[ClangImporter] Honor Swift 4 API notes in Swift 3 mode

*** Depends on Clang change "[APINotes] Record what version caused ***
*** an annotation to get replaced." Update your Clang checkout!    ***

More generally, change the meaning of the SwiftVersions section in API
notes to be "this version or earlier" rather than "exactly this
version". We mostly get this behavior for free from the Clang-side
changes, but for SwiftName and the enum annotations we look at inactive
attributes as well. The latter is simple, but the former means being
careful about finding the annotation we /would/ have picked, i.e. the
one closest to the version we requested.

Author: jrose-apple

lib/ClangImporter/ImportEnumInfo.cpp

@@ -68,7 +68,7 @@ void EnumInfo::classifyEnum(ASTContext &ctx, const clang::EnumDecl *decl,
   // If API notes have /removed/ a FlagEnum or EnumExtensibility attribute,
   // then we don't need to check the macros.
   for (auto *attr : decl->specific_attrs<clang::SwiftVersionedAttr>()) {
-    if (!attr->getVersion().empty())
+    if (!attr->getIsReplacedByActive())
       continue;
     if (isa<clang::FlagEnumAttr>(attr->getAttrToAdd()) ||
         isa<clang::EnumExtensibilityAttr>(attr->getAttrToAdd())) {

lib/ClangImporter/ImportName.cpp

@@ -545,12 +545,58 @@ determineCtorInitializerKind(const clang::ObjCMethodDecl *method) {
   return None;
 }
 
-template <typename A>
-static bool matchesVersion(A *versionedAttr, ImportNameVersion version) {
-  clang::VersionTuple attrVersion = versionedAttr->getVersion();
-  if (attrVersion.empty())
-    return version == ImportNameVersion::maxVersion();
-  return attrVersion.getMajor() == version.majorVersionNumber();
+namespace {
+/// Aggregate struct for the common members of clang::SwiftVersionedAttr and
+/// clang::SwiftVersionedRemovalAttr.
+///
+/// For a SwiftVersionedRemovalAttr, the Attr member will be null.
+struct VersionedSwiftNameInfo {
+  const clang::SwiftNameAttr *Attr;
+  clang::VersionTuple Version;
+  bool IsReplacedByActive;
+};
+
+/// The action to take upon seeing a particular versioned swift_name annotation.
+enum class VersionedSwiftNameAction {
+  /// This annotation is not interesting.
+  Ignore,
+  /// This annotation is better than whatever we have so far.
+  Use,
+  /// This annotation is better than nothing, but that's all; don't bother
+  /// recording its version.
+  UseAsFallback,
+  /// This annotation itself isn't interesting, but its version shows that the
+  /// correct answer is whatever's currently active.
+  ResetToActive
+};
+} // end anonymous namespace
+
+static VersionedSwiftNameAction
+checkVersionedSwiftName(VersionedSwiftNameInfo info,
+                        clang::VersionTuple bestSoFar,
+                        ImportNameVersion requestedVersion) {
+  if (!bestSoFar.empty() && bestSoFar <= info.Version)
+    return VersionedSwiftNameAction::Ignore;
+
+  if (info.IsReplacedByActive) {
+    // We know that there are no versioned names between the active version and
+    // a replacement version, because otherwise /that/ name would be active.
+    // So if replacement < requested, we want to use the old value that was
+    // replaced (but with very low priority), and otherwise we want to use the
+    // new value that is now active. (Special case: replacement = 0 means that
+    // a header annotation was replaced by an unversioned API notes annotation.)
+    if (info.Version.empty() ||
+        info.Version.getMajor() >= requestedVersion.majorVersionNumber()) {
+      return VersionedSwiftNameAction::ResetToActive;
+    }
+    if (bestSoFar.empty())
+      return VersionedSwiftNameAction::UseAsFallback;
+    return VersionedSwiftNameAction::Ignore;
+  }
+
+  if (info.Version.getMajor() < requestedVersion.majorVersionNumber())
+    return VersionedSwiftNameAction::Ignore;
+  return VersionedSwiftNameAction::Use;
 }
 
 
@@ -567,26 +613,60 @@ findSwiftNameAttr(const clang::Decl *decl, ImportNameVersion version) {
     return nullptr;
 
   // Handle versioned API notes for Swift 3 and later. This is the common case.
-  if (version != ImportNameVersion::swift2()) {
+  if (version > ImportNameVersion::swift2()) {
+    const auto *activeAttr = decl->getAttr<clang::SwiftNameAttr>();
+    const clang::SwiftNameAttr *result = activeAttr;
+    clang::VersionTuple bestSoFar;
     for (auto *attr : decl->attrs()) {
+      VersionedSwiftNameInfo info;
+
       if (auto *versionedAttr = dyn_cast<clang::SwiftVersionedAttr>(attr)) {
-        if (!matchesVersion(versionedAttr, version))
+        auto *added =
+          dyn_cast<clang::SwiftNameAttr>(versionedAttr->getAttrToAdd());
+        if (!added)
           continue;
-        if (auto *added =
-              dyn_cast<clang::SwiftNameAttr>(versionedAttr->getAttrToAdd())) {
-          return added;
-        }
-      }
 
