Fix .Append for StringSegment and add .Trim() methods for StringBuilder.

Author: electricessence

Source/StringBuilderExtensions.cs

@@ -404,7 +404,8 @@ public static StringBuilder AppendWithSeparator<T>(this StringBuilder target, ID
 	/// <exception cref="ArgumentNullException">If the target is null.</exception>
 	[ExcludeFromCodeCoverage] // Reason: component parts are tested.
 	[SuppressMessage("Style", "IDE0046:Convert to conditional expression")]
-	public static StringBuilder Append(this StringBuilder target, StringSegment value)
+	// Need to have a different name than just Append because of the potential collision with string.
+	public static StringBuilder AppendSegment(this StringBuilder target, StringSegment value)
 	{
 		if (target is null) throw new ArgumentNullException(nameof(target));
 		if (!value.HasValue) return target;
@@ -430,4 +431,101 @@ public static StringBuilder Append(this StringBuilder target, ReadOnlySpan<char>
 	}
 #endif
 
+	/// <summary>
+	/// Trims whitespace from the end of the <see cref="StringBuilder"/>.
+	/// </summary>
+	/// <exception cref="ArgumentNullException">If <paramref name="sb"/> is null.</exception>
+	public static StringBuilder TrimEnd(this StringBuilder sb)
+	{
+		if (sb is null) throw new ArgumentNullException(nameof(sb));
+		Contract.EndContractBlock();
+
+		var last = sb.Length - 1;
+		if (last == -1) return sb;
+
+		var end = last;
+		while (end >= 0 && char.IsWhiteSpace(sb[end]))
+			end--;
+
+		if (end < last)
+			sb.Remove(end + 1, sb.Length - end - 1);
+
+		return sb;
+	}
+
+	/// <summary>
+	/// Trims the specified characters from the end of the <see cref="StringBuilder"/>.
+	/// </summary>
+	/// <exception cref="ArgumentNullException">If <paramref name="sb"/> is null.</exception>
+	public static StringBuilder TrimEnd(this StringBuilder sb, ReadOnlySpan<char> characters)
+	{
+		if (sb is null) throw new ArgumentNullException(nameof(sb));
+		Contract.EndContractBlock();
+
+		var last = sb.Length - 1;
+		if (last == -1) return sb;
+
+		var end = last;
+		while (end >= 0 && characters.IndexOf(sb[end]) != -1)
+			end--;
+
+		if (end < last)
+			sb.Remove(end + 1, sb.Length - end - 1);
+
+		return sb;
+	}
+
+	/// <summary>
+	/// Trims whitespace from the beginning of the <see cref="StringBuilder"/>.
+	/// </summary>
+	/// <exception cref="ArgumentNullException">If <paramref name="sb"/> is null.</exception>
+	public static StringBuilder TrimStart(this StringBuilder sb)
+	{
+		if (sb is null) throw new ArgumentNullException(nameof(sb));
+		Contract.EndContractBlock();
+
+		var start = 0;
+		while (start < sb.Length && char.IsWhiteSpace(sb[start]))
+			start++;
+
+		if (start > 0)
+			sb.Remove(0, start);
+
+		return sb;
+	}
+
+
+	/// <summary>
+	/// Trims the specified characters from the beginning of the <see cref="StringBuilder"/>.
+	/// </summary>
+	/// <exception cref="ArgumentNullException">If <paramref name="sb"/> is null.</exception>
+	public static StringBuilder TrimStart(this StringBuilder sb, ReadOnlySpan<char> characters)
+	{
+		if (sb is null) throw new ArgumentNullException(nameof(sb));
+		Contract.EndContractBlock();
+
+		var start = 0;
+		while (start < sb.Length && characters.IndexOf(sb[start]) != -1)
+			start++;
+
+		if (start > 0)
+			sb.Remove(0, start);
+
+		return sb;
+	}
+
+	/// <summary>
+	/// Trims whitespace from the beginning and end of the <see cref="StringBuilder"/>.
+	/// </summary>
+	/// <exception cref="ArgumentNullException">If <paramref name="sb"/> is null.</exception>
+	public static StringBuilder Trim(this StringBuilder sb)
+		=> TrimEnd(sb).TrimStart();
+
+
+	/// <summary>
+	/// Trims the specified characters from the beginning and end of the <see cref="StringBuilder"/>.
+	/// </summary>
+	/// <exception cref="ArgumentNullException">If <paramref name="sb"/> is null.</exception>
+	public static StringBuilder Trim(this StringBuilder sb, ReadOnlySpan<char> characters)
+		=> TrimEnd(sb, characters).TrimStart(characters);
 }

Tests/StringBuilderTests.cs

@@ -212,4 +212,19 @@ public static void ToStringBuilderSeparatedString(string? source, string? separa
 			else Assert.Equal(source + separator + suffix, sb.ToString());
 		}
 	}
+
+	// Unit Tests: Theories for StringBuilder.Trim() extension that have multiple values added.
+	[Theory]
+	// Expected, A, B, C, D
+	[InlineData("Hello there.", "Hello", " ", "there.", "")]
+	[InlineData("Hello there.", " Hello", " ", "there.", "")]
+	[InlineData("Hello there.", "  Hello", " ", "there.", " ")]
+	[InlineData("Hello there.", "Hello", " ", "there.", " ")]
+	public static void Trim(string expected, string a, string b, string c, string d)
+	{
+		var sb = new StringBuilder();
+		sb.Append(a).Append(b).Append(c).Append(d).Trim();
+		Assert.Equal(expected, sb.ToString());
+	}
+
 }