Support raw identifiers (backtick-delimited identifiers containing non-identifier characters).

include/swift/AST/ASTContext.h

@@ -615,6 +615,10 @@ class ASTContext final {
   /// are the real (physical) module names on disk.
   void setModuleAliases(const llvm::StringMap<StringRef> &aliasMap);
 
+  /// Adds a given alias to the map of Identifiers between module aliases and
+  /// their actual names.
+  void addModuleAlias(StringRef moduleAlias, StringRef realName);
+
   /// Look up option used in \c getRealModuleName when module aliasing is applied.
   enum class ModuleAliasLookupOption {
     alwaysRealName,

include/swift/AST/ASTDemangler.h

@@ -306,6 +306,10 @@ class ASTBuilder {
 
   static GenericTypeDecl *getAcceptableTypeDeclCandidate(ValueDecl *decl,
                                               Demangle::Node::Kind kind);
+
+  /// Returns an identifier with the given name, automatically removing any
+  /// surrounding backticks that are present for raw identifiers.
+  Identifier getIdentifier(StringRef name);
 };
 
 SWIFT_END_INLINE_NAMESPACE

include/swift/AST/ASTPrinter.h

@@ -293,7 +293,8 @@ class ASTPrinter {
   void printEscapedStringLiteral(StringRef str);
 
   void printName(Identifier Name,
-                 PrintNameContext Context = PrintNameContext::Normal);
+                 PrintNameContext Context = PrintNameContext::Normal,
+                 bool IsSpecializedCxxType = false);
 
   void setIndent(unsigned NumSpaces) {
     CurrentIndentation = NumSpaces;
@@ -444,9 +445,10 @@ void printWithCompatibilityFeatureChecks(ASTPrinter &printer,
                                          Decl *decl,
                                          llvm::function_ref<void()> printBody);
 
-/// Determine whether we need to escape the given keyword within the
-/// given context, by wrapping it in backticks.
-bool escapeKeywordInContext(StringRef keyword, PrintNameContext context);
+/// Determine whether we need to escape the given name within the given
+/// context, by wrapping it in backticks.
+bool escapeIdentifierInContext(Identifier name, PrintNameContext context,
+                               bool isSpecializedCxxType = false);
 
 } // namespace swift
 

include/swift/AST/DiagnosticsSema.def

@@ -6417,6 +6417,14 @@ ERROR(objc_enum_case_multi,none,
 ERROR(objc_extension_not_class,none,
       "'@objc' can only be applied to an extension of a class", ())
 
+ERROR(objc_name_not_valid_identifier,none,
+      "'@objc' %0 name is not a valid Objective-C identifier",
+      (DescriptiveDeclKind))
+ERROR(objc_cannot_infer_name_raw_identifier,none,
+      "cannot infer '@objc' %0 name because the Swift name is not a valid "
+      "Objective-C identifier; specify the name in '@objc' explicitly",
+      (DescriptiveDeclKind))
+
 // If you change this, also change enum ObjCReason
 #define OBJC_ATTR_SELECT "select{marked @_cdecl|marked dynamic|marked @objc|marked @objcMembers|marked @IBOutlet|marked @IBAction|marked @IBSegueAction|marked @NSManaged|a member of an @objc protocol|implicitly @objc|an @objc override|an implementation of an @objc requirement|marked @IBInspectable|marked @GKInspectable|in an @objc extension of a class (without @nonobjc)|in an @objc @implementation extension of a class (without final or @nonobjc)|marked @objc by an access note}"
 

include/swift/AST/Identifier.h

@@ -101,19 +101,22 @@ class Identifier {
 
   /// isOperator - Return true if this identifier is an operator, false if it is
   /// a normal identifier.
-  /// FIXME: We should maybe cache this.
   bool isOperator() const {
     if (empty())
       return false;
     if (isEditorPlaceholder())
       return false;
-    if ((unsigned char)Pointer[0] < 0x80)
-      return isOperatorStartCodePoint((unsigned char)Pointer[0]);
 
     // Handle the high unicode case out of line.
     return isOperatorSlow();
   }
 
+  /// Returns true if this identifier contains non-identifier characters and
+  /// must always be escaped with backticks, even in contexts were other
+  /// escaped identifiers could omit backticks (like keywords as argument
+  /// labels).
+  bool mustAlwaysBeEscaped() const;
+
   bool isArithmeticOperator() const {
     return is("+") || is("-") || is("*") || is("/") || is("%");
   }
@@ -350,6 +353,10 @@ class DeclBaseName {
     return !isSpecial() && getIdentifier().isOperator();
   }
 
