From fb15e69cd5131c00193467c95632f05e75e81ccd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Rodr=C3=ADguez=20Troiti=C3=B1o?=
 <danielrodriguez@fb.com>
Date: Fri, 31 Aug 2018 15:37:49 -0700
Subject: [PATCH] Fix DateFormatter behaviour for nil locale and timeZone.

The locale and timeZone properties of DateFormatter seems to be "null
resetteable" in macOS, but the Swift Foundation behaviour differs.

Before this patch, setting locale to nil would segfault the program the
next time the formatter is used, while timeZone will incorrectly return
nil. After this patch a nil locale will simply reset to the current
locale and a nil timeZone will reset to the system one.

The tests check that the initial defaults are also correctly set.
---
 Foundation/DateFormatter.swift         | 26 +++++++++++++++++++++++---
 TestFoundation/TestDateFormatter.swift | 26 ++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/Foundation/DateFormatter.swift b/Foundation/DateFormatter.swift
index 1c604ac8f5..69644c0fb6 100644
--- a/Foundation/DateFormatter.swift
+++ b/Foundation/DateFormatter.swift
@@ -91,7 +91,7 @@ open class DateFormatter : Formatter {
 
     internal func _setFormatterAttributes(_ formatter: CFDateFormatter) {
         _setFormatterAttribute(formatter, attributeName: kCFDateFormatterIsLenient, value: isLenient._cfObject)
-        _setFormatterAttribute(formatter, attributeName: kCFDateFormatterTimeZone, value: timeZone?._cfObject)
+        _setFormatterAttribute(formatter, attributeName: kCFDateFormatterTimeZone, value: _timeZone?._cfObject)
         if let ident = _calendar?.identifier {
             _setFormatterAttribute(formatter, attributeName: kCFDateFormatterCalendarName, value: Calendar._toNSCalendarIdentifier(ident).rawValue._cfObject)
         } else {
@@ -160,11 +160,31 @@ open class DateFormatter : Formatter {
         }
     }
 
-    /*@NSCopying*/ open var locale: Locale! = .current { willSet { _reset() } }
+    /*@NSCopying*/ internal var _locale: Locale? { willSet { _reset() } }
+    open var locale: Locale! {
+        get {
+            guard let locale = _locale else { return .current }
+            return locale
+        }
+        set {
+            _locale = newValue
+        }
+    }
 
     open var generatesCalendarDates = false { willSet { _reset() } }
 
-    /*@NSCopying*/ open var timeZone: TimeZone! = NSTimeZone.system { willSet { _reset() } }
+    /*@NSCopying*/ internal var _timeZone: TimeZone? { willSet { _reset() } }
+    open var timeZone: TimeZone! {
+        get {
+            guard let timeZone = _timeZone else {
+                return (CFDateFormatterCopyProperty(_cfObject, kCFDateFormatterTimeZone) as! NSTimeZone)._swiftObject
+            }
+            return timeZone
+        }
+        set {
+            _timeZone = timeZone
+        }
+    }
 
     /*@NSCopying*/ internal var _calendar: Calendar! { willSet { _reset() } }
     open var calendar: Calendar! {
diff --git a/TestFoundation/TestDateFormatter.swift b/TestFoundation/TestDateFormatter.swift
index 2ba14339ae..98c636f620 100644
--- a/TestFoundation/TestDateFormatter.swift
+++ b/TestFoundation/TestDateFormatter.swift
@@ -22,6 +22,8 @@ class TestDateFormatter: XCTestCase {
             ("test_customDateFormat", test_customDateFormat),
             ("test_setLocalizedDateFormatFromTemplate", test_setLocalizedDateFormatFromTemplate),
             ("test_dateFormatString", test_dateFormatString),
+            ("test_setLocaleToNil", test_setLocaleToNil),
+            ("test_setTimeZoneToNil", test_setTimeZoneToNil),
         ]
     }
     
@@ -330,4 +332,28 @@ class TestDateFormatter: XCTestCase {
             XCTAssertEqual(f.dateFormat, dateFormat)
         }
     }
+
+    func test_setLocaleToNil() {
+        let f = DateFormatter()
+        // Locale should be the current one by default
+        XCTAssertEqual(f.locale, .current)
+
+        f.locale = nil
+
+        // Locale should go back to current.
+        XCTAssertEqual(f.locale, .current)
+
+        // A nil locale should not crash a subsequent operation
+        let result: String? = f.string(from: Date())
+        XCTAssertNotNil(result)
+    }
+
+    func test_setTimeZoneToNil() {
+        let f = DateFormatter()
+        // Time zone should be the system one by default.
+        XCTAssertEqual(f.timeZone, NSTimeZone.system)
+        f.timeZone = nil
+        // Time zone should go back to the system one.
+        XCTAssertEqual(f.timeZone, NSTimeZone.system)
+    }
 }