WIP hack combinator to try and improve error messages.

peg.js

@@ -183,3 +183,26 @@ Peg.End = () => {
   }).expects("<eof>");
   return end;
 };
+
+/**
+ * Creates a pattern that never succeeds, but reports how far its wrapped pattern could match before failing.
+ *
+ * This is a hack, meant to improve error messages after an AtLeast(). Maybe this can be removed by patterns returning both success and failure
+ *
+ * Never consumes input, and fails with zero length if the pattern succeeds.
+ * @param {Peg.Pattern<unknown>} pattern
+ * @return {Peg.Pattern<never>}
+ */
+Peg.Hint = function (pattern) {
+  return /** @type {Peg.Pattern<never>} */ (
+    Peg.WrapPattern(function (source, index) {
+      const match = pattern(source, index);
+      if (match[0]) {
+        console.log("oops match", match);
+        return [false, index, pattern.expectLabel];
+      } else {
+        return match;
+      }
+    })
+  ).expects(pattern.expectLabel);
+};