From 2975de61335c3e6455a1331efa80828766f53060 Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Wed, 4 Nov 2020 14:41:44 -0800
Subject: [PATCH 1/7] Add StartupHookSupport feature-switch

---
 .../targets/Microsoft.NET.Sdk.targets                         | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets
index ac8adce6d755..1b22ccfb838e 100644
--- a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets
+++ b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets
@@ -413,6 +413,10 @@ Copyright (c) .NET Foundation. All rights reserved.
                                     Condition="'$(ThreadPoolMaxThreads)' != ''"
                                     Value="$(ThreadPoolMaxThreads)" />
 
+    <RuntimeHostConfigurationOption Include="System.StartupHookProvider.IsSupported"
+                                    Condition="'$(StartupHookSupport)' != ''"
+                                    Value="$(StartupHookSupport)"
+                                    Trim="true" />
   </ItemGroup>
 
   <!--

From 9e749e51fc28c2324fc3dde10e04a984418e9d4d Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Wed, 4 Nov 2020 21:06:09 -0800
Subject: [PATCH 2/7] Disable startup hooks on trimmed apps by default Add test

---
 .../targets/Microsoft.NET.ILLink.targets      |  9 +++++++
 .../GivenThatWeWantToRunILLink.cs             | 24 +++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
index 7e97ab1accd2..d52db8478d45 100644
--- a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
+++ b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
@@ -22,6 +22,15 @@ Copyright (c) .NET Foundation. All rights reserved.
     <_LinkSemaphore>$(IntermediateOutputPath)Link.semaphore</_LinkSemaphore>
   </PropertyGroup>
 
+  <!-- We disable startup hooks for trimmed apps here so that the feature
+       switch can flow to the runtimeconfig.json. Startup hooks are disabled
+       by default since they may require assemblies, types or members that
+       could be removed by the linker, causing a trimmed app to crash. -->
+  <PropertyGroup Condition="'$(EnableUnsafeBinaryFormatterSerialization)' == '' And
+                            '$(PublishTrimmed)' == 'true'">
+    <StartupHookSupport>false</StartupHookSupport>
+  </PropertyGroup>
+
   <!--
     ============================================================
                      ILLink
diff --git a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
index 08251a459901..d54472ba1156 100644
--- a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
+++ b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
@@ -18,6 +18,7 @@
 using Microsoft.NET.TestFramework.Assertions;
 using Microsoft.NET.TestFramework.Commands;
 using Microsoft.NET.TestFramework.ProjectConstruction;
+using Newtonsoft.Json.Linq;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -372,6 +373,29 @@ public void ILLink_verify_analysis_warnings_hello_world_app(string targetFramewo
             Assert.True(!missingWarnings.Any() && !extraWarnings.Any(), errorMessage);
         }
 
+        [Theory]
+        [InlineData("net5.0")]
+        public void StartupHookSupport_is_false_by_default_on_trimmed_apps(string targetFramework)
+        {
+            var projectName = "HelloWorld";
+            var rid = EnvironmentInfo.GetCompatibleRid(targetFramework);
+
+            var testProject = CreateTestProjectForILLinkTesting(targetFramework, projectName);
+            var testAsset = _testAssetsManager.CreateTestProject(testProject, identifier: projectName);
+
+            var publishCommand = new PublishCommand(Log, Path.Combine(testAsset.TestRoot, testProject.Name));
+            publishCommand.Execute($"/p:RuntimeIdentifier={rid}", "/p:PublishTrimmed=true")
+                .Should().Pass();
+
+            string outputDirectory = publishCommand.GetOutputDirectory(targetFramework: targetFramework, runtimeIdentifier: rid).FullName;
+            string runtimeConfigFile = Path.Combine(outputDirectory, $"{projectName}.runtimeconfig.json");
+            string runtimeConfigContents = File.ReadAllText(runtimeConfigFile);
+            JObject runtimeConfig = JObject.Parse(runtimeConfigContents);
+            runtimeConfig["runtimeOptions"]["configProperties"]
+                ["System.StartupHookProvider.IsSupported"].Value<bool>()
+                .Should().Be(false);
+        }
+
         [Theory]
         [InlineData("netcoreapp3.0")]
         public void ILLink_accepts_root_descriptor(string targetFramework)

