PsqlTetris.Formatter (PsqlTetris v0.1.2)

Mix formatter plugin.

Add this module to the :plugins list of your project's .formatter.exs and mix format will quietly reorder columns in new (and existing) Ecto migrations for optimal PostgreSQL column alignment:

# .formatter.exs
[
  inputs: ["{mix,.formatter}.exs", "{config,lib,test,priv}/**/*.{ex,exs}"],
  plugins: [PsqlTetris.Formatter],
  psql_tetris: [
    migration_paths: ["priv/repo/migrations/", "priv/*/migrations/"]
  ]
]

Only .exs files whose path matches one of the configured migration paths are rewritten. Every other file is returned untouched. The default match is anything containing priv/ and /migrations/ in the path, which covers the standard Phoenix/Ecto layout.

Safety: only runs on PostgreSQL projects

The reordering argument follows from how PostgreSQL aligns column values on disk (per-column alignment classes, the varlena tail). It does not apply to MySQL or MariaDB (no per-column alignment to optimize), SQLite (dynamic typing, no fixed column slots), or MSSQL. Running this formatter against a non-Postgres project would shuffle columns for no benefit, so by default it won't.

Detection is done at format time by checking whether the Postgrex driver module is loaded in the project. Postgrex is the canonical Postgres driver for Elixir and only shows up as a dep on actual Postgres projects, so its presence is a reliable signal. Checking for Ecto.Adapters.Postgres alone would not be enough, because ecto_sql bundles adapter modules for several databases together.

If you have an unusual setup (e.g. a tooling-only project that doesn't ship Postgrex), you can force the plugin on or off explicitly:

psql_tetris: [enabled: true | false]

in .formatter.exs.