Disable BinaryFormatter across most .NET 8 project types (#31591)

Author: GrabYourPitchforks

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.CSharp.targets

@@ -44,7 +44,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     When https://github.com/Microsoft/visualfsharp/issues/3207 is fixed,
     remove the block below and move it into the shared .targets file.
   -->
-  <PropertyGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '7.0'))">
-    <WarningsAsErrors Condition="'$(EnableUnsafeBinaryFormatterSerialization)' != 'true'">$(WarningsAsErrors);SYSLIB0011</WarningsAsErrors>
+  <PropertyGroup>
+    <WarningsAsErrors Condition="'$(_BinaryFormatterObsoleteAsError)' == 'true'">$(WarningsAsErrors);SYSLIB0011</WarningsAsErrors>
   </PropertyGroup>
 </Project>

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.VisualBasic.targets

@@ -130,8 +130,8 @@ Copyright (c) .NET Foundation. All rights reserved.
     When https://github.com/Microsoft/visualfsharp/issues/3207 is fixed,
     remove the block below and move it into the shared .targets file.
   -->
-  <PropertyGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '7.0'))">
-    <WarningsAsErrors Condition="'$(EnableUnsafeBinaryFormatterSerialization)' != 'true'">$(WarningsAsErrors);SYSLIB0011</WarningsAsErrors>
+  <PropertyGroup>
+    <WarningsAsErrors Condition="'$(_BinaryFormatterObsoleteAsError)' == 'true'">$(WarningsAsErrors);SYSLIB0011</WarningsAsErrors>
   </PropertyGroup>
 
   <!--

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets

@@ -130,6 +130,44 @@ Copyright (c) .NET Foundation. All rights reserved.
     <IncludeProjectsNotInAssetsFileInDepsFile Condition="'$(IncludeProjectsNotInAssetsFileInDepsFile)' == ''">true</IncludeProjectsNotInAssetsFileInDepsFile>
   </PropertyGroup>
 
+  <!--
+    BinaryFormatter Disabling
+    ===========================
+
+    The EnableUnsafeBinaryFormatterSerialization setting controls both runtime and compile-time behavior.
+    The behavior is slightly different depending on the project type and target runtime.
+
+    If the property is explicitly set to TRUE:
+      - The APIs are obsolete as warning, and calls to the APIs will succeed at runtime.
+    
+    If the property is explicitly set to FALSE:
+      - On .NET 5 & 6, the APIs are obsolete as warning, and calls to the APIs will fail at runtime.
+      - On .NET 7+, the APIs are obsolete as error, and calls to the APIs will fail at runtime.
+
+    If the property is not explicitly TRUE or FALSE:
+      - On .NET 5 & 6, the APIs are obsolete as warning, and calls to the APIs will succeed at runtime.
+      - On .NET 7, the APIs are obsolete as error, but calls to the APIs will succeed at runtime.
+      - On .NET 8+, the APIs are obsolete as error, and calls to the APIs will fail at runtime
+        unless the SDK has opted in to keeping legacy BinaryFormatter behavior around.
+    
+    n.b. The APIs are already marked obsolete (as warning) in .NET 5, so we don't need to special-case
+    them unless we want to upgrade them to warn-as-error.
+  -->
+
+  <PropertyGroup Condition="'$(EnableUnsafeBinaryFormatterSerialization)' != 'true' AND '$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '7.0'))">
+    <!--
+      Certain project types need to re-enable BinaryFormatter by default; it will still be warn-as-error but will work at runtime.
+      WinForms: enabled through 8.0 (but not after)
+      WPF: enabled through 8.0 (but not after)
+    -->
+    <_ProjectTypeRequiresBinaryFormatter Condition="'$(UseWindowsForms)' == 'true' AND $([MSBuild]::VersionLessThanOrEquals($(TargetFrameworkVersion), '8.0'))">true</_ProjectTypeRequiresBinaryFormatter>
+    <_ProjectTypeRequiresBinaryFormatter Condition="'$(UseWPF)' == 'true' AND $([MSBuild]::VersionLessThanOrEquals($(TargetFrameworkVersion), '8.0'))">true</_ProjectTypeRequiresBinaryFormatter>
+    <!-- controls warn as error -->
+    <_BinaryFormatterObsoleteAsError>true</_BinaryFormatterObsoleteAsError>
+    <!-- controls runtime behavior (AppContext & trimming) -->
+    <EnableUnsafeBinaryFormatterSerialization Condition="$([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), '8.0')) AND '$(_ProjectTypeRequiresBinaryFormatter)' != 'true'">false</EnableUnsafeBinaryFormatterSerialization>
+  </PropertyGroup>
+
   <PropertyGroup>
     <CoreBuildDependsOn>
       _CheckForBuildWithNoBuild;

src/WebSdk/ProjectSystem/Targets/Microsoft.NET.Sdk.Web.ProjectSystem.targets

@@ -37,11 +37,11 @@ Copyright (c) .NET Foundation. All rights reserved.
 
   <PropertyGroup>
     <!--
-      ASP.NET 5.0 explicitly disables this functionality by default, requiring the app author
+      ASP.NET 5.0+ explicitly disables this functionality by default, requiring the app author
       to opt-in to re-enabling the feature. The way to opt back in is to specify the below
-      element with the value "true". It is anticipated that future releases of .NET will
-      disable this functionality by default across all project types, at which point this logic
-      can be removed from the ASP.NET-specific SDK.
+      element with the value "true". This functionality is disabled across most project types
+      by default in .NET 8; however, we need to keep the line below since it's not conditioned
+      on a version check like the normal SDK targets logic is.
     -->
     <EnableUnsafeBinaryFormatterSerialization Condition="'$(EnableUnsafeBinaryFormatterSerialization)' == ''">false</EnableUnsafeBinaryFormatterSerialization>
   </PropertyGroup>