charlie: ESM update of alias package

[shellscape]

@CharlieHelps your task is described below. read the instructions and reply with an implementation plan:

Objective: Update the alias package in packages/alias to use ESM only and update minimum platform dependencies

Steps:

• Update the minimum node version in package.json to 20.19.0. (20.19.0 is the first LTS maintenance version which supports frictionless inline ESM/CJS imports/requires)
• Update the minimum rollup version in package.json to 4.0.0
• Given the minimum Node version of 20.19.0, update any code within packages/alias to use modern Node APIs unless it is detrimental to performance
• Create a new .config directory at the repo root
• Create a copy of shared/rollup.config.mjs at .config/rollup-plugin.mjs and remove the typescript rollup plugin from .config/rollup-plugin.mjs
• Create a copy of tsconfig.base.json at .config/tsconfig.base.json
• Create a copy of shared/tsconfig.json at .config/tsconfig.plugin.json, and change the extended config to ./tsconfig.base.json
• Update.config/tsconfig.base.json to use the latest module, resolution, lib settings which corresponds to the alias plugin moving to ESM only
• Update.config/tsconfig.plugin.json, set noEmit: false and outDir: tsc.out
• Update the packages/alias/tsconfig.json symlink to point to .config/tsconfig.plugin.json
• Update the plugin's build scripts to execute tsc --project tsconfig.json before rollup is executed
• Update the packages/alias/rollup.config.mjs file to use .config/rollup-plugin.mjs
• Update the packages/alias/rollup.config.mjs file to target the files in ./tsc.out
• Update the packages/alias/rollup.config.mjs file to use the appropriate rollup plugin (if one exists, otherwise use code) to include/copy source maps and type definitions from tsc.out to dist
• Update the packages/alias/package.json file to properly setup properties and exports for an ESM only package
• Compare the types created from tsc to those which were previously hand-authored in packages/alias/types/index.d.ts - improve the code in packages/alias/src/index.ts if the hand-authored types contain information that the generated types do not - we want to make sure we're not degrading the developer experience
• Install vitest 4.0.1 at the repository root using pnpm add vitest@latest -w -D
• Create a new vitest config file in .config which forces snapshots to be saved in the relative test directory under .snapshots
• Run current tests to understand how they work
• Remove all CJS branches in tests, they will no longer be relevant
• Convert tests in packages/alias/test from Ava to vitest and update the test files to use typescript (.ts) instead of plain javascript
• Run tests and include the snapshot files in any commits. Any existing snapshot files will need to be overwritten as existing files will be in the Ava format. This is OK since we know that tests are passing
• Update CONTRIBUTING.md to include information about the current-package symlink described below

Notes:

• Each package’s tests include a symlink at test/node_modules/current-package pointing back to the
  package root (../..). If you see import ... from 'current-package' that's where the import points to
• PR title should follow the format feat({plugin})!: ESM only. Update Node and Rollup minimum versions

[charliecreates]

Expand this to see my work.

• Read and scoped #1925, enumerating required updates to packages/alias/package.json (engines.node: ">=20.19.0", devDependencies.rollup: "^4.0.0", type: "module", exports map) plus changes in packages/alias/rollup.config.mjs, .config/*, and build scripts.
• Completed an initial code audit of packages/alias/src/index.ts against Node 20 ESM APIs, covering matches, getEntries, resolveCustomResolver, and default alias.
• Baseline-reviewed packages/alias/types/index.d.ts to capture current public types for later comparison with tsc output after ESM-only changes.
• Verified test fixture symlink: packages/alias/test/node_modules/current-package resolves to ../.. (via directory listing), confirming local package linkage for end-to-end tests.

[charliecreates]

Here’s a concrete implementation plan updated per choice #2 (use a runtime alias and import from ~package) and the follow-up guidance.

Summary

• Make @rollup/plugin-alias ESM‑only, raise minimum engines/peer ranges, and modernize to Node 20.19 APIs.
• Introduce a shared .config toolbelt (rollup + tsconfigs + vitest config).
• Switch the package build to “tsc first, then rollup from tsc.out,” and copy d.ts + maps into dist with a plain shell cp step.
• Migrate tests from Ava to Vitest (TypeScript), drop CJS branches, and adopt .snapshots per suite.
• Replace the current-package symlink with a Vitest runtime alias and import from ~package in tests.
• Make exports/types in package.json ESM‑only with types co-located in dist.

