Revise doc comments and add test

Author: xwu

stdlib/public/core/IntegerParsing.swift

@@ -102,7 +102,7 @@ extension FixedWidthInteger {
   ///
   /// The string passed as `text` may begin with a plus or minus sign character
   /// (`+` or `-`), followed by one or more numeric digits (`0-9`) or letters
-  /// (`a-z` or `A-Z`). The string is case-insensitive.
+  /// (`a-z` or `A-Z`). Parsing of the string is case insensitive.
   ///
   ///     let x = Int("123")
   ///     // x == 123
@@ -116,7 +116,7 @@ extension FixedWidthInteger {
   ///     // z == 123
   ///
   /// If `text` is in an invalid format or contains characters that are out of
-  /// range for the given `radix`, or if the value it denotes in the given
+  /// bounds for the given `radix`, or if the value it denotes in the given
   /// `radix` is not representable, the result is `nil`. For example, the
   /// following conversions result in `nil`:
   ///
@@ -171,8 +171,9 @@ extension FixedWidthInteger {
   ///     Int(" 100")                       // Includes whitespace
   ///     Int("21-50")                      // Invalid format
   ///     Int("ff6600")                     // Characters out of bounds
+  ///     Int("10000000000000000000000000") // Out of range
   ///
-  /// - Parameter description: The ASCII representation of a number in base 10.
+  /// - Parameter description: The ASCII representation of a number.
   @_semantics("optimize.sil.specialize.generic.partial.never")
   @inline(__always)
   public init?(_ description: String) {

test/stdlib/Integers.swift.gyb

@@ -364,6 +364,21 @@ tests.test("extendingOrTruncating") {
   expectEqual(129, UInt8(extendingOrTruncating: 129 + 1024 as UDWord))
 }
 
+tests.test("Parsing/LosslessStringConvertible") {
+  func _toArray<T: LosslessStringConvertible>(_ text: String) -> [T] {
+    return text.split(separator: " ").map { T(String($0)) }.flatMap { $0 }
+  }
+
+  let i: [Int] = _toArray("1 2 3")
+  expectEqual(i.count, 3)
+  expectEqual(i[0], 1)
+  expectEqual(i[1], 2)
+  expectEqual(i[2], 3)
+
+  let j: [Int] = _toArray("21-50 ff6600 10000000000000000000000000")
+  expectEqual(j.count, 0)
+}
+
 tests.test("HeterogeneousEquality") {
   expectTrue(-1 as DWord != UDWord.max)
   expectTrue(DWord.max == UDWord.max / 2)