Fix PathUtils.IsSymlink throwing on common lstat failures

IsSymlink previously threw an exception for any lstat failure, including
ENOENT (file not found) and EACCES (permission denied). These are expected
non-exceptional conditions — especially when walking directory trees to check
for symlinks via IsSymlinkOrHasParentSymlink.

Now returns false for ENOENT, EACCES, and ENOTDIR, and only throws for
genuinely unexpected errno values.

Also adds InternalsVisibleTo for the test project and new PathUtilsTests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: rmarinho

Xamarin.MacDev/PathUtils.cs

@@ -56,8 +56,15 @@ public static bool IsSymlink (string file)
 			}
 			Stat buf;
 			var rv = lstat (file, out buf);
-			if (rv != 0)
-				throw new Exception (string.Format ("Could not lstat '{0}': {1}", file, Marshal.GetLastWin32Error ()));
+			if (rv != 0) {
+				var errno = Marshal.GetLastWin32Error ();
+				// ENOENT (2) = file not found, EACCES (13) = permission denied,
+				// ENOTDIR (20) = path component is not a directory.
+				// These are expected non-exceptional conditions.
+				if (errno == 2 || errno == 13 || errno == 20)
+					return false;
+				throw new Exception (string.Format ("Could not lstat '{0}': {1}", file, errno));
+			}
 			const int S_IFLNK = 40960;
 			return (buf.st_mode & S_IFLNK) == S_IFLNK;
 		}

Xamarin.MacDev/Xamarin.MacDev.csproj

@@ -38,6 +38,9 @@
   <ItemGroup Condition=" '$(TargetFramework)' != 'netstandard2.0' ">
     <Compile Remove="NullableAttributes.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="tests" />
+  </ItemGroup>
   <ItemGroup>
     <PackageReference Include="System.Text.Json" Version="8.0.5" Condition=" '$(TargetFramework)' == 'netstandard2.0' " />
   </ItemGroup>

tests/PathUtilsTests.cs

@@ -0,0 +1,60 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+#nullable enable
+
+using System;
+using System.IO;
+using NUnit.Framework;
+using Xamarin.MacDev;
+
+namespace tests {
+
+	[TestFixture]
+	public class PathUtilsTests {
+
+		[Test]
+		[Platform ("MacOsX")]
+		public void IsSymlink_ReturnsFalse_ForNonExistentFile ()
+		{
+			var path = Path.Combine (Path.GetTempPath (), Path.GetRandomFileName ());
+			// Should not throw; returns false for ENOENT
+			Assert.That (PathUtils.IsSymlink (path), Is.False);
+		}
+
+		[Test]
+		[Platform ("MacOsX")]
+		public void IsSymlink_ReturnsFalse_ForRegularFile ()
+		{
+			var path = Path.GetTempFileName ();
+			try {
+				Assert.That (PathUtils.IsSymlink (path), Is.False);
+			} finally {
+				File.Delete (path);
+			}
+		}
+
+		[Test]
+		[Platform ("MacOsX")]
+		public void IsSymlink_ReturnsTrue_ForSymlink ()
+		{
+			var target = Path.GetTempFileName ();
+			var link = target + ".link";
+			try {
+				File.CreateSymbolicLink (link, target);
+				Assert.That (PathUtils.IsSymlink (link), Is.True);
+			} finally {
+				File.Delete (link);
+				File.Delete (target);
+			}
+		}
+
+		[Test]
+		[Platform ("MacOsX")]
+		public void IsSymlinkOrHasParentSymlink_ReturnsFalse_ForNonExistentPath ()
+		{
+			var path = Path.Combine (Path.GetTempPath (), Path.GetRandomFileName ());
+			Assert.That (PathUtils.IsSymlinkOrHasParentSymlink (path), Is.False);
+		}
+	}
+}