From 19ed5a558b14d7b542498b9541dd572cd18d10f2 Mon Sep 17 00:00:00 2001
From: Piotr Puszkiewicz <piotrp@microsoft.com>
Date: Tue, 24 Jan 2017 21:59:18 -0800
Subject: [PATCH] WiP

---
 build_projects/dotnet-cli-build/DotNetTool.cs |  5 ++
 .../EnvironmentVariableFilter.cs              | 54 +++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 build_projects/dotnet-cli-build/EnvironmentVariableFilter.cs

diff --git a/build_projects/dotnet-cli-build/DotNetTool.cs b/build_projects/dotnet-cli-build/DotNetTool.cs
index d074856b0..58f813cab 100644
--- a/build_projects/dotnet-cli-build/DotNetTool.cs
+++ b/build_projects/dotnet-cli-build/DotNetTool.cs
@@ -1,5 +1,6 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
+using System.Linq;
 
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
@@ -12,6 +13,10 @@ namespace Microsoft.DotNet.Cli.Build
     {
         public DotNetTool()
         {
+            EnvironmentVariables = new EnvironmentFilter()
+                .GetEnvironmentVariableNamesToRemove()
+                .Select(e => $"{e}=")
+                .ToArray();
         }
 
         protected abstract string Command { get; }
diff --git a/build_projects/dotnet-cli-build/EnvironmentVariableFilter.cs b/build_projects/dotnet-cli-build/EnvironmentVariableFilter.cs
new file mode 100644
index 000000000..54f5272f7
--- /dev/null
+++ b/build_projects/dotnet-cli-build/EnvironmentVariableFilter.cs
@@ -0,0 +1,54 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class EnvironmentFilter
+    {
+        private const string _MSBuildEnvironmentVariablePrefix = "MSBuild";
+        private const string _DotNetEnvironmentVariablePrefix = "DOTNET";
+        private const string _NugetEnvironmentVariablePrefix = "NUGET";
+
+        private IEnumerable<string> _prefixesOfEnvironmentVariablesToRemove = new string []
+        {
+            _MSBuildEnvironmentVariablePrefix,
+            _DotNetEnvironmentVariablePrefix,
+            _NugetEnvironmentVariablePrefix
+        };
+
+        private IEnumerable<string> _environmentVariablesToRemove = new string []
+        {
+            "CscToolExe"
+        };
+
+        private IEnumerable<string> _environmentVariablesToKeep = new string []
+        {
+            "DOTNET_CLI_TELEMETRY_SESSIONID"
+        };
+
+        public IEnumerable<string> GetEnvironmentVariableNamesToRemove()
+        {
+            var allEnvironmentVariableNames = (IEnumerable<string>)Environment
+                .GetEnvironmentVariables()
+                .Keys
+                .Cast<string>();
+
+            var environmentVariablesToRemoveByPrefix = allEnvironmentVariableNames
+                .Where(e => _prefixesOfEnvironmentVariablesToRemove.Any(p => e.StartsWith(p)));
+            
+            var environmentVariablesToRemoveByName = allEnvironmentVariableNames
+                .Where(e => _environmentVariablesToRemove.Contains(e));
+            
+            var environmentVariablesToRemove = environmentVariablesToRemoveByName
+                .Concat(environmentVariablesToRemoveByPrefix)
+                .Distinct()
+                .Except(_environmentVariablesToKeep);
+
+            return environmentVariablesToRemoveByName;
+        }
+    }
+}