[stdlib] Availability macros don't work in inlinable code 😩

Author: lorentey

stdlib/public/core/Assert.swift

@@ -311,7 +311,8 @@ internal func _internalInvariant_5_1(
   // FIXME: The below won't run the assert on 5.1 stdlib if testing on older
   // OSes, which means that testing may not test the assertion. We need a real
   // solution to this.
-  guard #available(SwiftStdlib 5.1, *) else { return }
+  guard #available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *) //SwiftStdlib 5.1
+  else { return }
   _internalInvariant(condition(), message, file: file, line: line)
 #endif
 }

stdlib/public/core/FloatingPoint.swift

@@ -1895,7 +1895,8 @@ extension BinaryFloatingPoint {
     switch (Source.exponentBitCount, Source.significandBitCount) {
 #if !((os(macOS) || targetEnvironment(macCatalyst)) && arch(x86_64))
     case (5, 10):
-      guard #available(SwiftStdlib 5.3, *) else {
+      guard #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) //SwiftStdlib 5.3
+      else {
         // Convert signaling NaN to quiet NaN by multiplying by 1.
         self = Self._convert(from: value).value * 1
         break

stdlib/public/core/FloatingPointParsing.swift.gyb

@@ -165,7 +165,7 @@ extension ${Self}: LosslessStringConvertible {
   %if bits == 16:
     self.init(Substring(text))
   %else:
-    if #available(SwiftStdlib 5.3, *) {
+    if #available(macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0, *) { //SwiftStdlib 5.3
       self.init(Substring(text))
     } else {
       self = 0.0

stdlib/public/core/TemporaryAllocation.swift

@@ -89,7 +89,8 @@ internal func _isStackAllocationSafe(byteCount: Int, alignment: Int) -> Bool {
 
   // Finally, take a slow path through the standard library to see if the
   // current environment can accept a larger stack allocation.
-  guard #available(SwiftStdlib 5.6, *) else {
+  guard #available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *) //SwiftStdlib 5.6
+  else {
     return false
   }
   return swift_stdlib_isStackAllocationSafe(byteCount, alignment)