Fix TagList.CopyTo to not throw when TagList is empty

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/TagList.netcore.cs

@@ -154,13 +154,17 @@ public readonly void CopyTo(Span<KeyValuePair<string, object?>> tags)
         /// <param name="array">The one-dimensional Array that is the destination of the elements copied from <see cref="T:System.Diagnostics.TagList" />. The Array must have zero-based indexing.</param>
         /// <param name="arrayIndex">The zero-based index in <paramref name="array" /> at which copying begins.</param>
         /// <exception cref="T:System.ArgumentNullException"> <paramref name="array" /> is null.</exception>
-        /// <exception cref="T:System.ArgumentOutOfRangeException"> <paramref name="arrayIndex " /> is less than 0 or greater that or equal the <paramref name="array" /> length.</exception>
+        /// <exception cref="T:System.ArgumentOutOfRangeException"> <paramref name="arrayIndex" /> is less than 0 or greater than the <paramref name="array" /> length.</exception>
         public readonly void CopyTo(KeyValuePair<string, object?>[] array, int arrayIndex)
         {
             ArgumentNullException.ThrowIfNull(array);
-            ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual((uint)arrayIndex, (uint)array.Length, nameof(arrayIndex));
+            ArgumentOutOfRangeException.ThrowIfGreaterThan((uint)arrayIndex, (uint)array.Length, nameof(arrayIndex));
 
-            CopyTo(array.AsSpan(arrayIndex));
+            if (_tagsCount > 0)
+            {
+                ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual((uint)arrayIndex, (uint)array.Length, nameof(arrayIndex));
+                CopyTo(array.AsSpan(arrayIndex));
+            }
         }
 
         /// <summary>

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Metrics/TagList.netfx.cs

@@ -257,17 +257,25 @@ public readonly void CopyTo(Span<KeyValuePair<string, object?>> tags)
         /// <param name="array">The one-dimensional Array that is the destination of the elements copied from <see cref="T:System.Diagnostics.TagList" />. The Array must have zero-based indexing.</param>
         /// <param name="arrayIndex">The zero-based index in <paramref name="array" /> at which copying begins.</param>
         /// <exception cref="T:System.ArgumentNullException"> <paramref name="array" /> is null.</exception>
-        /// <exception cref="T:System.ArgumentOutOfRangeException"> <paramref name="arrayIndex " /> is less than 0 or greater that or equal the <paramref name="array" /> length.</exception>
+        /// <exception cref="T:System.ArgumentOutOfRangeException"> <paramref name="arrayIndex" /> is less than 0 or greater than the <paramref name="array" /> length.</exception>
         public readonly void CopyTo(KeyValuePair<string, object?>[] array, int arrayIndex)
         {
             ArgumentNullException.ThrowIfNull(array);
 
-            if ((uint)arrayIndex >= array.Length)
+            if ((uint)arrayIndex > (uint)array.Length)
             {
                 throw new ArgumentOutOfRangeException(nameof(arrayIndex));
             }
 
-            CopyTo(array.AsSpan(arrayIndex));
+            if (_tagsCount > 0)
+            {
+                if ((uint)arrayIndex >= (uint)array.Length)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(arrayIndex));
+                }
+
+                CopyTo(array.AsSpan(arrayIndex));
+            }
         }
 
         /// <summary>

src/libraries/System.Diagnostics.DiagnosticSource/tests/TagListTests.cs

@@ -3,6 +3,7 @@
 
 using Xunit;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace System.Diagnostics.Tests
 {
@@ -82,6 +83,9 @@ public void TestCopyTo()
                 array = new KeyValuePair<string, object?>[tagList.Count];
                 tagList.CopyTo(array);
                 ValidateTags(tagList, array);
+                array = new KeyValuePair<string, object?>[tagList.Count];
+                ((ICollection<KeyValuePair<string, object?>>)tagList).CopyTo(array, 0);
+                ValidateTags(tagList, array);
             }
         }
 
@@ -277,6 +281,31 @@ public void TestIndex(int count)
             }
         }
 
+        [Fact]
+        public void TestEmptyTagListCopyTo()
+        {
+            TagList emptyList = new TagList();
+            Assert.Equal(0, emptyList.Count);
+
+            KeyValuePair<string, object?>[] emptyArray = Array.Empty<KeyValuePair<string, object?>>();
+            emptyList.CopyTo(emptyArray, 0);
+            emptyList.CopyTo(emptyArray.AsSpan());
+            emptyList.CopyTo(emptyArray);
+
+            KeyValuePair<string, object?>[] nonEmptyArray = new KeyValuePair<string, object?>[3];
+            emptyList.CopyTo(nonEmptyArray, 0);
+            emptyList.CopyTo(nonEmptyArray, 2);
+            emptyList.CopyTo(nonEmptyArray, 3);
+            emptyList.CopyTo(nonEmptyArray.AsSpan());
+            emptyList.CopyTo(nonEmptyArray);
+
+            Assert.Throws<ArgumentOutOfRangeException>(() => emptyList.CopyTo(nonEmptyArray, -1));
+            Assert.Throws<ArgumentOutOfRangeException>(() => emptyList.CopyTo(nonEmptyArray, 4));
+
+            KeyValuePair<string, object?>[] result = emptyList.ToArray();
+            Assert.Empty(result);
+        }
+
         [Fact]
         public void TestNegativeCases()
         {