Sema: Take a SourceLoc in getUnmetDeclAvailabilityRequirement().

Introduce a convenience overload for the common case where the
AvailabilityContext must first be looked up by source location.

Author: tshortli

lib/Sema/ConstraintSystem.cpp

@@ -4682,9 +4682,7 @@ bool ConstraintSystem::isDeclUnavailable(const Decl *D,
       loc = getLoc(anchor);
   }
 
-  auto availabilityContext = TypeChecker::availabilityAtLocation(loc, DC);
-  return getUnmetDeclAvailabilityRequirement(D, DC, availabilityContext)
-      .has_value();
+  return getUnmetDeclAvailabilityRequirement(D, DC, loc).has_value();
 }
 
 bool ConstraintSystem::isConformanceUnavailable(ProtocolConformanceRef conformance,

lib/Sema/TypeCheckAvailability.cpp

@@ -3127,6 +3127,15 @@ swift::getUnmetDeclAvailabilityRequirement(
   return std::nullopt;
 }
 
+std::optional<UnmetAvailabilityRequirement>
+swift::getUnmetDeclAvailabilityRequirement(const Decl *decl,
+                                           const DeclContext *referenceDC,
+                                           SourceLoc referenceLoc) {
+  return getUnmetDeclAvailabilityRequirement(
+      decl, referenceDC,
+      TypeChecker::availabilityAtLocation(referenceLoc, referenceDC));
+}
+
 /// Check if this is a subscript declaration inside String or
 /// Substring that returns String, and if so return true.
 bool isSubscriptReturningString(const ValueDecl *D, ASTContext &Context) {

lib/Sema/TypeCheckAvailability.h

@@ -252,6 +252,13 @@ getUnmetDeclAvailabilityRequirement(const Decl *decl,
                                     const DeclContext *declContext,
                                     AvailabilityContext availabilityContext);
 
+/// Checks whether a declaration should be considered unavailable when referred
+/// to at the given source location in the given decl context and, if so,
+/// returns a result that describes the unmet availability requirements.
+/// Returns `std::nullopt` if the declaration is available.
+std::optional<UnmetAvailabilityRequirement> getUnmetDeclAvailabilityRequirement(
+    const Decl *decl, const DeclContext *referenceDC, SourceLoc referenceLoc);
+
 /// Diagnose uses of the runtime support of the given type, such as
 /// type metadata and dynamic casting.
 ///

lib/Sema/TypeCheckPattern.cpp

@@ -36,12 +36,10 @@ using namespace swift;
 ///
 /// This requires the getter's body to have a certain syntactic form. It should
 /// be kept in sync with importEnumCaseAlias in the ClangImporter library.
-static EnumElementDecl *
-extractEnumElement(DeclContext *DC, SourceLoc UseLoc,
-                   const VarDecl *constant) {
-  auto availabilityContext = TypeChecker::availabilityAtLocation(UseLoc, DC);
-  if (auto requirement = getUnmetDeclAvailabilityRequirement(
-          constant, DC, availabilityContext)) {
+static EnumElementDecl *extractEnumElement(DeclContext *DC, SourceLoc UseLoc,
+                                           const VarDecl *constant) {
+  if (auto requirement =
+          getUnmetDeclAvailabilityRequirement(constant, DC, UseLoc)) {
     // Only diagnose explicit unavailability.
     if (!requirement->isConditionallySatisfiable())
       diagnoseDeclAvailability(constant, UseLoc, nullptr,