High‑level steps

1. Package constraints

• packages/alias/package.json
  • engines.node: ">=20.19.0"
  • peerDependencies.rollup: ">=4.0.0"
  • Add "type": "module" (ESM‑only package)
  • Update exports/types for ESM‑only (see snippet below).

2. Modernize alias source for Node 20.19

• Use node: specifiers (e.g., import path from "node:path").
• No behavioral change expected; keep performance characteristics.

3. Shared config toolbelt

• Create .config/
  • .config/rollup-plugin.mjs: copy of shared/rollup.config.mjs with:
    • typescript rollup plugin removed
    • output limited to ESM
    • no custom copy plugin (we'll use cp in the package build script)
  • .config/tsconfig.base.json: copy of root tsconfig.base.json, update for latest TS with bundler semantics (after bumping TS to latest):
    • module: "bundler", moduleResolution: "bundler", target: "ES2022", lib: ["ES2022"]
    • keep noEmit: true here (overridden per‑package)
  • .config/tsconfig.plugin.json: copy of shared/tsconfig.json, extend "./tsconfig.base.json", and set:
    • compilerOptions: { noEmit: false, outDir: "tsc.out", rootDir: "src", declaration: true, declarationMap: true, sourceMap: true,
      baseUrl: ".", paths: { "~package": ["./"] } } // editor support for the alias
    • include: ["src/**/*"] (types are generated; we'll stop maintaining packages/alias/types going forward)

4. Package build wiring

• packages/alias/tsconfig.json: update symlink target to ../../.config/tsconfig.plugin.json
• packages/alias/rollup.config.mjs:
  • import { createConfig } from "../../.config/rollup-plugin.mjs"
  • set input to tsc.out/src/index.js
• packages/alias/package.json scripts:
  • prebuild: "del-cli dist tsc.out"
  • build: "tsc --project tsconfig.json && rollup -c && cp -v tsc.out/src/.d.ts dist/"
  • pretest: "pnpm build"
  • test: "vitest --config ../../.config/vitest.config.ts run"

5. ESM‑only package.json exports (alias)

• Remove "main" and "module"
• Exports/types only target ESM (see snippet below)
• Keep files list to ["dist", "!dist/**/*.map", "README.md", "LICENSE"] (we copy d.ts into dist, so no top‑level types/)

6. Types parity

• Generate types via tsc, compare against existing packages/alias/types/index.d.ts.
• If the generated surface is missing intent (e.g., overload detail or helpful aliases), refine src/index.ts types (e.g., explicit exported interfaces, named exports) until parity is met.
• Once parity is good, delete packages/alias/types from source and rely on the emitted types in dist.

7. Vitest setup and test migration (runtime alias; no symlink)

• At repo root: pnpm add vitest@latest -w -D (and earlier: pnpm add typescript@latest -w -D).
• .config/vitest.config.ts:
  • Force snapshots into /.snapshots via resolveSnapshotPath.
  • Add a runtime alias: map ~package → the package root (process.cwd()).
• Convert packages/alias/test tests to TypeScript and update imports:
  • import from "~package" instead of "current-package"
  • Replace Ava API with Vitest (expect/it/describe)
  • Use node: specifiers in imports
  • Remove the CJS‑only test(s)
• Run tests and commit newly created snapshots (overwrite prior Ava snapshots if present).

8. Documentation

• .github/CONTRIBUTING.md: update the “Testing packages” note to reflect Vitest and the ~package alias (no symlink needed). Include an example of running tests via the package script.

9. PR

• Title: feat(alias)!: ESM only. Update Node and Rollup minimum versions
• Changes summarized; note breaking change (CJS no longer supported).
• Verification: lint, typecheck, build, and vitest for @rollup/plugin-alias.

