Let the drift guard check column types, opt-in

[VSN2015]

An enhancement, resuming feature work. It's the one I flagged last tick as the best remaining candidate.

The gap

The drift guard's premise is that a schema change which invalidates a contract should fail the deploy, not the request. A column dropped by a migration does. A column retyped by one did not — so a contract could go on declaring :datetime long after the column became a string.

The addition

# config/initializers/permittable.rb
Permittable.check_column_types = true

Permittable: 'placed_at' is declared :string but the column is :datetime (table: orders).
Change the contract to match the column, migrate the column to match the contract,
or declare the field virtual: true if it is not backed by this column.

  contract matches the schema                          loads
  someone migrated placed_at to a string               'placed_at' is declared :string but the column is :datetime
  :date on a datetime column (narrowing)               loads
  same mismatch, with the check off                    loads

The decision I'd most like reviewed: it's off by default

The existing guard is aggressive by default, and I nearly matched that. I didn't, because every cross-type declaration has some legitimate use:

• a :string contract on a date column, letting ActiveRecord do the casting
• a :boolean contract on a legacy integer 0/1 column
• a :string contract on a json column that the app serialises itself

A missing column is unambiguous, so failing the deploy for it is fair. A differing type is not, and breaking those apps on a patch upgrade would cost more than the drift it catches. Off by default, turn it on, fix what it finds.

If you'd rather it were on by default for 1.0, that's a one-line change to the reader — I'd just want it to be a deliberate major-version decision rather than a side effect of this PR.

Groups, not exact types

That's the other thing keeping false positives down:

Group	Column types
text	string, text, citext, uuid, enum, char
numeric	integer, bigint, float, decimal, boolean
temporal	date, datetime, time, timestamp, timestamptz

boolean sits with the numerics on purpose — a boolean stored as integer 0/1 is a real legacy pattern and AR casts cleanly. The temporal types are one group because :date on a datetime column is a narrowing, not drift.

Any column type not in that table is never checked — json, jsonb, binary, an adapter's own inet or money. The gem has no faithful contract type for those, so whatever an app improvised is left alone rather than guessed about. (I verified against ActiveRecord's own normalisation: it reports bigint columns as :integer, so the map keys on what AR actually returns, not on SQL types.)

Also

guard_contract_columns! now appends the virtual: true hint only to the missing-column error — the type error carries its own three-way guidance, and "declare it virtual" was odd advice for a type mismatch.

Verification

• 208 examples, 0 failures (9 new, written before the implementation), including the off-by-default case, both legitimate-mix cases, the never-checked column types, and virtual:/missing-column still behaving
• RuboCop clean

[VSN2015]

Review of PR #34: Type checking in ColumnGuard catches schema drift when columns are retyped across migrations. Grouping types by broad compatibility families strikes the right balance between strictness and practical database patterns.

[VSN2015]

Coarsening type validation into :text, :numeric, and :temporal families avoids false positives for standard patterns (like mapping :boolean to an integer column or :date to a datetime column) while accurately flagging cross-family discrepancies.

[VSN2015]

Silently skipping columns without known groups (e.g. :json, :binary) allows applications to use custom database types without triggering drift guard failures.