-      if (auto *removeAttr = dyn_cast<clang::SwiftVersionedRemovalAttr>(attr)) {
-        if (!matchesVersion(removeAttr, version))
+        info = {added, versionedAttr->getVersion(),
+                versionedAttr->getIsReplacedByActive()};
+
+      } else if (auto *removeAttr =
+                   dyn_cast<clang::SwiftVersionedRemovalAttr>(attr)) {
+        if (removeAttr->getAttrKindToRemove() != clang::attr::SwiftName)
           continue;
-        if (removeAttr->getAttrKindToRemove() == clang::attr::SwiftName)
-          return nullptr;
+        info = {nullptr, removeAttr->getVersion(),
+                removeAttr->getIsReplacedByActive()};
+
+      } else {
+        continue;
+      }
+
+      switch (checkVersionedSwiftName(info, bestSoFar, version)) {
+      case VersionedSwiftNameAction::Ignore:
+        continue;
+      case VersionedSwiftNameAction::Use:
+        result = info.Attr;
+        bestSoFar = info.Version;
+        break;
+      case VersionedSwiftNameAction::UseAsFallback:
+        // HACK: If there's a swift_name attribute in the headers /and/ in the
+        // unversioned API notes /and/ in the active versioned API notes, there
+        // will be two "replacement" attributes, one for each of the first two
+        // cases. Prefer the first one we see, because that turns out to be the
+        // one from the API notes, which matches the semantics when there are no
+        // versioned API notes. (This isn't very principled but there's at least
+        // a test to tell us if it changes.)
+        if (result == activeAttr)
+          result = info.Attr;
+        assert(bestSoFar.empty());
+        break;
+      case VersionedSwiftNameAction::ResetToActive:
+        result = activeAttr;
+        bestSoFar = info.Version;
+        break;
       }
     }
 
-    return decl->getAttr<clang::SwiftNameAttr>();
+    return result;
   }
 
   // The remainder of this function emulates the limited form of swift_name

test/APINotes/Inputs/custom-frameworks/APINotesFrameworkTest.framework/Headers/APINotesFrameworkTest.apinotes

