Introduce special decl names

Special DeclNames represent names that do not have an identifier in the
surface language. This implies serializing the information about whether
a name is special together with its identifier (if it is not special)
in both the module file and the swift lookup table.

Author: ahoppen

include/swift/AST/Identifier.h

@@ -51,6 +51,8 @@ enum class DeclRefKind {
 /// ASTContext.  It just wraps a nul-terminated "const char*".
 class Identifier {
   friend class ASTContext;
+  friend class DeclBaseName;
+
   const char *Pointer;
 
   /// Constructor, only accessible by ASTContext, which handles the uniquing.
@@ -207,14 +209,39 @@ namespace swift {
 /// Wrapper that may either be an Identifier or a special name
 /// (e.g. for subscripts)
 class DeclBaseName {
+public:
+  enum class Kind: uint8_t {
+    Normal,
+    Subscript
+  };
+  
+private:
+  /// In a special DeclName represenenting a subscript, this opaque pointer
+  /// is used as the data of the base name identifier.
+  /// This is an implementation detail that should never leak outside of
+  /// DeclName.
+  static void *SubscriptIdentifierData;
+
   Identifier Ident;
 
 public:
   DeclBaseName() : DeclBaseName(Identifier()) {}
 
   DeclBaseName(Identifier I) : Ident(I) {}
 
-  bool isSpecial() const { return false; }
+  static DeclBaseName createSubscript() {
+    return DeclBaseName(Identifier((const char *)SubscriptIdentifierData));
+  }
+
+  Kind getKind() const {
+    if (Ident.get() == SubscriptIdentifierData) {
+      return Kind::Subscript;
+    } else {
+      return Kind::Normal;
+    }
+  }
+
+  bool isSpecial() const { return getKind() != Kind::Normal; }
 
   /// Return the identifier backing the name. Assumes that the name is not
   /// special.
@@ -238,12 +265,17 @@ class DeclBaseName {
   StringRef userFacingName() const {
     if (empty())
       return "_";
-    return getIdentifier().str();
+
+    switch (getKind()) {
+    case Kind::Normal:
+      return getIdentifier().str();
+    case Kind::Subscript:
+      return "subscript";
+    }
   }
 
   int compare(DeclBaseName other) const {
-    // TODO: Sort special names cleverly
-    return getIdentifier().compare(other.getIdentifier());
+    return userFacingName().compare(other.userFacingName());
   }
 
   bool operator==(StringRef Str) const {

include/swift/AST/KnownIdentifiers.def

@@ -90,7 +90,6 @@ IDENTIFIER(simd)
 IDENTIFIER(some)
 IDENTIFIER(storage)
 IDENTIFIER(stringValue)
-IDENTIFIER(subscript)
 IDENTIFIER(super)
 IDENTIFIER(superDecoder)
 IDENTIFIER(superEncoder)

include/swift/Serialization/ModuleFile.h

@@ -740,7 +740,11 @@ class ModuleFile : public LazyMemberLoader {
   /// Returns the type with the given ID, deserializing it if needed.
   llvm::Expected<Type> getTypeChecked(serialization::TypeID TID);
 
-  /// Returns the identifier with the given ID, deserializing it if needed.
+  /// Returns the base name with the given ID, deserializing it if needed.
+  DeclBaseName getDeclBaseName(serialization::IdentifierID IID);
+
+  /// Convenience method to retrieve the identifier backing the name with
+  /// given ID. Asserts that the name with this ID is not special.
   Identifier getIdentifier(serialization::IdentifierID IID);
 
   /// Returns the decl with the given ID, deserializing it if needed.

include/swift/Serialization/ModuleFormat.h

@@ -54,7 +54,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// in source control, you should also update the comment to briefly
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
-const uint16_t VERSION_MINOR = 349; // Last change: '@autoclosure' and '@noescape' no longer decl attributes.
+const uint16_t VERSION_MINOR = 350; // Last change: special decl names
 
 using DeclID = PointerEmbeddedInt<unsigned, 31>;
 using DeclIDField = BCFixed<31>;
@@ -342,18 +342,27 @@ using OptionalTypeKindField = BCFixed<2>;
 
 // These IDs must \em not be renumbered or reordered without incrementing
 // VERSION_MAJOR.
-enum SpecialModuleID : uint8_t {
+enum class DeclNameKind: uint8_t {
+  Normal,
+  Subscript
+};
+
+// These IDs must \em not be renumbered or reordered without incrementing
+// VERSION_MAJOR.
+enum SpecialIdentifierID : uint8_t {
   /// Special IdentifierID value for the Builtin module.
   BUILTIN_MODULE_ID = 0,
   /// Special IdentifierID value for the current module.
   CURRENT_MODULE_ID,
   /// Special value for the module for imported Objective-C headers.
   OBJC_HEADER_MODULE_ID,
+  /// Special value for the special subscript name
+  SUBSCRIPT_ID,
 
