Sema: Retire ExportContext::shouldDiagnoseDeclAsUnavailable().

NFC.

Author: tshortli

lib/Sema/TypeCheckAvailability.cpp

@@ -345,40 +345,6 @@ static bool computeContainedByDeploymentTarget(AvailabilityScope *scope,
       AvailabilityRange::forDeploymentTarget(ctx));
 }
 
-/// Returns true if the reference or any of its parents is an
-/// unconditional unavailable declaration for the same platform.
-static bool isInsideCompatibleUnavailableDeclaration(
-    const Decl *D, AvailabilityContext availabilityContext,
-    const SemanticAvailableAttr &attr) {
-  if (!availabilityContext.isUnavailable())
-    return false;
-
-  if (!attr.isUnconditionallyUnavailable())
-    return false;
-
-  // Refuse calling universally unavailable functions from unavailable code,
-  // but allow the use of types.
-  auto declDomain = attr.getDomain();
-  if (!isa<TypeDecl>(D) && !isa<ExtensionDecl>(D)) {
-    if (declDomain.isUniversal() || declDomain.isSwiftLanguage())
-      return false;
-  }
-
-  return availabilityContext.containsUnavailableDomain(declDomain);
-}
-
-std::optional<SemanticAvailableAttr>
-ExportContext::shouldDiagnoseDeclAsUnavailable(const Decl *D) const {
-  auto attr = D->getUnavailableAttr();
-  if (!attr)
-    return std::nullopt;
-
-  if (isInsideCompatibleUnavailableDeclaration(D, Availability, *attr))
-    return std::nullopt;
-
-  return attr;
-}
-
 static bool shouldAllowReferenceToUnavailableInSwiftDeclaration(
     const Decl *D, const ExportContext &where) {
   auto *DC = where.getDeclContext();

lib/Sema/TypeCheckAvailability.h

@@ -201,13 +201,6 @@ class ExportContext {
   /// Get the ExportabilityReason for diagnostics. If this is 'None', there
   /// are no restrictions on referencing unexported declarations.
   std::optional<ExportabilityReason> getExportabilityReason() const;
-
-  /// If \p decl is unconditionally unavailable in this context, and the context
-  /// is not also unavailable in the same way, then this returns the specific
-  /// `@available` attribute that makes the decl unavailable. Otherwise, returns
-  /// nullptr.
-  std::optional<SemanticAvailableAttr>
-  shouldDiagnoseDeclAsUnavailable(const Decl *decl) const;
 };
 
 /// Check if a declaration is exported as part of a module's external interface.

lib/Sema/TypeCheckProtocol.cpp

@@ -4963,12 +4963,16 @@ static bool diagnoseTypeWitnessAvailability(
   bool shouldError =
       ctx.LangOpts.EffectiveLanguageVersion.isVersionAtLeast(warnBeforeVersion);
 
-  if (auto attr = where.shouldDiagnoseDeclAsUnavailable(witness)) {
+  auto constraint =
+      getAvailabilityConstraintsForDecl(witness, where.getAvailability())
+          .getPrimaryConstraint();
+  if (constraint && constraint->isUnavailable()) {
+    auto attr = constraint->getAttr();
     ctx.addDelayedConformanceDiag(
         conformance, shouldError,
         [witness, assocType, attr](NormalProtocolConformance *conformance) {
           SourceLoc loc = getLocForDiagnosingWitness(conformance, witness);
-          EncodedDiagnosticMessage encodedMessage(attr->getMessage());
+          EncodedDiagnosticMessage encodedMessage(attr.getMessage());
           auto &ctx = conformance->getDeclContext()->getASTContext();
           ctx.Diags
               .diagnose(loc, diag::witness_unavailable, witness,