workaround for Microsoft.CodeAnalysis.Differencing.Match makes not optimal matches (#18802)

src/EditorFeatures/CSharpTest/EditAndContinue/RudeEditStatementTests.cs

@@ -960,6 +960,36 @@ public void InterpolationFormatClause_update()
             edits.VerifyEdits("Update [x = $\"Hello{123:N1}\"]@8 -> [x = $\"Hello{123:N2}\"]@8");
         }
 
+        [Fact]
+        public void MatchCasePattern_UpdateDelete()
+        {
+            var src1 = @"
+switch(shape)
+{
+    case Point p: return 0;
+    case Circle c: return 1;
+}
+";
+
+            var src2 = @"
+switch(shape)
+{
+    case Circle circle: return 1;
+}
+";
+
+            var match = GetMethodMatches(src1, src2, kind: MethodKind.Regular);
+            var actual = ToMatchingPairs(match);
+
+            var expected = new MatchingPairs {
+                { "switch(shape) {     case Point p: return 0;     case Circle c: return 1; }", "switch(shape) {     case Circle circle: return 1; }" },
+                { "case Circle c: return 1;", "case Circle circle: return 1;" },
+                { "return 1;", "return 1;" }
+            };
+
+            expected.AssertEqual(actual);
+        }
+
         #endregion
 
         #region Variable Declaration
@@ -1035,6 +1065,32 @@ public void Switch_Case_Update()
                 "Update [case 1: f(); break;]@18 -> [case 2: f(); break;]@18");
         }
 
+        [Fact]
+        public void CasePatternLabel_UpdateDelete()
+        {
+            var src1 = @"
+switch(shape)
+{
+    case Point p: return 0;
+    case Circle c: return 1;
+}
+";
+
+            var src2 = @"
+switch(shape)
+{
+    case Circle circle: return 1;
+}
+";
+
+            var edits = GetMethodEdits(src1, src2);
+
+            edits.VerifyEdits(
+                "Update [case Circle c: return 1;]@55 -> [case Circle circle: return 1;]@26",
+                "Delete [case Point p: return 0;]@26",
+                "Delete [return 0;]@40");
+        }
+
         #endregion
 
         #region Try Catch Finally

src/Workspaces/Core/Portable/Differencing/Match.cs

@@ -12,10 +12,9 @@ public sealed partial class Match<TNode>
     {
         private const double ExactMatchDistance = 0.0;
         private const double EpsilonDistance = 0.00001;
-        private const double MatchingDistance1 = 0.5;
-        private const double MatchingDistance2 = 1.0;
-        private const double MatchingDistance3 = 1.5;
-        private const double MaxDistance = 2.0;
+        private const double MatchingDistance1 = 0.25;
+        private const double MatchingDistance2 = 0.5;
+        private const double MaxDistance = 1.0;
 
         private readonly TreeComparer<TNode> _comparer;
         private readonly TNode _root1;
@@ -154,7 +153,6 @@ private void ComputeMatchForLabel(int label, List<TNode> s1, List<TNode> s2)
             ComputeMatchForLabel(s1, s2, tiedToAncestor, EpsilonDistance);     // almost exact match
             ComputeMatchForLabel(s1, s2, tiedToAncestor, MatchingDistance1);   // ok match
             ComputeMatchForLabel(s1, s2, tiedToAncestor, MatchingDistance2);   // ok match
-            ComputeMatchForLabel(s1, s2, tiedToAncestor, MatchingDistance3);   // ok match 
             ComputeMatchForLabel(s1, s2, tiedToAncestor, MaxDistance);         // any match
         }
 
@@ -168,6 +166,7 @@ private void ComputeMatchForLabel(List<TNode> s1, List<TNode> s2, int tiedToAnce
             // So in the case of totally matching sequences, we process them in O(n) - 
             // both node1 and firstNonMatch2 will be advanced simultaneously.
 
+            Debug.Assert(maxAcceptableDistance >= ExactMatchDistance && maxAcceptableDistance <= MaxDistance);
             int count1 = s1.Count;
             int count2 = s2.Count;
             int firstNonMatch2 = 0;
@@ -184,7 +183,7 @@ private void ComputeMatchForLabel(List<TNode> s1, List<TNode> s2, int tiedToAnce
 
                 // Find node2 that matches node1 the best, i.e. has minimal distance.
 
-                double bestDistance = MaxDistance;
+                double bestDistance = MaxDistance * 2;
                 TNode bestMatch = default(TNode);
                 bool matched = false;
                 int i2;
@@ -258,6 +257,11 @@ private void ComputeMatchForLabel(List<TNode> s1, List<TNode> s2, int tiedToAnce
                     {
                         firstNonMatch2 = i2 + 1;
                     }
+
+                    if (firstNonMatch2 == count2)
+                    {
+                        return;
+                    }
                 }
             }
         }