File edits and representative snippets

.config/rollup-plugin.mjs (ESM‑only, no TS plugin, no copy plugin)

import { builtinModules } from "node:module";
import { readFileSync } from "node:fs";

/**
 * Create a base rollup config (ESM‑only)
 * @param {object} opts
 * @param {Record<string,any>} opts.pkg parsed package.json of the package
 * @param {string[]} [opts.external]
 * @param {string} [opts.input] default: 'tsc.out/src/index.js'
 * @returns {import('rollup').RollupOptions}
 */
export function createConfig({ pkg, external = [], input = "tsc.out/src/index.js" }) {
  return {
    input,
    external: Object.keys(pkg.dependencies || {})
      .concat(Object.keys(pkg.peerDependencies || {}))
      .concat(builtinModules)
      .concat(external),
    onwarn: (warning) => { throw Object.assign(new Error(), warning); },
    strictDeprecations: true,
    output: [{ format: "es", file: pkg.exports?.import ?? "./dist/index.js", sourcemap: true }]
  };
}

.config/tsconfig.base.json (bundler semantics)

{
  "compilerOptions": {
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "lib": ["ES2022"],
    "module": "bundler",
    "moduleResolution": "bundler",
    "noEmit": true,
    "noEmitOnError": false,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "pretty": true,
    "sourceMap": true,
    "strict": true,
    "target": "ES2022"
  },
  "exclude": ["dist", "node_modules", "test/types"]
}

.config/tsconfig.plugin.json (adds editor alias for ~package)

{
  "extends": "./tsconfig.base.json",
  "compilerOptions": {
    "noEmit": false,
    "outDir": "tsc.out",
    "rootDir": "src",
    "declaration": true,
    "declarationMap": true,
    "sourceMap": true,
    "baseUrl": ".",
    "paths": { "~package": ["./"] }
  },
  "include": ["src/**/*"]
}

packages/alias/rollup.config.mjs

import { readFileSync } from "node:fs";
import { createConfig } from "../../.config/rollup-plugin.mjs";

export default createConfig({
  pkg: JSON.parse(readFileSync(new URL("./package.json", import.meta.url), "utf8")),
  input: "tsc.out/src/index.js"
});

packages/alias/package.json (key fields)

{
  "name": "@rollup/plugin-alias",
  "type": "module",
  "engines": { "node": ">=20.19.0" },
  "peerDependencies": { "rollup": ">=4.0.0" },
  "exports": { "types": "./dist/index.d.ts", "import": "./dist/index.js" },
  "types": "./dist/index.d.ts",
  "files": ["dist", "!dist/**/*.map", "README.md", "LICENSE"],
  "scripts": {
    "prebuild": "del-cli dist tsc.out",
    "build": "tsc --project tsconfig.json && rollup -c && cp -v tsc.out/src/*.d.ts* dist/",
    "pretest": "pnpm build",
    "test": "vitest --config ../../.config/vitest.config.ts run"
  }
}

.config/vitest.config.ts (snapshots under /.snapshots; runtime alias for ~package)

import { defineConfig } from "vitest/config";
import path from "node:path";

export default defineConfig({
  test: {
    resolveSnapshotPath: (testPath, snapExt) =>
      path.join(path.dirname(testPath), ".snapshots", path.basename(testPath) + snapExt)
  },
  resolve: {
    alias: [{ find: /^~package$/, replacement: path.resolve(process.cwd()) }]
  }
});

packages/alias/test updates (example)

// before
// import alias from "current-package";
// after
import alias from "~package";

Decisions applied (no further confirmation needed)

• Use ~package as the import target in tests and provide a Vitest runtime alias; drop the symlink approach.
• Update the workspace to the latest TypeScript and use TS "bundler" module semantics in the new .config tsconfigs.
• Copy emitted .d.ts and .d.ts.map with a shell cp step after Rollup; no extra rollup plugin.
• Keep the single ESM entry at dist/index.js with types at dist/index.d.ts.

[shellscape]

@CharlieHelps could the current-package approach be replaced by using paths in tsconfig.plugin.json?

TypeScript version: repo currently uses 4.8.3. To stay within that, I’ve set "module"/"moduleResolution" to "nodenext" instead of "bundler". Sound good?

