Building Remix Design System

Building a Design System Package on Remix

Use using-remix for application UI that consumes base Remix or Fortal. This skill owns the standalone package, source-traceability, token-pipeline, and public-API workflow for a different design system. Use the project's Mix skill alongside it when implementation depends on exact versioned Mix or codegen syntax.

The result of following this skill is a standalone package under packages/ that:

• reuses Naked UI for interaction behavior, Mix for styling mechanics, and Remix for component machinery — and adds only the target system's design decisions on top;
• generates its entire token surface from pinned, traceable sources (never hand-copied values), reproducibly and CI-enforced;
• exposes an idiomatic public API in the target system's vocabulary, not Remix's or Fortal's.

remix_fortal is the in-repo precedent for the packages/<name> shape this skill describes: a standalone, separately versioned package that depends on remix, owns its own token scope, and generates its widget catalog with @MixWidget. Follow that structure. Do not clone Fortal's content and swap colors — its values are hand-authored against a pinned Radix parity contract, whereas a new design system generates its tokens from its own pinned sources.

Architecture at a glance

naked_ui        interaction primitives (focus, press, semantics, keyboard)
   ↑
mix             styling engine, tokens, MixScope, variants
   ↑
remix           reusable component machinery (ButtonStyler, specs, widgets)
   ↑
<your package>  generated tokens + <System>Scope + component recipes/facades
                exposes ONLY <System>* widgets and tokens publicly

Three layers per package:

The pipeline that produces generated/ lives in tool/ and is development-only — consumers never need its toolchain or network access.

Design sources — any input works

The pipeline is source-agnostic. Classify what is available per token domain (colors may come from a better source than spacing) and take the highest tier per domain — see references/source-extraction.md:

Everything converges on one committed snapshot; normalize → generate → verify run identically no matter where the values came from. Mixed tiers are normal. When the input is a brief, there is nothing to extract — design the tokens (confidence designed), record the rationale in the ADR, and treat the brief itself as the pinned source (commit it, or quote it verbatim in the ADR).

Workflow

Work through the phases in order. Each phase ends with something verifiable.

Phase 0 — Pin sources and record decisions

1. Inventory every available source and classify each token domain by tier (table above). Record the tiers plus a conflict-precedence order in the ADR.
2. Pin whatever can be pinned: exact versions and commit SHAs for tier 1; file versions, URLs + retrieval dates, and sha256 hashes for everything else. No caret ranges, no "latest", no un-dated web sources. For a brief, commit the brief.
3. Record in an ADR (docs/adr/0001-…): source tiers, dependency strategy, what the first release covers, what is explicitly out of scope, font/icon strategy, and naming/trademark constraints.
4. Decide the theme model up front: how many themes, whether the system uses role-based tokens (semantic names like interactivePrimary), numbered scales (like Radix/Fortal's accent1–12), or something else. Preserve the target system's model — never translate it into another system's concepts. When designing from a brief, pick one model deliberately and record why.

Phase 1 — Package scaffold

Create packages/<name>/ with pubspec.yaml, analysis_options.yaml, README.md, CHANGELOG.md, LICENSE, NOTICE, .gitignore, lib/<name>.dart.

Non-obvious requirements (each one has produced a real failure):

• Read the current root managed dependencies and packages/remix/pubspec.yaml, then use that workspace-tested Remix/Mix/ annotations/generator set. Do not copy dependency floors from an older design-system example or upgrade one member of the codegen set in isolation.
• publish_to: none while remix is a path dependency — otherwise the analyzer emits a fatal invalid_dependency warning. Leave a comment saying when to remove it.
• Add the package to the root pubspec.yaml in two places: the workspace: list and the melos: packages: globs. Nested members (packages/<name>/example) must be listed explicitly — packages/* does not cross path separators, so melos scripts silently skip them.
• NOTICE must carry upstream attribution (license of the design system, font licenses, trademark disclaimer) and the package license must be compatible with the upstream token license.
• Exclude tool/ from Dart analysis and gitignore tool/build/ and any toolchain dependency directories (e.g. tool/**/node_modules/).
• The main entry point (lib/<name>.dart) must not re-export the full Remix or Mix API — export only the package's scopes, tokens, and components.

Phase 2 — Token pipeline

Read references/token-pipeline.md before writing any pipeline code. When the source is not executable code, also read references/source-extraction.md — only the extract stage changes:

• Tier 1 sources use an automated extract script.
• Everything else replaces it with a committed, hand-authored tool/authored/<sys>-authored-tokens.json where every value carries a citation and a confidence level (specified/derived/measured/ assumed/designed), authored inventory-first so gaps are explicit. Normalize, generate, and verify run unchanged on top of it.

The contract (runtime-agnostic — pick whatever single toolchain best reads the source, as long as these properties hold):

• Four stages: extract → normalize → generate → verify, with all conversion rules in one shared module so stages can never disagree.
• The normalized JSON snapshot and the generated Dart are committed.
• Regeneration from the same source lock is byte-identical, and the verify script is read-only (every writer takes --out).
• Every generated file carries provenance headers (source, versions, commit, SPDX license) and contains no unparsed CSS units.
• Add a CI workflow that runs the verifier on PRs touching the package — it needs only the script runtime, no dependency install (generation runs from the committed snapshot). Docs may only claim "CI enforced" once this workflow file exists.

