[Phathdt]

Summary

This PR fixes three critical bugs affecting index generation and migration reversibility.

Bugs Fixed

🔴 Issue #21: @@index not generated in migrations

Root cause: Differ only created CreateTable operation for new tables, without separate CreateIndex operations.

Fix: Generate CreateIndex operations for each index when creating new tables.

Impact: Indexes are now correctly included in migrations for new tables.

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🔴 Bug #2: Migration builder loses indexes from history

Root cause: applyCreateIndex modified table.Indexes but didn't save table back to map (Go value semantics issue).

Fix: Add b.tables[stmt.Table] = table after modifying indexes.

Impact: Schema loaded from migration history now preserves indexes correctly.

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🔴 Bug #3: DropIndex with unnamed indexes generates invalid SQL

Root cause: DropIndex operation only stored Name (empty for auto-generated indexes), resulting in DROP INDEX ; (invalid SQL).

Fixes:

• Add Index field to DropIndex struct to store full index definition
• Populate Index object when creating DropIndex operations
• Auto-generate index name from columns when Name is empty
• Generate CREATE INDEX for reverse DropIndex operations

Impact: DROP INDEX now generates valid SQL and fully reversible Down migrations.

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Changes

• internal/diff/differ.go: Generate CreateIndex ops for new tables, populate Index in DropIndex
• internal/diff/operation.go: Add Index field to DropIndex struct
• internal/migration/builder.go: Save modified table back to map after applying index
• internal/prisma/converter.go: Extract index name from @@index attributes
• internal/sql/postgres/generator.go: Auto-generate index names, implement reversible DROP INDEX
• internal/sql/postgres/generator_reverse_test.go: Update test expectations for reversible DropIndex

Tests Added

• ✅ internal/diff/differ_dropindex_test.go: Unit tests for DropIndex with unnamed/named indexes
• ✅ internal/sql/postgres/generator_dropindex_test.go: Unit tests for DROP INDEX SQL generation and reverse
• ✅ internal/prisma/converter_test.go: Test for index name extraction
• ✅ internal/diff/differ_test.go: Tests for new tables with indexes

Verification

• ✅ All unit tests pass
• ✅ E2E manual testing confirms indexes generated correctly
• ✅ Down migrations fully reversible
• ✅ Zero regressions

Example

Before (Bug):

-- +goose Up
CREATE TABLE users (...);
-- Missing CREATE INDEX!

-- +goose Down
DROP INDEX ;  -- Invalid SQL!

After (Fixed):

-- +goose Up
CREATE TABLE users (...);
CREATE INDEX idx_users_email ON users (email);

-- +goose Down
CREATE INDEX idx_users_email ON users (email);
DROP TABLE users;

Closes #21