TS dev files: unchecked, or published to npm

[manzoorwanijk]

What problem does this address?

tsconfig.base.json excludes **/test/**: 397 TS test files across 44 packages are never checked:

$ echo "const brokenOnPurpose: number = 'not a number';" >> packages/blob/src/test/index.ts
$ npx tsc -b packages/blob --force; echo $?
0

packages/blob/src/test/index.ts(40,11): error TS2304: Cannot find name 'global'.
packages/blob/src/test/index.ts(82,31): error TS2339: Property 'toHaveStyle' does not exist on type 'JestMatchers<HTMLAnchorElement>'.

Stories are the inverse, type checked but shipped: the components tarball carries 248 story .d.ts files:

$ cd packages/components && npm pack --dry-run
npm notice 672B build-types/alignment-matrix-control/stories/index.story.d.ts
npm notice 422B build-types/alignment-matrix-control/stories/index.story.d.ts.map
...

Jest types leak into 10+ src projects; theme copes with five bespoke tsconfigs.

What is your proposed solution?

Constraints:

• All TS files type checked: src, tests, stories, scripts.
• No test or story output in build-types or tarballs.
• Build does not check dev files.
• IDE checking works everywhere, correct ambient types.
• Jest globals never leak into src (CLI and IDE).
• Isolated installs compatible: type deps per package - Explore using npm install-strategy=linked #75814.
• Incremental references, low boilerplate, lint:tsconfig enforced, per-package migration.

Options:

• A: test projects in the root solution; build checks them.
• B (preferred): root tsconfig.json checks everything; build uses src-only tsconfig.build.json; package default configs hold dev files (jest types) and reference build configs.
• C: one root project for all dev files; unioned ambient types.
• D: strip dev output at publish; rejected, jest leaks.
• Orthogonal: emit-only builds via --noCheck.

[manzoorwanijk]

CC: @aduth @jsnajdr @tyxla @ciampo @Mamaduka @t-hamano @sirreal

[manzoorwanijk]

I prototyped the options and settled on Option B.

Approach

• Two root solutions: the default tsconfig.json checks everything (used by npm run typecheck and the IDE) and references tsconfig.build.json, the src-only solution used by npm run build.
• Each package splits into tsconfig.build.json (composite, emits build-types, src only, no jest types) and a default tsconfig.json dev project (noEmit; tests and stories; extends a shared tsconfig.dev.base.json). Cross-package references point at build configs.
• Jest globals stop being valid in src: the dev project excludes src and the build project has no jest types.
• Test-only type packages (@types/jest, @types/node, @testing-library/jest-dom) become per-package devDependencies, compatible with the isolated installs strategy.
• validate-tsconfig enforces the layout.

Prototype findings

• Nested solution references work with tsc -b, so the src project list is not duplicated across the two root solutions.
• theme's five bespoke tsconfigs collapse to three under this layout.
• Hidden errors surface as packages migrate (85 in interactivity tests alone), so includes narrow per package until they are fixed.

Plan

1. Land the infrastructure plus a first batch of migrated packages (blob, grid, interactivity, theme).
2. Migrate the remaining ~40 packages incrementally.
3. Emit-only builds via --noCheck plus a CI typecheck job.