Adds fallback folder for full framework and multi-tfm projects.

src/Tasks/Microsoft.NET.Build.Tasks/build/Microsoft.NET.NuGetOfflineCache.targets

@@ -0,0 +1,38 @@
+<!--
+***********************************************************************************************
+Microsoft.NET.NuGetOfflineCache.targets
+
+WARNING:  DO NOT MODIFY this file unless you are knowledgeable about MSBuild and have
+          created a backup copy.  Incorrect changes to this file will make it
+          impossible to load or build your projects from the command-line or the IDE.
+
+Copyright (c) .NET Foundation. All rights reserved. 
+***********************************************************************************************
+-->
+<Project ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <_NugetFallbackFolder>$(MSBuildThisFileDirectory)..\..\..\..\NuGetFallbackFolder</_NugetFallbackFolder>
+  </PropertyGroup>
+
+  <Target Name="_SetIsNETCoreOrNETStandard1x"
+          Returns="$(_IsNETCoreOrNETStandard1x)">
+    <PropertyGroup>
+      <_IsNETCoreOrNETStandard1x Condition=" '$(_IsNETCoreOrNETStandard)' == 'true' and '$(_TargetFrameworkVersionWithoutV)' &lt; '2.0' ">true</_IsNETCoreOrNETStandard1x>
+    </PropertyGroup>
+  </Target>
+
+  <Target Name="_SetNuGetSDKOfflineCache"
+          DependsOnTargets="_SetIsNETCoreOrNETStandard1x"
+          BeforeTargets="_GetRestoreSettings">
+    <PropertyGroup Condition=" '$(DisableImplicitNuGetFallbackFolder)' != 'true' and Exists($(_NugetFallbackFolder)) ">
+      <RestoreAdditionalProjectSources Condition=" '$(_IsNETCoreOrNETStandard1x)' == 'true' ">$(RestoreAdditionalProjectSources);$(_NugetFallbackFolder)</RestoreAdditionalProjectSources>
+
+      <RestoreAdditionalProjectFallbackFolders Condition=" '$(_IsNETCoreOrNETStandard1x)' != 'true' ">$(RestoreAdditionalProjectFallbackFolders);$(_NugetFallbackFolder)</RestoreAdditionalProjectFallbackFolders>
+    </PropertyGroup>
+  </Target>
+</Project>

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

@@ -14,7 +14,6 @@ Copyright (c) .NET Foundation. All rights reserved.
   <PropertyGroup>
     <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
     <_IsExecutable Condition="'$(OutputType)' == 'Exe' or '$(OutputType)'=='WinExe'">true</_IsExecutable>
-    <_NugetFallbackFolder>$(MSBuildThisFileDirectory)..\..\..\..\NuGetFallbackFolder</_NugetFallbackFolder>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(HasRuntimeOutput)' == ''">
@@ -88,11 +87,11 @@ Copyright (c) .NET Foundation. All rights reserved.
     <_TargetFrameworkVersionWithoutV Condition="$(TargetFrameworkVersion.StartsWith('v'))">$(TargetFrameworkVersion.Substring(1))</_TargetFrameworkVersionWithoutV>
   </PropertyGroup>
 
-  <PropertyGroup Condition=" '$(DisableImplicitNuGetFallbackFolder)' != 'true' and '$(_IsNETCoreOrNETStandard)' == 'true' and Exists($(_NugetFallbackFolder)) ">
-    <RestoreAdditionalProjectSources Condition=" '$(_TargetFrameworkVersionWithoutV)' &lt; '2.0' ">$(RestoreAdditionalProjectSources);$(_NugetFallbackFolder)</RestoreAdditionalProjectSources>
-
-    <RestoreAdditionalProjectFallbackFolders Condition=" '$(_TargetFrameworkVersionWithoutV)' >= '2.0' ">$(RestoreAdditionalProjectFallbackFolders);$(_NugetFallbackFolder)</RestoreAdditionalProjectFallbackFolders>
-  </PropertyGroup>
+  <!--
+    Sets RestoreAdditionalProjectSources or RestoreAdditionalProjectFallbackFolders to the SDK Offline Cache based
+    on the TargetFramework.
+  -->
+  <Import Project="$(MSBuildThisFileDirectory)Microsoft.NET.NuGetOfflineCache.targets" />
 
   <ItemGroup Condition=" '$(DisableImplicitFrameworkReferences)' != 'true' and '$(TargetFrameworkIdentifier)' == '.NETFramework'">
 

