Add warning for ref to netstandard >= 1.5 from netfx without built-in support

src/Tasks/Common/Resources/Strings.resx

@@ -393,4 +393,8 @@ The following are names of parameters or literal values and should not be transl
     <value>NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</value>
     <comment>{StrBegin="NETSDK1068: "}</comment>
   </data>
+  <data name="NETFrameworkToNonBuiltInNETStandard" xml:space="preserve">
+    <value>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</value>
+    <comment>{StrBegin="NETSDK1069: "}</comment>
+  </data>
 </root>

src/Tasks/Common/Resources/xlf/Strings.cs.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">Cílem projektu {0} je {2}. Nemůže na něj odkazovat projekt, jehož cílem je {1}.</target>

src/Tasks/Common/Resources/xlf/Strings.de.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">Das Projekt "{0}" hat das Ziel "{2}". Ein Verweis von einem Projekt mit dem Ziel "{1}" ist nicht möglich.</target>

src/Tasks/Common/Resources/xlf/Strings.es.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">El proyecto "{0}" tiene como destino "{2}". No se puede hacer referencia a él mediante un proyecto que tenga como destino "{1}".</target>

src/Tasks/Common/Resources/xlf/Strings.fr.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">Le projet '{0}' cible '{2}'. Il ne peut pas être référencé par un projet qui cible '{1}'.</target>

src/Tasks/Common/Resources/xlf/Strings.it.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">Il progetto '{0}' è destinato a '{2}'. Non può essere usato come riferimento in un progetto destinato a '{1}'.</target>

src/Tasks/Common/Resources/xlf/Strings.ja.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">プロジェクト '{0}' は、'{2}' を対象としています。'{1}' を対象とするプロジェクトは、これを参照できません。</target>

src/Tasks/Common/Resources/xlf/Strings.ko.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">'{0}' 프로젝트가 '{2}'을(를) 대상으로 합니다. '{1}'을(를) 대상으로 하는 프로젝트에서 참조할 수 없습니다.</target>

src/Tasks/Common/Resources/xlf/Strings.pl.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">Projekt „{0}” ma platformę docelową „{2}”. Nie może on być przywoływany przez projekt z platformą docelową „{1}”.</target>

src/Tasks/Common/Resources/xlf/Strings.pt-BR.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">O projeto '{0}' tem como destino '{2}'. Ele não pode ser referenciado por um projeto que tenha '{1}' como destino.</target>

src/Tasks/Common/Resources/xlf/Strings.ru.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">Проект "{0}" предназначен для платформы "{2}". На него не может ссылаться проект, предназначенный для платформы "{1}".</target>

src/Tasks/Common/Resources/xlf/Strings.tr.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">'{0}' projesi, '{2}' çerçevesini hedefliyor. Bu projeye '{1}' çerçevesini hedefleyen bir proje tarafından başvurulamaz.</target>

src/Tasks/Common/Resources/xlf/Strings.zh-Hans.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">项目“{0}”以“{2}”为目标。它不可由面向“{1}”的项目引用。</target>

src/Tasks/Common/Resources/xlf/Strings.zh-Hant.xlf

@@ -22,6 +22,11 @@
         <target state="new">NETSDK1068: The framework-dependent application host requires a target framework of at least 'netcoreapp2.1'.</target>
         <note>{StrBegin="NETSDK1068: "}</note>
       </trans-unit>
+      <trans-unit id="NETFrameworkToNonBuiltInNETStandard">
+        <source>NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</source>
+        <target state="new">NETSDK1069: This project uses a library that targets .NET Standard 1.5 or higher, and the project targets a version of .NET Framework that doesn't have built-in support for that version of .NET Standard. Visit https://aka.ms/net-standard-known-issues for a set of known issues. Consider retargeting to .NET Framework 4.7.2.</target>
+        <note>{StrBegin="NETSDK1069: "}</note>
+      </trans-unit>
       <trans-unit id="NoCompatibleTargetFramework">
         <source>NETSDK1002: Project '{0}' targets '{2}'. It cannot be referenced by a project that targets '{1}'.</source>
         <target state="needs-review-translation">專案 '{0}' 以 '{2}' 為目標。以 '{1}' 為目標的專案無法參考該專案。</target>

src/Tasks/Microsoft.NET.Build.Extensions.Tasks/msbuildExtensions/Microsoft/Microsoft.NET.Build.Extensions/Microsoft.NET.Build.Extensions.NETFramework.targets

@@ -97,6 +97,10 @@ Copyright (c) .NET Foundation. All rights reserved.
                                           Exclude="@(_NETStandardLibraryNETFrameworkLib->'$(MSBuildThisFileDirectory)net461\lib\%(FileName).dll')" />
     </ItemGroup>
 
+    <NETBuildExtensionsWarning Condition="'@(_NETStandardLibraryNETFrameworkLib)' != ''"
+                               ResourceName="NETFrameworkToNonBuiltInNETStandard"
+                               />
+
     <ItemGroup Condition="'@(_NETStandardLibraryNETFrameworkLib)' != ''">
       <!-- Remove simple name references if we're directly providing a reference assembly to the compiler. For example,
            consider a project with a Reference Include="System.Net.Http" or "System.IO.Compression", which are both in