fix issue mochajs#4551 by adding file to error message

lib/esm-utils.js

@@ -3,7 +3,29 @@ const url = require('url');
 
 const formattedImport = async file => {
   if (path.isAbsolute(file)) {
-    return import(url.pathToFileURL(file));
+    try {
+      return await import(url.pathToFileURL(file));
+    } catch (err) {
+      // This is a hack created because ESM in Node.js (at least in Node v15.5.1) does not emit
+      // the location of the syntax error in the error thrown.
+      // This is problematic because the user can't see what file has the problem,
+      // so we add the file location to the error.
+      // This `if` should be removed once Node.js fixes the problem.
+      if (
+        err instanceof SyntaxError &&
+        err.message &&
+        err.stack &&
+        !err.stack.includes(file)
+      ) {
+        const newErrorWithFilename = new SyntaxError(err.message);
+        newErrorWithFilename.stack = err.stack.replace(
+          /^SyntaxError/,
+          `SyntaxError[ @${file} ]`
+        );
+        throw newErrorWithFilename;
+      }
+      throw err;
+    }
   }
   return import(file);
 };