
> +    CGid(..), GroupID, UserID,
>
> #endif
>
>      withFilePathException, withCEnvironment,
>
>      translate,
>
>
>
> _______________________________________________
> ghc-devs mailing list
> ghc-devs at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
> <https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.haskell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc-devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7cdd25a0d693de489171bb08d2e38a505d%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=YdqpMC5wr2K6oUOw9WImRGpSl6EsV8zQyAK%2ba26oF9M%3d>
>
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20151102/7ab52d77/attachment-0001.html>