Fix ABI mismatch involving Sendable-refining protocols and deployment targets

A change to the way we determined whether a protocol conformance is
"dependent" for marker protocols caused an ABI break for
Sendable-refining protocols built with pre-6.0 Swift compilers. The
fix for this issue (https://github.com/swiftlang/swift/pull/75769)
gated the change on deployment target.

The deployment target change fixed the original problem, then caused a
related issue when a project mixes deployment targets (pre-6.0 and
6.0+) with non-resilient protocols. Exempt non-resilient protocols from
this change so we get consistent behavior.

Fixes rdar://134953989.

lib/IRGen/GenProto.cpp

@@ -1037,7 +1037,10 @@ static bool isSynthesizedNonUnique(const RootProtocolConformance *conformance) {
 }
 
 /// Determine whether a protocol can ever have a dependent conformance.
-static bool protocolCanHaveDependentConformance(ProtocolDecl *proto) {
+static bool protocolCanHaveDependentConformance(
+    ProtocolDecl *proto,
+    bool isResilient
+) {
   // Objective-C protocols have never been able to have a dependent conformance.
   if (proto->isObjC())
     return false;
@@ -1047,13 +1050,14 @@ static bool protocolCanHaveDependentConformance(ProtocolDecl *proto) {
   // is a marker protocol (since they don't have requirements), but we must
   // retain backward compatibility with binaries built for earlier deployment
   // targets that concluded that these protocols might involve dependent
-  // conformances.
-  ASTContext &ctx = proto->getASTContext();
-  if (auto runtimeCompatVersion = getSwiftRuntimeCompatibilityVersionForTarget(
-          ctx.LangOpts.Target)) {
-    if (runtimeCompatVersion < llvm::VersionTuple(6, 0) &&
-        proto->isSpecificProtocol(KnownProtocolKind::Sendable))
-      return true;
+  // conformances. Only do this for resilient protocols.
+  if (isResilient && proto->isSpecificProtocol(KnownProtocolKind::Sendable)) {
+    ASTContext &ctx = proto->getASTContext();
+    if (auto runtimeCompatVersion = getSwiftRuntimeCompatibilityVersionForTarget(
+            ctx.LangOpts.Target)) {
+      if (runtimeCompatVersion < llvm::VersionTuple(6, 0))
+        return true;
+    }
   }
 
   return Lowering::TypeConverter::protocolRequiresWitnessTable(proto);
@@ -1062,6 +1066,7 @@ static bool protocolCanHaveDependentConformance(ProtocolDecl *proto) {
 static bool isDependentConformance(
               IRGenModule &IGM,
               const RootProtocolConformance *rootConformance,
+              bool isResilient,
               llvm::SmallPtrSet<const NormalProtocolConformance *, 4> &visited){
   // Self-conformances are never dependent.
   auto conformance = dyn_cast<NormalProtocolConformance>(rootConformance);
@@ -1091,7 +1096,8 @@ static bool isDependentConformance(
       continue;
 
     auto assocProtocol = req.getProtocolDecl();
-    if (!protocolCanHaveDependentConformance(assocProtocol))
+    if (!protocolCanHaveDependentConformance(
+            assocProtocol, isResilient))
       continue;
 
     auto assocConformance =
@@ -1105,6 +1111,7 @@ static bool isDependentConformance(
         isDependentConformance(IGM,
                                assocConformance.getConcrete()
                                  ->getRootConformance(),
+                               isResilient,
                                visited))
       return true;
   }
@@ -1173,7 +1180,8 @@ static bool hasConditionalConformances(IRGenModule &IGM,
 bool IRGenModule::isDependentConformance(
     const RootProtocolConformance *conformance) {
   llvm::SmallPtrSet<const NormalProtocolConformance *, 4> visited;
-  return ::isDependentConformance(*this, conformance, visited);
+  return ::isDependentConformance(
+      *this, conformance, conformance->getProtocol()->isResilient(), visited);
 }
 
 static llvm::Value *

test/IRGen/protocol_resilience_sendable.swift

@@ -1,6 +1,7 @@
 // RUN: %empty-directory(%t)
 
 // RUN: %target-swift-frontend -emit-module -enable-library-evolution -emit-module-path=%t/resilient_protocol.swiftmodule -module-name=resilient_protocol %S/../Inputs/resilient_protocol.swift
+// RUN: %target-swift-frontend -emit-module -emit-module-path=%t/non_resilient_protocol.swiftmodule -module-name=non_resilient_protocol %S/../Inputs/non_resilient_protocol.swift
 
 // RUN: %target-swift-frontend -I %t -emit-ir %s -target %target-cpu-apple-macos14.0 | %FileCheck %s -DINT=i%target-ptrsize -check-prefix=CHECK-USAGE -check-prefix=CHECK-USAGE-BEFORE
 // RUN: %target-swift-frontend -I %t -emit-ir %s -target %target-cpu-apple-macos15.0 | %FileCheck %s -DINT=i%target-ptrsize -check-prefix=CHECK-USAGE -check-prefix=CHECK-USAGE-AFTER
@@ -8,6 +9,7 @@
 // REQUIRES: OS=macosx
 
 import resilient_protocol
+import non_resilient_protocol
 
 func acceptResilientSendableBase<T: ResilientSendableBase>(_: T.Type) { }
 
@@ -20,3 +22,12 @@ func passResilientSendableBase() {
   // CHECK-USAGE-AFTER-NEXT: call swiftcc void @"$s28protocol_resilience_sendable27acceptResilientSendableBaseyyxm010resilient_A00efG0RzlF"(ptr [[METATYPE]], ptr [[METATYPE]], ptr @"$s18resilient_protocol27ConformsToResilientSendableVAA0eF4BaseAAWP")
   acceptResilientSendableBase(ConformsToResilientSendable.self)
 }
+
+func acceptNonResilientSendableBase<T: NonResilientSendableBase>(_: T.Type) { }
+
+// CHECK-USAGE: define{{.*}}swiftcc void @"$s28protocol_resilience_sendable28passNonResilientSendableBaseyyF"()
+func passNonResilientSendableBase() {
+  // CHECK-USAGE-NOT: ret
+  // CHECK-USAGE: call swiftcc void @"$s28protocol_resilience_sendable30acceptNonResilientSendableBaseyyxm014non_resilient_A00efgH0RzlF"(ptr @"$s22non_resilient_protocol30ConformsToNonResilientSendableVN", ptr @"$s22non_resilient_protocol30ConformsToNonResilientSendableVN", ptr @"$s22non_resilient_protocol30ConformsToNonResilientSendableVAA0fgH4BaseAAWP")
+  acceptNonResilientSendableBase(ConformsToNonResilientSendable.self)
+}

test/Inputs/non_resilient_protocol.swift

@@ -0,0 +1,12 @@
+public protocol NonResilientSendableBase: Sendable {
+  func f()
+}
+
+public protocol NonResilientSendable: NonResilientSendableBase {
+  func g()
+}
+
+public struct ConformsToNonResilientSendable: NonResilientSendable {
+  public func f() { }
+  public func g() { }
+}