Add `nodiscard` attribute to StatusCode (C++17)

this allow spotting unchecked StatusCodes at compile time instead of at run time.

I also fixed O(250) unchecked StatusCodes in Gaudi (in ~60 files), using the script $587.

With this we can remove StatusCodeSvc with the overhead it implies (@graven noted that removing ~StatusCode we will also save some time because the return will be done via registers).

This also remove the WARN_UNUSED macro introduced with !386 (merged) (redundant).

• [2018-09-26 13:38] Validation started with lhcb-gaudi-merge#590

marked as a Work In Progress

changed the description

added 2 commits

• 0405fe1d - Declare StausCode as [[nodiscard]] (C++17)
• 9a0aa258 - Fixed "unchecked" StatusCodes

Compare with previous version

mentioned in merge request lhcb/Online!258 (merged)

mentioned in commit lhcb/LHCb@ee8427b2

mentioned in merge request lhcb/LHCb!1524 (closed)

I'd like to suggest to split this MR in two pieces:

1. just the part which adds the various .ignore() (and which can be merged today!)
2. the parts which adds [[nodiscard]] to StatusCode (and which has to wait for C++17, and maybe until the "users" have had a change to fix the (trivial) fall-out before it gets merged)

mentioned in commit lhcb/Lbcom@81aa6e99

mentioned in merge request lhcb/Lbcom!281 (closed)

mentioned in commit lhcb/Boole@8a6af0d1

mentioned in merge request lhcb/Boole!173 (closed)

mentioned in commit lhcb/Boole@8f65d0a0

@graven, indeed it could be splitted. OTOH, I think is more urgent to get the [[nodiscard]] in, rather than a bunch of .ignore() nobody ever notice were missing.

In any case, as you may notice from the mentions, I'm already going through all LHCb projects (with my script it's pretty quick).

assigned to @leggett

mentioned in commit lhcb/Online@c80dd880

mentioned in commit lhcb/Rec@5e1c98fc

mentioned in merge request lhcb/Rec!1221 (closed)

mentioned in commit lhcb/LHCb@003a4784

mentioned in commit lhcb/Boole@becdd37a