AST: Don't stub unavailable functions when building zippered libraries.

The declarations in a zippered macOS library may be referenced by clients that
build either for macOS or for macCatalyst. It is therefore inappropriate to
stub functions in zippered libraries as "unreachable" when they are only
unavailable on macOS. Making this logic correct is a larger project, so for now
just disable stubbing when there is a target variant.

Resolves rdar://125371621

Author: tshortli

lib/AST/Availability.cpp

@@ -350,6 +350,17 @@ static bool shouldStubOrSkipUnavailableDecl(const Decl *D) {
   if (!unavailableAttr->isUnconditionallyUnavailable())
     return false;
 
+  // Universally unavailable declarations are always unreachable.
+  if (unavailableAttr->Platform == PlatformKind::none)
+    return true;
+
+  // FIXME: Support zippered frameworks (rdar://125371621)
+  // If we have a target variant (e.g. we're building a zippered macOS
+  // framework) then the decl is only unreachable if it is unavailable for both
+  // the primary target and the target variant.
+  if (D->getASTContext().LangOpts.TargetVariant.has_value())
+    return false;
+
   return true;
 }
 

test/SILGen/unavailable_decl_optimization_stub_macos.swift

@@ -30,7 +30,7 @@ public func unavailableFunc() {}
 public func unavailableOnMacOSFunc() {}
 
 // CHECK-LABEL:     sil{{.*}}@$s4Test31unavailableOnMacOSExtensionFuncyyF
-// CHECK-NOT:         function_ref @$ss36_diagnoseUnavailableCodeReached{{.*}} : $@convention(thin) () -> Never
+// CHECK-NOT:         _diagnoseUnavailableCodeReached
 // CHECK:           } // end sil function '$s4Test31unavailableOnMacOSExtensionFuncyyF'
 @available(macOSApplicationExtension, unavailable)
 public func unavailableOnMacOSExtensionFunc() {}

test/SILGen/unavailable_decl_optimization_stub_macos_zippered.swift

@@ -0,0 +1,58 @@
+// RUN: %target-swift-emit-silgen -target %target-cpu-apple-macosx13 -target-variant %target-cpu-apple-ios16-macabi -module-name Test -parse-as-library %s -verify -unavailable-decl-optimization=stub | %FileCheck %s
+
+// REQUIRES: OS=macosx
+
+// CHECK-LABEL:     sil{{.*}}@$s4Test15unavailableFuncyyF
+// CHECK:             [[FNREF:%.*]] = function_ref @$ss36_diagnoseUnavailableCodeReached_aeics5NeverOyF : $@convention(thin) () -> Never
+// CHECK-NEXT:        [[APPLY:%.*]] = apply [[FNREF]]()
+// CHECK:           } // end sil function '$s4Test15unavailableFuncyyF'
+@available(*, unavailable)
+public func unavailableFunc() {}
+
+// CHECK-LABEL:     sil{{.*}}@$s4Test22unavailableOnMacOSFuncyyF
+// CHECK-NOT:         _diagnoseUnavailableCodeReached
+// CHECK:           } // end sil function '$s4Test22unavailableOnMacOSFuncyyF'
+@available(macOS, unavailable)
+public func unavailableOnMacOSFunc() {}
+
+// CHECK-LABEL:     sil{{.*}}@$s4Test20unavailableOniOSFuncyyF
+// CHECK-NOT:         _diagnoseUnavailableCodeReached
+// CHECK:           } // end sil function '$s4Test20unavailableOniOSFuncyyF'
+@available(iOS, unavailable)
+public func unavailableOniOSFunc() {}
+
+// FIXME: This function should diagnose (rdar://125930716)
+// CHECK-LABEL:     sil{{.*}}@$s4Test28unavailableOnMacCatalystFuncyyF
+// CHECK-NOT:         _diagnoseUnavailableCodeReached
+// CHECK:           } // end sil function '$s4Test28unavailableOnMacCatalystFuncyyF'
+@available(macCatalyst, unavailable)
+public func unavailableOnMacCatalystFunc() {}
+
+// FIXME: This function should diagnose (rdar://125930716)
+// CHECK-LABEL:     sil{{.*}}@$s4Test28unavailableOnMacOSAndiOSFuncyyF
+// CHECK-NOT:         _diagnoseUnavailableCodeReached
+// CHECK:           } // end sil function '$s4Test28unavailableOnMacOSAndiOSFuncyyF'
+@available(macOS, unavailable)
+@available(iOS, unavailable)
+public func unavailableOnMacOSAndiOSFunc() {}
+
+@available(iOS, unavailable)
+public struct UnavailableOniOS {
+  // CHECK-LABEL:     sil{{.*}}@$s4Test16UnavailableOniOSV15availableMethodyyF
+  // CHECK-NOT:         _diagnoseUnavailableCodeReached
+  // CHECK:           } // end sil function '$s4Test16UnavailableOniOSV15availableMethodyyF'
+  public func availableMethod() {}
+
+  // FIXME: This function should diagnose (rdar://125930716)
+  // CHECK-LABEL:     sil{{.*}}@$s4Test16UnavailableOniOSV24unavailableOnMacOSMethodyyF
+  // CHECK-NOT:         _diagnoseUnavailableCodeReached
+  // CHECK:           } // end sil function '$s4Test16UnavailableOniOSV24unavailableOnMacOSMethodyyF'
+  @available(macOS, unavailable)
+  public func unavailableOnMacOSMethod() {}
+}
+
+// CHECK-LABEL:     sil{{.*}}@$s4Test37unavailableOnMacCatalystExtensionFuncyyF
+// CHECK-NOT:         _diagnoseUnavailableCodeReached
+// CHECK:           } // end sil function '$s4Test37unavailableOnMacCatalystExtensionFuncyyF'
+@available(macCatalystApplicationExtension, unavailable)
+public func unavailableOnMacCatalystExtensionFunc() {}