Test .sqlx/ files without needing source code access.

[w1ll-i-code]

I have found these related issues/pull requests

Followup to #4054 since I don't have the permission to reopen it.

I know that cargo sqlx prepare --check exists already, however that also re-checks the source code. I want to only test that the files are still valid.

Description

Here is my use-case: I want to be able to build a project sqlx with all the guarantees from checking the queries against the database, but without actually having to have a database running for the CI build. For that I can use the .sqlx/*.json files. So after the build I know already that the files are valid for the code I want to build.

Later in the build pipeline I still need to check if the files are still up-to-date with the database. Since cargo sqlx prepare --check needs access to the source code to check it and will do a full cargo check run. I'd like to avoid needing access to cargo or the source code for that validation.

Since the check against the database should succeed in 99.99% of the time, only possibly breaking if I touch the schema (or update the db), it should run in parallel to the tests later to reduce build times.

I have already a working version of sqlx to solve this problem. If my proposal sounds good, I can open a PR. Lmk if there is anything else I need to do for the PR.

Prefered solution

I would like to have a new sqlx sub-command, e.g. sqlx revalidate that will take just the files in .sqlx/*.json, re-execute the query that is already stored in there and check that everything still works.

Is this a breaking change? Why or why not?

This is not a breaking change, I want to add a completely new command.