Merge pull request #710 from hvitved/csharp/extractor/standalone-runtimes

C#: Improve logic for looking up .NET runtime in standalone mode

Author: calumgrant

csharp/extractor/Semmle.Extraction.CSharp.Standalone/Runtime.cs

@@ -3,6 +3,7 @@
 using System.Runtime.InteropServices;
 using System.IO;
 using System.Linq;
+using Semmle.Util;
 
 namespace Semmle.Extraction.CSharp.Standalone
 {
@@ -20,11 +21,14 @@ public static IEnumerable<string> CoreRuntimes
         {
             get
             {
-                string[] dotnetDirs = { "/usr/share/dotnet", @"C:\Program Files\dotnet" };
+                var dotnetPath = FileUtils.FindProgramOnPath(Win32.IsWindows() ? "dotnet.exe" : "dotnet");
+                var dotnetDirs = dotnetPath != null
+                    ? new[] { dotnetPath }
+                    : new[] { "/usr/share/dotnet", @"C:\Program Files\dotnet" };
+                var coreDirs = dotnetDirs.Select(d => Path.Combine(d, "shared", "Microsoft.NETCore.App"));
 
-                foreach (var dir in dotnetDirs.Where(Directory.Exists))
-                    return Directory.EnumerateDirectories(Path.Combine(dir, "shared", "Microsoft.NETCore.App")).
-                        OrderByDescending(d => Path.GetFileName(d));
+                foreach (var dir in coreDirs.Where(Directory.Exists))
+                    return Directory.EnumerateDirectories(dir).OrderByDescending(Path.GetFileName);
                 return Enumerable.Empty<string>();
             }
         }
@@ -37,19 +41,22 @@ public static IEnumerable<string> DesktopRuntimes
         {
             get
             {
-                string[] monoDirs = { "/usr/lib/mono", @"C:\Program Files\Mono\lib\mono" };
+                var monoPath = FileUtils.FindProgramOnPath(Win32.IsWindows() ? "mono.exe" : "mono");
+                var monoDirs = monoPath != null
+                    ? new[] { monoPath }
+                    : new[] { "/usr/lib/mono", @"C:\Program Files\Mono\lib\mono" };
 
                 if (Directory.Exists(@"C:\Windows\Microsoft.NET\Framework64"))
                 {
-                    return System.IO.Directory.EnumerateDirectories(@"C:\Windows\Microsoft.NET\Framework64", "v*").
-                        OrderByDescending(d => Path.GetFileName(d));
+                    return Directory.EnumerateDirectories(@"C:\Windows\Microsoft.NET\Framework64", "v*").
+                        OrderByDescending(Path.GetFileName);
                 }
 
                 foreach (var dir in monoDirs.Where(Directory.Exists))
                 {
-                    return System.IO.Directory.EnumerateDirectories(dir).
+                    return Directory.EnumerateDirectories(dir).
                         Where(d => Char.IsDigit(Path.GetFileName(d)[0])).
-                        OrderByDescending(d => Path.GetFileName(d));
+                        OrderByDescending(Path.GetFileName);
                 }
 
                 return Enumerable.Empty<string>();

csharp/extractor/Semmle.Util/FileUtils.cs

@@ -1,4 +1,6 @@
+using System;
 using System.IO;
+using System.Linq;
 
 namespace Semmle.Util
 {
@@ -50,5 +52,31 @@ public static void TryDelete(string file)
                 // Ignore
             }
         }
+
+        /// <summary>
+        /// Finds the path for the program <paramref name="prog"/> based on the
+        /// <code>PATH</code> environment variable, and in the case of Windows the
+        /// <code>PATHEXT</code> environment variable.
+        /// 
+        /// Returns <code>null</code> of no path can be found.
+        /// </summary>
+        public static string FindProgramOnPath(string prog)
+        {
+            var paths = Environment.GetEnvironmentVariable("PATH")?.Split(Path.PathSeparator);
+            string[] exes;
+            if (Win32.IsWindows())
+            {
+                var extensions = Environment.GetEnvironmentVariable("PATHEXT")?.Split(';')?.ToArray();
+                exes = extensions == null || extensions.Any(prog.EndsWith)
+                    ? new[] { prog }
+                    : extensions.Select(ext => prog + ext).ToArray();
+            }
+            else
+            {
+                exes = new[] { prog };
+            }
+            var candidates = paths?.Where(path => exes.Any(exe0 => File.Exists(Path.Combine(path, exe0))));
+            return candidates?.FirstOrDefault();
+        }
     }
 }