889136 - MSVC build warning: "usrsctp.h(241) : warning C4200: nonstandard extension used : zero-sized array in struct/union", and similar

Status: RESOLVED FIXED

(Core :: WebRTC, defect)

Description

[Daniel Holbert [:dholbert]]

Quoting a log from an attempt to mark netwerk/sctp/datachannel as FAIL_ON_WARNINGS:
{
DataChannel.cpp

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(241) : error C2220: warning treated as error - no 'object' file generated

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(241) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(350) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(400) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(615) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(626) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(695) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(700) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

e:\builds\moz2_slave\try-w32-0000000000000000000000\build\netwerk\sctp\src\usrsctp.h(765) : warning C4200: nonstandard extension used : zero-sized array in struct/union

        Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array
}
https://tbpl.mozilla.org/php/getParsedLog.php?id=24802161&tree=Try


This is in a third-party library, so rather than trying to fix the code, it might be saner to just disable this warning for this chunk of code. (Fortunately, this is pretty easy in MSVC.)

Comment 1

[Daniel Holbert [:dholbert]]

Attachment: fix: #pragma warning(disable:4200) for the #include

This patch wraps datachannel's #include of (third-party header) usrsctp.h with "#pragma warning disable" for the warning in question.

See e.g. http://mxr.mozilla.org/mozilla-central/source/content/base/public/nsINode.h?mark=310-314,327-330&rev=731a5fcf1328#310 for another place where we use this technique.

This suppresses the warning, and it lets us build on windows with FAIL_ON_WARNINGS in the datachannel directory as shown by this try push:
https://tbpl.mozilla.org/?tree=Try&rev=5fc593544f85

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: fix v1a: #pragma warning(disable:4200) for the #include

(first version had the commit message split into 2 lines; merged into 1 line here.)

Comment 3

[Masatoshi Kimura [:emk]]

(In reply to Daniel Holbert [:dholbert] from comment #1)
> See e.g.
> http://mxr.mozilla.org/mozilla-central/source/content/base/public/nsINode.h?mark=310-314,327-330&rev=731a5fcf1328#310
> for another place where we use this technique.

As an aside, this should be replaced with MOZ_THIS_IN_INITIALIZER_LIST().

Comment 4

[Daniel Holbert [:dholbert]]

(In reply to Masatoshi Kimura [:emk] from comment #3)
> (In reply to Daniel Holbert [:dholbert] from comment #1)
> > See e.g.
> > http://mxr.mozilla.org/mozilla-central/source/content/base/public/nsINode.h?mark=310-314,327-330&rev=731a5fcf1328#310
> > for another place where we use this technique.
> 
> As an aside, this should be replaced with MOZ_THIS_IN_INITIALIZER_LIST().

Sure. I was just linking to it to demonstrate the #pragma syntax for disabling MSVC warnings, but yes, that particular warning (4355) is frequent enough that we have a macro to handle it now. Feel free to file a separate bug on using the macro there. :)

Comment 5

[Daniel Holbert [:dholbert]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/477d313cc2ab

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/477d313cc2ab