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System.Reflection.Metadata: preserve pre-linked suffix chain when linking into empty BlobBuilder #127246

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Merged
jkoritzinsky merged 3 commits into from
Apr 24, 2026
Merged

System.Reflection.Metadata: preserve pre-linked suffix chain when linking into empty BlobBuilder #127246

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3bbfa65
Initial plan
Copilot Apr 21, 2026
6665c80
Fix BlobBuilder.LinkSuffix when destination is empty and suffix is pr…
Copilot Apr 21, 2026
9b7f329
Add 3-chunk suffix-chain regression test for empty LinkSuffix destina…
Copilot Apr 24, 2026
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7 changes: 6 additions & 1 deletion src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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:
//
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19 changes: 19 additions & 0 deletions src/libraries/System.Reflection.Metadata/tests/Metadata/BlobTests.cs
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Expand Up @@ -514,6 +514,25 @@ public void LinkSuffix_Empty3()
Assert.Equal(16, builder2.Count);
}

[Fact]
public void LinkSuffix_EmptyDestination_SuffixAlreadyLinked()
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{
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()
{
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