module: allow subpath imports that start with #/

It's a common ecosystem pattern to map a source root directory to
`@/` but it requires special tooling support. This turns `#/*` into
a more realistic alternative for that pattern.

Author: hybrist

doc/api/esm.md

@@ -1102,7 +1102,7 @@ Note: This function is directly invoked by the CommonJS resolution algorithm.
 Note: This function is directly invoked by the CommonJS resolution algorithm.
 
 > 1. Assert: _specifier_ begins with _"#"_.
-> 2. If _specifier_ is exactly equal to _"#"_ or starts with _"#/"_, then
+> 2. If _specifier_ is exactly equal to _"#"_, then
 >    1. Throw an _Invalid Module Specifier_ error.
 > 3. Let _packageURL_ be the result of **LOOKUP\_PACKAGE\_SCOPE**(_parentURL_).
 > 4. If _packageURL_ is not **null**, then

lib/internal/modules/esm/resolve.js

@@ -692,8 +692,7 @@ function patternKeyCompare(a, b) {
  * @returns {URL} The resolved import URL.
  */
 function packageImportsResolve(name, base, conditions) {
-  if (name === '#' || StringPrototypeStartsWith(name, '#/') ||
-      StringPrototypeEndsWith(name, '/')) {
+  if (name === '#' || StringPrototypeEndsWith(name, '/')) {
     const reason = 'is not a valid internal imports specifier name';
     throw new ERR_INVALID_MODULE_SPECIFIER(name, reason, fileURLToPath(base));
   }

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

@@ -15,6 +15,10 @@ const { requireImport, importImport } = importer;
   const internalImports = new Map([
     // Base case
     ['#test', maybeWrapped({ default: 'test' })],
+    // Root wildcard import
+    ['#/foo', maybeWrapped({ default: 'foo' })],
+    // Explicit #/ mapping
+    ['#/initialslash', maybeWrapped({ default: 'test' })],
     // import / require conditions
     ['#branch', maybeWrapped({ default: isRequire ? 'requirebranch' : 'importbranch' })],
     // Subpath imports
@@ -64,8 +68,6 @@ const { requireImport, importImport } = importer;
     ['#external/subpath/x%5Cy', 'must not include encoded "/" or "\\"'],
     // Target must have a name
     ['#', '#'],
-    // Initial slash target must have a leading name
-    ['#/initialslash', '#/initialslash'],
     // Percent-encoded target paths
     ['#encodedslash', 'must not include encoded "/" or "\\"'],
     ['#encodedbackslash', 'must not include encoded "/" or "\\"'],

test/fixtures/es-modules/pkgimports/package.json

@@ -1,5 +1,6 @@
 {
   "imports": {
+    "#/*": "./src/*.js",
     "#branch": {
       "import": "./importbranch.js",
       "require": "./requirebranch.js"

test/fixtures/es-modules/pkgimports/src/foo.js

@@ -0,0 +1 @@
+module.exports = 'foo';