Optimize removing nonexistent attributes in AttributedString (#1150)

Author: jmschonfeld

Benchmarks/Benchmarks/AttributedString/BenchmarkAttributedString.swift

@@ -432,6 +432,12 @@ let benchmarks = {
         blackHole(hasher.finalize())
     }
 
+    Benchmark("removeNonExistentAttribute") { benchmark in
+        var str = manyAttributesString
+        str.testBool = nil
+        blackHole(str)
+    }
+    
     struct TestAttribute : AttributedStringKey {
         static var name = "0"
         typealias Value = Int

Benchmarks/Package.swift

@@ -88,7 +88,7 @@ switch usePackage {
 
 let package = Package(
     name: "benchmarks",
-    platforms: [.macOS("13.3"), .iOS("16.4"), .tvOS("16.4"), .watchOS("9.4")], // Should match parent project
+    platforms: [.macOS("15"), .iOS("18"), .tvOS("18"), .watchOS("11")], // Should match parent project
     dependencies: packageDependency,
     targets: [
         .executableTarget(

Sources/FoundationEssentials/AttributedString/AttributedString+Guts.swift

@@ -391,7 +391,7 @@ extension AttributedString.Guts {
     ) where K.Value: Sendable {
         let utf8Range = unicodeScalarRange(roundingDown: range)._utf8OffsetRange
         self.runs(in: utf8Range).updateEach { attributes, range, mutated in
-            attributes[K.self] = nil
+            mutated = attributes.removeValue(forKey: K.self)
         }
         if K.runBoundaries != nil {
             self.enforceAttributeConstraintsAfterMutation(

Sources/FoundationEssentials/AttributedString/AttributedStringAttributeStorage.swift

@@ -216,6 +216,12 @@ extension AttributedString._AttributeStorage {
             _attributeModified(attributeName, old: oldValue, new: newValue)
         }
     }
+    
+    mutating func removeValue<T: AttributedStringKey>(forKey: T.Type) -> Bool {
+        let oldValue = self.contents.removeValue(forKey: T.name)
+        _attributeModified(T.name, old: oldValue, new: nil)
+        return oldValue != nil
+    }
 
     internal mutating func mergeIn(_ other: Self, mergePolicy: AttributeMergePolicy = .keepNew) {
         for (key, value) in other.contents {