CmdPal: Add actionable hint to empty results in File Search extension (#41982)

## Summary of the Pull Request

This PR improves the user experience when no indexed files match the
query in the File Search extension.

- Show a hint on the empty results page when no indexed files are found.
- Provide fallback actions:
- Search entire PC – opens new File Explorer window with the query
searched in This PC.
- Open Windows Search settings – navigates to Windows Search settings to
review indexed locations.

<img width="1719" height="1072" alt="image"
src="https://github.com/user-attachments/assets/51bd7b4a-563f-4339-b179-8125c057b0af"
/>


<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] Related to: #38509
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Indexer/Pages/IndexerPage.cs

@@ -4,6 +4,8 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
+using System.Text.Encodings.Web;
 using System.Threading.Tasks;
 using Microsoft.CmdPal.Ext.Indexer.Properties;
 using Microsoft.CommandPalette.Extensions;
@@ -23,6 +25,9 @@ internal sealed partial class IndexerPage : DynamicListPage, IDisposable
 
     private bool _isEmptyQuery = true;
 
+    private CommandItem _noSearchEmptyContent;
+    private CommandItem _nothingFoundEmptyContent;
+
     public IndexerPage()
     {
         Id = "com.microsoft.indexer.fileSearch";
@@ -31,6 +36,7 @@ internal sealed partial class IndexerPage : DynamicListPage, IDisposable
         PlaceholderText = Resources.Indexer_PlaceholderText;
         _searchEngine = new();
         _queryCookie = 10;
+        CreateEmptyContent();
     }
 
     public IndexerPage(string query, SearchEngine searchEngine, uint queryCookie, IList<IListItem> firstPageData)
@@ -43,9 +49,42 @@ internal sealed partial class IndexerPage : DynamicListPage, IDisposable
         initialQuery = query;
         SearchText = query;
         disposeSearchEngine = false;
+        CreateEmptyContent();
     }
 
-    public override ICommandItem EmptyContent => GetEmptyContent();
+    private void CreateEmptyContent()
+    {
+        _noSearchEmptyContent = new CommandItem(new NoOpCommand())
+        {
+            Icon = Icon,
+            Title = Resources.Indexer_Subtitle,
+            Subtitle = Resources.Indexer_NoSearchQueryMessageTip,
+        };
+
+        _nothingFoundEmptyContent = new CommandItem(new AnonymousCommand(StartManualSearch) { Name = Resources.Indexer_Command_SearchAllFiles! })
+        {
+            Icon = Icon,
+            Title = Resources.Indexer_NoResultsMessage,
+            Subtitle = Resources.Indexer_NoResultsMessageTip,
+            MoreCommands = [
+                new CommandContextItem(new OpenUrlCommand("ms-settings:search") { Name = Resources.Indexer_Command_OpenIndexerSettings! })
+                {
+                    Title = Resources.Indexer_Command_SearchAllFiles!,
+                },
+                ],
+        };
+    }
+
+    private void StartManualSearch()
+    {
+        // {20D04FE0-3AEA-1069-A2D8-08002B30309D} is CLSID for "This PC"
+        const string template = "search-ms:query={0}&crumb=location:::{{20D04FE0-3AEA-1069-A2D8-08002B30309D}}";
+        var encodedSearchText = UrlEncoder.Default.Encode(SearchText);
+        var command = string.Format(CultureInfo.CurrentCulture, template, encodedSearchText);
+        ShellHelpers.OpenInShell(command);
+    }
+
+    public override ICommandItem EmptyContent => _isEmptyQuery ? _noSearchEmptyContent : _nothingFoundEmptyContent;
 
     public override void UpdateSearchText(string oldSearch, string newSearch)
     {
@@ -74,16 +113,6 @@ internal sealed partial class IndexerPage : DynamicListPage, IDisposable
         RaiseItemsChanged(_indexerListItems.Count);
     }
 
-    private CommandItem GetEmptyContent()
-    {
-        return new CommandItem(new NoOpCommand())
-        {
-            Icon = Icon,
-            Title = _isEmptyQuery ? Resources.Indexer_Subtitle : Resources.Indexer_NoResultsMessage,
-            Subtitle = Resources.Indexer_NoResultsMessageTip,
-        };
-    }
-
     private void Query(string query)
     {
         ++_queryCookie;

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Indexer/Properties/Resources.Designer.cs

@@ -96,6 +96,15 @@ namespace Microsoft.CmdPal.Ext.Indexer.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Open Windows Search settings.
+        /// </summary>
+        internal static string Indexer_Command_OpenIndexerSettings {
+            get {
+                return ResourceManager.GetString("Indexer_Command_OpenIndexerSettings", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Open path in console.
         /// </summary>
@@ -123,6 +132,15 @@ namespace Microsoft.CmdPal.Ext.Indexer.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Search all files.
+        /// </summary>
+        internal static string Indexer_Command_SearchAllFiles {
+            get {
+                return ResourceManager.GetString("Indexer_Command_SearchAllFiles", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Show in folder.
         /// </summary>
@@ -187,7 +205,8 @@ namespace Microsoft.CmdPal.Ext.Indexer.Properties {
         }
         
         /// <summary>
-        ///   Looks up a localized string similar to Tip: Improve your search result using filters like in Windows Explorer. (For example: type:directory).
+        ///   Looks up a localized string similar to Nothing was found in the indexed locations.
+        ///You can try searching all files on this PC or adjust your indexing settings..
         /// </summary>
         internal static string Indexer_NoResultsMessageTip {
             get {
@@ -195,6 +214,15 @@ namespace Microsoft.CmdPal.Ext.Indexer.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Tip: Refine your search using filters, just like in File Explorer (e.g., type:directory)..
+        /// </summary>
+        internal static string Indexer_NoSearchQueryMessageTip {
+            get {
+                return ResourceManager.GetString("Indexer_NoSearchQueryMessageTip", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Search for files and folders....
         /// </summary>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Indexer/Properties/Resources.resx

@@ -184,6 +184,16 @@
     <value>No items found</value>
   </data>
   <data name="Indexer_NoResultsMessageTip" xml:space="preserve">
+    <value>Nothing was found in the indexed locations.
+You can try searching all files on this PC or adjust your indexing settings.</value>
+  </data>
+  <data name="Indexer_NoSearchQueryMessageTip" xml:space="preserve">
     <value>Tip: Refine your search using filters, just like in File Explorer (e.g., type:directory).</value>
   </data>
+  <data name="Indexer_Command_OpenIndexerSettings" xml:space="preserve">
+    <value>Open Windows Search settings</value>
+  </data>
+  <data name="Indexer_Command_SearchAllFiles" xml:space="preserve">
+    <value>Search all files</value>
+  </data>
 </root>