Refactor workspace folder guard into a pure, testable filter

Extract the null/URI-less filtering from `AddWorkspaceFolders` into a pure
`GetValidWorkspaceFolders` helper. `WorkspaceService` remains the single
chokepoint where client-supplied folders are ingested, so every downstream
`Uri` dereference stays protected, but the filtering logic is now trivially
unit-testable without constructing a service or logger.

Drop the per-folder warning so the filter is a simple, allocation-free
expression, and add direct tests covering null, empty, and mixed
(null folder / URI-less folder / valid folder) inputs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: andyleejordan

src/PowerShellEditorServices/Services/Workspace/WorkspaceService.cs

@@ -118,23 +118,23 @@ public WorkspaceService(ILoggerFactory factory)
         /// </remarks>
         public void AddWorkspaceFolders(IEnumerable<WorkspaceFolder> workspaceFolders)
         {
-            if (workspaceFolders is null)
+            foreach (WorkspaceFolder workspaceFolder in GetValidWorkspaceFolders(workspaceFolders))
             {
-                return;
-            }
-
-            foreach (WorkspaceFolder workspaceFolder in workspaceFolders)
-            {
-                if (workspaceFolder?.Uri is null)
-                {
-                    logger.LogWarning("Ignored workspace folder without a URI: " + workspaceFolder?.Name);
-                    continue;
-                }
-
                 WorkspaceFolders.Add(workspaceFolder);
             }
         }
 
+        /// <summary>
+        /// Filters workspace folders down to those usable by the service: non-null folders with a
+        /// non-null URI. The <c>workspaceFolders</c> field is optional in LSP, so the collection
+        /// itself may also be null.
+        /// </summary>
+        /// <param name="workspaceFolders">The workspace folders from the initialize parameters.</param>
+        /// <returns>The folders that have a non-null URI, or an empty sequence.</returns>
+        internal static IEnumerable<WorkspaceFolder> GetValidWorkspaceFolders(IEnumerable<WorkspaceFolder> workspaceFolders)
+            => workspaceFolders?.Where(static folder => folder?.Uri is not null)
+                ?? Enumerable.Empty<WorkspaceFolder>();
+
         /// <summary>
         /// Gets an open file in the workspace. If the file isn't open but exists on the filesystem, load and return it.
         /// <para>IMPORTANT: Not all documents have a backing file e.g. untitled: scheme documents.  Consider using

test/PowerShellEditorServices.Test/Session/WorkspaceTests.cs

@@ -112,6 +112,31 @@ public void AddWorkspaceFoldersIgnoresNullAndUrilessFolders()
             Assert.Equal(s_workspacePath, Assert.Single(workspace.WorkspacePaths));
         }
 
+        [Fact]
+        public void GetValidWorkspaceFoldersReturnsEmptyWhenNull()
+            => Assert.Empty(WorkspaceService.GetValidWorkspaceFolders(null));
+
+        [Fact]
+        public void GetValidWorkspaceFoldersReturnsEmptyWhenEmpty()
+            => Assert.Empty(WorkspaceService.GetValidWorkspaceFolders(new Container<WorkspaceFolder>()));
+
+        [Fact]
+        public void GetValidWorkspaceFoldersSkipsNullFoldersAndNullUris()
+        {
+            WorkspaceFolder valid = new()
+            {
+                Uri = DocumentUri.FromFileSystemPath(s_workspacePath),
+                Name = "valid"
+            };
+
+            Container<WorkspaceFolder> folders = new(
+                null,
+                new WorkspaceFolder { Name = "missing-uri" },
+                valid);
+
+            Assert.Equal(valid, Assert.Single(WorkspaceService.GetValidWorkspaceFolders(folders)));
+        }
+
         [Fact]
         public void HasDefaultForWorkspacePaths()
         {