1 files changed, 52 insertions, 0 deletions
diff --git a/scripts/frontend/postinstall.js b/scripts/frontend/postinstall.js
index 682039a41b3..7f0abd88a15 100644
--- a/scripts/frontend/postinstall.js
+++ b/scripts/frontend/postinstall.js
@@ -1,3 +1,5 @@
+const fs = require('fs');
+const path = require('path');
 const chalk = require('chalk');
 
 // check that fsevents is available if we're on macOS
@@ -19,4 +21,54 @@ if (process.platform === 'darwin') {
   }
 }
 
+if (process.env.NODE_ENV !== 'production') {
+  const lockfileParser = require('@yarnpkg/lockfile');
+
+  // check that certain packages are only listed once in the yarn.lock
+  const packagesToCheck = ['@gitlab-org/gitlab-svgs', 'bootstrap'];
+  const file = fs.readFileSync(path.join(__dirname, '../../yarn.lock'), 'utf8');
+  const packages = lockfileParser.parse(file);
+
+  if (packages.type !== 'success') {
+    console.error(`${chalk.red('error')} Could not parse 'yarn.lock'. Please make sure it exists`);
+    process.exit(1);
+  }
+
+  function checkUniqueYarnLockEntry(hasError, packageName) {
+    const resolved = Object.entries(packages.object).reduce((result, [name, value]) => {
+      if (name.replace(/"/g, '').startsWith(`${packageName}@`)) {
+        const resolvedUrl = value.resolved;
+
+        if (!result.includes(resolvedUrl)) {
+          result.push(resolvedUrl);
+        }
+      }
+      return result;
+    }, []);
+
+    if (resolved.length !== 1) {
+      console.error(
+        chalk.red(`
+        The dependency ${packageName} has ${resolved.length} entries in 'yarn.lock'.
+        It is supposed to have exactly one entry, please fix that by:
+
+           1. Delete all lines starting with '${packageName}@' from the yarn.lock
+           2. Re-run \`${chalk.cyan('yarn install')}\`
+           3. Commit changes to yarn.lock
+      `)
+      );
+      return true;
+    }
+
+    return hasError;
+  }
+
+  const hasError = packagesToCheck.reduce(checkUniqueYarnLockEntry, false);
+
+  if (hasError) {
+    console.error(`${chalk.red('error')} Dependency postinstall check failed.`);
+    process.exit(1);
+  }
+}
+
 console.log(`${chalk.green('success')} Dependency postinstall check passed.`);