<div dir="ltr">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:<div><br></div><div>1. Expose the constructor, allowing users to set a value, and that value will be ignored</div><div>2. Make the fields themselves conditional on the OS being used</div><div><br></div><div>I don't think there's a strong argument in any direction for this.</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Nov 2, 2015 at 5:37 AM, Simon Peyton Jones <span dir="ltr"><<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d">I’m puzzled. Internals.hs defines a newtype<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-family:"Calibri",sans-serif;color:#1f497d">newtype CGid = CGid Word32<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d">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?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d">Looks to me as if the warning has nailed a real bug<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:#1f497d">Simon<u></u><u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <a href="mailto:michael.snoyman@gmail.com" target="_blank">michael.snoyman@gmail.com</a> [mailto:<a href="mailto:michael.snoyman@gmail.com" target="_blank">michael.snoyman@gmail.com</a>]
<b>On Behalf Of </b>Michael Snoyman<br>
<b>Sent:</b> 02 November 2015 13:34<br>
<b>To:</b> Simon Peyton Jones<br>
<b>Cc:</b> <a href="mailto:ghc-devs@haskell.org" target="_blank">ghc-devs@haskell.org</a><br>
<b>Subject:</b> Re: process library broken on Windows<u></u><u></u></span></p>
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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:<u></u><u></u></p>
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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.<u></u><u></u></p>
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2. base could export CGid for Windows (currently, it does not).<u></u><u></u></p>
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On Mon, Nov 2, 2015 at 5:17 AM, Michael Snoyman <<a href="mailto:michael@snoyman.com" target="_blank">michael@snoyman.com</a>> wrote:<u></u><u></u></p>
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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.<u></u><u></u></p>
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On Mon, Nov 2, 2015 at 5:15 AM, Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">I’m getting this on HEAD in te ‘<u></u><u></u></p>
<p>libraries\process\System\Process\Internals.hs:106:16: warning:<u></u><u></u></p>
<p> Defined but not used: data constructor ‘CGid’<u></u><u></u></p>
<p class="MsoNormal">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<u></u><u></u></p>
<p class="MsoNormal">Simon<u></u><u></u></p>
<p>diff --git a/System/Process/Internals.hs b/System/Process/Internals.hs<u></u><u></u></p>
<p>index 5575ac4..3e23ad5 100644<u></u><u></u></p>
<p>--- a/System/Process/Internals.hs<u></u><u></u></p>
<p>+++ b/System/Process/Internals.hs<u></u><u></u></p>
<p>@@ -37,6 +37,8 @@ module System.Process.Internals (<u></u><u></u></p>
<p>#if !defined(mingw32_HOST_OS) && !defined(__MINGW32__)<u></u><u></u></p>
<p> pPrPr_disableITimers, c_execvpe,<u></u><u></u></p>
<p> ignoreSignal, defaultSignal,<u></u><u></u></p>
<p>+#else<u></u><u></u></p>
<p>+ CGid(..), GroupID, UserID,<u></u><u></u></p>
<p>#endif<u></u><u></u></p>
<p> withFilePathException, withCEnvironment,<u></u><u></u></p>
<p> translate,<u></u><u></u></p>
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