Only print "no difference detected" when diff output is the same (#85)

* Only print "no difference detected" when diff output is the same

* wip

* fix for Xcode 13.4.1

Author: stephencelis

Sources/CustomDump/Diff.swift

@@ -94,32 +94,34 @@ public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String
 
       guard !isMirrorEqual(lhsChildren, rhsChildren)
       else {
-        print(
-          "// Not equal but no difference detected:"
-            .indenting(by: indent)
-            .indenting(with: format.both + " "),
-          to: &out
+        let lhsDump = _customDump(
+          lhs,
+          name: lhsName,
+          indent: indent,
+          isRoot: false,
+          maxDepth: 0
         )
-        print(
-          _customDump(
-            lhs,
-            name: lhsName,
-            indent: indent,
-            isRoot: false,
-            maxDepth: 0
+        let rhsDump = _customDump(
+          rhs,
+          name: rhsName,
+          indent: indent,
+          isRoot: false,
+          maxDepth: 0
+        )
+        if lhsDump == rhsDump {
+          print(
+            "// Not equal but no difference detected:"
+              .indenting(by: indent)
+              .indenting(with: format.both + " "),
+            to: &out
           )
-          .indenting(with: format.first + " "),
+        }
+        print(
+          lhsDump.indenting(with: format.first + " "),
           to: &out
         )
         print(
-          _customDump(
-            rhs,
-            name: rhsName,
-            indent: indent,
-            isRoot: false,
-            maxDepth: 0
-          )
-          .indenting(with: format.second + " "),
+          rhsDump.indenting(with: format.second + " "),
           terminator: "",
           to: &out
         )

Tests/CustomDumpTests/DiffTests.swift

@@ -1066,25 +1066,6 @@ final class DiffTests: XCTestCase {
   }
 
   func testCustomDictionary() {
-    struct Stack: CustomDumpReflectable {
-      var elements: [(ID, String)]
-
-      struct ID: CustomDumpStringConvertible, Hashable {
-        let rawValue: Int
-        var customDumpDescription: String {
-          "#\(self.rawValue)"
-        }
-      }
-
-      var customDumpMirror: Mirror {
-        Mirror(
-          self,
-          unlabeledChildren: self.elements,
-          displayStyle: .dictionary
-        )
-      }
-    }
-
     XCTAssertEqual(
       String(customDumping: Stack(elements: [(.init(rawValue: 0), "Hello")])),
       """
@@ -1106,5 +1087,51 @@ final class DiffTests: XCTestCase {
         ]
       """
     )
+
+    struct Child {
+      struct State: Equatable {}
+    }
+    struct Parent {
+      struct State: Equatable {
+        var children: Stack<Child.State>
+      }
+    }
+    XCTAssertNoDifference(
+      diff(
+        Parent.State(children: Stack(elements: [(.init(rawValue: 0), Child.State())])),
+        Parent.State(children: Stack(elements: [(.init(rawValue: 1), Child.State())]))
+      ),
+      """
+        DiffTests.Parent.State(
+          children: [
+      -     #0: DiffTests.Child.State()
+      +     #1: DiffTests.Child.State()
+          ]
+        )
+      """
+    )
+  }
+}
+
+fileprivate struct Stack<State: Equatable>: CustomDumpReflectable, Equatable {
+  static func == (lhs: Self, rhs: Self) -> Bool {
+    zip(lhs.elements, rhs.elements ).allSatisfy(==)
+  }
+
+  var elements: [(ID, State)]
+
+  struct ID: CustomDumpStringConvertible, Hashable {
+    let rawValue: Int
+    var customDumpDescription: String {
+      "#\(self.rawValue)"
+    }
+  }
+
+  var customDumpMirror: Mirror {
+    Mirror(
+      self,
+      unlabeledChildren: self.elements,
+      displayStyle: .dictionary
+    )
   }
 }