Parse module selectors in permitted locations

Author: beccadax

include/swift/AST/DiagnosticsParse.def

@@ -93,6 +93,15 @@ ERROR(forbidden_interpolated_string,none,
 ERROR(forbidden_extended_escaping_string,none,
       "%0 cannot be an extended escaping string literal", (StringRef))
 
+ERROR(expected_identifier_in_module_selector,none,
+      "expected module name in module selector", ())
+ERROR(expected_identifier_after_module_selector,none,
+      "expected identifier after module selector", ())
+NOTE(extra_whitespace_module_selector,none,
+     "remove extraneous whitespace after '::'", ())
+ERROR(module_selector_submodule_not_allowed,none,
+      "module selector cannot specify a submodule", ())
+
 //------------------------------------------------------------------------------
 // MARK: Lexer diagnostics
 //------------------------------------------------------------------------------

include/swift/Parse/Parser.h

@@ -1820,6 +1820,23 @@ class Parser {
   void parseOptionalArgumentLabel(Identifier &name, SourceLoc &loc,
                                   bool isAttr = false);
 
+  /// If a \c module-selector is present, returns a true value (specifically,
+  /// 1 or 2 depending on how many tokens should be consumed to skip it).
+  unsigned isAtModuleSelector();
+
+  /// Attempts to parse a \c module-selector if one is present.
+  ///
+  /// \verbatim
+  ///   module-selector: identifier '::'
+  /// \endverbatim
+  ///
+  /// \return \c None if no selector is present or a selector is present but
+  ///         is not allowed; an instance with an empty \c Identifier if a
+  ///         selector is present but has no valid identifier; an instance with
+  ///         a valid \c Identifier if a selector is present and includes a
+  ///         module name.
+  std::optional<Located<Identifier>> parseModuleSelector();
+
   enum class DeclNameFlag : uint8_t {
     /// If passed, operator basenames are allowed.
     AllowOperators = 1 << 0,
@@ -1832,6 +1849,9 @@ class Parser {
     /// not ordinary identifiers.
     AllowKeywordsUsingSpecialNames = AllowKeywords | 1 << 2,
 
+    /// If passed, module selectors are not permitted on this declaration name.
+    ModuleSelectorUnsupported = 1 << 3,
+
     /// If passed, compound names with argument lists are allowed, unless they
     /// have empty argument lists.
     AllowCompoundNames = 1 << 4,
@@ -1876,7 +1896,8 @@ class Parser {
       SourceLoc &rightAngleLoc, ArgumentList *&argList, bool isExprBasic,
       DiagRef diag);
 
-  ParserResult<Expr> parseExprIdentifier(bool allowKeyword);
+  ParserResult<Expr> parseExprIdentifier(bool allowKeyword,
+                                         bool allowModuleSelector = true);
   Expr *parseExprEditorPlaceholder(Token PlaceholderTok,
                                    Identifier PlaceholderId);
 

lib/Parse/Lexer.cpp

@@ -819,9 +819,12 @@ static bool isLeftBound(const char *tokBegin, const char *bufferBegin) {
 static bool isRightBound(const char *tokEnd, bool isLeftBound,
                          const char *codeCompletionPtr) {
   switch (*tokEnd) {
+  case ':':     // ':' is an expression separator; '::' is not
+    return tokEnd[1] == ':';
+
   case ' ': case '\r': case '\n': case '\t': // whitespace
   case ')': case ']': case '}':              // closing delimiters
-  case ',': case ';': case ':':              // expression separators
+  case ',': case ';':                        // expression separators
     return false;
 
   case '\0':
@@ -2765,7 +2768,7 @@ void Lexer::lexImpl() {
   case '\\': return formToken(tok::backslash, TokStart);
 
   case ':':
-    if (CurPtr[0] == ':') {
+    if (CurPtr[0] == ':' && LangOpts.hasFeature(Feature::ModuleSelector)) {
       CurPtr++;
       return formToken(tok::colon_colon, TokStart);
     }
@@ -2879,6 +2882,7 @@ Token Lexer::getTokenAtLocation(const SourceManager &SM, SourceLoc Loc,
   // Use fake language options; language options only affect validity
   // and the exact token produced.
   LangOptions FakeLangOpts;
+  FakeLangOpts.enableFeature(Feature::ModuleSelector);
 
   // Here we return comments as tokens because either the caller skipped
   // comments and normally we won't be at the beginning of a comment token

lib/Parse/ParseDecl.cpp

@@ -682,7 +682,8 @@ bool Parser::parseSpecializeAttributeArguments(
               DeclNameFlag::AllowZeroArgCompoundNames |
                   DeclNameFlag::AllowKeywordsUsingSpecialNames |
                   DeclNameFlag::AllowOperators |
-                  DeclNameFlag::AllowLowercaseAndUppercaseSelf);
+                  DeclNameFlag::AllowLowercaseAndUppercaseSelf |
+                  DeclNameFlag::ModuleSelectorUnsupported);
         }
       }
       if (ParamLabel == "spiModule") {
@@ -1136,7 +1137,8 @@ Parser::parseImplementsAttribute(SourceLoc AtLoc, SourceLoc Loc) {
           MemberNameLoc, diag::attr_implements_expected_member_name,
           DeclNameFlag::AllowZeroArgCompoundNames |
               DeclNameFlag::AllowOperators |
-              DeclNameFlag::AllowLowercaseAndUppercaseSelf);
+              DeclNameFlag::AllowLowercaseAndUppercaseSelf |
+              DeclNameFlag::ModuleSelectorUnsupported);
       if (!MemberName) {
         Status.setIsParseError();
       }
@@ -1159,7 +1161,7 @@ Parser::parseImplementsAttribute(SourceLoc AtLoc, SourceLoc Loc) {
     return Status;
   }
 
