Fix bad Debug.Assert statements in UTF-8 processing (#23627)

2 files changed, 4 insertions, 7 deletions

diff --git a/src/System.Private.CoreLib/shared/System/Text/Unicode/Utf8.cs b/src/System.Private.CoreLib/shared/System/Text/Unicode/Utf8.cs
index 9e6f245c10..6c8197d22b 100644
--- a/src/System.Private.CoreLib/shared/System/Text/Unicode/Utf8.cs
+++ b/src/System.Private.CoreLib/shared/System/Text/Unicode/Utf8.cs
@@ -106,8 +106,8 @@ namespace System.Text.Unicode
             numCharsRead = originalSourceLength - source.Length;
             numBytesWritten = originalDestinationLength - destination.Length;
 
-            Debug.Assert(numCharsRead < originalSourceLength || status != OperationStatus.Done,
-                "Cannot report OperationStatus.Done if we haven't consumed the entire input buffer.");
+            Debug.Assert((status == OperationStatus.Done) == (numCharsRead == originalSourceLength),
+                "Should report OperationStatus.Done if and only if we've consumed the entire input buffer.");
 
             return status;
         }
@@ -189,8 +189,8 @@ namespace System.Text.Unicode
             numBytesRead = originalSourceLength - source.Length;
             numCharsWritten = originalDestinationLength - destination.Length;
 
-            Debug.Assert(numBytesRead < originalSourceLength || status != OperationStatus.Done,
-                "Cannot report OperationStatus.Done if we haven't consumed the entire input buffer.");
+            Debug.Assert((status == OperationStatus.Done) == (numBytesRead == originalSourceLength),
+                    "Should report OperationStatus.Done if and only if we've consumed the entire input buffer.");
 
             return status;
         }
diff --git a/src/System.Private.CoreLib/src/System/Utf8String.Manipulation.cs b/src/System.Private.CoreLib/src/System/Utf8String.Manipulation.cs
index 6e5209962f..9ca72f1729 100644
--- a/src/System.Private.CoreLib/src/System/Utf8String.Manipulation.cs
+++ b/src/System.Private.CoreLib/src/System/Utf8String.Manipulation.cs
@@ -4,8 +4,6 @@
 
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-using System.Text;
 
 namespace System
 {
@@ -21,7 +19,6 @@ namespace System
             Debug.Assert(length >= 0, "Length cannot be negative.");
             Debug.Assert(startIndex + length <= this.Length, "StartIndex and Length cannot point beyond the end of the string.");
 
-            Debug.Assert(startIndex != 0 && startIndex != this.Length, "Caller should handle StartIndex boundary conditions.");
             Debug.Assert(length != 0 && length != this.Length, "Caller should handle Length boundary conditions.");
 
             Utf8String newString = FastAllocate(length);