Add a storage consistency script

package.json

@@ -31,7 +31,9 @@
     "test": "hardhat test",
     "test:inheritance": "node scripts/inheritanceOrdering artifacts/build-info/*",
     "gas-report": "env ENABLE_GAS_REPORT=true npm run test",
-    "slither": "npm run clean && slither . --detect reentrancy-eth,reentrancy-no-eth,reentrancy-unlimited-gas"
+    "slither": "npm run clean && slither . --detect reentrancy-eth,reentrancy-no-eth,reentrancy-unlimited-gas",
+    "layout:build": "node scripts/upgradeable/layout.js artifacts/build-info/* --build storage-layout-cache.json",
+    "layout:test": "node scripts/upgradeable/layout.js artifacts/build-info/* --check storage-layout-cache.json"
   },
   "repository": {
     "type": "git",

scripts/upgradeable/layout.js

+const fs = require('fs');
+const path = require('path');
+const { findAll } = require('solidity-ast/utils');
+const { astDereferencer } = require('@openzeppelin/upgrades-core/dist/ast-dereferencer');
+const { solcInputOutputDecoder } = require('@openzeppelin/upgrades-core/dist/src-decoder');
+const { extractStorageLayout } = require('@openzeppelin/upgrades-core/dist/storage/extract');
+const { StorageLayoutComparator } = require('@openzeppelin/upgrades-core/dist/storage/compare');
+const { LayoutCompatibilityReport } = require('@openzeppelin/upgrades-core/dist/storage/report');
+
+
+const { build, check, _: artifacts } = require('yargs').argv;
+
+
+// build layout for current version of the code
+const layout = {}
+for (const artifact of artifacts) {
+    const { input, output } = require(path.resolve(__dirname, '../..', artifact));
+
+    const decoder = solcInputOutputDecoder(input, output);
+    const deref = astDereferencer(output);
+
+    for (const src in output.contracts) {
+        for (const contractDef of findAll('ContractDefinition', output.sources[src].ast)) {
+            layout[contractDef.name] = extractStorageLayout(
+                contractDef,
+                decoder,
+                deref,
+                output.contracts[src][contractDef.name].storageLayout
+            ).storage;
+        }
+    }
+}
+
+// if the --check option is set, check compatibility of the current layout against the cache
+if (check) {
+    const cache = JSON.parse(fs.readFileSync(path.resolve(__dirname, '../..', check)));
+
+    for (id in cache) {
+        const comparator = new StorageLayoutComparator();
+        const report = new LayoutCompatibilityReport(comparator.layoutLevenshtein(cache[id], layout[id], { allowAppend: false }));
+
+        if (!report.ok) {
+            console.log(`Storage incompatibility in ${id}`);
+            console.log(report.explain());
+            process.exitCode = 1;
+        }
+    }
+}
+
+// if the --build option is set, write the layout results
+if (build) {
+    fs.writeFileSync(path.resolve(__dirname, '../..', build), JSON.stringify(layout));
+}