Custom Rules

Custom Rules

Manage the project's custom rules file at .ruby-upgrade-toolkit/rules.yml. The other commands (audit, plan, fix, upgrade, status) pick this file up automatically — this skill is purely for authoring and introspection.

Design philosophy. The rules file is project policy, committed to the repo. This skill is a convenience layer over it: power users can edit the YAML by hand and everything still works. Every mutating subcommand shows a diff and confirms before writing.

Backward compatibility guarantee. With no rules.yml, every command in this toolkit behaves byte-identically to a version without this feature. The file is strictly additive.

Canonical references

Load once at the start, reuse for every subcommand:

• Schema — $CLAUDE_PLUGIN_ROOT/skills/rules/references/schema.md Data model for every rule type, all fields, all constraints.
• Engine — $CLAUDE_PLUGIN_ROOT/skills/rules/references/rules-engine.md The shared load/validate/preflight logic used by this skill AND by the other skills that consume rules. Same algorithms, one source of truth.
• Starter template — $CLAUDE_PLUGIN_ROOT/skills/rules/references/starter-template.yml Exact YAML written by init. Kept valid against the current schema as a golden-test subject.

Subcommand Dispatch

Parse the first argument; everything after is subcommand-specific.

Arg	Handler
(none)	list --active
init	Step 1
validate	Step 2
list	Step 3
show	Step 4
add	Step 5
remove	Step 6
disable	Step 7
enable	Step 7
explain	Step 8

Any unknown subcommand: print the subcommand table and exit.

---

Step 1: init

Create .ruby-upgrade-toolkit/rules.yml with a starter template.

1a. Guard against overwrite

test -f .ruby-upgrade-toolkit/rules.yml && echo EXISTS

If the file exists, print and exit:

.ruby-upgrade-toolkit/rules.yml already exists.
Use /ruby-upgrade-toolkit:rules list to see active rules,
or /ruby-upgrade-toolkit:rules validate to check it.

1b. Create the directory

mkdir -p .ruby-upgrade-toolkit

1c. Copy the starter template

Read the file at $CLAUDE_PLUGIN_ROOT/skills/rules/references/starter-template.yml and write its contents verbatim to .ruby-upgrade-toolkit/rules.yml.

1d. Announce

✓ Created .ruby-upgrade-toolkit/rules.yml with commented examples of all 8 rule types.

All examples are disabled by default (enabled: false). Edit the file or use
`/ruby-upgrade-toolkit:rules enable <id>` to activate any you want.

Next:
  /ruby-upgrade-toolkit:rules list --all     # see every example
  /ruby-upgrade-toolkit:rules validate       # schema-check
  /ruby-upgrade-toolkit:rules add gem-swap   # add your own rule interactively

---

Step 2: validate

Run the full validation pipeline from the engine reference.

2a. Load and parse

Apply the "Load" section from rules-engine.md. If the file is missing, print:

No .ruby-upgrade-toolkit/rules.yml found.
Run /ruby-upgrade-toolkit:rules init to create one.

Exit 0 (missing file is not an error — the toolkit behaves correctly without one).

2b. Schema check

Apply the "Schema check" and "Conflict detection" sections from rules-engine.md. Collect all findings with severity error | warning | info.

2c. Preflight check (credentials)

For any rule with a source.credentials_env, verify the env var is set and non-empty. Missing credentials are warning (not error) here — at /validate time the file may be authored before the env var is configured. (At audit/upgrade preflight time they become error.)

2d. Report

.ruby-upgrade-toolkit/rules.yml — Validation Report

Schema: OK (N rules, M active, K disabled)

Errors: 0
Warnings: 2
  - [devise-pin] constraint '~> 4.9' has no effect on swap target (phantomjs-to-selenium replaces the gem)
  - [reek-gate] credentials_env 'BUNDLE_REEK__CO' is not currently set; will need to be set before /upgrade runs
Info: 0

Exit: 0 (no errors)

On any error, exit non-zero so CI can gate on this. On warnings only, exit 0.

