Respect DOTNET_ROOT

src/MSBuildLocator/DotNetSdkLocationHelper.cs

@@ -78,6 +78,10 @@ public static IEnumerable<VisualStudioInstance> GetInstances(string workingDirec
  }
  }
 
+ /// <summary>
+ /// This native method call determines the actual location of path, including
+ /// resolving symbolic links.
+ /// </summary>
  private static string realpath(string path)
  {
  IntPtr ptr = NativeMethods.realpath(path, IntPtr.Zero);
@@ -86,33 +90,63 @@ private static string realpath(string path)
  return result;
  }
 
+ private static string FindDotnetFromEnvironmentVariable(string environmentVariable, string exeName)
+ {
+ string dotnet_root = Environment.GetEnvironmentVariable(environmentVariable);
+ if (!string.IsNullOrEmpty(dotnet_root))
+ {
+ string fullPathToDotnetFromRoot = Path.Combine(dotnet_root, exeName);
+ if (File.Exists(fullPathToDotnetFromRoot))
+ {
+ return realpath(fullPathToDotnetFromRoot) ?? fullPathToDotnetFromRoot;
+ }
+ }
+
+ return null;
+ }
+
  private static IEnumerable<string> GetDotNetBasePaths(string workingDirectory)
  {
  string dotnetPath = null;
  bool isWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
  string exeName = isWindows ? "dotnet.exe" : "dotnet";
 
- // We will generally find the dotnet exe on the path, but on linux, it is often just a 'dotnet' symlink (possibly even to more symlinks) that we have to resolve
- // to the real dotnet executable.
- // This will work as often as just invoking dotnet from the command line, but we can be more confident in finding a dotnet executable by following
- // https://github.com/dotnet/designs/blob/main/accepted/2021/install-location-per-architecture.md
- // This can be done using the nethost library. We didn't do this previously, so I did not implement this extension.
- foreach (string dir in Environment.GetEnvironmentVariable("PATH").Split(Path.PathSeparator))
+ // First check for the DOTNET_ROOT environment variable, as it's often there as with, for example, dotnet format.
+ if (IntPtr.Size == 4)
  {
- string filePath = Path.Combine(dir, exeName);
- if (File.Exists(filePath))
+ // 32-bit architecture
+ dotnetPath ??= FindDotnetFromEnvironmentVariable("DOTNET_ROOT(x86)", exeName);
+ }
+ else if (IntPtr.Size == 8)
+ {
+ // 64-bit architecture
+ dotnetPath ??= FindDotnetFromEnvironmentVariable("DOTNET_ROOT", exeName);
+ }
+
+ if (dotnetPath is null)
+ {
+ // We will generally find the dotnet exe on the path, but on linux, it is often just a 'dotnet' symlink (possibly even to more symlinks) that we have to resolve
+ // to the real dotnet executable.
+ // This will work as often as just invoking dotnet from the command line, but we can be more confident in finding a dotnet executable by following
+ // https://github.com/dotnet/designs/blob/main/accepted/2021/install-location-per-architecture.md
+ // This can be done using the nethost library. We didn't do this previously, so I did not implement this extension.
+ foreach (string dir in Environment.GetEnvironmentVariable("PATH").Split(Path.PathSeparator))
  {
- if (!isWindows)
+ string filePath = Path.Combine(dir, exeName);
+ if (File.Exists(filePath))
  {
- filePath = realpath(filePath) ?? filePath;
- if (!File.Exists(filePath))
+ if (!isWindows)
  {
- continue;
+ filePath = realpath(filePath) ?? filePath;
+ if (!File.Exists(filePath))
+ {
+ continue;
+ }
  }
- }
 
- dotnetPath = Path.GetDirectoryName(filePath);
- break;
+ dotnetPath = dir;
+ break;
+ }
  }
  }