Rails 8 upgrade

Skill davidteren/hotwire-codex-skills/skills/rails-8-upgrade

Upgrade a Rails 7 app to Rails 8 safely, and catch the subtle test-suite flake it introduces. Use when bumping Rails 7.x to 8.x (or auditing readiness), when planning a Ruby/Rails version bump, or when Rails 8 tests fail intermittently with "undefined method 'login_path'/'root_path'" / pass on serial but flake on parallel runs. Provides a pre-flight audit, a detector + fix for the LazyRouteSet route-test flake, and a 7→8 checklist grounded in a real upgrade.From its SKILL.md

Install

npx -y skills add davidteren/hotwire-codex-skills --skill rails-8-upgrade

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

2 things to look at

3 stars3 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.
runs commandsInstructs the agent to run 3 commands, including `scripts/upgrade_audit.sh path/to/app` and 2 more.

SKILL.md

3.3 KB, 762 tokens by cl100k_base, as published. Nobody here has run it

Rails 7 → 8 upgrade

Two things kill time in a 7→8 upgrade: deciding what to bump vs defer, and a flaky route-helper test that Rails 8's LazyRouteSet introduces and that hides behind single green test runs. This skill handles both.

Read references/rails-7-to-8.md for the full checklist and the why.

When to use

Bumping rails 7.x → 8.x, or checking whether an app is ready.
Tests started flaking after a Rails 8 bump with undefined method 'login_path'/'root_path' in unrelated controllers; serial runs stay green.
Reviewing a PR that adds/edits a draw_test_routes-style route helper.

1. Pre-flight audit (read-only)

scripts/upgrade_audit.sh path/to/app

Reports: Ruby/Rails versions (+ flags a Gemfile.lock RUBY VERSION mismatch that makes bundle refuse), config.load_defaults vs Rails major, presence of a new_framework_defaults_*.rb, known-risky gems (notably pagy <6 with custom pagy view helpers — a real porting cost), and whether the test suite uses the flaky route pattern. Changes nothing.

2. The recommended path

Baseline green on current versions first (a bisectable starting point).
Bump rails ~> 8.x and Ruby; leave config.load_defaults where it is (run new library code with old framework behavior — low risk).
bundle update; only hand-pin where a transitive conflict forces it.
Run the suite ≥6× (parallel flakes hide — see below). Boot the server, check a public (200) and a protected (401/redirect) route.
Flip framework defaults separately later, via config/initializers/new_framework_defaults_8_1.rb, one line at a time.

3. The LazyRouteSet route-test flake (the expensive one)

If the suite appends test-only routes via a helper that toggles Rails.application.routes.disable_clear_and_finalize, Rails 8 makes it flaky under parallel runs. Detect it:

scripts/lint_route_test_helper.sh path/to/app

It checks the helper (a) materializes the LazyRouteSet (reload_routes_unless_loaded) before setting the flag, (b) resets the flag in an ensure, (c) doesn't use the finalize! dead-end, and (d) every draw_test_routes caller has a teardown { reload_routes! }. Exits non-zero on risk and prints the fix.

Apply templates/routes_helper.rb.fixed (drop into test/support/) and add the missing teardowns. Then run the suite ≥6× to confirm — a 35%-flake bug passes ~2 of 3 single runs.

Root cause + dead-ends: references/rails-7-to-8.md. Real-world instance: piazza-web/wip/analysis/01.

Why the scripts are heuristic

Plain grep/awk text scans, not Ruby parsers — conservative and dependency-free, meant to gate a PR and point you at the fix, not to be a type checker. They name their ceiling in the output.

What ships with it: 4 files

11.8 KB alongside SKILL.md, 2 of them executable

Gives 0 of the 12 instructions most test skills give in 762 tokens

Counted across 1,201 of the 2,096 authors here whose files we hold, read 2026-09-06

Write a failing test before writing codein 43 of 1201, across 36 files
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Define primary, secondary, and guardrail metricsin 33 of 1201, across 16 files
Pre-determine sample size before startingin 31 of 1201, across 14 files
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Formulate a hypothesis before designing a testin 30 of 1201, across 13 files
Document every test hypothesis, variant, and resultin 29 of 1201, across 11 files
Use descriptive test function namesin 25 of 1201, across 21 files
Commit to the methodology without stopping earlyin 24 of 1201, across 8 files

Said here and by no other author read

Bump Rails and Ruby versions
Keep existing config load defaults
Run test suite at least six times
Check public and protected routes
Flip framework defaults one line at a time
Apply route helper fix to test support

Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once. Length counted with cl100k_base; the agent that loads this file may tokenize it differently.