Update the root package.json to use the latest version of TypeScript. use pnpm add typescript@latest -D -w

For copying artifacts: prefer zero new deps (custom copy plugin above) vs adding rollup‑plugin‑copy. OK to proceed with the custom plugin?

you're overthinking this. just use cp with a glob after rollup completes its run.

Package.json layout: do you prefer dist/index.js + dist/index.d.ts at the top level of dist (as proposed), or to keep the historical dist/es structure? The proposal simplifies to a single ESM entry at dist/index.js.

dist/index.js

[charliecreates]

Short answer: not by itself. TypeScript “paths” only affects the TS compiler/editor. Node/Vitest/Rollup won’t see it at runtime, so import 'current-package' would stop resolving unless we add extra runtime aliasing.

What I recommend:

• Keep the symlink for runtime reliability across JS/TS tests and tools.
• Optionally add a paths entry purely for editor/TS ergonomics (no runtime reliance), e.g. in .config/tsconfig.plugin.json:

  {
    "compilerOptions": {
      "baseUrl": ".",
      "paths": { "current-package": ["./"] }
    }
  }

If you want to drop the symlink anyway, we’d need one of:

• Per‑package Vitest configs with resolve.alias pointing current-package → package root; or
• A repo‑level dependency like vite-tsconfig-paths to honor TS paths at runtime; or
• Changing tests to import the package by its real name (ties tests to the name).

Given the “no extra deps” preference, I’ll keep the symlink and add the optional paths mapping for IDEs.

Acknowledged on the other points:

• I’ll bump TypeScript to latest at the workspace (pnpm add typescript@latest -D -w) and switch the new .config tsconfigs to module/moduleResolution: "bundler".
• I’ll replace the copy plugin with a simple post‑build cp step to move .d.ts/maps from tsc.out into dist.
• Layout will be ESM‑only at dist/index.js (and dist/index.d.ts).

[shellscape]

@CharlieHelps current package isn't referenced within rollup execution within tests, correct? since tests are being converted to typescript, and the tsconfig will have paths, vitest should automatically pick that up correct? since we're not compiling the tests to disc to run as JS, paths doesnt matter in that scenario correct?

[charliecreates]

You're right on the first point but not the next two:

• Correct: Rollup doesn’t resolve current-package in these tests. The test file imports the plugin from current-package and passes the plugin instance to Rollup; Rollup never tries to import current-package itself.
• Not quite: Vitest/Vite do not automatically honor tsconfig "paths". That mapping is compile-time/editor-only unless you add a runtime resolver (e.g., vite-tsconfig-paths) or an explicit alias.
• Whether tests are emitted to disk doesn’t change module resolution. The import specifier still has to resolve at runtime.

Two safe ways forward

1. Keep the existing test/node_modules/current-package symlink

• Zero changes, works the same under Vitest, and keeps tests tool-agnostic.

2. If you want to drop the symlink, add a zero‑dep alias in the shared Vitest config

• This maps current-package to the package root when tests run from the package dir.

// .config/vitest.config.ts
import { defineConfig } from 'vitest/config';
import path from 'node:path';

export default defineConfig({
  test: {
    resolveSnapshotPath: (testPath, snapExt) =>
      path.join(path.dirname(testPath), '.snapshots', path.basename(testPath) + snapExt)
  },
  resolve: {
    alias: [{ find: /^current-package$/, replacement: path.resolve(process.cwd()) }]
  }
});

I’ll proceed with option 1 (keep the symlink) unless you prefer the alias route.

[shellscape]

@CharlieHelps choose #2 and use ~package as the import target, and update the first reply with the updated plan. or, if you're unable to update that comment, post a new comment with the revised plan

[charliecreates]

Updated the first reply with the revised plan choosing option #2 and using the ~package import target.

