feat(alias): add npm: registry alias spec (#34)

npa.js

@@ -62,6 +62,8 @@ function resolve (name, spec, where, arg) {
 
   if (spec && (isFilespec.test(spec) || /^file:/i.test(spec))) {
     return fromFile(res, where)
+  } else if (spec && /^npm:/i.test(spec)) {
+    return fromAlias(res, where)
   }
   if (!HostedGit) HostedGit = require('hosted-git-info')
   const hosted = HostedGit.fromUrl(spec, {noGitPlus: true, noCommittish: true})
@@ -253,6 +255,22 @@ function fromURL (res) {
   return res
 }
 
+function fromAlias (res, where) {
+  const subSpec = npa(res.rawSpec.substr(4), where)
+  if (subSpec.type === 'alias') {
+    throw new Error('nested aliases not supported')
+  }
+  if (!subSpec.registry) {
+    throw new Error('aliases only work for registry deps')
+  }
+  res.subSpec = subSpec
+  res.registry = true
+  res.type = 'alias'
+  res.saveSpec = null
+  res.fetchSpec = null
+  return res
+}
+
 function fromRegistry (res) {
   res.registry = true
   const spec = res.rawSpec === '' ? 'latest' : res.rawSpec

test/basic.js

@@ -88,6 +88,26 @@ require('tap').test('basic', function (t) {
       rawSpec: '=v1.2.3'
     },
 
+    'foo@npm:bar': {
+      name: 'foo',
+      escapedName: 'foo',
+      type: 'alias',
+      saveSpec: null,
+      fetchSpec: null,
+      raw: 'foo@npm:bar',
+      rawSpec: 'npm:bar',
+      subSpec: {
+        registry: true,
+        name: 'bar',
+        escapedName: 'bar',
+        type: 'tag',
+        raw: 'bar',
+        rawSpec: '',
+        saveSpec: null,
+        fetchSpec: 'latest'
+      }
+    },
+
     'git+ssh://[email protected]/user/foo#1.2.3': {
       name: null,
       escapedName: null,
@@ -472,6 +492,14 @@ require('tap').test('basic', function (t) {
     npa.resolve('invalid/name', '1.0.0')
   }, 'Invalid names throw errrors')
 
+  t.throws(() => {
+    npa('foo@npm:bar@npm:baz')
+  }, 'nested aliases not supported')
+
+  t.throws(() => {
+    npa('foo@npm:foo/bar')
+  }, 'aliases only work for registry deps')
+
   t.has(npa.resolve('foo', '^1.2.3', '/test/a/b'), {type: 'range'}, 'npa.resolve')
   t.has(npa.resolve('foo', 'file:foo', '/test/a/b'), {type: 'directory', fetchSpec: '/test/a/b/foo'}, 'npa.resolve file:')
   t.has(npa.resolve('foo', '../foo/bar', '/test/a/b'), {type: 'directory'}, 'npa.resolve no protocol')