ClangImporter: Import clang::DomainAvailabilityAttr.

Import `__attribute__((availability(domain:MyDomain, ...)))` as
`@available(SomeDomain, ...)`.

Resolves rdar://138441266.

Author: tshortli

lib/ClangImporter/ImportDecl.cpp

@@ -9186,6 +9186,34 @@ void ClangImporter::Implementation::importAttributes(
       MappedDecl->getAttrs().add(AvAttr);
     }
 
+    // __attribute__((availability(domain:)))
+    //
+    if (auto avail = dyn_cast<clang::DomainAvailabilityAttr>(*AI)) {
+      auto *declContext = MappedDecl->getInnermostDeclContext();
+
+      // FIXME: [availability] Don't look up the availability domain. Clang
+      // should be serializing the resolved VarDecl for the availability domain
+      // it found when type checking the attribute.
+      auto domainIdentifier = SwiftContext.getIdentifier(avail->getDomain());
+      llvm::SmallVector<AvailabilityDomain, 4> results;
+      declContext->lookupAvailabilityDomains(domainIdentifier, results);
+
+      if (results.size() > 0) {
+        // FIXME: [availability] Diagnose ambiguous availabilty domain name?
+        auto AttrKind = avail->getUnavailable()
+                            ? AvailableAttr::Kind::Unavailable
+                            : AvailableAttr::Kind::Default;
+
+        auto avAttr = new (C) AvailableAttr(
+            SourceLoc(), SourceRange(), results.front(), SourceLoc(), AttrKind,
+            /*Message=*/"", /*Rename=*/"", /*Introduced=*/{}, SourceRange(),
+            /*Deprecated=*/{}, SourceRange(), /*Obsoleted=*/{}, SourceRange(),
+            /*Implicit=*/false, /*IsSPI=*/false);
+
+        MappedDecl->getAttrs().add(avAttr);
+      }
+    }
+
     // __attribute__((swift_attr("attribute"))) are handled by
     // importSwiftAttrAttributes(). Other attributes are ignored.
   }

test/ClangImporter/Inputs/availability_custom_domains_other.swift

@@ -7,5 +7,5 @@ func availableInArctic() { }
 func availableInMediterranean() { }
 
 func testOtherClangDecls() {
-  available_in_baltic()
+  available_in_baltic() // expected-error {{'available_in_baltic()' is only available in Baltic}}
 }

test/ClangImporter/availability_custom_domains.swift

@@ -9,11 +9,10 @@
 import Oceans // re-exports Rivers
 
 func testClangDecls() {
-  // FIXME: [availability] These references should be diagnosed as unavailable
-  available_in_arctic()
-  unavailable_in_pacific()
-  available_in_colorado_river_delta()
-  available_in_colorado()
+  available_in_arctic() // expected-error {{'available_in_arctic()' is only available in Arctic}}
+  unavailable_in_pacific() // expected-error {{'unavailable_in_pacific()' is unavailable}}
+  available_in_colorado_river_delta() // expected-error {{'available_in_colorado_river_delta()' is only available in Pacific}}
+  available_in_colorado() // expected-error {{'available_in_colorado()' is only available in Colorado}}
   available_in_baltic() // expected-error {{cannot find 'available_in_baltic' in scope}}
 }