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author | sterni <sternenseemann@systemli.org> | 2022-09-21T11·47+0200 |
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committer | sterni <sternenseemann@systemli.org> | 2022-09-21T14·23+0000 |
commit | 083fc1dbe59e28bb25cc1dc7405ee45d9d9244b7 (patch) | |
tree | e968148f948aa1bbe0e9de2ed17c6b7bcee35b3f /users | |
parent | 9a8a6a33f9265a3844e91f2c1aab0b28ac46decf (diff) |
fix(tvix/eval): compare versions with an extra empty component r/4950
This is necessary because builtins.compareVersions compares versions in a subtly not-quite-but-still-lexicographical way: `pre` for example can have an effect if it is post-fixed: `2.3 < 2.3pre`. This is a violation of the rule that in a lexicographical ordering, the longer string is considered greater if they are otherwise equal. builtins.compareVersion is comparing lexicographically though, if you do the following transformation beforehand: 2.3 --split--> [ "2" "3" ] --append--> [ "2" "3" "" ] 2.3pre --split--> [ "2" "3" "pre" ] --append--> [ "2" "3" "pre" "" ] Comparing the transformed version is then done lexicographically: 2.3 < 2.3.0pre since [ "2" "3" "" ] < [ "2" "3" "0" "pre" ] Here, the `pre` rule never comes into effect because no comparison on it happens, instead we use the longer string rule of a lexicographical comparison. In the C++ codebase, the reason for this behavior is that the iterator-esque construct they use always yields the empty string before it exposes it has been fully consumed. This is probably intentional to support the postfixed `pre` which is, for example, used by NixOS versions (e.g. unstable post 22.05 is 22.11-pre). We replicate this behavior using the `Chain` iterator in `VersionPartsIter::new_for_cmp`. Change-Id: I021c69aa27b0b7deb949dffe50ed18b6de3a7b1f Reviewed-on: https://cl.tvl.fyi/c/depot/+/6720 Tested-by: BuildkiteCI Reviewed-by: tazjin <tazjin@tvl.su>
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