Ripwire Layers

Layers with ripwire

Nearest neighbours: • You want the file→file dependency graph itself (not a health read) → --deps is step 2 below, or go straight to it if you already know you want godfiles/cycles. • Reviewing YOUR OWN diff for coupling risk, not a repo-wide sweep → ripwire-change-check. • Unfamiliar subsystem, general risk sweep (not architecture-specific) → ripwire-fresh-eyes.

Trigger: you want a factual picture of architectural health before a large refactor, or you're reviewing whether the codebase is trending toward or away from clean layering.

<dir> = repo root. Every metric below has a NUMBER → THRESHOLD → ACTION — don't stop at reporting it.

1. Layering rules (if a rules file exists) — ripwire <dir> --arch=rules.txt Output: <arch> with violations listed by layer pair and file. Exit 2 = NEW violations found (CI gate). If no rules file exists yet, this step is the prompt to write one (grammar: layer NAME = substr…, deny FROM -> TO, allow FROM -> TO; # comments). Action: every violation is a concrete edge to either fix (remove the dependency) or explicitly allow (document why it's intentional) — don't leave it silently baselined forever.

   Adopting rules on a codebase with existing debt — the baseline workflow:

   • ripwire <dir> --arch=rules.txt --baseline — accept every CURRENT violation as known debt: writes a .ripwire_arch_baseline sidecar in the CWD (commit it), exits 0.
   • From then on, plain --arch=rules.txt suppresses baselined violations and exits 2 only on NEW ones — the gate stops the bleeding without demanding an up-front cleanup.
   • --arch=rules.txt --baseline-update — deliberately accept new debt by merging current violations into the sidecar (exit 0). Use sparingly, in its own reviewed commit.

   --arch=rules.txt also emits <metrics propagation_cost="X.XXX"> — the DSM (design-structure-matrix) transitive-closure density: the fraction of the file-dep graph reachable from an average file (MacCormack; a validated coupling form, computed here as a directory-level estimate from name-based deps). Direction: lower is better — 0 means files are mostly isolated from each other's transitive reach, 1 means touching any file risks rippling through the whole tree. Action at a high reading (no fixed universal threshold — compare against this same repo's own history/other modules, or treat >0.3 as worth a look): a high propagation cost is a change-amplification TAX — every edit here is more likely to have knock-on effects. Don't just report the number; find which directories are driving it (the <m path=... ca= ce=> per-module rows) and formalize a boundary between them — a layer/deny rule in rules.txt that would have caught the coupling.

2. Dependency health — ripwire <dir> --deps --legend=compact Output: <deps> with <health> metrics:

   • acd (average component dependency) — lower is better
   • nccd (normalized CCD) — < 0.25 is healthy
   • shape — "horizontal" (layered, good) vs "vertical" (coupled, risk) Then <godfiles> ranked by afferent (dependents) — each godfile is an implicit layer boundary that hasn't been formalized. afferent/cycles are validated defect predictors; nccd (Lakos) and the --arch Martin Ca/Ce/I/A/D I/A/D/zone= block are design heuristics — mechanistically plausible, widely implemented, but no independent outcome-based study has validated them. Trust the god-file/cycle read hardest; treat nccd/D as descriptive, not proof. Action: a file in the top-3 by afferent is doing double duty as a de-facto layer boundary with no rule enforcing it — that's the concrete next step, not just a note: add it as a named layer in rules.txt and write the deny rules that keep new dependents out of its internals. A cycle in --report is worse than a high-afferent file — break it before formalizing anything downstream of it.

3. Module clustering — ripwire <dir> --communities --legend=compact Output: <communities modules="N"> clusters with dominant directory and lead symbols. <bridge edges="N"> shows where clusters are tightly coupled across module boundaries. High bridge counts between non-adjacent modules are the layering violations --arch catches. Action: a high bridge count between two clusters that AREN'T adjacent in your intended layering is the specific violation to gate — turn it into a deny FROM -> TO rule rather than leaving it as an observation; a high bridge count between clusters that ARE meant to talk to each other is fine and doesn't need a rule.

4. Mermaid diagram (optional, for visual review) — ripwire <dir> --mermaid Output: a flowchart LR Mermaid snippet with module nodes and inter-module call counts. Paste at mermaid.live to render. Edges labeled with high counts are the hot coupling seams — same action as step 3: a heavy edge crossing an intended boundary becomes a deny rule.