In portage-126.96.36.199 and 2.2.0_alpha133 there’s support for expermental EAPI 5-hdepend which adds the HDEPEND variable which is used to represent build-time host dependencies. For build-time target dependencies, use DEPEND (if the host is the target then both HDEPEND and DEPEND will be installed on it). There’s a special “targetroot” USE flag that will be automatically enabled for packages that are built for installation into a target ROOT, and will otherwise be automatically disabled. This flag may be used to control conditional dependencies, and ebuilds that use this flag need to add it to IUSE unless it happens to be included in the profile’s IUSE_IMPLICIT variable.
For those who may not be familiar with the history of HDEPEND, it was originally suggested in bug #317337. That was in 2010, and later that year there was some discussion about it on the chromium-os-dev mailing list. Recently, I suggested on the gentoo-dev mail list that it be included in EAPI 5, but it didn’t make it in. Since then, there’s been some renewed effort , and now the patch is included in mainline Portage.
EAPI 5 includes support for automatic rebuilds via the slot-operator and sub-slots, which has potential to make @preserved-rebuild unnecessary (see Diego’s blog post regarding symbol collisions and bug #364425 for some examples of @preserved-rebuild shortcomings). Since this support for automatic rebuilds has potential to greatly improve the user-friendliness of preserve-libs, I have decided to make preserve-libs available in the 2.1 branch of portage (beginning with portage-188.8.131.52). It’s not enabled by default, so you’ll have to set FEATURES=”preserve-libs” in make.conf if you want to enable it. After EAPI 5 and automatic rebuilds have gained widespread adoption, I might consider enabling preserve-libs by default.
In portage-184.108.40.206 and 2.2.0_alpha130 there’s support for EAPI 5, which implements all of the features that were approved by the Gentoo Council for EAPI 5. There are no differences since EAPI 5_pre2.
In portage-220.127.116.11 and 2.2.0_alpha127 there’s support for EAPI 5_pre2, which implements all of the features that were approved for EAPI 5 in the Gentoo Council meeting on September 11. The only difference from EAPI 5_pre1 is that the “user patches” feature has been removed.
In portage-18.104.22.168 and 2.2.0_alpha124 there’s support for EAPI 5_pre1, which implements all of the features that are currently in the eapi-5 branch of PMS (including the features from EAPI 4-slot-abi, which I’ve blogged about before). For additional references about the upcoming EAPI 5, see the “EAPI 5 tentative features” wiki page.
If you’d like to experiment with EAPI 5_pre1, then you can refer to the corresponding portage documentation, and you may need to pay special attention to the new “Profile IUSE Injection” feature. Since the profiles currently aren’t configured for this feature yet, you’ll have to configure these variables yourself if your experimental ebuilds reference special flags (like x86, kernel_linux, elibc_glibc, and userland_GNU) without listing them explicitly in IUSE. Here’s an abbreviated example of what the variables should look like, which you can put in make.conf:
USE_EXPAND="ELIBC KERNEL USERLAND"
USE_EXPAND_IMPLICIT="ARCH ELIBC KERNEL USERLAND"
USE_EXPAND_VALUES_ARCH="amd64 ppc ppc64 x86 x86-fbsd x86-solaris"
USE_EXPAND_VALUES_KERNEL="FreeBSD linux SunOS"
I have not populated all of the above variables exhaustively, but these values should be enough to get you started. If you need a more complete set of ARCH values to list in USE_EXPAND_VALUES_ARCH, then you can grab the exhaustive set of values from arch.list.