don't run for dependencies

Author: ds300

README.md

@@ -18,10 +18,15 @@ git commit -m "fix brokenFile.js in some-package"
 ```
 
 Patches created by `patch-package` are automatically and gracefully applied when
-you use `npm`(>=5) or `yarn`.
+you use `npm` or `yarn`.
 
-No more waiting around for pull requests to be merged and published. No more
-forking repos just to fix that one tiny thing preventing your app from working.
+No more waiting around for pull requests to be merged and published! No more
+forking repos just to change one line!
+
+ⓘ <em>Is your project a published npm package? If so you should only patch dev
+dependencies. Because of the way node_modules folders are managed, patch files
+can't be reliably applied for your dependents. `patch-package` won't even
+try.</em>
 
 ## Set-up
 

src/index.ts

@@ -7,10 +7,11 @@ import { getAppRootPath } from "./getAppRootPath"
 import { makePatch } from "./makePatch"
 import { makeRegExp } from "./makeRegExp"
 import { detectPackageManager } from "./detectPackageManager"
-import { join } from "./path"
-import { normalize, sep } from "path"
+import { join, resolve } from "./path"
+import { basename, normalize, sep } from "path"
 import slash = require("slash")
 import isCi from "is-ci"
+import { existsSync } from "fs"
 
 const appPath = getAppRootPath()
 const argv = minimist(process.argv.slice(2), {
@@ -33,6 +34,16 @@ console.log(
   require(join(__dirname, "../package.json")).version,
 )
 
+if (
+  basename(resolve(process.cwd(), "../")) === "node_modules" &&
+  existsSync(resolve(process.cwd(), "../../package.json"))
+) {
+  console.log(
+    `patch-package seems to be running as part of a dependency's postinstall script and will not attempt to apply patches.`,
+  )
+  process.exit(0)
+}
+
 if (argv.version || argv.v) {
   // noop
 } else if (argv.help || argv.h) {