tiny-pattern-ts/project-specs.md

# Project Specifications for TypeScript NPM Module

- name of package: tiny-pattern-ts

## 0. References

typescript-lib-starter-tiny => https://github.com/tmueller/typescript-lib-starter-tiny/

## 1. Development Environment

- **TypeScript**: Use strictest practical rules. Inline in `tsconfig.json` (not
  via `@tsconfig/strictest`). The rule set is: `strict`, `noImplicitAny`,
  `noImplicitThis`, `alwaysStrict`, `strictNullChecks`, `strictFunctionTypes`,
  `strictBindCallApply`, `strictPropertyInitialization`, `noImplicitReturns`,
  `noFallthroughCasesInSwitch`, `noUncheckedIndexedAccess`, `noImplicitOverride`,
  `noUnusedLocals`, `noUnusedParameters`, `forceConsistentCasingInFileNames`,
  `isolatedModules`, `verbatimModuleSyntax`.
- **EditorConfig**: Use `.editorconfig` from typescript-lib-starter-tiny.
- **oxfmt**: Rust-based formatter, Prettier-compatible. Replaces Prettier.
  Config in `.oxfmtrc.json` (same shape as `.prettierrc`).
- **oxlint**: Rust-based linter. Replaces ESLint. Config in `.oxlintrc.json`
  with `typescript`, `unicorn`, `oxc`, `import` plugins. Categories enabled
  as errors: `correctness`, `suspicious`, `restriction`. As warnings: `perf`,
  `style`. `nursery` is off.
- **oxlint rules disabled by design** (in `.oxlintrc.json`):
    - `eslint/no-undefined` — we use `undefined` as the no-match sentinel.
    - `eslint/sort-keys` — handler/case order is semantic, not alphabetical.
    - `eslint/id-length` — `T`, `R`, `U`, `V` are standard TS generics.
    - `import/no-named-export` — false positive on library entry re-exports.
  For `*.test.ts` files additionally: `no-unused-expressions` (for
  `expectTypeOf(...)` calls), `no-empty-file` (we have a single import
  per test file in some cases), `import/no-nodejs-modules` (we use
  `node:test`/`node:assert`/`node:fs` intentionally), `eslint/no-magic-numbers`
  (literals in tests are fine).
- **Import sorting**: built into oxfmt (no separate plugin).
- **cspell**: Basic spelling configuration. Words dictionary in `cspell.json`
  covers tooling names (`oxlint`, `oxfmt`, `oxc`, `nodenext`,
  `oxfmtrc`, `oxlintrc`, `sortpackagerc`, `EDITMSG`, `typescriptteam`,
  `gitmoji`, `dbaeumer`, `msvc`) and a few library names (`tslib`,
  `typefest`, `lefthook`).
- **Lefthook**: Pre-commit checks (run in parallel, lefthook v2 schema).
  Single source of truth for the underlying commands is in
  `package.json#scripts`; the lefthook config only describes *what to
  run on which files*. Hooks that should run on staged files
  (`oxlint`, `oxfmt`, `cspell`) set the `LEFTHOOK_FILES` env var to
  the staged-files list via a `sh -c` wrapper, and the npm script
  uses `${LEFTHOOK_FILES:-<default>}` to default to the full project
  when invoked manually:
    - `pre-commit.commands.oxlint` (glob `*.{ts,tsx,js,jsx,mjs,cjs}`):
      `sh -c 'LEFTHOOK_FILES="$0" npm run check:oxlint' {staged_files}`
    - `pre-commit.commands.oxfmt` (glob `*.{ts,tsx,js,jsx,mjs,cjs}`):
      `sh -c 'LEFTHOOK_FILES="$0" npm run check:oxfmt' {staged_files}`
    - `pre-commit.commands.cspell`:
      `sh -c 'LEFTHOOK_FILES="$0" npm run check:cspell' {staged_files}`
    - `pre-commit.commands.sort-package-json`:
      `npm run check:package` (no file args needed)
    - `pre-commit.commands.typecheck`:
      `npm run check:tsc` (no file args needed)
  `outdated` is intentionally NOT a pre-commit check (it can flag
  upstream patch releases that aren't actionable locally); it runs in
  CI and via the explicit `lefthook run outdated` command.

