Add every listed checksums of a given archive to the cache when fetching from it

[kit-ty-kate]

Fixes #6064

Backported in 2.2 by #6069

[rjbou]

I've updated

• the test (in admin-cache.*.test now) for linux/mac and windows: they show more easily the different behaviour, the links, etc.
  • add an md5 corrupted/collision test too
• the changelog
• commit messages to be more accurate with current PR content.

[rjbou]

I'm not sure if readlink is portable enough. I need here to retrieve the target of the link, not the fully resolved one

[rjbou]

there is a regression in extrasource

--- a/_build/default/tests/reftests/extrasource.test
+++ b/_build/default/tests/reftests/extrasource.out
@@ -1177,16 +1177,12 @@ The following actions will be performed:
   - install good-sha256-good-md5 1
 
 <><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-[ERROR] Conflicting file hashes, or broken or compromised cache!
-          - sha256=hash (MISMATCH)
-          - md5=hash (MISMATCH)
-
--> retrieved good-sha256-good-md5.1  (file://${BASEDIR}/p.patch)
+-> retrieved good-sha256-good-md5.1  (cached)
 -> installed good-sha256-good-md5.1
 Done.
 ### sh check-cache.sh
-MD5: link, to sha256 patch
-SHA256: patch, with matching checksum
+MD5: patch, with matching checksum
+SHA256: patch, with mismatching checksum

[kit-ty-kate]

there is a regression in extrasource

i don't think this is a regression. Only a change of behaviour stemming from the fact that now the chosen file from the cache is the last one in the list instead of the first one. We can keep the old behaviour but it requires more code. I don't think it's broken per-say.

[rjbou]

• pull_file_to_cache need an update doc as it no more a no op if the file exists and there is no links.
• update of test (full reproducibility depends on admin hashes cache: move under opam root #6103)
  Otherwise, lgtm!

[rjbou]

OpamSystem.link removes the existing link to create a new one. Do we want that behaviour or check beforehand here if the symlink checksum -> target exists, otherwise create it ?

[kit-ty-kate]

i think we should do this separately in OpamSystem.link directly. I've opened #6113 to track this

[kit-ty-kate]

• pull_file_to_cache need an update doc as it no more a no op if the file exists and there is no links.

• update of test (full reproducibility depends on admin hashes cache: move under opam root #6103)
  Otherwise, lgtm!

both done

[rjbou]

lgtm!