Draft: Handle snapshot missing root directory

fixes #4824

instead of using an assert to please mypy we raise a NotFoundExc when a snapshot is missing a root directory to avoid an unhandled exception in sentry (which happens only in staging due to a missing revision in staging storage)

assigned to @rboyer

mentioned in issue #4824

Jenkins job DWAPPS/gitlab-builds #1408 succeeded in 10 min.
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I think we should rather check if the object targeted by a branch (revision, release, directory or content) exists in the archive directly in the get_snapshot_context function and raise a NotFoundExc with a detailed error message like: Revision <rev_id> targeted by branch <branch_name> from snapshot <snapshot_id> cannot be found in the archive.

Currently there is already some of those checks performed by calls to archive.lookup_revision or archive.lookup_release but some are missing and the 404 error message only says Revision <rev_id> cannot be found. Some refactoring could be made in the get_snapshot_context to catch the NotFoundExc exceptions and reraise them with better error messages including snapshot info.

I think I disagree with this: there is no reason for a function called "get_snapshot_context" to raise a NotFoundError in this case. This function does a lot of things, no reason to make it fail in this particular case IMHO. It's the responsibility of the caller to do the right thing.

So I'd rather go for this proposal...

So what do you think about this @anlambert ?

marked this merge request as draft

added 22 commits

• a4249a6c...2d49d142 - 21 commits from branch swh/devel:master
• cf3e6554 - Handle snapshot missing root directory in staging

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Jenkins job DWAPPS/gitlab-builds #1455 succeeded in 9 min 7 sec.
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added 11 commits

• cf3e6554...ade2b0a1 - 10 commits from branch swh/devel:master
• 59e768c1 - Handle snapshot missing root directory in staging

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Jenkins job DWAPPS/gitlab-builds #1511 failed in 8 min 50 sec.
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added 2 commits

• 785899b7 - 1 commit from branch swh/devel:master
• 1d2090a4 - Handle snapshot missing root directory in staging

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Jenkins job DWAPPS/gitlab-builds #1515 failed in 8 min 52 sec.
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