From dee4ddbb5ba533586c3ac51da067196f4442a6cc Mon Sep 17 00:00:00 2001
From: Tom Hvitved <tom@semmle.com>
Date: Thu, 7 Nov 2019 14:14:36 +0100
Subject: [PATCH 1/3] C#: Only set `UseSharedCompilation=false` in autobuilder
 when needed

Since we are now able to trace shared compilation builds on Linux and macOS
(starting from .NET Core 3), and always were able to on Windows, there is
no need to set `UseSharedCompilation=false` in those cases. This may have a
positive performance impact, as shared compilation is generally faster then
non-shared compilation.
---
 .../Semmle.Autobuild.Tests/BuildScripts.cs    | 47 ++++++++++-----
 .../Semmle.Autobuild/Autobuilder.cs           | 13 +++-
 .../Semmle.Autobuild/BuildActions.cs          |  8 +--
 .../Semmle.Autobuild/BuildScript.cs           | 34 ++++++-----
 .../Semmle.Autobuild/CommandBuilder.cs        |  7 ++-
 .../Semmle.Autobuild/DotNetRule.cs            | 59 ++++++++++++++++---
 6 files changed, 118 insertions(+), 50 deletions(-)

diff --git a/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs b/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs
index 20d19a3525c..8037cf98065 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs
@@ -185,7 +185,7 @@ namespace Semmle.Extraction.Tests
         // Records the arguments passed to StartCallback.
         IList<string> StartCallbackIn = new List<string>();
 
-        void StartCallback(string s)
+        void StartCallback(string s, bool silent)
         {
             StartCallbackIn.Add(s);
         }
@@ -194,7 +194,7 @@ namespace Semmle.Extraction.Tests
         IList<string> EndCallbackIn = new List<string>();
         IList<int> EndCallbackReturn = new List<int>();
 
-        void EndCallback(int ret, string s)
+        void EndCallback(int ret, string s, bool silent)
         {
             EndCallbackReturn.Add(ret);
             EndCallbackIn.Add(s);
@@ -203,7 +203,7 @@ namespace Semmle.Extraction.Tests
         [Fact]
         public void TestBuildCommand()
         {
-            var cmd = BuildScript.Create("abc", "def ghi", null, null);
+            var cmd = BuildScript.Create("abc", "def ghi", false, null, null);
 
             Actions.RunProcess["abc def ghi"] = 1;
             cmd.Run(Actions, StartCallback, EndCallback);
@@ -216,7 +216,7 @@ namespace Semmle.Extraction.Tests
         [Fact]
         public void TestAnd1()
         {
-            var cmd = BuildScript.Create("abc", "def ghi", null, null) & BuildScript.Create("odasa", null, null, null);
+            var cmd = BuildScript.Create("abc", "def ghi", false, null, null) & BuildScript.Create("odasa", null, false, null, null);
 
             Actions.RunProcess["abc def ghi"] = 1;
             cmd.Run(Actions, StartCallback, EndCallback);
@@ -230,7 +230,7 @@ namespace Semmle.Extraction.Tests
         [Fact]
         public void TestAnd2()
         {
-            var cmd = BuildScript.Create("odasa", null, null, null) & BuildScript.Create("abc", "def ghi", null, null);
+            var cmd = BuildScript.Create("odasa", null, false, null, null) & BuildScript.Create("abc", "def ghi", false, null, null);
 
             Actions.RunProcess["abc def ghi"] = 1;
             Actions.RunProcess["odasa "] = 0;
@@ -250,7 +250,7 @@ namespace Semmle.Extraction.Tests
         [Fact]
         public void TestOr1()
         {
-            var cmd = BuildScript.Create("odasa", null, null, null) | BuildScript.Create("abc", "def ghi", null, null);
+            var cmd = BuildScript.Create("odasa", null, false, null, null) | BuildScript.Create("abc", "def ghi", false, null, null);
 
             Actions.RunProcess["abc def ghi"] = 1;
             Actions.RunProcess["odasa "] = 0;
@@ -266,7 +266,7 @@ namespace Semmle.Extraction.Tests
         [Fact]
         public void TestOr2()
         {
-            var cmd = BuildScript.Create("abc", "def ghi", null, null) | BuildScript.Create("odasa", null, null, null);
+            var cmd = BuildScript.Create("abc", "def ghi", false, null, null) | BuildScript.Create("odasa", null, false, null, null);
 
             Actions.RunProcess["abc def ghi"] = 1;
             Actions.RunProcess["odasa "] = 0;
@@ -375,7 +375,7 @@ namespace Semmle.Extraction.Tests
             Actions.RunProcess["cmd.exe /C dotnet --info"] = 0;
             Actions.RunProcess["cmd.exe /C dotnet clean test.csproj"] = 0;
             Actions.RunProcess["cmd.exe /C dotnet restore test.csproj"] = 0;
-            Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\odasa index --auto dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
+            Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\odasa index --auto dotnet build --no-incremental test.csproj"] = 0;
             Actions.RunProcess[@"cmd.exe /C C:\codeql\tools\java\bin\java -jar C:\codeql\csharp\tools\extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\odasa index --xml --extensions config csproj props xml"] = 0;
             Actions.FileExists["csharp.log"] = true;
@@ -404,6 +404,9 @@ namespace Semmle.Extraction.Tests
             Actions.RunProcess["dotnet --info"] = 0;
             Actions.RunProcess["dotnet clean test.csproj"] = 0;
             Actions.RunProcess["dotnet restore test.csproj"] = 0;
+            Actions.RunProcess["dotnet --list-runtimes"] = 0;
+            Actions.RunProcessOut["dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
+Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -424,7 +427,7 @@ namespace Semmle.Extraction.Tests
             Actions.LoadXml["test.csproj"] = xml;
 
             var autobuilder = CreateAutoBuilder("csharp", false);
-            TestAutobuilderScript(autobuilder, 0, 6);
+            TestAutobuilderScript(autobuilder, 0, 7);
         }
 
