css-modules-contentmapper-poc

Typed CSS Modules for TypeScript 7 (the native, Go-based compiler) via the experimental Content Mapper API (PR microsoft/typescript-go#4712, merged into main on 2026-08-19 as 01b9e72). The Go implementation has since been migrated from the microsoft/typescript-go staging repo into the main microsoft/TypeScript repo (PR microsoft/TypeScript#63763, 2026-08-20), where it now lives in the tsc/ subdirectory. Importing a *.module.css file is type-checked: the imported object's keys are exactly the class names in the CSS, unknown names are compile errors, and go-to-definition jumps from styles.button into the .button selector.

• css-modules-mapper/ — the content mapper: a JSON-RPC stdio server (src/server.ts) and the CSS → TS transform with span-map generation (src/transform.ts, PostCSS-based).
• demo/ — consumer project registering the mapper via contentMappers in its tsconfig.
• scripts/lsp-goto-def.mjs — minimal LSP client used to demonstrate go-to-definition through the span map.
• RESULTS.md — acceptance evidence; NOTES.md — spec/code divergences and production considerations.

Running it

Requires tsc built from main of microsoft/TypeScript (this PoC last verified against 6d44e05, see RESULTS.md). Since the repo migration the Go module lives in the tsc/ subdirectory and the entry point was renamed cmd/tsgo → cmd/tsc:

git clone --depth 1 https://github.com/microsoft/TypeScript
cd TypeScript/tsc && go build -o built/tsc ./cmd/tsc

Then:

npm install
npm run build -w css-modules-mapper
npm test -w css-modules-mapper                        # unit tests
path/to/built/tsc -p demo --runExternalCode           # type-check the demo
node scripts/lsp-goto-def.mjs path/to/built/tsc demo src/app.ts "button;"   # go-to-def