Merge pull request #2945 from jaredpar/fix-2630

Use correct count in ReplaceSeparator

src/Compilers/CSharp/Test/Syntax/Syntax/SeparatedSyntaxListTests.cs

@@ -285,5 +285,28 @@ public void Extensions()
             Assert.Equal(-1, list.IndexOf(SyntaxKind.WhereClause));
             Assert.False(list.Any(SyntaxKind.WhereClause));
         }
+
+        [Fact]
+        [WorkItem(2630, "https://github.com/dotnet/roslyn/issues/2630")]
+        public void ReplaceSeparator()
+        {
+            var list = SyntaxFactory.SeparatedList<SyntaxNode>(
+                new[] {
+                    SyntaxFactory.IdentifierName("A"),
+                    SyntaxFactory.IdentifierName("B"),
+                    SyntaxFactory.IdentifierName("C"),
+                });
+
+            var newComma = SyntaxFactory.Token(
+                SyntaxFactory.TriviaList(SyntaxFactory.Space),
+                SyntaxKind.CommaToken,
+                SyntaxFactory.TriviaList());
+            var newList = list.ReplaceSeparator(
+                list.GetSeparator(1),
+                newComma);
+            Assert.Equal(3, newList.Count);
+            Assert.Equal(2, newList.SeparatorCount);
+            Assert.Equal(1, newList.GetSeparator(1).GetLeadingTrivia().Count);
     }
 }
+}

src/Compilers/Core/Portable/Syntax/SeparatedSyntaxList.cs

@@ -524,7 +524,7 @@ public SeparatedSyntaxList<TNode> ReplaceSeparator(SyntaxToken separatorToken, S
         {
             var nodesWithSeps = this.GetWithSeparators();
             var index = nodesWithSeps.IndexOf(separatorToken);
-            if (index < 0 || index >= this.Count)
+            if (index < 0)
             {
                 throw new ArgumentException("separatorToken");
             }