Don't set a default ProjectAssetsFile path in the SDK

src/Tasks/Common/Resources/Strings.resx

@@ -346,4 +346,7 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</comment>
   </data>
+  <data name="AssetsFileNotSet" xml:space="preserve">
+    <value>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</value>
+  </data>
 </root>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

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

@@ -379,6 +379,11 @@
 {1} - Restored version of platform package
 {2} - Current version of platform package</note>
       </trans-unit>
+      <trans-unit id="AssetsFileNotSet">
+        <source>The path to the project assets file was not set. Run a NuGet package restore to generate this file.</source>
+        <target state="new">The path to the project assets file was not set. Run a NuGet package restore to generate this file.</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

src/Tasks/Microsoft.NET.Build.Tasks/CheckForTargetInAssetsFile.cs

@@ -11,7 +11,6 @@ namespace Microsoft.NET.Build.Tasks
 {
     public class CheckForTargetInAssetsFile : TaskBase
     {
-        [Required]
         public string AssetsFilePath { get; set; }
 
         [Required]

src/Tasks/Microsoft.NET.Build.Tasks/FilterResolvedFiles.cs

@@ -19,7 +19,6 @@ public class FilterResolvedFiles : TaskBase
         private readonly List<ITaskItem> _assembliesToPublish = new List<ITaskItem>();
         private readonly List<ITaskItem> _packagesResolved = new List<ITaskItem>();
 
-        [Required]
         public string AssetsFilePath { get; set; }
 
         [Required]

src/Tasks/Microsoft.NET.Build.Tasks/GenerateDepsFile.cs

@@ -23,7 +23,6 @@ public class GenerateDepsFile : TaskBase
         [Required]
         public string ProjectPath { get; set; }
 
-        [Required]
         public string AssetsFilePath { get; set; }
 
         [Required]

src/Tasks/Microsoft.NET.Build.Tasks/GenerateRuntimeConfigurationFiles.cs

@@ -21,7 +21,6 @@ namespace Microsoft.NET.Build.Tasks
     /// </summary>
     public class GenerateRuntimeConfigurationFiles : TaskBase
     {
-        [Required]
         public string AssetsFilePath { get; set; }
 
         [Required]

src/Tasks/Microsoft.NET.Build.Tasks/LoadAssetsFile.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Microsoft.NET.Build.Tasks
+{
+    public sealed class LoadAssetsFile : TaskBase
+    {
+        /// <summary>
+        /// The assets file to process
+        /// </summary>
+        public string ProjectAssetsFile
+        {
+            get; set;
+        }
+
+        protected override void ExecuteCore()
+        {
+            var lockFile = new LockFileCache(this).GetLockFile(ProjectAssetsFile);
+        }
+    }
+}

src/Tasks/Microsoft.NET.Build.Tasks/LockFileCache.cs

@@ -24,6 +24,10 @@ public LockFileCache(Task task)
 
         public LockFile GetLockFile(string path)
         {
+            if (string.IsNullOrEmpty(path))
+            {
+                throw new BuildErrorException(Strings.AssetsFileNotSet);
+            }
             if (!Path.IsPathRooted(path))
             {
                 throw new BuildErrorException(Strings.AssetsFilePathNotRooted, path);

src/Tasks/Microsoft.NET.Build.Tasks/ReportAssetsLogMessages.cs

@@ -30,7 +30,6 @@ public sealed class ReportAssetsLogMessages : TaskBase
         /// <summary>
         /// The assets file to process
         /// </summary>
-        [Required]
         public string ProjectAssetsFile
         {
             get; set;

src/Tasks/Microsoft.NET.Build.Tasks/ResolvePackageAssets.cs

@@ -28,7 +28,6 @@ public sealed class ResolvePackageAssets : TaskBase
         /// <summary>
         /// Path to assets.json.
         /// </summary>
-        [Required]
         public string ProjectAssetsFile { get; set; }
 
         /// <summary>
@@ -225,6 +224,11 @@ public sealed class ResolvePackageAssets : TaskBase
 
         protected override void ExecuteCore()
         {
+            if (string.IsNullOrEmpty(ProjectAssetsFile))
+            {
+                throw new BuildErrorException(Strings.AssetsFileNotSet);
+            }
+
             ReadItemGroups();
             SetImplicitMetadataForCompileTimeAssemblies();
             SetImplicitMetadataForFrameworkAssemblies();
@@ -317,7 +321,7 @@ internal byte[] HashSettings()
                     writer.Write(MarkPackageReferencesAsExternallyResolved);
                     writer.Write(ImplicitPlatformPackageIdentifier ?? "");
                     writer.Write(ProjectAssetsCacheFile);
-                    writer.Write(ProjectAssetsFile);
+                    writer.Write(ProjectAssetsFile ?? "");
                     writer.Write(ProjectLanguage ?? "");
                     writer.Write(ProjectPath);
                     writer.Write(RuntimeIdentifier ?? "");

