Merge pull request #135 from dotnet/sdk-version-warning

Add a build error if building on an unsupported SDK

Microsoft.NET.Build.Containers/build/Microsoft.NET.Build.Containers.targets

@@ -1,4 +1,18 @@
 <Project>
+    <Target Name="_ContainerVerifySDKVersion"
+        Condition="'$(WebPublishMethod)' == 'Container' or '$(PublishProfile)' == 'DefaultContainer'"
+        BeforeTargets="AfterPublish">
+        <!-- If the user has opted into container publishing via their own profile (WebPublishMethod = Container) or
+            via the default Profile (PublishProfile = DefaultContainer), make sure they're on a supported SDK version.
+            We do the explicit profile name check here because for preview6 for example the profile didn't exist, so we
+            can't rely only on the WebPublishMethod. -->
+        <PropertyGroup>
+            <!-- Allow preview 7, any RC, or any stable version of 7 -->
+            <_IsAllowedVersion Condition="$(NETCoreSdkVersion.StartsWith('7.0.100-preview.7')) or $(NETCoreSdkVersion.StartsWith('7.0.100-rc')) or ($(NETCoreSdkVersion.StartsWith('7.0.10')) and $(NETCoreSdkVersion.Contains('-')) == false)">true</_IsAllowedVersion>
+        </PropertyGroup>
+        <Error Condition="'$(_IsAllowedVersion)' != 'true'" Code="CONTAINER002" Text="The current .NET SDK ($(NETCoreSdkVersion)) doesn't support containerization. Please use version 7.0.100-preview.7 or higher." />
+    </Target>
+
     <Target Name="ComputeContainerConfig">
         <!-- Reference data about this project -->
         <PropertyGroup>
@@ -58,6 +72,7 @@
 
     <PropertyGroup>
         <PublishContainerDependsOn>
+            _ContainerVerifySDKVersion;
             ComputeContainerConfig
         </PublishContainerDependsOn>
     </PropertyGroup>