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

@@ -16,6 +16,7 @@ Copyright (c) .NET Foundation. All rights reserved.
   </PropertyGroup>
 
   <Import Project="..\build\Microsoft.NET.Sdk.Common.targets"/>
+  <Import Project="..\build\Microsoft.NET.NuGetOfflineCache.targets"/>
 
   <!--
   ============================================================
@@ -31,6 +32,22 @@ Copyright (c) .NET Foundation. All rights reserved.
     <Error Text="The 'Publish' target is not supported without specifying a target framework. The current project targets multiple frameworks, please specify the framework for the published application." />
   </Target>
 
+  <Target Name="_SetIsNETCoreOrNETStandard1x">
+    <ItemGroup>
+      <_SetIsNETCoreOrNETStandard1xTargetFrameworks Include="$(TargetFrameworks)" />
+    </ItemGroup>
+
+    <MSBuild Projects="$(MSBuildProjectFile)"
+             Targets="_SetIsNETCoreOrNETStandard1x"
+             Properties="TargetFramework=%(_SetIsNETCoreOrNETStandard1xTargetFrameworks.Identity)">
+      <Output ItemName="_AllIsNETCoreOrNETStandard1x" TaskParameter="TargetOutputs" />
+    </MSBuild>
+
+    <PropertyGroup>
+      <_IsNETCoreOrNETStandard1x Condition=" '%(_AllIsNETCoreOrNETStandard1x.Identity)' == 'true' ">true</_IsNETCoreOrNETStandard1x>
+    </PropertyGroup>
+  </Target>
+
   <!--
   ============================================================
                                       GetAllRuntimeIdentifiers

test/Microsoft.NET.Restore.Tests/GivenThatWeWantToRestoreProjectsUsingNuGetConfigProperties.cs

@@ -27,15 +27,18 @@ public GivenThatWeWantToRestoreProjectsUsingNuGetConfigProperties(ITestOutputHel
         [InlineData("netstandard1.3", "1.3", true)]
         [InlineData("netcoreapp1.0", "1.0", true)]
         [InlineData("netcoreapp1.1", "1.1", true)]
+        [InlineData("netcoreapp1.0;netcoreapp2.0", "multiTFM1020app", true)]
         [InlineData("netstandard2.0", "2.0", false)]
         [InlineData("netcoreapp2.0", "2.0app", false)]
+        [InlineData("net461", "461app", false)]
+        [InlineData("netcoreapp2.0;net461", "multiTFM20app", false)]
         public void I_can_restore_a_project_with_implicit_msbuild_nuget_config(
-            string framework,
+            string frameworks,
             string projectPrefix,
             bool fileExists)
         {
             string testProjectName = $"{projectPrefix}Fallback";
-            TestAsset testProjectTestAsset = CreateTestAsset(testProjectName, framework);
+            TestAsset testProjectTestAsset = CreateTestAsset(testProjectName, frameworks);
 
             var packagesFolder = Path.Combine(RepoInfo.TestsFolder, "packages", testProjectName);
 
@@ -56,24 +59,24 @@ public void I_can_restore_a_project_with_implicit_msbuild_nuget_config(
         [InlineData("netcoreapp1.1", "1.1")]
         [InlineData("netstandard2.0", "2.0")]
         [InlineData("netcoreapp2.0", "2.0app")]
-        public void I_can_disable_implicit_msbuild_nuget_config(string framework, string projectPrefix)
+        public void I_can_disable_implicit_msbuild_nuget_config(string frameworks, string projectPrefix)
         {
             string testProjectName = $"{projectPrefix}DisabledFallback";
-            TestAsset testProjectTestAsset = CreateTestAsset(testProjectName, framework);
+            TestAsset testProjectTestAsset = CreateTestAsset(testProjectName, frameworks);
 
             var restoreCommand = testProjectTestAsset.GetRestoreCommand(Log, relativePath: testProjectName);
             restoreCommand.Execute($"/p:DisableImplicitNuGetFallbackFolder=true").Should().Fail();
         }
 
-        private TestAsset CreateTestAsset(string testProjectName, string framework)
+        private TestAsset CreateTestAsset(string testProjectName, string frameworks)
         {
             var packageInNuGetFallbackFolder = CreatePackageInNuGetFallbackFolder();
 
             var testProject =
                 new TestProject
                 {
                     Name = testProjectName,
-                    TargetFrameworks = framework,
+                    TargetFrameworks = frameworks,
                     IsSdkProject = true
                 };