Raise more useful error if mismatch between feature enabled and db url

[katrinabrock]

@sgrif

Problem Description

If proper features are not enabled, error messages to not point to this being the issue.

What are you trying to accomplish?

Started project with one backend, switched to a different backend and forgot to change Cargo.toml.

What is the expected output?

If DATABASE_URL is for a database where feature is not enabled, there should at least be a warning about this.

What is the actual output?

help: message: Could not load table names from databasepostgresql://sammy:sam
my@localhost/diesel_demo: StringError("Failed to establish a database connection a t postgresql://sammy:sammy@localhost/diesel_demo. Error: BadConnection(\"Unable to open the database file\")")

Steps to reproduce

Cargo.toml
[dependencies] diesel = { version = "0.15.0", features = ["sqlite"] } diesel_codegen = { version = "0.15.0", features = ["sqlite"] } dotenv = "0.9.0"
.env
DATABASE_URL=postgres://username:password@localhost/diesel_demo > .env

Checklist

• I have already looked over the issue tracker for similar issues.

[sgrif]

To clarify, specifically I think we should be checking for the URL starting with mysql://, postgres:// or postgresql:// when those features are not enabled. I think we can safely assume that the user is not trying to connect to a SQLite database in that case.

[sgrif]

Related: We should strip sqlite:// from the URL if it's present. I've had a couple people try that expecting it to work.

[bbqsrc]

This just broke my mind for a while, as I changed computers and couldn't understand the error that diesel-cli was giving me. Trying to connect to a postgres db with only the sqlite feature enabled provides the following:

$ diesel migration run
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ConnectionError(BadConnection("Unable to open the database file"))', libcore/result.rs:945:5

So yeah, this is still less than ideal. :)

[christiansakai]

I literally just encountered this problem and went on for 2 days.... Glad I found this issue.

[AndrewSpeed]

I'll take a look at implementing this