Highlights

• Tests now import from ~~package; shared .config/vitest.config.ts adds a runtime alias mapping for /^~~package$/ → process.cwd(); TS “paths” mapping is added for editor ergonomics.
• Use a plain cp step after Rollup to copy .d.ts and .d.ts.map from tsc.out into dist; no custom Rollup plugin.
• Bump TypeScript to latest at the workspace and use module/moduleResolution: "bundler" in the new .config tsconfigs.
• Keep a single ESM entry at dist/index.js with types at dist/index.d.ts.
• CONTRIBUTING will reference the ~package alias (no current-package symlink).

See the updated plan and snippets here:
#1925 (comment)

[charliecreates]

Expand this to see my work.

• Scoped migration per #1925, covering Node >=20.19.0, Rollup ^4.0.0, a tsc-first build to tsc.out, and updates to packages/alias/{package.json,tsconfig.json,rollup.config.mjs} plus new centralized configs under .config/*.
• Reviewed packages/alias/test/test.mjs, including getModuleIdsFromBundle and test('Works as CJS plugin', ...) using createRequire/require('current-package'), highlighting a CJS assumption that conflicts with ESM-only exports.
• Audited shared/rollup.config.mjs: captured createConfig(...) and emitModulePackageFile(), and pinpointed @rollup/plugin-typescript as the piece to remove for .config/rollup-plugin.mjs.
• Assessed shared/tsconfig.json and root tsconfig.base.json and drafted ESM-only compiler settings for .config/tsconfig.base.json and .config/tsconfig.plugin.json (extends: './tsconfig.base.json', noEmit: false, outDir: 'tsc.out').

[charliecreates]

Here’s a concrete, repo‑specific implementation plan to move @rollup/plugin-alias to ESM‑only, raise minimums, and migrate tests.

Summary

• Make alias ESM‑only and bump minimums to Node 20.19.0 and Rollup 4.
• Add a shared .config toolbelt (rollup + tsconfigs + vitest config).
• Switch build to “tsc first, then rollup from tsc.out,” and copy .d.ts(+.map) into dist.
• Modernize source to Node 20 ESM (node: specifiers).
• Migrate tests from Ava to Vitest (TypeScript), drop CJS branches, use ~package alias.

Implementation steps

1. Tooling and shared config (repo root)

• Create .config/ and add:

  • .config/rollup-plugin.mjs: copy of shared/rollup.config.mjs with the TypeScript rollup plugin removed, ESM‑only output, default input tsc.out/src/index.js.
  • .config/tsconfig.base.json: copy of tsconfig.base.json, then update for ESM‑only + modern TS:
    • compilerOptions: { module: "bundler", moduleResolution: "bundler", target: "ES2022", lib: ["ES2022"], strict: true, sourceMap: true, allowSyntheticDefaultImports: true, esModuleInterop: true, noEmit: true, noUnusedLocals: true, noUnusedParameters: true }.
  • .config/tsconfig.plugin.json: copy of shared/tsconfig.json; change extends to "./tsconfig.base.json" and set:
    • compilerOptions: { noEmit: false, outDir: "tsc.out", rootDir: "src", declaration: true, declarationMap: true, sourceMap: true, baseUrl: ".", paths: { "~package": ["./"] } }
    • include: ["src/**/*"]
  • .config/vitest.config.ts: Vitest config that
    • maps snapshots into /.snapshots
    • provides a runtime alias for "~package" → path.resolve(process.cwd()).

• Bump TypeScript at the workspace and add Vitest:

  • pnpm add -D -w typescript@latest
  • pnpm add -D -w vitest@4.0.1

2. Package metadata and build wiring (packages/alias)

• package.json

  • engines.node: ">=20.19.0"
  • peerDependencies.rollup: ">=4.0.0" (already compatible; normalize to stable range)
  • "type": "module"
  • Remove "main" and "module"
  • exports: { "types": "./dist/index.d.ts", "import": "./dist/index.js" }
  • types: "./dist/index.d.ts"
  • files: ["dist", "!dist/**/*.map", "README.md", "LICENSE"] (remove top‑level types/ from publish list)
  • scripts:
    • "prebuild": "del-cli dist tsc.out"
    • "build": "tsc --project tsconfig.json && rollup -c && cp -v tsc.out/src/.d.ts dist/"
    • "pretest": "pnpm build"
    • "test": "vitest --config ../../.config/vitest.config.ts run"

• tsconfig.json

  • Update the symlink to point to ../../.config/tsconfig.plugin.json.