         [Fact]
@@ -748,7 +751,7 @@ namespace Semmle.Extraction.Tests
             TestAutobuilderScript(autobuilder, 0, 6);
         }
 
-    [Fact]
+        [Fact]
         public void TestWindowCSharpMsBuildMultipleSolutions()
         {
             Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\csharp\nuget\nuget.exe restore test1.csproj"] = 0;
@@ -874,6 +877,9 @@ namespace Semmle.Extraction.Tests
             Actions.RunProcess["dotnet --info"] = 0;
             Actions.RunProcess["dotnet clean test.csproj"] = 0;
             Actions.RunProcess["dotnet restore test.csproj"] = 0;
+            Actions.RunProcess["dotnet --list-runtimes"] = 0;
+            Actions.RunProcessOut["dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
+Microsoft.NETCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto dotnet build --no-incremental /p:UseSharedCompilation=false --no-restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -894,7 +900,7 @@ namespace Semmle.Extraction.Tests
             Actions.LoadXml["test.csproj"] = xml;
 
             var autobuilder = CreateAutoBuilder("csharp", false, dotnetArguments: "--no-restore");  // nugetRestore=false does not work for now.
-            TestAutobuilderScript(autobuilder, 0, 6);
+            TestAutobuilderScript(autobuilder, 0, 7);
         }
 
         [Fact]
@@ -909,7 +915,10 @@ namespace Semmle.Extraction.Tests
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet --info"] = 0;
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet clean test.csproj"] = 0;
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet restore test.csproj"] = 0;
-            Actions.RunProcess[@"C:\odasa/tools/odasa index --auto C:\Project/.dotnet/dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet --list-runtimes"] = 0;
+            Actions.RunProcessOut[@"C:\Project/.dotnet/dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
+Microsoft.NETCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
+            Actions.RunProcess[@"C:\odasa/tools/odasa index --auto C:\Project/.dotnet/dotnet build --no-incremental test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
             Actions.FileExists["csharp.log"] = true;
@@ -930,14 +939,15 @@ namespace Semmle.Extraction.Tests
             Actions.LoadXml["test.csproj"] = xml;
 
             var autobuilder = CreateAutoBuilder("csharp", false, dotnetVersion: "2.1.3");
-            TestAutobuilderScript(autobuilder, 0, 11);
+            TestAutobuilderScript(autobuilder, 0, 12);
         }
 
         [Fact]
         public void TestDotnetVersionAlreadyInstalled()
         {
             Actions.RunProcess["dotnet --list-sdks"] = 0;
-            Actions.RunProcessOut["dotnet --list-sdks"] = "2.1.3 [C:\\Program Files\\dotnet\\sdks]\n2.1.4 [C:\\Program Files\\dotnet\\sdks]";
+            Actions.RunProcessOut["dotnet --list-sdks"] = @"2.1.3 [C:\Program Files\dotnet\sdks]
+2.1.4 [C:\Program Files\dotnet\sdks]";
             Actions.RunProcess[@"curl -L -sO https://dot.net/v1/dotnet-install.sh"] = 0;
             Actions.RunProcess[@"chmod u+x dotnet-install.sh"] = 0;
             Actions.RunProcess[@"./dotnet-install.sh --channel release --version 2.1.3 --install-dir C:\Project/.dotnet"] = 0;
@@ -945,6 +955,11 @@ namespace Semmle.Extraction.Tests
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet --info"] = 0;
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet clean test.csproj"] = 0;
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet restore test.csproj"] = 0;
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet --list-runtimes"] = 0;
+            Actions.RunProcessOut[@"C:\Project/.dotnet/dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
+Microsoft.AspNetCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
+Microsoft.NETCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
+Microsoft.NETCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto C:\Project/.dotnet/dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -966,7 +981,7 @@ namespace Semmle.Extraction.Tests
             Actions.LoadXml["test.csproj"] = xml;
 
             var autobuilder = CreateAutoBuilder("csharp", false, dotnetVersion: "2.1.3");
-            TestAutobuilderScript(autobuilder, 0, 11);
+            TestAutobuilderScript(autobuilder, 0, 12);
         }
 
         [Fact]
@@ -979,7 +994,7 @@ namespace Semmle.Extraction.Tests
             Actions.RunProcess[@"cmd.exe /C C:\Project\.dotnet\dotnet --info"] = 0;
             Actions.RunProcess[@"cmd.exe /C C:\Project\.dotnet\dotnet clean test.csproj"] = 0;
             Actions.RunProcess[@"cmd.exe /C C:\Project\.dotnet\dotnet restore test.csproj"] = 0;
-            Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\odasa index --auto C:\Project\.dotnet\dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
+            Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\odasa index --auto C:\Project\.dotnet\dotnet build --no-incremental test.csproj"] = 0;
             Actions.RunProcess[@"cmd.exe /C C:\codeql\tools\java\bin\java -jar C:\codeql\csharp\tools\extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"cmd.exe /C C:\odasa\tools\odasa index --xml --extensions config csproj props xml"] = 0;
             Actions.FileExists["csharp.log"] = true;
diff --git a/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs b/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs
index 001934f489d..71653f0a93b 100644
--- a/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs
@@ -214,8 +214,17 @@ namespace Semmle.Autobuild
             if (Options.IgnoreErrors)
                 script |= BuildScript.Success;
 