-  /// The number of special modules. This value should never be encoded;
+  /// The number of special Identifier IDs. This value should never be encoded;
   /// it should only be used to count the number of names above. As such, it
   /// is correct and necessary to add new values above this one.
-  NUM_SPECIAL_MODULES
+  NUM_SPECIAL_IDS
 };
 
 // These IDs must \em not be renumbered or reordered without incrementing

lib/AST/ASTMangler.cpp

@@ -540,8 +540,15 @@ void ASTMangler::appendDeclName(const ValueDecl *decl) {
         break;
     }
   } else if (decl->hasName()) {
-    // TODO: Handle special names
-    appendIdentifier(decl->getBaseName().getIdentifier().str());
+    // FIXME: Should a mangled subscript name contain the string "subscript"?
+    switch (decl->getBaseName().getKind()) {
+    case DeclBaseName::Kind::Normal:
+      appendIdentifier(decl->getBaseName().getIdentifier().str());
+      break;
+    case DeclBaseName::Kind::Subscript:
+      appendIdentifier("subscript");
+      break;
+    }
   } else {
     assert(AllowNamelessEntities && "attempt to mangle unnamed decl");
     // Fall back to an unlikely name, so that we still generate a valid

lib/AST/Identifier.cpp

@@ -20,6 +20,8 @@
 #include "llvm/Support/ConvertUTF.h"
 using namespace swift;
 
+void *DeclBaseName::SubscriptIdentifierData =
+    &DeclBaseName::SubscriptIdentifierData;
 
 raw_ostream &llvm::operator<<(raw_ostream &OS, Identifier I) {
   if (I.get() == nullptr)

lib/ClangImporter/ClangImporter.cpp

@@ -2974,7 +2974,7 @@ void ClangImporter::Implementation::lookupValue(
   auto &clangCtx = getClangASTContext();
   auto clangTU = clangCtx.getTranslationUnitDecl();
 
-  for (auto entry : table.lookup(name.getBaseIdentifier().str(), clangTU)) {
+  for (auto entry : table.lookup(name.getBaseName(), clangTU)) {
     // If the entry is not visible, skip it.
     if (!isVisibleClangEntry(clangCtx, entry)) continue;
 
@@ -3070,7 +3070,7 @@ void ClangImporter::Implementation::lookupVisibleDecls(
 
   // Look for namespace-scope entities with each base name.
   for (auto baseName : baseNames) {
-    lookupValue(table, SwiftContext.getIdentifier(baseName), consumer);
+    lookupValue(table, baseName.toDeclBaseName(SwiftContext), consumer);
   }
 }
 
@@ -3079,9 +3079,8 @@ void ClangImporter::Implementation::lookupObjCMembers(
        DeclName name,
        VisibleDeclConsumer &consumer) {
   auto &clangCtx = getClangASTContext();
-  auto baseName = name.getBaseIdentifier().str();
 
-  for (auto clangDecl : table.lookupObjCMembers(baseName)) {
+  for (auto clangDecl : table.lookupObjCMembers(name.getBaseName())) {
     // If the entry is not visible, skip it.
     if (!isVisibleClangEntry(clangCtx, clangDecl)) continue;
 
@@ -3121,7 +3120,7 @@ void ClangImporter::Implementation::lookupAllObjCMembers(
 
   // Look for Objective-C members with each base name.
   for (auto baseName : baseNames) {
-    lookupObjCMembers(table, SwiftContext.getIdentifier(baseName), consumer);
+    lookupObjCMembers(table, baseName.toDeclBaseName(SwiftContext), consumer);
   }
 }
 

lib/ClangImporter/ImportDecl.cpp

@@ -5410,7 +5410,7 @@ SwiftDeclConverter::getImplicitProperty(ImportedName importedName,
       Impl.findLookupTable(*getClangSubmoduleForDecl(accessor));
   assert(lookupTable && "No lookup table?");
   bool foundAccessor = false;
-  for (auto entry : lookupTable->lookup(propertyName.str(),
+  for (auto entry : lookupTable->lookup(SerializedSwiftName(propertyName),
                                         importedName.getEffectiveContext())) {
     auto decl = entry.dyn_cast<clang::NamedDecl *>();
     if (!decl)
@@ -6246,7 +6246,7 @@ SwiftDeclConverter::importSubscript(Decl *decl,
   // Build the subscript declaration.
   auto &C = Impl.SwiftContext;
   auto bodyParams = getterThunk->getParameterList(1)->clone(C);
-  DeclName name(C, C.Id_subscript, {Identifier()});
+  DeclName name(C, DeclBaseName::createSubscript(), {Identifier()});
   auto subscript = Impl.createDeclWithClangNode<SubscriptDecl>(
       getter->getClangNode(), getOverridableAccessibility(dc), name,
       decl->getLoc(), bodyParams, decl->getLoc(),