libdv @1.0.0 build failure with Xcode 12

[MaurizioLoreti]

I just upgraded to Big Sur, and I am reinstalling ports from scratch. I need transcode, that depends from libdv, that does not compile (report attached). libdv is maintained by (nobody). May some kind peolpe help?

[jmroot (Joshua Root)]

:info:build dvconnect.c:873:7: error: implicit declaration of function 'sched_setscheduler' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
:info:build                 if (sched_setscheduler (0, SCHED_RR, &scp) < 0) {
:info:build                     ^

[ryandesign (Ryan Carsten Schmidt)]

There hasn't been a release of libdv since 2006 so I don't expect upstream to help, but I'll see what I can do.

[ryandesign (Ryan Carsten Schmidt)]

sched_setscheduler is a Linux function that has never existed on macOS, as far as I can tell, so I'm scratching my head how this ever compiled on macOS before.

[ryandesign (Ryan Carsten Schmidt)]

A patch for this was submitted in 2009: ​https://sourceforge.net/p/libdv/patches/43/

[ryandesign (Ryan Carsten Schmidt)]

Initially the patch didn't work for me: it adds a configure test for sched_setscheduler but it surprisingly determined that it was available, and then the build failed as before.

I noticed that the port forces the use of -flat_namespace -undefined suppress which has been in the port ever since it was added in 2005 in [8ed1835344effbeda34c7df31fce834174521fcf/macports-ports]. That was right after the release of Mac OS X 10.3 10.4. The use of the flat namespace was typical on Mac OS X 10.2 and earlier but in 10.3 and later the two-level namespace should be used instead. After removing the lines that forced the flat namespace, the configure test correctly determines that sched_setscheduler doesn't exist and the build succeeds.

[ryandesign (Ryan Carsten Schmidt)]

In 3a44daacbc5f67cc1b95835810f04e3868a5a973/macports-ports (master):

libdv: Fix implicit declaration of function

Don't try to use sched_setscheduler on macOS where it doesn't exist.

Closes: #61580