-            void startCallback(string s) => Log(Severity.Info, $"\nRunning {s}");
-            void exitCallback(int ret, string msg) => Log(Severity.Info, $"Exit code {ret}{(string.IsNullOrEmpty(msg) ? "" : $": {msg}")}");
+            void startCallback(string s, bool silent)
+            {
+                if (!silent) Log(Severity.Info, $"\nRunning {s}");
+            }
+
+            void exitCallback(int ret, string msg, bool silent)
+            {
+                if (!silent)
+                    Log(Severity.Info, $"Exit code {ret}{(string.IsNullOrEmpty(msg) ? "" : $": {msg}")}");
+            }
+
             return script.Run(Actions, startCallback, exitCallback);
         }
 
diff --git a/csharp/autobuilder/Semmle.Autobuild/BuildActions.cs b/csharp/autobuilder/Semmle.Autobuild/BuildActions.cs
index edf4fc752c1..837f6e3f69e 100644
--- a/csharp/autobuilder/Semmle.Autobuild/BuildActions.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/BuildActions.cs
@@ -141,12 +141,8 @@ namespace Semmle.Autobuild
                 pi.WorkingDirectory = workingDirectory;
 
             // Environment variables can only be used when not redirecting stdout
-            if (!redirectStandardOutput)
-            {
-                pi.Environment["UseSharedCompilation"] = "false";
-                if (environment != null)
-                    environment.ForEach(kvp => pi.Environment[kvp.Key] = kvp.Value);
-            }
+            if (!redirectStandardOutput && environment != null)
+                environment.ForEach(kvp => pi.Environment[kvp.Key] = kvp.Value);
             return pi;
         }
 
diff --git a/csharp/autobuilder/Semmle.Autobuild/BuildScript.cs b/csharp/autobuilder/Semmle.Autobuild/BuildScript.cs
index a41011e159f..93ea941d58b 100644
--- a/csharp/autobuilder/Semmle.Autobuild/BuildScript.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/BuildScript.cs
@@ -25,7 +25,7 @@ namespace Semmle.Autobuild
         /// an exit message.
         /// </param>
         /// <returns>The exit code from this build script.</returns>
-        public abstract int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack);
+        public abstract int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack);
 
         /// <summary>
         /// Run this build command.
@@ -44,33 +44,36 @@ namespace Semmle.Autobuild
         /// </param>
         /// <param name="stdout">Contents of standard out.</param>
         /// <returns>The exit code from this build script.</returns>
-        public abstract int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack, out IList<string> stdout);
+        public abstract int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack, out IList<string> stdout);
 
         class BuildCommand : BuildScript
         {
             readonly string exe, arguments, workingDirectory;
             readonly IDictionary<string, string> environment;
+            readonly bool silent;
 
             /// <summary>
             /// Create a simple build command.
             /// </summary>
             /// <param name="exe">The executable to run.</param>
             /// <param name="argumentsOpt">The arguments to the executable, or null.</param>
+            /// <param name="silent">Whether this command should run silently.</param>
             /// <param name="workingDirectory">The working directory (<code>null</code> for current directory).</param>
             /// <param name="environment">Additional environment variables.</param>
-            public BuildCommand(string exe, string argumentsOpt, string workingDirectory = null, IDictionary<string, string> environment = null)
+            public BuildCommand(string exe, string argumentsOpt, bool silent, string workingDirectory = null, IDictionary<string, string> environment = null)
             {
                 this.exe = exe;
                 this.arguments = argumentsOpt ?? "";
+                this.silent = silent;
                 this.workingDirectory = workingDirectory;
                 this.environment = environment;
             }
 
             public override string ToString() => exe + " " + arguments;
 
-            public override int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack)
+            public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack)
             {
-                startCallback(this.ToString());
+                startCallback(this.ToString(), silent);
                 var ret = 1;
                 var retMessage = "";
                 try
@@ -83,13 +86,13 @@ namespace Semmle.Autobuild
                     retMessage = ex.Message;
                 }
 
-                exitCallBack(ret, retMessage);
+                exitCallBack(ret, retMessage, silent);
                 return ret;
             }
 
-            public override int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack, out IList<string> stdout)
+            public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack, out IList<string> stdout)
             {
-                startCallback(this.ToString());
+                startCallback(this.ToString(), silent);
                 var ret = 1;
                 var retMessage = "";
                 try
@@ -102,7 +105,7 @@ namespace Semmle.Autobuild
                     retMessage = ex.Message;
                     stdout = new string[0];
                 }
-                exitCallBack(ret, retMessage);
+                exitCallBack(ret, retMessage, silent);
                 return ret;
             }
 
@@ -116,9 +119,9 @@ namespace Semmle.Autobuild
                 this.func = func;
             }
 
-            public override int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack) => func(actions);
+            public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack) => func(actions);
 
-            public override int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack, out IList<string> stdout)
+            public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack, out IList<string> stdout)
             {
                 stdout = new string[0];
                 return func(actions);
@@ -142,7 +145,7 @@ namespace Semmle.Autobuild
                 this.s2b = s2;
             }
 
-            public override int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack)
+            public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack)
             {
                 int ret1;
                 if (s2a != null)
@@ -155,7 +158,7 @@ namespace Semmle.Autobuild
                 return s2b(ret1).Run(actions, startCallback, exitCallBack);
             }
 
-            public override int Run(IBuildActions actions, Action<string> startCallback, Action<int, string> exitCallBack, out IList<string> stdout)
+            public override int Run(IBuildActions actions, Action<string, bool> startCallback, Action<int, string, bool> exitCallBack, out IList<string> stdout)
             {
                 var ret1 = s1.Run(actions, startCallback, exitCallBack, out var stdout1);
                 var ret2 = (s2a != null ? s2a(stdout1, ret1) : s2b(ret1)).Run(actions, startCallback, exitCallBack, out var stdout2);
@@ -171,10 +174,11 @@ namespace Semmle.Autobuild
         /// Creates a simple build script that runs the specified exe.
         /// </summary>
         /// <param name="argumentsOpt">The arguments to the executable, or null.</param>
+        /// <param name="silent">Whether the executable should run silently.</param>
         /// <param name="workingDirectory">The working directory (<code>null</code> for current directory).</param>
         /// <param name="environment">Additional environment variables.</param>
-        public static BuildScript Create(string exe, string argumentsOpt, string workingDirectory, IDictionary<string, string> environment) =>
-            new BuildCommand(exe, argumentsOpt, workingDirectory, environment);
+        public static BuildScript Create(string exe, string argumentsOpt, bool silent, string workingDirectory, IDictionary<string, string> environment) =>
+            new BuildCommand(exe, argumentsOpt, silent, workingDirectory, environment);
 