+  bool mustAlwaysBeEscaped() const {
+    return !isSpecial() && getIdentifier().mustAlwaysBeEscaped();
+  }
+
   bool isEditorPlaceholder() const {
     return !isSpecial() && getIdentifier().isEditorPlaceholder();
   }
@@ -571,7 +578,12 @@ class DeclName {
   bool isOperator() const {
     return getBaseName().isOperator();
   }
-
+
+  /// True if this name is an escaped identifier.
+  bool mustAlwaysBeEscaped() const {
+    return getBaseName().mustAlwaysBeEscaped();
+  }
+
   /// True if this name should be found by a decl ref or member ref under the
   /// name specified by 'refName'.
   ///
@@ -728,6 +740,8 @@ class DeclNameRef {
     return FullName.isOperator();
   }
 
+  bool mustAlwaysBeEscaped() const { return FullName.mustAlwaysBeEscaped(); }
+
   bool isCompoundName() const {
     return FullName.isCompoundName();
   }

include/swift/Basic/Features.def

@@ -252,6 +252,7 @@ LANGUAGE_FEATURE(NonescapableTypes, 446, "Nonescapable types")
 LANGUAGE_FEATURE(BuiltinEmplaceTypedThrows, 0, "Builtin.emplace typed throws")
 SUPPRESSIBLE_LANGUAGE_FEATURE(MemorySafetyAttributes, 458, "@unsafe attribute")
 LANGUAGE_FEATURE(ValueGenerics, 452, "Value generics feature (integer generics)")
+LANGUAGE_FEATURE(RawIdentifiers, 451, "Raw identifiers")
 
 // Swift 6
 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)

include/swift/Basic/Mangler.h

@@ -114,6 +114,13 @@ class Mangler {
     print(llvm::dbgs());
   }
 
+  /// Appends the given raw identifier to the buffer in the form required to
+  /// mangle it. This handles the transformations needed for such identifiers
+  /// to retain compatibility with older runtimes.
+  static void
+  appendRawIdentifierForRuntime(StringRef ident,
+                                llvm::SmallVectorImpl<char> &buffer);
+
 protected:
   /// Removes the last characters of the buffer by setting it's size to a
   /// smaller value.
@@ -143,7 +150,7 @@ class Mangler {
   SWIFT_DEBUG_DUMP;
 
   /// Appends a mangled identifier string.
-  void appendIdentifier(StringRef ident);
+  void appendIdentifier(StringRef ident, bool allowRawIdentifiers = true);
 
   // NOTE: the addSubstitution functions perform the value computation before
   // the assignment because there is no sequence point synchronising the

include/swift/Demangling/ManglingUtils.h

@@ -58,10 +58,16 @@ inline bool isWordEnd(char ch, char prevCh) {
   return false;
 }
 
+/// Returns true if \p ch is a valid character which may appear at the start
+/// of a symbol mangling.
+inline bool isValidSymbolStart(char ch) {
+  return isLetter(ch) || ch == '_' || ch == '$';
+}
+
 /// Returns true if \p ch is a valid character which may appear in a symbol
-/// mangling.
+/// mangling anywhere other than the first character.
 inline bool isValidSymbolChar(char ch) {
-  return isLetter(ch) || isDigit(ch) || ch == '_' || ch == '$';
+  return isValidSymbolStart(ch) || isDigit(ch);
 }
 
 /// Returns true if \p str contains any character which may not appear in a

include/swift/Frontend/ModuleInterfaceLoader.h

@@ -318,10 +318,11 @@ class ExplicitModuleMapParser {
 public:
   ExplicitModuleMapParser(llvm::BumpPtrAllocator &Allocator) : Saver(Allocator) {}
 
-  std::error_code
-  parseSwiftExplicitModuleMap(llvm::MemoryBufferRef BufferRef,
-                              llvm::StringMap<ExplicitSwiftModuleInputInfo> &swiftModuleMap,
-                              llvm::StringMap<ExplicitClangModuleInputInfo> &clangModuleMap) {
+  std::error_code parseSwiftExplicitModuleMap(
+      llvm::MemoryBufferRef BufferRef,
+      llvm::StringMap<ExplicitSwiftModuleInputInfo> &swiftModuleMap,
+      llvm::StringMap<ExplicitClangModuleInputInfo> &clangModuleMap,
+      llvm::StringMap<std::string> &moduleAliases) {
     using namespace llvm::yaml;
     // Use a new source manager instead of the one from ASTContext because we
     // don't want the JSON file to be persistent.
@@ -331,7 +332,8 @@ class ExplicitModuleMapParser {
       assert(DI != Stream.end() && "Failed to read a document");
       if (auto *MN = dyn_cast_or_null<SequenceNode>(DI->getRoot())) {
         for (auto &entry : *MN) {
-          if (parseSingleModuleEntry(entry, swiftModuleMap, clangModuleMap)) {
+          if (parseSingleModuleEntry(entry, swiftModuleMap, clangModuleMap,
+                                     moduleAliases)) {
             return std::make_error_code(std::errc::invalid_argument);
           }
         }
@@ -359,16 +361,19 @@ class ExplicitModuleMapParser {
       llvm_unreachable("Unexpected JSON value for isFramework");
   }
 