• rollup.config.mjs

  • Import createConfig from "../../.config/rollup-plugin.mjs"
  • Set input to "tsc.out/src/index.js"
  • Read pkg as before with readFileSync from node:fs

3. Source modernization (packages/alias/src)

• Update Node imports to ESM with node: specifiers:
  • import path from "node:path" (replace "path")
  • Keep the rest of the logic intact; no behavioral changes.
• Prefer minor cleanups only when they don’t impact perf. No extra abstractions.

4. Types parity

• Run tsc to emit declarations into tsc.out.
• Compare tsc.out/src/index.d.ts to existing packages/alias/types/index.d.ts:
  • Ensure public names are preserved: ResolverFunction, ResolverObject, Alias, ResolvedAlias, RollupAliasOptions, default export signature.
  • If any helpful intent is lost (e.g., mapped types on PluginHooks), surface those explicitly in src/index.ts so tsc emits equivalent information.
• Once parity is verified, remove packages/alias/types from the package (not published anymore) and rely on dist/index.d.ts.

5. Tests: Ava → Vitest (TypeScript)

• Replace packages/alias/test/test.mjs with one or more *.test.ts files.
  • Use Vitest API: import { describe, it, expect } from "vitest"
  • Update imports:
    • from: import alias from "current-package"
    • to: import alias from "~package"
  • Replace OS path imports with node: forms where applicable (node:path, node:os).
  • Keep the Rollup‑driven resolution helpers, but remove the CJS‑only test:
    • Delete “Works as CJS plugin” entirely.
  • Convert assertions from Ava t.deepEqual/t.is to expect(...).toEqual(...) / toBe(...).
• No existing snapshot tests in this package today; still configure Vitest to write snapshots under .snapshots for consistency.

6. Docs

• Update CONTRIBUTING.md
  • Add a short section “Running package tests” showing that tests import from "~package" and that .config/vitest.config.ts provides the runtime alias.
  • Mention snapshots are stored next to tests under .snapshots.

7. PR details

• Title: feat(alias)!: ESM only. Update Node and Rollup minimum versions
• Call out breaking change: CJS entry removed; package is ESM‑only.
• Note minimums raised: Node >=20.19.0, Rollup >=4.
• Summarize test migration and the move to generated types in dist.

Representative snippets

.config/rollup-plugin.mjs (ESM‑only, no TS plugin)

import { builtinModules } from 'node:module';

export function createConfig({ pkg, external = [], input = 'tsc.out/src/index.js' }) {
  return {
    input,
    external: Object.keys(pkg.dependencies || {})
      .concat(Object.keys(pkg.peerDependencies || {}))
      .concat(builtinModules)
      .concat(external),
    onwarn: (warning) => { throw Object.assign(new Error(), warning); },
    strictDeprecations: true,
    output: [{ format: 'es', file: './dist/index.js', sourcemap: true }]
  };
}

.config/tsconfig.base.json (bundler semantics)

{
  "compilerOptions": {
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "lib": ["ES2022"],
    "module": "bundler",
    "moduleResolution": "bundler",
    "noEmit": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "pretty": true,
    "sourceMap": true,
    "strict": true,
    "target": "ES2022"
  },
  "exclude": ["dist", "node_modules", "test/types"]
}

.config/tsconfig.plugin.json

{
  "extends": "./tsconfig.base.json",
  "compilerOptions": {
    "noEmit": false,
    "outDir": "tsc.out",
    "rootDir": "src",
    "declaration": true,
    "declarationMap": true,
    "sourceMap": true,
    "baseUrl": ".",
    "paths": { "~package": ["./"] }
  },
  "include": ["src/**/*"]
}