- **Additional Dev Dependencies**:
    - lefthook
    - sort-package-json
    - check-outdated
    - c8 (coverage for `node --test`)
    - expect-type (type-level assertions in tests)
    - oxfmt, oxlint (with their native bindings as `optionalDependencies`
      so the correct binding is selected per platform automatically)
    - typescript (TS 7)
    - @types/node
    - tslib (available for future runtime helper imports)
    - type-fest (utility types)

## 2. Build & Test

- **Build Tool**: TypeScript 7 (`tsc`) — no bundler, no Vite. The build
  is a plain `tsc -p tsconfig.build.json` invocation that emits ESM
  JavaScript and `.d.ts` declarations to `dist/`. ESM only, no CJS.
- **Testing**: Node's built-in `node --test` with `--strip-types` (Node
  22.6+, unflagged on Node 24/26). Test files are co-located with
  source as `*.test.ts`. No Vitest.
- **TypeScript Build Output**: `dist` directory (set in
  `tsconfig.build.json#outDir`; `tsconfig.json` keeps `outDir` for
  editor tooling but excludes tests from emission via
  `tsconfig.build.json#exclude`).
- **Import extensions**: Source uses `.ts` extensions in imports
  (e.g. `from "./match.ts"`) so `node --strip-types` resolves them
  at test time. TypeScript's `rewriteRelativeImportExtensions` (in
  `tsconfig.build.json`) rewrites these to `.js` in the emitted
  `dist/*` output, so consumers see conventional ESM imports.
- **TypeScript Compiler Options Notes**:
    - `allowImportingTsExtensions: true` is set in the root
      `tsconfig.json` (works because the root config has `noEmit: true`).
    - `rewriteRelativeImportExtensions: true` is set in
      `tsconfig.build.json` to rewrite `.ts` to `.js` on emit.
    - `module: nodenext`, `moduleResolution: nodenext` for ESM-first
      Node packages.
    - `verbatimModuleSyntax: true` enforces explicit `import type`.
    - `target: es2024`, `lib: ["es2024"]` (Node 26 supports all ES2024
      features natively).
- **Additional Dev Dependencies** (for types and tests):
    - `tslib` — available for runtime helper imports; not currently
      used by source (kept for future use per the original spec).
    - `type-fest` — utility types; not currently used by source
      (kept for future use per the original spec).
    - `@types/node` — types for `node:test`, `node:assert`, `node:fs`.
- **Node Version**: `>=26` (engines field). Pinned via `.node-version`
  for fnm/nvm/volta/mise auto-switching and CI
  (`actions/setup-node@v4` with `node-version-file: .node-version`).

## 3. Project Structure & Files

- **.gitignore**: Ignore `dist`, `node_modules`, `coverage`, and other
  common files.
- **.node-version**: Single line containing the Node major version
  (currently `26`). Used by version managers and CI.
- **.npmignore**: Ignore `node_modules/`, `coverage/`, `*.log`,
  `*.tsbuildinfo`, `src/`, `.vscode/`, `.editorconfig`,
  `.oxfmtrc.json`, `.oxlintrc.json`, `.node-version`, `cspell.json`,
  `lefthook.yml`, `.sortpackagerc.json`, `commit-message-template`.
  (Note: `dist/` is included via `package.json#files`, not by absence
  from `.npmignore`.)
- **.oxfmtrc.json**: oxfmt configuration (Prettier-shaped).
- **.oxlintrc.json**: oxlint configuration.
- **.oxlintrc.json + .oxfmtrc.json** replace the old `.eslintrc.cjs`
  and `.prettierrc`.
- **LICENSE**: MIT.
- **README.md**: Scaffolded.
- **commit-message-template**: From typescript-lib-starter-tiny.
- **Target Environments**: Node 26 LTS only (no browser target; this
  is a pure Node library, no DOM, no DOM lib in tsconfig).
- **No React, No CJS, ESM only**.

