Arch Linux

makepkg should resolve makedepends and depends simultanously, or at least makedepends not after depends.

The current issue occures when you have:
in the PKGBUILD:
depends=(a)
makedepends=(b)

and the following package:
c: provides=(a)
b: provides=(a), conflicts=(c)

If for whatever reason pacman decides to install c to resolve depends=(a), then the makedepends cannot be resolved.
This happens for example, if c is in testing, while b is in extra.
I have seen this issue (when building for archlinux32) with openoffice-{still,fresh} and with jre[89]-openjdk (the latter being somewhat different, because they do not "conflict" via PKGBUILD variable, but if jre8 is installed after jre9, the default jre is still 9 and the build will/may fail).