Instead of having checks in AddRoleMems() and DelRoleMems(), have
the callers perform checks where it's required. In some cases it
isn't, either because the caller has already performed a check for
the same condition, or because the check couldn't possibly fail.
The "Skip permission check if nothing to do" check in each of
AddRoleMems() and DelRoleMems() is pointless. Some call sites
can't pass an empty list. Others can, but in those cases, the role
being modified is one that the current user has just created.
Therefore, they must have permission to modify it, and so no
permission check is required at all.
This patch is intended to have no user-visible consequences. It is
intended to simplify future work in this area.
Patch by me, reviewed by Mark Dilger.
Discussion: http://postgr.es/m/CA+TgmobFzTLkLwOquFrAcdsWBsOWDr-_H-jw+qBvfx-wSzMwDA@mail.gmail.com
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