[Bugfix] Ensure stability of filename cache-keys

`JSON.stringify(structure)` isn’t inherently stable as it relies on various
internal details of how `structure` was created.

As written, if a given babel configuration is create in an dynamic manner,
it is possible for babel-loader to have spurious cache misses.

To address this, we can use one of the many stable stringify alternatives. 

For this PR I have selected [fast-json-stable-stringify](https://github.com/epoberezkin/fast-json-stable-stringify)
for that task, as it appears both popular and it’s benchmarks look promising.


This PR does not explicitly include tests, as testing this is both tricky
to test in this context, and the important tests are contained within
fast-json-stable-stringify itself.

package.json

@@ -10,6 +10,7 @@
     "node": ">= 8.9"
   },
   "dependencies": {
+    "fast-json-stable-stringify": "^2.1.0",
     "find-cache-dir": "^3.3.1",
     "loader-utils": "^1.4.0",
     "make-dir": "^3.1.0",

src/cache.js

@@ -24,6 +24,7 @@ const writeFile = promisify(fs.writeFile);
 const gunzip = promisify(zlib.gunzip);
 const gzip = promisify(zlib.gzip);
 const makeDir = require("make-dir");
+const stringify = require("fast-json-stable-stringify");
 
 /**
  * Read the contents from the compressed file.
@@ -65,7 +66,7 @@ const write = async function (filename, compress, result) {
 const filename = function (source, identifier, options) {
   const hash = crypto.createHash("md4");
 
-  const contents = JSON.stringify({ source, options, identifier });
+  const contents = stringify({ source, options, identifier });
 
   hash.update(contents);
 

src/index.js

@@ -28,6 +28,7 @@ const schema = require("./schema");
 const { isAbsolute } = require("path");
 const loaderUtils = require("loader-utils");
 const validateOptions = require("schema-utils");
+const stringify = require("fast-json-stable-stringify");
 
 function subscribe(subscriber, metadata, context) {
   if (context[subscriber]) {
@@ -186,7 +187,7 @@ async function loader(source, inputSourceMap, overrides) {
 
     const {
       cacheDirectory = null,
-      cacheIdentifier = JSON.stringify({
+      cacheIdentifier = stringify({
         options,
         "@babel/core": transform.version,
         "@babel/loader": version,

yarn.lock

@@ -2140,6 +2140,7 @@ __metadata:
     eslint-config-prettier: ^6.3.0
     eslint-plugin-flowtype: ^5.2.0
     eslint-plugin-prettier: ^3.0.0
+    fast-json-stable-stringify: ^2.1.0
     find-cache-dir: ^3.3.1
     husky: ^4.3.0
     lint-staged: ^10.5.1
@@ -3711,7 +3712,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"fast-json-stable-stringify@npm:^2.0.0":
+"fast-json-stable-stringify@npm:^2.0.0, fast-json-stable-stringify@npm:^2.1.0":
   version: 2.1.0
   resolution: "fast-json-stable-stringify@npm:2.1.0"
   checksum: 7df3fabfe445d65953b2d9d9d3958bd895438b215a40fb87dae8b2165c5169a897785eb5d51e6cf0eb03523af756e3d82ea01083f6ac6341fe16db532fee3016