C#: Pass .dotnet path to standalone extractor

Author: mbg

csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpAutobuilder.cs

@@ -48,10 +48,10 @@ public override BuildScript GetBuildScript()
                     attempt = new BuildCommandRule(DotNetRule.WithDotNet).Analyse(this, false) & CheckExtractorRun(true);
                     break;
                 case CSharpBuildStrategy.Buildless:
-                    attempt = DotNetRule.WithDotNet(this, env =>
+                    attempt = DotNetRule.WithDotNet(this, (dotNetPath, env) =>
                         {
                             // No need to check that the extractor has been executed in buildless mode
-                            return new StandaloneBuildRule().Analyse(this, false);
+                            return new StandaloneBuildRule(dotNetPath).Analyse(this, false);
                         });
                     break;
                 case CSharpBuildStrategy.MSBuild:

csharp/autobuilder/Semmle.Autobuild.CSharp/StandaloneBuildRule.cs

@@ -8,6 +8,13 @@ namespace Semmle.Autobuild.CSharp
     /// </summary>
     internal class StandaloneBuildRule : IBuildRule<CSharpAutobuildOptions>
     {
+        private readonly string? dotNetPath;
+
+        internal StandaloneBuildRule(string? dotNetPath)
+        {
+            this.dotNetPath = dotNetPath;
+        }
+
         public BuildScript Analyse(IAutobuilder<CSharpAutobuildOptions> builder, bool auto)
         {
             BuildScript GetCommand(string? solution)
@@ -35,6 +42,12 @@ BuildScript GetCommand(string? solution)
                     cmd.Argument("--skip-nuget");
                 }
 
+                if (!string.IsNullOrEmpty(this.dotNetPath))
+                {
+                    cmd.Argument("--dotnet");
+                    cmd.QuoteArgument(this.dotNetPath);
+                }
+
                 return cmd.Script;
             }