Add checks that the endpoints of partial ranges are not-NaN.

stdlib/public/core/ClosedRange.swift

@@ -330,10 +330,12 @@ extension Comparable {
   /// - Parameters:
   ///   - minimum: The lower bound for the range.
   ///   - maximum: The upper bound for the range.
+  ///
+  /// - Precondition: `minimum <= maximum`.
   @_transparent
   public static func ... (minimum: Self, maximum: Self) -> ClosedRange<Self> {
     _precondition(
-      minimum <= maximum, "Can't form Range with upperBound < lowerBound")
+      minimum <= maximum, "Range requires lowerBound <= upperBound")
     return ClosedRange(uncheckedBounds: (lower: minimum, upper: maximum))
   }
 }

stdlib/public/core/Range.swift

@@ -723,10 +723,12 @@ extension Comparable {
   /// - Parameters:
   ///   - minimum: The lower bound for the range.
   ///   - maximum: The upper bound for the range.
+  ///
+  /// - Precondition: `minimum <= maximum`.
   @_transparent
   public static func ..< (minimum: Self, maximum: Self) -> Range<Self> {
     _precondition(minimum <= maximum,
-      "Can't form Range with upperBound < lowerBound")
+      "Range requires lowerBound <= upperBound")
     return Range(uncheckedBounds: (lower: minimum, upper: maximum))
   }
 
@@ -752,8 +754,12 @@ extension Comparable {
   ///     // Prints "[10, 20, 30]"
   ///
   /// - Parameter maximum: The upper bound for the range.
+  ///
+  /// - Precondition: `maximum` must compare equal to itself (i.e. cannot be NaN).
   @_transparent
   public static prefix func ..< (maximum: Self) -> PartialRangeUpTo<Self> {
+    _precondition(maximum == maximum,
+      "Range cannot have an unordered upper bound.")
     return PartialRangeUpTo(maximum)
   }
 
@@ -779,8 +785,12 @@ extension Comparable {
   ///     // Prints "[10, 20, 30, 40]"
   ///
   /// - Parameter maximum: The upper bound for the range.
+  ///
+  /// - Precondition: `maximum` must compare equal to itself (i.e. cannot be NaN).
   @_transparent
   public static prefix func ... (maximum: Self) -> PartialRangeThrough<Self> {
+    _precondition(maximum == maximum,
+      "Range cannot have an unordered upper bound.")
     return PartialRangeThrough(maximum)
   }
 
@@ -806,8 +816,12 @@ extension Comparable {
   ///     // Prints "[40, 50, 60, 70]"
   ///
   /// - Parameter minimum: The lower bound for the range.
+  ///
+  /// - Precondition: `minimum` must compare equal to itself (i.e. cannot be NaN).
   @_transparent
   public static postfix func ... (minimum: Self) -> PartialRangeFrom<Self> {
+    _precondition(minimum == minimum,
+      "Range cannot have an unordered lower bound.")
     return PartialRangeFrom(minimum)
   }
 }

test/stdlib/RangeTraps.swift

@@ -74,7 +74,47 @@ RangeTraps.test("CountablePartialRangeFrom")
     _ = it.next()
 }
 
+RangeTraps.test("nanLowerBound")
+  .code {
+  expectCrashLater()
+  _ = Double.nan ... 0
+}
+
+RangeTraps.test("nanUpperBound")
+  .code {
+  expectCrashLater()
+  _ = 0 ... Double.nan
+}
+
+RangeTraps.test("nanLowerBoundPartial")
+  .code {
+  expectCrashLater()
+  _ = Double.nan ..< 0
+}
+
+RangeTraps.test("nanUpperBoundPartial")
+  .code {
+  expectCrashLater()
+  _ = 0 ..< Double.nan
+}
 
+RangeTraps.test("fromNaN")
+  .code {
+  expectCrashLater()
+  _ = Double.nan...
+}
+
+RangeTraps.test("toNaN")
+  .code {
+  expectCrashLater()
+  _ = ..<Double.nan
+}
+
+RangeTraps.test("throughNaN")
+  .code {
+  expectCrashLater()
+  _ = ...Double.nan
+}
 
 runAllTests()
 

validation-test/stdlib/Range.swift.gyb

@@ -401,7 +401,7 @@ ${TestSuite}.test("Equatable") {
 
 ${TestSuite}.test("'${op}' traps when upperBound < lowerBound")
   .crashOutputMatches(_isDebugAssertConfiguration() ?
-    "Can't form Range with upperBound < lowerBound" : "")
+    "Range requires lowerBound <= upperBound" : "")
   .code {
   let _1 = ${Bound}(1)
   let _2 = ${Bound}(2)