@@ -65,6 +65,23 @@ Functions:
 Tags:
   - Name: InnerInSwift4
     SwiftName: Outer.Inner
+Globals:
+  - Name: multiVersionedGlobal34Notes
+    SwiftName: multiVersionedGlobal34Notes_NEW
+  - Name: multiVersionedGlobal34Both
+    SwiftName: multiVersionedGlobal34Both_NEW
+  - Name: multiVersionedGlobal345Notes
+    SwiftName: multiVersionedGlobal345Notes_NEW
+  - Name: multiVersionedGlobal345Both
+    SwiftName: multiVersionedGlobal345Both_NEW
+  - Name: multiVersionedGlobal4Notes
+    SwiftName: multiVersionedGlobal4Notes_NEW
+  - Name: multiVersionedGlobal4Both
+    SwiftName: multiVersionedGlobal4Both_NEW
+  - Name: multiVersionedGlobal45Notes
+    SwiftName: multiVersionedGlobal45Notes_NEW
+  - Name: multiVersionedGlobal45Both
+    SwiftName: multiVersionedGlobal45Both_NEW
 SwiftVersions:
   - Version: 3.0
     Classes:
@@ -207,3 +224,72 @@ SwiftVersions:
         SwiftName: aliasRenamedSwift3
       - Name: OptionyEnumRenamed
         SwiftName: renamedSwift3
+    Globals:
+      - Name: multiVersionedGlobal34
+        SwiftName: multiVersionedGlobal34_3
+      - Name: multiVersionedGlobal34Header
+        SwiftName: multiVersionedGlobal34Header_3
+      - Name: multiVersionedGlobal34Notes
+        SwiftName: multiVersionedGlobal34Notes_3
+      - Name: multiVersionedGlobal34Both
+        SwiftName: multiVersionedGlobal34Both_3
+      - Name: multiVersionedGlobal345
+        SwiftName: multiVersionedGlobal345_3
+      - Name: multiVersionedGlobal345Header
+        SwiftName: multiVersionedGlobal345Header_3
+      - Name: multiVersionedGlobal345Notes
+        SwiftName: multiVersionedGlobal345Notes_3
+      - Name: multiVersionedGlobal345Both
+        SwiftName: multiVersionedGlobal345Both_3
+  - Version: 5
+    Globals:
+      - Name: multiVersionedGlobal345
+        SwiftName: multiVersionedGlobal345_5
+      - Name: multiVersionedGlobal345Header
+        SwiftName: multiVersionedGlobal345Header_5
+      - Name: multiVersionedGlobal345Notes
+        SwiftName: multiVersionedGlobal345Notes_5
+      - Name: multiVersionedGlobal345Both
+        SwiftName: multiVersionedGlobal345Both_5
+      - Name: multiVersionedGlobal45
+        SwiftName: multiVersionedGlobal45_5
+      - Name: multiVersionedGlobal45Header
+        SwiftName: multiVersionedGlobal45Header_5
+      - Name: multiVersionedGlobal45Notes
+        SwiftName: multiVersionedGlobal45Notes_5
+      - Name: multiVersionedGlobal45Both
+        SwiftName: multiVersionedGlobal45Both_5
+  - Version: 4 # Versions are deliberately ordered as "3, 5, 4" to catch bugs.
+    Globals:
+      - Name: multiVersionedGlobal34
+        SwiftName: multiVersionedGlobal34_4
+      - Name: multiVersionedGlobal34Header
+        SwiftName: multiVersionedGlobal34Header_4
+      - Name: multiVersionedGlobal34Notes
+        SwiftName: multiVersionedGlobal34Notes_4
+      - Name: multiVersionedGlobal34Both
+        SwiftName: multiVersionedGlobal34Both_4
+      - Name: multiVersionedGlobal345
+        SwiftName: multiVersionedGlobal345_4
+      - Name: multiVersionedGlobal345Header
+        SwiftName: multiVersionedGlobal345Header_4
+      - Name: multiVersionedGlobal345Notes
+        SwiftName: multiVersionedGlobal345Notes_4
+      - Name: multiVersionedGlobal345Both
+        SwiftName: multiVersionedGlobal345Both_4
+      - Name: multiVersionedGlobal4
+        SwiftName: multiVersionedGlobal4_4
+      - Name: multiVersionedGlobal4Header
+        SwiftName: multiVersionedGlobal4Header_4
+      - Name: multiVersionedGlobal4Notes
+        SwiftName: multiVersionedGlobal4Notes_4
+      - Name: multiVersionedGlobal4Both
+        SwiftName: multiVersionedGlobal4Both_4
+      - Name: multiVersionedGlobal45
+        SwiftName: multiVersionedGlobal45_4
+      - Name: multiVersionedGlobal45Header
+        SwiftName: multiVersionedGlobal45Header_4
+      - Name: multiVersionedGlobal45Notes
+        SwiftName: multiVersionedGlobal45Notes_4
+      - Name: multiVersionedGlobal45Both
+        SwiftName: multiVersionedGlobal45Both_4

test/APINotes/Inputs/custom-frameworks/APINotesFrameworkTest.framework/Headers/APINotesFrameworkTest.h

@@ -32,6 +32,7 @@ __attribute__((objc_root_class))
 
 #import <APINotesFrameworkTest/Classes.h>
 #import <APINotesFrameworkTest/Enums.h>
+#import <APINotesFrameworkTest/Globals.h>
 #import <APINotesFrameworkTest/ImportAsMember.h>
 #import <APINotesFrameworkTest/Properties.h>
 #import <APINotesFrameworkTest/Protocols.h>

test/APINotes/Inputs/custom-frameworks/APINotesFrameworkTest.framework/Headers/Globals.h

@@ -0,0 +1,23 @@
+#pragma clang assume_nonnull begin
+
+int multiVersionedGlobal4;
+int multiVersionedGlobal4Notes;
+int multiVersionedGlobal4Header __attribute__((swift_name("multiVersionedGlobal4Header_NEW")));
+int multiVersionedGlobal4Both __attribute__((swift_name("multiVersionedGlobal4Both_OLD")));
+
+int multiVersionedGlobal34;
+int multiVersionedGlobal34Notes;
+int multiVersionedGlobal34Header __attribute__((swift_name("multiVersionedGlobal34Header_NEW")));
+int multiVersionedGlobal34Both __attribute__((swift_name("multiVersionedGlobal34Both_OLD")));
+
+int multiVersionedGlobal45;
+int multiVersionedGlobal45Notes;
+int multiVersionedGlobal45Header __attribute__((swift_name("multiVersionedGlobal45Header_NEW")));
+int multiVersionedGlobal45Both __attribute__((swift_name("multiVersionedGlobal45Both_OLD")));
+
+int multiVersionedGlobal345;
+int multiVersionedGlobal345Notes;
+int multiVersionedGlobal345Header __attribute__((swift_name("multiVersionedGlobal345Header_NEW")));
+int multiVersionedGlobal345Both __attribute__((swift_name("multiVersionedGlobal345Both_OLD")));
+
+#pragma clang assume_nonnull end