[squash] Use a pair integers rather than a single Double

Author: lorentey

stdlib/public/core/Availability.swift

@@ -50,34 +50,46 @@ public func _stdlib_isOSVersionAtLeast(
 /// Returns the version number for the Swift Standard Library that the code
 /// calling this was originally compiled with.
 ///
-/// The version number is an arbitrary `Double` value that is monotonically
-/// increasing between toolchain releases. It does not correlate with toolchain
-/// or OS version numbers, and it is not a semantic version number.
-@_alwaysEmitIntoClient @_transparent
-public var _stdlibStaticVersion: Double {
-  return 1001.0
+/// The version number is an arbitrary pair of integers, with lexicographical
+/// ordering. Version numbers of (logically) successive stdlib releases form a
+/// monotonically increasing sequence; i.e., versions should not decrease, but
+/// they are allowed to stay the same.
+///
+/// The two integer components are not intended to correspond to major or minor
+/// versions in a semantic versioning scheme. Neither do they correlate with
+/// toolchain or OS version numbers.
+@_alwaysEmitIntoClient
+public var _stdlibStaticVersion: (Int, Int) {
+  // On the master branch, increment the first number.
+  // On release branches, increment the second number.
+  return (1001, 0)
 }
 
 /// Returns the version number for the Swift Standard Library that is currently
 /// loaded.
 ///
-/// The version number is an arbitrary `Double` value that is monotonically
-/// increasing between toolchain releases. It does not correlate with toolchain
-/// or OS version numbers, and it is not a semantic version number.
+/// The version number is an arbitrary pair of integers, with lexicographical
+/// ordering. Version numbers of (logically) successive stdlib releases form a
+/// monotonically increasing sequence; i.e., versions should not decrease, but
+/// they are allowed to stay the same.
+///
+/// The two integer components are not intended to correspond to major or minor
+/// versions in a semantic versioning scheme. Neither do they correlate with
+/// toolchain or OS version numbers.
 @_alwaysEmitIntoClient // Introduced in 5.1
-public var _stdlibDynamicVersion: Double {
+public var _stdlibDynamicVersion: (Int, Int) {
   if #available(macOS 9999, iOS 9999, tvOS 9999, watchOS 9999, *) {
     return _stdlibOpaqueVersion
   }
   else {
     // When linked with the 5.0 stdlib, we return this default value.
-    return 1000.0
+    return (1000, 0)
   }
 }
 
 @available(macOS 9999, iOS 9999, tvOS 9999, watchOS 9999, *)
 @usableFromInline
-internal var _stdlibOpaqueVersion: Double {
+internal var _stdlibOpaqueVersion: (Int, Int) {
   return _stdlibStaticVersion
 }