Fix ESM main no exports check

pkg/src/index.js

@@ -137,7 +137,7 @@ export async function publint({ pkgDir, vfs, level, _include }) {
           type: 'warning'
         })
       }
-      if (expectFormat === 'ESM') {
+      if (expectFormat === 'ESM' && !exports) {
         messages.push({
           code: 'HAS_ESM_MAIN_BUT_NO_EXPORTS',
           args: {},

pkg/src/message.js

@@ -38,7 +38,7 @@ export function printMessage(m, pkg) {
       return `${c.bold(fp(m.path))} is ${pv(m.path)} but file does not exist.`
     case 'HAS_ESM_MAIN_BUT_NO_EXPORTS':
       // prettier-ignore
-      return `${c.bold('pkg.main')} is an ESM file, but it is usually better to use ${c.bold('pkg.exports')} instead, and remove ${c.bold('pkg.main')} alongside, as compatible NodeJS versions support it as well. (This will be a breaking change)`
+      return `${c.bold('pkg.main')} is an ESM file, but it is usually better to use ${c.bold('pkg.exports')} instead. If you don't support NodeJS 12.6 and below, you can also remove ${c.bold('pkg.main')}. (This will be a breaking change)`
     case 'HAS_MODULE_BUT_NO_EXPORTS':
       // prettier-ignore
       return `${c.bold('pkg.module')} is used to output ESM, but ${c.bold('pkg.exports')} is not defined. As NodeJS doesn't read ${c.bold('pkg.module')}, the ESM output may be skipped. Consider adding ${c.bold('pkg.exports')} to export the ESM output. ${c.bold('pkg.module')} can usually be removed alongside too. (This will be a breaking change)`

pkg/tests/fixtures/test-2/main.mjs

@@ -0,0 +1 @@
+export const foo = 'bar'

pkg/tests/fixtures/test-2/package.json

@@ -2,6 +2,7 @@
   "name": "publint-test-2",
   "version": "0.0.1",
   "private": true,
+  "main": "./main.mjs",
   "browser": "./lib/bar.js",
   "exports": {
     "./*.js": "./lib/*.js",

site/rules.html

@@ -43,10 +43,14 @@ <h2><code>HAS_MODULE_BUT_NO_EXPORTS</code></h2>
       </p>
       <h2><code>HAS_ESM_MAIN_BUT_NO_EXPORTS</code></h2>
       <p>
-        If the <code>main</code> entrypoint is an ES module, you can likely
-        remove it as environments that supports so also supports
-        <code>exports</code>, which should be used instead, and the
-        <code>main</code> can then be removed alongside too.
+        If the <code>main</code> entrypoint is an ES module, it's recommended to
+        use the <code>exports</code> field instead as it's initially introduced
+        for better ESM compatibility.
+      </p>
+      <p>
+        If you're not supporting NodeJS 12.6 and below, you can also remove the
+        <code>main</code> field as all tooling would read from
+        <code>exports</code> only and skip <code>main</code>.
       </p>
       <h2><code>EXPORTS_GLOB_NO_MATCHED_FILES</code></h2>
       <p>

site/src/utils/message.js

@@ -30,7 +30,7 @@ export function printMessage(m, pkg) {
       return `File does not exist`
     case 'HAS_ESM_MAIN_BUT_NO_EXPORTS':
       // prettier-ignore
-      return `${bold('pkg.main')} is an ESM file, but it is usually better to use ${bold('pkg.exports')} instead, and remove ${bold('pkg.main')} alongside, as compatible NodeJS versions support it as well. (This will be a breaking change)`
+      return `${bold('pkg.main')} is an ESM file, but it is usually better to use ${bold('pkg.exports')} instead. If you don't support NodeJS 12.6 and below, you can also remove ${bold('pkg.main')}. (This will be a breaking change)`
     case 'HAS_MODULE_BUT_NO_EXPORTS':
       // prettier-ignore
       return `${bold('pkg.module')} is used to output ESM, but ${bold('pkg.exports')} is not defined. As NodeJS doesn't read ${bold('pkg.module')}, the ESM output may be skipped. Consider adding ${bold('pkg.exports')} to export the ESM output. ${bold('pkg.module')} can usually be removed alongside too. (This will be a breaking change)`