Fixing windows build and addressing code review comments.

src/Microsoft.DotNet.MSBuildSdkResolver/EnvironmentProvider.cs

@@ -12,7 +12,6 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
     internal class EnvironmentProvider
     {
         private IEnumerable<string> _searchPaths;
-        private IEnumerable<string> _executableExtensions;
 
         private readonly Func<string, string> _getEnvironmentVariable;
 
@@ -21,21 +20,11 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
             _getEnvironmentVariable = getEnvironmentVariable;
         }
 
-        public IEnumerable<string> ExecutableExtensions
+        public string ExecutableExtension
         {
             get
             {
-                if (_executableExtensions == null)
-                {
-
-                    _executableExtensions = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
-                        ? _getEnvironmentVariable("PATHEXT")
-                            .Split(';')
-                            .Select(e => e.ToLower().Trim('"'))
-                        : new [] { string.Empty };
-                }
-
-                return _executableExtensions;
+                return Interop.RunningOnWindows ? ".exe" : string.Empty;
             }
         }
 
@@ -45,7 +34,7 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
             {
                 if (_searchPaths == null)
                 {
-                    var searchPaths = new List<string> { GetApplicationBasePath() };
+                    var searchPaths = new List<string>();
 
                     searchPaths.AddRange(
                         _getEnvironmentVariable("PATH")
@@ -61,18 +50,12 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
 
         public string GetCommandPath(string commandName)
         {
-            var commandPath = SearchPaths.Join(
-                ExecutableExtensions.ToArray(),
-                    p => true, s => true,
-                    (p, s) => Path.Combine(p, commandName + s))
+            var commandNameWithExtension = commandName + ExecutableExtension;
+            var commandPath = SearchPaths
+                .Select(p => Path.Combine(p, commandNameWithExtension))
                 .FirstOrDefault(File.Exists);
 
             return commandPath;
         }
-
-        private static string GetApplicationBasePath()
-        {
-            return Path.GetFullPath(AppContext.BaseDirectory);
-        }
     }
 }

src/Microsoft.DotNet.MSBuildSdkResolver/Interop.NETFramework.cs

@@ -12,6 +12,8 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
 {
     internal static partial class Interop
     {
+        internal static readonly bool RunningOnWindows = true;
+
         static Interop()
         {
             PreloadLibrary("hostfxr.dll");

src/Microsoft.DotNet.MSBuildSdkResolver/Interop.NETStandard.cs

@@ -14,13 +14,13 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
 {
     internal static partial class Interop
     {
-        internal static readonly bool s_runningOnWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+        internal static readonly bool RunningOnWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
 
         private static int hostfxr_resolve_sdk(string exe_dir, string working_dir, [Out] StringBuilder buffer, int buffer_size)
         {
             // hostfxr string encoding is platform -specific so dispatch to the 
             // appropriately annotated P/Invoke for the current platform.
-            return s_runningOnWindows
+            return RunningOnWindows
                 ? windows_hostfxr_resolve_sdk(exe_dir, working_dir, buffer, buffer_size)
                 : unix_hostfxr_resolve_sdk(exe_dir, working_dir, buffer, buffer_size);
         }

src/Microsoft.DotNet.MSBuildSdkResolver/MSBuildSdkResolver.cs

@@ -106,14 +106,14 @@ namespace Microsoft.DotNet.MSBuildSdkResolver
 
         private string ResolveNetcoreSdkDirectory(SdkResolverContext context)
         {
-            string exeDir = GetDotnetExeDirectoryCandidates();
+            string exeDir = GetDotnetExeDirectory();
             string workingDir = context.SolutionFilePath ?? context.ProjectFilePath;
             string netcoreSdkDir = Interop.hostfxr_resolve_sdk(exeDir, workingDir);
 
             return netcoreSdkDir;
         }
 
-        private string GetDotnetExeDirectoryCandidates()
+        private string GetDotnetExeDirectory()
         {
             string environmentOverride = _getEnvironmentVariable("DOTNET_MSBUILD_SDK_RESOLVER_CLI_DIR");
             if (environmentOverride != null)

test/Microsoft.DotNet.MSBuildSdkResolver.Tests/GivenAnMSBuildSdkResolver.cs

@@ -175,8 +175,6 @@ namespace Microsoft.DotNet.Cli.Utils.Tests
                 {
                     case "PATH":
                         return PathEnvironmentVariable;
-                    case "PATHEX":
-                        return ".exe";
                     default:
                         return null;
                 }