.config/vitest.config.ts

import { defineConfig } from 'vitest/config';
import path from 'node:path';

export default defineConfig({
  test: {
    resolveSnapshotPath: (testPath, snapExt) =>
      path.join(path.dirname(testPath), '.snapshots', path.basename(testPath) + snapExt)
  },
  resolve: {
    alias: [{ find: /^~package$/, replacement: path.resolve(process.cwd()) }]
  }
});

packages/alias/rollup.config.mjs

import { readFileSync } from 'node:fs';
import { createConfig } from '../../.config/rollup-plugin.mjs';

export default createConfig({
  pkg: JSON.parse(readFileSync(new URL('./package.json', import.meta.url), 'utf8')),
  input: 'tsc.out/src/index.js'
});

packages/alias/package.json (key fields)

{
  "type": "module",
  "engines": { "node": ">=20.19.0" },
  "peerDependencies": { "rollup": ">=4.0.0" },
  "exports": { "types": "./dist/index.d.ts", "import": "./dist/index.js" },
  "types": "./dist/index.d.ts",
  "files": ["dist", "!dist/**/*.map", "README.md", "LICENSE"],
  "scripts": {
    "prebuild": "del-cli dist tsc.out",
    "build": "tsc --project tsconfig.json && rollup -c && cp -v tsc.out/src/*.d.ts* dist/",
    "pretest": "pnpm build",
    "test": "vitest --config ../../.config/vitest.config.ts run"
  }
}

Notes and assumptions

• We’ll copy only declaration files and their maps (tsc.out/src/.d.ts) into dist. We will not copy tsc’s .js.map to avoid mismatched maps; Rollup will emit the runtime sourcemap for dist/index.js.
• Ava remains in the workspace for other packages; only alias moves to Vitest now.
• If you want the workspace to type‑check tests, we can add an optional “vitest typecheck” step later; not needed for this migration.

If this plan looks good, I’ll start a draft PR on branch ai-1925-charlie-esm-update-of-alias-package and implement in the order above.

[shellscape]

@CharlieHelps that's a good point about the source maps that I hadn't considered. the bundle will ultimately make tsc's source maps incorrect. looking at the rollup configs, the only real reason that we were using rollup on the package itself was for dual outputs (cjs and esm). now that we don't need that any longer, I think we can remove rollup from the alias build process altogether. please amend your plan.

[charliecreates]

Agreed—let’s drop Rollup from @rollup/plugin-alias and go tsc‑only. Here’s the amended plan.

• Build becomes tsc-only: no bundling step, no package‑local rollup config, no copy plugin/step.
• Keep the shared .config toolbelt, but it’s TS + Vitest only (no .config/rollup-plugin.mjs).
• Emit JS, d.ts, and .js.map straight into dist; publish the maps so they stay correct.
• Inline the public types in src/index.ts so tsc emits complete declarations; remove the hand‑authored types/ directory once parity is verified.
• Tests still migrate to Vitest (TypeScript) and import the package via ~package runtime alias.

Revised steps (tsc‑only)

1. Shared config and tooling (repo root)

• Create:

  • .config/tsconfig.base.json (ESM‑only, modern TS):
    • compilerOptions: { module: "bundler", moduleResolution: "bundler", target: "ES2022", lib: ["ES2022"], strict: true, sourceMap: true, allowSyntheticDefaultImports: true, esModuleInterop: true, noEmit: true, noUnusedLocals: true, noUnusedParameters: true }
  • .config/tsconfig.plugin.json (for packages/alias):
    • extends: "./tsconfig.base.json"
    • compilerOptions: { noEmit: false, outDir: "dist", rootDir: "src", declaration: true, declarationMap: true, sourceMap: true, baseUrl: ".", paths: { "~package": ["./"] } }
    • include: ["src/**/*"]
  • .config/vitest.config.ts:
    • test.resolveSnapshotPath → /.snapshots
    • resolve.alias: [{ find: /^~package$/, replacement: path.resolve(process.cwd()) }]

• Bump TypeScript and add Vitest (as discussed earlier):

  • pnpm add -D -w typescript@latest
  • pnpm add -D -w vitest@4.0.1

Note: No .config/rollup-plugin.mjs anymore.

