Implement RestorePackages in MSBuild.

This adds the DotNetTool custom task, with `dotnet restore` implemented.

build/Microsoft.DotNet.Cli.Prepare.targets

@@ -5,12 +5,13 @@
   <UsingTask TaskName="GenerateBuildVersionInfo" AssemblyFile="$(CLIBuildDll)" />
   <UsingTask TaskName="CheckPrereqs" AssemblyFile="$(CLIBuildDll)" />
   <UsingTask TaskName="SetEnvVar" AssemblyFile="$(CLIBuildDll)" />
+  <UsingTask TaskName="DotNetRestore" AssemblyFile="$(CLIBuildDll)" />
 
   <Target DependsOnTargets="BuildDotnetCliBuildFramework" Name="Prepare">
     <PrepareTargets />
   </Target>
 
-  <Target Name="Init" >
+  <Target Name="Init">
     <!-- Current Runtime Information -->
     <GetCurrentRuntimeInformation>
       <Output TaskParameter="Rid" PropertyName="Rid" />
@@ -20,6 +21,10 @@
 
     <!-- Common Properties -->
     <PropertyGroup>
+      <Stage0Path Condition=" '$(OSName)' == 'win' ">$(RepoRoot)/.dotnet_stage0/Windows/$(Architecture)</Stage0Path>
+      <Stage0Path Condition=" '$(OSName)' != 'win' ">$(RepoRoot)/.dotnet_stage0/$(OSName)</Stage0Path>
+      <DotNetPath>$(Stage0Path)</DotNetPath>
+
       <BaseOutputDirectory>$(RepoRoot)/artifacts/$(Rid)</BaseOutputDirectory>
       <OutputDirectory>$(BaseOutputDirectory)/stage2</OutputDirectory>
       <Stage2CompilationDirectory>$(BaseOutputDirectory)/stage2compilation</Stage2CompilationDirectory>
@@ -95,4 +100,18 @@
     <!-- SetTelemetryProfile -->
     <SetEnvVar Name="DOTNET_CLI_TELEMETRY_PROFILE" Value="https://github.com/dotnet/cli;$(CommitHash)" />
   </Target>
+
+  <Target DependsOnTargets="Init" Name="RestorePackages">
+
+    <!-- Clean NuGet Temp Cache on Linux (seeing some issues on Linux) -->
+    <!-- TODO: do we still need this?  Seems unnecessary -->
+    <RemoveDir
+      Condition=" '$(OSName)' != 'win' AND '$(OSName)' != 'osx' "
+      Directories="/tmp/NuGet" />
+
+    <DotNetRestore WorkingDirectory="$(RepoRoot)/src" ToolPath="$(DotNetPath)" />
+    <DotNetRestore WorkingDirectory="$(RepoRoot)/tools" ToolPath="$(DotNetPath)" />
+
+  </Target>
+
 </Project>

build_projects/dotnet-cli-build/DotNetTool.cs

@@ -0,0 +1,85 @@
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public abstract class DotNetTool : ToolTask
+    {
+        private const string ExeName = "dotnet.exe";
+
+        public DotNetTool()
+        {
+        }
+
+        protected abstract string Command { get; }
+
+        protected abstract string Args { get; }
+
+        public string WorkingDirectory { get; set; }
+
+        protected override string ToolName
+        {
+            get { return ExeName; }
+        }
+
+        protected override MessageImportance StandardOutputLoggingImportance
+        {
+            get { return MessageImportance.High; } // or else the output doesn't get logged by default
+        }
+
+        protected override string GenerateFullPathToTool()
+        {
+            string path = ToolPath;
+
+            // if ToolPath was not provided by the MSBuild script 
+            if (string.IsNullOrEmpty(path))
+            {
+                Log.LogError($"Could not find the Path to {ExeName}");
+
+                return string.Empty;
+            }
+
+            return path;
+        }
+
+        protected override string GetWorkingDirectory()
+        {
+            return WorkingDirectory ?? base.GetWorkingDirectory();
+        }
+
+        protected override string GenerateCommandLineCommands()
+        {
+            return $"{Command} {Args}";
+        }
+
+        protected override void LogToolCommand(string message)
+        {
+            base.LogToolCommand($"{GetWorkingDirectory()}> {message}");
+        }
+    }
+
+    public class DotNetRestore : DotNetTool
+    {
+        protected override string Command
+        {
+            get { return "restore"; }
+        }
+
+        protected override string Args
+        {
+            get { return $"{GetVerbosity()}"; }
+        }
+
+        public string Verbosity { get; set; }
+
+        private string GetVerbosity()
+        {
+            if (!string.IsNullOrEmpty(Verbosity))
+            {
+                return $"--verbosity {Verbosity}";
+            }
+
+            return null;
+        }
+    }
+}