## 4. Automation & Quality

- **Version Automation**: Use standard `npm version` for versioning.
- **Unused Dependency Check**: Use `check-outdated` (devDep, runs in CI
  and via the explicit `lefthook run outdated` command).
- **No commitlint, no conventional commits**. Commits use gitmoji
  prefixes (e.g. `:sparkles:`, `:wrench:`, `:bug:`, `:fire:`,
  `:white_check_mark:`, `:tada:`) for at-a-glance categorization.

## 5. Scripts

### SETUP

- `use:git-commit-message`: Set up commit message template (if needed).

### TEST

- `test`: Run `tsc --noEmit` then `node --test --strip-types src/`.
- `test:unit`: Run unit tests with `node --test --strip-types src/`
  (no preceding typecheck).
- `test:ci`: Run tests in CI mode with c8 coverage (text + lcov + html
  reporters), uploading `coverage/` as an artifact.

### BUILD

- `build`: Build the project using `tsc -p tsconfig.build.json`
  (emits `dist/*.js` + `dist/*.d.ts` + sourcemaps, with `.ts`
  imports rewritten to `.js`).

### CLEAN

- `clean`: Remove `dist/` via `node -e "fs.rmSync('dist', {recursive:true, force:true})"`.
  (Replaces `clean:build` from the original spec — same effect,
  no `rimraf` dep needed.)

### CHECK

- `check`: Run all checks in order — `check:oxlint`, `check:oxfmt`,
  `check:tsc`, `check:cspell`, `check:package`, `check:outdated`.
- `check:oxlint`: `oxlint ${LEFTHOOK_FILES:-src}` — lints `src/`
  by default; when invoked from the lefthook pre-commit hook with
  `LEFTHOOK_FILES` set to the staged-files list, lints only those
  files. This is the single source of truth for the oxlint command
  and is shared between the manual `npm run check` and the pre-commit
  hook.
- `check:oxfmt`: `oxfmt --check ${LEFTHOOK_FILES:-src}` — same
  pattern as `check:oxlint` (whole `src/` by default, staged files
  from lefthook).
- `check:tsc`: `tsc --noEmit`.
- `check:cspell`: `cspell lint ${LEFTHOOK_FILES:-.}` — walks the
  project root by default; from lefthook, only the staged files.
- `check:package`: `sort-package-json --check`.
- `check:outdated`: `check-outdated --ignore-pre-releases --ignore-packages @oxfmt/binding-*,@oxlint/binding-*`. The oxc native bindings are declared as `optionalDependencies` so the correct one is selected per platform automatically; the `*`-platform bindings show as "not installed" on the current platform and are explicitly ignored here.

### FIX

- `fix:oxlint`: `oxlint --fix src`.
- `fix:oxfmt`: `oxfmt src`.
- `fix:package`: `sort-package-json --write`.
  (There is no `fix` aggregator in the scripts; run the `fix:*` scripts
  individually.)

### HOOKS

- Lefthook runs the relevant `check:*` scripts on staged files in
  parallel for pre-commit. See `lefthook.yml`.

---

## 6. Repository & CI/CD

- **Repository**: Hosted on GitHub.
- **Build Pipeline**: GitHub Actions (`.github/workflows/ci.yml`).
    - `build` job on push and pull_request to `main` and on
      `workflow_dispatch`. Steps: `actions/checkout@v4`,
      `actions/setup-node@v4` (with `node-version-file: .node-version`,
      `cache: npm`), `npm ci`, `npm run build`, `npm run check`,
      `npm run test:ci`, then upload `coverage/` as an artifact.
    - `publish` job: only on `refs/tags/*`, depends on `build`. Steps:
      `actions/checkout@v4`, `actions/setup-node@v4` (with
      `node-version-file: .node-version` and `registry-url`),
      `npm ci`, `npm run build`, `npm publish --access public`
      with `NODE_AUTH_TOKEN` from secrets.