---

Step 3: list

Flag: --all includes disabled rules (default shows active only).

3a. Load

Apply the "Load" section from rules-engine.md. If the file doesn't exist, print:

No .ruby-upgrade-toolkit/rules.yml found.
Run /ruby-upgrade-toolkit:rules init to scaffold one.

and exit.

3b. Render table

One row per rule. Columns: id, type, target (gem name, target name, or pattern abbreviation), enabled, when.

Custom Rules (N active, K disabled)

ID                      TYPE                TARGET           ENABLED  WHEN
devise-pin              gem-constraint      devise           yes      all
phantomjs-to-selenium   gem-swap            phantomjs        yes      all
rails-lts-substitute    target-substitute   rails            yes      all
brakeman-gate           verification-gate   brakeman         yes      all
no-reek                 verification-gate   reek             no       all
load-defaults-6         policy-override     load_defaults    yes      rails-phases

Full schema: /ruby-upgrade-toolkit:rules show <id>

For --all, also include rules where enabled: false.

---

Step 4: show <id>

4a. Load and find

Apply the "Load" section. If <id> not found:

No rule found with id '<id>'.
Active rules: devise-pin, phantomjs-to-selenium, rails-lts-substitute, brakeman-gate

4b. Render

Show:

1. The raw YAML block for the rule.
2. Computed effects — human-readable description of what this rule will do when applied, derived from the schema reference.
3. Phases it will fire in — given the current project state (detected Ruby/Rails versions) and the rule's when clause, list the exact phase names.
4. Preflight status — credentials env vars (if any), their set/unset state.
5. Potential conflicts — other rules in the file that touch the same gem/target, with their resolution (who wins on what).

Example:

─── rule: phantomjs-to-selenium ──────────────────────────────────────

Raw YAML:
  - id: phantomjs-to-selenium
    type: gem-swap
    from: phantomjs
    to:
      - { name: selenium-webdriver, constraint: '~> 4.0' }
      - { name: webdrivers, constraint: '~> 5.0' }
    code_transforms:
      - pattern: "Capybara.javascript_driver = :poltergeist"
        replacement: "Capybara.javascript_driver = :selenium_chrome_headless"
    description: "Replace phantomjs with selenium + headless chromium"

Computed effects:
  - Remove 'phantomjs' from Gemfile
  - Add 'selenium-webdriver ~> 4.0' and 'webdrivers ~> 5.0' to Gemfile
  - Rewrite 1 pattern in application code (literal match)

Will fire in phases (current: Ruby 3.2.4, Rails 6.1):
  - Ruby Phase 2: Ruby 3.3.1 (first phase that runs apply steps)

Preflight: no private gem source required ✓

Conflicts: none

─────────────────────────────────────────────────────────────────────

---

Step 5: add <type>

Interactive Q&A authoring. <type> must be one of the eight rule types. If missing or invalid, print the list of types and exit.

5a. Look up field requirements

Load the "Field schema per type" section from schema.md. Collect the required and optional fields for the given <type>.

5b. Run the Q&A

For each required field, ask one question. For optional fields, ask "? (y/N)" and branch on answer. For enum fields, present numbered choices.

Type-specific prompts — see the "Authoring prompts" section of schema.md. Every type has a canonical question set documented there. Follow it exactly so authored rules are consistent.

Generating the id. After collecting fields, propose a default id derived from type + targets (e.g., gem-swap from=phantomjs → phantomjs-swap). Always let the user override. Check for collisions with existing IDs; if collision, append -2, -3, etc. and re-ask for confirmation.

5c. Preview

Render the new rule as YAML. Show the diff against the current file (conceptually: the new block will be appended under rules:).

5d. Validate before write

Run the same validation pipeline as validate against the in-memory merged file (existing rules + new rule). If any errors, print them and abort; the user can re-run add with corrections. Warnings are OK to proceed but are shown.

5e. Write

Append the new rule to rules.yml. If the file doesn't exist yet, create it with the minimal version: 1 / rules: [] skeleton first.