         /// <summary>
         /// Creates a simple build script that runs the specified function.
diff --git a/csharp/autobuilder/Semmle.Autobuild/CommandBuilder.cs b/csharp/autobuilder/Semmle.Autobuild/CommandBuilder.cs
index 273cc52b036..7b95e495697 100644
--- a/csharp/autobuilder/Semmle.Autobuild/CommandBuilder.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/CommandBuilder.cs
@@ -17,13 +17,15 @@ namespace Semmle.Autobuild
         readonly EscapeMode escapingMode;
         readonly string workingDirectory;
         readonly IDictionary<string, string> environment;
+        readonly bool silent;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="T:Semmle.Autobuild.CommandBuilder"/> class.
         /// </summary>
         /// <param name="workingDirectory">The working directory (<code>null</code> for current directory).</param>
         /// <param name="environment">Additional environment variables.</param>
-        public CommandBuilder(IBuildActions actions, string workingDirectory = null, IDictionary<string, string> environment = null)
+        /// <param name="silent">Whether this command should be run silently.</param>
+        public CommandBuilder(IBuildActions actions, string workingDirectory = null, IDictionary<string, string> environment = null, bool silent = false)
         {
             arguments = new StringBuilder();
             if (actions.IsWindows())
@@ -40,6 +42,7 @@ namespace Semmle.Autobuild
             firstCommand = true;
             this.workingDirectory = workingDirectory;
             this.environment = environment;
+            this.silent = silent;
         }
 
         void OdasaIndex(string odasa)
@@ -190,6 +193,6 @@ namespace Semmle.Autobuild
         /// <summary>
         /// Returns a build script that contains just this command.
         /// </summary>
-        public BuildScript Script => BuildScript.Create(executable, arguments.ToString(), workingDirectory, environment);
+        public BuildScript Script => BuildScript.Create(executable, arguments.ToString(), silent, workingDirectory, environment);
     }
 }
diff --git a/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs b/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs
index 789d68db30a..d44f32e4b56 100644
--- a/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs
@@ -5,6 +5,7 @@ using Newtonsoft.Json.Linq;
 using System.Collections.Generic;
 using System.IO;
 using Semmle.Util;
+using System.Text.RegularExpressions;
 
 namespace Semmle.Autobuild
 {
@@ -47,9 +48,7 @@ namespace Semmle.Autobuild
                         restoreCommand.QuoteArgument(projectOrSolution.FullPath);
                         var restore = restoreCommand.Script;
 
-                        var buildCommand = GetBuildCommand(builder, dotNet);
-                        buildCommand.QuoteArgument(projectOrSolution.FullPath);
-                        var build = buildCommand.Script;
+                        var build = GetBuildScript(builder, dotNet, projectOrSolution.FullPath);
 
                         ret &= clean & BuildScript.Try(restore) & build;
                     }
@@ -225,7 +224,7 @@ Invoke-Command -ScriptBlock $ScriptBlock";
 
         static BuildScript GetInstalledSdksScript(IBuildActions actions)
         {
-            var listSdks = new CommandBuilder(actions).
+            var listSdks = new CommandBuilder(actions, silent: true).
                 RunCommand("dotnet").
                 Argument("--list-sdks");
             return listSdks.Script;
@@ -258,14 +257,56 @@ Invoke-Command -ScriptBlock $ScriptBlock";
             return restore;
         }
 
-        CommandBuilder GetBuildCommand(Autobuilder builder, (string DotNetPath, IDictionary<string, string> Environment)? arg)
+        static BuildScript GetInstalledRuntimesScript(IBuildActions actions, (string DotNetPath, IDictionary<string, string> Environment)? arg)
+        {
+            var listSdks = new CommandBuilder(actions, environment: arg?.Environment, silent: true).
+                RunCommand(DotNetCommand(actions, arg?.DotNetPath)).
+                Argument("--list-runtimes");
+            return listSdks.Script;
+        }
+
+        /// <summary>
+        /// Gets the `dotnet build` script.
+        ///
+        /// The CLR tracer only works on .NET Core >= 3 on Linux and macOS (see
+        /// https://github.com/dotnet/coreclr/issues/19622), so in case we are
+        /// running on an older .NET Core, we disable shared compilation (and
+        /// hence the need for CLR tracing), by adding a
+        /// `/p:UseSharedCompilation=false` argument.
+        /// </summary>
+        BuildScript GetBuildScript(Autobuilder builder, (string DotNetPath, IDictionary<string, string> Environment)? arg, string projOrSln)
         {
             var build = new CommandBuilder(builder.Actions, null, arg?.Environment);
-            return builder.MaybeIndex(build, DotNetCommand(builder.Actions, arg?.DotNetPath)).
+            var script = builder.MaybeIndex(build, DotNetCommand(builder.Actions, arg?.DotNetPath)).
                 Argument("build").
-                Argument("--no-incremental").
-                Argument("/p:UseSharedCompilation=false").
-                Argument(builder.Options.DotNetArguments);
+                Argument("--no-incremental");
+
+            if (builder.Actions.IsWindows())
+                return script.Argument(builder.Options.DotNetArguments).
+                    QuoteArgument(projOrSln).
+                    Script;
+
+            return BuildScript.Bind(GetInstalledRuntimesScript(builder.Actions, arg), (runtimes, runtimesRet) =>
+            {
+                var compatibleClr = false;
+                if (runtimesRet == 0)
+                {
+                    var regex = new Regex(@"Microsoft\.NETCore\.App (\d)");
+                    compatibleClr = runtimes.
+                        Select(runtime => regex.Match(runtime)).
+                        Where(m => m.Success).
+                        Any(m => int.TryParse(m.Groups[1].Value, out var version) && version >= 3);
+                }
+
+                return compatibleClr ?
+                    script.Argument(builder.Options.DotNetArguments).
+                        QuoteArgument(projOrSln).
+                        Script :
+                    script.Argument("/p:UseSharedCompilation=false").
+                        Argument(builder.Options.DotNetArguments).
+                        QuoteArgument(projOrSln).
+                        Script;
+            });
         }
     }
 }

