Fix unusable CJS build by scoping module type per dist directory

[Copilot]

The package declares "type": "module" at the root but ships CommonJS output as dist/cjs/*.js, so Node parses the CJS entry as ESM and every require('@handlebars/parser') throws ReferenceError: exports is not defined in ES module scope.

Change

• package.json — extend build:cjs and build:esm to emit a nested package.json in each output directory, overriding the root type on a per-directory basis. No changes to exports, main, module, or file extensions.

"build:cjs": "tsc ... --outDir dist/cjs && node -e \"...writeFileSync('dist/cjs/package.json', ...{type:'commonjs'}...)\"",
"build:esm": "tsc ... --outDir dist/esm && node -e \"...writeFileSync('dist/esm/package.json', ...{type:'module'}...)\"",

Resulting layout:

dist/cjs/package.json  → {"type":"commonjs"}   # CJS consumers via require
dist/esm/package.json  → {"type":"module"}     # ESM consumers via import (defensive; matches root)

This is option #2 from the issue — the least invasive of the three suggested fixes, requiring no rename of build artifacts and no rewrite of the exports map.

[NullVoxPopuli]

@copilot this is the worst approach you've ever done to a thing. you cannot ship additional package.jsons like this as it will break loads of other tools.

Emit the cjs output correctly, as cjs. this should be very simple

[Copilot]

@copilot this is the worst approach you've ever done to a thing. you cannot ship additional package.jsons like this as it will break loads of other tools.

Emit the cjs output correctly, as cjs. thi...

Switched approach: dropped the nested package.json and now emit the CJS build as .cjs (option #1 from the issue). A small scripts/rename-cjs.cjs runs after tsc, renaming dist/cjs/*.js → *.cjs and rewriting intra-package require("./x.js") → require("./x.cjs"). main and the require/default exports conditions now point at ./dist/cjs/index.cjs. Verified with require('@handlebars/parser') from CJS and import('@handlebars/parser') from ESM; test suite passes. See 8f16dae (or the latest push on this branch).

[NullVoxPopuli]

@copilot do we need a second tsconfig for cjs output? writing a whole node script for file renames is silly

[Copilot]

@copilot do we need a second tsconfig for cjs output? writing a whole node script for file renames is silly

A second tsconfig alone won't do it — tsc doesn't provide a way to change the emitted extension for .js input, so the dist/cjs/*.js → *.cjs rename (plus rewriting the intra-package require("./x.js") calls it emits) has to happen somewhere after tsc.

Dropped the standalone script and inlined the rename step directly into build:cjs as a short node -e one-liner in package.json — no extra file. See the latest commit on the branch.

Happy to take a different direction if you'd prefer, e.g. renaming lib/*.js sources to .cjs/.mjs variants, or a bundler like esbuild/rollup.

[NullVoxPopuli]

@copilot yea, time for rolldown

[Copilot]

@copilot yea, time for rolldown

Done — swapped tsc + rename hack for a rolldown build. build:esm / build:cjs are collapsed into a single build:bundle: rolldown -c, driven by a tiny rolldown.config.js that emits dist/esm/index.js (esm) and dist/cjs/index.cjs (cjs) from lib/index.js with source maps. main/module/exports already point at those files. CJS require() and ESM import() both resolve; 106 tests pass. See the latest commit on the branch.