Tests: Move some availability tests into a new test/Availability directory.

Un-reverts 9c01ee2.

Also, add myself as a reviewer for more availability related files.

NFC.

Author: tshortli

.github/CODEOWNERS

@@ -166,6 +166,7 @@
 /lib/SIL/IR/SILLocation*                            @adrian-prantl
 /lib/SIL/IR/SILProfiler.cpp                         @bnbarham @hamishknight @rintaro
 /lib/SILGen/                                        @jckarter
+/lib/SILGen/*Availability*                          @tshortli
 /lib/SILGen/*Distributed*                           @ktoso
 /lib/SILOptimizer/                                  @eeckstein
 /lib/SILOptimizer/**/*DebugInfo*                    @adrian-prantl
@@ -213,6 +214,7 @@
 
 # test
 /test/*Demangl*/                                    @rjmccall
+/test/Availability/                                 @tshortli
 /test/ASTGen/                                       @bnbarham @CodaFi @hamishknight @rintaro
 /test/Concurrency/                                  @ktoso
 /test/Constraints/                                  @hborla @xedin

test/Sema/Inputs/availability_enum_case_other.swift renamed to test/Availability/Inputs/availability_enum_case_other.swift

@@ -86,3 +86,90 @@ struct DeferBody {
     // expected-error@-1 {{'No' is unavailable}}
   }
 }
+
+// Ensure that we do not select the unavailable failable init as the
+// only solution and then fail to typecheck.
+protocol P {}
+
+class C : P {
+  @available(swift, obsoleted: 4)
+  public init?(_ c: C) {
+  }
+
+  public init<T : P>(_ c: T) {}
+}
+
+func f(c: C) {
+  let _: C? = C(c)
+}
+
+// rdar://problem/60047439 - unable to disambiguate expression based on availability
+func test_contextual_member_with_availability() {
+  struct A {
+    static var foo: A = A()
+  }
+
+  struct B {
+    @available(*, unavailable, renamed: "bar")
+    static var foo: B = B()
+  }
+
+  struct Test {
+    init(_: A) {}
+    init(_: B) {}
+  }
+
+  _ = Test(.foo) // Ok
+}
+
+@available(*, unavailable)
+func unavailableFunction(_ x: Int) -> Bool { true } // expected-note {{'unavailableFunction' has been explicitly marked unavailable here}}
+
+/// https://github.com/apple/swift/issues/55700
+/// Availability checking not working in the `where` clause of a `for` loop
+func f_55700(_ arr: [Int]) {
+  for x in arr where unavailableFunction(x) {} // expected-error {{'unavailableFunction' is unavailable}}
+}
+
+// rdar://101814209
+public struct Box<T> {
+  @usableFromInline
+  let value: T
+}
+
+@available(macOS, unavailable)
+extension Box where T == Int {
+  @usableFromInline
+  init(value: T) {
+    self.value = value
+  }
+}
+
+@available(macOS, unavailable)
+@_alwaysEmitIntoClient public func aeicFunction() {
+  // Select the unavailable @usableFromInline init over the synthesized internal
+  // memberwise initializer.
+  _ = Box(value: 42)
+}
+
+// rdar://87403752 - ambiguity with member declared in unavailable extension
+struct HasUnavailableExtesion {
+}
+
+@available(*, unavailable)
+extension HasUnavailableExtesion {
+  static var foo: Self = HasUnavailableExtesion()
+}
+
+func test_contextual_member_with_unavailable_extension() {
+  struct A {
+    static var foo: A = A()
+  }
+
+  struct Test {
+    init(_: A) {}
+    init(_: HasUnavailableExtesion) {}
+  }
+
+  _ = Test(.foo) // Ok `A.foo` since `foo` from `HasUnavailableExtesion` is unavailable
+}