From e0d05e0215d05e967f7c63065bab0b10f6050429 Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Thu, 5 Nov 2020 09:09:45 -0800
Subject: [PATCH 3/7] Fix property condition

---
 .../targets/Microsoft.NET.ILLink.targets                        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
index d52db8478d45..633143058317 100644
--- a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
+++ b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
@@ -26,7 +26,7 @@ Copyright (c) .NET Foundation. All rights reserved.
        switch can flow to the runtimeconfig.json. Startup hooks are disabled
        by default since they may require assemblies, types or members that
        could be removed by the linker, causing a trimmed app to crash. -->
-  <PropertyGroup Condition="'$(EnableUnsafeBinaryFormatterSerialization)' == '' And
+  <PropertyGroup Condition="'$(StartupHookSupport)' == '' And
                             '$(PublishTrimmed)' == 'true'">
     <StartupHookSupport>false</StartupHookSupport>
   </PropertyGroup>

From 3ec30d7dc3c3f07bc3ba24219d35b904e3c079b4 Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Tue, 10 Nov 2020 16:45:54 -0800
Subject: [PATCH 4/7] Add new feature switch to test

---
 .../GivenThatWeWantToPublishAProjectWithAllFeatures.cs           | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithAllFeatures.cs b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithAllFeatures.cs
index b93ff93a4612..ce3b8cd90551 100644
--- a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithAllFeatures.cs
+++ b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithAllFeatures.cs
@@ -77,6 +77,7 @@ public void It_publishes_the_project_correctly(string targetFramework, string []
             ""System.Runtime.TieredCompilation"": true,
             ""System.Runtime.TieredCompilation.QuickJit"": true,
             ""System.Runtime.TieredCompilation.QuickJitForLoops"": true,
+            ""System.StartupHookProvider.IsSupported"": false,
             ""System.Text.Encoding.EnableUnsafeUTF7Encoding"": false,
             ""System.Threading.ThreadPool.MinThreads"": 2,
             ""System.Threading.ThreadPool.MaxThreads"": 9,

From cb4df10fb071bfb38a449a0250d9596b7558b9e6 Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Tue, 10 Nov 2020 20:40:20 -0800
Subject: [PATCH 5/7] Add feature switch to csproj

---
 src/Assets/TestProjects/KitchenSink/TestApp/TestApp.csproj | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/Assets/TestProjects/KitchenSink/TestApp/TestApp.csproj b/src/Assets/TestProjects/KitchenSink/TestApp/TestApp.csproj
index bb06727b9573..c66add5cd310 100644
--- a/src/Assets/TestProjects/KitchenSink/TestApp/TestApp.csproj
+++ b/src/Assets/TestProjects/KitchenSink/TestApp/TestApp.csproj
@@ -17,6 +17,7 @@
     <TieredCompilation>true</TieredCompilation>
     <TieredCompilationQuickJit>true</TieredCompilationQuickJit>
     <TieredCompilationQuickJitForLoops>true</TieredCompilationQuickJitForLoops>
+    <StartupHookSupport>false</StartupHookSupport>
     <EventSourceSupport>false</EventSourceSupport>
     <UseSystemResourceKeys>true</UseSystemResourceKeys>
     <EnableUnsafeUTF7Encoding>false</EnableUnsafeUTF7Encoding>

From d1d9db8d5698792fe2d0ee2f26ceb6f88799992f Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Wed, 11 Nov 2020 21:41:05 -0800
Subject: [PATCH 6/7] Update default condition

---
 .../targets/Microsoft.NET.ILLink.targets               |  3 ++-
 .../targets/Microsoft.NET.Sdk.targets                  | 10 +++++-----
 .../GivenThatWeWantToRunILLink.cs                      |  2 +-
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
index 633143058317..37f5db7d436d 100644
--- a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
+++ b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.ILLink.targets
@@ -27,7 +27,8 @@ Copyright (c) .NET Foundation. All rights reserved.
        by default since they may require assemblies, types or members that
        could be removed by the linker, causing a trimmed app to crash. -->
   <PropertyGroup Condition="'$(StartupHookSupport)' == '' And
-                            '$(PublishTrimmed)' == 'true'">
+                            '$(PublishTrimmed)' == 'true' And
+                            '$(_TargetFrameworkVersionWithoutV)' >= '6.0'">
     <StartupHookSupport>false</StartupHookSupport>
   </PropertyGroup>
 
diff --git a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets
index 1b22ccfb838e..2d8cb433c492 100644
--- a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets
+++ b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets
@@ -400,6 +400,11 @@ Copyright (c) .NET Foundation. All rights reserved.
                                     Condition="'$(TieredCompilationQuickJitForLoops)' != ''"
                                     Value="$(TieredCompilationQuickJitForLoops)" />
 