src/Tasks/Microsoft.NET.Build.Tasks/ResolvePackageDependencies.cs

@@ -93,7 +93,6 @@ public string ProjectPath
         /// <summary>
         /// The assets file to process
         /// </summary>
-        [Required]
         public string ProjectAssetsFile
         {
             get; set;

src/Tasks/Microsoft.NET.Build.Tasks/ResolvePublishAssemblies.cs

@@ -20,7 +20,6 @@ public class ResolvePublishAssemblies : TaskBase
         [Required]
         public string ProjectPath { get; set; }
 
-        [Required]
         public string AssetsFilePath { get; set; }
 
         [Required]

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

@@ -23,19 +23,12 @@ Copyright (c) .NET Foundation. All rights reserved.
     <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
   </PropertyGroup>
 
-  <!-- Project Assets File -->
   <PropertyGroup>
-    <ProjectAssetsFile Condition="'$(ProjectAssetsFile)' == ''">$(BaseIntermediateOutputPath)/project.assets.json</ProjectAssetsFile>
-    <ProjectAssetsFile>$([MSBuild]::NormalizePath($(MSBuildProjectDirectory), $(ProjectAssetsFile)))</ProjectAssetsFile>
-
     <!-- Note that the assets.cache file has contents that are unique to the current TFM and configuration and therefore cannot
          be stored in a shared directory next to the assets.json file -->
     <ProjectAssetsCacheFile Condition="'$(ProjectAssetsCacheFile)' == ''">$(IntermediateOutputPath)$(MSBuildProjectName).assets.cache</ProjectAssetsCacheFile>
     <ProjectAssetsCacheFile>$([MSBuild]::NormalizePath($(MSBuildProjectDirectory), $(ProjectAssetsCacheFile)))</ProjectAssetsCacheFile>
-  </PropertyGroup>
-
-  <PropertyGroup>
-    <ResolvePackageDependenciesForBuild Condition="'$(ResolvePackageDependenciesForBuild)' == ''">true</ResolvePackageDependenciesForBuild>
+
     <CopyLocalLockFileAssemblies Condition="'$(CopyLocalLockFileAssemblies)' == ''">true</CopyLocalLockFileAssemblies>
 
     <ContentPreprocessorOutputDirectory Condition="'$(ContentPreprocessorOutputDirectory)' == ''">$(IntermediateOutputPath)NuGet\</ContentPreprocessorOutputDirectory>
@@ -130,7 +123,7 @@ Copyright (c) .NET Foundation. All rights reserved.
     </ResolvePackageDependenciesForBuildDependsOn>
   </PropertyGroup>
   <Target Name="ResolvePackageDependenciesForBuild"
-          Condition="'$(ResolvePackageDependenciesForBuild)' == 'true' and Exists('$(ProjectAssetsFile)')"
+          Condition=" '$(DesignTimeBuild)' != 'true' Or Exists('$(ProjectAssetsFile)')"
           BeforeTargets="AssignProjectConfiguration"
           DependsOnTargets="$(ResolvePackageDependenciesForBuildDependsOn)" />
 
@@ -370,6 +363,8 @@ Copyright (c) .NET Foundation. All rights reserved.
 
   <UsingTask TaskName="Microsoft.NET.Build.Tasks.ReportAssetsLogMessages"
              AssemblyFile="$(MicrosoftNETBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.NET.Build.Tasks.LoadAssetsFile"
+             AssemblyFile="$(MicrosoftNETBuildTasksAssembly)" />
 
   <!-- The condition on this target causes it to be skipped during design-time builds if
         the restore operation hasn't run yet.  This is to avoid displaying an error in
@@ -378,6 +373,10 @@ Copyright (c) .NET Foundation. All rights reserved.
   <Target Name="ReportAssetsLogMessages"
           Condition="'$(EmitAssetsLogMessages)' == 'true' And ('$(DesignTimeBuild)' != 'true' Or Exists('$(ProjectAssetsFile)'))">
 
+    <!-- Load the assets file in a separate task, so that if the file itself can't be loaded (or isn't set), we
+         can generate an error without continuing (since ReportAssetsLogMessages uses ContinueOnError="ErrorAndContinue" -->
+    <LoadAssetsFile ProjectAssetsFile="$(ProjectAssetsFile)" />
+
     <ReportAssetsLogMessages
       ProjectAssetsFile="$(ProjectAssetsFile)"
       ContinueOnError="ErrorAndContinue">