Sema: Check result builder availability

Author: slavapestov

include/swift/AST/DiagnosticsSema.def

@@ -2734,6 +2734,7 @@ NOTE(construct_raw_representable_from_unwrapped_value,none,
 
 ERROR(decl_from_hidden_module,none,
       "cannot use %0 %1 %select{here|as property wrapper here|"
+      "as result builder here|"
       "in an extension with public or '@usableFromInline' members|"
       "in an extension with conditional conformances}2; "
       "%select{%3 has been imported as implementation-only|"
@@ -2742,12 +2743,14 @@ ERROR(decl_from_hidden_module,none,
       (DescriptiveDeclKind, DeclName, unsigned, Identifier, unsigned))
 WARNING(decl_from_hidden_module_warn,none,
       "cannot use %0 %1 %select{in SPI|as property wrapper in SPI|"
+      "as result builder in SPI|"
       "in an extension with public or '@usableFromInline' members|"
       "in an extension with conditional conformances}2; "
       "%select{%3 has been imported as implementation-only}4",
       (DescriptiveDeclKind, DeclName, unsigned, Identifier, unsigned))
 ERROR(conformance_from_implementation_only_module,none,
       "cannot use conformance of %0 to %1 %select{here|as property wrapper here|"
+      "as result builder here|"
       "in an extension with public or '@usableFromInline' members|"
       "in an extension with conditional conformances}2; "
       "%select{%3 has been imported as implementation-only|"

lib/Sema/TypeCheckAccess.cpp

@@ -1591,10 +1591,18 @@ class DeclAvailabilityChecker : public DeclVisitor<DeclAvailabilityChecker> {
               TP->getTypeRepr(), anyVar ? (Decl *)anyVar : (Decl *)PBD);
 
     // Check the property wrapper types.
-    if (anyVar)
-      for (auto attr : anyVar->getAttachedPropertyWrappers())
+    if (anyVar) {
+      for (auto attr : anyVar->getAttachedPropertyWrappers()) {
         checkType(attr->getType(), attr->getTypeRepr(), anyVar,
                   ExportabilityReason::PropertyWrapper);
+      }
+
+      if (auto attr = anyVar->getAttachedResultBuilder()) {
+        checkType(anyVar->getResultBuilderType(),
+                  attr->getTypeRepr(), anyVar,
+                  ExportabilityReason::ResultBuilder);
+      }
+    }
   }
 
   void visitPatternBindingDecl(PatternBindingDecl *PBD) {
@@ -1683,6 +1691,12 @@ class DeclAvailabilityChecker : public DeclVisitor<DeclAvailabilityChecker> {
   void visitFuncDecl(FuncDecl *FD) {
     visitAbstractFunctionDecl(FD);
     checkType(FD->getResultInterfaceType(), FD->getResultTypeRepr(), FD);
+
+    if (auto attr = FD->getAttachedResultBuilder()) {
+      checkType(FD->getResultBuilderType(),
+                attr->getTypeRepr(), FD,
+                ExportabilityReason::ResultBuilder);
+    }
   }
 
   void visitEnumElementDecl(EnumElementDecl *EED) {

lib/Sema/TypeCheckAvailability.h

@@ -62,6 +62,7 @@ using DeclAvailabilityFlags = OptionSet<DeclAvailabilityFlag>;
 enum class ExportabilityReason : unsigned {
   General,
   PropertyWrapper,
+  ResultBuilder,
   ExtensionWithPublicMembers,
   ExtensionWithConditionalConformances
 };
@@ -101,7 +102,7 @@ class ExportContext {
   unsigned Implicit : 1;
   unsigned Unavailable : 1;
   unsigned Platform : 8;
-  unsigned Reason : 2;
+  unsigned Reason : 3;
 
   ExportContext(DeclContext *DC,
                 AvailabilityContext runningOSVersion,

test/Constraints/result_builder_availability.swift

@@ -2,6 +2,16 @@
 
 // REQUIRES: OS=macosx
 
+@available(*, unavailable)
+@resultBuilder
+struct UnavailableBuilder {
+// expected-note@-1 {{'UnavailableBuilder' has been explicitly marked unavailable here}}
+  static func buildBlock() {}
+}
+
+@UnavailableBuilder public func usesUnavailableBuilder() {}
+// expected-error@-1 {{'UnavailableBuilder' is unavailable}}
+
 enum Either<T,U> {
   case first(T)
   case second(U)