Changing identities leads to generation of erroneous migrations

[spacebat]

Describe the bug
Attempting to use the latest Ash 3.0.7 support for where clauses in identities:

# in the identities block
identity :name, [:name] do
  nils_distinct? false
  where expr(is_nil(archived_at))
end

# and in the postgres block
identity_wheres_to_sql name: "archived_at is null"

The migration generated for this, when run throws this error:

** (Postgrex.Error) ERROR 42601 (syntax_error) syntax error at or near "NULLS"
    query: CREATE UNIQUE INDEX "pipeline_defns_name_index" ON "pipeline_defns" (name) NULLS NOT DISTINCT WHERE archived_at is null

Upon removing the nils_distinct? false line and regenerating the migration then running it gives:

** (Postgrex.Error) ERROR 42P07 (duplicate_table) relation "pipeline_defns_name_index" already exists

Indeed, the migration up function just does a create unique_index(...) and does not attempt to alter the index or delete and recreate it.

To Reproduce
See above for reproduction.

Expected behavior
The SQL for NULLS NOT DISTINCT should be correct, but postgresql doesn't like it.
The migration generated should alter or recreate the index, not attempt to create an already-extant index.

Runtime

• Elixir version 1.16.2
• Erlang version 26
• OS Ubuntu 22.04
• Ash version 3.0.7
• any related extension versions
  Postgresql is version 14.11

[zachdaniel]

Fixed in 9f1936a