## 7. Versioning & Publishing

- **Version Update**: Use `npm version` to bump version after merging
  to main and before publishing.
- **Publishing to npm**: Only publish from CI on tagged commits.
- **Recommended Workflow**:
   1. Develop and merge PRs to main
   2. Run all checks via CI
   3. Bump version with `npm version <patch|minor|major>`
   4. Push tag to GitHub
   5. CI builds and publishes to npm on tag

## 8. NPM Keywords

- pattern-matching
- pattern
- match
- algebraic-data-types
- adt
- typescript

> The library is for pattern matching (not regex), similar to F#'s
> pattern matching, for TypeScript/ESM environments.

## 9. Code Coverage

- **Tool**: c8 (V8-native coverage, no instrumentation step).
- **Configuration**: c8 has no project config; the report shape is
  pinned in the `test:ci` script:

```jsonc
"test:ci": "c8 --reporter=text --reporter=lcov --reporter=html node --test --strip-types src/"
```

- **Reporters**: text summary, HTML, and lcov (matching the original
  spec).
- **CI**: `coverage/` is uploaded as a workflow artifact via
  `actions/upload-artifact@v4` (see `.github/workflows/ci.yml`).
- **Optional**: Coverage thresholds can be added in c8 config when the
  library surface stabilizes.

## 10. Source Structure & Tree Shaking

- **Source Directory**: All source code resides in `src/` and is
  exported via `src/index.ts`.
- **Configuration**:
   - `sideEffects: false` in `package.json` (set).
   - ESM-only exports; `package.json#exports` field maps `.` to
     `{"types": "./dist/index.d.ts", "import": "./dist/index.js"}`.
   - Avoid top-level side effects in modules.
   - Explicit re-exports in `index.ts` for best results.
- Source structure (current):
   - `src/index.ts` — public barrel.
   - `src/match.ts` — `match(value).with(...).exhaustive() / .otherwise(...)` builder.
   - `src/pattern.ts` — `P.literal`, `P.type`, `P.when`, `P.any`, `P.shape` constructors and the `Matcher<T>` interface.
   - `src/index.test.ts` — runtime + type-level tests using `node --test` + `expect-type`.
- The human will implement the source code.

## 11. Included Templates from typescript-lib-starter-tiny

### .editorconfig

```plaintext
# Editor configuration, see http://editorconfig.org
root = true

[*]
charset = utf-8
indent_style = space
indent_size = 4
insert_final_newline = true
max_line_length = 80
trim_trailing_whitespace = true
quote_type = double

[*.md]
max_line_length = 0
trim_trailing_whitespace = false

[COMMIT_EDITMSG]
max_line_length = 0
```

### commit-message-template

```plaintext
# If applied, this commit will... (Max 50 char)


# Explain why this change is being made (Max 72 Char) [WHAT and WHY vs HOW]


# Provide links or keys to any relevant tickets, articles or other resources
Resolves #...

# --- COMMIT END ---
# Remember to
#    Use the imperative mood in the subject line
#    Capitalize the subject line
#    Do not end the subject line with a period
#    Separate subject from body with a blank line
#    Use the body to explain what and why vs. how
#    Can use multiple lines with "-" for bullet points in body
```

### README.md Structure (scaffolded)

- Project title and description
- Development
  - Build: `npm run build`
  - Test: `npm run test`, `npm run test:ci`
  - Checks: `npm run check`, `npm run fix:oxfmt`, `npm run fix:oxlint`
- Tooling section listing TypeScript 7, node --test, c8, oxlint, oxfmt,
  cspell, sort-package-json, lefthook
- Requirements: Node.js >= 26
- VSCode integration
  - Debugging
  - Running tests
  - oxc.oxc-vscode provides oxlint and oxfmt in-editor
- Workflows
  - Version updates via `npm version`
  - Publishing via GitHub Actions on tagged commits
- Contribution guidelines
  - Commit signing (GPG)
  - How to set up commit message template (`npm run use:git-commit-message`)
  - Reference to commit-message-template
  - Type-level tests use `expect-type`'s `expectTypeOf(...)` inside
    `node --test` cases

