Add a flag to enable ConcurrentValue inference for public structs/enums.

include/swift/Basic/LangOptions.h

@@ -247,6 +247,9 @@ namespace swift {
     /// Enable experimental flow-sensitive concurrent captures.
     bool EnableExperimentalFlowSensitiveConcurrentCaptures = false;
 
+    /// Enable inference of ConcurrentValue conformances for public types.
+    bool EnableInferPublicConcurrentValue = false;
+
     /// Enable experimental derivation of `Codable` for enums.
     bool EnableExperimentalEnumCodableDerivation = false;
 

include/swift/Option/FrontendOptions.td

@@ -188,6 +188,12 @@ def batch_scan_input_file
 def import_prescan : Flag<["-"], "import-prescan">,
    HelpText<"When performing a dependency scan, only dentify all imports of the main Swift module sources">;
 
+def enable_infer_public_concurrent_value : Flag<["-"], "enable-infer-public-concurrent-value">,
+    HelpText<"Enable inference of ConcurrentValue conformances for public structs and enums">;
+
+def disable_infer_public_concurrent_value : Flag<["-"], "disable-infer-public-concurrent-value">,
+    HelpText<"Disable inference of ConcurrentValue conformances for public structs and enums">;
+
 } // end let Flags = [FrontendOption, NoDriverOption]
 
 def debug_crash_Group : OptionGroup<"<automatic crashing options>">;

lib/Frontend/CompilerInvocation.cpp

@@ -385,6 +385,10 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 
   Opts.EnableExperimentalConcurrency |=
     Args.hasArg(OPT_enable_experimental_concurrency);
+  Opts.EnableInferPublicConcurrentValue |=
+    Args.hasFlag(OPT_enable_infer_public_concurrent_value,
+                 OPT_disable_infer_public_concurrent_value,
+                 false);
   Opts.EnableExperimentalFlowSensitiveConcurrentCaptures |=
     Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures);
 

lib/Sema/TypeCheckConcurrency.cpp

@@ -2510,7 +2510,8 @@ NormalProtocolConformance *GetImplicitConcurrentValueRequest::evaluate(
 
   // Public, non-frozen structs and enums defined in Swift don't get implicit
   // ConcurrentValue conformances.
-  if (nominal->getFormalAccessScope(
+  if (!nominal->getASTContext().LangOpts.EnableInferPublicConcurrentValue &&
+      nominal->getFormalAccessScope(
           /*useDC=*/nullptr,
           /*treatUsableFromInlineAsPublic=*/true).isPublic() &&
       !(nominal->hasClangNode() ||

test/Concurrency/concurrent_value_inference_public.swift

@@ -0,0 +1,16 @@
+// RUN: %target-typecheck-verify-swift -enable-infer-public-concurrent-value
+
+func acceptCV<T: ConcurrentValue>(_: T) { }
+
+public struct PublicStruct {
+  var i: Int
+}
+
+public enum PublicEnum {
+  case some
+}
+
+func testCV(ps: PublicStruct, pe: PublicEnum) {
+  acceptCV(ps)
+  acceptCV(pe)
+}