Not wrapping `index` or `unique_index` migration macro in `create` silently fails

[deepankar-j]

Elixir version

1.18.1

Database and Version

SQL Server 2017

Ecto Versions

ecto v3.12.5, ecto_sql v3.12.1

Database Adapter and Versions (postgrex, myxql, etc)

tds 2.3.5

Current behavior

Steps:

• Create a migration with the following declarations in the change (note that we're purposely forgetting to wrap the functions in a create macro)

       unique_index(:my_table, [:my_column])
       index(:my_table, [:my_column2])

• Run migration

Expected behavior

Running the migration should fail.

Actual behavior: The migration passes without creating the indices.

This is dangerous because developers (especially with the help of AI coding tools) can easily forget to wrap the index declarations with the requisite create(...) function macro.

[josevalim]

Unfortunately there isn't much we can do here. It is like saying if you have this code:

IO.puts compute_message_for_printing()

If someone forgets the IO.puts, you want us to detect it was forgotten. The index simply returns a data structure, if you forget to do an operation with it, it isn't straight-forward for us to know or guess.

[deepankar-j]

Thank you, @josevalim. That makes sense from the system perspective.

From a developer perspective, I feel like this is a trap that the community as a whole can fall into, especially with AI code suggestions.

Is there a credo check that Ecto can provide that can help catch such errors of omission?

[josevalim]

I think Credo checks is a great idea and I recommend exploring those as a separate library, such as credo_ecto! Perhaps there are also suggestions from the Safe Ecto Migrations that could be encoded as Credo checks? https://fly.io/phoenix-files/safe-ecto-migrations/ - Go for it!!!