-  // FIXME(ModQual): Reject module qualification on MemberName.
+  assert(MemberName.getModuleSelector().empty());
   return ParserResult<ImplementsAttr>(
     ImplementsAttr::create(Context, AtLoc, SourceRange(Loc, rParenLoc),
                            ProtocolType.get(), MemberName.getFullName(),
@@ -2440,7 +2442,8 @@ Parser::parseMacroRoleAttribute(
             (DeclNameFlag::AllowOperators | DeclNameFlag::AllowKeywords |
              DeclNameFlag::AllowKeywordsUsingSpecialNames |
              DeclNameFlag::AllowCompoundNames |
-             DeclNameFlag::AllowZeroArgCompoundNames));
+             DeclNameFlag::AllowZeroArgCompoundNames |
+             DeclNameFlag::ModuleSelectorUnsupported));
         if (!name) {
           status.setIsParseError();
           return status;
@@ -4256,11 +4259,15 @@ ParserStatus Parser::parseDeclAttribute(DeclAttributes &Attributes,
         .warnUntilSwiftVersion(6);
   }
 
+  bool hasModuleSelector = Context.LangOpts.hasFeature(Feature::ModuleSelector)
+                              && peekToken().is(tok::colon_colon);
+
   // If this not an identifier, the attribute is malformed.
   if (Tok.isNot(tok::identifier) &&
       Tok.isNot(tok::kw_in) &&
       Tok.isNot(tok::kw_inout) &&
-      Tok.isNot(tok::kw_rethrows)) {
+      Tok.isNot(tok::kw_rethrows) &&
+      !hasModuleSelector) {
 
     if (Tok.is(tok::code_complete)) {
       if (CodeCompletionCallbacks) {
@@ -4281,7 +4288,7 @@ ParserStatus Parser::parseDeclAttribute(DeclAttributes &Attributes,
 
   // If the attribute follows the new representation, switch
   // over to the alternate parsing path.
-  std::optional<DeclAttrKind> DK =
+  std::optional<DeclAttrKind> DK = hasModuleSelector ? std::nullopt :
       DeclAttribute::getAttrKindFromString(Tok.getText());
   if (DK == DeclAttrKind::Rethrows) {
     DK = DeclAttrKind::AtRethrows;
@@ -4293,7 +4300,7 @@ ParserStatus Parser::parseDeclAttribute(DeclAttributes &Attributes,
   auto checkInvalidAttrName =
       [&](StringRef invalidName, StringRef correctName, DeclAttrKind kind,
           std::optional<Diag<StringRef, StringRef>> diag = std::nullopt) {
-        if (!DK && Tok.getText() == invalidName) {
+        if (!DK && !hasModuleSelector && Tok.getText() == invalidName) {
           DK = kind;
 
           if (diag) {
@@ -4357,7 +4364,7 @@ ParserStatus Parser::parseDeclAttribute(DeclAttributes &Attributes,
                        DeclAttrKind::Preconcurrency,
                        diag::attr_renamed_warning);
 
-  if (!DK && Tok.getText() == "warn_unused_result") {
+  if (!DK && !hasModuleSelector && Tok.getText() == "warn_unused_result") {
     // The behavior created by @warn_unused_result is now the default. Emit a
     // Fix-It to remove.
     SourceLoc attrLoc = consumeToken();
@@ -4432,9 +4439,10 @@ ParserStatus Parser::parseDeclAttribute(DeclAttributes &Attributes,
     return parseNewDeclAttribute(Attributes, AtLoc, *DK, isFromClangAttribute);
   }
 
-  if (TypeAttribute::getAttrKindFromString(Tok.getText()).has_value())
+  if (!hasModuleSelector &&
+        TypeAttribute::getAttrKindFromString(Tok.getText()).has_value())
     diagnose(Tok, diag::type_attribute_applied_to_decl);
-  else if (Tok.isContextualKeyword("unknown")) {
+  else if (!hasModuleSelector && Tok.isContextualKeyword("unknown")) {
     diagnose(Tok, diag::unknown_attr_name, "unknown");
   } else {
     // Change the context to create a custom attribute syntax.
@@ -5761,6 +5769,8 @@ static void skipAttribute(Parser &P) {
   // Parse the attribute name, which can be qualified, have
   // generic arguments, and so on.
   do {
+    P.parseModuleSelector();
+
     if (!(P.consumeIf(tok::identifier) || P.consumeIf(tok::kw_rethrows)) && 
         !P.consumeIf(tok::code_complete))
       return;
@@ -10343,9 +10353,11 @@ Parser::parseDeclOperatorImpl(SourceLoc OperatorLoc, Identifier Name,
       return makeParserCodeCompletionResult<OperatorDecl>();
     }
 
+    // TODO: We could support module selectors for precedence groups if we
+    //       implemented the lookup for it.
     groupName = parseDeclNameRef(groupLoc,
                                  diag::operator_decl_expected_precedencegroup,
-                                 {});
+                                 DeclNameFlag::ModuleSelectorUnsupported);
 
     if (Context.TypeCheckerOpts.EnableOperatorDesignatedTypes) {
       // Designated types have been removed; consume the list (mainly for source
@@ -10643,7 +10655,7 @@ Parser::parseDeclPrecedenceGroup(ParseDeclOptions flags,
         auto name = parseDeclNameRef(nameLoc,
                                      { diag::expected_precedencegroup_relation,
                                        attrName },
-                                     {});
+                                     DeclNameFlag::ModuleSelectorUnsupported);
         if (!name) {
           return abortBody();
         }