Respond to PR feedback.

Make the change smaller until @jaredpar gets back. Only make the minimal change required, which is to check DOTNET_HOST_PATH.

src/Compilers/Core/MSBuildTaskTests/TestUtilities/TaskTestUtil.cs

@@ -4,7 +4,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.IO;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
@@ -41,23 +40,7 @@ public static void AssertCommandLine(
 
  var message = engine.BuildMessages.OfType<TaskCommandLineEventArgs>().Single();
  var commandLine = message.CommandLine.Replace(" ", " ").Trim();
-
- var dotnetPath = RuntimeHostInfo.GetDotNetPathOrDefault();
- var expectedCommandLine = $@"{dotnetPath} exec ""{task.PathToManagedTool}"" {line}";
-
- bool isOnlyFileName = Path.GetFileName(dotnetPath).Length == dotnetPath.Length;
- if (isOnlyFileName)
- {
- // When ToolTask.GenerateFullPathToTool() returns only a file name (not a path to a file), MSBuild's ToolTask
- // will search the %PATH% (see https://github.com/dotnet/msbuild/blob/5410bf323451e04e99e79bcffd158e6d8d378149/src/Utilities/ToolTask.cs#L494-L513)
- // and log the full path to the exe. In this case, only assert that the commandLine ends with the expected
- // command line, and ignore the full path at the beginning.
- Assert.EndsWith(expectedCommandLine, commandLine);
- }
- else
- {
- Assert.Equal(expectedCommandLine, commandLine);
- }
+ Assert.Equal($@"{RuntimeHostInfo.GetDotNetPathOrDefault()} exec ""{task.PathToManagedTool}"" {line}", commandLine);
 
  compilerTask.NoConfig = true;
  Assert.Equal("/noconfig", compilerTask.GenerateToolArguments());

src/Compilers/Shared/RuntimeHostInfo.cs

@@ -53,11 +53,40 @@ internal static (string processFilePath, string commandLineArguments, string too
 
  /// <summary>
  /// Get the path to the dotnet executable. In the case the .NET SDK did not provide this information
- /// in the environment this will return simply "dotnet".
+ /// in the environment this tries to find "dotnet" on the PATH. In the case it is not found,
+ /// this will return simply "dotnet".
  /// </summary>
- internal static string GetDotNetPathOrDefault() =>
- Environment.GetEnvironmentVariable(DotNetHostPathEnvironmentName) ??
- (PlatformInformation.IsWindows ? "dotnet.exe" : "dotnet");
+ internal static string GetDotNetPathOrDefault()
+ {
+ if (Environment.GetEnvironmentVariable(DotNetHostPathEnvironmentName) is string pathToDotNet)
+ {
+ return pathToDotNet;
+ }
+
+ var (fileName, sep) = PlatformInformation.IsWindows
+ ? ("dotnet.exe", ';')
+ : ("dotnet", ':');
+
+ var path = Environment.GetEnvironmentVariable("PATH") ?? "";
+ foreach (var item in path.Split(sep, StringSplitOptions.RemoveEmptyEntries))
+ {
+ try
+ {
+ var filePath = Path.Combine(item, fileName);
+ if (File.Exists(filePath))
+ {
+ return filePath;
+ }
+ }
+ catch
+ {
+ // If we can't read a directory for any reason just skip it
+ }
+ }
+
+ return fileName;
+ }
+
 #else
 
  internal static bool IsCoreClrRuntime => false;