Add StringInterpolation helpers to render errors

Sources/ErrorKit/Helpers/String+ErrorKit.swift

@@ -17,3 +17,13 @@ extension String {
    }
    #endif
 }
+
+extension String.StringInterpolation {
+   mutating public func appendInterpolation(error: some Error) {
+      appendInterpolation(ErrorKit.userFriendlyMessage(for: error))
+   }
+
+   mutating public func appendInterpolation(errorChain error: some Error) {
+      appendInterpolation(ErrorKit.errorChainDescription(for: error))
+   }
+}

Tests/ErrorKitTests/ErrorKitTests.swift

@@ -38,6 +38,27 @@ enum ErrorKitTests {
          let nestedError = DatabaseError.caught(FileError.caught(PermissionError.denied(permission: "~/Downloads/Profile.png")))
          #expect(ErrorKit.userFriendlyMessage(for: nestedError) == "Access to ~/Downloads/Profile.png was declined. To use this feature, please enable the permission in your device Settings.")
       }
+
+      @Test
+      static func errorStringInterpolation() async throws {
+         #expect("\(error: SomeThrowable())" == "Something failed hard.")
+      }
+
+      @Test
+      static func nestedErrorStringInterpolation() async throws {
+         let nestedError = DatabaseError.caught(FileError.caught(PermissionError.denied(permission: "~/Downloads/Profile.png")))
+         #expect("\(error: nestedError)" == "Access to ~/Downloads/Profile.png was declined. To use this feature, please enable the permission in your device Settings.")
+      }
+
+      @Test
+      static func chainedErrorStringInterpolation() async throws {
+         #expect(
+            "\(errorChain: SomeLocalizedError())" == """
+            SomeLocalizedError [Struct]
+            └─ userFriendlyMessage: "Something failed. It failed because it wanted to. Try again later."
+            """
+         )
+      }
    }
 
    enum ErrorChainDescription {