Add hash of Babel plugin to Jest transform

Jest caches based on the hash of the babel config. This caused us to not break 
that cache when the we made changes to the plugin. 

Fixes #643

compiler/forget/package.json

@@ -8,7 +8,7 @@
     "src"
   ],
   "scripts": {
-    "build": "tsc",
+    "build": "tsc && scripts/hash-dist.sh",
     "bundle:meta": "scripts/bundle-meta.sh",
     "dev": "concurrently \"yarn:build --watch\" \"yarn:playground\"",
     "playground": "cd packages/playground && yarn && yarn dev",

compiler/forget/scripts/hash-dist.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+set -eo pipefail
+
+# Hashes JS files in the dist directory to create a cache-breaker
+
+find dist -name '*.js' | sort | xargs shasum | shasum | awk '{ print $1 }' > dist/HASH

compiler/forget/scripts/jest/makeTransform.js

@@ -7,6 +7,7 @@
 
 const ReactForgetBabelPlugin = require("../../dist").default;
 const babelJest = require("babel-jest");
+const { readFileSync } = require("fs");
 
 module.exports = (useForget) => {
   function createTransformer() {
@@ -17,7 +18,17 @@ module.exports = (useForget) => {
         {
           plugins: [
             "@babel/plugin-syntax-jsx",
-            ...(useForget ? [ReactForgetBabelPlugin, {}] : []),
+            ...(useForget
+              ? [
+                  [
+                    ReactForgetBabelPlugin,
+                    {
+                      // Jest hashes the babel config as a cache breaker.
+                      cacheBreaker: readFileSync("dist/HASH", "utf8"),
+                    },
+                  ],
+                ]
+              : []),
           ],
         },
         "@babel/preset-react",