From b0a565e458146171d41a25f9647b4b908da35ad0 Mon Sep 17 00:00:00 2001
From: Doug Gregor <dgregor@apple.com>
Date: Mon, 3 Nov 2025 22:25:54 -0800
Subject: [PATCH 1/2] [Custom availability] Fix conformance availability
 diagnostic

Emit a proper diagnostic for a conformance that is not available due to
custom availability that doesn't have version information, eliminating
an assertion.
---
 include/swift/AST/DiagnosticsSema.def         |  4 +++
 lib/Frontend/Frontend.cpp                     | 15 ++++++++++
 lib/Sema/TypeCheckAvailability.cpp            | 17 +++++++----
 .../availability_custom_domains.swift         | 28 +++++++++++++++++++
 4 files changed, 59 insertions(+), 5 deletions(-)

diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index ba121d384b9ad..f28e4fb06ff65 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -7282,6 +7282,10 @@ ERROR(conformance_availability_only_version_newer, none,
       "conformance of %0 to %1 is only available in %2 %3 or newer",
       (Type, Type, AvailabilityDomain, AvailabilityRange))
 
+ERROR(conformance_availability_not_available, none,
+      "conformance of %0 to %1 is only available in %2",
+      (Type, Type, AvailabilityDomain))
+
 //------------------------------------------------------------------------------
 // MARK: if #available(...)
 //------------------------------------------------------------------------------
diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index 7e196020dfe4c..6510af9e95bc3 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -1465,6 +1465,21 @@ static void configureAvailabilityDomains(const ASTContext &ctx,
   for (auto dynamic : opts.AvailabilityDomains.DynamicDomains)
     createAndInsertDomain(dynamic, CustomAvailabilityDomain::Kind::Dynamic);
 
+  // If we didn't see the UnicodeNormalization availability domain, set it
+  // appropriately.
+  if (domainMap.count(ctx.getIdentifier("UnicodeNormalization")) == 0) {
+    if (ctx.LangOpts.hasFeature(Feature::Embedded)) {
+      // Embedded Swift disables this domain by default.
+      createAndInsertDomain("UnicodeNormalization",
+                            CustomAvailabilityDomain::Kind::Enabled);
+    } else {
+      // Non-Embedded Swift always enables the Unicode tables.
+      createAndInsertDomain("UnicodeNormalization",
+                            CustomAvailabilityDomain::Kind::AlwaysEnabled);
+    }
+  }
+
+
   mainModule->setAvailabilityDomains(std::move(domainMap));
 }
 
diff --git a/lib/Sema/TypeCheckAvailability.cpp b/lib/Sema/TypeCheckAvailability.cpp
index bb799e6c65390..6497ff3609656 100644
--- a/lib/Sema/TypeCheckAvailability.cpp
+++ b/lib/Sema/TypeCheckAvailability.cpp
@@ -1041,15 +1041,22 @@ static bool diagnosePotentialUnavailability(
   {
     auto type = rootConf->getType();
     auto proto = rootConf->getProtocol()->getDeclaredInterfaceType();
-    auto err = ctx.Diags.diagnose(
-        loc, diag::conformance_availability_only_version_newer, type, proto,
-        domain, availability);
+    auto err = availability.hasMinimumVersion()
+        ? ctx.Diags.diagnose(
+            loc, diag::conformance_availability_only_version_newer, type, proto,
+            domain, availability)
+        : ctx.Diags.diagnose(
+            loc, diag::conformance_availability_not_available, type, proto,
+            domain);
 
     auto behaviorLimit = behaviorLimitForExplicitUnavailability(rootConf, dc);
-    if (behaviorLimit >= DiagnosticBehavior::Warning)
+    if (!availability.hasMinimumVersion()) {
+      // Don't downgrade
+    } else if (behaviorLimit >= DiagnosticBehavior::Warning) {
       err.limitBehavior(behaviorLimit);
-    else
+    } else {
       err.warnUntilSwiftVersion(6);
+    }
 
     // Direct a fixit to the error if an existing guard is nearly-correct
     if (fixAvailabilityByNarrowingNearbyVersionCheck(loc, dc, domain,
diff --git a/test/Availability/availability_custom_domains.swift b/test/Availability/availability_custom_domains.swift
index a30f5e38aadf3..55086c0e07434 100644
--- a/test/Availability/availability_custom_domains.swift
+++ b/test/Availability/availability_custom_domains.swift
@@ -568,3 +568,31 @@ class DerivedUnavailable2: BaseAvailableInEnabledDomain { } // expected-error {{
 @available(DisabledDomain, unavailable)
 class DerivedUnavailable3: BaseAvailableInEnabledDomain { }
 
+
+// Protocol conformance availability.
+protocol P { }
+
+struct MyType1 { }
+
+@available(EnabledDomain)
+extension MyType1: P { }
+
+struct MyType2 { }
+
+@available(AlwaysEnabledDomain)
+extension MyType2: P { }
+
+struct MyType3 { }
+
+@available(DisabledDomain)
+extension MyType3: P { }
+
+func acceptP<T: P>(_: T.Type) { }
+
+func testP() { // expected-note 2{{add '@available' attribute to enclosing global function}}
+  acceptP(MyType1.self) // expected-error{{conformance of 'MyType1' to 'P' is only available in EnabledDomain}}
+  // expected-note@-1{{add 'if #available' version check}}
+  acceptP(MyType2.self) // okay
+  acceptP(MyType3.self)  // expected-error{{conformance of 'MyType3' to 'P' is only available in DisabledDomain}}
+  // expected-note@-1{{add 'if #available' version check}}
+}

From ba3d8e0c2b0b8397444cf374a64eb872f57b140b Mon Sep 17 00:00:00 2001
From: Doug Gregor <dgregor@apple.com>
Date: Tue, 4 Nov 2025 10:07:40 -0800
Subject: [PATCH 2/2] Remove unused variable

---
 lib/SILGen/SILGenDestructor.cpp | 2 --
 1 file changed, 2 deletions(-)

diff --git a/lib/SILGen/SILGenDestructor.cpp b/lib/SILGen/SILGenDestructor.cpp
index d80309d21a61d..4e78114122f85 100644
--- a/lib/SILGen/SILGenDestructor.cpp
+++ b/lib/SILGen/SILGenDestructor.cpp
@@ -58,8 +58,6 @@ void SILGenFunction::emitDistributedRemoteActorDeinit(
 
     auto cleanupLoc = CleanupLocation(loc);
 
-    auto &C = cd->getASTContext();
-
     {
       FullExpr CleanupScope(Cleanups, cleanupLoc);
       ManagedValue borrowedSelf = emitManagedBeginBorrow(loc, selfValue);