Introduce an ABI checker that diffs symbols

back to x86_64

Author: Azoy

stdlib/public/core/Algorithm.swift

@@ -158,3 +158,8 @@ extension EnumeratedSequence: Sequence {
     return Iterator(_base: _base.makeIterator())
   }
 }
+
+@available(SwiftStdlib 5.11, *)
+public func hello() {
+  print("hello!")
+}

stdlib/public/core/LegacyABI.swift

@@ -13,13 +13,13 @@
 // This file contains non-API (or underscored) declarations that are needed to
 // be kept around for ABI compatibility
 
-extension Unicode.UTF16 {
-  @available(*, unavailable, renamed: "Unicode.UTF16.isASCII")
-  @inlinable
-  public static func _isASCII(_ x: CodeUnit) -> Bool  {
-    return Unicode.UTF16.isASCII(x)
-  }
-}
+// extension Unicode.UTF16 {
+//   @available(*, unavailable, renamed: "Unicode.UTF16.isASCII")
+//   @inlinable
+//   public static func _isASCII(_ x: CodeUnit) -> Bool  {
+//     return Unicode.UTF16.isASCII(x)
+//   }
+// }
 
 @available(*, unavailable, renamed: "Unicode.UTF8.isASCII")
 @inlinable