Enable SwiftLint rule: empty_string (#25467)

* Enable SwiftLint rule: empty_string

Part of the Orchard SwiftLint rollout campaign.

`NSString.wp_isValidString()` uses `length > 0` instead of `!isEmpty`
because `isEmpty` is not directly available on `NSString` in this context.

---

Generated with the help of Claude Code, https://claude.ai/code

Co-Authored-By: Claude Code Opus 4.6 <noreply@anthropic.com>

* Fix optional chaining on non-optional String

`blog.version` is non-optional, so `?.isEmpty` causes a compile error.

---

Generated with the help of Claude Code, https://code.claude.com

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Clarify `empty_string` rule

---------

Co-authored-by: Claude Code Opus 4.6 <noreply@anthropic.com>

Author: mokagio

.swiftlint.yml

@@ -36,6 +36,9 @@ only_rules:
   # Prefer `() -> ` over `Void -> `.
   - empty_parameters
 
+  # Prefer checking `isEmpty` over comparing to empty string literal `""`.
+  - empty_string
+
   # MARK comment should be in valid format.
   - mark
 

Modules/Sources/WordPressKitModels/ObjectValidation.swift

@@ -16,6 +16,6 @@ import Foundation
     ///
     /// - Returns: Bool value
     func wp_isValidString() -> Bool {
-        return wp_isValidObject() && self != ""
+        return wp_isValidObject() && length > 0
     }
 }

Sources/WordPressAuthenticator/Extensions/WPStyleGuide+Login.swift

@@ -273,7 +273,7 @@ extension WPStyleGuide {
 
         let labelString = NSMutableAttributedString(string: firstPart, attributes: [.foregroundColor: WPStyleGuide.greyDarken30()])
 
-        if lastPart != "" {
+        if !lastPart.isEmpty {
             labelString.append(formattedGoogleString(forHyperlink: true))
         }
 

Tests/KeystoneTests/Helpers/JSONObject.swift

@@ -10,7 +10,7 @@ extension JSONObject {
     /// - Parameter fileName: The name of the json file to load. The "json" file extension can be omitted.
     init(fromFileNamed fileName: String) throws {
         let type = (fileName as NSString).pathExtension
-        if type != "" && type != "json" {
+        if !type.isEmpty && type != "json" {
             throw NSError(
                 domain: "JSONObject",
                 code: 1,

Tests/KeystoneTests/Tests/Utility/RemoteFeatureFlagTests.swift

@@ -18,7 +18,7 @@ class RemoteFeatureFlagTests: XCTestCase {
         exp.expectedFulfillmentCount = 2
 
         mock.deviceIdCallback = {
-            deviceId == "" ? deviceId = $0 : XCTAssertEqual(deviceId, $0)
+            deviceId.isEmpty ? deviceId = $0 : XCTAssertEqual(deviceId, $0)
             exp.fulfill()
         }
 

Tests/WordPressDataTests/BlogTests.swift

@@ -202,7 +202,7 @@ struct BlogTests {
             .build()
 
         #expect((blog.version as Any) is String)
-        #expect(blog.version == "")
+        #expect(blog.version.isEmpty)
     }
 
     @Test func removeDuplicates() async throws {

Tests/WordPressDataTests/PostMetadataTests.swift

@@ -79,7 +79,7 @@ struct PostMetadataTests {
         metadata.encode(in: &container)
 
         // THEN
-        #expect(container.getString(for: .jetpackNewsletterEmailDisabled) == "")
+        #expect(container.getString(for: .jetpackNewsletterEmailDisabled)?.isEmpty == true)
     }
 }
 

WordPress/Classes/ViewRelated/Aztec/ViewControllers/AztecAttachmentViewController.swift

@@ -222,7 +222,7 @@ class AztecAttachmentViewController: UITableViewController {
     }
 
     @objc func handleDoneButtonTapped(sender: UIBarButtonItem) {
-        let checkedAlt = alt == "" ? nil : alt
+        let checkedAlt = alt?.isEmpty == true ? nil : alt
         onUpdate?(alignment, size, linkURL, checkedAlt, caption)
         dismiss(animated: true)
     }

WordPress/Classes/ViewRelated/CustomPostTypes/CustomPostListViewModel.swift

@@ -406,7 +406,7 @@ final class CustomPostListViewModel: ObservableObject {
     func menuNavigation(forBlaze post: AnyPostWithEditContext) -> PostMenuNavigation? {
         guard endpoint == .posts
                 && BlazeHelper.isBlazeFlagEnabled() && blog.canBlaze
-                && post.status == .publish && (post.password ?? "") == "" else { return nil }
+                && post.status == .publish && (post.password ?? "").isEmpty else { return nil }
         return .blaze(post: post)
     }
 

WordPress/Classes/ViewRelated/NUX/Controllers/Social Signup/SignupEpilogueViewController.swift

@@ -194,7 +194,7 @@ private extension SignupEpilogueViewController {
     }
 
     func changeUsername(to newUsername: String, finished: @escaping (() -> Void)) {
-        guard newUsername != "" else {
+        guard !newUsername.isEmpty else {
             finished()
             return
         }