use our fork of es6-promise with flush exposed as the promise polyfill

package.json

@@ -47,6 +47,7 @@
     "xxhashjs": "^0.2.2"
   },
   "dependencies": {
+    "es6-promise": "https://github.com/bwindels/es6-promise.git#bwindels/expose-flush",
     "aes-js": "^3.1.2",
     "another-json": "^0.2.0",
     "base64-arraybuffer": "^0.2.0",

scripts/post-install.mjs

@@ -96,6 +96,15 @@ async function populateLib() {
         path.join(modulesDir, 'aes-js/index.js'),
         path.join(libDir, "aes-js/index.js")
     );
+    // es6-promise is already written as an es module,
+    // but it does need to be babelified, and current we don't babelify
+    // anything in node_modules in the build script, so make a bundle that
+    // is conveniently not placed in node_modules rather than symlinking.
+    await fs.mkdir(path.join(libDir, "es6-promise/"));
+    await commonjsToESM(
+        path.join(modulesDir, 'es6-promise/lib/es6-promise/promise.js'),
+        path.join(libDir, "es6-promise/index.js")
+    );
 }
 
 populateLib();

src/legacy-polyfill.js

@@ -26,8 +26,8 @@ import "mdn-polyfills/Element.prototype.closest";
 // it will also include the file supporting *all* the encodings,
 // weighing a good extra 500kb :-(
 import "text-encoding";
-import Promise from "../lib/es6-promise/lib/es6-promise/promise.js";
 import {checkNeedsSyncPromise} from "./matrix/storage/idb/utils.js";
+import Promise from "../lib/es6-promise/index.js";
 
 const flush = Promise._flush;
 Promise._flush = function() {

src/worker-polyfill.js

@@ -48,3 +48,8 @@ import "core-js/modules/es.typed-array.to-locale-string";
 import "core-js/modules/es.typed-array.to-string";
 import "core-js/modules/es.typed-array.iterator";
 import "core-js/modules/es.object.to-string";
+
+import Promise from "../lib/es6-promise/index.js";
+// not calling checkNeedsSyncPromise from here as we don't do any idb in the worker,
+// mainly because IE doesn't handle multiple concurrent connections well
+self.Promise = Promise;

yarn.lock

@@ -1205,6 +1205,10 @@ entities@^2.0.0:
   resolved "https://registry.yarnpkg.com/entities/-/entities-2.0.0.tgz#68d6084cab1b079767540d80e56a39b423e4abf4"
   integrity sha512-D9f7V0JSRwIxlRI2mjMqufDrRDnx8p+eEOz7aUM9SuvF8gsBzra0/6tbjl1m8eQHrZlYj6PxqE00hZ1SAIKPLw==
 
+"es6-promise@https://github.com/bwindels/es6-promise.git#bwindels/expose-flush":
+  version "4.2.8"
+  resolved "https://github.com/bwindels/es6-promise.git#112f78f5829e627055b0ff56a52fecb63f6003b1"
+
 escalade@^3.0.2:
   version "3.0.2"
   resolved "https://registry.yarnpkg.com/escalade/-/escalade-3.0.2.tgz#6a580d70edb87880f22b4c91d0d56078df6962c4"