From a9f08671cabdf4f951e99bc705744079677ef0c6 Mon Sep 17 00:00:00 2001
From: Tom Hvitved <tom@semmle.com>
Date: Thu, 14 Nov 2019 11:00:19 +0100
Subject: [PATCH 2/3] C#: Address review comments

---
 csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs b/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs
index 71653f0a93b..73e6fcd181f 100644
--- a/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/Autobuilder.cs
@@ -216,13 +216,12 @@ namespace Semmle.Autobuild
 
             void startCallback(string s, bool silent)
             {
-                if (!silent) Log(Severity.Info, $"\nRunning {s}");
+                Log(silent ? Severity.Debug : Severity.Info, $"\nRunning {s}");
             }
 
             void exitCallback(int ret, string msg, bool silent)
             {
-                if (!silent)
-                    Log(Severity.Info, $"Exit code {ret}{(string.IsNullOrEmpty(msg) ? "" : $": {msg}")}");
+                Log(silent ? Severity.Debug : Severity.Info, $"Exit code {ret}{(string.IsNullOrEmpty(msg) ? "" : $": {msg}")}");
             }
 
             return script.Run(Actions, startCallback, exitCallback);

From 07e18c88a8f1dcb6a3b55bbbbad7ccb207c307f1 Mon Sep 17 00:00:00 2001
From: Tom Hvitved <tom@semmle.com>
Date: Mon, 25 Nov 2019 16:51:09 +0100
Subject: [PATCH 3/3] C#: Address review comments

---
 .../Semmle.Autobuild.Tests/BuildScripts.cs    |  40 +++--
 .../Semmle.Autobuild/BuildCommandAutoRule.cs  |   4 +-
 .../Semmle.Autobuild/BuildCommandRule.cs      |   4 +-
 .../Semmle.Autobuild/DotNetRule.cs            | 141 ++++++++++--------
 4 files changed, 107 insertions(+), 82 deletions(-)

diff --git a/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs b/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs
index 8037cf98065..a2e59cf7ac3 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Tests/BuildScripts.cs
@@ -401,12 +401,12 @@ namespace Semmle.Extraction.Tests
         [Fact]
         public void TestLinuxCSharpAutoBuilder()
         {
-            Actions.RunProcess["dotnet --info"] = 0;
-            Actions.RunProcess["dotnet clean test.csproj"] = 0;
-            Actions.RunProcess["dotnet restore test.csproj"] = 0;
             Actions.RunProcess["dotnet --list-runtimes"] = 0;
             Actions.RunProcessOut["dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
 Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
+            Actions.RunProcess["dotnet --info"] = 0;
+            Actions.RunProcess["dotnet clean test.csproj"] = 0;
+            Actions.RunProcess["dotnet restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -601,6 +601,8 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
         [Fact]
         public void TestLinuxBuildCommand()
         {
+            Actions.RunProcess["dotnet --list-runtimes"] = 1;
+            Actions.RunProcessOut["dotnet --list-runtimes"] = "";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto ""./build.sh --skip-tests"""] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -613,7 +615,7 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             SkipVsWhere();
 
             var autobuilder = CreateAutoBuilder("csharp", false, buildCommand: "./build.sh --skip-tests");
-            TestAutobuilderScript(autobuilder, 0, 3);
+            TestAutobuilderScript(autobuilder, 0, 4);
         }
 
         [Fact]
@@ -624,6 +626,8 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             Actions.GetEnvironmentVariable["CODEQL_EXTRACTOR_CSHARP_TRAP_DIR"] = "";
             Actions.GetEnvironmentVariable["CODEQL_EXTRACTOR_CSHARP_SOURCE_ARCHIVE_DIR"] = "";
             Actions.RunProcess["/bin/chmod u+x build/build.sh"] = 0;
+            Actions.RunProcess["dotnet --list-runtimes"] = 1;
+            Actions.RunProcessOut["dotnet --list-runtimes"] = "";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto build/build.sh"] = 0;
             Actions.RunProcessWorkingDirectory[@"C:\odasa/tools/odasa index --auto build/build.sh"] = "build";
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
@@ -631,7 +635,7 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             Actions.FileExists["csharp.log"] = true;
 
             var autobuilder = CreateAutoBuilder("csharp", false);
-            TestAutobuilderScript(autobuilder, 0, 4);
+            TestAutobuilderScript(autobuilder, 0, 5);
         }
 
         [Fact]
@@ -643,12 +647,14 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             Actions.GetEnvironmentVariable["CODEQL_EXTRACTOR_CSHARP_SOURCE_ARCHIVE_DIR"] = "";
 
