Add ProcessStartOptions class with platform-aware path resolution

src/libraries/Common/src/Interop/Windows/Kernel32/Interop.GetWindowsDirectoryW.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.InteropServices;
+
+internal static partial class Interop
+{
+    internal static partial class Kernel32
+    {
+        [LibraryImport(Libraries.Kernel32, SetLastError = true, StringMarshalling = StringMarshalling.Utf16)]
+        internal static partial uint GetWindowsDirectoryW(ref char lpBuffer, uint uSize);
+    }
+}

src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs

@@ -261,6 +261,17 @@ public ProcessStartInfo(string fileName, System.Collections.Generic.IEnumerable<
         [System.Diagnostics.CodeAnalysis.AllowNullAttribute]
         public string WorkingDirectory { get { throw null; } set { } }
     }
+    public sealed partial class ProcessStartOptions
+    {
+        public ProcessStartOptions(string fileName) { }
+        public System.Collections.Generic.IList<string> Arguments { get { throw null; } set { } }
+        public bool CreateNewProcessGroup { get { throw null; } set { } }
+        public System.Collections.Generic.IDictionary<string, string?> Environment { get { throw null; } }
+        public string FileName { get { throw null; } }
+        public System.Collections.Generic.IList<System.Runtime.InteropServices.SafeHandle> InheritedHandles { get { throw null; } set { } }
+        public bool KillOnParentExit { get { throw null; } set { } }
+        public string? WorkingDirectory { get { throw null; } set { } }
+    }
     [System.ComponentModel.DesignerAttribute("System.Diagnostics.Design.ProcessThreadDesigner, System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a")]
     public partial class ProcessThread : System.ComponentModel.Component
     {

src/libraries/System.Diagnostics.Process/src/Resources/Strings.resx

@@ -336,4 +336,7 @@
   <data name="InvalidPerfData" xml:space="preserve">
     <value>Invalid performance counter data with type '{0}'.</value>
   </data>
+  <data name="FileNotFoundResolvePath" xml:space="preserve">
+    <value>Could not resolve the file.</value>
+  </data>
 </root>

src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj

@@ -12,6 +12,7 @@
     <TargetPlatformIdentifier>$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)'))</TargetPlatformIdentifier>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetPlatformIdentifier)' == ''">SR.Process_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
     <IsiOSLike Condition="'$(TargetPlatformIdentifier)' == 'maccatalyst' or '$(TargetPlatformIdentifier)' == 'ios' or '$(TargetPlatformIdentifier)' == 'tvos'">true</IsiOSLike>
+    <DefineConstants Condition="'$(TargetPlatformIdentifier)' == 'windows'">$(DefineConstants);WINDOWS</DefineConstants>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' != ''">
@@ -26,6 +27,7 @@
     <Compile Include="System\Diagnostics\ProcessModuleCollection.cs" />
     <Compile Include="System\Diagnostics\ProcessPriorityClass.cs" />
     <Compile Include="System\Diagnostics\ProcessStartInfo.cs" />
+    <Compile Include="System\Diagnostics\ProcessStartOptions.cs" />
     <Compile Include="System\Diagnostics\ProcessThread.cs" />
     <Compile Include="System\Diagnostics\ProcessThreadCollection.cs" />
     <Compile Include="System\Diagnostics\ProcessWindowStyle.cs" />
@@ -47,6 +49,8 @@
              Link="Common\System\Text\ValueStringBuilder.cs" />
     <Compile Include="$(CommonPath)System\Collections\Generic\ArrayBuilder.cs"
              Link="Common\System\Collections\Generic\ArrayBuilder.cs" />
+    <Compile Include="$(CommonPath)System\IO\StringParser.cs"
+             Link="Common\System\IO\StringParser.cs" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'windows'">
@@ -136,6 +140,10 @@
              Link="Common\Interop\Windows\Kernel32\Interop.GetProcessPriorityBoost.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.SetProcessPriorityBoost.cs"
              Link="Common\Interop\Windows\Kernel32\Interop.SetProcessPriorityBoost.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.GetSystemDirectoryW.cs"
+             Link="Common\Interop\Windows\Kernel32\Interop.GetSystemDirectoryW.cs" />
+    <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.GetWindowsDirectoryW.cs"
+             Link="Common\Interop\Windows\Kernel32\Interop.GetWindowsDirectoryW.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.OpenThread.cs"
              Link="Common\Interop\Windows\Kernel32\Interop.OpenThread.cs" />
     <Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.SetThreadPriority.cs"
@@ -235,8 +243,6 @@
     <Compile Include="System\Diagnostics\ProcessStartInfo.Unix.cs" />
     <Compile Include="System\Diagnostics\ProcessWaitHandle.Unix.cs" />
     <Compile Include="System\Diagnostics\ProcessWaitState.Unix.cs" />
-    <Compile Include="$(CommonPath)System\IO\StringParser.cs"
-             Link="Common\System\IO\StringParser.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Libraries.cs"
              Link="Common\Interop\Unix\Interop.Libraries.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\Interop.Errors.cs"

