Fix mismatched app and test versions for indirect dependencies

lib/DependencyProvider.js

@@ -9,8 +9,15 @@ const collator = new Intl.Collator('en', { numeric: true }); // for sorting SemV
 
 // Initialization work done only once.
 wasm.init();
-const syncGetWorker /*: {| get: (string) => string, shutDown: () => void |} */ =
-  SyncGet.startWorker();
+// Lazily start the worker until needed.
+// This is important for the tests, which never exit otherwise.
+let syncGetWorker_ /*: void | typeof SyncGet.SyncGetWorker */ = undefined;
+function syncGetWorker() /*: typeof SyncGet.SyncGetWorker */ {
+  if (syncGetWorker_ === undefined) {
+    syncGetWorker_ = SyncGet.startWorker();
+  }
+  return syncGetWorker_;
+}
 
 // Cache of existing versions according to the package website.
 class OnlineVersionsCache {
@@ -55,7 +62,7 @@ class OnlineVersionsCache {
 
     // Complete cache with a remote call to the package server.
     const remoteUrl = remotePackagesUrl + '/since/' + (versionsCount - 1); // -1 to check if no package was deleted.
-    const newVersions = JSON.parse(syncGetWorker.get(remoteUrl));
+    const newVersions = JSON.parse(syncGetWorker().get(remoteUrl));
     if (newVersions.length === 0) {
       // Reload from scratch since it means at least one package was deleted from the registry.
       this.map = onlineVersionsFromScratch(cachePath, remotePackagesUrl);
@@ -230,7 +237,7 @@ function fetchElmJsonOnline(
     // or because there was an error parsing `pkg` and `version`.
     // In such case, this will throw again with `cacheElmJsonPath()` so it's fine.
     const remoteUrl = remoteElmJsonUrl(pkg, version);
-    const elmJson = syncGetWorker.get(remoteUrl);
+    const elmJson = syncGetWorker().get(remoteUrl);
     const cachePath = cacheElmJsonPath(pkg, version);
     const parentDir = path.dirname(cachePath);
     fs.mkdirSync(parentDir, { recursive: true });
@@ -261,7 +268,7 @@ function onlineVersionsFromScratch(
   cachePath /*: string */,
   remotePackagesUrl /*: string */
 ) /*: Map<string, Array<string>> */ {
-  const onlineVersionsJson = syncGetWorker.get(remotePackagesUrl);
+  const onlineVersionsJson = syncGetWorker().get(remotePackagesUrl);
   fs.writeFileSync(cachePath, onlineVersionsJson);
   const onlineVersions = JSON.parse(onlineVersionsJson);
   try {

lib/SyncGet.js

@@ -8,12 +8,19 @@ const {
   // $FlowFixMe[cannot-resolve-module]: Flow doesn’t seem to know about the `worker_threads` module yet.
 } = require('worker_threads');
 
-// Start a worker thread and return a `syncGetWorker`
-// capable of making sync requests until shut down.
-function startWorker() /*: {
+// Poor man’s type alias. We can’t use /*:: type SyncGetWorker = ... */ because of:
+// https://github.com/prettier/prettier/issues/2597
+const SyncGetWorker /*: {
   get: (string) => string,
   shutDown: () => void,
-} */ {
+} */ = {
+  get: (string) => string,
+  shutDown: () => {},
+};
+
+// Start a worker thread and return a `syncGetWorker`
+// capable of making sync requests until shut down.
+function startWorker() /*: typeof SyncGetWorker */ {
   const { port1: localPort, port2: workerPort } = new MessageChannel();
   const sharedLock = new SharedArrayBuffer(4);
   // $FlowFixMe[incompatible-call]: Flow is wrong and says `sharedLock` is not an accepted parameter here.
@@ -41,5 +48,6 @@ function startWorker() /*: {
 }
 
 module.exports = {
+  SyncGetWorker,
   startWorker,
 };