             Actions.RunProcess["/bin/chmod u+x build.sh"] = 0;
+            Actions.RunProcess["dotnet --list-runtimes"] = 1;
+            Actions.RunProcessOut["dotnet --list-runtimes"] = "";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto build.sh"] = 0;
             Actions.RunProcessWorkingDirectory[@"C:\odasa/tools/odasa index --auto build.sh"] = "";
             Actions.FileExists["csharp.log"] = false;
 
             var autobuilder = CreateAutoBuilder("csharp", false);
-            TestAutobuilderScript(autobuilder, 1, 2);
+            TestAutobuilderScript(autobuilder, 1, 3);
         }
 
         [Fact]
@@ -660,12 +666,14 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             Actions.GetEnvironmentVariable["CODEQL_EXTRACTOR_CSHARP_SOURCE_ARCHIVE_DIR"] = "";
 
             Actions.RunProcess["/bin/chmod u+x build.sh"] = 0;
+            Actions.RunProcess["dotnet --list-runtimes"] = 1;
+            Actions.RunProcessOut["dotnet --list-runtimes"] = "";
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto build.sh"] = 5;
             Actions.RunProcessWorkingDirectory[@"C:\odasa/tools/odasa index --auto build.sh"] = "";
             Actions.FileExists["csharp.log"] = true;
 
             var autobuilder = CreateAutoBuilder("csharp", false);
-            TestAutobuilderScript(autobuilder, 1, 2);
+            TestAutobuilderScript(autobuilder, 1, 3);
         }
 
         [Fact]
@@ -874,12 +882,12 @@ Microsoft.NETCore.App 2.2.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
         [Fact]
         public void TestSkipNugetDotnet()
         {
-            Actions.RunProcess["dotnet --info"] = 0;
-            Actions.RunProcess["dotnet clean test.csproj"] = 0;
-            Actions.RunProcess["dotnet restore test.csproj"] = 0;
             Actions.RunProcess["dotnet --list-runtimes"] = 0;
             Actions.RunProcessOut["dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
 Microsoft.NETCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
+            Actions.RunProcess["dotnet --info"] = 0;
+            Actions.RunProcess["dotnet clean test.csproj"] = 0;
+            Actions.RunProcess["dotnet restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto dotnet build --no-incremental /p:UseSharedCompilation=false --no-restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -912,12 +920,12 @@ Microsoft.NETCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             Actions.RunProcess[@"chmod u+x dotnet-install.sh"] = 0;
             Actions.RunProcess[@"./dotnet-install.sh --channel release --version 2.1.3 --install-dir C:\Project/.dotnet"] = 0;
             Actions.RunProcess[@"rm dotnet-install.sh"] = 0;
-            Actions.RunProcess[@"C:\Project/.dotnet/dotnet --info"] = 0;
-            Actions.RunProcess[@"C:\Project/.dotnet/dotnet clean test.csproj"] = 0;
-            Actions.RunProcess[@"C:\Project/.dotnet/dotnet restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet --list-runtimes"] = 0;
             Actions.RunProcessOut[@"C:\Project/.dotnet/dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
 Microsoft.NETCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet --info"] = 0;
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet clean test.csproj"] = 0;
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto C:\Project/.dotnet/dotnet build --no-incremental test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
@@ -952,14 +960,14 @@ Microsoft.NETCore.App 3.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.Ap
             Actions.RunProcess[@"chmod u+x dotnet-install.sh"] = 0;
             Actions.RunProcess[@"./dotnet-install.sh --channel release --version 2.1.3 --install-dir C:\Project/.dotnet"] = 0;
             Actions.RunProcess[@"rm dotnet-install.sh"] = 0;
-            Actions.RunProcess[@"C:\Project/.dotnet/dotnet --info"] = 0;
-            Actions.RunProcess[@"C:\Project/.dotnet/dotnet clean test.csproj"] = 0;
-            Actions.RunProcess[@"C:\Project/.dotnet/dotnet restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\Project/.dotnet/dotnet --list-runtimes"] = 0;
             Actions.RunProcessOut[@"C:\Project/.dotnet/dotnet --list-runtimes"] = @"Microsoft.AspNetCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
 Microsoft.AspNetCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
 Microsoft.NETCore.App 2.1.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
 Microsoft.NETCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]";
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet --info"] = 0;
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet clean test.csproj"] = 0;
+            Actions.RunProcess[@"C:\Project/.dotnet/dotnet restore test.csproj"] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --auto C:\Project/.dotnet/dotnet build --no-incremental /p:UseSharedCompilation=false test.csproj"] = 0;
             Actions.RunProcess[@"C:\codeql\tools\java/bin/java -jar C:\codeql\csharp/tools/extractor-asp.jar ."] = 0;
             Actions.RunProcess[@"C:\odasa/tools/odasa index --xml --extensions config csproj props xml"] = 0;
diff --git a/csharp/autobuilder/Semmle.Autobuild/BuildCommandAutoRule.cs b/csharp/autobuilder/Semmle.Autobuild/BuildCommandAutoRule.cs
index 09c41ccf74c..e7e2c9255dd 100644
--- a/csharp/autobuilder/Semmle.Autobuild/BuildCommandAutoRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/BuildCommandAutoRule.cs
@@ -43,9 +43,9 @@ namespace Semmle.Autobuild
             var dir = Path.GetDirectoryName(scriptPath);
 
             // A specific .NET Core version may be required
-            return chmodScript & DotNetRule.WithDotNet(builder, dotNet =>
+            return chmodScript & DotNetRule.WithDotNet(builder, environment =>
             {
-                var command = new CommandBuilder(builder.Actions, dir, dotNet?.Environment);
+                var command = new CommandBuilder(builder.Actions, dir, environment);
 
