Order aggregated CSS by module dependency in styled-ppx.generate

[davesnx]

styled-ppx.generate now emits a module's rules after the rules of every module it depends on, instead of in the order dune lists the files. Every atomic rule has the same specificity, so a consumer's equal-specificity declaration now beats its dependency's by construction, and renaming a file no longer moves rules. Modules with no dependency between them keep alphabetical path order, so output changes only where a dependency forces it. Dedup by first occurrence runs after the sort.

Mechanism: a new packages/generate/order.ml computes each file's referenced module names with compiler-libs Depend on the AST the generator already reads (the same walk ocamldep -modules uses), resolves them to input files by longest shared directory prefix, and runs a Kahn sort that always picks the smallest path among ready nodes. A cycle can only come from an ambiguous module name; the generator warns once, drops the edge whose source sorts last, and continues. --order source keeps the previous behaviour for one release; --log info prints the module order and --log debug the edges.

$ styled-ppx.generate a_consumer.ml z_base.ml   # a_consumer references Z_base
/* This file is generated by styled-ppx, do not edit manually */
.css-...-base{...}
.css-...-consumer{...}

Evidence at a594d02:

• New cram tests order-dependency, order-unrelated, order-ambiguous-name, order-source-flag, order-cycle in packages/generate/test; log-flags.t gains the new order: info line.
• On the Ahrefs monorepo's 5,824 post-PPX files: source and dependency order produce the identical set of 23,274 rules; dependency order took 3.7 s against 2.7 s for source order; two runs with different input order gave byte-identical dependency-order output.
• make format-check, make build, make test: all exit 0.

Review from packages/generate/order.ml, then order_by_dependency in generate.ml. The resolution rule for same-named modules is deliberately conservative (no edge on a tie) and is replaced by library membership in the follow-up library-order PR.

Risk: two-way door. A revert restores input-order emission. Until then, consumers aggregating several modules see rules move relative to today; a winner-diff script in the next PR of this stack lists exactly which cascade ties flip.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
styled-ppx	Ignored	Preview	Sep 23, 2026 6:40am UTC

[davesnx]

Superseded by #616, which carries this branch's commits rebased onto main together with the rest of the CSS ordering work.