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Linux.cs

@@ -108,7 +108,7 @@ private static DateTime BootTime
             ReadOnlySpan<string> allowedProgramsToRun = ["xdg-open", "gnome-open", "kfmclient"];
             foreach (var program in allowedProgramsToRun)
             {
-                string? pathToProgram = FindProgramInPath(program);
+                string? pathToProgram = ProcessStartOptions.FindProgramInPath(program);
                 if (!string.IsNullOrEmpty(pathToProgram))
                 {
                     return pathToProgram;

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.SunOS.cs

@@ -38,7 +38,7 @@ internal DateTime StartTimeCore
         /// <summary>Gets execution path</summary>
         private static string? GetPathToOpenFile()
         {
-            return FindProgramInPath("xdg-open");
+            return ProcessStartOptions.FindProgramInPath("xdg-open");
         }
 
         /// <summary>

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs

@@ -446,7 +446,7 @@ private bool StartCore(ProcessStartInfo startInfo)
             }
             else
             {
-                filename = ResolvePath(startInfo.FileName);
+                filename = ProcessStartOptions.ResolvePath(startInfo.FileName);
                 argv = ParseArgv(startInfo);
                 if (Directory.Exists(filename))
                 {
@@ -663,7 +663,7 @@ private static string[] CreateEnvp(ProcessStartInfo psi)
                 // find filename on PATH
                 else
                 {
-                    resolvedFilename = FindProgramInPath(filename);
+                    resolvedFilename = ProcessStartOptions.FindProgramInPath(filename);
                 }
             }
 
@@ -682,79 +682,7 @@ private static string[] CreateEnvp(ProcessStartInfo psi)
             }
         }
 
-        /// <summary>Resolves a path to the filename passed to ProcessStartInfo. </summary>
-        /// <param name="filename">The filename.</param>
-        /// <returns>The resolved path. It can return null in case of URLs.</returns>
-        private static string? ResolvePath(string filename)
-        {
-            // Follow the same resolution that Windows uses with CreateProcess:
-            // 1. First try the exact path provided
-            // 2. Then try the file relative to the executable directory
-            // 3. Then try the file relative to the current directory
-            // 4. then try the file in each of the directories specified in PATH
-            // Windows does additional Windows-specific steps between 3 and 4,
-            // and we ignore those here.
-
-            // If the filename is a complete path, use it, regardless of whether it exists.
-            if (Path.IsPathRooted(filename))
-            {
-                // In this case, it doesn't matter whether the file exists or not;
-                // it's what the caller asked for, so it's what they'll get
-                return filename;
-            }
-
-            // Then check the executable's directory
-            string? path = Environment.ProcessPath;
-            if (path != null)
-            {
-                try
-                {
-                    path = Path.Combine(Path.GetDirectoryName(path)!, filename);
-                    if (File.Exists(path))
-                    {
-                        return path;
-                    }
-                }
-                catch (ArgumentException) { } // ignore any errors in data that may come from the exe path
-            }
-
-            // Then check the current directory
-            path = Path.Combine(Directory.GetCurrentDirectory(), filename);
-            if (File.Exists(path))
-            {
-                return path;
-            }
-
-            // Then check each directory listed in the PATH environment variables
-            return FindProgramInPath(filename);
-        }
-
-        /// <summary>
-        /// Gets the path to the program
-        /// </summary>
-        /// <param name="program"></param>
-        /// <returns></returns>
-        private static string? FindProgramInPath(string program)
-        {
-            string path;
-            string? pathEnvVar = Environment.GetEnvironmentVariable("PATH");
-            if (pathEnvVar != null)
-            {
-                var pathParser = new StringParser(pathEnvVar, ':', skipEmpty: true);
-                while (pathParser.MoveNext())
-                {
-                    string subPath = pathParser.ExtractCurrent();
-                    path = Path.Combine(subPath, program);
-                    if (IsExecutable(path))
-                    {
-                        return path;
-                    }
-                }
-            }
-            return null;
-        }
-
-        private static bool IsExecutable(string fullPath)
+        internal static bool IsExecutable(string fullPath)
         {
             Interop.Sys.FileStatus fileinfo;