Merge pull request swiftlang#59765 from tshortli/experimental-ad-hoc-availability

Frontend: Introduce the `-enable-ad-hoc-availability` flag

Author: tshortli

include/swift/Basic/LangOptions.h

@@ -164,6 +164,10 @@ namespace swift {
     /// Only check the availability of the API, ignore function bodies.
     bool CheckAPIAvailabilityOnly = false;
 
+    /// Causes the compiler to treat declarations available at the current
+    /// runtime OS version as potentially unavailable.
+    bool EnableAdHocAvailability = false;
+
     /// Should conformance availability violations be diagnosed as errors?
     bool EnableConformanceAvailabilityErrors = false;
 

include/swift/Option/FrontendOptions.td

@@ -1064,5 +1064,9 @@ def clang_header_expose_public_decls:
   Flag<["-"], "clang-header-expose-public-decls">,
   HelpText<"Expose all public declarations in the generated clang header">,
   Flags<[FrontendOption, HelpHidden]>;
+  
+def enable_ad_hoc_availability :
+  Flag<["-"], "enable-ad-hoc-availability">,
+  HelpText<"Enable experimental support for ad hoc availability">;
 
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]

lib/AST/Decl.cpp

@@ -1002,13 +1002,17 @@ bool Decl::isWeakImported(ModuleDecl *fromModule) const {
   if (isAlwaysWeakImported())
     return true;
 
-  auto containingContext = getAvailabilityForLinkage();
-  if (containingContext.isAlwaysAvailable())
+  auto availability = getAvailabilityForLinkage();
+  if (availability.isAlwaysAvailable())
     return false;
 
-  auto fromContext = AvailabilityContext::forDeploymentTarget(
-      fromModule->getASTContext());
-  return !fromContext.isContainedIn(containingContext);
+  auto &ctx = fromModule->getASTContext();
+  auto deploymentTarget = AvailabilityContext::forDeploymentTarget(ctx);
+
+  if (ctx.LangOpts.EnableAdHocAvailability)
+    return !availability.isSupersetOf(deploymentTarget);
+
+  return !deploymentTarget.isContainedIn(availability);
 }
 
 GenericContext::GenericContext(DeclContextKind Kind, DeclContext *Parent,

lib/Frontend/CompilerInvocation.cpp

@@ -490,6 +490,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       Args.hasArg(OPT_disable_availability_checking);
   Opts.CheckAPIAvailabilityOnly |=
       Args.hasArg(OPT_check_api_availability_only);
+  Opts.EnableAdHocAvailability |=
+      Args.hasArg(OPT_enable_ad_hoc_availability);
 
   if (auto A = Args.getLastArg(OPT_enable_conformance_availability_errors,
                                OPT_disable_conformance_availability_errors)) {

lib/SIL/IR/SILFunction.cpp

@@ -385,9 +385,13 @@ bool SILFunction::isWeakImported() const {
   if (Availability.isAlwaysAvailable())
     return false;
 
-  auto fromContext = AvailabilityContext::forDeploymentTarget(
-      getASTContext());
-  return !fromContext.isContainedIn(Availability);
+  auto deploymentTarget =
+      AvailabilityContext::forDeploymentTarget(getASTContext());
+
+  if (getASTContext().LangOpts.EnableAdHocAvailability)
+    return !Availability.isSupersetOf(deploymentTarget);
+
+  return !deploymentTarget.isContainedIn(Availability);
 }
 
 SILBasicBlock *SILFunction::createBasicBlock() {

test/IRGen/weak_import_availability.swift

@@ -2,11 +2,13 @@
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/weak_import_availability_helper.swiftmodule -parse-as-library %S/Inputs/weak_import_availability_helper.swift -enable-library-evolution
 //
 // RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir | %FileCheck %s --check-prefix=CHECK-OLD
-// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target x86_64-apple-macosx10.50 | %FileCheck %s --check-prefix=CHECK-NEW
-// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target x86_64-apple-macosx10.60 | %FileCheck %s --check-prefix=CHECK-NEW
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target %target-cpu-apple-macosx10.50 | %FileCheck %s --check-prefix=CHECK-NEW
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target %target-cpu-apple-macosx10.60 | %FileCheck %s --check-prefix=CHECK-NEW
+
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target %target-cpu-apple-macosx10.50 -enable-ad-hoc-availability | %FileCheck %s --check-prefix=CHECK-OLD
+// RUN: %target-swift-frontend -primary-file %s -I %t -emit-ir -target %target-cpu-apple-macosx10.60 -enable-ad-hoc-availability | %FileCheck %s --check-prefix=CHECK-NEW
 
 // REQUIRES: OS=macosx
-// REQUIRES: CPU=x86_64
 
 import weak_import_availability_helper