feat(git): support packages in a subdirectory

Author: sspiff

lib/git.js

@@ -16,6 +16,7 @@ const npm = require('./util/npm.js')
 const _resolvedFromRepo = Symbol('_resolvedFromRepo')
 const _resolvedFromHosted = Symbol('_resolvedFromHosted')
 const _resolvedFromClone = Symbol('_resolvedFromClone')
+const _subdirFromClone = Symbol('_subdirFromClone')
 const _tarballFromResolved = Symbol.for('pacote.Fetcher._tarballFromResolved')
 const _addGitSha = Symbol('_addGitSha')
 const _clone = Symbol('_clone')
@@ -138,6 +139,10 @@ class GitFetcher extends Fetcher {
     return this[_clone](dir => this.resolved)
   }
 
+  [_subdirFromClone] (handler) {
+    return this[_clone](dir => handler(`${dir}${this.spec.gitSubdir || ''}`))
+  }
+
   [_prepareDir] (dir) {
     return readPackageJson(dir + '/package.json').then(mani => {
       // no need if we aren't going to do any preparation.
@@ -168,7 +173,7 @@ class GitFetcher extends Fetcher {
     stream.from = this.from
 
     // check it out and then shell out to the DirFetcher tarball packer
-    this[_clone](dir => this[_prepareDir](dir)
+    this[_subdirFromClone](dir => this[_prepareDir](dir)
       .then(() => new Promise((res, rej) => {
         const df = new DirFetcher(`file:${dir}`, {
           ...this.opts,
@@ -256,7 +261,7 @@ class GitFetcher extends Fetcher {
 
     return this.spec.hosted && this.resolved
       ? FileFetcher.prototype.manifest.apply(this)
-      : this[_clone](dir =>
+      : this[_subdirFromClone](dir =>
           readPackageJson(dir + '/package.json')
             .then(mani => this.package = {
               ...mani,