Fix effective context construction for NS_OPTIONS in linkage spec

When the ClangImporter imports a name, it associates it with a
an EffectiveClangContext. An EffectiveClangContext can be thought of
as the Clang scope the declaration will reside in, as far as importing
into Swift is concerned. This helps API notes and NS_SWIFT_NAME
to manipulate the SDK interface presented to Swift users.

When a entry is added to the Swift lookup table, it is associated
with a context. This context is a type and a name, used to effectively
namespace entries in the table. This context is derived from the
EffectiveClangContext associated with the name. This translation is
handled by SwiftLookupTable::translateContextDecl among other machinery.
This method in particular, understands only how to translate a set of
Clang nodes, and fails to create a context in other cases.

Prior to this patch, the EffectiveClangContext of declarations annotated
with UIKIT_EXTERN, with cxx-interop turned on, was a LinkageSpecDecl.
This results in context translation failure, and warnings produced in
SwiftLookupTable::finalizeLookupTable. This patch corrects name import
behavior to skip over the LinkageSpecDecl, and use the enclosing
TranslationUnit instead. This is appropriate and performed by
`determineEffectiveContext` as a LinkageSpecDecl is a so called
"transparent" context. That is its members are semantically declared and
accessible outside the context without additional qualification.

This patch tests using API notes, as that is the method UIKit uses. The
issue could just as easily be surface with a NS_SWIFT_NAME annotation.
Even without any annotation at all, the we would still fail to
translate, though there would likely be no corresponding warnings.

Author: NuriAmari

lib/ClangImporter/SwiftLookupTable.h

@@ -188,6 +188,12 @@ class EffectiveClangContext {
   EffectiveClangContext(const clang::DeclContext *dc)
       : KindOrBiasedLength(DeclContext) {
     assert(dc != nullptr && "use null constructor instead");
+
+    // Skip over any linkage spec decl contexts
+    while (auto externCDecl = dyn_cast<clang::LinkageSpecDecl>(dc)) {
+      dc = externCDecl->getLexicalDeclContext();
+    }
+
     if (auto tagDecl = dyn_cast<clang::TagDecl>(dc)) {
       DC = tagDecl->getCanonicalDecl();
     } else if (auto oiDecl = dyn_cast<clang::ObjCInterfaceDecl>(dc)) {
@@ -198,11 +204,8 @@ class EffectiveClangContext {
       DC = omDecl->getCanonicalDecl();
     } else if (auto fDecl = dyn_cast<clang::FunctionDecl>(dc)) {
       DC = fDecl->getCanonicalDecl();
-    } else if (auto externCDecl = dyn_cast<clang::LinkageSpecDecl>(dc)) {
-      DC = externCDecl->getLexicalDeclContext();
     } else {
       assert(isa<clang::TranslationUnitDecl>(dc) ||
-             isa<clang::LinkageSpecDecl>(dc) ||
              isa<clang::NamespaceDecl>(dc) ||
              isa<clang::ObjCContainerDecl>(dc) &&
                  "No other kinds of effective Clang contexts");
@@ -526,7 +529,7 @@ class SwiftLookupTable {
 
   /// Retrieve the set of base names that are stored in the globals-as-members lookup table.
   SmallVector<SerializedSwiftName, 4> allGlobalsAsMembersBaseNames();
-  
+
   /// Lookup Objective-C members with the given base name, regardless
   /// of context.
   SmallVector<clang::NamedDecl *, 4>

test/Interop/Cxx/enum/Inputs/CenumsNSOptions.apinotes

@@ -0,0 +1,10 @@
+Name: CenumsNSOptions
+Tags:
+- Name: UIPrinterJobTypes
+  SwiftName: UIPrinter.JobTypes
+SwiftVersions:
+- Version: 4
+  Tags:
+  - Name: UIPrinterJobTypes
+    SwiftName: UIPrinterJobTypes
+

test/Interop/Cxx/enum/Inputs/c-enums-NS_OPTIONS.h

@@ -18,8 +18,10 @@ extern "C" {
 #define CF_OPTIONS(_type, _name) _type __attribute__((availability(swift, unavailable))) _name; enum __CF_OPTIONS_ATTRIBUTES : _name
 #define NS_OPTIONS(_type, _name) CF_OPTIONS(_type, _name)
 #define NS_REFINED_FOR_SWIFT __attribute__((swift_private))
+#define UIKIT_EXTERN extern "C" __attribute__((visibility("default")))
 
 typedef unsigned long NSUInteger;
+typedef long NSInteger;
 
 typedef NS_OPTIONS(NSUInteger, NSBinarySearchingOptions) {
 	NSBinarySearchingFirstEqual = (1UL << 8),
@@ -39,4 +41,21 @@ typedef NS_OPTIONS(NSUInteger, NSAttributedStringFormattingOptions) {
 - (instancetype)initWithOptions:(NSAttributedStringFormattingOptions)options
     NS_REFINED_FOR_SWIFT;
 @end
+
+UIKIT_EXTERN
+@interface UIPrinter
+
+typedef NS_OPTIONS(NSInteger, UIPrinterJobTypes) {
+  UIPrinterJobTypeUnknown = 0,
+  UIPrinterJobTypeDocument = 1 << 0,
+  UIPrinterJobTypeEnvelope = 1 << 1,
+  UIPrinterJobTypeLabel = 1 << 2,
+  UIPrinterJobTypePhoto = 1 << 3,
+  UIPrinterJobTypeReceipt = 1 << 4,
+  UIPrinterJobTypeRoll = 1 << 5,
+  UIPrinterJobTypeLargeFormat = 1 << 6,
+  UIPrinterJobTypePostcard = 1 << 7
+};
+
+@end
 }

test/Interop/Cxx/enum/c-enums-NS_OPTIONS-transparent-linkage-spec-decl.swift

@@ -0,0 +1,10 @@
+// RUN: %empty-directory(%t/cache)
+// RUN: %target-swift-frontend %s -swift-version 5 -I %S/Inputs -typecheck -module-cache-path %t/cache -enable-experimental-cxx-interop 2>&1 | %FileCheck --allow-empty %s
+
+// REQUIRES: objc_interop
+
+import CenumsNSOptions
+
+// CHECK-NOT: warning: imported declaration '' could not be mapped to 'UIPrinter.JobTypes'
+// CHECK-NOT: note: please report this issue to the owners of 'CenumsNSOptions'
+