Summary

When renaming a column with an inline UNIQUE constraint using the @renamed annotation, psqldef was incorrectly generating DROP CONSTRAINT for the unique index. This caused the UNIQUE constraint to be lost after applying the migration.

Problem

PostgreSQL automatically updates constraint column references when a column is renamed via ALTER TABLE ... RENAME COLUMN. Therefore, the DROP CONSTRAINT generated by psqldef was unnecessary and resulted in data integrity loss.

Before this fix:

-- Current schema
CREATE TABLE users (
  username varchar(100) NOT NULL UNIQUE
);

-- Desired schema  
CREATE TABLE users (
  user_name varchar(100) NOT NULL UNIQUE -- @renamed from=username
);

-- Generated DDL (incorrect)
ALTER TABLE "public"."users" RENAME COLUMN "username" TO "user_name";
ALTER TABLE "public"."users" DROP CONSTRAINT "users_username_key";  -- This was wrong!

After this fix:

-- Generated DDL (correct)
ALTER TABLE "public"."users" RENAME COLUMN "username" TO "user_name";
-- No DROP CONSTRAINT - PostgreSQL handles the constraint update automatically

Changes

• Modified generateDDLsForAbsentIndex in schema/generator.go to check if a column was renamed from the name referenced by the unique index
• Added test case RenameColumnWithInlineUniqueConstraint to verify the fix

Testing

• All existing tests pass
• New test case covers the specific scenario