module: deprecate trailing slash pattern mappings

doc/api/deprecations.md

@@ -2814,6 +2814,13 @@ Type: Documentation-only (supports [`--pending-deprecation`][])
 The `'hash'` and `'mgf1Hash'` options are replaced with `'hashAlgorithm'`
 and `'mgf1HashAlgorithm'`.
 
+### DEP0155: Trailing slashes in pattern specifier resolutions
+
+Type: Runtime
+
+The remapping of specifiers ending in `"/"` like `import 'pkg/x/'` is deprecated
+for package `"exports"` and `"imports"` pattern resolutions.
+
 [Legacy URL API]: url.md#legacy-url-api
 [NIST SP 800-38D]: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
 [RFC 6066]: https://tools.ietf.org/html/rfc6066#section-3

doc/api/esm.md

@@ -1191,6 +1191,8 @@ _isImports_, _conditions_)
 >       _expansionKey_ up to but excluding the first _"*"_ character.
 >    1. If _patternBase_ is not **null** and _matchKey_ starts with but is not
 >       equal to _patternBase_, then
+>       1. If _matchKey_ ends with _"/"_, throw an _Invalid Module Specifier_
+>          error.
 >       1. Let _patternTrailer_ be the substring of _expansionKey_ from the
 >          index after the first _"*"_ character.
 >       1. If _patternTrailer_ has zero length, or if _matchKey_ ends with

lib/internal/modules/esm/resolve.js

@@ -97,6 +97,21 @@ function emitFolderMapDeprecation(match, pjsonUrl, isExports, base) {
   );
 }
 
+function emitTrailingSlashPatternDeprecation(match, pjsonUrl, isExports, base) {
+  const pjsonPath = fileURLToPath(pjsonUrl);
+  if (emittedPackageWarnings.has(pjsonPath + '|' + match))
+    return;
+  emittedPackageWarnings.add(pjsonPath + '|' + match);
+  process.emitWarning(
+    `Use of deprecated trailing slash pattern mapping "${match}" in the ${
+      isExports ? '"exports"' : '"imports"'} field module resolution of the ` +
+      `package at ${pjsonPath}${base ? ` imported from ${fileURLToPath(base)}` :
+        ''}. Mapping specifiers ending in "/" is no longer supported.`,
+    'DeprecationWarning',
+    'DEP0155'
+  );
+}
+
 /**
  * @param {URL} url
  * @param {URL} packageJSONUrl
@@ -630,6 +645,9 @@ function packageExportsResolve(
     if (patternIndex !== -1 &&
         StringPrototypeStartsWith(packageSubpath,
                                   StringPrototypeSlice(key, 0, patternIndex))) {
+      if (StringPrototypeEndsWith(packageSubpath, '/'))
+        emitTrailingSlashPatternDeprecation(packageSubpath, packageJSONUrl,
+                                            true, base);
       const patternTrailer = StringPrototypeSlice(key, patternIndex + 1);
       if (packageSubpath.length >= key.length &&
           StringPrototypeEndsWith(packageSubpath, patternTrailer) &&

test/es-module/test-esm-exports.mjs

@@ -41,13 +41,19 @@ import fromInside from '../fixtures/node_modules/pkgexports/lib/hole.js';
     ['pkgexports/dir2/dir2/trailer', { default: 'index' }],
     ['pkgexports/a/dir1/dir1', { default: 'main' }],
     ['pkgexports/a/b/dir1/dir1', { default: 'main' }],
+
+    // Deprecated:
+    ['pkgexports/trailing-pattern-slash/',
+     { default: 'trailing-pattern-slash' }],
   ]);
 
   if (isRequire) {
     validSpecifiers.set('pkgexports/subpath/file', { default: 'file' });
     validSpecifiers.set('pkgexports/subpath/dir1', { default: 'main' });
+    // Deprecated:
     validSpecifiers.set('pkgexports/subpath/dir1/', { default: 'main' });
     validSpecifiers.set('pkgexports/subpath/dir2', { default: 'index' });
+    // Deprecated:
     validSpecifiers.set('pkgexports/subpath/dir2/', { default: 'index' });
   } else {
     // No exports or main field

test/es-module/test-esm-local-deprecations.mjs

@@ -9,10 +9,14 @@ const selfDeprecatedFolders =
 const deprecatedFoldersIgnore =
     fixtures.path('/es-modules/deprecated-folders-ignore/main.js');
 
+const deprecatedTrailingSlashPattern =
+    fixtures.path('/es-modules/pattern-trailing-slash.mjs');
+
 const expectedWarnings = [
   '"./" in the "exports" field',
   '"#self/" in the "imports" field',
   '"./folder/" in the "exports" field',
+  '"./trailing-pattern-slash/" in the "exports" field',
 ];
 
 process.addListener('warning', (warning) => {
@@ -28,5 +32,6 @@ process.on('exit', () => {
 (async () => {
   await import(pathToFileURL(selfDeprecatedFolders));
   await import(pathToFileURL(deprecatedFoldersIgnore));
+  await import(pathToFileURL(deprecatedTrailingSlashPattern));
 })()
 .catch((err) => console.error(err));

test/fixtures/es-modules/pattern-trailing-slash.mjs

@@ -0,0 +1 @@
+import 'pkgexports/trailing-pattern-slash/';