Sema: (Mostly) check conformance availability

include/swift/AST/Availability.h

@@ -182,46 +182,19 @@ class VersionRange {
 
 /// Records the reason a declaration is potentially unavailable.
 class UnavailabilityReason {
-public:
-  enum class Kind {
-    /// The declaration is potentially unavailable because it requires an OS
-    /// version range that is not guaranteed by the minimum deployment
-    /// target.
-    RequiresOSVersionRange,
-
-    /// The declaration is potentially unavailable because it is explicitly
-    /// weakly linked.
-    ExplicitlyWeakLinked
-  };
-
 private:
-  // A value of None indicates the declaration is potentially unavailable
-  // because it is explicitly weak linked.
-  Optional<VersionRange> RequiredDeploymentRange;
+  VersionRange RequiredDeploymentRange;
 
-  UnavailabilityReason(const Optional<VersionRange> &RequiredDeploymentRange)
+  explicit UnavailabilityReason(const VersionRange RequiredDeploymentRange)
       : RequiredDeploymentRange(RequiredDeploymentRange) {}
 
 public:
-  static UnavailabilityReason explicitlyWeaklyLinked() {
-    return UnavailabilityReason(None);
-  }
-
   static UnavailabilityReason requiresVersionRange(const VersionRange Range) {
     return UnavailabilityReason(Range);
   }
 
-  Kind getReasonKind() const {
-    if (RequiredDeploymentRange.hasValue()) {
-      return Kind::RequiresOSVersionRange;
-    } else {
-      return Kind::ExplicitlyWeakLinked;
-    }
-  }
-
   const VersionRange &getRequiredOSVersionRange() const {
-    assert(getReasonKind() == Kind::RequiresOSVersionRange);
-    return RequiredDeploymentRange.getValue();
+    return RequiredDeploymentRange;
   }
 };
 

include/swift/AST/DiagnosticsSema.def

@@ -5040,6 +5040,39 @@ ERROR(availabilty_string_subscript_migration, none,
       "subscripts returning String were obsoleted in Swift 4; explicitly "
       "construct a String from subscripted result", ())
 
+// Conformance availability checking diagnostics
+
+ERROR(conformance_availability_unavailable, none,
+      "conformance of %0 to %1 is unavailable"
+      "%select{ in %3|}2%select{|: %4}4",
+      (Type, Type, bool, StringRef, StringRef))
+
+NOTE(conformance_availability_marked_unavailable, none,
+     "conformance of %0 to %1 has been explicitly marked "
+     "unavailable here", (Type, Type))
+
+NOTE(conformance_availability_introduced_in_version, none,
+     "conformance of %0 to %1 was introduced in %2 %3",
+     (Type, Type, StringRef, llvm::VersionTuple))
+
+NOTE(conformance_availability_obsoleted, none,
+     "conformance of %0 to %1 was obsoleted in %2 %3",
+     (Type, Type, StringRef, llvm::VersionTuple))
+
+WARNING(conformance_availability_deprecated, none,
+        "conformance of %0 to %1 %select{is|%select{is|was}4}2 "
+        "deprecated%select{| in %3%select{| %5}4}2%select{|: %6}6",
+        (Type, Type, bool, StringRef, bool, llvm::VersionTuple,
+         StringRef))
+
+ERROR(conformance_availability_only_version_newer, none,
+      "conformance of %0 to %1 is only available in %2 %3 or newer",
+      (Type, Type, StringRef, llvm::VersionTuple))
+
+WARNING(conformance_availability_only_version_newer_warn, none,
+        "conformance of %0 to %1 is only available in %2 %3 or newer",
+        (Type, Type, StringRef, llvm::VersionTuple))
+
 //------------------------------------------------------------------------------
 // MARK: @discardableResult
 //------------------------------------------------------------------------------

include/swift/Basic/LangOptions.h

@@ -94,6 +94,9 @@ namespace swift {
     /// Disable API availability checking.
     bool DisableAvailabilityChecking = false;
 
+    /// Should conformance availability violations be diagnosed as errors?
+    bool EnableConformanceAvailabilityErrors = false;
+
     /// Maximum number of typo corrections we are allowed to perform.
     /// This is disabled by default until we can get typo-correction working within acceptable performance bounds.
     unsigned TypoCorrectionLimit = 0;

include/swift/Option/FrontendOptions.td

@@ -405,6 +405,14 @@ def disable_availability_checking : Flag<["-"],
   "disable-availability-checking">,
   HelpText<"Disable checking for potentially unavailable APIs">;
 
+def enable_conformance_availability_errors : Flag<["-"],
+  "enable-conformance-availability-errors">,
+  HelpText<"Diagnose conformance availability violations as errors">;
+
+def disable_conformance_availability_errors : Flag<["-"],
+  "disable-conformance-availability-errors">,
+  HelpText<"Diagnose conformance availability violations as warnings">;
+
 def report_errors_to_debugger : Flag<["-"], "report-errors-to-debugger">,
   HelpText<"Deprecated, will be removed in future versions.">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -391,6 +391,12 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DisableAvailabilityChecking |=
       Args.hasArg(OPT_disable_availability_checking);
 
+  if (auto A = Args.getLastArg(OPT_enable_conformance_availability_errors,
+                               OPT_disable_conformance_availability_errors)) {
+    Opts.EnableConformanceAvailabilityErrors
+      = A->getOption().matches(OPT_enable_conformance_availability_errors);
+  }
+
   if (auto A = Args.getLastArg(OPT_enable_access_control,
                                OPT_disable_access_control)) {
     Opts.EnableAccessControl

lib/Sema/ResilienceDiagnostics.cpp

@@ -160,17 +160,16 @@ TypeChecker::diagnoseDeclRefExportability(SourceLoc loc,
 bool
 TypeChecker::diagnoseConformanceExportability(SourceLoc loc,
                                               const RootProtocolConformance *rootConf,
+                                              const ExtensionDecl *ext,
                                               const ExportContext &where) {
   if (!where.mustOnlyReferenceExportedDecls())
     return false;
 
-  auto originKind = getDisallowedOriginKind(
-      rootConf->getDeclContext()->getAsDecl(),
-      where);
+  auto originKind = getDisallowedOriginKind(ext, where);
   if (originKind == DisallowedOriginKind::None)
     return false;
 
-  ModuleDecl *M = rootConf->getDeclContext()->getParentModule();
+  ModuleDecl *M = ext->getParentModule();
   ASTContext &ctx = M->getASTContext();
 
   auto reason = where.getExportabilityReason();