Add DefaultInterpolatedStringHandler.Text/Clear (#112171)

Author: stephentoub

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/DefaultInterpolatedStringHandler.cs

@@ -104,8 +104,8 @@ internal static int GetDefaultLength(int literalLength, int formattedCount) =>
         /// <remarks>
         /// This releases any resources used by the handler. The method should be invoked only
         /// once and as the last thing performed on the handler. Subsequent use is erroneous, ill-defined,
-        /// and may destabilize the process, as may using any other copies of the handler after ToStringAndClear
-        /// is called on any one of them.
+        /// and may destabilize the process, as may using any other copies of the handler after
+        /// <see cref="ToStringAndClear" /> is called on any one of them.
         /// </remarks>
         public string ToStringAndClear()
         {
@@ -114,20 +114,31 @@ public string ToStringAndClear()
             return result;
         }
 
-        /// <summary>Clears the handler, returning any rented array to the pool.</summary>
-        [MethodImpl(MethodImplOptions.AggressiveInlining)] // used only on a few hot paths
-        internal void Clear()
+        /// <summary>Clears the handler.</summary>
+        /// <remarks>
+        /// This releases any resources used by the handler. The method should be invoked only
+        /// once and as the last thing performed on the handler. Subsequent use is erroneous, ill-defined,
+        /// and may destabilize the process, as may using any other copies of the handler after <see cref="Clear"/>
+        /// is called on any one of them.
+        /// </remarks>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Clear()
         {
             char[]? toReturn = _arrayToReturnToPool;
-            this = default; // defensive clear
+
+            // Defensive clear
+            _arrayToReturnToPool = null;
+            _chars = default;
+            _pos = 0;
+
             if (toReturn is not null)
             {
                 ArrayPool<char>.Shared.Return(toReturn);
             }
         }
 
-        /// <summary>Gets a span of the written characters thus far.</summary>
-        internal ReadOnlySpan<char> Text => _chars.Slice(0, _pos);
+        /// <summary>Gets a span of the characters appended to the handler.</summary>
+        public ReadOnlySpan<char> Text => _chars.Slice(0, _pos);
 
         /// <summary>Writes the specified string to the handler.</summary>
         /// <param name="value">The string to write.</param>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -13422,6 +13422,8 @@ public void AppendFormatted<T>(T value, int alignment) { }
         public void AppendFormatted<T>(T value, int alignment, string? format) { }
         public void AppendFormatted<T>(T value, string? format) { }
         public void AppendLiteral(string value) { }
+        public void Clear() { }
+        public System.ReadOnlySpan<char> Text { get { throw null; } }
         public override string ToString() { throw null; }
         public string ToStringAndClear() { throw null; }
     }

src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/DefaultInterpolatedStringHandlerTests.cs

@@ -53,6 +53,16 @@ public void ToStringAndClear_Clears()
             Assert.Equal(string.Empty, handler.ToStringAndClear());
         }
 
+        [Fact]
+        public void Clear_Clears()
+        {
+            DefaultInterpolatedStringHandler handler = new DefaultInterpolatedStringHandler(0, 0);
+            handler.AppendLiteral("hi");
+            Assert.Equal("hi", handler.Text.ToString());
+            handler.Clear();
+            Assert.Equal(string.Empty, handler.Text.ToString());
+        }
+
         [Fact]
         public void AppendLiteral()
         {
@@ -65,6 +75,7 @@ public void AppendLiteral()
                 actual.AppendLiteral(s);
             }
 
+            Assert.Equal(expected.ToString(), actual.Text.ToString());
             Assert.Equal(expected.ToString(), actual.ToStringAndClear());
         }
 
@@ -96,6 +107,7 @@ public void AppendFormatted_ReadOnlySpanChar()
                 }
             }
 
+            Assert.Equal(expected.ToString(), actual.Text.ToString());
             Assert.Equal(expected.ToString(), actual.ToStringAndClear());
         }
 
@@ -127,6 +139,7 @@ public void AppendFormatted_String()
                 }
             }
 
+            Assert.Equal(expected.ToString(), actual.Text.ToString());
             Assert.Equal(expected.ToString(), actual.ToStringAndClear());
         }
 
@@ -157,6 +170,7 @@ public void AppendFormatted_String_ICustomFormatter()
                 actual.AppendFormatted(s, -3, "X2");
             }
 
+            Assert.Equal(expected.ToString(), actual.Text.ToString());
             Assert.Equal(expected.ToString(), actual.ToStringAndClear());
         }
 
@@ -217,6 +231,7 @@ public void AppendFormatted_ReferenceTypes()
                 }
             }
 
+            Assert.Equal(expected.ToString(), actual.Text.ToString());
             Assert.Equal(expected.ToString(), actual.ToStringAndClear());
         }
 
@@ -289,6 +304,7 @@ void AssertTss(IHasToStringState tss, string format)
                 }
             }
 
+            Assert.Equal(expected.ToString(), actual.Text.ToString());
             Assert.Equal(expected.ToString(), actual.ToStringAndClear());
         }
 
@@ -327,6 +343,7 @@ void Test<T>(T t)
                     AssertModeMatchesType(((IHasToStringState)t));
                 }
 
+                Assert.Equal(expected.ToString(), actual.Text.ToString());
                 Assert.Equal(expected.ToString(), actual.ToStringAndClear());
             }
 
@@ -406,6 +423,7 @@ void AssertTss(T tss, string format)
                 actual.AppendFormatted(t, -3, "X2");
                 AssertTss(t, "X2");
 
+                Assert.Equal(expected.ToString(), actual.Text.ToString());
                 Assert.Equal(expected.ToString(), actual.ToStringAndClear());
             }
 
@@ -434,6 +452,7 @@ public void Grow_Large(bool useScratch)
                 expected.AppendFormat("{0,3}", i);
             }
 
+            Assert.Equal(expected.ToString(), handler.Text.ToString());
             Assert.Equal(expected.ToString(), handler.ToStringAndClear());
         }