Attempting to apply/revert a failed hook now throws error

Author: lukaskubanek

Sources/InterposeKit/Hooks/Hook.swift

@@ -120,27 +120,37 @@ public final class Hook {
 
     /// Applies the hook by interposing the method implementation.
     public func apply() throws {
-        guard self.state == .pending else { return }
-        
-        do {
-            try self.strategy.replaceImplementation()
-            self.state = .active
-        } catch {
-            self.state = .failed
-            throw error
+        switch self.state {
+        case .pending:
+            do {
+                try self.strategy.replaceImplementation()
+                self.state = .active
+            } catch {
+                self.state = .failed
+                throw error
+            }
+        case .failed:
+            throw InterposeError.hookInFailedState
+        case .active:
+            return
         }
     }
 
     /// Reverts the hook, restoring the original method implementation.
     public func revert() throws {
-        guard self.state == .active else { return }
-        
-        do {
-            try self.strategy.restoreImplementation()
-            self.state = .pending
-        } catch {
-            self.state = .failed
-            throw error
+        switch self.state {
+        case .active:
+            do {
+                try self.strategy.restoreImplementation()
+                self.state = .pending
+            } catch {
+                self.state = .failed
+                throw error
+            }
+        case .failed:
+            throw InterposeError.hookInFailedState
+        case .pending:
+            return
         }
     }
 

Sources/InterposeKit/InterposeError.swift

@@ -2,6 +2,9 @@ import Foundation
 
 public enum InterposeError: Error {
 
+    /// A hook operation failed and the hook is no longer usable.
+    case hookInFailedState
+    
     /// No instance method found for the selector on the specified class.
     ///
     /// This typically occurs when mistyping a stringified selector or attempting to interpose
@@ -165,6 +168,14 @@ extension InterposeError: Equatable {
             default:
                 return false
             }
+            
+        case .hookInFailedState:
+            switch rhs {
+            case .hookInFailedState:
+                return true
+            default:
+                return false
+            }
         }
     }
 }

Tests/InterposeKitTests/ClassHookTests.swift

@@ -293,6 +293,11 @@ final class ClassHookTests: XCTestCase {
             hook.debugDescription,
             #"^Failed hook for -\[ExampleClass doSomething\]$"#
         )
+        
+        XCTAssertThrowsError(
+            try hook.revert(),
+            expected: InterposeError.hookInFailedState
+        )
     }
 
     func testCleanUp_implementationPreserved() throws {