## 12. Project Initialization & Commit Strategy

- Start by initializing git with a `main` branch.
- Initial commit: empty README + LICENSE.
- Create a feature branch: `feature/setup`.
- For each technology or tool added (and its configuration), create a
  separate commit:
   - Prepend each commit message with a matching gitmoji (e.g.
     `:sparkles:` for new features, `:wrench:` for config,
     `:bug:` for fixes, `:fire:` for removals,
     `:white_check_mark:` for tests, `:tada:` for initial commit).
   - Example commit messages used in this project:
     - `:tada: Initial commit with empty README`
     - `:wrench: Track .vscode/settings.json for workspace settings`
     - `:construction_worker: Added GitHub Actions workflow for CI/CD`
     - `:test_tube: Added Vitest configuration with coverage` (later removed)
     - `:sparkles: Scaffolded src/index.ts entry point for library code`
     - `:wrench: Replace Vite/Vitest with TypeScript 7 and node --test`
     - `:wrench: Replace ESLint and Prettier with oxlint and oxfmt`
     - `:fire: Remove Vite scaffold leftovers`
     - `:sparkles: Add initial pattern-matching API`
     - `:white_check_mark: Add expect-type for type-level tests`
     - `:wrench: Declare Node 26 as the supported runtime`
     - `:bug: Use .ts extensions in imports for node --strip-types`
     - `:wrench: Remove Prettier from editor formatter config`
- Each commit should include only the relevant files and configuration
  for that technology/tool. This approach ensures a clean, understandable
  project history and makes it easy to review or revert specific setup
  steps.

## 13. Changelog Automation

- Not currently configured. The intended workflow, when adopted, is a
  changesets-driven release process: feature PRs include a changeset,
  which gets consumed by a release workflow, producing a `CHANGELOG.md`
  and a version bump on merge to main.
- The changelog should be updated as part of the release process.

## 14. Publishing Public

- npm publishing is configured to be public by default.
- `publishConfig: { "access": "public" }` is set in `package.json`.
- The CI/CD pipeline publishes with `--access public` on tagged commits.

## 15. VSCode Integration

- `.vscode/settings.json` uses `oxc.oxc-vscode` as the default
  formatter for `[typescript]`, `[javascript]`, `[json]`, `[jsonc]`,
  `[markdown]`, `[mdx]`, and `[yaml]` (oxfmt under the hood).

```json
{
    "typescript.tsdk": "node_modules/typescript/lib",
    "js/ts.tsdk.path": "node_modules/typescript/lib",
    "[typescript]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "[javascript]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "[json]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "[jsonc]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "[markdown]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "[mdx]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "[yaml]": {
        "editor.defaultFormatter": "oxc.oxc-vscode",
        "editor.formatOnSave": true
    },
    "editor.defaultFormatter": "oxc.oxc-vscode",
    "editor.formatOnSave": true
}
```

- `.vscode/extensions.json` recommends:
   - `oxc.oxc-vscode` (oxlint + oxfmt, replaces eslint/prettier/vitest)
   - `streetsidesoftware.code-spell-checker` (cspell)
   - `typescriptteam.native-preview` (TypeScript 7 nightly support;
     replaces the older `ms-vscode.vscode-typescript-next`)

```json
{
    "recommendations": [
        "oxc.oxc-vscode",
        "streetsidesoftware.code-spell-checker",
        "typescriptteam.native-preview"
    ]
}
```

- `.vscode/tasks.json` is not currently provided; common tasks
  (build, test, lint, typecheck, format, spell, check:outdated) are
  run via the npm scripts in `package.json` from the integrated
  terminal.
- VSCode uses the workspace TypeScript version via
  `typescript.tsdk` (and the explicit `js/ts.tsdk.path`), with
  `oxc.oxc-vscode` for formatting and linting.