Am I right in thinking that the reason for this patch is: historically, Unix only had EWHATEVER and Windows only had WSAEWHATEVER, but recent mingw-w64 defines EWHATEVER to be WSAEWHATEVER as well?

If that's what you're dealing with here, this change looks like a reasonable way to fix that, although I'd prefer it with "#elif defined(WSAEADDRINUSE)" to avoid the extra level of nesting.

Would you mind revising the patch to use #elif, and mention why this change is needed in the commit message?

(Some notes on good commit messages: <http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html>; a good example of a commit message in dbus.git: <http://cgit.freedesktop.org/dbus/dbus/commit/?id=a8423067ceac1af6176e14fbc334fe5b82431e3d>)

At least on the 2.x branch of mingw-w64, both ESOMETHING and WSASOMETHING are defined (I was also surprised to see that). I will first double check with mingw-w64's maintainers whether this is intended or a bug.

Created attachment 59068 [details] [review]
Fix compilation with mingw-w64

Fixed unneeded nesting and commit message.

Mingw maintainers that this double definition is correct from their side.
From mingw-w64:

ylatuya: hi, I have proposed the following patch for DBUS to fix the compilation with mingw-w64: https://bugs.freedesktop.org/show_bug.cgi?id=47321
ylatuya: it looks like ESOMETHING and WSASOMETHING are both defined in mingw-w64, is that correct?
jon_y: ylatuya: yes

(In reply to comment #3)

> Mingw maintainers that this double definition is correct from their side.

This should be read: Mingw maintainers confirm that

Comment on attachment 59068 [details] [review]
Fix compilation with mingw-w64

Review of attachment 59068 [details] [review]:
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Looks great, I'll merge it. Thanks!

Fixed in 1.4.20, 1.5.12