Check license field is set if license file exists

close #111

pkg/index.d.ts

@@ -71,6 +71,7 @@ export type Message =
   | BaseMessage<'USE_EXPORTS_OR_IMPORTS_BROWSER'>
   | BaseMessage<'USE_FILES'>
   | BaseMessage<'USE_TYPE'>
+  | BaseMessage<'USE_LICENSE', { licenseFilePath: string }>
   | BaseMessage<
       'TYPES_NOT_EXPORTED',
       {

pkg/src/constants.js

@@ -30,3 +30,6 @@ export const commonInternalPaths = [
   '.eslintrc',
   '.eslintrc.js'
 ]
+
+// https://github.com/npm/npm-packlist/blob/53b2a4f42b7fef0f63e8f26a3ea4692e23a58fed/lib/index.js#L284-L286
+export const licenseFiles = [/^copying/i, /^licence/i, /^license/i]

pkg/src/index.js

@@ -1,7 +1,8 @@
 import {
   commonInternalPaths,
   invalidJsxExtensions,
-  knownBrowserishConditions
+  knownBrowserishConditions,
+  licenseFiles
 } from './constants.js'
 import {
   exportsGlob,
@@ -82,6 +83,30 @@ export async function publint({ pkgDir, vfs, level, strict, _packedFiles }) {
     })
   }
 
+  // Check if has license file but no license field
+  if (rootPkg.license == null) {
+    promiseQueue.push(async () => {
+      const topFiles = await vfs.readDir(pkgDir)
+      /** @type {string | undefined} */
+      let matchedLicenseFilePath
+      for (const f of topFiles) {
+        if (await vfs.isPathDir(vfs.pathJoin(pkgDir, f))) continue
+        if (licenseFiles.some((r) => r.test(f))) {
+          matchedLicenseFilePath = '/' + f
+          break
+        }
+      }
+      if (matchedLicenseFilePath) {
+        messages.push({
+          code: 'USE_LICENSE',
+          args: { licenseFilePath: matchedLicenseFilePath },
+          path: ['name'],
+          type: 'suggestion'
+        })
+      }
+    })
+  }
+
   // Check if "type" field is specified, help Node.js push towards an ESM default future:
   // https://nodejs.org/en/blog/release/v20.10.0
   if (rootPkg.type == null) {

pkg/src/message.js

@@ -114,7 +114,10 @@ export function formatMessage(m, pkg, opts = {}) {
       return `The package ${c.bold('publishes internal tests or config files')}. You can use ${c.bold('pkg.files')} to only publish certain files and save user bandwidth.`
     case 'USE_TYPE':
       // prettier-ignore
-      return `The package does not specify the ${c.bold('type')} field. NodeJS may attempt to detect the package type causing a small performance hit. Consider adding ${c.bold('"type"')}: "${c.bold('commonjs')}".`
+      return `The package does not specify the ${c.bold('"type"')} field. NodeJS may attempt to detect the package type causing a small performance hit. Consider adding ${c.bold('"type"')}: "${c.bold('commonjs')}".`
+    case 'USE_LICENSE':
+      // prettier-ignore
+      return `The package does not specify the ${c.bold('"license"')} field but a license file was detected at ${c.bold(m.args.licenseFilePath)}. Consider adding a ${c.bold('"license"')} field so it's displayed on npm.`
     case 'TYPES_NOT_EXPORTED': {
       const typesFilePath = exportsRel(m.args.typesFilePath)
       if (m.args.actualExtension && m.args.expectExtension) {

pkg/tests/fixtures/missing-license/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "publint-missing-license",
+  "version": "0.0.1",
+  "private": true,
+  "type": "commonjs"
+}

pkg/tests/playground.js

@@ -44,6 +44,8 @@ testFixture('missing-files', [
   'USE_EXPORTS_OR_IMPORTS_BROWSER'
 ])
 
+testFixture('missing-license', ['USE_LICENSE'])
+
 testFixture('no-exports-module', [])
 
 testFixture('not-missing-files', [])

site/rules.md

@@ -206,6 +206,10 @@ Internal tests or config files are published, which are usually not needed and u
 
 [Node.js v21.1.0](https://nodejs.org/en/blog/release/v21.1.0) adds a new `--experimental-detect-module`, which can be used to automatically run ES modules when ESM syntax can be detected. Node.js hopes to make detection enabled by default in the future. Detection increases startup time, so Node is encouraging everyone — especially package authors — to add a type field to `package.json`, even for the default `"type": "commonjs"`.
 
+## `USE_LICENSE`
+
+A license file is published but the `"license"` field is not set in `package.json`. Consider adding a `"license"` field so that it's correctly displayed on npm and allows other tooling to parse the package license.
+
 ## `FIELD_INVALID_VALUE_TYPE`
 
 Some `package.json` fields has a set of allowed types, e.g. `string` or `object` only. If an invalid type is passed, this error message will be showed.

site/src/utils/message.js

@@ -95,6 +95,9 @@ function messageToString(m, pkg) {
     case 'USE_TYPE':
       // prettier-ignore
       return `The package does not specify the ${bold('"type"')} field. NodeJS may attempt to detect the package type causing a small performance hit. Consider adding ${bold('"type"')}: "${bold('commonjs')}".`
+    case 'USE_LICENSE':
+      // prettier-ignore
+      return `The package does not specify the ${bold('"license"')} field but a license file was detected at ${bold(m.args.licenseFilePath)}. Consider adding a ${bold('"license"')} field so it's displayed on npm.`
     case 'TYPES_NOT_EXPORTED': {
       const typesFilePath = exportsRel(m.args.typesFilePath)
       if (m.args.actualExtension && m.args.expectExtension) {