5f. Announce

✓ Added rule '<id>' to .ruby-upgrade-toolkit/rules.yml

Next:
  /ruby-upgrade-toolkit:rules show <id>      # verify
  /ruby-upgrade-toolkit:rules explain        # see which phases it will fire in

---

Step 6: remove <id>

6a. Load and find

If not found, print the same "No rule found" message as show.

6b. Preview

Show the rule's YAML block and a one-line summary of what will be removed. Explicitly warn if this rule is enabled: true and is the only one of its type (e.g., removing the sole target-substitute for rails will restore mainline Rails upgrade behavior).

6c. Confirm

Remove rule '<id>'? This cannot be undone (use 'disable' for reversible deactivation). [y/N]

On y: delete the rule's entry from rules.yml, preserving comments and surrounding structure. On N: print "Aborted. File unchanged." and exit.

6d. Announce

✓ Removed rule '<id>' from .ruby-upgrade-toolkit/rules.yml

---

Step 7: disable <id> / enable <id>

7a. Load and find

Same as show.

7b. Flip the flag

Set enabled: false (for disable) or enabled: true (for enable) on the matching rule. If the field is missing, add it. If the value is already the target state, print:

Rule '<id>' is already <disabled|enabled>. No change.

and exit.

7c. Write and announce

✓ Rule '<id>' disabled. It will be ignored until re-enabled.
  /ruby-upgrade-toolkit:rules enable <id>

---

Step 8: explain

Dry-run: show which rules will fire against the current project, which are no-ops, and why.

8a. Load

Apply the "Load" section. If the file is missing, print the same message as list and exit.

8b. Detect current state

ruby -v
cat .ruby-version 2>/dev/null
grep "^ruby " Gemfile 2>/dev/null
grep -A2 "RUBY VERSION" Gemfile.lock 2>/dev/null
bundle exec rails -v 2>/dev/null || true

Record CURRENT_RUBY and CURRENT_RAILS.

8c. For each active rule, determine what will happen

Apply the "Rule resolution" section from rules-engine.md to each rule against the current state. Possible outcomes:

• Will fire — list the phases (e.g., "Ruby Phase 2", "all phases", "Rails Phase 1")
• Won't fire (no-op) — list the reason:
  • gem-swap: from gem is not in Gemfile
  • code-transform: pattern does not match any file content
  • target-substitute: target gem is not present
  • verification-gate: the command binary is not installed
  • when clause excludes current or future phases
• Will fail preflight — missing credentials env var (hard error at /upgrade time)

8d. Render

─── /ruby-upgrade-toolkit:rules explain ──────────────────────────────

Current state: Ruby 3.2.4, Rails 6.1.7

Active rules (4):

  [devise-pin]               gem-constraint
    Will fire: Ruby Phase 2, Rails Phase 1 (all apply phases)
    Effect: force devise >= 4.9 during bundle resolution

  [phantomjs-to-selenium]    gem-swap
    Will fire: Ruby Phase 2 (first apply phase)
    Matched: phantomjs found in Gemfile, 2 Capybara config sites match

  [rails-lts-substitute]     target-substitute
    Preflight: BUNDLE_RAILSLTS__COM is not set — /upgrade will fail

  [brakeman-gate]            verification-gate
    Will fire: verify step of every phase
    Command: 'bundle exec brakeman --no-pager --exit-on-warn'
    Binary check: OK (brakeman 6.1.2 found)

Disabled rules (1):
  [reek-gate]                verification-gate — re-enable with `/rules enable reek-gate`

─────────────────────────────────────────────────────────────────────

---

Output conventions

All subcommands respect these:

1. Mutating subcommands always preview + confirm. Never silently write.
2. Default to list when invoked with no arguments, so a bare /ruby-upgrade-toolkit:rules gives an at-a-glance summary.
3. Respect enabled: false. Disabled rules are shown in list --all and show <id> but never influence explain, audit, plan, fix, upgrade, or status.
4. Exit non-zero on validate errors. Warnings exit 0. This makes validate usable in CI without further flags.
5. Never print credential values. Only the env var name, and whether it's set/unset.