Add support for nulls_not_distinct option in create_constraint and create_index operations

[kvch]

Add support for nulls_not_distinct option in create_constraint and create_index operations for unique constraints and indexes.

NULLS NOT DISTINCT was introduced in PG 15, so I added some conditionals to check if we can retrieve the column from pg_index. Without this function, we get an exception because indnullsnotdisctict does not exist in PG 14.

Closes #730

[Copilot]

Pull Request Overview

This PR adds support for the new nulls_not_distinct option used to indicate that nulls are considered equal in unique constraints and indexes when supported by PostgreSQL 15. Key changes include:

• Adding a new boolean field for nulls_not_distinct in constraint and index migration types.
• Updating SQL generation functions to optionally include the "NULLS NOT DISTINCT" clause.
• Enforcing that nulls_not_distinct is only applicable for unique constraints and updating tests and duplicate operations accordingly.

Reviewed Changes

Copilot reviewed 9 out of 15 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pkg/migrations/types.go	Adds new bool field (NullsNotDistinct) to migration types
pkg/schema/schema.go	Adds new field in Index and UniqueConstraint structures with JSON mapping for nulls_not_distinct
pkg/migrations/op_create_constraint.go	Passes the new nullsNotDistinct parameter and validates constraint type
pkg/migrations/op_create_index.go	Condition to append "NULLS NOT DISTINCT" in index creation SQL
pkg/migrations/index.go	Updates function signatures and SQL generation for unique indexes
pkg/migrations/duplicate.go	Updates unique index duplication to include nullsNotDistinct flag
pkg/migrations/duplicate_test.go	Adjusts test calls to include the new parameter
pkg/migrations/op_set_unique.go	Updates call to createUniqueIndexConcurrently with false for nullsNotDistinct
pkg/migrations/op_add_column.go	Updates call to createUniqueIndexConcurrently with false for nullsNotDistinct

Files not reviewed (6)

• docs/operations/create_constraint.mdx: Language not supported
• docs/operations/create_index.mdx: Language not supported
• examples/44_add_table_unique_constraint.json: Language not supported
• internal/jsonschema/testdata/create-constraint-3-invalid-check-nulls.txtar: Language not supported
• pkg/state/init.sql: Language not supported
• schema.json: Language not supported

Comments suppressed due to low confidence (1)

pkg/schema/schema.go:118

• [nitpick] Consider using snake_case ("nulls_not_distinct") for the JSON tag to align with the migration types' naming convention.

NullsNotDistinct bool `json:"nullsNotDistinct"`

[andrew-farries]

👍 Left some comments.

In addition, we should also add tests in op_create_constraint_test.go and op_create_index_test.go to check that NULLS NOT DISTINCT is applied correctly when set.

[andrew-farries]

Looks good.

We still need to add tests in op_create_constraint_test.go and op_create_index_test.go to check that nulls_not_distinct: true is applied correctly when set. Currently we don't have anything to check that indexes/constraints created with nulls_not_distinct: true actually results in a NULLS NOT DISTINCT index/constraint.

[andrew-farries]

I think we also need a test for reading a unique constraint with created with NULLS NOT DISTINCT.

[kvch]

I am converting this to draft for now because we need to rework backfilling process significantly to get this working.

[kvch]

Closing because it is outdated.