Hosts: add “No leading spaces” option and honor it when saving (#41206)

## Summary of the Pull Request

Adds a new Hosts File Editor setting “No leading spaces” that prevents
prepending spaces to active lines when saving the hosts file (when any
entry is disabled). Default is Off to preserve current behavior.



## PR Checklist

- [x] Closes: #36386  

- [ ] Communication: N/A (small, scoped option)

- [x] Tests: Added/updated and all pass

- [x] Localization: New en-US strings added; other locales handled by
loc pipeline

- [ ] Dev docs: N/A

- [x] New binaries: None

- [x] Documentation updated: N/A



## Detailed Description of the Pull Request / Additional comments

- Settings surface:

  - `src/settings-ui/Settings.UI.Library/HostsProperties.cs`: add
`NoLeadingSpaces`

  - `src/modules/Hosts/HostsUILib/Settings/IUserSettings.cs`: add
`NoLeadingSpaces`

  - `src/modules/Hosts/Hosts/Settings/UserSettings.cs`: load/save value
from settings.json

  - `src/settings-ui/Settings.UI/ViewModels/HostsViewModel.cs`: expose
`NoLeadingSpaces`

  - `src/settings-ui/Settings.UI/SettingsXAML/Views/HostsPage.xaml`: new
SettingsCard toggle

  - `src/settings-ui/Settings.UI/Strings/en-us/Resources.resw`: add
`Hosts_NoLeadingSpaces.Header/Description`

- Writer change:

  - `src/modules/Hosts/HostsUILib/Helpers/HostsService.cs`: gate indent
with `anyDisabled && !_userSettings.NoLeadingSpaces`

- Tests:

  - `src/modules/Hosts/Hosts.Tests/HostsServiceTest.cs`:
`NoLeadingSpaces_Disabled_RemovesIndent`



Backward compatibility: default Off, current formatting unchanged unless
the user enables the option.



## Validation Steps Performed

- Automated: `HostsEditor.UnitTests` including
`NoLeadingSpaces_Disabled_RemovesIndent` passing.

- Manual:

  1. Run PowerToys (runner) as Admin.

  2. Settings → Hosts File Editor → enable “No leading spaces”.

  3. In editor, add active `127.0.0.10 example1` and disabled
`127.0.0.11 example2`; Save.

  4. Open `C:\Windows\System32\drivers\etc\hosts` in Notepad.

     - ON: active line starts at column 0; disabled is `# 127...`.

     - OFF: active line begins with two spaces when a disabled entry
exists.

src/modules/Hosts/Hosts.Tests/HostsServiceTest.cs

@@ -298,5 +298,34 @@ namespace Hosts.Tests
             var hidden = fileSystem.FileInfo.New(service.HostsFilePath).Attributes.HasFlag(FileAttributes.Hidden);
             Assert.IsTrue(hidden);
         }
+
+        [TestMethod]
+        public async Task NoLeadingSpaces_Disabled_RemovesIndent()
+        {
+            var content =
+        @"10.1.1.1 host host.local # comment
+10.1.1.2 host2 host2.local # another comment
+";
+
+            var expected =
+        @"10.1.1.1  host host.local     # comment
+10.1.1.2  host2 host2.local   # another comment
+# 10.1.1.30 host30 host30.local # new entry
+";
+
+            var fs = new CustomMockFileSystem();
+            var settings = new Mock<IUserSettings>();
+            settings.Setup(s => s.NoLeadingSpaces).Returns(true);
+            var svc = new HostsService(fs, settings.Object, _elevationHelper.Object);
+            fs.AddFile(svc.HostsFilePath, new MockFileData(content));
+
+            var data = await svc.ReadAsync();
+            var entries = data.Entries.ToList();
+            entries.Add(new Entry(0, "10.1.1.30", "host30 host30.local", "new entry", false));
+            await svc.WriteAsync(data.AdditionalLines, entries);
+
+            var result = fs.GetFile(svc.HostsFilePath);
+            Assert.AreEqual(expected, result.TextContents);
+        }
     }
 }

src/modules/Hosts/Hosts/Settings/UserSettings.cs

@@ -26,6 +26,8 @@ namespace Hosts.Settings
 
         private bool _loopbackDuplicates;
 
+        public bool NoLeadingSpaces { get; private set; }
+
         public bool LoopbackDuplicates
         {
             get => _loopbackDuplicates;
@@ -88,6 +90,7 @@ namespace Hosts.Settings
                             AdditionalLinesPosition = (HostsAdditionalLinesPosition)settings.Properties.AdditionalLinesPosition;
                             Encoding = (HostsEncoding)settings.Properties.Encoding;
                             LoopbackDuplicates = settings.Properties.LoopbackDuplicates;
+                            NoLeadingSpaces = settings.Properties.NoLeadingSpaces;
                         }
 
                         retry = false;

src/modules/Hosts/HostsUILib/Helpers/HostsService.cs

@@ -157,7 +157,7 @@ namespace HostsUILib.Helpers
                         {
                             lineBuilder.Append('#').Append(' ');
                         }
-                        else if (anyDisabled)
+                        else if (anyDisabled && !_userSettings.NoLeadingSpaces)
                         {
                             lineBuilder.Append(' ').Append(' ');
                         }

src/modules/Hosts/HostsUILib/Settings/IUserSettings.cs

@@ -19,5 +19,7 @@ namespace HostsUILib.Settings
         event EventHandler LoopbackDuplicatesChanged;
 
         public delegate void OpenSettingsFunction();
+
+        public bool NoLeadingSpaces { get; }
     }
 }