-  bool parseSingleModuleEntry(llvm::yaml::Node &node,
-                              llvm::StringMap<ExplicitSwiftModuleInputInfo> &swiftModuleMap,
-                              llvm::StringMap<ExplicitClangModuleInputInfo> &clangModuleMap) {
+  bool parseSingleModuleEntry(
+      llvm::yaml::Node &node,
+      llvm::StringMap<ExplicitSwiftModuleInputInfo> &swiftModuleMap,
+      llvm::StringMap<ExplicitClangModuleInputInfo> &clangModuleMap,
+      llvm::StringMap<std::string> &moduleAliases) {
     using namespace llvm::yaml;
     auto *mapNode = dyn_cast<MappingNode>(&node);
     if (!mapNode)
       return true;
     StringRef moduleName;
     std::optional<std::string> swiftModulePath, swiftModuleDocPath,
-        swiftModuleSourceInfoPath, swiftModuleCacheKey, clangModuleCacheKey;
+        swiftModuleSourceInfoPath, swiftModuleCacheKey, clangModuleCacheKey,
+        moduleAlias;
     std::optional<std::vector<std::string>> headerDependencyPaths;
     std::string clangModuleMapPath = "", clangModulePath = "";
     bool isFramework = false, isSystem = false,
@@ -405,6 +410,8 @@ class ExplicitModuleMapParser {
           clangModuleCacheKey = val.str();
         } else if (key == "isBridgingHeaderDependency") {
           isBridgingHeaderDependency = parseBoolValue(val);
+        } else if (key == "moduleAlias") {
+          moduleAlias = val.str();
         } else {
           // Being forgiving for future fields.
           continue;
@@ -439,6 +446,9 @@ class ExplicitModuleMapParser {
                                          clangModuleCacheKey);
       didInsert = clangModuleMap.try_emplace(moduleName, std::move(entry)).second;
     }
+    if (didInsert && moduleAlias.has_value()) {
+      moduleAliases[*moduleAlias] = moduleName;
+    }
     // Prevent duplicate module names.
     return !didInsert;
   }

include/swift/IDE/CompletionLookup.h

@@ -340,6 +340,8 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
   void addValueBaseName(CodeCompletionResultBuilder &Builder,
                         DeclBaseName Name);
 
+  void addIdentifier(CodeCompletionResultBuilder &Builder, Identifier Name);
+
   void addLeadingDot(CodeCompletionResultBuilder &Builder);
 
   void addTypeAnnotation(CodeCompletionResultBuilder &Builder, Type T,

include/swift/Parse/Lexer.h

@@ -395,6 +395,15 @@ class Lexer {
   /// identifier, without escaping characters.
   static bool isIdentifier(StringRef identifier);
 
+  // Returns true if the given string is a raw identifier that must always
+  // be escaped by backticks when printing it back in source form or writing
+  // its name into runtime metadata.
+  static bool identifierMustAlwaysBeEscaped(StringRef str);
+
+  /// Determines if the given string is a valid non-operator
+  /// identifier if it were surrounded by backticks.
+  static bool isValidAsEscapedIdentifier(StringRef identifier);
+
   /// Determine the token kind of the string, given that it is a valid
   /// non-operator identifier. Return tok::identifier if the string is not a
   /// reserved word.

lib/AST/ASTContext.cpp

@@ -2136,16 +2136,20 @@ void ASTContext::setModuleAliases(const llvm::StringMap<StringRef> &aliasMap) {
   for (auto k: aliasMap.keys()) {
     auto v = aliasMap.lookup(k);
     if (!v.empty()) {
-      auto key = getIdentifier(k);
-      auto val = getIdentifier(v);
-      // key is a module alias, val is its corresponding real name
-      ModuleAliasMap[key] = std::make_pair(val, true);
-      // add an entry with an alias as key for an easier lookup later
-      ModuleAliasMap[val] = std::make_pair(key, false);
+      addModuleAlias(k, v);
     }
   }
 }
 
+void ASTContext::addModuleAlias(StringRef moduleAlias, StringRef realName) {
+  auto key = getIdentifier(moduleAlias);
+  auto val = getIdentifier(realName);
+  // key is a module alias, val is its corresponding real name
+  ModuleAliasMap[key] = std::make_pair(val, true);
+  // add an entry with an alias as key for an easier lookup later
+  ModuleAliasMap[val] = std::make_pair(key, false);
+}
+
 Identifier ASTContext::getRealModuleName(Identifier key, ModuleAliasLookupOption option) const {
   auto found = ModuleAliasMap.find(key);
   if (found == ModuleAliasMap.end())