Simplify conditional compilation

Author: dtchepak

src/NSubstitute/Extensions/ExceptionExtensions.cs

@@ -1,9 +1,7 @@
 using System;
 using System.Linq;
 using System.Reflection;
-#if !NET45
 using System.Threading.Tasks;
-#endif
 using NSubstitute.Core;
 
 // Disable nullability for client API, so it does not affect clients.
@@ -73,15 +71,14 @@ public static ConfiguredCall ThrowsForAnyArgs<TException>(this object value)
         public static ConfiguredCall ThrowsForAnyArgs(this object value, Func<CallInfo, Exception> createException) =>
             value.ReturnsForAnyArgs(ci => throw createException(ci));
 
-#if !NET45
         /// <summary>
         /// Throw an exception for this call.
         /// </summary>
         /// <param name="value"></param>
         /// <param name="ex">Exception to throw</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsync(this Task value, Exception ex) =>
-            value.Returns(_ => Task.FromException(ex));
+            value.Returns(_ => TaskFromException(ex));
 
         /// <summary>
         /// Throw an exception for this call.
@@ -90,7 +87,7 @@ public static ConfiguredCall ThrowsAsync(this Task value, Exception ex) =>
         /// <param name="ex">Exception to throw</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsync<T>(this Task<T> value, Exception ex) =>
-            value.Returns(_ => Task.FromException<T>(ex));
+            value.Returns(_ => TaskFromException<T>(ex));
 
         /// <summary>
         /// Throw an exception of the given type for this call.
@@ -111,7 +108,7 @@ public static ConfiguredCall ThrowsAsync<TException>(this Task value)
         /// <param name="createException">Func creating exception object</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsync(this Task value, Func<CallInfo, Exception> createException) =>
-            value.Returns(ci => Task.FromException(createException(ci)));
+            value.Returns(ci => TaskFromException(createException(ci)));
 
         /// <summary>
         /// Throw an exception for this call, as generated by the specified function.
@@ -120,7 +117,7 @@ public static ConfiguredCall ThrowsAsync(this Task value, Func<CallInfo, Excepti
         /// <param name="createException">Func creating exception object</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsync<T>(this Task<T> value, Func<CallInfo, Exception> createException) =>
-            value.Returns(ci => Task.FromException<T>(createException(ci)));
+            value.Returns(ci => TaskFromException<T>(createException(ci)));
 
         /// <summary>
         /// Throw an exception for this call made with any arguments.
@@ -129,7 +126,7 @@ public static ConfiguredCall ThrowsAsync<T>(this Task<T> value, Func<CallInfo, E
         /// <param name="ex">Exception to throw</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsyncForAnyArgs(this Task value, Exception ex) =>
-            value.ReturnsForAnyArgs(_ => Task.FromException(ex));
+            value.ReturnsForAnyArgs(_ => TaskFromException(ex));
 
         /// <summary>
         /// Throw an exception for this call made with any arguments.
@@ -138,7 +135,7 @@ public static ConfiguredCall ThrowsAsyncForAnyArgs(this Task value, Exception ex
         /// <param name="ex">Exception to throw</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsyncForAnyArgs<T>(this Task<T> value, Exception ex) =>
-            value.ReturnsForAnyArgs(_ => Task.FromException<T>(ex));
+            value.ReturnsForAnyArgs(_ => TaskFromException<T>(ex));
 
         /// <summary>
         /// Throws an exception of the given type for this call made with any arguments.
@@ -159,7 +156,7 @@ public static ConfiguredCall ThrowsAsyncForAnyArgs<TException>(this Task value)
         /// <param name="createException">Func creating exception object</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsyncForAnyArgs(this Task value, Func<CallInfo, Exception> createException) =>
-            value.ReturnsForAnyArgs(ci => Task.FromException(createException(ci)));
+            value.ReturnsForAnyArgs(ci => TaskFromException(createException(ci)));
 
         /// <summary>
         /// Throws an exception for this call made with any arguments, as generated by the specified function.
@@ -168,7 +165,7 @@ public static ConfiguredCall ThrowsAsyncForAnyArgs(this Task value, Func<CallInf
         /// <param name="createException">Func creating exception object</param>
         /// <returns></returns>
         public static ConfiguredCall ThrowsAsyncForAnyArgs<T>(this Task<T> value, Func<CallInfo, Exception> createException) =>
-            value.ReturnsForAnyArgs(ci => Task.FromException<T>(createException(ci)));
+            value.ReturnsForAnyArgs(ci => TaskFromException<T>(createException(ci)));
 
 #if NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_1_OR_GREATER
         /// <summary>
@@ -245,8 +242,23 @@ private static object FromException(object value, Exception exception)
                 return specificFromExceptionMethod.Invoke(null, new object[] {exception});
             }
 
-            return Task.FromException(exception);
+            return TaskFromException(exception);
+        }
+
+        private static Task TaskFromException(Exception ex)  {
+#if NET45
+            return new Task(() => throw ex);
+#endif
+            return Task.FromException(ex);
         }
+
+        private static Task<T> TaskFromException<T>(Exception ex)
+        {
+#if NET45
+            return new Task<T>(() => throw ex);
 #endif
+            return Task<T>.FromException<T>(ex);
+        }
+
     }
 }