feat(check-peer-dependencies-optional-dependency): Added a workaround for yarn swallowing postinstall script output

Author: christopherthielen

README.md

@@ -86,3 +86,6 @@ Searching for solutions:
 yarn upgrade @angular/[email protected]
 ```
 
+## Running as postinstall script using `yarn` package manager
+
+Please see [check-peer-dependencies-optional-dependency](https://github.com/christopherthielen/check-peer-dependencies/tree/master/packages/check-peer-dependencies-optional-dependency)

packages/check-peer-dependencies-optional-dependency/README.md

@@ -0,0 +1,36 @@
+# check-peer-dependencies-optional-dependency
+
+## This is a hack to make check-peer-dependency output visible as a postinstall script when using yarn.
+
+### Motivation
+
+I wanted to create a meta-package that provides a set of peerDependencies to downstream projects.
+I wanted to run `check-peer-dependencies` as a `postinstall` script to inform users which dependencies are not met and offer a solution.
+
+### Problem
+
+By default, `yarn` package manager hides output from postinstall scripts.
+I noticed, however, that output from `optionalDependencies` is visible.
+
+### Using
+
+To run `check-peer-dependencies` as when your package is installed, add `check-peer-dependencies-optional-dependency` as an optional dependency.
+This package has a `postinstall` script which invokes `check-peer-dependencies`.
+
+```
+{
+  "name": "my-installable-package",
+  ...
+  "dependencies": {
+    ...
+    "check-peer-dependencies": "latest"
+  },
+  "peerDependencies": {
+    "this-package-should-be-installed-downstream": "10.0.0"
+  },
+  "optionalDependencies: {
+    "check-peer-dependencies-optional-dependency": "latest"
+  }
+}
+```
+

packages/check-peer-dependencies-optional-dependency/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "check-peer-dependencies-optional-dependency",
+  "version": "1.0.0",
+  "description": "Add this module as an optional dependency to check peer dependencies as a postinstall script (yarn)",
+  "author": "Chris Thielen",
+  "license": "MIT",
+  "scripts": {
+    "postinstall": "npx check-peer-dependencies"
+  }
+}