Test sqlx offline files

[w1ll-i-code]

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Description

The problem I have is the following: I want to have the cached data for local and CI builds, such that they do not need to have access to the database. However, when I change the database schema, I don't want to forget to update the files if there was a breaking change. So I want to re-run the cached files and make sure that the database still returns the same data.

The alternatives would otherwise be:

1. Needing a database access for e.g. the unit tests
2. Recompiling / rechecking the whole application for the check
3. Copying the target directory from the build environment to the test environment

Prefered solution

I would like to have a sub-command in sqlx e.g. sqlx verify, that takes all the cached files .sqlx/*.json, re-runs the query and if the result miss-matches, throws an error.

Is this a breaking change? Why or why not?

This is not a breaking change.

[abonander]

cargo sqlx prepare --check https://github.com/launchbadge/sqlx/tree/main/sqlx-cli#enable-building-in-offline-mode-with-query

[w1ll-i-code]

@abonander cargo sqlx prepare --check still needs the source code. I cannot just validate the cached offline queries...

[abonander]

Sorry, you didn't specify that you were aware of --check already.

I suppose we could add a command that only looks at the data files, but that would have weaker guarantees. You couldn't be certain that the cached data was still valid for the queries in the source code unless you checked the source code anyway.

[w1ll-i-code]

The source code is checked against the data files already during compilation, but I want the common case for that to go fast. Only later I'll check that the data files are up-to-date in a separate CI step that can be done in parallel with the test. It should be exceptionally rare for that to happen anyways, so I try to optimize for the common case.

[w1ll-i-code]

@abonander I have put my mind to it for a while and have now a working version. If you think the feature could be useful, I'd love to open a PR and get some feedback on it.