fix: specifier === '#' or '#/'

.changeset/hot-lizards-watch.md

@@ -0,0 +1,5 @@
+---
+'resolve.imports': patch
+---
+
+Returns `undefined` if specifier is exactly '#' or '#/'.

.changeset/metal-planets-end.md

@@ -4,5 +4,6 @@
 
 Do not support recursive resolution.
 
-There is no spec for it.
-It will return `undefined` if the import is recursive.
+The spec does not support recursion: https://nodejs.org/api/esm.html#esm_resolver_algorithm_specification
+
+`resolve()` will return `undefined` if the import is recursive.

packages/resolve.imports/README.md

@@ -179,8 +179,8 @@ Here are the key notes:
 > Return PACKAGE_RESOLVE(target with every instance of "*" replaced by patternMatch, packageURL + "/").
 
 The phrase `target with every instance of "*" replaced by patternMatch` indicates it can contain multiple `*`s.
-However, in `PATTERN_KEY_COMPARE`, it is asserted that the pattern only contains one `*`.
-So this module only supports one `*` in the pattern.
+This module supports multiple `*`s in the replacer pattern as described,
+but it is likely a bug in the spec, as the resulting string likely does not make sense.
 
 ### `PATTERN_KEY_COMPARE`
 

packages/resolve.imports/ts/index.spec.ts

@@ -12,6 +12,16 @@ describe('subpath imports', () => {
     expect(r).toBeUndefined()
   })
 
+  it('returns undefined when specifier does not start with #', () => {
+    expect(resolve({ imports: { x: 'y' } }, 'x')).toBeUndefined()
+  })
+
+  it('returns undfined if specifier is exactly # or #/', () => {
+    const pkg = { imports: { '#': 'y', '#/': 'x' } }
+    expect(resolve(pkg, '#')).toBeUndefined()
+    expect(resolve(pkg, '#/')).toBeUndefined()
+  })
+
   it('returns undefined when entry does not start with #', () => {
     const r = resolve(
       {

packages/resolve.imports/ts/resolve.ts

@@ -9,14 +9,15 @@ export type ResolveOptions = {
  * Resolve an import specifier based on package.json#imports.
  *
  * @param pkg contents of package.json
- * @param entry import specifier
+ * @param specifier import specifier
  * @return resolved specifier or undefined if not found
  */
-export function resolve(pkg: any, entry: string, options?: ResolveOptions) {
+export function resolve(pkg: any, specifier: string, options?: ResolveOptions) {
   if (!pkg.imports) return undefined
-  if (!entry.startsWith('#')) return undefined
+  if (!specifier.startsWith('#')) return undefined
+  if (specifier === '#' || specifier === '#/') return undefined
 
-  const matched = pkg.imports[entry]
+  const matched = pkg.imports[specifier]
   if (matched) {
     return noRecursive(lookupReplacer(matched, options?.conditions?.slice()))
   }
@@ -26,7 +27,7 @@ export function resolve(pkg: any, entry: string, options?: ResolveOptions) {
     const keyParts = key.split('*')
 
     const [prefix, suffix] = keyParts
-    if (entry.startsWith(prefix)) {
+    if (specifier.startsWith(prefix)) {
       const replacer = lookupReplacer(pkg.imports[key], options?.conditions?.slice())
 
       if (replacer) return noRecursive(
@@ -35,7 +36,7 @@ export function resolve(pkg: any, entry: string, options?: ResolveOptions) {
     }
 
     function replacePattern(replacer: string) {
-      const toKeep = suffix ? entry.slice(prefix.length, -suffix.length) : entry.slice(prefix.length)
+      const toKeep = suffix ? specifier.slice(prefix.length, -suffix.length) : specifier.slice(prefix.length)
       return replacer.replace(/\*/g, toKeep)
     }
   }