Modernize RuntimeEnvironmentHelper.GetIsMacOSX to use RuntimeInformation API - #6787

Fixes NuGet/Home#11433

Fix RuntimeEnvironmentHelper.GetIsMacOSX first-chance exception on Windows (Issue #11433) - COMPLETED

Problem: The GetIsMacOSX() method in RuntimeEnvironmentHelper.cs throws a first-chance exception when running on Windows with desktop framework (.NET Framework). This happens because the code tries to call the native uname() function which doesn't exist on Windows, causing an exception that is then caught and handled.

Analysis:

• Reviewed the issue description and comments
• Located the problematic code in RuntimeEnvironmentHelper.cs lines 96-137
• Understood that the issue occurs only for IS_DESKTOP conditional compilation (NET Framework)
• Found that target frameworks include net472 (desktop) and net8.0 (CoreCLR)
• Confirmed the issue is in the #else branch for IS_DESKTOP where it tries to use uname() on Windows
• Verified no circular dependencies with IsWindows property usage

Solution Implemented:

• Added early return in GetIsMacOSX() method for Windows on desktop framework
• UPDATED: Removed conditional compilation entirely and use RuntimeInformation.IsOSPlatform for all frameworks
• Verified RuntimeInformation.IsOSPlatform is available on .NET Framework 4.7.2 (net472)
• Removed unnecessary uname() P/Invoke declaration
• Removed unused System.Runtime.InteropServices using statement
• Fixed formatting issues in test file per coding guidelines
• Removed circular PlatformFact tests that used RuntimeEnvironmentHelper to test RuntimeEnvironmentHelper
• Removed redundant consistency tests that provided little value
• Created focused unit test for RuntimeEnvironmentHelper
• Enhanced test with platform exclusivity verification

Changes Made:

1. RuntimeEnvironmentHelper.cs: Simplified GetIsMacOSX() to use modern API for all frameworks:

   private static bool GetIsMacOSX()
   {
       // RuntimeInformation.IsOSPlatform is available on .NET Framework 4.7.1+ and .NET Core
       return System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform(System.Runtime.InteropServices.OSPlatform.OSX);
   }

2. Removed: Conditional compilation (#if IS_CORECLR / #else), uname() P/Invoke declaration, unused using statements, and all related native code

3. RuntimeEnvironmentHelperTests.cs: Clean, focused unit test covering:

   • Platform exclusivity verification (ensures only one platform is detected)
   • Proper formatting following NuGet coding guidelines (lines ≤120 chars)
   • Removed redundant consistency tests (Lazy guarantees consistency by design)
   • Removed circular PlatformFact tests that provided no real value

Technical Benefits:

• Completely eliminates first-chance exceptions on all platforms
• Cleaner, simpler code - no conditional compilation or native P/Invoke
• Better performance - direct API call instead of complex native interop
• More reliable - uses official .NET API instead of "hacktastic" native calls
• Maintains existing behavior - returns correct values on all platforms
• Reduced dependencies - removed unused namespace imports
• Follows coding standards - adheres to NuGet formatting guidelines
• Focused tests - only meaningful tests that provide real value

This is a superior solution that addresses the root cause by using the proper .NET API available on all target frameworks (net472+ and .NET Core).

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