fix: bug with errors from partial failures in described rules

Author: pdubroy

packages/ohm-js/src/pexprs-eval.js

@@ -303,6 +303,7 @@ pexprs.Apply.prototype.reallyEval = function (state) {
     }
     if (memoRec) {
       memoRec.failuresAtRightmostPosition = state.cloneRecordedFailures();
+      memoRec.rightmostFailureOffset = state._getRightmostFailureOffset();
     }
   }
 

packages/ohm-js/test/test-errors.js

@@ -401,3 +401,33 @@ test('wrongNumberOfArguments includes the interval', t => {
     {message}
   );
 });
+
+// When a described rule partially matches, getRightmostFailures should return
+// the description failure. The bug was that memoRec.rightmostFailureOffset wasn't
+// updated after processFailure for described rules, causing hasNecessaryInfo to
+// incorrectly consider the memo valid.
+test('getRightmostFailures with described rule that partially matches', t => {
+  const g = ohm.grammar(`G {
+    foo (a foo) = "x" "y"
+  }`);
+
+  // At position 0
+  const r1 = g.match('x', 'foo');
+  t.is(r1.getRightmostFailurePosition(), 0);
+  t.deepEqual(
+    r1.getRightmostFailures().map(f => f.toString()),
+    ['a foo']
+  );
+
+  // At position 5 (via a wrapper rule)
+  const g2 = ohm.grammar(`G {
+    start = "abcde" foo
+    foo (a foo) = "x" "y"
+  }`);
+  const r2 = g2.match('abcdex', 'start');
+  t.is(r2.getRightmostFailurePosition(), 5);
+  t.deepEqual(
+    r2.getRightmostFailures().map(f => f.toString()),
+    ['a foo']
+  );
+});

packages/ohm-js/test/test-ohm-syntax.js

@@ -119,7 +119,7 @@ test('unicode code point escapes', t => {
 
   // More than 6 hex digits is just a parse error. (We'd like to make this nicer.)
   t.throws(() => ohm.grammar(String.raw`G { start = "\u{0000000} }`), {
-    message: /Expected "\\"" or not "\\\\"/,
+    message: /Expected "\\"", not "\\\\", or an escape sequence/,
   });
 
   t.throws(() => ohm.grammar('G { start = "\\u{FFFFFF}" }'), {