+    <RuntimeHostConfigurationOption Include="System.StartupHookProvider.IsSupported"
+                                    Condition="'$(StartupHookSupport)' != ''"
+                                    Value="$(StartupHookSupport)"
+                                    Trim="true" />
+
     <RuntimeHostConfigurationOption Include="System.Text.Encoding.EnableUnsafeUTF7Encoding"
                                     Condition="'$(EnableUnsafeUTF7Encoding)' != ''"
                                     Value="$(EnableUnsafeUTF7Encoding)"
@@ -412,11 +417,6 @@ Copyright (c) .NET Foundation. All rights reserved.
     <RuntimeHostConfigurationOption Include="System.Threading.ThreadPool.MaxThreads"
                                     Condition="'$(ThreadPoolMaxThreads)' != ''"
                                     Value="$(ThreadPoolMaxThreads)" />
-
-    <RuntimeHostConfigurationOption Include="System.StartupHookProvider.IsSupported"
-                                    Condition="'$(StartupHookSupport)' != ''"
-                                    Value="$(StartupHookSupport)"
-                                    Trim="true" />
   </ItemGroup>
 
   <!--
diff --git a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
index d54472ba1156..ad8aaed5a4ba 100644
--- a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
+++ b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
@@ -374,7 +374,7 @@ public void ILLink_verify_analysis_warnings_hello_world_app(string targetFramewo
         }
 
         [Theory]
-        [InlineData("net5.0")]
+        [InlineData("net6.0")]
         public void StartupHookSupport_is_false_by_default_on_trimmed_apps(string targetFramework)
         {
             var projectName = "HelloWorld";

From f6147768be787095bf7732ed09a09ee34fa6ae65 Mon Sep 17 00:00:00 2001
From: Mateo Torres Ruiz <matorre@microsoft.com>
Date: Thu, 12 Nov 2020 11:11:41 -0800
Subject: [PATCH 7/7] Test that .NET 5 remains unchanged

---
 .../GivenThatWeWantToRunILLink.cs             | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
index ad8aaed5a4ba..d82fb5eabb5d 100644
--- a/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
+++ b/src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToRunILLink.cs
@@ -374,6 +374,7 @@ public void ILLink_verify_analysis_warnings_hello_world_app(string targetFramewo
         }
 
         [Theory]
+        [InlineData("net5.0")]
         [InlineData("net6.0")]
         public void StartupHookSupport_is_false_by_default_on_trimmed_apps(string targetFramework)
         {
@@ -390,10 +391,20 @@ public void StartupHookSupport_is_false_by_default_on_trimmed_apps(string target
             string outputDirectory = publishCommand.GetOutputDirectory(targetFramework: targetFramework, runtimeIdentifier: rid).FullName;
             string runtimeConfigFile = Path.Combine(outputDirectory, $"{projectName}.runtimeconfig.json");
             string runtimeConfigContents = File.ReadAllText(runtimeConfigFile);
-            JObject runtimeConfig = JObject.Parse(runtimeConfigContents);
-            runtimeConfig["runtimeOptions"]["configProperties"]
-                ["System.StartupHookProvider.IsSupported"].Value<bool>()
-                .Should().Be(false);
+
+
+            if (Version.TryParse(targetFramework.TrimStart("net".ToCharArray()), out Version parsedVersion) &&
+                parsedVersion.Major >= 6)
+            {
+                JObject runtimeConfig = JObject.Parse(runtimeConfigContents);
+                runtimeConfig["runtimeOptions"]["configProperties"]
+                    ["System.StartupHookProvider.IsSupported"].Value<bool>()
+                    .Should().Be(false);
+            }
+            else
+            {
+                runtimeConfigContents.Should().NotContain("System.StartupHookProvider.IsSupported");
+            }
         }
 
         [Theory]