Diesel: formatter error

[remexre]

Setup

Versions

• Rust: 1.32.0
• Diesel: 1.4.1
• Database: Postgres 11
• Operating System Linux

Feature Flags

• diesel: chrono, postgres, r2d2, uuid

Problem Description

On connecting to a DB and embedded_migrations::run(&pool.get()?)?;-ing, I get the incredibly unhelpful error "formatter error," which seems to be from deep in std, if the migrations would introduce a constraint violation.

What are you trying to accomplish?

Apply some migrations to prod that worked in dev

What is the expected output?

[INFO] Started!

What is the actual output?

[ERROR] Failed with: formatter error

Are you seeing any additional errors?

Not from the app/diesel, but from diesel migration run, which shows the error.

Steps to reproduce

have a DB
ALTER TABLE some check constraints on in a migration
run the migration

Checklist

• [x] I have already looked over the issue tracker for similar issues.
• [x] This issue can be reproduced on Rust's stable channel. (Your issue will be
  closed if this is not the case)

[weiznich]

I'm not sure what exactly are you expecting here.
The steps for reproducing this are quite sparse. (We will need to exact sql that has caused this)

As a blind guess: Maybe something is wrong with the hand written sql?

[iptq]

I'm having the exact same problem trying to run a SQLite migration.

CREATE TABLE `chals` (
    `id` INTEGER PRIMARY KEY AUTO_INCREMENT,
);

This is the full contents of the up.sql in question. Here's some parts of the code:

mod sqlite {
    #[derive(EmbedMigrations)]
    #[embed_migrations_options(migrations_path = "migrations/sqlite")]
    struct _Dummy;
}
...
sqlite::run_with_output(conn, out) // fails

[iptq]

nvm my syntax is wrong, trailing comma

[sorccu]

This is a real error that occurs if anything whatsoever goes wrong during a migration run. For example, the following migration:

up.sql

SELECT 1 FROM does_not_exist;

Executed with:

embedded_migrations::run_with_output(&conn, &mut std::io::stdout()).expect("unable to migrate");

Will result in the following output:

Running migration 20190221123919
thread 'main' panicked at 'unable to migrate: MigrationError(IoError(Custom { kind: Other, error: StringError("formatter error") }))', src/libcore/result.rs:997:5
note: Run with RUST_BACKTRACE=1 environment variable to display a backtrace.
Executing migration script

What SHOULD be shown is something along the lines of:

thread 'main' panicked at 'unable to migrate: QueryError(DatabaseError(__Unknown, "relation \"does_not_exist\" does not exist"))', src/libcore/result.rs:997:5

It turns out that the reason is very simple. Upon encountering an error, diesel attempts to display the filename of the failed migration:

https://github.com/diesel-rs/diesel/blob/03ec1d96ffa8a4f957ba6dc9bd5ab5b556a96d12/diesel_migrations/migrations_internals/src/lib.rs#L337-L344

Since the embedded migration's impl Migration is left without a file_path() implementation:

https://github.com/diesel-rs/diesel/blob/03ec1d96ffa8a4f957ba6dc9bd5ab5b556a96d12/diesel_migrations/migrations_macros/src/embed_migrations.rs#L37-L49

... it returns the default None, which then triggers the formatting error here:

https://github.com/diesel-rs/diesel/blob/03ec1d96ffa8a4f957ba6dc9bd5ab5b556a96d12/diesel_migrations/migrations_internals/src/migration.rs#L49-L52

And since the writeln!() for the error message uses ?, the formatting error from above ends up replacing the original error entirely.

[sgrif]

Your explanation of the issue makes sense, but I do not think that pretending an embedded migration has a file path is the right solution. Can we try fixing this by handling the None case in impl Display for MigrationFileName?