changed msbuild's withProperty to forward multiple parameters as a comma separated list

Author: Markus

src/Cake.Common.Tests/Unit/Tools/MSBuild/MSBuildRunnerTests.cs

@@ -713,7 +713,7 @@ public void Should_Append_Property_With_Multiple_Values_To_Process_Arguments()
                 var result = fixture.Run();
 
                 // Then
-                Assert.Equal("/v:normal /p:A=B /p:A=E /p:C=D /target:Build " +
+                Assert.Equal("/v:normal /p:A=\"B,E\" /p:C=D /target:Build " +
                              "\"C:/Working/src/Solution.sln\"", result.Args);
             }
 

src/Cake.Common/Tools/MSBuild/MSBuildRunner.cs

@@ -275,9 +275,14 @@ private static IEnumerable<string> GetPropertyArguments(IDictionary<string, ILis
         {
             foreach (var propertyKey in properties.Keys)
             {
-                foreach (var propertyValue in properties[propertyKey])
+                if (properties[propertyKey].Count > 1)
                 {
-                    yield return string.Concat("/p:", propertyKey, "=", propertyValue.EscapeMSBuildPropertySpecialCharacters());
+                    var commaSeparatedValues = string.Join(",", properties[propertyKey].Select(x => x.EscapeMSBuildPropertySpecialCharacters()));
+                    yield return string.Concat("/p:", propertyKey, "=", '"', commaSeparatedValues, '"');
+                }
+                else if (properties[propertyKey].Count == 1)
+                {
+                    yield return string.Concat("/p:", propertyKey, "=", properties[propertyKey].First().EscapeMSBuildPropertySpecialCharacters());
                 }
             }
         }