                 // A specific Visual Studio version may be required
                 var vsTools = MsBuildRule.GetVcVarsBatFile(builder);
diff --git a/csharp/autobuilder/Semmle.Autobuild/BuildCommandRule.cs b/csharp/autobuilder/Semmle.Autobuild/BuildCommandRule.cs
index 2e582b707f2..fe91503ec8f 100644
--- a/csharp/autobuilder/Semmle.Autobuild/BuildCommandRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/BuildCommandRule.cs
@@ -11,9 +11,9 @@
                 return BuildScript.Failure;
 
             // Custom build commands may require a specific .NET Core version
-            return DotNetRule.WithDotNet(builder, dotNet =>
+            return DotNetRule.WithDotNet(builder, environment =>
                 {
-                    var command = new CommandBuilder(builder.Actions, null, dotNet?.Environment);
+                    var command = new CommandBuilder(builder.Actions, null, environment);
 
                     // Custom build commands may require a specific Visual Studio version
                     var vsTools = MsBuildRule.GetVcVarsBatFile(builder);
diff --git a/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs b/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs
index d44f32e4b56..c9b33cef8d1 100644
--- a/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild/DotNetRule.cs
@@ -35,20 +35,20 @@ namespace Semmle.Autobuild
                 builder.Log(Severity.Info, "Attempting to build using .NET Core");
             }
 
-            return WithDotNet(builder, dotNet =>
+            return WithDotNet(builder, (dotNetPath, environment, compatibleClr) =>
                 {
-                    var ret = GetInfoCommand(builder.Actions, dotNet);
+                    var ret = GetInfoCommand(builder.Actions, dotNetPath, environment);
                     foreach (var projectOrSolution in builder.ProjectsOrSolutionsToBuild)
                     {
-                        var cleanCommand = GetCleanCommand(builder.Actions, dotNet);
+                        var cleanCommand = GetCleanCommand(builder.Actions, dotNetPath, environment);
                         cleanCommand.QuoteArgument(projectOrSolution.FullPath);
                         var clean = cleanCommand.Script;
 
-                        var restoreCommand = GetRestoreCommand(builder.Actions, dotNet);
+                        var restoreCommand = GetRestoreCommand(builder.Actions, dotNetPath, environment);
                         restoreCommand.QuoteArgument(projectOrSolution.FullPath);
                         var restore = restoreCommand.Script;
 
-                        var build = GetBuildScript(builder, dotNet, projectOrSolution.FullPath);
+                        var build = GetBuildScript(builder, dotNetPath, environment, compatibleClr, projectOrSolution.FullPath);
 
                         ret &= clean & BuildScript.Try(restore) & build;
                     }
@@ -56,38 +56,73 @@ namespace Semmle.Autobuild
                 });
         }
 
-        /// <summary>
-        /// Returns a script that attempts to download relevant version(s) of the
-        /// .NET Core SDK, followed by running the script generated by <paramref name="f"/>.
-        ///
-        /// The first element <code>DotNetPath</code> of the argument to <paramref name="f"/>
-        /// is the path where .NET Core was installed, and the second element <code>Environment</code>
-        /// is any additional required environment variables. The tuple argument is <code>null</code>
-        /// when the installation failed.
-        /// </summary>
-        public static BuildScript WithDotNet(Autobuilder builder, Func<(string DotNetPath, IDictionary<string, string> Environment)?, BuildScript> f)
+        static BuildScript WithDotNet(Autobuilder builder, Func<string, IDictionary<string, string>, bool, BuildScript> f)
         {
             var installDir = builder.Actions.PathCombine(builder.Options.RootDirectory, ".dotnet");
             var installScript = DownloadDotNet(builder, installDir);
             return BuildScript.Bind(installScript, installed =>
+            {
+                Dictionary<string, string> env;
+                if (installed == 0)
                 {
-                    if (installed == 0)
-                    {
-                        // The installation succeeded, so use the newly installed .NET Core
-                        var path = builder.Actions.GetEnvironmentVariable("PATH");
-                        var delim = builder.Actions.IsWindows() ? ";" : ":";
-                        var env = new Dictionary<string, string>{
+                    // The installation succeeded, so use the newly installed .NET Core
+                    var path = builder.Actions.GetEnvironmentVariable("PATH");
+                    var delim = builder.Actions.IsWindows() ? ";" : ":";
+                    env = new Dictionary<string, string>{
                             { "DOTNET_MULTILEVEL_LOOKUP", "false" }, // prevent look up of other .NET Core SDKs
                             { "DOTNET_SKIP_FIRST_TIME_EXPERIENCE", "true" },
                             { "PATH", installDir + delim + path }
                         };
-                        return f((installDir, env));
+                }
+                else
+                {
+                    installDir = null;
+                    env = null;
+                }
+
+                // The CLR tracer is always compatible on Windows
+                if (builder.Actions.IsWindows())
+                    return f(installDir, env, true);
+
+                // The CLR tracer is only compatible on .NET Core >= 3 on Linux and macOS (see
+                // https://github.com/dotnet/coreclr/issues/19622)
+                return BuildScript.Bind(GetInstalledRuntimesScript(builder.Actions, installDir, env), (runtimes, runtimesRet) =>
+                {
+                    var compatibleClr = false;
+                    if (runtimesRet == 0)
+                    {
+                        var minimumVersion = new Version(3, 0);
+                        var regex = new Regex(@"Microsoft\.NETCore\.App (\d\.\d\.\d)");
+                        compatibleClr = runtimes.
+                            Select(runtime => regex.Match(runtime)).
+                            Where(m => m.Success).
+                            Select(m => m.Groups[1].Value).
+                            Any(m => Version.TryParse(m, out var v) && v >= minimumVersion);
                     }
 
-                    return f(null);
+                    if (!compatibleClr)
+                    {
+                        if (env == null)
+                            env = new Dictionary<string, string>();
+                        env.Add("UseSharedCompilation", "false");
+                    }
+
+                    return f(installDir, env, compatibleClr);
                 });
+            });
         }
 
