Check schema when performing a sln build.

src/Build.UnitTests/Construction/SolutionFile_Tests.cs

@@ -7,10 +7,9 @@
 using System.IO;
 
 using Microsoft.Build.Construction;
+using Microsoft.Build.Engine.UnitTests;
 using Microsoft.Build.Shared;
-
-
-
+using Shouldly;
 using InvalidProjectFileException = Microsoft.Build.Exceptions.InvalidProjectFileException;
 using Xunit;
 
@@ -259,6 +258,56 @@ public void CanBeMSBuildFile()
             }
         }
 
+        /// <summary>
+        /// Test CanBeMSBuildFile
+        /// </summary>
+        [Fact]
+        public void CanBeMSBuildFileRejectsMSBuildLikeFiles()
+        {
+            using (var env = TestEnvironment.Create())
+            {
+                string rptprojProjContent = @"<?xml version=""1.0"" encoding=""utf-8""?>
+                    <Project xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" ToolsVersion=""2.0"">
+                      <DataSources />
+                      <Reports />
+                    </Project>";
+                string dwprojProjContent = @"<?xml version=""1.0"" encoding=""utf-8""?>
+                    <Project xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:ddl2=""http://schemas.microsoft.com/analysisservices/2003/engine/2"" xmlns:ddl2_2=""http://schemas.microsoft.com/analysisservices/2003/engine/2/2"" xmlns:ddl100_100=""http://schemas.microsoft.com/analysisservices/2008/engine/100/100"" xmlns:ddl200=""http://schemas.microsoft.com/analysisservices/2010/engine/200"" xmlns:ddl200_200=""http://schemas.microsoft.com/analysisservices/2010/engine/200/200"" xmlns:dwd=""http://schemas.microsoft.com/DataWarehouse/Designer/1.0"">
+                      <ProductVersion />
+                      <SchemaVersion />
+                      <State />
+                      <Database />
+                      <Cubes />
+                    </Project>";
+
+                string rptprojPath = env.CreateFile(".rptproj").Path;
+                File.WriteAllText(rptprojPath, rptprojProjContent);
+                string dqprojPath = env.CreateFile(".dwproj").Path;
+                File.WriteAllText(dqprojPath, dwprojProjContent);
+
+                // Create the SolutionFile object
+                string solutionFileContents =
+                    @"
+                    Microsoft Visual Studio Solution File, Format Version 8.00
+                        Project('{F14B399A-7131-4C87-9E4B-1186C45EF12D}') = 'PrtProj', '" + Path.GetFileName(rptprojPath) + @"', '{CCCCCCCC-9925-4D57-9DAF-E0A9D936ABDB}'
+                            ProjectSection(ProjectDependencies) = postProject
+                            EndProjectSection
+                        EndProject
+                        Project('{D2ABAB84-BF74-430A-B69E-9DC6D40DDA17}') = 'DwProj', '" + Path.GetFileName(dqprojPath) + @"', '{DEA89696-F42B-4B58-B7EE-017FF40817D1}'
+                            ProjectSection(ProjectDependencies) = postProject
+                            EndProjectSection
+                        EndProject";
+
+                string error = null;
+                SolutionFile solution = ParseSolutionHelper(solutionFileContents);
+                ProjectInSolution project1 = solution.ProjectsByGuid["{CCCCCCCC-9925-4D57-9DAF-E0A9D936ABDB}"];
+                ProjectInSolution project2 = solution.ProjectsByGuid["{DEA89696-F42B-4B58-B7EE-017FF40817D1}"];
+
+                project1.CanBeMSBuildProjectFile(out error).ShouldBe(false);
+                project2.CanBeMSBuildProjectFile(out error).ShouldBe(false);
+            }
+        }
+
         /// <summary>
         /// Test ParseEtpProject function.
         /// </summary>

src/Build/Construction/Solution/ProjectInSolution.cs

@@ -14,6 +14,7 @@
 using BuildEventFileInfo = Microsoft.Build.Shared.BuildEventFileInfo;
 using ErrorUtilities = Microsoft.Build.Shared.ErrorUtilities;
 using System.Collections.ObjectModel;
+using System.Linq;
 
 namespace Microsoft.Build.Construction
 {
@@ -323,8 +324,30 @@ internal bool CanBeMSBuildProjectFile(out string errorMessage)
 
                 if (mainProjectElement != null && mainProjectElement.LocalName == "Project")
                 {
-                    _canBeMSBuildProjectFile = true;
-                    return _canBeMSBuildProjectFile;
+                    // MSBuild supports project files with an empty (supported in Visual Studio 2017) or the default MSBuild
+                    // namespace.
+                    bool emptyNamespace = string.IsNullOrEmpty(mainProjectElement.NamespaceURI);
+                    bool defaultNamespace = String.Compare(mainProjectElement.NamespaceURI,
+                                                XMakeAttributes.defaultXmlNamespace,
+                                                StringComparison.OrdinalIgnoreCase) == 0;
+                    bool projectElementInvalid = ElementContainsInvalidNamespaceDefitions(mainProjectElement);
+
+                    // If the MSBuild namespace is declared, it is very likely an MSBuild project that should be built.
+                    if (defaultNamespace)
+                    {
+                        _canBeMSBuildProjectFile = true;
+                        return _canBeMSBuildProjectFile;
+                    }
+
+                    // This is a bit of a special case, but an rptproj file will contain a Project with no schema that is
+                    // not an MSBuild file. It will however have ToolsVersion="2.0" which is not supported with an empty
+                    // schema. This is not a great solution, but it should cover the customer reported issue. See:
+                    // https://github.com/Microsoft/msbuild/issues/2064
+                    if (emptyNamespace && !projectElementInvalid && mainProjectElement.GetAttribute("ToolsVersion") != "2.0")
+                    {
+                        _canBeMSBuildProjectFile = true;
+                        return _canBeMSBuildProjectFile;
+                    }
                 }
             }
             // catch all sorts of exceptions - if we encounter any problems here, we just assume the project file is not
@@ -463,6 +486,25 @@ static internal string DisambiguateProjectTargetName(string uniqueProjectName)
             return uniqueProjectName;
         }
 
+        /// <summary>
+        /// Check a Project element for known invalid namespace definitions.
+        /// </summary>
+        /// <param name="mainProjectElement">Project XML Element</param>
+        /// <returns>True if the element contains known invalid namespace definitions</returns>
+        private static bool ElementContainsInvalidNamespaceDefitions(XmlElement mainProjectElement)
+        {
+            if (mainProjectElement.HasAttributes)
+            {
+                // Data warehouse projects (.dwproj) will contain a Project element but are invalid MSBuild. Check attributes
+                // on Project for signs that this is a .dwproj file. If there are, it's not a valid MSBuild file.
+                return mainProjectElement.Attributes.OfType<XmlAttribute>().Any(a =>
+                    a.Name.Equals("xmlns:dwd", StringComparison.OrdinalIgnoreCase) ||
+                    a.Name.StartsWith("xmlns:dd", StringComparison.OrdinalIgnoreCase));
+            }
+
+            return false;
+        }
+
         #endregion
 
         #region Constants