Merge branch 'wip/string-interpolation'

# Conflicts:
#	Sources/ErrorKit/Helpers/String+ErrorKit.swift

Author: Jeehut

README.md

@@ -67,6 +67,9 @@ do {
     // Better than localizedDescription, works with any error type
     print(ErrorKit.userFriendlyMessage(for: error))
     // "You are not connected to the Internet. Please check your connection."
+    
+    // String interpolation automatically uses userFriendlyMessage(for:)
+    print("Request failed: \(error)")
 }
 ```
 

Sources/ErrorKit/ErrorKit.docc/Guides/Enhanced-Error-Descriptions.md

@@ -81,6 +81,22 @@ If the error already conforms to `Throwable`, its `userFriendlyMessage` is used.
 
 All enhanced error messages are fully localized using the `String(localized:)` pattern, ensuring users receive messages in their preferred language where available.
 
+### String Interpolation Convenience
+
+ErrorKit enhances Swift's string interpolation to automatically use `userFriendlyMessage(for:)`:
+
+```swift
+// Instead of:
+showAlert(message: "Save failed: \(ErrorKit.userFriendlyMessage(for: error))")
+
+// You can simply use:
+showAlert(message: "Save failed: \(error)")
+Text("Could not load data: \(error)")
+Logger().info("Sync completed with error: \(error)")
+```
+
+This works with any error type — both your custom `Throwable` errors and system errors.
+
 ### How It Works
 
 The `userFriendlyMessage(for:)` function follows this process to determine the best error message:

Sources/ErrorKit/ErrorKit.docc/Guides/Error-Chain-Debugging.md

@@ -63,6 +63,21 @@ For errors conforming to the `Catching` protocol, you get the complete error wra
 
 Even for errors that don't conform to `Catching`, you still get valuable information since most Swift errors are enums. The error chain description will show you the exact enum case (e.g., `FileError.notFound`), making it easy to search your codebase for the error's origin. This is much better than the default cryptic message you get for enum cases when using `localizedDescription`.
 
+### String Interpolation for Debug Logging
+
+ErrorKit enhances string interpolation for error chain debugging. Use either `chain:` or `debug:` (they're aliases) to get the complete hierarchical description:
+
+```swift
+// Instead of:
+Logger().error("Update failed: \(ErrorKit.errorChainDescription(for: error))")
+
+// You can simply use either:
+Logger().error("Update failed:\n\(chain: error)")
+Logger().error("Update failed:\n\(debug: error)")
+```
+
+Use `\(error)` for user-facing messages, `\(chain: error)` or `\(debug: error)` for debugging.
+
 ### Error Analytics with Grouping IDs
 
 To help prioritize which errors to fix, ErrorKit provides `groupingID(for:)` that generates stable identifiers for errors sharing the exact same type structure and enum cases:

Sources/ErrorKit/ErrorKit.swift

@@ -168,7 +168,7 @@ public enum ErrorKit {
          } else {
             // For enums, include the full case description with type name
             if let enclosingType {
-               return "\(enclosingType).\(error)"
+               return "\(enclosingType).\(String(describing: error))"
             } else {
                return String(describing: error)
             }

Sources/ErrorKit/Helpers/String+ErrorKit.swift

@@ -19,11 +19,57 @@ extension String {
 }
 
 extension String.StringInterpolation {
-   mutating public func appendInterpolation(error: some Error) {
-      appendInterpolation(ErrorKit.userFriendlyMessage(for: error))
+   /// Interpolates an error using its user-friendly message.
+   ///
+   /// Uses ``ErrorKit.userFriendlyMessage(for:)`` to provide clear, actionable error descriptions
+   /// suitable for displaying to users. For nested errors, returns the message from the root cause.
+   ///
+   /// ```swift
+   /// showAlert("Operation failed: \(error)")
+   /// ```
+   ///
+   /// - Parameter error: The error to interpolate using its user-friendly message
+   mutating public func appendInterpolation(_ error: some Error) {
+      self.appendInterpolation(ErrorKit.userFriendlyMessage(for: error))
    }
 
-   mutating public func appendInterpolation(errorChain error: some Error) {
-      appendInterpolation(ErrorKit.errorChainDescription(for: error))
+   /// Interpolates an error using its complete chain description for debugging.
+   ///
+   /// Uses ``ErrorKit.errorChainDescription(for:)`` to show the full error hierarchy,
+   /// type information, and nested structure. Ideal for logging and debugging.
+   ///
+   /// ```swift
+   /// Logger().error("Operation failed with:\n\(chain: error)")
+   /// // Operation failed with:
+   /// // DatabaseError
+   /// // └─ FileError
+   /// //    └─ PermissionError.denied(permission: "~/Downloads/Profile.png")
+   /// //       └─ userFriendlyMessage: "Access to ~/Downloads/Profile.png was declined..."
+   /// ```
+   ///
+   /// - Parameter error: The error to interpolate using its complete chain description
+   mutating public func appendInterpolation(chain error: some Error) {
+      self.appendInterpolation(ErrorKit.errorChainDescription(for: error))
+   }
+
+   /// Interpolates an error using its complete chain description for debugging.
+   ///
+   /// Uses ``ErrorKit.errorChainDescription(for:)`` to show the full error hierarchy,
+   /// type information, and nested structure. Ideal for logging and debugging.
+   ///
+   /// ```swift
+   /// Logger().error("Operation failed with:\n\(chain: error)")
+   /// // Operation failed with:
+   /// // DatabaseError
+   /// // └─ FileError
+   /// //    └─ PermissionError.denied(permission: "~/Downloads/Profile.png")
+   /// //       └─ userFriendlyMessage: "Access to ~/Downloads/Profile.png was declined..."
+   /// ```
+   ///
+   /// - Parameter error: The error to interpolate using its complete chain description
+   ///
+   /// - NOTE: Alias for ``appendInterpolation(chain:)``.
+   mutating public func appendInterpolation(debug error: some Error) {
+      self.appendInterpolation(chain: error)
    }
 }

Tests/ErrorKitTests/ErrorKitTests.swift

@@ -61,6 +61,45 @@ enum ErrorKitTests {
       }
    }
 
+   enum StringInterpolation {
+      @Test
+      static func implicitWithStruct() async throws {
+         #expect("\(SomeThrowable())" == "Something failed hard.")
+      }
+
+      @Test
+      static func implicitWithNestedError() async throws {
+         let nestedError = DatabaseError.caught(FileError.caught(PermissionError.denied(permission: "~/Downloads/Profile.png")))
+         #expect("\(nestedError)" == "Access to ~/Downloads/Profile.png was declined. To use this feature, please enable the permission in your device Settings.")
+      }
+
+      @Test
+      static func chainWithStruct() async throws {
+         #expect(
+            "\(chain: SomeThrowable())"
+            ==
+            """
+            SomeThrowable [Struct]
+            └─ userFriendlyMessage: "Something failed hard."
+            """
+         )
+      }
+
+      @Test
+      static func chainWithNestedError() async throws {
+         let nestedError = DatabaseError.caught(FileError.caught(PermissionError.denied(permission: "~/Downloads/Profile.png")))
+         #expect(
+            "\(chain: nestedError)"
+            ==
+            """
+            DatabaseError
+            └─ FileError
+               └─ PermissionError.denied(permission: "~/Downloads/Profile.png")
+                  └─ userFriendlyMessage: "Access to ~/Downloads/Profile.png was declined. To use this feature, please enable the permission in your device Settings."
+            """)
+      }
+   }
+
    enum ErrorChainDescription {
       @Test
       static func localizedError() {