Fix: Left-recursive rule fails to grow when it occupies a non-final field of an enclosing sequence (#150)

Author: georghinkel

AnyText/AnyText.Core/Matcher.cs

@@ -205,6 +205,11 @@ internal MatchOrMatchProcessor MatchOrCreateMatchProcessor(Rule rule, ParseConte
                         recursionContext = new RecursionContext(position, rule.Continuations);
                         createdRecursion = recursionContext;
                     }
+                    else if (!AllContinuationsPresent(recursionContext, rule.Continuations))
+                    {
+                        recursionContext = new RecursionContext(position, MergeContinuations(recursionContext.Continuations, rule.Continuations));
+                        createdRecursion = recursionContext;
+                    }
                     var cycleDetector = new FailedRuleApplication(rule, new ParsePositionDelta(1, 0), "Recursive");
                     cycleDetector.AddToColumn(column);
                     var processor = rule.NextMatchProcessor(context, recursionContext, ref position);
@@ -322,6 +327,31 @@ public override MatchOrMatchProcessor NextMatchProcessor(ParseContext context, R
             }
         }
 
+        private static bool AllContinuationsPresent(RecursionContext recursionContext, IReadOnlyCollection<RecursiveContinuation> continuations)
+        {
+            foreach (var continuation in continuations)
+            {
+                if (!recursionContext.Continuations.Contains(continuation))
+                {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+        private static List<RecursiveContinuation> MergeContinuations(IReadOnlyCollection<RecursiveContinuation> existing, IReadOnlyCollection<RecursiveContinuation> additional)
+        {
+            var merged = new List<RecursiveContinuation>(existing);
+            foreach (var continuation in additional)
+            {
+                if (!merged.Contains(continuation))
+                {
+                    merged.Add(continuation);
+                }
+            }
+            return merged;
+        }
+
         private static void ExtendContinuations(RecursionContext recursionContext, MemoColumn column, ParseContext context, ref ParsePosition position, ref RuleApplication ruleApplication)
         {
             var headRule = ruleApplication.Rule;

AnyText/AnyText.history

@@ -53,3 +53,4 @@ patch: update StreamJsonRpc version, improve error reporting
 patch: update dependencies
 patch: fix stack overflow in ChoiceRule synthesis for self-referential choices with a parantheses alternative
 patch: fix TextEdit.ApplyReconstructArray clobbering preceding text when an edit's end points past the last line
+patch: fix left-recursive rules losing their growing continuations when they start matching at a position already claimed by an unrelated left-recursive rule