fix: Handle SDK-style project references in WriteSolutionFile()

ICSharpCode.Decompiler/Solution/SolutionCreator.cs

@@ -33,6 +33,7 @@ namespace ICSharpCode.Decompiler.Solution
 
 		/// <summary>
 		/// Writes a solution file to the specified <paramref name="targetFile"/>.
+		/// Also fixes intra-solution project references in the project files.
 		/// </summary>
 		/// <param name="targetFile">The full path of the file to write.</param>
 		/// <param name="projects">The projects contained in this solution.</param>
@@ -164,22 +165,37 @@ namespace ICSharpCode.Decompiler.Solution
 			{
 				XDocument projectDoc = XDocument.Load(project.FilePath);
 
+				if (projectDoc.Root?.Name.LocalName != "Project")
+				{
+					throw new InvalidOperationException(
+						$"The file {project.FilePath} is not a valid project file, " +
+						$"no <Project> at the root; could not fix project references.");
+				}
+
+				var sdkStyle = projectDoc.Root.Attribute("Sdk") != null;
+				var itemGroupTagName = sdkStyle ? "ItemGroup" : ProjectFileNamespace + "ItemGroup";
+				var referenceTagName = sdkStyle ? "Reference" : ProjectFileNamespace + "Reference";
+
 				var referencesItemGroups = projectDoc.Root
-					.Elements(ProjectFileNamespace + "ItemGroup")
+					.Elements(itemGroupTagName)
-					.Where(e => e.Elements(ProjectFileNamespace + "Reference").Any());
+					.Where(e => e.Elements(referenceTagName).Any())
+					.ToList();
 
 				foreach (var itemGroup in referencesItemGroups)
 				{
-					FixProjectReferences(project.FilePath, itemGroup, projectsMap);
+					FixProjectReferences(project.FilePath, itemGroup, projectsMap, sdkStyle);
 				}
 
 				projectDoc.Save(project.FilePath);
 			}
 		}
 
-		private static void FixProjectReferences(string projectFilePath, XElement itemGroup, IDictionary<string, ProjectItem> projects)
+		static void FixProjectReferences(string projectFilePath, XElement itemGroup,
+			Dictionary<string, ProjectItem> projects, bool sdkStyle)
 		{
-			foreach (var item in itemGroup.Elements(ProjectFileNamespace + "Reference").ToList())
+			var referenceTagName = sdkStyle ? "Reference" : ProjectFileNamespace + "Reference";
+
+			foreach (var item in itemGroup.Elements(referenceTagName).ToList())
 			{
 				var assemblyName = item.Attribute("Include")?.Value;
 				if (assemblyName != null && projects.TryGetValue(assemblyName, out var referencedProject))
@@ -187,7 +203,7 @@ namespace ICSharpCode.Decompiler.Solution
 					item.Remove();
 
 					var projectReference = new XElement(ProjectFileNamespace + "ProjectReference",
-						new XElement(ProjectFileNamespace + "Project", referencedProject.Guid.ToString("B").ToUpperInvariant()),
+						new XElement(ProjectFileNamespace + "Project", referencedProject.Guid.ToString("B").ToLowerInvariant()),
 						new XElement(ProjectFileNamespace + "Name", referencedProject.ProjectName));
 					projectReference.SetAttributeValue("Include", GetRelativePath(projectFilePath, referencedProject.FilePath));