From 3bbfa658adf6042cb1ecc583874bb28f3a5c28cf Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 21 Apr 2026 21:04:34 +0000
Subject: [PATCH 1/3] Initial plan


From 6665c8069f0c2c1fd5c48266471674a5cac53a66 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Tue, 21 Apr 2026 21:30:56 +0000
Subject: [PATCH 2/3] Fix BlobBuilder.LinkSuffix when destination is empty and
 suffix is pre-linked

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/31683964-9cee-4d89-b561-87c8f1509e4b

Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>
---
 .../System/Reflection/Metadata/BlobBuilder.cs |  7 ++++++-
 .../tests/Metadata/BlobTests.cs               | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobBuilder.cs b/src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobBuilder.cs
index 21628b52aa48f1..c0adde048c093e 100644
--- a/src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobBuilder.cs
+++ b/src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobBuilder.cs
@@ -479,7 +479,12 @@ public void LinkSuffix(BlobBuilder suffix)
             // The value is not used, other than for calculating the value of Count property.
             suffix._previousLengthOrFrozenSuffixLengthDelta = suffixPreviousLength + oldSuffixLength - suffix.Length;
 
-            if (!isEmpty)
+            if (isEmpty)
+            {
+                var suffixLast = suffix._nextOrPrevious;
+                _nextOrPrevious = (suffixLast != suffix) ? suffixLast : this;
+            }
+            else
             {
                 // First and last chunks:
                 //
diff --git a/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs b/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
index e0dc3d055c5f0e..017894f868d4ef 100644
--- a/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
@@ -514,6 +514,25 @@ public void LinkSuffix_Empty3()
             Assert.Equal(16, builder2.Count);
         }
 
+        [Fact]
+        public void LinkSuffix_EmptyDestination_SuffixAlreadyLinked()
+        {
+            var emptyPrefix = new BlobBuilder(16);
+            var element = new BlobBuilder(16);
+            var tail = new BlobBuilder(16);
+
+            element.WriteByte(0x11);
+            tail.WriteByte(0x22);
+
+            element.LinkSuffix(tail);
+            emptyPrefix.LinkSuffix(element);
+
+            AssertEx.Equal(new byte[] { 0x11, 0x22 }, emptyPrefix.ToArray());
+            Assert.Equal(2, emptyPrefix.Count);
+            Assert.Equal(2, element.Count);
+            Assert.Equal(1, tail.Count);
+        }
+
         [Fact]
         public void LinkPrefix1()
         {

From 9b7f3294d6ddae1a97b6f1fb84a78c97a723e3d1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Fri, 24 Apr 2026 03:34:47 +0000
Subject: [PATCH 3/3] Add 3-chunk suffix-chain regression test for empty
 LinkSuffix destination

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/b69da8b3-ca72-4bb1-bcd7-b8c7ed3ff26c

Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>
---
 .../tests/Metadata/BlobTests.cs               | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs b/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
index 017894f868d4ef..2fbffd52e25c04 100644
--- a/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
+++ b/src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
@@ -533,6 +533,29 @@ public void LinkSuffix_EmptyDestination_SuffixAlreadyLinked()
             Assert.Equal(1, tail.Count);
         }
 
+        [Fact]
+        public void LinkSuffix_EmptyDestination_SuffixThreeChunkChain()
+        {
+            var emptyPrefix = new BlobBuilder(16);
+            var first = new BlobBuilder(16);
+            var second = new BlobBuilder(16);
+            var third = new BlobBuilder(16);
+
+            first.WriteByte(0x11);
+            second.WriteByte(0x22);
+            third.WriteByte(0x33);
+
+            first.LinkSuffix(second);
+            first.LinkSuffix(third);
+            emptyPrefix.LinkSuffix(first);
+
+            AssertEx.Equal(new byte[] { 0x11, 0x22, 0x33 }, emptyPrefix.ToArray());
+            Assert.Equal(3, emptyPrefix.Count);
+            Assert.Equal(3, first.Count);
+            Assert.Equal(1, second.Count);
+            Assert.Equal(1, third.Count);
+        }
+
         [Fact]
         public void LinkPrefix1()
         {