99cb85cd37
As summarized in
https://github.com/NixOS/nix/issues/77#issuecomment-2843228280 the
motivation is that the complicated retry logic this introduced was
making the cleanup task #12628 harder to accomplish. It was not easy to
ascertain just what policy / semantics the extra control-flow was
implementing, in order to figure out a different way to implementing it
either.
After talking to Eelco about it, he decided we could just....get rid of
the feature entirely! It's a bit scary removing a decade+ old feature,
but I think he is right. See the release notes for more explanation.
This reverts commit 299141ecbd.
Co-authored-by: Eelco Dolstra <edolstra@gmail.com>
1.5 KiB
| synopsis | issues | prs | |||
|---|---|---|---|---|---|
| Revert incomplete closure mixed download and build feature |
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Since Nix 1.3 (299141ecbd in 2013) Nix has attempted to mix together upstream fresh builds and downstream substitutions when remote substuters contain an "incomplete closure" (have some store objects, but not the store objects they reference).
This feature is now removed.
Worst case, removing this feature could cause more building downstream, but it should not cause outright failures, since this is not happening for opaque store objects that we don't know how to build if we decide not to substitute. In practice, however, we doubt even the more building is very likely to happen. Remote stores that are missing dependencies in arbitrary ways (e.g. corruption) don't seem to be very common.
On the contrary, when remote stores fail to implement the closure property, it is usually an intentional choice on the part of the remote store, because it wishes to serve as an "overlay" store over another store, such as https://cache.nixos.org.
If an "incomplete closure" is encountered in that situation, the right fix is not to do some sort of "franken-building" as this feature implemented, but instead to make sure both substituters are enabled in the settings.
(In the future, we should make it easier for remote stores to indicate this to clients, to catch settings that won't work in general before a missing dependency is actually encountered.)