From 9e21fc57c655660bae7cbe48bc784f1ed915a24b Mon Sep 17 00:00:00 2001
From: Matthew Edmondson <matthew.edmondson@gmail.com>
Date: Sun, 27 Sep 2026 01:23:50 +0000
Subject: [PATCH] Trim before case-mapping the first char in the first-char
 helpers

ToUppercaseFirstChar and ToLowercaseFirstChar mapped input[0] and only
then trimmed, so with leading whitespace the whitespace was "case-mapped"
and trimmed away while the first letter was left unchanged
(" hello" -> "hello"). They now collapse and trim first, then map the
first code point. The existing space collapsing is kept and now stated
in the XML summaries.

Fixes #79

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013qSqApi9HSiBjyHaJQYPTP
---
 CaseConverter.Test/CaseConverterTests.cs | 26 ++++++++++++++++++++++++
 CaseConverter/CaseConverter.cs           | 12 +++++++----
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/CaseConverter.Test/CaseConverterTests.cs b/CaseConverter.Test/CaseConverterTests.cs
index cbebe44..78c6598 100644
--- a/CaseConverter.Test/CaseConverterTests.cs
+++ b/CaseConverter.Test/CaseConverterTests.cs
@@ -357,6 +357,32 @@ public void ToUppercaseFirstCharShouldUppercaseAnAstralFirstLetter()
 		Assert.AreEqual($"{DeseretCapitalLongI}abc", result);
 	}
 
+	[TestMethod]
+	[DataRow(" hello", "Hello")]
+	[DataRow("\thello", "Hello")]
+	[DataRow("  hello  ", "Hello")]
+	public void ToUppercaseFirstCharShouldSkipLeadingWhitespace(string input, string expected)
+	{
+		Assert.AreEqual(expected, input.ToUppercaseFirstChar());
+	}
+
+	[TestMethod]
+	[DataRow(" Hello", "hello")]
+	[DataRow("\tHello", "hello")]
+	[DataRow("  Hello  ", "hello")]
+	public void ToLowercaseFirstCharShouldSkipLeadingWhitespace(string input, string expected)
+	{
+		Assert.AreEqual(expected, input.ToLowercaseFirstChar());
+	}
+
+	[TestMethod]
+	public void FirstCharHelpersShouldCollapseRunsOfSpaces()
+	{
+		// Documented behaviour: both helpers collapse runs of spaces to one.
+		Assert.AreEqual("A b", "a  b".ToUppercaseFirstChar());
+		Assert.AreEqual("a b", "A  b".ToLowercaseFirstChar());
+	}
+
 	[TestMethod]
 	public void ToSnakeCaseShouldStillDropAstralCharactersThatAreNotLetters()
 	{
diff --git a/CaseConverter/CaseConverter.cs b/CaseConverter/CaseConverter.cs
index 2644628..4987854 100644
--- a/CaseConverter/CaseConverter.cs
+++ b/CaseConverter/CaseConverter.cs
@@ -145,11 +145,13 @@ private static bool IsWordBoundary(string input, int previousStart, int start, i
 	}
 
 	/// <summary>
-	/// Returns a copy of this string with the first character converted to lowercase.
+	/// Returns a copy of this string, trimmed and with runs of spaces collapsed to one, with the first character converted to lowercase.
 	/// </summary>
 	/// <param name="input">The string to convert.</param>
 	/// <returns>A new string with the first character converted to lowercase.</returns>
 	/// <remarks>
+	/// The string is trimmed before the first character is chosen, so leading whitespace does not
+	/// take the place of the first letter.
 	/// The first character is the first code point, so a letter outside the Basic Multilingual
 	/// Plane is case-mapped as a whole rather than through its high surrogate alone, which would
 	/// leave it unchanged.
@@ -158,22 +160,24 @@ private static bool IsWordBoundary(string input, int previousStart, int start, i
 	public static string ToLowercaseFirstChar(this string input)
 	{
 		Ensure.NotNull(input);
-		return CollapseSpaces(MapFirstCodePoint(input, static first => first.ToLowerInvariant())).Trim();
+		return MapFirstCodePoint(CollapseSpaces(input).Trim(), static first => first.ToLowerInvariant());
 	}
 
 	/// <summary>
-	/// Returns a copy of this string with the first character converted to uppercase.
+	/// Returns a copy of this string, trimmed and with runs of spaces collapsed to one, with the first character converted to uppercase.
 	/// </summary>
 	/// <param name="input">The string to convert.</param>
 	/// <returns>A new string with the first character converted to uppercase.</returns>
 	/// <remarks>
+	/// The string is trimmed before the first character is chosen, so leading whitespace does not
+	/// take the place of the first letter.
 	/// The first character is the first code point, for the same reason as in
 	/// <see cref="ToLowercaseFirstChar(string)"/>.
 	/// </remarks>
 	public static string ToUppercaseFirstChar(this string input)
 	{
 		Ensure.NotNull(input);
-		return CollapseSpaces(MapFirstCodePoint(input, static first => first.ToUpperInvariant())).Trim();
+		return MapFirstCodePoint(CollapseSpaces(input).Trim(), static first => first.ToUpperInvariant());
 	}
 
 	/// <summary>