[danez]

Summary

Fix PostgreSQL partial-index migration drift for @db.VarChar fields.

This directly fixes prisma/orm#29386.

PostgreSQL normalizes partial-index predicates by adding ::text casts
to VARCHAR column identifiers and string literals. The schema differ
previously handled the literal cast but not the identifier cast, so
migrate dev repeatedly generated a no-op drop/create-index migration.

The predicate comparator now treats an identifier and its implicit
::text form as equivalent. Other casts remain significant.

Fixes prisma/orm#29386

Test

• Added a PostgreSQL regression test that creates a migration for a
  partial unique index on VARCHAR fields, then verifies an unchanged
  schema does not create a second migration.

• Ran:

  cargo test -p sql-migration-tests --test migration_tests -- --nocapture

AI assistance

AI assistance was used to investigate the PostgreSQL predicate normalization
and draft the regression test. The implementation and test result were
reviewed and verified locally.

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

Summary by CodeRabbit

• Bug Fixes

  • Improved PostgreSQL schema comparison for expressions using redundant ::text casts, reducing unnecessary migration changes.

• Tests

  • Added coverage for PostgreSQL partial unique indexes with string predicates.
  • Verified that unchanged schemas do not generate additional migrations.

Walkthrough

The PostgreSQL schema differ now treats identifier and compound-identifier expressions with equivalent ::text casts as semantically equal. The comparison checks both casted and uncasted forms recursively. A PostgreSQL migration test covers partial unique indexes with string predicates and verifies that unchanged schemas do not generate an additional migration.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing semantic matching for implicit PostgreSQL text casts.
Description check	✅ Passed	The description directly explains the PostgreSQL partial-index migration drift, the comparator fix, the regression test, and verification performed.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

✨ Simplify code

• Create PR with simplified code

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