+        /// <summary>
+        /// Returns a script that attempts to download relevant version(s) of the
+        /// .NET Core SDK, followed by running the script generated by <paramref name="f"/>.
+        ///
+        /// The argument to <paramref name="f"/> is any additional required environment
+        /// variables needed by the installed .NET Core (<code>null</code> when no variables
+        /// are needed).
+        /// </summary>
+        public static BuildScript WithDotNet(Autobuilder builder, Func<IDictionary<string, string>, BuildScript> f)
+            => WithDotNet(builder, (_1, env, _2) => f(env));
+
         /// <summary>
         /// Returns a script for downloading relevant versions of the
         /// .NET Core SDK. The SDK(s) will be installed at <code>installDir</code>
@@ -233,34 +268,34 @@ Invoke-Command -ScriptBlock $ScriptBlock";
         static string DotNetCommand(IBuildActions actions, string dotNetPath) =>
             dotNetPath != null ? actions.PathCombine(dotNetPath, "dotnet") : "dotnet";
 
-        BuildScript GetInfoCommand(IBuildActions actions, (string DotNetPath, IDictionary<string, string> Environment)? arg)
+        BuildScript GetInfoCommand(IBuildActions actions, string dotNetPath, IDictionary<string, string> environment)
         {
-            var info = new CommandBuilder(actions, null, arg?.Environment).
-                RunCommand(DotNetCommand(actions, arg?.DotNetPath)).
+            var info = new CommandBuilder(actions, null, environment).
+                RunCommand(DotNetCommand(actions, dotNetPath)).
                 Argument("--info");
             return info.Script;
         }
 
-        CommandBuilder GetCleanCommand(IBuildActions actions, (string DotNetPath, IDictionary<string, string> Environment)? arg)
+        CommandBuilder GetCleanCommand(IBuildActions actions, string dotNetPath, IDictionary<string, string> environment)
         {
-            var clean = new CommandBuilder(actions, null, arg?.Environment).
-                RunCommand(DotNetCommand(actions, arg?.DotNetPath)).
+            var clean = new CommandBuilder(actions, null, environment).
+                RunCommand(DotNetCommand(actions, dotNetPath)).
                 Argument("clean");
             return clean;
         }
 
-        CommandBuilder GetRestoreCommand(IBuildActions actions, (string DotNetPath, IDictionary<string, string> Environment)? arg)
+        CommandBuilder GetRestoreCommand(IBuildActions actions, string dotNetPath, IDictionary<string, string> environment)
         {
-            var restore = new CommandBuilder(actions, null, arg?.Environment).
-                RunCommand(DotNetCommand(actions, arg?.DotNetPath)).
+            var restore = new CommandBuilder(actions, null, environment).
+                RunCommand(DotNetCommand(actions, dotNetPath)).
                 Argument("restore");
             return restore;
         }
 
-        static BuildScript GetInstalledRuntimesScript(IBuildActions actions, (string DotNetPath, IDictionary<string, string> Environment)? arg)
+        static BuildScript GetInstalledRuntimesScript(IBuildActions actions, string dotNetPath, IDictionary<string, string> environment)
         {
-            var listSdks = new CommandBuilder(actions, environment: arg?.Environment, silent: true).
-                RunCommand(DotNetCommand(actions, arg?.DotNetPath)).
+            var listSdks = new CommandBuilder(actions, environment: environment, silent: true).
+                RunCommand(DotNetCommand(actions, dotNetPath)).
                 Argument("--list-runtimes");
             return listSdks.Script;
         }
@@ -274,39 +309,21 @@ Invoke-Command -ScriptBlock $ScriptBlock";
         /// hence the need for CLR tracing), by adding a
         /// `/p:UseSharedCompilation=false` argument.
         /// </summary>
-        BuildScript GetBuildScript(Autobuilder builder, (string DotNetPath, IDictionary<string, string> Environment)? arg, string projOrSln)
+        BuildScript GetBuildScript(Autobuilder builder, string dotNetPath, IDictionary<string, string> environment, bool compatibleClr, string projOrSln)
         {
-            var build = new CommandBuilder(builder.Actions, null, arg?.Environment);
-            var script = builder.MaybeIndex(build, DotNetCommand(builder.Actions, arg?.DotNetPath)).
+            var build = new CommandBuilder(builder.Actions, null, environment);
+            var script = builder.MaybeIndex(build, DotNetCommand(builder.Actions, dotNetPath)).
                 Argument("build").
                 Argument("--no-incremental");
 
-            if (builder.Actions.IsWindows())
-                return script.Argument(builder.Options.DotNetArguments).
+            return compatibleClr ?
+                script.Argument(builder.Options.DotNetArguments).
+                    QuoteArgument(projOrSln).
+                    Script :
+                script.Argument("/p:UseSharedCompilation=false").
+                    Argument(builder.Options.DotNetArguments).
                     QuoteArgument(projOrSln).
                     Script;
-
-            return BuildScript.Bind(GetInstalledRuntimesScript(builder.Actions, arg), (runtimes, runtimesRet) =>
-            {
-                var compatibleClr = false;
-                if (runtimesRet == 0)
-                {
-                    var regex = new Regex(@"Microsoft\.NETCore\.App (\d)");
-                    compatibleClr = runtimes.
-                        Select(runtime => regex.Match(runtime)).
-                        Where(m => m.Success).
-                        Any(m => int.TryParse(m.Groups[1].Value, out var version) && version >= 3);
-                }
-
-                return compatibleClr ?
-                    script.Argument(builder.Options.DotNetArguments).
-                        QuoteArgument(projOrSln).
-                        Script :
-                    script.Argument("/p:UseSharedCompilation=false").
-                        Argument(builder.Options.DotNetArguments).
-                        QuoteArgument(projOrSln).
-                        Script;
-            });
         }
     }
 }