2. Package wiring (packages/alias)

• tsconfig.json → symlink to ../../.config/tsconfig.plugin.json

• package.json

  • "type": "module"
  • "engines": { "node": ">=20.19.0" }
  • "peerDependencies": { "rollup": ">=4.0.0" } (range simplified)
  • Remove "main"/"module"
  • "exports": { "types": "./dist/index.d.ts", "import": "./dist/index.js" }
  • "types": "./dist/index.d.ts"
  • "files": ["dist", "README.md", "LICENSE"] // publish .js.map; drop the previous "!dist/**/*.map"
  • "scripts":
    • "prebuild": "del-cli dist"
    • "build": "tsc --project tsconfig.json"
    • "pretest": "pnpm build"
    • "test": "vitest --config ../../.config/vitest.config.ts run"
  • devDependencies: remove rollup and @rollup/plugin-typescript from this package

• Delete packages/alias/rollup.config.mjs

3. Source modernization (packages/alias/src)

• Switch Node built‑ins to node: specifiers (e.g., import path from "node:path").
• Inline public types from packages/alias/types/index.d.ts directly into src/index.ts (export them), so tsc emits complete declarations.
• After parity is confirmed, remove packages/alias/types and update any type‑only imports accordingly.

4. Types parity check

• Run tsc; compare dist/index.d.ts with the current hand‑authored types:
  • Ensure we keep ResolverFunction, ResolverObject, Alias, ResolvedAlias, RollupAliasOptions, and the default export signature intact.
• If anything is lost, adjust src/index.ts types/exports until parity matches, then delete types/.

5. Tests: Ava → Vitest (TypeScript)

• Convert packages/alias/test to *.test.ts; drop all CJS branches.
• Import the plugin via ~package (runtime alias provided by .config/vitest.config.ts).
• Keep current fixture structure; store snapshots under .snapshots per suite.

6. Docs

• Update CONTRIBUTING.md to mention:
  • Vitest runner
  • ~package runtime alias (no current-package symlink)
  • Snapshots location

7. Cleanup

• Remove any alias‑specific Rollup artifacts and references.
• Ensure package size looks reasonable with maps included; if you prefer to keep maps out of the published package, I can re‑add the exclude, but leaving them in is fine now that they’re accurate.

If you’re good with publishing .js.map, I’ll proceed with this version. Otherwise I’ll keep the tsc maps but exclude them from npm by reinstating "!dist/**/*.map".

[shellscape]

@CharlieHelps please proceed

[charliecreates]

Expand this to see my work.

• Reviewed current state: packages/alias/src/index.ts exports alias() with resolveId(...), and packages/alias/package.json dual-exports via exports.import -> ./dist/es/index.js and exports.default -> ./dist/cjs/index.js; working tree clean.
• Switched to ESM-only and modernized metadata in packages/alias/package.json (type: "module", exports.import -> ./dist/index.js, exports.types -> ./dist/index.d.ts, engines.node >=20.19.0, peerDependencies.rollup >=4.0.0), updating scripts to tsc build and Vitest test.
• Centralized TS and test configs and migrated tests: added .config/tsconfig.base.json, .config/tsconfig.plugin.json, .config/vitest.config.ts with ~package, replaced packages/alias/tsconfig.json, added packages/alias/test/alias.test.ts, and removed packages/alias/rollup.config.mjs, legacy test/test.mjs, and test/node_modules/current-package.
• Built with tsc and inspected output: saw TS5083 on symlinked extends, Node type mismatch (@types/node@14.x vs >=20), missing Symbol.asyncDispose under lib: ES2022, and TS1259 for default import of node:path; verified packages/alias/dist/index.js wires getEntries(...) to resolverFunctionFromOptions and resolveId(...) uses matchedEntry.resolverFunction, with ESM emit import path from 'node:path'.
• Noted missing parity for the AVA test “Global customResolver function” after migration and marked it for Vitest coverage.
• Committed and pushed the work as 26bb927 on ai-1925-charlie-esm-update-of-alias-package.
• Refined types in packages/alias/src/index.ts by replacing the conditional MapToFunction with export type ResolverFunction = NonNullable<PluginHooks['resolveId']> for clarity and correctness.
• Fixed Windows path normalization in packages/alias/test/alias.test.ts by changing .replace(/\\/g, '/') to normalize backslashes in warning messages.