Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/hardhat/env-artifacts.js

@@ -0,0 +1,24 @@
+const { HardhatError } = require('hardhat/internal/core/errors');
+
+// Modifies `artifacts.require(X)` so that instead of X it loads the XUpgradeable contract.
+// This allows us to run the same test suite on both the original and the transpiled and renamed Upgradeable contracts.
+
+extendEnvironment(env => {
+  const artifactsRequire = env.artifacts.require;
+
+  env.artifacts.require = name => {
+    for (const suffix of ['UpgradeableWithInit', 'Upgradeable', '']) {
+      try {
+        return artifactsRequire(name + suffix);
+      } catch (e) {
+        // HH700: Artifact not found - from https://hardhat.org/hardhat-runner/docs/errors#HH700
+        if (HardhatError.isHardhatError(e) && e.number === 700 && suffix !== '') {
+          continue;
+        } else {
+          throw e;
+        }
+      }
+    }
+    throw new Error('Unreachable');
+  };
+});