fix: added missing npm_package_json env variable (#49)

* Added missing env variable.

* Added a minimal test.

Author: uhop

index.js

@@ -80,6 +80,7 @@ function lifecycle (pkg, stage, wd, opts) {
         const env = makeEnv(pkg, opts)
         env.npm_lifecycle_event = stage
         env.npm_node_execpath = env.NODE = env.NODE || process.execPath
+        env.npm_package_json = path.join(wd, 'package.json')
         if (process.pkg != null) {
           // If the pnpm CLI was bundled by vercel/pkg then we cannot use the js path for npm_execpath
           // because in that case the js is in a virtual filesystem inside the executor.

test/fixtures/count-to-10/postinstall.js

@@ -3,3 +3,6 @@
 console.log('line 1')
 console.log('line 2')
 console.error('some error')
+if (process.env.npm_package_json) {
+  console.log('package.json')
+}

test/index.js

@@ -68,7 +68,8 @@ test("reports child's output", async (t) => {
   }
   const dir = path.join(__dirname, '..')
 
-  const pkg = require(path.join(fixture, 'package.json'))
+  const pkgFileName = path.resolve(fixture, 'package.json')
+  const pkg = require(pkgFileName)
 
   await lifecycle(pkg, 'postinstall', fixture, {
     stdio: 'pipe',
@@ -103,6 +104,15 @@ test("reports child's output", async (t) => {
     ),
     'stderr reported'
   )
+  t.ok(
+    verbose.calledWithMatch(
+      'lifecycle',
+      'undefined~postinstall:',
+      'stdout',
+      'package.json'
+    ),
+    'package json reported'
+  )
   t.ok(
     silly.calledWithMatch(
       'lifecycle',