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Dear David, |
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|
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David Seifert <soap@g.o> writes: |
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> We already have such a solution in the sci-overlay. It has proven |
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> extremely brittle and shaky. |
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What's more, using eselect set which library to link to was regarded |
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harmful. |
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|
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> The plan is to do this via USE flags similar to python-single-r1 |
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> flags. |
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Yes, that was the conclusion in 2017. |
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But now there is something to be renewed, see below. |
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> Optionally, we can leave a "virtual" USE flag, where users can switch |
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> implementation at runtime, but this will not be a supported |
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> configuration. |
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|
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[...] |
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> While I understand that runtime-switching sounds like a great feature, |
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> it has proven too difficult to get right and too hard to enforce |
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> invariants on correct symlinks. |
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I thought so, too. Back in 2017, I did an investigate of Debian runtime |
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switching, and concluded the patches were too heavy for us. That was the |
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main reason we did not consider the Debian runtime switching way.[0, 1] |
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However, I have made a deeper study this year, and concluded it is quite |
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doable in a simple way in Gentoo. |
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|
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Historically, in alternative{,-2}.eclass of the science overlay, |
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"alternative" is a name from Debian[2]. We have made it too complex over |
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the years, and now there is a good chance to make it simple again. |
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> People that want this can go the virtual+eselect approach in the |
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> overlay, |
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Which is brittle and shaky as we agree. |
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> but 99% of Gentoo users will be happy with just linking against |
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> OpenBLAS/reference-lapack and not having to fix weird stale symlinks |
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> that eselect-alternatives somehow lost track of. |
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|
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With the simplified approach Mo is after, there will no longer be weird |
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stale symlinks issues. The solution has been successfully proved by the |
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update-alternative mechanism in Debian. Actually, by adopting mgorny's |
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LDPATH way of handing gcc runtime, we don't need symlinks at all![3] |
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|
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For more details, please refer to |
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https://people.debian.org/~lumin/gsoc19-gentoo.pdf |
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|
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> See also: |
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> https://bugs.gentoo.org/632624 |
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> https://bugs.gentoo.org/348843#c30 |
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Thanks. That reminded me of all the discussions we all along. |
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Yours, |
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Benda |
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0. https://github.com/gentoo/sci/issues/805#issuecomment-345690034 |
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1. https://github.com/gentoo/sci/issues/805#issuecomment-345701064 |
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2. https://github.com/gentoo/sci/issues/805#issuecomment-332887691 |
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3. https://bugs.gentoo.org/632618 |
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