feat(orm): support custom migrations

[m4tx]

This adds support for user-defined migrations that might contain arbitrary code in them. This is primarily useful for data migrations which do not modify the schema, but fill in the data in the database instead.

This extends the migration engine to support a new type of migrations, as well as cot-cli with a new command that creates a new custom migration.

Fixes #211.

[github-actions]

Bencher Report

Branch	custom-migrations
Testbed	github-ubuntu-latest

Click to view all benchmark results

Benchmark	Latency	Benchmark Result microseconds (µs) (Result Δ%)	Upper Boundary microseconds (µs) (Limit %)
empty_router/empty_router	📈 view plot 🚷 view threshold	5,671.20 µs (-5.11%) Baseline: 5,976.29 µs	7,016.82 µs (80.82%)
json_api/json_api	📈 view plot 🚷 view threshold	1,026.40 µs (+0.56%) Baseline: 1,020.67 µs	1,152.78 µs (89.04%)
nested_routers/nested_routers	📈 view plot 🚷 view threshold	949.46 µs (+0.93%) Baseline: 940.68 µs	1,055.23 µs (89.98%)
single_root_route/single_root_route	📈 view plot 🚷 view threshold	915.10 µs (+1.47%) Baseline: 901.87 µs	1,012.96 µs (90.34%)
single_root_route_burst/single_root_route_burst	📈 view plot 🚷 view threshold	16,763.00 µs (-4.83%) Baseline: 17,613.55 µs	20,900.45 µs (80.20%)

🐰 View full continuous benchmarking report in Bencher

[Copilot]

Pull request overview

This PR adds support for custom migrations to the Cot ORM, allowing developers to define data migrations with arbitrary code that don't modify the database schema.

Changes:

• Added MigrationContext, CustomOperationFn, and CustomBuilder to the migration engine for defining custom migration operations
• Implemented migration_op attribute macro to transform async functions into migration operations
• Added cot migration new CLI command to create custom migrations with a user-defined name

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
cot/src/db/migrations.rs	Core implementation of custom migrations including the context type, operation builder, and execution logic
cot-macros/src/migration_op.rs	Macro implementation that transforms async functions to return pinned boxed futures
cot-macros/src/lib.rs	Export of the new migration_op macro
cot-macros/tests/ui/attr_migration_op.rs	UI test for correct usage of the macro
cot-macros/tests/ui/attr_migration_op_not_async.stderr	Expected error output for non-async functions
cot-macros/tests/ui/attr_migration_op_not_async.rs	UI test for error case
cot-macros/tests/compile_tests.rs	Test registration for macro compile tests
cot-cli/src/migration_generator.rs	Generator for custom migration files and refactored naming logic
cot-cli/src/main.rs	CLI command routing for the new migration command
cot-cli/src/handlers.rs	Handler implementation for creating custom migrations
cot-cli/src/args.rs	CLI argument definitions for the new command
cot-cli/tests/migration_generator.rs	Tests for custom migration generation and compilation
cot-cli/tests/snapshot_testing/help/snapshots/*.snap	Updated help text snapshots showing the new command
cot-cli/tests/snapshot_testing/cli/snapshots/*.snap	Updated shell completion snapshots for the new command

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[codecov]

Codecov Report

❌ Patch coverage is 88.39286% with 26 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cot-cli/src/migration_generator.rs	83.49%	7 Missing and 10 partials ⚠️
cot/src/db/migrations.rs	88.88%	4 Missing and 4 partials ⚠️
cot-macros/src/migration_op.rs	94.73%	1 Missing ⚠️

Flag	Coverage Δ
rust	90.39% <88.39%> (-0.03%)	⬇️

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Files with missing lines	Coverage Δ
cot-cli/src/handlers.rs	95.93% <100.00%> (+0.93%)	⬆️
cot-cli/src/main.rs	100.00% <100.00%> (ø)
cot-macros/src/lib.rs	94.84% <100.00%> (+0.33%)	⬆️
cot-macros/src/migration_op.rs	94.73% <94.73%> (ø)
cot/src/db/migrations.rs	84.39% <88.88%> (+0.51%)	⬆️
cot-cli/src/migration_generator.rs	87.68% <83.49%> (-0.34%)	⬇️

... and 2 files with indirect coverage changes

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[seqre]

Overall it LGTM, please write more tests before merging