Phase 3 — Foundation runtime

Read references/foundation-patterns.md. The essentials:

• <System>Scope resolves the generated token maps into a MixScope. Memoize the per-theme base map (top-level cache, Map.unmodifiable) so repeated scope rebuilds return the identical instance — Mix dependents then short-circuit equality checks. Rebuilding ~hundreds of map entries per ancestor rebuild is real, measured waste.
• Any typed overrides object needs value equality (==/hashCode), or the scope's updateShouldNotify always fires.
• Everything the scope configures must be readable back from context (e.g. overridesOf(context)) so helpers like type resolvers can honor it without re-plumbing at every call site. A setting that only affects half the system (e.g. a fontFamily override that reaches fixed text styles but not fluid ones or component labels) is a bug.
• Contextual scopes (of/maybeOf pattern): provide maybeOf whenever a component has its own default that differs from the scope's default — only maybeOf can distinguish "no scope present" from "scope chose its default".
• Runtime lookups keyed by name must throw ArgumentError in all build modes on unknown input — an assert-plus-silent-fallback ships typos to production as wrong-but-plausible rendering.
• If the system has an indexed/leveled concept (layered surfaces, elevation levels), generate the index mechanically and add a test asserting the hand-written enum covers every generated entry — hand-written switches over generated data drift.

Phase 4 — Components

Read references/component-playbook.md before the first component — it contains the Remix/Mix behavioral gotchas that have produced real bugs (loading-state styling, focus-ring layout shift, and others).

Per component:

1. Write the worksheet specs/components/<component>.yaml first (template in the playbook). It is the reviewable bridge between the design source and the Flutter code: anatomy, kinds, sizes, states, exact tokens, non-token measurements with sources, and approved approximations.
2. Apply the wrapper decision rule: generate a @MixWidget wrapper only when the target system's anatomy matches the Remix component, the public API reads in the target vocabulary, and no Remix-only types leak. Otherwise write a hand-written facade (a StatelessWidget that builds a *Styler recipe and calls it).
3. Style through tokens, never copied values: token() inside styler chains, TextStyler().style(textToken.mix()) for text styles, token.resolve(context) for direct widget use. A hand-copied measurement "kept in sync" with a token is a drift bug waiting to be found.
4. Memoize recipes. Styler chains are pure functions of a few enums; cache them in a top-level Map<(kind, size, …), Styler> keyed by records.

Phase 5 — Tests, example, docs

• Token tests: inventory counts against the source manifest, per-theme spot values, cached-and-unmodifiable base maps, override behavior, partial-theme omissions preserved (never fabricate a missing source value).
• Drift tests: every hand-written enum that mirrors generated data gets a coverage test against the generated structure.
• Widget tests: one regression test per state that has distinct visuals — including loading (assert the container color is the kind's fill, not the disabled treatment) and default size without any scope (assert the measured height). Spinners animate forever: use tester.pump(duration), never pumpAndSettle, in loading tests.
• Example app: must consume the package's own token system for its chrome (token.resolve(context)), never hand-picked palette values — the example is the first pattern adopters copy.
• Docs claims must match code. If the README promises something ("CI enforced", "applies to every text style"), verify the mechanism exists.

Definition of done (per release)

• dart analyze <pkg> <pkg>/example clean (package root included — catches pubspec lints).
• flutter test green, including the regression matrix above.
• The verify script passes; a full fresh extract→normalize→generate leaves git status clean.
• Worksheets exist for every shipped component; approximations documented.
• NOTICE/LICENSE/attribution complete; no temporary claims in docs.

Quick pitfall index

Ten rules that have caused real bugs or review findings, each explained where it applies — component gotchas (1, 2, 4, 5) in references/component-playbook.md, pipeline rules (3, 8, 9, 10) in references/token-pipeline.md, scaffold rules (6, 7) in Phase 1 above:

1. RemixButton folds loading into the disabled widget-state — style loading via the disabled variant, parameterized by a loading flag.
2. Focus rings via borderAll shift layout and clobber the kind's border — paint them with foregroundDecoration instead.
3. Mix tokens override == → they cannot be const-map keys; emit generated maps as top-level finals, not per-call functions.
4. num.clamp() returns num — add .toInt() before indexing.
5. pumpAndSettle never settles while a spinner animates.
6. melos/workspace globs don't cross path separators — list nested example packages explicitly.
7. Path dependency without publish_to: none = fatal analyzer warning.
8. Source color strings may use CSS Color 4 syntax (rgb(141 141 141 / 30%)) — parse both legacy and modern forms.
9. Version pins must have one source of truth (derive provenance from the pinned manifest, don't restate versions in scripts).
10. Never use Date.now()/randomness in generation — byte-identical output is the invariant that makes verification possible.

Additional resources

• references/source-extraction.md — getting tokens out of any source (code, Figma, websites, PDFs, screenshots, or a brand brief).
• references/token-pipeline.md — stage contracts for extract → normalize → generate → verify.
• references/foundation-patterns.md — scope, theme map, contextual scopes, type, and motion runtime patterns.
• references/component-playbook.md — per-component workflow, worksheet template, and Remix/Mix gotchas.