NSDateComponents.hash: Fix arithmetic overflows

Author: lorentey

Foundation/NSCalendar.swift

@@ -1276,49 +1276,94 @@ open class NSDateComponents : NSObject, NSCopying, NSSecureCoding {
     public override init() {
         super.init()
     }
-    
+
     open override var hash: Int {
-        var calHash = 0
-        if let cal = calendar {
-            calHash = cal.hashValue
-        }
-        if let tz = timeZone {
-            calHash ^= tz.hashValue
-        }
-        var y = year
-        if NSDateComponentUndefined == y {
-            y = 0
-        }
-        var m = month
-        if NSDateComponentUndefined == m {
-            m = 0
-        }
-        var d = day
-        if NSDateComponentUndefined == d {
-            d = 0
-        }
-        var h = hour
-        if NSDateComponentUndefined == h {
-            h = 0
-        }
-        var mm = minute
-        if NSDateComponentUndefined == mm {
-            mm = 0 
-        }
-        var s = second
-        if NSDateComponentUndefined == s {
-            s = 0 
-        }
-        var yy = yearForWeekOfYear
-        if NSDateComponentUndefined == yy {
-            yy = 0
-        }
-        return calHash + (32832013 * (y + yy) + 2678437 * m + 86413 * d + 3607 * h + 61 * mm + s) + (41 * weekOfYear + 11 * weekOfMonth + 7 * weekday + 3 * weekdayOrdinal + quarter) * (1 << 5)
+        var hasher = Hasher()
+        var mask = 0
+        // The list of fields fed to the hasher here must be exactly
+        // the same as the ones compared in isEqual(_:) (modulo
+        // ordering).
+        //
+        // Given that NSDateComponents instances usually only have a
+        // few fields present, it makes sense to only hash those, as
+        // an optimization. We keep track of the fields hashed in the
+        // mask value, which we also feed to the hasher to make sure
+        // any two unequal values produce different hash encodings.
+        //
+        // FIXME: Why not just feed _values, calendar & timeZone to
+        // the hasher?
+        if let calendar = calendar {
+            hasher.combine(calendar)
+            mask |= 1 << 0
+        }
+        if let timeZone = timeZone {
+            hasher.combine(timeZone)
+            mask |= 1 << 1
+        }
+        if era != NSDateComponentUndefined {
+            hasher.combine(era)
+            mask |= 1 << 2
+        }
+        if year != NSDateComponentUndefined {
+            hasher.combine(year)
+            mask |= 1 << 3
+        }
+        if quarter != NSDateComponentUndefined {
+            hasher.combine(quarter)
+            mask |= 1 << 4
+        }
+        if month != NSDateComponentUndefined {
+            hasher.combine(month)
+            mask |= 1 << 5
+        }
+        if day != NSDateComponentUndefined {
+            hasher.combine(day)
+            mask |= 1 << 6
+        }
+        if hour != NSDateComponentUndefined {
+            hasher.combine(hour)
+            mask |= 1 << 7
+        }
+        if minute != NSDateComponentUndefined {
+            hasher.combine(minute)
+            mask |= 1 << 8
+        }
+        if second != NSDateComponentUndefined {
+            hasher.combine(second)
+            mask |= 1 << 9
+        }
+        if nanosecond != NSDateComponentUndefined {
+            hasher.combine(nanosecond)
+            mask |= 1 << 10
+        }
+        if weekOfYear != NSDateComponentUndefined {
+            hasher.combine(weekOfYear)
+            mask |= 1 << 11
+        }
+        if weekOfMonth != NSDateComponentUndefined {
+            hasher.combine(weekOfMonth)
+            mask |= 1 << 12
+        }
+        if yearForWeekOfYear != NSDateComponentUndefined {
+            hasher.combine(yearForWeekOfYear)
+            mask |= 1 << 13
+        }
+        if weekday != NSDateComponentUndefined {
+            hasher.combine(weekday)
+            mask |= 1 << 14
+        }
+        if weekdayOrdinal != NSDateComponentUndefined {
+            hasher.combine(weekdayOrdinal)
+            mask |= 1 << 15
+        }
+        hasher.combine(isLeapMonth)
+        hasher.combine(mask)
+        return hasher.finalize()
     }
-    
+
     open override func isEqual(_ object: Any?) -> Bool {
         guard let other = object as? NSDateComponents else { return false }
-        
+        // FIXME: Why not just compare _values, calendar & timeZone?
         return self === other
             || (era == other.era
                 && year == other.year

TestFoundation/TestCalendar.swift

@@ -198,10 +198,26 @@ class TestNSDateComponents: XCTestCase {
 
     static var allTests: [(String, (TestNSDateComponents) -> () throws -> Void)] {
         return [
+            ("test_hash", test_hash),
             ("test_copyNSDateComponents", test_copyNSDateComponents),
         ]
     }
 
+    func test_hash() {
+        let c1 = NSDateComponents()
+        c1.year = 2018
+        c1.month = 8
+        c1.day = 1
+
+        let c2 = NSDateComponents()
+        c2.year = 2018
+        c2.month = 8
+        c2.day = 1
+
+        XCTAssertEqual(c1, c2)
+        XCTAssertEqual(c1.hash, c2.hash)
+    }
+
     func test_copyNSDateComponents() {
         let components = NSDateComponents()
         components.year = 1987