feat: add exit code support to sc_start and sc_stop

[janweinstock]

Hi all,

I though it could be useful to have and exit code that could be set using sc_stop which would be returned by sc_start, e.g.:

if (everything_ok)
    sc_stop(EXIT_SUCCESS);
else
    sc_stop(EXIT_FAILURE);

and then

int sc_main(int argc, char** argv) {
    // ...
    return sc_start();
}

Calling sc_stop() without an argument is backward-compatible and equivalent to sc_stop(0). The implementation stores the exit code in sc_simcontext and sc_start returns it on exit.

What do you think?

[janweinstock]

LRM PR https://github.com/OSCI-WG/lwg-documentation/pull/16

[markfoodyburton]

Looks very good to me.

[maehne]

I expressed my doubts about this change to the LRM in this comment. Changing the signature of sc_start() may have unexpected effects on legacy code. At least add [[maybe_unused]] to the user-facing sc_start() functions.

[janweinstock]

I expressed my doubts about this change to the LRM in this comment. Changing the signature of sc_start() may have unexpected effects on legacy code. At least add [[maybe_unused]] to the user-facing sc_start() functions.

The return value is intentionally not marked [[nodiscard]], so it is explicitly allowed to be ignored; [[maybe_unused]] is neither applicable nor necessary.

[janweinstock]

Retargeted to develop branch.

[janweinstock]

It was discussed in the LWG to include an update to sc_pause so that it can also specify an exit_code. Since the reference implementation allows to call sc_pause multiple times in the same delta-cycle, we need to decide which exit_code should be reported in such cases.

Example 1 (multiple sc_pause)

sc_pause(val_a);
sc_pause(val_b);
sc_pause(val_c);

Example 2 (mixed with sc_stop):

sc_pause(val_a);
sc_pause(val_b);
sc_stop(val_c);

Which values should be returned in each case? We could say val_c for both cases (exit code gets updated each time, last write wins). This would also simplify the implementation in sc_stop, since one should not call sc_pause after sc_stop anways.