Fix special character problem by making FindValues prefer exact matches

libraries/Microsoft.Bot.Builder.Dialogs/Choices/Find.cs

@@ -103,6 +103,11 @@ public static List<ModelResult<FoundChoice>> FindChoices(string utterance, IList
         /// <returns>A list of found values.</returns>
         public static List<ModelResult<FoundValue>> FindValues(string utterance, List<SortedValue> values, FindValuesOptions options = null)
         {
+            if (FindExactMatch(utterance, values) is ModelResult<FoundValue> exactMatch)
+            {
+                return new List<ModelResult<FoundValue>> { exactMatch };
+            }
+
             // Sort values in descending order by length so that the longest value is searched over first.
             var list = values;
             list.Sort((a, b) => b.Value.Length - a.Value.Length);
@@ -114,10 +119,8 @@ public static List<ModelResult<FoundValue>> FindValues(string utterance, List<So
             var tokens = tokenizer(utterance, opt.Locale);
             var maxDistance = opt.MaxTokenDistance ?? 2;
 
-            for (var index = 0; index < list.Count; index++)
+            foreach (var entry in list)
             {
-                var entry = list[index];
-
                 // Find all matches for a value
                 // - To match "last one" in "the last time I chose the last one" we need
                 //   to re-search the string starting from the end of the previous match.
@@ -278,5 +281,30 @@ private static ModelResult<FoundValue> MatchValue(IList<Token> sourceTokens, int
 
             return result;
         }
+
+        private static ModelResult<FoundValue> FindExactMatch(string utterance, List<SortedValue> values)
+        {
+            foreach (var entry in values)
+            {
+                if (entry.Value.Equals(utterance, StringComparison.OrdinalIgnoreCase))
+                {
+                    return new ModelResult<FoundValue>
+                    {
+                        Text = utterance,
+                        Start = 0,
+                        End = utterance.Length - 1,
+                        TypeName = "value",
+                        Resolution = new FoundValue
+                        {
+                            Value = entry.Value,
+                            Index = entry.Index,
+                            Score = 1,
+                        },
+                    };
+                }
+            }
+
+            return null;
+        }
     }
 }

tests/Microsoft.Bot.Builder.Dialogs.Tests/ChoicesRecognizersTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.Bot.Builder.Dialogs.Choices;
 using Xunit;
 
@@ -36,6 +37,13 @@ public class ChoicesRecognizersTests
             new SortedValue { Value = "option C", Index = 2 },
         };
 
+        private static List<SortedValue> valuesWithSpecialCharacters = new List<SortedValue>
+        {
+            new SortedValue { Value = "A < B", Index = 0 },
+            new SortedValue { Value = "A >= B", Index = 1 },
+            new SortedValue { Value = "A ??? B", Index = 2 },
+        };
+
         // FindValues
         [Fact]
         public void ShouldFindASimpleValueInAnSingleWordUtterance()
@@ -83,6 +91,16 @@ public void ShouldCorrectlyDisambiguateBetweenVerySimilarValues()
             AssertValue(found[0], "option B", 1, 1.0f);
         }
 
+        [Fact]
+        public void ShouldPreferExactMatch()
+        {
+            var index = 1;
+            var utterance = valuesWithSpecialCharacters[index].Value;
+            var found = Find.FindValues(utterance, valuesWithSpecialCharacters);
+
+            AssertValue(found.Single(), utterance, index, 1);
+        }
+
         [Fact]
         public void ShouldFindASingleChoiceInAnUtterance()
         {