From ac65e2172b16313ca712a275217b417fcf2fa394 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Thu, 8 Oct 2026 16:29:36 +0000
Subject: [PATCH] [patch] Title-case [IsTitleCase] values with invariant rules,
 not the thread culture
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IsTitleCaseAttribute lowercased with invariant rules but title-cased with
CultureInfo.CurrentCulture, so "Istanbul" validated under en-US and failed
under tr-TR and az, where "i" title-cases to "İ". It now title-cases with
CultureInfo.InvariantCulture, like the rest of the casing attributes.

The test project turns off the invariant globalization ktsu.Sdk enables, so
the culture test can set tr-TR and az at all. CA1304 and CA1307, which that
switches on, are suppressed there: SemanticStringTests calls the
culture-default overloads deliberately.

Fixes ktsu-dev/Semantics#309

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Co2rZq6e7TjwF2FMUzNoXu
---
 .../Attributes/Casing/IsTitleCaseAttribute.cs |  5 +++--
 Semantics.Test/CasingValidatorsTests.cs       | 21 +++++++++++++++++++
 Semantics.Test/Semantics.Test.csproj          |  7 +++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/Semantics.Strings/Validation/Attributes/Casing/IsTitleCaseAttribute.cs b/Semantics.Strings/Validation/Attributes/Casing/IsTitleCaseAttribute.cs
index 9a81628d..93ed2086 100644
--- a/Semantics.Strings/Validation/Attributes/Casing/IsTitleCaseAttribute.cs
+++ b/Semantics.Strings/Validation/Attributes/Casing/IsTitleCaseAttribute.cs
@@ -39,8 +39,9 @@ protected override ValidationResult ValidateValue(string value)
 				return ValidationResult.Success();
 			}
 
-			// Use TextInfo.ToTitleCase and compare with original
-			string titleCase = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(value.ToLowerInvariant());
+			// Title-case with invariant rules, as the lowercasing does, so the result does not depend
+			// on the thread culture (Turkish title-cases "istanbul" to "İstanbul")
+			string titleCase = CultureInfo.InvariantCulture.TextInfo.ToTitleCase(value.ToLowerInvariant());
 			bool isValid = string.Equals(value, titleCase, StringComparison.Ordinal);
 			return isValid
 				? ValidationResult.Success()
diff --git a/Semantics.Test/CasingValidatorsTests.cs b/Semantics.Test/CasingValidatorsTests.cs
index 014da889..cc41539b 100644
--- a/Semantics.Test/CasingValidatorsTests.cs
+++ b/Semantics.Test/CasingValidatorsTests.cs
@@ -2,6 +2,7 @@
 
 namespace ktsu.Semantics.Test;
 
+using System.Globalization;
 using ktsu.Semantics.Strings;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
@@ -66,6 +67,26 @@ public void TitleCase_Valid_Invalid_Empty()
 		Assert.AreEqual("", empty.WeakString);
 	}
 
+	[TestMethod]
+	[DataRow("en-US")]
+	[DataRow("tr-TR")]
+	[DataRow("az-Latn-AZ")]
+	public void TitleCase_DoesNotDependOnThreadCulture(string cultureName)
+	{
+		CultureInfo original = CultureInfo.CurrentCulture;
+		try
+		{
+			CultureInfo.CurrentCulture = new CultureInfo(cultureName);
+			TitleCaseString valid = SemanticString<TitleCaseString>.Create<TitleCaseString>("Istanbul Is Lovely");
+			Assert.AreEqual("Istanbul Is Lovely", valid.WeakString);
+			Assert.ThrowsExactly<ArgumentException>(() => SemanticString<TitleCaseString>.Create<TitleCaseString>("istanbul"));
+		}
+		finally
+		{
+			CultureInfo.CurrentCulture = original;
+		}
+	}
+
 	[TestMethod]
 	public void SentenceCase_Valid_Invalid_Empty()
 	{
diff --git a/Semantics.Test/Semantics.Test.csproj b/Semantics.Test/Semantics.Test.csproj
index a1edefde..c9919f97 100644
--- a/Semantics.Test/Semantics.Test.csproj
+++ b/Semantics.Test/Semantics.Test.csproj
@@ -10,6 +10,13 @@
     <TestingPlatformShowTestsFailure>true</TestingPlatformShowTestsFailure>
     <TestingPlatformShowTestsFailureDetails>true</TestingPlatformShowTestsFailureDetails>
     <NoWarn>$(NoWarn);MSTEST0032</NoWarn>
+    <!-- ktsu.Sdk turns on invariant globalization, where every culture but the invariant one fails
+         to construct. The libraries are consumed by projects that do not, so the tests that prove a
+         validator ignores the thread culture (tr-TR, az) need real cultures to set. With it off, the
+         analyzers start flagging culture-sensitive calls (CA1304, CA1307); SemanticStringTests makes
+         those calls on purpose, to cover SemanticString's own culture-default overloads. -->
+    <InvariantGlobalization>false</InvariantGlobalization>
+    <NoWarn>$(NoWarn);CA1304;CA1307</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>