Allow multiple state caches #4642
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Instead of writing state.cache, opam now writes state-magic.cache which means that two opam binaries / libraries no longer keep regenerating the state cache just because they can't read the one which was there before. Just prior to _writing_ the state cache (e.g. after opam update or any repo operation), all the .cache files in the directory are erased. opam 2.0 is either unable to read a 2.1 root or will never write to it (opam 2.0.9), so this change is backwards compatible.
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This is speculatively on the 2.1.0~rc milestone - we might remove it in the morning. |
AltGr
approved these changes
Apr 30, 2021
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At present
$OPAMROOT/repo/state.cachewill be reset if the magic string does not match the version of opam-state / opam. This is tedious when developing and also visible to users as opam-state has a slightly different version from an opam binary.The fix is quite simple: include the magic string in the filename as well, and tolerate having multiple cache files.
state.cacheis only ever written if something changed, and all that happens now is that$OPAMROOT/repo/*.cacheis erased prior to writing the new cache (since other opam-state / opam binaries actually must regenerate the file).As the cache files are all reset at
opam update, even developers shouldn't see too many of them accumulating.Fixes #4554. It can't directly be backported to 2.0.9, because 2.0.8 and earlier don't delete *.cache on a write. The "algorithm" could be adapted where opam 2.0.9 always erases its own cache of
state.cacheis newer, but I'm not convinced this is worth it. opam 2.1 does not require this kind of change, because even if opam 2.0.9 can read an opam root, it's never going to write to it, so the cache can't be invalidated.