Change PathInternal.IsCaseSensitive to a constant

src/libraries/Common/src/System/IO/PathInternal.CaseSensitivity.cs

@@ -31,29 +31,13 @@ internal static StringComparison StringComparison
         /// <summary>
         /// Determines whether the file system is case sensitive.
         /// </summary>
-        /// <remarks>
-        /// Ideally we'd use something like pathconf with _PC_CASE_SENSITIVE, but that is non-portable,
-        /// not supported on Windows or Linux, etc. For now, this function creates a tmp file with capital letters
-        /// and then tests for its existence with lower-case letters.  This could return invalid results in corner
-        /// cases where, for example, different file systems are mounted with differing sensitivities.
-        /// </remarks>
         private static bool GetIsCaseSensitive()
         {
-            try
-            {
-                string pathWithUpperCase = Path.Combine(Path.GetTempPath(), "CASESENSITIVETEST" + Guid.NewGuid().ToString("N"));
-                using (new FileStream(pathWithUpperCase, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.None, 0x1000, FileOptions.DeleteOnClose))
-                {
-                    string lowerCased = pathWithUpperCase.ToLowerInvariant();
-                    return !File.Exists(lowerCased);
-                }
-            }
-            catch
-            {
-                // In case something goes wrong (e.g. temp pointing to a privilieged directory), we don't
-                // want to fail just because of a casing test, so we assume case-insensitive-but-preserving.
-                return false;
-            }
+#if MS_IO_REDIST
+            return false; // Windows is always case-insensitive
+#else
+            return !(OperatingSystem.IsWindows() || OperatingSystem.IsMacOS() || OperatingSystem.IsMacCatalyst() || OperatingSystem.IsIOS() || OperatingSystem.IsTvOS() || OperatingSystem.IsWatchOS());
+#endif
         }
     }
 }

src/libraries/System.IO.FileSystem/tests/FileSystemTest.cs

@@ -127,5 +127,33 @@ protected void ReadOnly_FileSystemHelper(Action<string> testAction, string subDi
                 Assert.Equal(0, AdminHelpers.RunAsSudo($"umount {readOnlyDirectory}"));
             }
         }
+
+        /// <summary>
+        /// Determines whether the file system is case sensitive by creating a file in the specified folder and observing the result.
+        /// </summary>
+        /// <remarks>
+        /// Ideally we'd use something like pathconf with _PC_CASE_SENSITIVE, but that is non-portable,
+        /// not supported on Windows or Linux, etc. For now, this function creates a tmp file with capital letters
+        /// and then tests for its existence with lower-case letters.  This could return invalid results in corner
+        /// cases where, for example, different file systems are mounted with differing sensitivities.
+        /// </remarks>
+        protected static bool GetIsCaseSensitiveByProbing(string probingDirectory)
+        {
+            try
+            {
+                string pathWithUpperCase = Path.Combine(probingDirectory, "CASESENSITIVETEST" + Guid.NewGuid().ToString("N"));
+                using (new FileStream(pathWithUpperCase, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.None, 0x1000, FileOptions.DeleteOnClose))
+                {
+                    string lowerCased = pathWithUpperCase.ToLowerInvariant();
+                    return !File.Exists(lowerCased);
+                }
+            }
+            catch
+            {
+                // In case something goes wrong (e.g. temp pointing to a privilieged directory), we don't
+                // want to fail just because of a casing test, so we assume case-insensitive-but-preserving.
+                return false;
+            }
+        }
     }
 }

src/libraries/System.IO.FileSystem/tests/PathInternalTests.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Xunit;
+
+namespace System.IO.Tests
+{
+    public class PathInternalTests : FileSystemTest
+    {
+        [Fact]
+        public void PathInternalIsCaseSensitiveMatchesProbing()
+        {
+            var probingDirectory = TestDirectory;
+            Assert.Equal(GetIsCaseSensitiveByProbing(probingDirectory), PathInternal.IsCaseSensitive);
+        }
+    }
+}

src/libraries/System.IO.FileSystem/tests/System.IO.FileSystem.Tests.csproj

@@ -51,6 +51,7 @@
     <Compile Include="Enumeration\ExampleTests.cs" />
     <Compile Include="Enumeration\RemovedDirectoryTests.cs" />
     <Compile Include="Enumeration\SymbolicLinksTests.cs" />
+    <Compile Include="PathInternalTests.cs" />
     <Compile Include="RandomAccess\Base.cs" />
     <Compile Include="RandomAccess\GetLength.cs" />
     <Compile Include="RandomAccess\Read.cs" />
@@ -191,6 +192,8 @@
     <Compile Include="$(CommonTestPath)System\IO\TempFile.cs" Link="Common\System\IO\TempFile.cs" />
     <Compile Include="$(CommonTestPath)System\IO\PathFeatures.cs" Link="Common\System\IO\PathFeatures.cs" />
     <Content Include="DirectoryInfo\test-dir\dummy.txt" Link="test-dir\dummy.txt" />
+    <Compile Include="$(CommonPath)System\IO\PathInternal.CaseSensitivity.cs"
+             Link="Common\System\IO\PathInternal.CaseSensitivity.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CommonTestPath)StreamConformanceTests\StreamConformanceTests.csproj" />

src/libraries/System.Private.CoreLib/src/System/IO/Path.Unix.cs

@@ -129,17 +129,5 @@ public static ReadOnlySpan<char> GetPathRoot(ReadOnlySpan<char> path)
             return IsPathRooted(path) ? PathInternal.DirectorySeparatorCharAsString.AsSpan() : ReadOnlySpan<char>.Empty;
         }
 
-        /// <summary>Gets whether the system is case-sensitive.</summary>
-        internal static bool IsCaseSensitive
-        {
-            get
-            {
-                #if TARGET_OSX || TARGET_MACCATALYST || TARGET_IOS || TARGET_TVOS
-                    return false;
-                #else
-                    return true;
-                #endif
-            }
-        }
     }
 }

src/libraries/System.Private.CoreLib/src/System/IO/Path.Windows.cs

@@ -230,9 +230,6 @@ public static ReadOnlySpan<char> GetPathRoot(ReadOnlySpan<char> path)
             return pathRoot <= 0 ? ReadOnlySpan<char>.Empty : path.Slice(0, pathRoot);
         }
 
-        /// <summary>Gets whether the system is case-sensitive.</summary>
-        internal static bool IsCaseSensitive => false;
-
         /// <summary>
         /// Returns the volume name for dos, UNC and device paths.
         /// </summary>

src/libraries/System.Private.CoreLib/src/System/IO/Path.cs

@@ -957,11 +957,11 @@ private static string GetRelativePath(string relativeTo, string path, StringComp
             return sb.ToString();
         }
 
+        /// <summary>Gets whether the system is case-sensitive.</summary>
+        internal static bool IsCaseSensitive => PathInternal.IsCaseSensitive;
+
         /// <summary>Returns a comparison that can be used to compare file and directory names for equality.</summary>
-        internal static StringComparison StringComparison =>
-            IsCaseSensitive ?
-                StringComparison.Ordinal :
-                StringComparison.OrdinalIgnoreCase;
+        internal static StringComparison StringComparison => PathInternal.StringComparison;
 
         /// <summary>
         /// Trims one trailing directory separator beyond the root of the path.