Improve performance for calling Locale.identifier from NS/CFLocale (#1051)

- use @_effects(releasenone) to solemnly swear to the compiler that we won't release anything inside these getters, eliminating refcounting to call them

- micro-optimize identifierDoesNotRequireSpecialCaseHandling, allowing us to delete the cache of it without regressing perf

On the test app this goes from "so slow I didn't bother to see how long it takes to finish" to "finishes in around 1 second"

Resolves 137885111

Co-authored-by: David (Swift) Smith <[email protected]>

Author: itingliu

Sources/FoundationEssentials/Locale/Locale.swift

@@ -232,7 +232,10 @@ public struct Locale : Hashable, Equatable, Sendable {
 
     /// Returns the identifier of the locale.
     public var identifier: String {
-        _locale.identifier
+        @_effects(releasenone)
+        get {
+            _locale.identifier
+        }
     }
 
     /// Returns the language code of the locale, or nil if has none.
@@ -743,12 +746,15 @@ public struct Locale : Hashable, Equatable, Sendable {
     /// - "el": Greek
     /// For all other locales such as en_US, this is `false`.
     package static func identifierDoesNotRequireSpecialCaseHandling(_ identifier: String) -> Bool {
-        guard identifier.count >= 2 else { return true }
-
-        let first = identifier.prefix(2)
-        switch first {
-        case "az", "lt", "tr", "nl", "el":
-            return false // Does require special handling
+        var byteIterator = identifier.utf8.makeIterator()
+        switch (byteIterator.next(), byteIterator.next()) {
+        case
+            (UInt8(ascii: "a"), UInt8(ascii: "z")),
+            (UInt8(ascii: "l"), UInt8(ascii: "t")),
+            (UInt8(ascii: "t"), UInt8(ascii: "r")),
+            (UInt8(ascii: "n"), UInt8(ascii: "l")),
+            (UInt8(ascii: "e"), UInt8(ascii: "l")):
+            return false
         default:
             return true // Does not require special handling
         }

Sources/FoundationEssentials/Locale/Locale_Unlocalized.swift

@@ -257,10 +257,6 @@ internal final class _LocaleUnlocalized : _LocaleProtocol, @unchecked Sendable {
         identifier
     }
 
-    var doesNotRequireSpecialCaseHandling: Bool {
-        true
-    }
-    
 #if FOUNDATION_FRAMEWORK
     func pref(for key: String) -> Any? {
         nil

Sources/FoundationInternationalization/Locale/Locale_ObjC.swift

@@ -218,7 +218,6 @@ extension NSLocale {
 
     @objc(_doesNotRequireSpecialCaseHandling)
     func _doesNotRequireSpecialCaseHandling() -> Bool {
-        // Unable to use cached locale; create a new one. Subclass `_NSSwiftLocale` implements a better version
         Locale.identifierDoesNotRequireSpecialCaseHandling(localeIdentifier)
     }
 }
@@ -228,12 +227,9 @@ extension NSLocale {
 @objc(_NSSwiftLocale)
 internal class _NSSwiftLocale: _NSLocaleBridge, @unchecked Sendable {
     var locale: Locale
-    var doesNotRequireSpecialHandling: Bool?
 
     internal init(_ locale: Locale) {
         self.locale = locale
-        // We cannot call `locale.identifier` to get the actual value here because that could trigger a recursive call into  LocaleCache. If we enter from this `init` just lazily fetch the variable.
-        self.doesNotRequireSpecialHandling = nil
 
         // The superclass does not care at all what the identifier is. Avoid a potentially recursive call into the Locale cache here by just using an empty string.
         super.init(localeIdentifier: "")
@@ -251,7 +247,6 @@ internal class _NSSwiftLocale: _NSLocaleBridge, @unchecked Sendable {
 
     override init(localeIdentifier string: String) {
         self.locale = Locale(identifier: string)
-        self.doesNotRequireSpecialHandling = Locale.identifierDoesNotRequireSpecialCaseHandling(string)
         super.init(localeIdentifier: "")
     }
 
@@ -271,7 +266,6 @@ internal class _NSSwiftLocale: _NSLocaleBridge, @unchecked Sendable {
         }
 
         locale = Locale(identifier: ident)
-        doesNotRequireSpecialHandling = Locale.identifierDoesNotRequireSpecialCaseHandling(ident)
 
         // Must call a DI; this one does nothing so it's safe to call here.
         super.init(localeIdentifier: "")
@@ -366,7 +360,10 @@ internal class _NSSwiftLocale: _NSLocaleBridge, @unchecked Sendable {
     // MARK: -
 
     override var localeIdentifier: String {
-        locale.identifier
+        @_effects(releasenone)
+        get {
+            return locale.identifier
+        }
     }
 
     @available(macOS, deprecated: 13) @available(iOS, deprecated: 16) @available(tvOS, deprecated: 16) @available(watchOS, deprecated: 9)
@@ -526,12 +523,9 @@ internal class _NSSwiftLocale: _NSLocaleBridge, @unchecked Sendable {
         return _NSSwiftLocale(copy)
     }
 
+    @_effects(releasenone)
     override func _doesNotRequireSpecialCaseHandling() -> Bool {
-        if let doesNotRequireSpecialHandling {
-            return doesNotRequireSpecialHandling
-        }
-
-        return Locale.identifierDoesNotRequireSpecialCaseHandling(locale.identifier)
+        Locale.identifierDoesNotRequireSpecialCaseHandling(locale.identifier)
     }
 }